Lower Limb Anatomy Manual 2023 (PDF)

LOWER LIMB ANATOMY MANUAL 13th Edition November 2023 Des Moines University 1 Lauren Butaric, Ph.D. | Craig Canby, Ph.D. | Rachel Dunn, Ph.D. | William Dyche, Ph.D. | M. A. Khan, Ph.D. | Donald Matz, Ph.D. | Julie Meachen, Ph.D. TABLE OF CONTENTS 1 | EMBRYOLOGY OF THE LOWER LIMB 1 Genetic Signaling a...

LOWER LIMB ANATOMY MANUAL 13th Edition November 2023 Des Moines University 1 Lauren Butaric, Ph.D. | Craig Canby, Ph.D. | Rachel Dunn, Ph.D. | William Dyche, Ph.D. | M. A. Khan, Ph.D. | Donald Matz, Ph.D. | Julie Meachen, Ph.D. TABLE OF CONTENTS 1 | EMBRYOLOGY OF THE LOWER LIMB 1 Genetic Signaling and Limb Growth Limb Skeleton Limb Rotation Limb Defects 1 2 2 3 2 | OSTEOLOGY OF THE FOOT 4 Tarsal Bones 4 Calcaneus Talus Cuboid Navicular Cuneiform Bones 4 6 7 8 9 Metatarsal Bones 11 1st Metatarsal 2nd Metatarsal 3rd Metatarsal 4th Metatarsal 5th Metatarsal 12 12 13 13 14 Phalanges Great Toe Lesser Toes Sesamoid Bones Accessory Bones Ossi cation of Foot Bones Sequence of Ossi cation 15 15 16 16 16 3 | DORSUM OF THE FOOT 17 Fascia 17 Muscles Nerves Saphenous Nerve Sural Nerve Common Fibular Nerve Arteries Anterior Tibial Perforating Branch of Fibular Artery Veins Super cial Veins Deep Veins 17 18 19 20 20 20 20 21 21 24 24 24 24 4 | PLANTAR SURFACE OF THE FOOT 25 Fascia 25 Plantar Aponeurosis Retinacula Vincula fi i fi 14 15 Arches of the Foot Retinacula Extensor Expansions fi 14 25 25 26 Muscles 1st Layer 2nd Layer 3rd Layer 4th Layer Nerves Sural Nerve Tibial Nerve Arteries Posterior Tibial Artery Veins Super cial Veins Deep Veins 30 30 30 31 31 34 34 34 35 Ankle Joint 35 Intertarsal Joints Talocalcaneal Joint Talocalcaneonavicular Joint Calcaneocuboid Joint Great Tarsal Joint Functional vs. Anatomical Intertarsal Joints 36 36 36 36 37 37 38 38 39 Tarsometatarsal Joints Intermetatarsal Joints Metatarsophalangeal Joints Interphalangeal Joints 39 40 41 41 6 | LEG 42 Osteology 42 Tibia Fibula 42 44 Joints and Ligaments Knee Joint Proximal Tibio bular Joint Distal Tibio bular Joint Fascia Muscles Anterior Compartment Lateral Compartment Posterior Compartment of the Leg Nerves Saphenous Nerve Tibial Nerve Common Fibular Nerve Sural Nerve Arteries Popliteal Artery Genicular Anastomosis Veins fi ii fi 26 27 28 29 5 | JOINTS AND LIGAMENTS OF THE FOOT Deltoid Ligament Lateral Collateral Ligament Fibulotalocalcaneal Ligament fi 26 45 45 47 47 47 48 48 49 50 53 53 53 53 54 54 54 57 58 Super cial Veins of the Leg Deep Veins of the Leg Lymphatics Lymph Nodes Lymphatic Vessels Osteology 60 Femur Patella 60 63 Fascia Muscles 63 64 Lumbar Plexus (L1–5) Arteries Femoral Artery Veins Super cial Veins Deep Veins Perforating Veins Lymphatics Popliteal Nodes Inguinal Nodes 64 66 68 69 69 71 71 73 73 73 74 74 74 75 8 | PELVIS AND GLUTEAL REGION 76 Osteology 76 Os Coxae Sacrum Coccyx Variation Associated with Sex Joints and Ligaments Hip Joint Sacroiliac Joint Fascia Muscles Iliac Region Gluteal Region Nerves Plexuses of the Lower Limb Arteries Internal Iliac Artery External Iliac Artery Cruciate Anastomosis Veins Superior Gluteal Veins Inferior Gluteal Veins Lymphatics Super cial Inguinal Nodes Deep Inguinal Nodes iii fi 59 59 60 Nerves fi 59 7 | THIGH AND PATELLA Anterior Compartment Medial Compartment Posterior Compartment of the Thigh fi 58 58 76 78 78 79 79 79 81 81 82 82 83 85 85 88 88 89 91 91 91 91 92 92 92 External Iliac Nodes Internal Iliac Nodes 92 92 ADDENDA 93 Addendum I: Variations at DMU Addendum II: Keys to the Bone Kingdom 93 94 iv 1 | EMBRYOLOGY OF THE LOWER LIMB During the later part of the 4th week (as soon as the trilaminar embryo completes its lateral folding), limb buds start to develop along the ventrolateral side of the cylindrical embryonic body. These limb buds, one pair for the upper limbs and one pair for the lower limbs, will undergo further development and eventually give rise to the adult limbs. The upper limb buds (for the upper limbs) appear first as two elevations one on each side of the body of the embryo. These limb buds can be seen by day 26-27 at the inferior segment of the developing cervical region (C5-T1). The lower limb buds appear as two elevations from the inferior part of the ventrolateral segment (L2-S2) of the embryo. Note that the lower limbs originate from a slightly larger segment than the upper limb buds. The development of the lower limb buds, however, lags about 2 days behind the upper buds. This follows the normal pattern of cranial to caudal development true for all other systems of the embryo. The cranial structures appear first. The limb buds originally contain a core of mesenchymal cells that are derived from the somatic component of the lateral mesoderm layer of the embryo. Further development and enlargement of the limb buds initially begins by a very fast division of the mesenchymal cells. Experimental evidence has shown that this cell division is under direct control of HOX (homeobox- containing) genes. Genetic Signaling and Limb Growth The proliferating mesenchyme at the site of limb development is covered externally by cells of the ectoderm layer similar to other parts of the body. However, at the distal segment of the limb bud (apex) the ectodermal cells undergo cell proliferation and shows considerable thickening known as the apical ectodermal ridge (AER). During growth and development, a zone of polarizing activity (ZPA) will also appear in the caudal region of the limb bud. The AER is vital in that it controls the future development of the limb. Under the inductive influence of AER, the limb buds undergo growth in a proximal to distal direction. There is much experimental evidence that indicates that the limbs will not develop in the absence of AER. There is also evidence showing that transplantation of this ridge at a different location will induce the development of a limb at that location. The inductive influence of AER is known to be a result of the expression of fibroblast growth factor (FGF-8). Under the influence of the HOX gene, patterning of the limbs also takes place where the distal ends of the buds flatten into paddle-like hands and feet. By the end of the 6th week, the hand paddles show presence of digital rays that will eventually give rise to individual fingers. Eventually five rays develop, one for each finger. During early part of the 7th week, toe rays can be seen in the foot plates. Similar to that seen in the hand, these rays will give rise to individual toes. More recent research also indicates that sonic-hedgehog (Shh), found within the zone of polarizing activity, helps in cranialcaudal differentiation of the digits (e.g., the thumb/big toe versus the 5th digits). Additionally, BMP and WnT signaling, although not well known, likely help differentiate ventral and dorsal surface components, respectively. Initially, the digits are attached to each other by loose connective tissue. Separation of individual digits takes place during the 8th week by the process of programmed cell death (apoptosis) in the mesenchymal tissue between digital rays. This process gives rise to individual digits. If apoptosis is interrupted, or does not happen for some reason, one or more digits will remain attached (syndactyly). Occasionally additional rays develop in the hand or foot plates. If this happens it will lead to development of a condition called polydactyly (extra digits). The extra digits are usually smaller in size than the regular digits, and often occur at the edges of the hand/foot (e.g., you will more likely have an extra digit external to the 1st or 5th digit). 1 Limb Skeleton The mesenchyme of the limb buds, under the influence of the HOX gene, gives rise to the following components of the limbs: Bones Joints Cartilage Fascial layers Blood vessels Lymphatic vessels At one time, the entire limb skeleton consists of cartilage models of bones. The cells of the cartilage models are derived from the original mesenchymal cells of the embryo beginning by the 5th week of development. By the 6th week, the entire cartilaginous skeleton is complete. During the 7th week, the cartilage models start to undergo endochondral ossification, whereby bone producing cells replace the chondrocytes. The formation of endochondral bone begins in the diaphysis of long bones (e.g., femur, phalanx, metatarsals) as the primary center of ossifications. The long bones also develop secondary ossification centers in the epiphysis. So, each long bone will have one primary and at least two secondary ossification centers. The developing limbs get other migrant cells in addition to the original mesenchymal cells as follows: Myogenic Cells—These cells originate from the dermomyotome region of the somites and migrate into the mesenchymal cells of the limb buds where they eventually differentiate into myoblasts. The myoblasts will give rise to the muscle cells of the limbs. The cervical myotomes will give rise to the pectoral girdle muscles, and the lumbosacral myotomes provide precursor cells for the pelvic girdle. Dermatomal Cells—These somite-derived cells provide cells that stay deep to the ectoderm and give rise to the dermis of the skin. Typically, dermatomal levels invade into the limb bud in a cranialcaudal process (whereby higher spinal levels are found in the more cranial-aspects of the limb). This pattern, however, becomes complicated with limb rotation (see below). Axonal Processes—Axonal processes of neurons of spinal cord become established as nerves of the limbs. Note that motor nerves will develop first, followed by sensory nerves. Neural Crest Cells—The supporting cells of the nervous system (Schwann cells) are derived from the neural crest cells. There is evidence which indicates that the mesenchymal cells of the limbs organize the migrant cells and control their expression. Limb Rotation Both the upper and lower limb buds at one time protrude anteriorly from the embryonic body. Before we can understand limb rotation, however, we need to go over some directional terminology. The limb buds extend from the trunk so that the longitudinal axis (or the axial line) of the limb bud is at about 90 degrees to the long axis of the trunk. The area of the limb superior (cranial) to the axial line is the preaxial compartment, and the part inferior (caudal) to the axial line is the postaxial compartment. The superior border of the preaxial compartment is the preaxial border, and is along the same line as the thumb or great toe. The inferior border of the postaxial compartment is the postaxial border, which corresponds to the location of the 5th toe or the little finger. The muscle masses of the limbs can also be divided into pre- and postaxial muscles depending on their location. The preaxial compartments contain flexor muscles on the ventral surface of the bud, and the postaxial compartments contain the extensor muscles on the dorsal surface of the bud. This easy to 2 understand pre- and postaxial arrangement, however, changes during the early part of the 7th week when the limbs undergo a rotation along their long axis. Both limbs go through a 90-degree rotation, but in the opposite direction. The upper limbs rotate along their long axis in a lateral direction, while the lower limbs undergo a 90-degree medial. Because of this differential rotation, the pre- and postaxial compartments of the upper and lower limbs do not correspond with each other in the neonate or adult. In the anatomical position, the flexor compartment (preaxial) of the upper limb faces anteriorly, while the extensor compartment is located posteriorly to the longitudinal axis. Additionally, the first digit (thumb/pollex) is located laterally. Because of the medial rotation of the lower limbs, the opposite is true for the lower limbs. In anatomical position, the flexor compartment (preaxial), including the muscles that flex the knee and plantarflex the foot, are in the posterior compartment. The extensor compartment (postaxial) muscles, including those that extend the knee/leg and dorsiflex the foot, are in the anterior compartment of the leg. Additionally, the first digit (big toe/hallux) is located medially. This opposite rotation also explains why the two homologous bones (tibia and radius) are located on the opposite side of the limbs, and why the knee and elbow, two homologous joints, face in the opposite direction as well. Additionally, the seemingly complicated pattern of the lower-limb dermatomes can be explained by this 90-degree, medial rotation. Limb Defects The most susceptible time for producing limb defects was found to be between day 24 -36. Overall, limb defects appear relatively infrequently (2/1000 births); however, since they are usually often not life-threatening, they make up a large portion of congenital defects. Multiple environmental and genetic factors affect limb development. In the early 60’s, there was a large incidence of limb abnormalities, which were traced back to a drug known as thalidomide used in pregnant women to prevent morning sickness. Polydactyly—Extra digits resulting from having extra digital rays; this is often caused by too much or upregulation of Shh. Syndactyly—Attached digits. Malformation in the act of apoptosis (programmed cell death) will result in two or more digits that remain attached via a web a skin. You can also have a type of syndactyly where digital rays (and subsequent bony elements) are fused together. Amelia—Absence of a limb in its entirety. Meromelia—Absence of a part of a limb. Cleft Foot (or Hand)—This is also known as the lobster-claw deformity. It results from a failure of development of one or more digital rays. The hand or the foot appears to be split down the middle. Brachydactyly—Short digits. Congenital Club Foot—This defect applies to any abnormality of the foot involving the talus. It is more common than some of the other defects (1/1000). The affected individual walks on the ankle rather than the foot. The sole of the foot is usually turned medially and the foot is inverted. 3 2 | OSTEOLOGY OF THE FOOT The bones of the foot are grouped into the following five categories: Tarsals (7), Metatarsals (5), Phalanges (14), Sesamoids (variable), Accessory bones (variable). Tarsal Bones Each of the seven tarsal bones is a short, irregular bone. The proximal row comprises two bones, the calcaneus and talus. The distal row is made up of four bones, the cuboid, and three cuneiforms (medial, intermediate, and lateral). The navicular lies between the proximal and distal rows. In general, each tarsal bone has six surfaces: dorsal (superior), plantar (inferior), medial, lateral, anterior, and posterior. When surfaces are narrow, they are called crests or borders. In all tarsals except for the talus and calcaneus, the anterior and posterior surfaces are also called distal and proximal, respectively. In the talus and calcaneus, the dorsal surface is proximal and the inferior surface is distal. Calcaneus This is the strongest and largest bone of the foot. It is somewhat rectangular in shape, being elongated in an anterior-posterior direction. The width and height of the calcaneus are subequal, both being about 50% of its length. Dorsal Surface The dorsal surface is concave anteroposteriorly and convex mediolaterally, and is divided into anterior, middle, and posterior thirds. The anterior third contains two facets, anterior and middle, that articulate with the talus. The middle facet of the dorsal surface of the calcaneus is located on the dorsal surface of the sustentaculum tali and lies slightly medial and posterior to the anterior facet. The anterior and middle facets are often confluent. The calcaneal sulcus (sulcus calcanei ) is a deep groove located between the middle and posterior calcaneal facets. The sulcus calcanei combines with a deep groove on the plantar surface of the talus (sulcus tali, or talar sulcus) to form the tarsal canal. The tarsal canal is directed anterolaterally and is continuous at its anterior end with the tarsal sinus (sinus tarsi), a widening of the tarsal canal. The interosseous talocalcaneal ligament lies within the tarsal canal. Several structures attach to the tarsal sinus: inferior extensor retinaculum, inferior fibular retinaculum, cervical ligament, bifurcate ligament, dorsal calcaneocuboid ligament, lateral calcaneocuboid ligament (sometimes absent). The middle third of the dorsal surface consists of the posterior articular facet, the largest of the three talar facets. This facet is oval in shape and strongly convex anteroposteriorly. The posterior third of the dorsal surface of the calcaneus is a nonarticular area with numerous vascular foramina. Two ligaments attach to the posterior third of the calcaneus: posterior talocalcaneal ligament, calcaneofibular ligament. Plantar Surface The plantar surface of the calcaneus is wider posteriorly than anteriorly, making it somewhat triangular in shape, and convex mediolaterally. The plantar surface is limited posteriorly by the calcaneal tuberosity, which consists of two processes, lateral and medial, separated by a depression. The lateral process (posterolateral tubercle) is small but prominent and serves as the attachment for several structures: abductor digiti minimi, lateral head of quadratus plantae, long plantar ligament, plantar aponeurosis. 4 The medial process (posteromedial tubercle) is broader and larger than the lateral process. Several structures attach to the medial process: abductor hallucis, medial head of quadratus plantae long plantar ligament, plantar aponeurosis, flexor retinaculum, flexor digitorum brevis, abductor digiti minimi. The area between the two processes is depressed and serves as an attachment point for two structures: long plantar ligament, abductor digiti minimi. The anterior tubercle, located near the anterior border of the plantar surface of the calcaneus, serves as an attachment for the plantar calcaneocuboid ligament (short plantar ligament). Lateral Surface The lateral surface of the calcaneus is deeper posteriorly than anteriorly and can exhibit one, two, or three tubercles. The most constant feature of the lateral surface is the retrotrochlear eminence, located in the middle third of this surface. This tubercle is so named because it lies directly behind (posterior) to the fibular trochlea (tubercle). This bony prominence forms as a consequence of the internal architecture of calcaneal trabeculae; no structures attach to it. The fibular trochlea is an oblique ridge of bone separating a groove for the tendon of fibularis longus posteriorly and inferiorly, from a groove for the tendon of the fibularis brevis anteriorly and superiorly. The fibular trochlea and the grooves surrounding it are absent in the majority of cases, and variable in presentation when present. It serves as an attachment for deep fibers of the inferior fibular retinaculum. A third, unnamed tubercle for attachment of the calcaneofibular ligament may be present on the lateral surface of the calcaneus, located posterior and superior to the retrotrochlear eminence. This tubercle is present less than 50% of the time. The lateral talocalcaneal ligament also attaches to the lateral surface of the calcaneus, just anterior and superior to the calcaneofibular ligament which partially overlies it. Medial Surface The medial surface of the calcaneus is deeply concave, allowing accommodation for the plantar nerves and vessels located there. The medial head of the quadratus plantae has an extensive attachment to the medial surface more extensive than its attachment to the medial process (plantar surface) which was described previously. The most obvious feature of the medial surface of the calcaneus is the sustentaculum tali, a shelflike projection that articulates with the talus superiorly. The inferior surface of the sustentaculum tali is grooved by the tendon of flexor hallucis longus. Structures attaching to the sustentaculum tali: tibiocalcaneal ligament (part of the deltoid ligament), medial talocalcaneal ligament, recurrent band of tibialis posterior (partial insertion), plantar calcaneonavicular (spring) ligament. Anterior Surface The anterior surface is the smallest surface of the calcaneus and consists entirely of the facet for articulation with the cuboid. The facet is saddle-shaped, being convex transversely and concave vertically. The plantar calcaneonavicular (spring) ligament attaches to the medial margin. Posterior Surface The posterior surface of the calcaneus forms the prominence of the heel, or calcaneal tuberosity. It consists of three areas: superior, middle, and inferior that are separated by two horizontal lines: superior and inferior. 5 The superior area of the posterior surface is smooth. It is covered by a bursa that lies deep to the calcaneal tendon (tendo calcaneus). The major feature of the middle area of the posterior surface of the calcaneus is a roughened area for the attachment of calcaneal and plantaris tendons. The plantaris tendon usually attaches medial to the calcaneal tendon but sometimes they attach together. The inferior area of the posterior surface is the largest area of the posterior calcaneus. It is rough and covered by fatty, fibrous tissue. Talus The talus is the most proximal bone of the ankle, articulating with the tibia and fibula. It is divided into three parts, the body, neck, and head. No muscles or tendons attach to the talus. Body The body of the talus is somewhat cubical in shape. Whereas the anterior surface of the body of the talus blends with the neck, the other five surfaces are free. Superior Surface This surface covered with articular cartilage and articulates with the tibial plafond (inferior surface of the tibia). It is strongly convex anteroposteriorly and is often called the talar trochlea. Because the inferior tibiofibular ligaments form a portion of the articular area of the talocrural joint (specifically the anterior (inferior) tibiofibular ligament and inferior transverse ligament), these ligaments also articulate with the talar trochlea. Inferior Surface The inferior surface of the body has a large, concave, oval facet for articulation with the calcaneus at the subtalar joint, posterior articular facet. Anterior and medial to this facet at the union of body and neck is a deep groove, the talar sulcus (sulcus tali). The talar sulcus combines with the calcaneal sulcus of the calcaneus to form the tarsal canal and sinus (sinus tarsi), which contains the interosseous talocalcaneal ligament. Lateral Surface The lateral surface is triangular in shape, with the apex pointing inferiorly. The inferior, tapered end of the lateral surface projects laterally and is known as the lateral process. This surface has a large triangular facet for the lateral malleolus and is continuous superiorly with the talar trochlea. Rough areas are found anterior and posterior to the articular facet for attachment of the anterior talofibular and posterior talofibular ligaments. There are usually two tubercles for the anterior talofibular ligament and a groove for the posterior talofibular ligament. The lateral talocalcaneal ligament attaches to the anteroinferior aspect of the lateral process, just inferior to the anterior talofibular ligament. Medial Surface Superiorly, this surface has a comma-shaped facet for articulation with the medial malleolus of the tibia and is continuous with the trochlea. Inferior to the articular facet, the medial surface is rough for attachment of the anterior tibiotalar ligament (part of the deltoid ligament). 6 Posterior Surface The posterior surface comprises a posterior projection of bone called the posterior process. The posterior process is divided into posteromedial and posterolateral tubercles by a groove for the tendon of flexor hallucis longus. The posteromedial tubercle (=medial tubercle of the posterior process) serves as an attachment for the medial talocalcaneal ligament and posterior tibiotalar ligament (part of the deltoid ligament). If a medial band of the posterior talocalcaneal ligament is present, it also attaches to the medial tubercle. The posterolateral tubercle (=lateral tubercle of the posterior process) is larger than the medial and serves as an attachment for the posterior talofibular, posterior talocalcaneal, and fibulotalocalcaneal ligaments. This tubercle has its own secondary ossification center, which occasionally fails to fuse with the body of the talus, resulting in an accessory bone called the os trigonum. Neck The neck of the talus is a constricted area between the body and head. The dorsal talonavicular ligament attaches to the anterior aspect of the superior surface of the neck, just posterior to the articular facet for the navicular. The inferior surface is reduced to a narrow nonarticular area corresponding to the talar sulcus. The cervical ligament is attached to the anterior aspect of the talar sulcus, just lateral to the anterior calcaneal facet. Head The head of the talus is directed anteriorly, medially and slightly inferiorly and has two major surfaces, anterior and inferior. The anterior surface of the head of the talus has a large ovoid, convex facet for its articulation with the navicular. The inferior surface of the head of the talus has three articular facets. The anterior and middle calcaneal facets articulate with the corresponding facet on the calcaneus. The middle calcaneal facet is variable in shape and is confluent with both the anterior calcaneal facet and the facet for the spring ligament. The third facet articulates with the plantar calcaneonavicular (spring) ligament and is located in between the anterior and middle facets. Cuboid The cuboid is the most lateral bone in the distal row of tarsals. The overall orientation of this bone is such that the dorsal surface is directed superolaterally and the plantar surface is directed inferomedially. Dorsal Surface The dorsal surface serves as an attachment for the dorsal calcaneocuboid, dorsal cuneocuboid, dorsal cuboideonavicular, lateral calcaneocuboid (variable), and two dorsal cuboideometatarsal ligements (to the 4th and 5th metatarsals). Plantar Surface The plantar surface of the cuboid is a rough area for the attachment of several ligaments and muscles. The medial and posterior borders of the plantar surface meet at a sharp point, called the beak or coronoid process of the cuboid. The most prominent features of the plantar surface of the cuboid are the fibular ridge and fibular sulcus (groove) distal to it. Both sulcus and ridge course obliquely from posterolateral to anteromedial. The tendon of fibularis longus lies either in the fibular groove or against the anterior aspect of the fibular ridge. The fibular ridge terminates laterally as the cuboid 7 tuberosity, which may exhibit an oval facet for articulation with the os peroneum, a sesamoid bone in the tendon of the fibularis longus muscle (variably present). Deep fibers of the long plantar ligament attach to the fibular ridge. Superficial fibers of the long plantar ligament course over the tendon of fibularis longus. Therefore, the long plantar ligament and cuboid form an osseofibrous canal for the tendon of the fibularis longus. The plantar surface serves as an attachment for the tibialis posterior and flexor hallucis brevis muscles, long and short plantar ligaments, plantar cuboideonavicular ligament, plantar cuneocuboid ligament, and two plantar cuboideometatarsal ligaments (to the 4th and 5th metatarsals). Lateral Surface The lateral surface is narrow, often called the lateral border. The fibular notch, marking the beginning of the fibular sulcus, is located at the plantar edge of this surface. Medial Surface The medial surface is quadrilateral in shape. It typically exhibits a triangular facet for the lateral cuneiform dorsally, however, there can be a small facet for the navicular. There are three ligaments attached to the medial surface of the cuboid, the interosseous cuboideonavicular, interosseous cuneocuboid, and calcaneocuboid portion of the bifurcated ligament. Distal Surface The anterior surface is divided into two articular facets by a vertical ridge. The medial facet is quadrilateral in shape and articulates with the base of the 4th metatarsal. The lateral facet for the 5th metatarsal is triangular with the apex directed laterally. Proximal Surface This surface has a saddle-shaped articular facet for the anterior surface calcaneus. This facet is concave dorsoplantarly and convex mediolaterally with respect to the bone itself. Many texts describe the saddle-shaped proximal cuboid as being concave transversely and convex dorsoplantarly; this is because the dorsoplantar axis of the cuboid is rotated so that it lines up with the mediolateral axis of the anterior surface of the calcaneus. Navicular The navicular is boat shaped (“navicula” = navy in Latin), being concave proximally and convex distally. The navicular typically articulates with the talus proximally and the three cuneiforms distally, but it may articulate with the cuboid and, in very rare cases, the calcaneus. Dorsal Surface The dorsal surface of the navicular is convex, oriented superomedially and serves as the attachment for the dorsal cuboideonavicular ligament, dorsal talonavicular ligament, calcaneonavicular portion of the bifurcated ligament, tibionavicular portion of the deltoid ligament, and three dorsal cuneonavicular ligaments (one to each cuneiform). Plantar Surface The plantar surface is convex and separated from the navicular tuberosity medially by a groove for the tendon of tibialis posterior muscle. Near the middle of the plantar surface there is a tubercle for the attachment of the plantar calcaneonavicular (spring) ligament. The plantar surface also serves as 8 an attachment for the plantar cuboideonavicular ligament and three plantar cuneonavicular ligaments (one to each cuneiform). Lateral Surface The lateral surface of the navicular forms a narrow border for attachment of the lateral calcaneonavicular portion of the bifurcated ligament and the interosseous cuboideonavicular ligament. Medial Surface The medial surface forms a tuberosity (navicular tuberosity) that is variable in size. The medial tuberosity may develop from a secondary ossification center that fails to unite with the navicular, resulting in an accessory bone, the os tibiale (externum). This structure serves as an attachment for the tibialis posterior muscle and the medial cuneonavicular ligament (to the medial cuneiform). Distal Surface This surface convex mediolaterally and forms a large articular surface that is subdivided by two vertical crests or ridges into three articular facets. The medial facet, for articulation with the medial cuneiform, is the largest facet and may be pear-shaped (piriform), triangular, or quadrilateral. The middle (intermediate) and the lateral facets are both roughly triangular and articulate with the intermediate and lateral cuneiforms, respectively. Proximal Surface The proximal surface consists of a single concave, oval facet for the head of the talus. Cuneiform Bones There are three cuneiform bones, medial, intermediate, and lateral. The word “cuneiform” means “wedge-shaped” (“cuneus” = wedge in Latin), referring to the shape of the bones, each of which has a narrow apex and a wider base. The apex of the medial cuneiform is directed dorsally, whereas that of the other two bones is directed plantarly. The medial cuneiform is the largest of the three bones. The intermediate cuneiform is the most typical (that is, it looks most similar to a wedge) and smallest of the seven tarsal bones. Medial Cuneiform Dorsal Surface The dorsal surface forms the apex of the wedge and is therefore more of a crest or border than a surface. This surface is palpable subcutaneously. Plantar Surface The plantar surface of the medial cuneiform is its base. Tendons of three muscles have partial insertion here: tibialis anterior, tibialis posterior, and fibularis longus. Additionally, several ligaments attach to the plantar surface: plantar cuneonavicular, plantar intercuneiform, plantar cuneometatarsal (to 1st metatarsal), and plantar cuneometatarsal (to 2nd metatarsal). 9 Lateral Surface The lateral surface of the medial cuneiform is concave and has two articular facets: a small oval facet is present distally for the base of the 2nd metatarsal, and a facet for the intermediate cuneiform in the shape of an inverted “L”, with the stem oriented proximally. Two ligaments, Lisfranc's ligament and an interosseous intercuneiform ligament (to the intermediate cuneiform) attach to the lateral surface of the medial cuneiform. Lisfranc's ligament is an interosseous tarsometatarsal ligament between the medial cuneiform and the 2nd metatarsal. Medial Surface The medial surface of the medial cuneiform is quadrilateral in shape and is often palpable subcutaneously. Although this surface does not articulate with another tarsal bone, it usually has a small facet near its anteroinferior aspect for a sesamoid bone within the tendon of tibialis anterior. The medial cuneonavicular, dorsal cuneonavicular, dorsal intercuneiform, dorsal cuneometatarsal (to 1st metatarsal), and dorsal cuneometatarsal (to 2nd metatarsal) ligaments attach to the medial surface of the medial cuneiform. Distal Surface The distal surface forms a kidney shaped (reniform) surface for the base of the 1st metatarsal. Proximal Surface The proximal surface of the medial cuneiform has a concave articular facet for the navicular. The shape of the facet can be triangular, piriform, or quadrilateral. Intermediate Cuneiform Dorsal Surface This surface is quadrilateral or square and forms the base of the intermediate cuneiform. It is rough due to the attachment of four ligaments, one to each of the four bones that articulate with the intermediate cuneiform: dorsal cuneonavicular, dorsal intercuneiform (2), dorsal cuneometatarsal. Plantar Surface This surface forms a thin crest, serving as the apex of the wedge. The tibialis posterior has partial attachment to this surface. The plantar cuneonavicular ligament, and plantar intercuneiform ligaments (2) also attach to this surface. Lateral Surface An elongated ovoid articular facet is present at the proximal edge of this surface for the lateral cuneiform. Distal to this facet is a nonarticular area is for attachment of the interosseous intercuneiform ligament (to the lateral cuneiform). Medial Surface The medial surface exhibits an articular facet for the medial cuneiform that also resembles an inverted “L”. Distal to this facet is a nonarticular area for attachment of an interosseous intercuneiform ligament (to the medial cuneiform). 10 Distal Surface This surface forms a triangular facet for articulation with the 2nd metatarsal. Proximal Surface The proximal surface is a triangular facet for articulation with the navicular. Lateral Cuneiform Dorsal Surface This surface is rectangular in shape and rough due to the attachment of several ligaments: dorsal cuneocuboid, dorsal cuneonavicular, dorsal intercuneiform, and dorsal cuneometatarsal (2). Plantar Surface The plantar surface forms the apex of the wedge. The flexor hallucis brevis and tibialis posterior muscles attach to this surface, as do the plantar cuneocuboid, plantar cuneonavicular, plantar intercuneiform, and plantar cuneometatarsal ligaments. Lateral Surface This surface is also rectangular with two articular facets. Proximally, there is a large triangular facet for the cuboid. A smaller, oval facet, for the 4th metatarsal is found distally. An interosseous cuneocuboid ligament also attaches to this surface. Medial Surface This surface is rectangular in shape with a vertically oriented oval facet for articulation with the intermediate cuneiform at the proximal edge. Distally, there are two oval facets for articulation with the 2nd metatarsal. An interosseous intercuneiform ligament also attaches to this surface. Distal Surface This surface forms a triangular facet for articulation with the base of the 3rd metatarsal. Proximal Surface This surface forms a triangular facet for the navicular. Metatarsal Bones Each of the five metatarsal bones is a miniature long bone, composed of a proximal end (base), a shaft (or body), and a distal end (head). The bases of the metatarsal bones articulate with the distal row of tarsal bones. The bases of the lesser metatarsals (2nd – 5th metatarsals) articulate with each other. Except for the first metatarsal which has a very thick, short shaft, the shafts of the metatarsals are thin and long. The shafts of the metatarsals have a longitudinal curve that is convex dorsally and concave plantarly. Unless otherwise noted, each shaft has three surfaces, dorsal, lateral, and medial, giving the shaft of the bone a roughly triangular cross-section. The heads of the metatarsals are convex and form smooth articular surfaces for the proximal phalanges. Plantarly, the articular surface diverges into medial and lateral condyles, which the flexor 11 tendons pass between. The deep transverse metatarsal ligament is attached to the heads of all five metatarsal bones. 1st Metatarsal This bone is the heaviest and strongest of the metatarsals. It is also the shortest. Base The base of the 1st metatarsal exhibits a reniform articular surface for the medial cuneiform. The base is somewhat triangular, with a plantar, medial, and lateral surface. The tibialis anterior attaches to the medial surface of the base, whereas the fibularis longus attaches to the lateral surface of the base. Dorsal and plantar cuneometatarsal ligaments attach to the medial and plantar surfaces of the base, respectively. Shaft The shaft of the 1st metatarsal is concave plantarly and has lateral, dorsomedial, and plantar surfaces. The medial head of the first dorsal interosseous muscle is attached to the lateral surface of the shaft. Head The transverse diameter of the head of the 1st metatarsal is greater than the vertical diameter, in contrast to the other four metatarsals where the vertical diameter is greater. The distal articular surface for the proximal phalanx extends onto plantar surface of the head, where it is continuous with facets for medial and lateral sesamoid bones. These two facets for the sesamoid bones are separated by a small ridge of bone, the median crista (intersesamoidal crest/ridge). 2nd Metatarsal This bone is the longest of the metatarsals; it extends more proximally than do the other metatarsals and articulates with all three cuneiforms. Base The base of the second metatarsal is triangular with three borders (dorsal, lateral, and medial); the apex is directed plantarly and forms a crest. The proximal surface of the base forms a triangular articular facet for the intermediate cuneiform. The medial surface of the base has a small, oval facet for the medial cuneiform. Occasionally, a second small oval facet is present distal and plantar to the facet for the medial cuneiform. This facet forms when there is contact between the 1st and 2nd metatarsal bones. Lisfranc’s ligament is attached to the medial surface. There are two articular surfaces (one dorsal and one plantar) on the lateral surface of the base, each divided into two facets by a ridge of bone. The two anterior facets (one dorsal, one plantar) articulate with the 3rd metatarsal. The two posterior facets (one dorsal, one plantar) articulate with the lateral cuneiform. The interosseous intermetatarsal and interosseous cuneometatarsal ligaments attach to the lateral surface of the base. The dorsal surface of the base serves for attachment of the dorsal intermetatarsal (to the 3rd metatarsal), and dorsal cuneometatarsal ligaments (one to each cuneiform). The narrow plantar crest of the base of the 2nd metatarsal serves as an attachment for several ligaments and muscles. The long plantar, plantar cuneometatarsal, and plantar intermetatarsal 12 ligaments attach the 2nd metatarsal to other metatarsal and tarsal bones. The tendon of the tibialis posterior muscle inserts onto this crest, whereas the oblique head of the adductor hallucis originates here. Shaft The lateral head of 1st dorsal interosseous, and the medial head of the 2nd dorsal interosseous originate from the medial and lateral surfaces of the shaft, respectively. 3rd Metatarsal Base The base of the 3rd metatarsal articulates with the lateral cuneiform, and the 2nd and 4th metatarsals. The proximal surface of the base has a triangular facet for the lateral cuneiform. The medial surface of the base has two small facets, one dorsal and one plantar, for articulation with the 2nd metatarsal. An interosseous intermetatarsal ligament attaches to the medial surface. The lateral surface of the base has an oval facet for the 4th metatarsal on its dorsal aspect. Just inferior to this facet, there is a groove for the interosseous intermetatarsal ligament. This groove is a distinctive characteristic of this bone. The dorsal surface of the base serves as an attachment point for the dorsal intermetatarsal (2) and dorsal cuneometatarsal ligaments. The crest or plantar aspect of the base serves as an attachment for the long plantar, plantar cuneometatarsal, and plantar intermetatarsal (2) ligaments. The tendon of the tibialis posterior has an insertion on this ridge, whereas the oblique head of the adductor hallucis originates here. Shaft The lateral head of 2nd dorsal interosseous, medial head of the 3rd dorsal interosseous, and 1st plantar interosseous muscles originate from the shaft of the 3rd metatarsal. 4th Metatarsal Base The proximal surface of the base is a quadrilateral articular surface for articulation with the cuboid. The medial surface of the base has an oval articular surface divided into proximal and distal facets by a ridge. The distal facet articulates with the 3rd metatarsal and the proximal facet articulates with the lateral cuneiform. The dorsal cuneometatarsal and dorsal intermetatarsal ligaments (2) attach to the dorsal surface of the base. Like the 2nd and 3rd metatarsals, the plantar surface of the base of the 4th metatarsal is thin and crest-like. It serves as origin for the oblique head of adductor hallucis, as an insertion for the tibialis posterior tendon, and attachment for the long plantar ligament, plantar cuboideometatarsal ligament, and plantar intermetatarsal ligaments (2). The lateral surface of the base has a large oval to triangular facet for the 5th metatarsal. An interosseous intermetatarsal ligament also attaches to this surface. Shaft The lateral head of 3rd dorsal interosseous, medial head of 4th dorsal interosseous, and 2nd plantar interosseous muscles originate from the shaft of the 4th metatarsal. 13 5th Metatarsal Base The base of the fifth metatarsal is triangular or pyramidal in shape with its apex directed plantarly and laterally. The tuberosity (styloid process) of the 5th metatarsal forms the apex of the base. The proximal surface of the base has a triangular facet for the cuboid. The medial surface has a triangular or oval facet for the 4th metatarsal and serves as an attachment for an interosseous intermetatarsal ligament. The tuberosity of the 5th metatarsal is the primary feature of the lateral surface of the base. The tendon of fibularis brevis inserts onto the tuberosity and the tendon of fibularis tertius inserts onto the dorsal surface of the base and shaft just distal to the tuberosity. The dorsal cuboideometatarsal and dorsal intermetatarsal ligaments also attach to the dorsal surface of the base of the 5th metatarsal. The plantar surface of the base is grooved by the tendon of abductor digiti minimi just medial to the tuberosity and the flexor digiti minimi brevis takes partial origin from this surface. Occasionally, an accessory muscle called abductor os metatarsi digiti minimi also inserts into the plantar surface of the base of the 5th metatarsal. The calcaneometatarsal ligament (plantar ligament of the sole, a thickening of the plantar aponeurosis), plantar cuboideometatarsal, and plantar intermetatarsal ligaments also attach to the plantar surface of the base. Shaft The shaft of the 5th metatarsal has a different orientation than those of the 2nd–4th, having a dorsal, medial, and plantar surface. The lateral head of the 4th dorsal interosseous and the 3rd plantar interosseous muscles originate from the shaft of the 5th metatarsal. Phalanges The 1st (great) toe has two phalanges, proximal and distal. The lesser toes (2nd – 5th) have three phalanges per toe: proximal, middle, and distal (terminal). Great Toe Proximal Phalanx The proximal end of the proximal phalanx is wider transversely than dorsoplantarly deep. It has an oval, concave proximal articular surface known as the glenoid cavity. The glenoid cavity is smaller than the head of the metatarsal, which articulates with it. A short, transverse crest or tubercle is present on the dorsal surface of the base marking the insertion of the extensor hallucis brevis. Two tubercles are present near the base of the plantar surface of the proximal phalanx. The medial plantar tubercle is larger than the lateral and serves as the insertion for the medial head of flexor hallucis brevis and abductor hallucis muscles. The lateral head of flexor hallucis brevis and adductor hallucis muscles insert onto the lateral plantar tubercle. The shaft of the proximal phalanx of the great toe is concave plantarly and convex dorsally. Its plantar surface is grooved proximally and distally by the tendon of flexor hallucis longus. The head of the proximal phalanx is wide transversely and flattened dorsoventrally. The articular surface is trochlear in shape and extends farther plantarly than dorsally. 14 Distal Phalanx The distal phalanx of the great toe has a large, transversely oriented base. The long axis of the distal phalanx deviates approximately 15º lateral to that of the proximal phalanx. The extensor hallucis longus inserts to a tuberosity near the base of the dorsal surface of this phalanx. The flexor hallucis longus has a more substantial insertion on the base of the plantar surface. Lesser Toes The proximal phalanges of the lesser toes are the longest phalanges, longer than the middle and distal phalanges combined. The bases have oval facets for the metatarsal heads. Each proximal phalanx has two plantar tubercles, one medial and one lateral. On the 3rd – 5th toes, the medial plantar tubercle is for attachment of plantar interossei. Both tubercles of the 2nd toe and the lateral tubercle of the 3rd and 4th toes are for dorsal interossei. The lateral tubercle of the 5th toe is for abductor digiti minimi and flexor digiti minimi brevis. Sesamoid Bones Sesamoid bones are usually small bones that develop within tendons. There are more sesamoid bones in the foot than anywhere else in the body. The two most constant sesamoid bones of the foot are the medial (tibial) and lateral (fibular) bones within the tendons of flexor hallucis brevis, located at the 1st metatarsophalangeal joint. The medial sesamoid bone is usually larger than the lateral. Two other sesamoid bones of the foot are quite constant. One of these bones is located within the tendon of tibialis anterior as it crosses the smooth facet on the medial cuneiform. This bone, although almost always present, gets no special name. The other relatively constant bone, the os peroneum, is located within the tendon of fibularis longus as it crosses the cuboid. There are numerous other sesamoid bones that are variably present. The following list of these bones is arranged in sequence of decreasing frequency: tendon of flexor digitorum brevis to the 2nd toe at the metatarsophalangeal joint (MPJ). tendon of flexor digitorum brevis to the 5th toe at the MPJ. tendon of tibialis posterior plantar to the navicular. tendon of flexor digitorum brevis to 3rd toe at the MPJ. tendon of flexor digitorum brevis to the 4th toe at the MPJ. tendon of flexor hallucis longus at the interphalangeal joint (IPJ). tendon of flexor digitorum longus at the proximal interphalangeal joints: 2nd > 5th > 3rd > 4th any of the following tendons as they cross the malleoli: tibialis posterior flexor digitorum longus flexor hallucis longus fibularis longus fibularis brevis Accessory Bones Accessory bones, supernumerary or extra bones, are more common in the foot than anywhere else in the body. Accessory bones form because of anomalies in ossification in which secondary ossification centers fail to fuse with the major portion of a bone. Some accessory bones are fairly common while others are quite rare. Knowledge of these bones and their locations is important in distinguishing them from possible fractures. 15 The most common accessory bones of the foot are os trigonum, os tibiale (externum) and os intermetatarseum I. The os trigonum is associated with the lateral tubercle of the posterior process of the talus, the os tibiale (externum) occurs when the secondary ossification center in the navicular tuberosity fails to fuse with the rest of the navicular, and the os intermetatarseum is located between the medial cuneiform and the bases of the first and second metatarsals. The following accessory bones occur rarely: Os uncinatum—associated with the lateral cuneiform Os intercuneiform Os vesalianum— “Vesalius’ Bone”, associated with the tuberosity of the 5th met. Os supratalare Os cuboideum secondarium Os calcaneus secondarium Os supranaviculare Os sustentaculum tali Ossi cation of Foot Bones All tarsal bones typically have a single ossification center except for the calcaneus, which has a secondary ossification center in the calcaneal tuberosity. The talus, navicular, and medial cuneiform also sometimes have secondary ossification centers1, 2, 3, although this is uncommon. Each metatarsal has two ossification centers, a diaphysis in the shaft (appears in utero) and a secondary ossification center (epiphysis). For the 1st metatarsal, the epiphysis is proximal (appears during year 3). For the 2nd – 5th metatarsals, the epiphysis is at the head (appears during years 5-8). Each phalanx has two ossification centers; a diaphysis in the shaft, and epiphysis at the base. Sequence of Ossi cation Bone Metatarsals & Phalanges Calcaneus Talus Cuboid Lateral Cuneiform Medial Cuneiform Intermediate Cuneiform Navicular Age Ossification Begins 9–12 weeks in utero 4–7 months in utero 6 months in utero At birth 1 year 2 years 3 years 3 years Arches of the Foot The bones of the foot are arranged in two longitudinal arches. The medial arch consists of the 1st – metatarsals, all three cuneiforms, navicular, talus, and calcaneus; the talar head forms the keystone of this arch. The lateral arch includes the 4th and 5th metatarsals, cuboid, and calcaneus. The cuboid is the keystone of this arch. The transverse arch of the foot originates at the tarsometatarsal articulation and includes the distal row of tarsal bones and all five metatarsals. The intermediate cuneiform forms the keystone of the transverse arch. 3rd 1 Draves, DJ. 1986. Anatomy of the Lower Extremity. Williams & Wilkins, Baltimore, MD McDougall, A. 1955. Journal of Bone and Joint Surgery 37A:257–265. 3 Warwick, R. and Williams, P.L. 1973. Gray’s Anatomy, 35th British Edition. W.B. Saunders Company, Philadelphia, PA. 2 fi fi 16 3 | DORSUM OF THE FOOT Fascia The superficial fascia of the dorsum of the foot is the relatively thin continuation of the superficial fascia of the leg and contains superficial vessels and cutaneous nerves. The deep fascia (dorsalis pedis fascia) is continuous with the crural fascia of the leg. At the ankle, the deep fascia forms several specialized thickenings, or retinacula (described below), that prevent bowstringing of the tendons of the extrinsic muscles of the foot. The deep fascia also divides the dorsum of the foot into three layers arranged from superficial to deep. The first layer contains the tendons and accompanying synovial sheaths of the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius muscles. The second layer contains the extensor digitorum brevis muscle. The third layer contains the dorsalis pedis artery and its branches, the deep fibular nerve and its branches, the veins accompanying the dorsalis pedis artery, and the termination of the perforating branch of the fibular artery. The deep fascia of the dorsal foot is continuous with the plantar aponeurosis and attaches to the fibular trochlea, cuboid, and the tuberosity of the 5th metatarsal laterally, and the navicular tuberosity, sustentaculum tali, and 1st metatarsal medially. Retinacula Superior Extensor Retinaculum The superior extensor retinaculum (ligamentum transversum cruris; superior part of the anterior annular ligament) attaches laterally to the anterior border of the distal fibula and to the lateral surface of the lateral malleolus. Medially, it attaches to the anterior border of the tibia and to the medial malleolus. It blends with the superior fibular retinaculum laterally, and with the superomedial oblique band of the inferior extensor retinaculum and the flexor retinaculum medially. The tendons and tendon sheaths of the extensor digitorum longus, extensor hallucis longus, fibularis tertius, and tibialis anterior pass deep to the superior extensor retinaculum. Inferior Extensor Retinaculum The inferior extensor retinaculum (frondiform ligament of Retzius; anterior ligament of the tarsus; ligamentum cruciatum of Weitbrecht; ligamentum lambdoideum) is usually Y-shaped but may have an oblique superolateral band making it an X-shaped structure. The laterally directed stem of the "Y" (frondiform ligament) consists of three roots. The lateral root is attached to the sinus tarsi lateral to the origin of the extensor digitorum brevis. The intermediate root attaches to the sinus tarsi medial to the origin of extensor digitorum brevis. The medial (deep) root attaches to the sulcus tali posterior to the attachment of the interosseous talocalcaneal ligament and may blend with it. The frondiform ligament forms a loop or sling around the tendons of the extensor digitorum longus and fibularis tertius muscles, and fibers of the intermediate root continue medially to form the superomedial and inferomedial oblique bands. The extensor digitorum brevis muscle takes partial origin from the deep surface of the frondiform ligament. The superomedial oblique band forms the superior arm of the "Y" of the inferior extensor retinaculum and has both deep and superficial components. The superficial portion passes superficial to the tendon of the extensor hallucis longus, the anterior tibial artery and vein, and deep fibular nerve. Medial to the extensor hallucis longus tendon, the superficial and deep layers fuse to form a tunnel for the tendon of the tibialis anterior. The superomedial oblique band attaches medially on the anterior surface of the medial malleolus. 17 The inferomedial oblique band (the inferior arm of the inferior extensor retinaculum) passes superficial to the dorsalis pedis artery, deep fibular nerve, and tendons of the extensor hallucis longus and tibialis anterior muscles. Some fibers may pass deep to the tibialis anterior tendon forming a tunnel for it. The inferomedial oblique band attaches medially to the plantar fascia, navicular tuberosity, and medial cuneiform. The superolateral oblique band is present in about 25% of people and extends from the superomedial oblique band and frondiform ligament to attach on the lateral surface of the lateral malleolus. It merges with the superior extensor retinaculum and the superior fibular retinaculum. Extensor Expansions The extensor expansions (extensor apparatus, dorsal digital expansions) are formed by the tendons of the extensor digitorum longus (EDL) and extensor hallucis longus (EHL) muscles and are similar in configuration to the extensor expansions of the fingers. Extensor expansions of the 2nd, 3rdand 4th digits are comparable and will be discussed together. The extensor expansion of the hallux and 5th digit differ slightly and are discussed separately. What follows is a short summary of the structure and function of the extensor expansions of the toes, however, the anatomical details of these structures are poorly documented and the actions produced by the pull of each of the contributing muscles has not been extensively tested or described. Structure Digits 2–4 The EDL tendons of the 2nd – 4th digits divide into three slips over the proximal phalanx, one central slip and two lateral slips. The central slip passes distally along the dorsum of the proximal phalanx and inserts on the base of the middle phalanx. The two lateral slips run along each side of the proximal and middle phalanges and converge over the distal end of the middle phalanx. This combined tendinous slip passes distally as the terminal slip to insert on the base of the distal phalanx. Tendons of the extensor digitorum brevis (EDB) join the lateral aspect of the EDL tendons at or distal to the level of the division into three slips. When the EDB joins lateral to the trifurcation, it forms the lateral slip of the extensor expansion. The proximal part of the extensor expansion is known as the extensor sling (transverse lamina, quadrilateral lamina). It is formed by transverse fibers that encircle the digit at the level of the metatarsophalangeal joint to attach to the plantar plate and deep transverse metatarsal ligament. The distal part of the extensor expansion, called the extensor wing (extensor hood), consists of oblique fibers and is triangular in shape. The extensor wing is continuous proximally with the extensor sling and attaches to the lateral and middle slips of the EDL tendon dorsally. The extensor wing is welldeveloped on the medial side of the digit but sources vary about its relative development on the laterally4, 5. Lumbrical tendons insert onto the extensor wing on the medial side of the digit, forming the inferior margin of the wing. The contribution of the dorsal and plantar interossei to the extensor expansions is debated. Seraffian & Topuzian (1969) describe the interossei as contributing fibers to the deep surface of the extensor sling, whereas Dalmau-Pastor et al. (2014) did not find a contribution from the lumbricals to any part of the extensor expansion. Digit 1 Only the tendon of the extensor hallucis longus contributes to the formation of the extensor expansion dorsally and the plantar plate is attached to the deep transverse metatarsal ligament on the 4 5 Seraffian & Topouzian. 1969. Journal of Bone and Joint Surgery 51 A:669–679. Dalmau-Pastor et al. 2014. Foot and Ankle International 35: 957–969. 18 lateral side only. A wing and sling are present, but lumbricals and interossei do not contribute to them. Rather, they are formed by the abductor hallucis and the medial head of the flexor hallucis brevis medially, and by the adductor hallucis and lateral head of the flexor hallucis brevis laterally. Digit 5 Because digit 5 lacks a tendon from EDB, the abductor digiti minimi and flexor digiti minimi contribute to the extensor expansion laterally. Function Extensor Digitorum Longus The EDL has no attachment to the dorsal aspect of the proximal phalanx. When this muscle contracts, it pulls on the extensor sling, which pulls the plantar plate and proximal phalanx into extension (or hyperextension) at the metatarsophalangeal joints. Once the metatarsophalangeal joint is hyperextended, the EDL cannot extend the interphalangeal joints. Extension of the interphalangeal joints occurs through concurrent contraction of the extensor digitorum longus tendon and the other muscles contributing to the extensor expansions. Extensor Digitorum Brevis Contraction of the EDB pulls on the lateral slip and terminal slips of the digits and acts to extend the interphalangeal joints. Lumbricals Because the lumbricals travel plantar to the metatarsophalangeal joints, these muscles act to flex this joint. Because their tendons join the wings of the extensor expansions, which ultimately attach to the dorsum of the digits, contraction of the lumbricals extends the interphalangeal joints. Interossei The action of the interossei on flexion/extension of the digits depends on whether or not they contribute to the extensor expansions. The interossei lie plantar to the metatarsophalangeal joint, making them flexors of this joint. If the interossei do contribute to the extensor expansions, they may also act as weak flexors of the interphalangeal joints. Muscles EXTENSOR DIGITORUM BREVIS Origin Insertion 19 A tubercle on the superolateral surface of the calcaneus just anterior to the calcaneal sulcus, interosseous talocalcaneal ligament, and frondiform ligament. From its origin it passes diagonally across the foot from lateral to medial, to end in four tendons. The most medial of these tendons crosses the dorsalis pedis artery and it is sometimes described as a separate muscle, the extensor hallucis brevis (see below). Lateral surface of the extensor digitorum longus tendons of the 2nd, 3rd, and 4th digits, just distal to the metatarsophalangeal joints. Innervation Lateral branch of the deep fibular nerve. In 20% of individuals, an accessory fibular branch of the superficial fibular nerve assists in innervating the muscle. Function Aids extensor digitorum longus in extension of the phalanges and MP joints of the 2nd, 3rd, and 4th digits. When the long and short extensors act without the lumbricals, they tighten the extensor sling, extending the MP joints (see discussion of extensor expansion below) and pulling the plantar pad against the proximal phalanx. Variations There may be accessory slips of origin from the talus and navicular, or lateral cuneiform and third metatarsal, or cuboid. There may be only two tendons, or the tendons may be doubled. Finally, an accessory tendon to the fifth digit may be present. EXTENSOR HALLUCIS BREVIS Origin Insertion Same as extensor digitorum brevis. Dorsal surface of the base of the proximal phalanx of the hallux. Innervation Same as extensor digitorum brevis. Function Extends the MP joint of the hallux. Nerves Saphenous Nerve The saphenous nerve is a cutaneous branch of the femoral nerve that runs along the lateral side of the great saphenous vein in the leg and enters the dorsum of the foot anterior to the medial malleolus. It follows the medial marginal vein in the foot as far as the first metatarsal bone. to provide cutaneous innervation to the medial arch of the foot. The saphenous nerve is also described with the veins of the leg and thigh. Sural Nerve The sural nerve is a cutaneous branch from the tibial and common fibular nerves that enters the foot inferior to the lateral malleolus together with the small saphenous vein. The nerve courses into the lateral side of the foot where it becomes the lateral dorsal cutaneous nerve. The terminal part of the nerve courses distally along the lateral side of the 5th toe where it becomes the 10th dorsal digital nerve. On occasion the lateral dorsal cutaneous nerve will give rise to or anastomose with the intermediate dorsal cutaneous nerve of the foot. Common Fibular Nerve The origin of the superficial and deep fibular nerves from the common fibular nerve is described with the leg. Super cial Fibular Nerve This nerve penetrates through the crural fascia in the inferior third of the leg and divides into its two terminal branches, the medial and intermediate dorsal cutaneous nerves, which provide cutaneous innervation to the dorsum of the foot. fi 20 Medial Dorsal Cutaneous Nerve This nerve gives rise to one dorsal digital branch (1st dorsal digital nerve) and one common dorsal digital branch (1st common dorsal digital nerve). The 1st dorsal digital nerve travels medially over the dorsum of the foot to innervate the medial side of the great toe. The 1st common dorsal digital nerve courses to the space between the 2nd and 3rd toes, where it divides into the 4th and 5th dorsal digital nerves. Branches of the medial dorsal cutaneous nerve communicate with the saphenous nerve and on occasion, with the medial branch of the deep fibular nerve. Intermediate Dorsal Cutaneous Nerve This nerve divides into the 2nd and 3rd common dorsal digital nerves for the 3rd and 4th intermetatarsal spaces. In the web space, each common dorsal digital branch divides into two dorsal digital nerves, the 6th – 9th dorsal digital nerves. The intermediate dorsal cutaneous nerve has some communication with the lateral dorsal cutaneous nerve. Deep Fibular Nerve This nerve accompanies the anterior tibial artery deep to the extensor retinaculum into the dorsum of the foot, where it divides into its two terminal branches: medial and lateral branches. It also provides an articular branch to the ankle joint. Lateral Branch The lateral branch follows the lateral tarsal artery deep to the extensor digitorum brevis and provides motor innervation to this muscle. It has three interosseous branches which serve the intertarsal joints and the metatarsophalangeal joints of the 2nd, 3rd, and 4th digits. Medial Branch This branch runs with the dorsalis pedis artery on the dorsum of the foot. In the 1st intermetatarsal space, it divides into two dorsal digital nerves (2nd and 3rd) which supply the skin of adjacent sides of the 1st and 2nd toes. The medial branch sometimes communicates with the medial dorsal cutaneous branch of the superficial fibular nerve. It has one interosseous branch, which supplies the metatarsophalangeal joint of the 1st digit. Arteries Anterior Tibial Structures of the dorsum of the foot are supplied by branches of the anterior tibial artery. Other branches of this artery supplying the anterior compartment of the leg are described with the arteries of the leg. Anterior Medial Malleolar The anterior medial malleolar artery branches from the anterior tibial artery about 5 cm proximal to the ankle joint. This small vessel travels inferomedially across the superior extensor retinaculum, deep to the extensor hallucis longus and tibialis anterior muscles to ramify around medial malleolus. Here it anastomoses with branches of the dorsalis pedis, posterior tibial, and medial plantar arteries, forming the medial malleolar rete (medial malleolar network). 21 Anterior Lateral Malleolar The anterior lateral malleolar artery originates from the lateral aspect of the anterior tibial artery close to the origin of the anterior medial malleolar branch. It passes deep to the tendons of extensor digitorum longus and the fibularis tertius muscles to supply the lateral side of the ankle joint and contributes to the lateral malleolar rete. Dorsalis Pedis The anterior tibial artery changes its name to the dorsalis pedis artery at the transmalleolar line (an imaginary line joining the medial and lateral malleoli) and continues to supply the dorsum of the foot. In about 75% of cases, the dorsalis pedis can be traced distally across the talus, navicular, intermediate cuneiform and the base of the second metatarsal bone into the 1st intermetatarsal space, where it divides into its two terminal branches, the deep plantar and the 1st dorsal metatarsal arteries. The course of the artery across the dorsum of the foot can be approximated by drawing a line from the middle of the transmalleolar line to the proximal part of the first intermetatarsal space, however, there is a great deal of variation in the location and size of the dorsalis pedis artery. In about 10% of cases, the artery is either deviated to the medial or the lateral side. The dorsalis pedis artery is usually about two or three mm in diameter, however, it may be very large or so small that it is virtually absent (5–10% of individuals). It In cases where the artery is deficient or absent, the plantar arteries or the perforating branch of the fibular artery take over. If the anterior tibial artery is absent (5%), the dorsalis pedis then usually originates from the perforating branch of the fibular artery. The first part of the artery is very superficial, being covered by skin, fascia and the inferior extensor retinaculum. The artery travels in between the tendons of the extensor hallucis longus (on its medial side) and the extensor digitorum longus (on its lateral side). At its distal end, it is crossed by the tendon of the extensor hallucis brevis. Although the dorsalis pedis for the most part lies deep to the superficial structures of the dorsum of the foot, it is superficial enough to demonstrate a pulse while the artery is passing anterior to the tarsal bones, between the tendons of extensor hallucis longus and extensor digitorum longus. If the pulse cannot be detected, it is often because the anterior tibial artery terminates after giving off its malleolar branches at the ankle joint. There are many unnamed muscular and nutrient twigs that arise from the dorsalis pedis as it works its way towards the 1st intermetatarsal space; those described below are the major branches supplying the dorsum of the foot. Other small branches arising from the dorsalis pedis, along with branches of the lateral tarsal and arcuate arteries, form an anastomotic network (rete) along the dorsum of the foot. Lateral Tarsal Artery This is often the largest branch of the dorsalis pedis and branches from the dorsalis pedis at the neck of the talus. Occasionally, a second, much smaller, lateral tarsal artery branches from the dorsalis pedis as it crosses the intermediate cuneiform. In this case, they are known as the proximal and distal lateral tarsal arteries. The lateral tarsal artery courses laterally and distally across the talonavicular junction and dorsum of the cuboid deep to the extensor digitorum brevis muscle, which it supplies. It then continues laterally deep to the tendon of the fibularis brevis muscle to anastomose with the lateral plantar artery. It also provides branches that anastomose with the perforating branch of the fibular artery, the arcuate artery, and the anterior lateral malleolar rete. Branches from the proximal part of the lateral tarsal artery provide vascular supply to the head and neck of the talus. Smaller branches supply the other tarsal bones and intertarsal joints. In 20 to 30% of cases, the artery to the sinus tarsi originates from the lateral tarsal artery. 22 Medial Tarsal Arteries There are usually two medial tarsal arteries that originate from the dorsalis pedis opposite the origin of the proximal lateral tarsal artery. They supply the medial aspect of the tarsal bones and terminate by contributing to the medial malleolar rete. Arcuate Artery In about 65% of cases, this artery originates from the dorsalis pedis artery at the level of the first tarsometatarsal joint. In other cases, its origin can be slightly more proximal and, therefore, it can be confused with the lateral tarsal artery. From its origin, the arcuate artery runs laterally across the bases of the second, third and fourth metatarsals deep to the tendons of the extensor digitorum brevis muscle. On the lateral side of the foot, it anastomoses with the lateral tarsal and lateral plantar arteries. As it crosses the foot from medial to lateral, it gives rise to the 2nd, 3rd, and 4th dorsal metatarsal arteries. Dorsal Metatarsal Arteries 2-4 There are four dorsal metatarsal arteries. The 1st dorsal metatarsal artery is a direct branch of the dorsalis pedis (discussed below), whereas the other three (2nd–4th) are branches of the arcuate artery. These arteries are numbered 2–4 from medial to lateral. Each artery courses in an intermetatarsal space superficial to the dorsal interosseous muscle and terminates at the metatarsophalangeal joint by dividing into two dorsal digital arteries. At the proximal end of each interosseous space each artery receives a posterior perforating branch from the deep plantar arch, and at the distal end of each interosseous space, the dorsal metatarsal arteries receive an anterior perforating artery from the plantar metatarsal arteries. In the absence of the arcuate artery, the posterior perforating arteries are usually larger and give rise to the 2nd, 3rd, and 4th dorsal metatarsal arteries. After receiving the distal perforating arteries, the dorsal metatarsal arteries sometimes called common dorsal digital arteries. Dorsal Digital Arteries These arteries supply the adjacent sides of toes 2 to 5 and are numbered 4 to 9 from medial to lateral. The dorsal digital arteries of each toe communicate with each other at the distal end of the toes. The 10th dorsal digital artery branches either from the lateral part of the arcuate artery or from the 4th dorsal metatarsal artery. The 1st– 3rd dorsal digital arteries are branches of the 1st dorsal metatarsal artery. 1st Dorsal Metatarsal Artery After giving off the arcuate artery, the dorsalis pedis continues into the 1st interosseous space where it provides its terminal branches, the deep plantar and the 1st dorsal metatarsal arteries. The 1st dorsal metatarsal artery runs distally in the first interosseous space over the dorsum of the first dorsal interosseous muscle and gives off the 1st dorsal digital artery, whcih travels medially over the head of the first metatarsal bone and deep to the tendons of extensor hallucis longus and brevis to vascularize the medial side of the great toe. The 1st dorsal metatarsal artery continues distally and at the webbing of the toes divides into the 2nd and 3rd dorsal digital arteries, which supply the adjoining sides of the 1st and 2nd toes respectively. The 1st dorsal metatarsal artery supplies the 1st dorsal interosseous muscle, 1st metatarsophalangeal joint (via articular branches), and the soft tissues around the medial side of the 1st toe and the adjacent sides of the 1st and 2nd toes. 23 Deep Plantar Artery The deep plantar artery arises from the dorsalis pedis at the proximal part of the 1st interosseous space and penetrates the first dorsal interosseous muscle to reach the plantar side of the foot where it joins with the deep plantar arch. Occasionally the 1st plantar metatarsal artery is a branch of or a direct continuation of the deep plantar artery, rather than originating from the deep plantar arch. Perforating Branch of Fibular Artery The perforating branch of fibular artery pierces the interosseous membrane, about 5 cm superior to the lateral malleolus to gain access to the anterior aspect of the leg and dorsum of the foot. In the anterior leg, it courses along the anterior side of the distal tibiofibular joint deep to the tendon of fibularis tertius muscle. While traveling distally and laterally, it anastomoses with the anterior lateral malleolar branch of the anterior tibial artery and contributes to the lateral malleolar rete. Terminal branches of the perforating branch of the fibular artery anastomose with the lateral tarsal artery. In about 1 to 5% of cases, the perforating branch of the fibular artery continues along the dorsum of the foot as the dorsalis pedis or lateral tarsal artery. Veins There are two sets of veins in the foot—a superficial and a deep group. Super cial Veins There are ten dorsal digital veins that run on the medial and lateral sides of each toe. The 2nd – 9th dorsal digital veins unite to form four dorsal metatarsal veins, which contribute to the formation of the dorsal venous arch at the level of the distal ends of the metatarsal bones. Laterally, the arch is joined by the 10th dorsal digital vein (lateral dorsal digital vein of the 5th toe) to form the lateral marginal vein. The medial marginal vein is formed by the union of the 1st dorsal digital vein (medial dorsal digital vein of the 1st/great toe) and the medial end of the dorsal venous arch. Anterior to the medial malleolus, the medial marginal vein becomes the great saphenous vein and the lateral marginal vein becomes the small saphenous vein inferior to the lateral malleolus. Deep Veins Deep veins of the foot typically form venae comitantes, paired veins that encircle and anastomose around the arteries. These veins take the same names as the arteries they follow. Tributaries to the dorsalis pedis veins arise from the dorsal venous plexus and follow the dorsalis pedis artery and its branches proximally up the ankle to become the anterior tibial veins. fi 24 4 | PLANTAR SURFACE OF THE FOOT Fascia The superficial fascia of the plantar foot is thicker in areas in contact with the ground, such as the heel and ball of the foot, than in other areas. Fat in the superficial fascia acts as a shock absorber and is divided into compartments by fibers that connect the superficial fascia to skin and to deep fascia. The deep fascia of the plantar foot thickens to form the superior and inferior fibular retinacula (external or lateral annular ligament of the tarsus) on the lateral side of the ankle, flexor retinaculum on the medial side of the ankle, and the plantar aponeurosis overlying the muscles of the plantar foot. Plantar Aponeurosis The plantar aponeurosis is a highly specialized, three-part structure with strong, longitudinally oriented fibers. The central part of the plantar aponeurosis is the thickest. It attaches posteriorly on the medial process of the calcaneal tuberosity and becomes thinner as it passes anteriorly. At the metatarsal heads, it divides into five processes, one for each digit. Each digital process is divided into a deep and a superficial layer. The superficial layer is attached to the skin of the transverse sulcus. The deep layer further divides into two slips, one on each side of the flexor tendons of each digit, that blend with the tendon sheaths. Digital nerves, vessels, and tendons of the lumbricals become superficial in between the digital slips. The superficial transverse metatarsal ligament, a band of transversely oriented fibers, is also located at the level of the metatarsal heads and blends with the superficial layer of the digital processes. The lateral part of the plantar aponeurosis is attached to the lateral process of the calcaneal tuberosity proximally and lies superficial to the abductor digiti minimi muscle. Proximally, it forms a strong band between the lateral process of the calcaneal tuberosity and the base of the 5th metatarsal called the calcaneometatarsal ligament. The medial part of the plantar aponeurosis is continuous proximally with the flexor retinaculum and lies superficial to the abductor hallucis muscle. There are two vertical intermuscular septa which pass deep into the foot from the junction between lateral and central and medial and central parts of the plantar aponeurosis. These septa divide the plantar musculature into three compartments. The medial compartment contains the intrinsic muscles of the 1st digit and the lateral compartment contains the intrinsic muscles of the 5th digit. The central compartment contains the quadratus plantae, flexor digitorum brevis, lumbricals, and interosseous muscles. Muscles of the plantar foot are more conventionally described in four layers arranged from superficial to deep. These layers are separated by thin transverse septa that arise from the medial and lateral intermuscular septa. Retinacula Flexor Retinaculum The flexor retinaculum (laciniate ligament; medial annular ligament) attaches superiorly to the anteromedial surface of the medial malleolus and inferiorly to the superior border of the abductor hallucis muscle and to the medial process of the calcaneus, forming a triangular band of deep fascia. It is continuous with the deep fascia of the foot and with the deep fascia of the leg. The flexor retinaculum forms the roof of the tarsal (talocalcaneal) tunnel which is divided into four compartments housing the tendon of the tibialis posterior (1st compartment), tendon of the flexor digitorum longus (2nd compartment), posterior tibial artery and tibial nerve (3rd compartment), and the tendon of the flexor hallucis longus muscle (4th compartment). 25 Superior Fibular Retinaculum The superior fibular retinaculum attaches anteriorly on the posterior border of the lateral malleolus and posteriorly to the lateral surface of the calcaneus and the calcaneal tendon. It forms a single tunnel for the tendons of the fibularis brevis and longus muscles. Inferior Fibular Retinaculum The inferior fibular retinaculum is attached anteriorly to the lateral rim of the calcaneal sulcus and posteriorly to the lateral surface of the calcaneus. Deep fibers from the inferior fibular retinaculum attach to the fibular trochlea, forming two tunnels, one each for the tendon of fibularis brevis superiorly and fibularis longus inferiorly. Vincula Vincula are extensions of the synovial sheaths of tendons that surround neurovascular structures running between joint capsules and tendons. Each digit typically has five vincula; two vincula brevia (short vincula) and three vincula longa (long vincula). Vincula Brevia These vincula are short, triangular sheets located at the distal ends of the tendons close to their attachments to the phalanges. The most proximal vinculum brevis connects the flexor digitorum brevis tendon to the proximal interphalangeal joint, and the distal one the flexor digitorum longus tendon to the distal interphalangeal joint. Vincula Longa The vincula longa are longer cord-like structures. There are typically two proximal and one distal vincula longa. The two proximal vincula longa are attached to the two slips of the flexor digitorum brevis on either side of the flexor digitorum longus tendon and connect to either side of the proximal end of the proximal phalanx. The distal vinculum longum runs between the flexor digitorum longus and the proximal interphalangeal joint, sometimes blending with the proximal vinculum brevis. Muscles 1st Layer ABDUCTOR HALLUCIS The abductor hallucis is a large muscle that forms a roof over the porta pedis, teh entrance of the plantar vessels and nerves into the foot. Origin Insertion 26 Medial process of the calcaneal tuberosity, flexor retinaculum, plantar aponeurosis, and the medial intermuscular septum. Medial side of the plantar surface of the base of the proximal phalanx of the 1st digit via a flattened tenson in common with the flexor hallucis brevis. Some fibers may attach to the medial sesamoid of the first MP joint. Innervation Trunk of medial plantar nerve. Function Abducts 1st toe. FLEXOR DIGITORUM BREVIS The flexor digitorum brevis lies deep to the central part of the plantar aponeurosis. The lateral plantar vessels and nerve pass deep to this muscle. Origin Insertion Plantar aponeurosis, medial and lateral intermuscular septa, and medial process of the calcaneal tuberosity. Medial and lateral base of the middle phalanges of the 2nd – 5th digits. Each tendon runs in the tendon sheath of the flexor digitorum longus until the level of the of the proximal phalanx where it divides into two slips that surround the tendon of the flexor digitorum longus. Deep to the flexor digitorum longus tendon the slips share fibers before they insert. Innervation Trunk of medial plantar nerve. Function Flexes the PIP and MP joints of the 2nd – 5th digits. Variations The tendon to the fifth digit may be absent. ABDUCTOR DIGITI MINIMI The abductor digiti minimi lies superficially, along the lateral margin of the foot. Origin Lateral and medial processes of the calcaneal tuberosity, and the depression between them. Insertion Lateral side of the plantar surface of the base of the proximal phalanx of the 5th digit, in common with flexor digiti minimi brevis. Its tendon it lies in a groove on the plantar surface of the fifth metatarsal medial to the tuberosity. Innervation Nerve to abductor digiti minimi from lateral plantar nerve (Baxter’s nerve). Function Abducts and flexes the 5th digit. Variations There may be an accessory insertion into the base of the fifth metatarsal. If present it forms a separate muscle, the abductor os metatarsi digiti minimi. 2nd Layer QUADRATUS PLANTAE Also known as the flexor (digitorum) accessorius muscle. Origin Medial head: medial process of the calcaneal tuberosity. Lateral head: lateral process of the calcaneal tuberosity. The two heads are separated by the long plantar ligament. Insertion Tendon of the flexor digitorum longus. 27 Innervation Trunk of lateral plantar nerve. Function Contraction of the quadratus plantae straightens the tendons of the flexor digitorum longus, to assist in flexion of the 2nd – 5th digits. Variations Either the lateral head or the entire muscle may be absent. LUMBRICALS There are four lumbricals, numbered from medial to lateral. Origin Insertion Tendons of the flexor digitorum longus. The 2nd – 4th lumbricals arise from the adjacent sides of flexor tendons. The 1st lumbrical originates from the medial side of the most medial tendon only. The lumbricals, pass distally medial to the flexor tendons and superficial to the deep transverse metatarsal ligament. Medial extensor expansion wings of the 2nd – 5th digits. Innervation 1st lumbrical: 1st common plantar digital nerve (from medial plantar) 2nd – 4th lumbricals: Deep branch of the lateral plantar nerve. Function The lumbricals flex the MP joints and extend the IP joints. The mechanism for these actions is discussed in the section on extensor expansions. Variations One or more lumbricals may be absent. The third or fourth lumbrical may be doubled. They may insert directly into the bone of the proximal phalanx instead of the extensor expansion. 3rd Layer FLEXOR HALLUCIS BREVIS Origin Insertion Lateral head: Cuboid near the fibular groove, lateral cuneiform adjacent to the cuboid and, occasionally, from the long and short plantar ligaments. Medial head: Tendon of the tibialis posterior, medial intermuscular septum. Medial head: Medial side of the plantar surface of the base of the proximal phalanx, the medial sesamoid and the plantar pad of the hallux in common with the abductor hallucis. Lateral head: Lateral side of the plantar surface of the base of the proximal phalanx, the lateral sesamoid and the plantar pad of the hallux in common with the adductor hallucis. As the muscle passes toward the first digit, fibers from the two heads fuse briefly and then divide into two bellies. Innervation 1st proper plantar digital nerve (medial plantar nerve). Function Flexes the 1st MP joint. Variations The attachment to the cuboid may be absent and there may be an additional insertion into the proximal phalanx of the second digit. 28 ADDUCTOR HALLUCIS Origin Insertion Oblique head: Plantar surface of the bases of the 2nd – 4th metatarsals and the tendon of the fibularis longus. Transverse head: Plantar plates, plantar metatarsophalangeal ligaments, and deep transverse metatarsal ligament. In common with the lateral head of the flexor hallucis brevis (see above). Innervation Deep branch of the lateral plantar nerve. Function Adducts the 1st MP joint. Variations The origin of both heads is highly variable. Sometimes a portion may insert into the first metatarsal forming an opponens hallucis muscle. FLEXOR DIGITI MINIMI BREVIS Origin Insertion Plantar surface of the base of the 5th metatarsal, tendon of the fibularis longus, and plantar aponeurosis. Plantar surface of the proximal phalanx of the 5th digit in common with the abductor digiti minimi. Innervation Superficial branch of the lateral plantar nerve. Function Flexes and abducts the 5th digit. Variations Deeper fibers may form part of a separate muscle, the opponens digiti minimi. 4th Layer PLANTAR INTEROSSEI Origin Insertion Bases and medial sides of the shafts of the 3rd – 5th metatarsals. Medial sides of the bases of the 3rd – 5th proximal phalanges, capsules of the metatarsophalangeal joints, and extensor expansions. Innervation 1st and 2nd: Deep branch of the lateral plantar nerve. 3rd: Superficial branch of the lateral plantar nerve. Function Adduct the 3rd – 5th digits. DORSAL INTEROSSEI Origin 29 Adjacent sides of the metatarsal bones as follows: 1st: Lateral side of 1st and medial side of 2nd metatarsals. 2nd: Lateral side of 2nd and medial side of 3rd metatarsals. Insertion 3rd: Lateral side of 3rd and medial side of 4th metatarsals. 4th: Lateral side of 4th and medial side of 5th metatarsals. Bases of the proximal phalanges and extensor expansions as follows: 1st: Medial side of the second digit. 2nd: Lateral side of the second digit. 3rd: Lateral side of the third digit. 4th: Lateral side of the fourth digit. Innervation 1st – 3rd: Deep branch of the lateral plantar nerve. 4th: Superficial branch of the lateral plantar nerve. Function Abduct the 2nd – 4th digits. Nerves Sural Nerve Lateral Calcaneal Nerve This nerve supplies the lateral aspect of the plantar surface of the skin overlying the heel. It is the only nerve supplying the plantar surface of the foot that is not a branch if the tibial nerve. Tibial Nerve All of the motor and sensory nerves in the plantar foot are branches of the tibial nerve. Refer to the sections on the leg and thigh for detailed information on the more proximal branches of this nerve. Medial Calcaneal Nerve This is the last branch of the tibial nerve before it bifurcates into medial and lateral plantar nerves. The medial calcaneal nerve pierces the flexor retinaculum to supply cutaneous innervation to the medial and plantar aspects of the heel. Medial Plantar Nerve This is the largest of the terminal branches of the tibial nerve in the foot. It originates deep to the flexor retinaculum and enters the foot deep to the muscle belly of the abductor hallucis. Between the abductor hallucis and flexor digitorum brevis muscles, it gives off a proper plantar digital branch to the 1st toe, which sends a motor branch to the flexor hallucis brevis and then is distributed as a cutaneous nerve to the skin of medial side of the 1st digit. The trunk of the medial plantar nerve provides muscular branches to the abductor hallucis and flexor digitorum brevis as well as articular branches to the tarsal and metatarsal joints. Three common plantar digital nerves arise from the medial plantar nerve at the bases of the metatarsals and pass between the digital slips of the plantar aponeurosis. Each divides into two proper digital nerves which supply skin of adjacent sides of the 1st–4th digits. The 1st common plantar digital nerve sends a motor branch to the first lumbrical, while the 3rd common plantar digital nerve communicates with the lateral plantar nerve. Each proper plantar digital nerve sends articular branches to metatarsophalangeal and interphalangeal joints and sensory branches to the dorsum of the foot to innervate structures around the nail. 30 Lateral Plantar Nerve The lateral plantar nerve accompanies the lateral plantar artery to the lateral side of the foot between the flexor digitorum brevis and quadratus plantae muscles. The first branch from the lateral plantar nerve is the nerve to the abductor digiti minimi (“Baxter’s Nerve”). This nerve often branches from the lateral plantar in or proximal to the porta pedis, deep to the abductor hallucis muscle and travels tight against the calcaneal tuberosity in between the flexor digitorum brevis and quadratus plantae muscles to enter the proximal end of the abductor digiti minimi. The trunk of the lateral plantar nerve also supplies muscular branches to the quadratus plantae and abductor os metatarsi digiti minimi when present. The lateral plantar nerve divides into superficial and deep branches between the flexor digitorum brevis and abductor digiti minimi. The superficial branch provides a proper plantar digital nerve for the skin of the lateral surface of the fifth digit, and a common plantar digital nerve, which divides into proper plantar digital nerves for adjacent sides of the 4th and 5th toes. The superficial branch also provides muscular branches to the flexor digiti minimi brevis and the two interossei of the 4th intermetatarsal space. The deep branch of the lateral plantar nerve travels deep with the lateral plantar artery in between the 3rd and 4th layer of plantar muscles and sends muscular branches to all of the interossei but those in the fourth intermetatarsal space, the 2nd, 3rd, and 4th lumbricals, and the adductor hallucis. Arteries Posterior Tibial Artery The posterior tibial artery and its proximal branches are discussed with the arteries of the leg. At the ankle, the posterior tibial artery and tibial nerve travel in a neurovascular fascial tunnel deep to the flexor retinaculum and superficial to the flexor hallucis longus. The artery and its venae comitantes are located medial to the tibial nerve. The posterior tibial artery may divide into its terminal branches (medial and lateral plantar arteries) anywhere between the proximal part of the medial malleolus and before entering the foot, deep to the abductor hallucis muscle. At the ankle joint, before giving off its terminal branches, the posterior tibial artery provides small branches that supply structures of the ankle. Medial Calcaneal Arteries These arteries originate from the posterior tibial artery posterior to the medial malleolus, and occasionally from the lateral plantar artery. They pierce the flexor retinaculum and supply the area of the calcaneal tendon and the heel. The medial calcaneal arteries terminate by anastomosing with the posterior medial malleolar branches of the posterior tibial and the lateral calcaneal branches of the fibular artery to form the calcaneal rete. Artery of Tarsal Canal This artery passes between the tendons of the flexor digitorum longus and flexor hallucis longus to enter the tarsal canal where it anastomoses with a branch from the dorsalis pedis artery (artery of the tarsal sinus). Medial Plantar Artery The medial plantar artery is usually (about 80% of the time) the smaller of the two terminal branches of the posterior tibial artery. It arises deep to the flexor retinaculum between the medial malleolus and the calcaneus. It enters the medial compartment of the plantar surface of the foot deep 31 to the origin of the abductor hallucis muscle and continues distally between the abductor hallucis muscle and the tendons of flexor digitorum longus muscle, giving off small muscular branches to the abductor hallucis muscle. After crossing the tendon of the flexor digitorum longus, it divides into a superficial and a deep branch. Super cial Branch This artery courses between the flexor digitorum brevis and abductor hallucis muscles and divides into its two terminal branches, the superficial tibial plantar arteries and the common plantar digital artery. Super cial Tibial Plantar Artery The superficial tibial plantar artery (also called the medial marginal plantar artery) can be located superficial to the flexor hallucis brevis muscle (lateral to the tendon of the abductor hallucis). At the distal end of the first metatarsal bone, the artery can anastomose with the 1st plantar metatarsal artery, a branch of the deep plantar arch, or continue distally along the medial side of the 1st toe as the 1st proper plantar digital artery. The superficial tibial plantar artery is usually very small, but can be fairly large and, in that case, replaces the first plantar metatarsal artery of the deep plantar arch. Common Plantar Digital Artery This is the lateral branch of the superficial branch of the medial plantar artery. The stem of the common plantar digital artery passes obliquely across the flexor hallucis brevis muscle to be located between the flexor digitorum brevis muscle and the plantar aponeurosis. Here it gives rise to the superficial plantar arch by providing three small branches, the superficial plantar digital arteries. These arteries proceed distally and terminate by anastomosing with the 1st, 2nd and 3rd plantar metatarsal arteries of the deep plantar arch. After giving off the 3rd superficial plantar digital artery, the superficial plantar arch proceeds laterally to anastomose with the superficial fibular plantar branch of the lateral plantar artery. If this anastomosis is present (less than 30%), it completes the superficial arch on the lateral side. Deep Branch (Ramus Profundus) This branch arises from the medial plantar artery near its origin from the posterior tibial artery. It travels deep into the plantar foot and divides into a medial (tibial) and a lateral (fibular) branch. Medial (Tibial) Branch This branch travels along the plantar surface of the navicular and medial cuneiform bones deep to the 4th layer of plantar foot muscles. Upon reaching the base of the 1st metatarsal bone anastomoses with the 1st plantar metatarsal artery. Lateral (Fibular) Branch The lateral branch crosses dorsally over the tendon of fibularis longus muscle and joins with the medial side of the deep plantar arch. Lateral Plantar Artery This is usually much larger than the medial plantar artery and enters the foot with it, deep to the abductor hallucis muscle. This artery pierces the medial intermuscular septum to enter the middle compartment of the foot where it passes between the flexor digitorum brevis and quadratus plantae muscles before penetrating the lateral intermuscular septum to enter the lateral compartment. Here it fi fi 32 proceeds distally along the medial side of the abductor digiti minimi muscle. It divides into two branches near the base of the 5th metatarsal. Super cial Fibular Plantar Artery This branch courses laterally along the fibular side of the fifth metatarsal bone and becomes the 10th proper plantar digital artery at the lateral side of the 5th toe. Deep Plantar Arch This branch is much larger than the superficial fibular plantar artery and often appears as a continuation of the lateral plantar artery. After branching, the deep plantar arch dives in between the flexor digiti minimi brevis and quadratus plantae muscles and penetrates the lateral intermuscular septum to enter the middle compartment in between the 3rd and 4th layers, deep to the oblique head of the adductor hallucis and superficial to the interossei muscles. The artery travels medially across the 4th, 3rd, and 2nd metatarsals before anastomosing with the deep plantar artery of the dorsalis pedis artery and the lateral branch of the ramus profundus of the medial plantar artery in the 1st metatarsal space. If the dorsalis pedis is missing, there is usually no contribution to the deep plantar arch from the dorsal side of the foot. In some rare cases, the perforating branch of the fibular artery may contribute to the arch. Besides providing many branches to the deep muscles of the plantar surface of the foot, it also gives rise to the posterior perforating arteries and the plantar metatarsal arteries. The arch can be used as a landmark to separate the 3rd and 4th layers of plantar muscles. Posterior Perforating Arteries There are three posterior (proximal) perforating arteries branching from the deep plantar arch. There is no posterior perforating artery in the first interosseous space because the deep plantar artery of the dorsalis pedis takes its place. The posterior perforating arteries proceed towards the dorsum of the foot to anastomose with the dorsal metatarsal arteries. Plantar Metatarsal Arteries There are usually four plantar metatarsal arteries, which course along the plantar side of the medial four metatarsal bones superficial to the interossei muscles. The first plantar metatarsal artery, however, may branch from the dorsalis pedis or from the superficial tibial plantar branch of the medial plantar artery. In about 2 or 3% of cases the plantar metatarsal arteries can be missing altogether, in which case the superficial plantar arterial system, from the medial plantar artery, is very well developed and takes over the blood supply of the digits. Anterior Perforating Arteries Close to the webbing of the toes, the plantar metatarsal arteries give off anterior (distal) perforating arteries. These arteries penetrate through the interosseous muscles to reach the dorsal side of the foot where they anastomose with the dorsal metatarsal arteries. Proper Plantar Digital Arteries After giving o