Anatomy and the Body Systems PDF

What is anatomy? Anatomy includes those structures that can be seen grossly (without the aid of magnification) and microscopically (with the aid of magnification). Typically, when used by itself, the term *anatomy* tends to mean gross or macroscopic anatomy---that is, the study of structures that c...

What is anatomy? Anatomy includes those structures that can be seen grossly (without the aid of magnification) and microscopically (with the aid of magnification). Typically, when used by itself, the term *anatomy* tends to mean gross or macroscopic anatomy---that is, the study of structures that can be seen without using a microscope. Microscopic anatomy, also called histology, is the study of cells and tissues using a microscope. Anatomy forms the basis for the practice of medicine. Anatomy leads the physician toward an understanding of a patient's disease, whether he or she is carrying out a physical examination or using the most advanced imaging techniques. Anatomy is also important for dentists, chiropractors, physical therapists, and all others involved in any aspect of patient treatment that begins with an analysis of clinical signs. The ability to interpret a clinical observation correctly is therefore the endpoint of a sound anatomical understanding. Observation and visualization are the primary techniques a student should use to learn anatomy. Anatomy is much more than just memorization of lists of names. Although the language of anatomy is important, the network of information needed to visualize the position of physical structures in a patient goes far beyond simple memorization. Knowing the names of the various branches of the external carotid artery is not the same as being able to visualize the course of the lingual artery from its origin in the neck to its termination in the tongue. Similarly, understanding the organization of the soft palate, how it is related to the oral and nasal cavities, and how it moves during swallowing is very different from being able to recite the names of its individual muscles and nerves. An understanding of anatomy requires an understanding of the context in which the terminology can be remembered. How can gross anatomy be studied? The term *anatomy* is derived from the Greek word *temnein* , meaning "to cut." Clearly, therefore, the study of anatomy is linked, at its root, to dissection, although dissection of cadavers by students is now augmented, or even in some cases replaced, by viewing prosected (previously dissected) material and plastic models, or using computer teaching modules and other learning aids such as virtual and augmented reality experiences. Anatomy can be studied following either a regional or a systemic approach. - With a **regional approach **, each *region *of the body is studied separately and all aspects of that region are studied at the same time. For example, if the thorax is to be studied, all of its structures are examined. This includes the vasculature, the nerves, the bones, the muscles, and all other structures and organs located in the region of the body defined as the thorax. After studying this region, the other regions of the body (i.e., the abdomen, pelvis, lower limb, upper limb, back, head, and neck) are studied in a similar fashion. - In contrast, in a **systemic approach **, each *system *of the body is studied and followed throughout the entire body. For example, a study of the cardiovascular system looks at the heart and all of the blood vessels in the body. When this is completed, the nervous system (brain, spinal cord, and all the nerves) might be examined in detail. This approach continues for the whole body until every system, including the nervous, skeletal, muscular, gastrointestinal, respiratory, lymphatic, and reproductive systems, has been studied. Each of these approaches has benefits and deficiencies. The regional approach works very well if the anatomy course involves cadaver dissection but falls short when it comes to understanding the continuity of an entire system throughout the body. Similarly, the systemic approach fosters an understanding of an entire system throughout the body, but it is very difficult to coordinate this directly with a cadaver dissection or to acquire sufficient detail. Important anatomical terms **The anatomical position** The anatomical position is the standard reference position of the body used to describe the location of structures ( [Fig. 1.1](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0010) ). The body is in the anatomical position when standing upright with feet together, hands by the side, and face looking forward. The mouth is closed and the facial expression is neutral. The rim of bone under the eyes is in the same horizontal plane as the top of the opening to the ear, and the eyes are open and focused on something in the distance. The palms of the hands face forward with the fingers straight and together and with the pad of the thumb turned 90 degrees to the pads of the fingers. The toes point forward. Fig. 1.1 The Anatomical Position, Planes, and Terms of Location and Orientation. Anatomical planes Three major groups of planes pass through the body in the anatomical position (see [Fig. 1.1](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0010) ). - **Coronal planes **are oriented vertically and divide the body into anterior and posterior parts. - **Sagittal planes **also are oriented vertically but are at right angles to the coronal planes and divide the body into right and left parts. The plane that passes through the center of the body dividing it into equal right and left halves is termed the **median sagittal plane.** - **Transverse, horizontal**, or **axial planes **divide the body into superior and inferior parts. Terms to describe location Anterior (ventral) and posterior (dorsal), medial and lateral, superior and inferior Three major pairs of terms are used to describe the location of structures relative to the body as a whole or to other structures (see [Fig. 1.1](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0010) ). - **Anterior **(or **ventral **) and **posterior **(or **dorsal **) describe the position of structures relative to the "front" and "back" of the body. For example, the nose is an anterior (ventral) structure, whereas the vertebral column is a posterior (dorsal) structure. Also, the nose is anterior to the ears and the vertebral column is posterior to the sternum. - **Medial **and **lateral **describe the position of structures relative to the median sagittal plane and the sides of the body. For example, the thumb is lateral to the little finger. The nose is in the median sagittal plane and is medial to the eyes, which are in turn medial to the external ears. - **Superior **and **inferior **describe structures in reference to the vertical axis of the body. For example, the head is superior to the shoulders and the knee joint is inferior to the hip joint. Proximal and distal, cranial and caudal, and rostral Other terms used to describe positions include proximal and distal, cranial and caudal, and rostral. - **Proximal **and **distal **are used with reference to being closer to or farther from a structure's origin, particularly in the limbs. For example, the hand is distal to the elbow joint. The glenohumeral joint is proximal to the elbow joint. These terms are also used to describe the relative positions of branches along the course of linear structures, such as airways, vessels, and nerves. For example, distal branches occur farther away toward the ends of the system, whereas proximal branches occur closer to and toward the origin of the system. - **Cranial **(toward the head) and **caudal **(toward the tail) are sometimes used instead of superior and inferior, respectively. - **Rostral **is used, particularly in the head, to describe the position of a structure with reference to the nose. For example, the forebrain is rostral to the hindbrain. Superficial and deep Two other terms used to describe the position of structures in the body are **superficial** and **deep**. These terms are used to describe the relative positions of two structures with respect to the surface of the body. For example, the sternum is superficial to the heart, and the stomach is deep to the abdominal wall. Superficial and deep can also be used in a more absolute fashion to define two major regions of the body. The superficial region of the body is external to the outer layer of deep fascia. Deep structures are enclosed by this layer. Structures in the superficial region of the body include the skin, superficial fascia, and mammary glands. Deep structures include most skeletal muscles and viscera. Superficial wounds are external to the outer layer of deep fascia, whereas deep wounds penetrate through it. Trans/non-binary anatomical terminology While anatomy is typically discussed in the sex-binary classification of female and male, many individuals do not fit into these models. These individuals include intersex, non-binary, and transgender people. In some areas of this text, relevant anatomical/clinical distinctions are made between "ciswomen and cismen" and "transwomen and transmen." "Cis" refers to individuals whose gender identity aligns with their assigned sex at birth, whereas "trans" refers to individuals whose gender identity does not align with their assigned sex at birth. "Non-binary" refers to an individual whose gender identity does not fit the binary model. Many trans or non-binary individuals receive a spectrum of gender-affirming care including hormones and surgery to meet their goals for gender transition that will alter their anatomy. The anatomical terminology in this text will reflect this (e.g., "In transwomen post-vaginoplasty"). These differences are clinically relevant and vary from cisgender individuals. Clinically, the anatomical terminology preferred by the patient should be used, which may include non-binary terms for classically gendered anatomy. In general, it is appropriate to use gender-inclusive anatomical language when engaging with non-binary/transgender patients. Some common examples are as follows: Preferred Term Instead Of ----------------- ---------------- Upper body Chest/Breast Erectile tissue Penis/Clitoris Gonads Testes/Ovaries Clinicians should not assume based on an individual's gender presentation which anatomical features are present. Acquiring a history of the patient's relevant anatomy (organ inventory) should be considered, including the patient's preferred terminology, to guide appropriate and sensitive care. Clinicians should base their clinical care on the present anatomy to diagnose, screen, and treat appropriately. Throughout this text, many anatomical features are still described using a gender-binary model (women and men). Anatomy has classically been taught in this way, which, for the time being, has some advantages in its use. First, it is important to understand that these gendered terms are conceptual models that help us approximate the realworld in order to more easily understand it, but they do not adequately describe all forms of variation. This includes biological variation in the anatomy that can be seen in intersex individuals or variations seen in persons receiving various degrees of gender-affirming care. Second, these terms continue to be used heavily in the literature, and so their use here helps maintain a degree of congruence with pre-existing information. The use of these terms is not intended to exclude individuals who do not fit sex-binary models. As we continue to develop our anatomical models, these terms may diminish in their use and be replaced by non-binary terminology such as "individuals with a prostate" or "individuals with a uterus." Whenever possible, it is best practice both scientifically and clinically to discuss the anatomy present without assumptions based on gender presentation. Body systems **Skeletal System** The skeleton can be divided into two subgroups, the axial skeleton and the appendicular skeleton. The axial skeleton consists of the bones of the skull (cranium), vertebral column, ribs, and sternum, whereas the appendicular skeleton consists of the bones of the upper and lower limbs ( [Fig. 1.14](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0075) ).   Fig. 1.14 The Axial Skeleton and the Appendicular Skeleton. The skeletal system consists of cartilage and bone. **Cartilage** Cartilage is an avascular form of connective tissue consisting of extracellular fibers embedded in a matrix that contains cells localized in small cavities. The amount and kind of extracellular fibers in the matrix vary depending on the type of cartilage. In heavy weight-bearing areas or areas prone to pulling forces, the amount of collagen is greatly increased and the cartilage is almost inextensible. In contrast, in areas where weight-bearing demands and stress are less, cartilage containing elastic fibers and fewer collagen fibers is common. The functions of cartilage are to: - support soft tissues - provide a smooth, gliding surface for bone articulations at joints, and - enable the development and growth of long bones. There are three types of cartilage: - hyaline---most common; matrix contains a moderate amount of collagen fibers (e.g., articular surfaces of bones); - elastic---matrix contains collagen fibers along with a large number of elastic fibers (e.g., external ear); - fibrocartilage---matrix contains a limited number of cells and ground substance amidst a substantial amount of collagen fibers (e.g., intervertebral discs). Cartilage is nourished by diffusion and has no blood vessels, lymphatics, or nerves. **Bone** Bone is a calcified, living, connective tissue that forms the majority of the skeleton. It consists of an intercellular calcified matrix, which also contains collagen fibers, and several types of cells within the matrix. Bones function as: - supportive structures for the body, - protectors of vital organs, - reservoirs of calcium and phosphorus, - levers on which muscles act to produce movement, and - containers for blood-producing cells. There are two types of bone, compact and spongy (trabecular or cancellous). Compact bone is dense bone that forms the outer shell of all bones and surrounds spongy bone. Spongy bone consists of spicules of bone enclosing cavities containing blood-forming cells (marrow). Classification of bones is by shape. - Long bones are tubular (e.g., humerus in upper limb; femur in lower limb). - Short bones are cuboidal (e.g., bones of the wrist and ankle). - Flat bones consist of two compact bone plates separated by spongy bone (e.g., skull). - Irregular bones are bones with various shapes (e.g., bones of the face). - Sesamoid bones are round or oval bones that develop in tendons. **In the clinic** Accessory and sesamoid bones These are extra bones that are not usually found as part of the normal skeleton but can exist as a normal variant in many people. They are typically found in multiple locations in the wrist and hands, ankles, and feet ( [Fig. 1.15](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0080) ). These should not be mistaken for fractures on imaging. Fig. 1.15 Accessory and Sesamoid Bones. (**A**) Radiograph of the ankle region showing an accessory bone (os trigonum). (**B**) Radiograph of the feet showing numerous sesamoid bones and an accessory bone (os naviculare). Sesamoid bones are embedded within tendons, the largest of which is the patella. There are many other sesamoids in the body, particularly in tendons of the hands and feet, and most frequently in flexor tendons of the thumb and big toe. Degenerative and inflammatory changes of, as well as mechanical stresses on, the accessory bones and sesamoids can cause pain, which can be treated with physiotherapy and targeted steroid injections, but in some severe cases it may be necessary to surgically remove the bone. Bones are vascular and are innervated. Generally, an adjacent artery gives off a nutrient artery, usually one per bone, that directly enters the internal cavity of the bone and supplies the marrow, spongy bone, and inner layers of compact bone. In addition, all bones are covered externally, except in the area of a joint where articular cartilage is present, by a fibrous connective tissue membrane called the periosteum, which has the unique capability of forming new bone. This membrane receives blood vessels whose branches supply the outer layers of compact bone. A bone stripped of its periosteum will not survive. Nerves accompany the vessels that supply the bone and the periosteum. Most of the nerves passing into the internal cavity with the nutrient artery are vasomotor fibers that regulate blood flow. Bone itself has few sensory nerve fibers. On the other hand, the periosteum is supplied with numerous sensory nerve fibers and is very sensitive to any type of injury. Developmentally, all bones come from mesenchyme by either intramembranous ossification, in which mesenchymal models of bones undergo ossification, or endochondral ossification, in which cartilaginous models of bones form from mesenchyme and undergo ossification. **In the clinic** Determination of skeletal age Throughout life the bones develop in a predictable way to form the skeletally mature adult at the end of puberty. Skeletal maturity tends to occur between the ages of 20 and 25 years. However, this may well vary according to geography and socioeconomic conditions. Skeletal maturity will also be determined by genetic factors and disease states. Up until the age of skeletal maturity, bony growth and development follows a typically predictable ordered state, which can be measured through either ultrasound, plain radiographs, or MRI scanning. Typically, the nondominant (left) hand is radiographed, and the radiograph is compared to a series of standard radiographs. From these images the bone age can be determined ( [Fig. 1.16](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0085) ). Traditionally, this comparison was done manually, but more recently, software packages employing artificial algorithms have automated this process. Fig. 1.16 A developmental series of radiographs showing the progressive ossification of carpal (wrist) bones from 3 (**A**) to 10 (**D**) years of age. In certain disease states, such as malnutrition and hypothyroidism, bony maturity may be slow. If the skeletal bone age is significantly reduced from the patient's true age, treatment may be required. In the healthy individual, the bone age accurately represents the true age of the patient. This is important in determining the true age of the subject. This may also have medicolegal importance. **In the clinic** Bone marrow transplants The bone marrow serves an important function. There are two types of bone marrow, red marrow (otherwise known as myeloid tissue) and yellow marrow. Red blood cells, platelets, and most white blood cells arise from within the red marrow. In the yellow marrow, a few white cells are made; however, this marrow is dominated by large fat globules (producing its yellow appearance) ( [Fig. 1.17](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0090) ). T1-weighted image in the coronal plane, demonstrating the relatively high signal intensity returned from the femoral heads and proximal femoral necks, consistent with yellow marrow. In this young patient, the vertebral bodies return an intermediate darker signal that represents red marrow. There is relatively little fat in these vertebrae, hence the lower signal return. From birth most of the body's marrow is red; however, as the subject ages, more red marrow is converted into yellow marrow within the medulla of the long and flat bones. Bone marrow contains two types of stem cells. Hemopoietic stem cells give rise to the white blood cells, red blood cells, and platelets. Mesenchymal stem cells differentiate into structures that form bone, cartilage, and muscle. There are a number of diseases that may involve the bone marrow, including infection and malignancy. In patients who develop a bone marrow malignancy (e.g., leukemia) it may be possible to harvest nonmalignant cells from the patient's bone marrow or cells from another person's bone marrow. The patient's own marrow can be destroyed with chemotherapy or radiation and the new cells infused. This treatment is bone marrow transplantation. **\ ** **In the clinic** Bone fractures Fractures occur in normal bone because of abnormal load or stress, in which the bone gives way ( [Fig. 1.18A](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0095) ). Fractures may also occur in bone that is of poor quality (osteoporosis); in such cases a normal stress is placed upon a bone that is not of sufficient quality to withstand this force and subsequently fractures. Fig. 1.18 Radiograph, lateral view, showing fracture of the ulna at the elbow joint ( **A **) and repair of this fracture ( **B **) using internal fixation with a plate and multiple screws. In children whose bones are still developing, fractures may occur across the growth plate or across the shaft. These shaft fractures typically involve partial cortical disruption, similar to breaking a branch of a young tree; hence they are termed "greenstick" fractures. After a fracture has occurred, the natural response is to heal the fracture. Between the fracture margins a blood clot is formed into which new vessels grow. A jelly-like matrix is formed, and further migration of collagen-producing cells occurs. On this soft tissue framework, calcium hydroxyapatite is produced by osteoblasts and forms insoluble crystals, and then bone matrix is laid down. As more bone is produced, a callus can be demonstrated forming across the fracture site. Treatment of fractures requires a fracture line reduction. If this cannot be maintained in a plaster of Paris cast, it may require internal or external fixation with screws and metal rods ( [Fig. 1.18B](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0095) ).  **In the clinic** Avascular necrosis Avascular necrosis is cellular death of bone resulting from a temporary or permanent loss of blood supply to that bone. Avascular necrosis may occur in a variety of medical conditions, some of which have an etiology that is less than clear. A typical site for avascular necrosis is a fracture across the femoral neck in an elderly patient. In these patients there is loss of continuity of the cortical medullary blood flow with loss of blood flow deep to the retinacular fibers. This essentially renders the femoral head bloodless; it subsequently undergoes necrosis and collapses ( [Fig. 1.19](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0100) ). In these patients it is necessary to replace the femoral head with a prosthesis. Fig. 1.19 Image of the hip joints demonstrating loss of height of the right femoral head with juxta-articular bony sclerosis and subchondral cyst formation secondary to avascular necrosis. There is also significant wasting of the muscles supporting the hip, which is secondary to disuse and pain. **In the clinic** Epiphyseal fractures As the skeleton develops, there are stages of intense growth typically around the ages of 7 to 10 years and later in puberty. These growth spurts are associated with increased cellular activity around the growth plate between the head and shaft of a bone. This increase in activity renders the growth plates more vulnerable to injuries, which may occur from dislocation across a growth plate or fracture through a growth plate. Occasionally an injury may result in growth plate compression, destroying that region of the growth plate, which may result in asymmetrical growth across that joint region. All fractures across the growth plate must be treated with care and expediency, requiring fracture reduction. **Joints** The sites where two skeletal elements come together are termed joints. The two general categories of joints ( [Fig. 1.20](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0105) ) are those in which: - the skeletal elements are separated by a cavity (i.e., **synovial joints **), and - there is no cavity and the components are held together by connective tissue (i.e., **solid joints **). Fig. 1.20 Joints. ( **A **) Synovial joint. ( **B **) Solid joint. Blood vessels that cross over a joint and nerves that innervate muscles acting on a joint usually contribute articular branches to that joint. **Synovial joints** Synovial joints are connections between skeletal components where the elements involved are separated by a narrow articular cavity ( [Fig. 1.21](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0110) ). In addition to containing an articular cavity, these joints have a number of characteristic features.   Fig. 1.21 Synovial Joints. ( **A **) Major features of a synovial joint. ( **B **) Accessory structures associated with synovial joints. First, a layer of cartilage, usually **hyaline cartilage** , covers the articulating surfaces of the skeletal elements. In other words, bony surfaces do not normally contact one another directly. As a consequence, when these joints are viewed in normal radiographs, a wide gap seems to separate the adjacent bones because the cartilage that covers the articulating surfaces is more transparent to X-rays than bone is. A second characteristic feature of synovial joints is the presence of a **joint capsule** consisting of an inner **synovial membrane** and an outer **fibrous membrane**. - The synovial membrane attaches to the margins of the joint surfaces at the interface between the cartilage and bone and encloses the articular cavity. The synovial membrane is highly vascular and produces synovial fluid, which percolates into the articular cavity and lubricates the articulating surfaces. Closed sacs of synovial membrane also occur outside joints, where they form synovial bursae or tendon sheaths. Bursae often intervene between structures, such as tendons and bone, tendons and joints, or skin and bone, and reduce the friction of one structure moving over the other. Tendon sheaths surround tendons and also reduce friction. - The **fibrous membrane **is formed by dense connective tissue and surrounds and stabilizes the joint. Parts of the fibrous membrane may thicken to form ligaments, which further stabilize the joint. Ligaments outside the capsule usually provide additional reinforcement. Another common but not universal feature of synovial joints is the presence of additional structures within the area enclosed by the capsule or synovial membrane, such as **articular discs** (usually composed of fibrocartilage), **fat pads**, and **tendons**. Articular discs absorb compression forces, adjust to changes in the contours of joint surfaces during movements, and increase the range of movements that can occur at joints. Fat pads usually occur between the synovial membrane and the capsule and move into and out of regions as joint contours change during movement. Redundant regions of the synovial membrane and fibrous membrane allow for large movements at joints. **Descriptions of synovial joints based on shape and movement** Synovial joints are described based on shape and movement: - based on the shape of their articular surfaces, synovial joints are described as plane (flat), hinge, pivot, bicondylar (two sets of contact points), condylar (ellipsoid), saddle, and ball and socket; - based on movement, synovial joints are described as uniaxial (movement in one plane), biaxial (movement in two planes), and multiaxial (movement in three planes). Hinge joints are uniaxial, whereas ball and socket joints are multiaxial. Specific types of synovial joints ( [Fig. 1.22 ](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0115)) - Plane joints---allow sliding or gliding movements when one bone moves across the surface of another (e.g., acromioclavicular joint)   Fig. 1.22 Various Types of Synovial Joints. ( **A **) Condylar (wrist). ( **B **) Gliding (radio-ulnar). ( **C **) Hinge (elbow). ( **D **) Ball and socket (hip). ( **E **) Saddle (carpometacarpal of thumb). ( **F **) Pivot (atlanto-axial). - Hinge joints---allow movement around one axis that passes transversely through the joint; permit flexion and extension (e.g., elbow \[humero-ulnar\] joint) - Pivot joints---allow movement around one axis that passes longitudinally along the shaft of the bone; permit rotation (e.g., atlanto-axial joint) - Bicondylar joints---allow movement mostly in one axis with limited rotation around a second axis; formed by two convex condyles that articulate with concave or flat surfaces (e.g., knee joint) - Condylar (ellipsoid) joints---allow movement around two axes that are at right angles to each other; permit flexion, extension, abduction, adduction, and circumduction (limited) (e.g., wrist joint) - Saddle joints---allow movement around two axes that are at right angles to each other; the articular surfaces are saddle shaped; permit flexion, extension, abduction, adduction, and circumduction (e.g., carpometacarpal joint of the thumb) - Ball-and-socket joints---allow movement around multiple axes; permit flexion, extension, abduction, adduction, circumduction, and rotation (e.g., hip joint) **Solid joints** Solid joints are connections between skeletal elements where the adjacent surfaces are linked together either by fibrous connective tissue or by cartilage, usually fibrocartilage ( [Fig. 1.23](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0120) ). Movements at these joints are more restricted than at synovial joints.  Fig. 1.23 Solid Joints. **Fibrous joints** include sutures, gomphoses, and syndesmoses. - **Sutures **occur only in the skull where adjacent bones are linked by a thin layer of connective tissue termed a *sutural ligament.* - **Gomphoses **occur only between the teeth and adjacent bone. In these joints, short collagen tissue fibers in the periodontal ligament run between the root of the tooth and the bony socket. - **Syndesmoses **are joints in which two adjacent bones are linked by a ligament. Examples are the ligamentum flavum, which connects adjacent vertebral laminae, and an interosseous membrane, which links, for example, the radius and ulna in the forearm. **Cartilaginous joints** include synchondroses and symphyses. - **Synchondroses **occur where two ossification centers in a developing bone remain separated by a layer of cartilage, for example, the growth plate that occurs between the head and shaft of developing long bones. These joints allow bone growth and eventually become completely ossified. - **Symphyses **occur where two separate bones are interconnected by cartilage. Most of these types of joints occur in the midline and include the pubic symphysis between the two pelvic bones, and intervertebral discs between adjacent vertebrae. **In the clinic** Degenerative joint disease Degenerative joint disease is commonly known as osteoarthritis or osteoarthrosis. The disorder is related to aging but not caused by aging. Typically there are decreases in water and proteoglycan content within the cartilage. The cartilage becomes more fragile and more susceptible to mechanical disruption ( [Fig. 1.24](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0125) ). As the cartilage wears, the underlying bone becomes fissured and also thickens. Synovial fluid may be forced into small cracks that appear in the bone's surface, which produces large cysts. Furthermore, reactive juxta-articular bony nodules are formed (osteophytes) ( [Fig. 1.25](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0130) ). As these processes occur, there is slight deformation, which alters the biomechanical forces through the joint. This in turn creates abnormal stresses, which further disrupt the joint. Fig. 1.24 This operative photograph demonstrates the focal areas of cartilage loss in the patella and femoral condyles throughout the knee joint.   Fig. 1.25 Osteoarthritis accounts for a large percentage of primary health care visits and is regarded as a significant problem. The etiology of osteoarthritis is not clear; however, osteoarthritis can occur secondary to other joint diseases, such as rheumatoid arthritis and infection. Overuse of joints and abnormal strains, such as those experienced by people who play sports, often cause one to be more susceptible to chronic joint osteoarthritis. Various treatments are available, including weight reduction, proper exercise, anti-inflammatory drug treatment, and joint replacement. **In the Clinic** Arthroscopy Arthroscopy is a technique of visualizing the inside of a joint using a small telescope placed through a tiny incision in the skin. Arthroscopy can be performed in most joints. However, it is most commonly performed in the knee, shoulder, ankle, and hip joints ( [Fig. 1.26](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0135) ). Fig. 1.26 Arthroscopic Procedure on Knee Joint. Arthroscopy allows the surgeon to view the inside of the joint and its contents. Notably, in the knee, the menisci and the ligaments are easily seen, and it is possible using separate puncture sites and specific instruments to remove the menisci and replace the cruciate ligaments. The advantages of arthroscopy are that it is performed through small incisions, it enables patients to quickly recover and return to normal activity, and it only requires either a light anesthetic or regional anesthesia during the procedure. **In the clinic** Joint replacement Joint replacement is undertaken for a variety of reasons. These predominantly include degenerative joint disease and joint destruction. Joints that have severely degenerated or lack their normal function are painful. In some patients, the pain may be so severe that it prevents them from leaving the house and undertaking even the smallest of activities without discomfort. Large joints are commonly affected, including the hip, knee, and shoulder. However, with ongoing developments in joint replacement materials and surgical techniques, even small joints of the fingers can be replaced. Typically, both sides of the joint are replaced; in the hip joint the acetabulum will be reamed, and a plastic or metal cup will be introduced. The femoral component will be fitted precisely to the femur and cemented in place ( [Fig. 1.27](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0140) ). Radiograph, Anteroposterior View, of the Pelvis After a Right Total Hip Replacement. There are additional significant degenerative changes in the left hip joint, which will also need to be replaced. Most patients derive significant benefit from joint replacement and continue to lead an active life afterward. In a minority of patients who have been fitted with a metal acetabular cup and metal femoral component, an aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) may develop, possibly caused by a hypersensitivity response to the release of metal ions in adjacent tissues. These patients often have chronic pain and might need additional surgery to replace these joint replacements with safer models. **Skin and Fascias** Skin The skin is the largest organ of the body. It consists of the epidermis and the dermis. The epidermis is the outer cellular layer of stratified squamous epithelium, which is avascular and varies in thickness. The dermis is a dense bed of vascular connective tissue. The skin functions as a mechanical and permeability barrier, and as a sensory and thermoregulatory organ. It also can initiate primary immune responses. **Fascia** Fascia is connective tissue containing varying amounts of fat that separate, support, and interconnect organs and structures, enable movement of one structure relative to another, and allow the transit of vessels and nerves from one area to another. There are two general categories of fascia: superficial and deep. - Superficial (subcutaneous) fascia lies just deep to and is attached to the dermis of the skin. It is made up of loose connective tissue usually containing a large amount of fat. The thickness of the superficial fascia (subcutaneous tissue) varies considerably, both from one area of the body to another and from one individual to another. The superficial fascia allows movement of the skin over deeper areas of the body, acts as a conduit for vessels and nerves coursing to and from the skin, and serves as an energy (fat) reservoir. - Deep fascia usually consists of dense, organized connective tissue. The outer layer of deep fascia is attached to the deep surface of the superficial fascia and forms a thin fibrous covering over most of the deeper region of the body. Inward extensions of this fascial layer form intermuscular septa that compartmentalize groups of muscles with similar functions and innervations. Other extensions surround individual muscles and groups of vessels and nerves, forming an investing fascia. Near some joints the deep fascia thickens, forming retinacula. These fascial retinacula hold tendons in place and prevent them from bowing during movements at the joints. Finally, there is a layer of deep fascia separating the membrane lining the abdominal cavity (the parietal peritoneum) from the fascia covering the deep surface of the muscles of the abdominal wall (the transversalis fascia). This layer is referred to as **extraperitoneal fascia. **A similar layer of fascia in the thorax is termed the **endothoracic fascia.** **In the clinic** The importance of fascias Clinically, fascias are extremely important because they often limit the spread of infection and malignant disease. When infections or malignant diseases cross a fascial plain, a primary surgical clearance may require a far more extensive dissection to render the area free of tumor or infection. A typical example of the clinical importance of a fascial layer would be of that covering the psoas muscle. Infection within an intervertebral body secondary to tuberculosis can pass laterally into the psoas muscle. Pus fills the psoas muscle but is limited from further spread by the psoas fascia, which surrounds the muscle and extends inferiorly into the groin, pointing below the inguinal ligament. **In the clinic** Placement of skin incisions and scarring Surgical skin incisions are ideally placed along or parallel to lines of skin tension (Langer's lines) that correspond to the orientation of the dermal collagen fibers. They tend to run in the same direction as the underlying muscle fibers and incisions that are made along these lines tend to heal better with less scarring. In contrast, incisions made perpendicular to these lines are more likely to heal with a prominent scar and, in some severe cases, can lead to raised, firm, hypertrophic, or keloid, scars. **Function** [Support the body weight] A major function of the lower limb is to support the weight of the body with minimal expenditure of energy. When standing erect, the center of gravity is anterior to the edge of the SII vertebra in the pelvis ( [Fig. 6.4](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0025) ). The vertical line through the center of gravity is slightly posterior to the hip joints, anterior to the knee and ankle joints, and directly over the almost circular support base formed by the feet on the ground and holds the knee and hip joints in extension. Fig. 6.4 Center and Line of Gravity. The organization of ligaments at the hip and knee joints, together with the shape of the articular surfaces, particularly at the knee, facilitates "locking" of these joints into position when standing, thereby reducing the muscular energy required to maintain a standing position. [Locomotion] A second major function of the lower limbs is to move the body through space. This involves the integration of movements at all joints in the lower limb to position the foot on the ground and to move the body over the foot. Movements at the hip joint are flexion, extension, abduction, adduction, medial and lateral rotation, and circumduction ( [Fig. 6.5](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0030) ). Fig. 6.5 Movements of the Hip Joint. (**A**) Flexion and extension. (**B**) Abduction and adduction. (**C**) External and internal rotation. (**D**) Circumduction. The knee and ankle joints are primarily hinge joints. Movements at the knee are mainly flexion and extension ( [Fig. 6.6A](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0035) ). Movements at the ankle are dorsiflexion (movement of the dorsal side of the foot toward the leg) and plantarflexion ( [Fig. 6.6B](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0035) ).    Fig. 6.6 Movements of the Knee and Ankle. (**A**) Knee flexion and extension. (**B**) Ankle dorsiflexion and plantarflexion. During walking, many anatomical features of the lower limbs contribute to minimizing fluctuations in the body's center of gravity and thereby reduce the amount of energy needed to maintain locomotion and produce a smooth, efficient gait ( [Fig. 6.7](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0040) ). They include pelvic tilt in the coronal plane, pelvic rotation in the transverse plane, movement of the knees toward the midline, flexion of the knees, and complex interactions between the hip, knee, and ankle. As a result, during walking, the body's center of gravity normally fluctuates only 5 cm in both vertical and lateral directions. Quadriceps femoris---vastus medialis, intermedius, and lateralis and rectus femoris The large **quadriceps femoris** muscle consists of three vastus muscles (vastus medialis, vastus intermedius, and vastus lateralis) and the rectus femoris muscle ( [Fig. 6.59](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300) ). Afbeelding met skelet, tekst Automatisch gegenereerde beschrijving Fig. 6.59 Muscles of the Anterior Compartment of the Thigh. The quadriceps femoris muscle mainly extends the leg at the knee joint, but the rectus femoris component also assists flexion of the thigh at the hip joint. Because the vastus muscles insert into the margins of the patella as well as into the quadriceps femoris tendon, they stabilize the position of the patella during knee joint movement. The quadriceps femoris is innervated by the femoral nerve with contributions mainly from spinal segments L3 and L4. A tap with a tendon hammer on the patellar ligament therefore tests reflex activity mainly at spinal cord levels L3 and L4. Vastus muscles The vastus muscles originate from the femur, whereas the rectus femoris muscle originates from the pelvic bone. All attach first to the patella by the quadriceps femoris tendon and then to the tibia by the **patellar ligament**. The **vastus medialis** originates from a continuous line of attachment on the femur, which begins anteromedially on the intertrochanteric line and continues posteroinferiorly along the pectineal line and then descends along the medial lip of the linea aspera and onto the medial supracondylar line. The fibers converge onto the medial aspect of the quadriceps femoris tendon and the medial border of the patella (see [Fig. 6.59](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300) ). The **vastus intermedius** originates mainly from the upper two-thirds of the anterior and lateral surfaces of the femur and the adjacent intermuscular septum (see [Fig. 6.59](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300) ). It merges into the deep aspect of the quadriceps femoris tendon and also attaches to the lateral margin of the patella and lateral condyle of the tibia. A tiny muscle ( **articularis genus** ) originates from the femur just inferior to the origin of the vastus intermedius and inserts into the suprapatellar bursa associated with the knee joint (see [Fig. 6.59](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300) ). This articular muscle, which is often part of the vastus intermedius muscle, pulls the bursa away from the knee joint during extension. The **vastus lateralis** is the largest of the vastus muscles (see [Fig. 6.59](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300) ). It originates from a continuous line of attachment, which begins anterolaterally from the superior part of the intertrochanteric line of the femur and then circles laterally around the bone to attach to the lateral margin of the gluteal tuberosity and continues down the upper part of the lateral lip of the linea aspera. Muscle fibers converge mainly onto the quadriceps femoris tendon and the lateral margin of the patella. Rectus femoris Unlike the vastus muscles, which cross only the knee joint, the **rectus femoris** muscle crosses both the hip and the knee joints (see [Fig. 6.59](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300) ). The rectus femoris has two tendinous heads of origin from the pelvic bone: - one from the anterior inferior iliac spine (**straight head**), and - the other from a roughened area of the ilium immediately superior to the acetabulum ( **reflected head **) (see [Fig. 6.59 ](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300)). The two heads of the rectus femoris unite to form an elongate muscle belly, which lies anterior to the vastus intermedius muscle and between the vastus lateralis and vastus medialis muscles, to which it is attached on either side. At the distal end, the rectus femoris muscle converges on the quadriceps femoris tendon and inserts on the base of the patella. Patellar ligament The patellar ligament is functionally the continuation of the quadriceps femoris tendon below the patella and is attached above to the apex and margins of the patella and below to the tibial tuberosity (see [Fig. 6.59](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300) ). The more superficial fibers of the quadriceps femoris tendon and the patellar ligament are continuous over the anterior surface of the patella, and lateral and medial fibers are continuous with the ligament beside the margins of the patella. Sartorius The **sartorius** muscle is the most superficial muscle in the anterior compartment of the thigh and is a long strap-like muscle that descends obliquely through the thigh from the anterior superior iliac spine to the medial surface of the proximal shaft of the tibia (see [Fig. 6.59](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0300) ). Its flat aponeurotic insertion into the tibia is immediately anterior to the insertion of the gracilis and semitendinosus muscles. The sartorius, gracilis, and semitendinosus muscles attach to the tibia in a three-pronged pattern on the tibia, so their combined tendons of insertion are often termed the **pes anserinus** (Latin for "goose foot"). In the upper one-third of the thigh, the medial margin of the sartorius forms the lateral margin of the femoral triangle. In the middle one-third of the thigh, the sartorius forms the anterior wall of the adductor canal. The sartorius muscle assists in flexing the thigh at the hip joint and the leg at the knee joint. It also abducts the thigh and rotates it laterally, as when resting the foot on the opposite knee when sitting. The sartorius is innervated by the femoral nerve. Posterior compartment There are three long muscles in the posterior compartment of the thigh: biceps femoris, semitendinosus, and semimembranosus ( [Table 6.5](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/t0030) )---and they are collectively known as the hamstrings ( [Fig. 6.63](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0320) ). All except the short head of the biceps femoris cross both the hip and knee joints. As a group, the hamstrings flex the leg at the knee joint and extend the thigh at the hip joint. They are also rotators at both joints. Table 6.5 Muscles of the posterior compartment of the thigh (spinal segments in bold are the major segments innervating the muscle) Muscle Origin Insertion Innervation Function ----------------- --------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------- --------------------------------- -------------------------------------------------------------------------------------------------------------------- Biceps femoris Long head---inferomedial part of the upper area of the ischial tuberosity; short head---lateral lip of linea aspera Head of fibula Sciatic nerve (L5, **S1 **, S2) Flexes leg at knee joint; extends and laterally rotates thigh at hip joint and laterally rotates leg at knee joint Semitendinosus Inferomedial part of the upper area of the ischial tuberosity Medial surface of proximal tibia Sciatic nerve (L5, **S1 **, S2) Flexes leg at knee joint and extends thigh at hip joint; medially rotates thigh at hip joint and leg at knee joint Semimembranosus Superolateral impression on the ischial tuberosity Groove and adjacent bone on medial and posterior surface of medial tibial condyle Sciatic nerve (L5, **S1 **, S2) Flexes leg at knee joint and extends thigh at hip joint; medially rotates thigh at hip joint and leg at knee joint Fig. 6.63 Muscles of the Posterior Compartment of the Thigh. Posterior view. Biceps femoris The **biceps femoris** muscle is lateral in the posterior compartment of the thigh and has two heads (see [Fig. 6.63](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0320) ): - The **long head **originates with the semitendinosus muscle from the inferomedial part of the upper area of the ischial tuberosity. - The **short head **arises from the lateral lip of the linea aspera on the shaft of the femur. The muscle belly of the long head crosses the posterior thigh obliquely from medial to lateral and is joined by the short head distally. Together, fibers from the two heads form a tendon, which is palpable on the lateral side of the distal thigh. The main part of the tendon inserts into the lateral surface of the head of the fibula. Extensions from the tendon blend with the fibular collateral ligament and with ligaments associated with the lateral side of the knee joint. The biceps femoris flexes the leg at the knee joint. The long head also extends and laterally rotates the hip. When the knee is partly flexed, the biceps femoris can laterally rotate the leg at the knee joint. The long head is innervated by the tibial division of the sciatic nerve and the short head is innervated by the common fibular division of the sciatic nerve. Semitendinosus The **semitendinosus** muscle is medial to the biceps femoris muscle in the posterior compartment of the thigh (see [Fig. 6.63](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0320) ). It originates with the long head of the biceps femoris muscle from the inferomedial part of the upper area of the ischial tuberosity. The spindle-shaped muscle belly ends in the lower half of the thigh and forms a long cord-like tendon, which lies on the semimembranosus muscle and descends to the knee. The tendon curves around the medial condyle of the tibia and inserts into the medial surface of the tibia just posterior to the tendons of the gracilis and sartorius muscles as part of the pes anserinus. The semitendinosus flexes the leg at the knee joint and extends the thigh at the hip joint. Working with the semimembranosus, it also medially rotates the thigh at the hip joint and medially rotates the leg at the knee joint. The semitendinosus muscle is innervated by the tibial division of the sciatic nerve. Semimembranosus The **semimembranosus** muscle lies deep to the semitendinosus muscle in the posterior compartment of the thigh (see [Fig. 6.63](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0320) ). It is attached above to the superolateral impression on the ischial tuberosity and below mainly to the groove and adjacent bone on the medial and posterior surfaces of the medial tibial condyle. Expansions from the tendon also insert into and contribute to the formation of ligaments and fascia around the knee joint. The semimembranosus flexes the leg at the knee joint and extends the thigh at the hip joint. Working with the semitendinosus muscle, it medially rotates the thigh at the hip joint and the leg at the knee joint. The semimembranosus muscle is innervated by the tibial division of the sciatic nerve. **In the clinic: Muscle injuries to the lower limb** Muscle injuries may occur as a result of direct trauma or as part of an overuse syndrome. Muscle injuries may occur as a minor muscle tear, which may be demonstrated as a focal area of fluid within the muscle. With increasingly severe injuries, more muscle fibers are torn and this may eventually result in a complete muscle tear. The usual muscles in the thigh that tear are the hamstring muscles. Tears in the muscles below the knee typically occur within the soleus muscle, though other muscles may be affected. Hamstring muscle injury Injury to the hamstring muscles is a common source of pain in athletes, particularly in those competing in sports requiring a high degree of power and speed (such as sprinting, track and field, football), where the hamstring muscles are very susceptible to injury from excessive stretching. The injury can range from a mild muscle strain to a complete tear of a muscle or a tendon. It usually occurs during sudden accelerations and decelerations or rapid change in direction. In adults, the most commonly injured is the muscle-tendon junction, which is a wide transition zone between the muscle and the tendon. An avulsion of the ischial tuberosity with proximal hamstring origin attachment is common in the adolescent population, particularly during sudden hip flexion because the ischial apophysis is the weakest element of the proximal hamstring unit in this age group ( [Fig. 6.64](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0325) ). Both ultrasound and MRI can be used to assess the hamstring injury with the MRI providing not only the information about the extent of the injury but also some indication about the prognosis (future risk of re-tear, loss of function, etc.). Fig. 6.64 Coronal MRI of the Posterior Pelvis and Thigh Showing a Hamstring Avulsion Injury. **Knee joint** The knee joint is the largest synovial joint in the body. It consists of: - the articulation between the femur and tibia, which is weight-bearing, and - the articulation between the patella and the femur, which allows the pull of the quadriceps femoris muscle to be directed anteriorly over the knee to the tibia without tendon wear ( [Fig. 6.73 ](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0370)).    Fig. 6.73 Knee Joint. Joint capsule is not shown. Two fibrocartilaginous menisci, one on each side, between the femoral condyles and tibia accommodate changes in the shape of the articular surfaces during joint movements. The detailed movements of the knee joint are complex, but basically the joint is a hinge joint that allows mainly flexion and extension. Like all hinge joints, the knee joint is reinforced by collateral ligaments, one on each side of the joint. In addition, two very strong ligaments (the cruciate ligaments) interconnect the adjacent ends of the femur and tibia and maintain their opposed positions during movement. Because the knee joint is involved in weight-bearing, it has an efficient "locking" mechanism to reduce the amount of muscle energy required to keep the joint extended when standing. **\ ** **Articular surfaces** The articular surfaces of the bones that contribute to the knee joint are covered by hyaline cartilage. The major surfaces involved include: - the two femoral condyles, and - the adjacent surfaces of the superior aspect of the tibial condyles. Fig. 6.74 Articular Surfaces of the Knee Joint. (**A**) Extended. (**B**) Flexed. (**C**) Anterior view (flexed). The articular surfaces between the femur and patella are the V-shaped trench on the anterior surface of the distal end of the femur where the two condyles join and the adjacent surfaces on the posterior aspect of the patella. The joint surfaces are all enclosed within a single articular cavity, as are the intraarticular menisci between the femoral and tibial condyles. **Menisci** There are two menisci, which are fibrocartilaginous C-shaped cartilages, in the knee joint, one medial (**medial meniscus**) and the other lateral (**lateral meniscus**) ( [Fig. 6.75](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0380) ). Both are attached at each end to facets in the intercondylar region of the tibial plateau.  Fig. 6.75 Menisci of the Knee Joint. (**A**) Superior view. (**B**) Normal knee joint showing the medial meniscus. T2-weighted magnetic resonance image in the sagittal plane. (**C**) Normal knee joint showing the lateral meniscus. T2-weighted magnetic resonance image in the sagittal plane. The medial meniscus is attached around its margin to the capsule of the joint and to the tibial collateral ligament, whereas the lateral meniscus is unattached to the capsule. Therefore, the lateral meniscus is more mobile than the medial meniscus. The menisci are interconnected anteriorly by a transverse ligament of the knee. The lateral meniscus is also connected to the tendon of the popliteus muscle, which passes superolaterally between this meniscus and the capsule to insert on the femur. The menisci improve congruency between the femoral and tibial condyles during joint movements where the surfaces of the femoral condyles articulating with the tibial plateau change from small curved surfaces in flexion to large flat surfaces in extension. **In the clinic: Meniscal injuries** Menisci can get torn during forceful rotation or twisting of the knee, but significant trauma is not always necessary for a tear to occur. There are various patterns of meniscal tearing depending on the cleavage plane such as vertical tears (perpendicular to the tibial plateau), horizontal tears (parallel to the long axis of the meniscus and perpendicular to the tibial plateau), or bucket handle tears (longitudinal tear where the torn portion of the meniscus forms a handle-shaped fragment which gets displaced into the intercondylar notch). The patient usually complains of pain localized to the medial or lateral side of the knee, knee locking or clicking, sensation of knee giving way, and swelling, which can be intermittent and usually delayed. MRI is the modality of choice to assess meniscal tears and detect other associated injuries, such as ligamentous tears and articular cartilage damage ( [Fig. 6.76A](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0385) ). Arthroscopy is usually performed to repair a tear, debride the damaged meniscal material, or rarely remove the entire torn meniscus ( [Fig. 6.76B](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0385) ).  Fig. 6.76 Meniscal Injury and Repair. (**A**) Sagittal MRI of a knee joint showing tear of the medial meniscus. (**B**) Coronal MRI of a knee showing a truncated lateral meniscus after partial meniscectomy to treat a tear. **Synovial membrane** The synovial membrane of the knee joint attaches to the margins of the articular surfaces and to the superior and inferior outer margins of the menisci ( [Fig. 6.77A](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0390) ). The two cruciate ligaments, which attach in the intercondylar region of the tibia below and the intercondylar fossa of the femur above, are outside the articular cavity but enclosed within the fibrous membrane of the knee joint. Fig. 6.77 Synovial Membrane of the Knee Joint and Associated Bursae. (**A**) Superolateral view; patella and femur not shown. (**B**) Paramedial sagittal section through the knee. Posteriorly, the synovial membrane reflects off the fibrous membrane of the joint capsule on either side of the posterior cruciate ligament and loops forward around both ligaments, thereby excluding them from the articular cavity. Anteriorly, the synovial membrane is separated from the patellar ligament by an **infrapatellar fat pad**. On each side of the pad, the synovial membrane forms a fringed margin (an **alar fold**), which projects into the articular cavity. In addition, the synovial membrane covering the lower part of the infrapatellar fat pad is raised into a sharp midline fold directed posteriorly (the **infrapatellar synovial fold**), which attaches to the margin of the intercondylar fossa of the femur. The synovial membrane of the knee joint forms pouches in two locations to provide low-friction surfaces for the movement of tendons associated with the joint: - The smallest of these expansions is the **subpopliteal recess **(see [Fig. 6.77A ](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0390)), which extends posterolaterally from the articular cavity and lies between the lateral meniscus and the tendon of the popliteus muscle, which passes through the joint capsule. - The second expansion is the **suprapatellar bursa **( [Fig. 6.77B ](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0390)), a large bursa that is a continuation of the articular cavity superiorly between the distal end of the shaft of the femur and the quadriceps femoris muscle and tendon---the apex of this bursa is attached to the small articularis genus muscle, which pulls the bursa away from the joint during extension of the knee. Other bursae associated with the knee but not normally communicating with the articular cavity include the subcutaneous prepatellar bursa, deep and subcutaneous infrapatellar bursae, and numerous other bursae associated with tendons and ligaments around the joint (see [Fig. 6.77B](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0390) ). The prepatellar bursa is subcutaneous and anterior to the patella. The deep and subcutaneous infrapatellar bursae are on the deep and subcutaneous sides of the patellar ligament, respectively. **Fibrous membrane** The fibrous membrane of the knee joint is extensive and is partly formed and reinforced by extensions from tendons of the surrounding muscles ( [Fig. 6.78](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0395) ). In general, the fibrous membrane encloses the articular cavity and the intercondylar region: - On the medial side of the knee joint, the fibrous membrane blends with the tibial collateral ligament and is attached on its internal surface to the medial meniscus. - Laterally, the external surface of the fibrous membrane is separated by a space from the fibular collateral ligament and the internal surface of the fibrous membrane is not attached to the lateral meniscus. - Anteriorly, the fibrous membrane is attached to the margins of the patella where it is reinforced with tendinous expansions from the vastus lateralis and vastus medialis muscles, which also merge above with the quadriceps femoris tendon and below with the patellar ligament.  Fig. 6.78 Fibrous Membrane of the Knee Joint Capsule. (**A**) Anterior view. (**B**) Posterior view. The fibrous membrane is reinforced anterolaterally by a fibrous extension from the iliotibial tract and posteromedially by an extension from the tendon of the semimembranosus (the **oblique popliteal ligament**), which reflects superiorly across the back of the fibrous membrane from medial to lateral. The upper end of the popliteus muscle passes through an aperture in the posterolateral aspect of the fibrous membrane of the knee and is enclosed by the fibrous membrane as its tendon travels around the joint to insert on the lateral aspect of the lateral femoral condyle. **Ligaments** The major ligaments associated with the knee joint are the patellar ligament, the tibial (medial) and fibular (lateral) collateral ligaments, and the anterior and posterior cruciate ligaments. [Patellar ligament] The **patellar ligament** is basically the continuation of the quadriceps femoris tendon inferior to the patella (see [Fig. 6.78](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0395) ). It is attached above to the margins and apex of the patella and below to the tibial tuberosity. [Collateral ligaments] The collateral ligaments, one on each side of the joint, stabilize the hinge-like motion of the knee ( [Fig. 6.79](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0400) ). Afbeelding met röntgenfilm, Medische beeldbewerking, medisch, radiologie Automatisch gegenereerde beschrijving Fig. 6.79 Collateral Ligaments of the Knee Joint. (**A**) Lateral view. (**B**) Medial view. (**C**) Normal knee joint showing the patellar ligament and the fibular collateral ligament. T1-weighted magnetic resonance image in the sagittal plane. (**D**) Normal knee joint showing the tibial collateral ligament, the medial and lateral menisci, and the anterior and posterior cruciate ligaments. T1-weighted magnetic resonance image in the coronal plane. The cord-like **fibular collateral ligament** is attached superiorly to the lateral femoral epicondyle just above the groove for the popliteus tendon. Inferiorly, it is attached to a depression on the lateral surface of the fibular head. It is separated from the fibrous membrane by a bursa. The broad and flat **tibial collateral ligament** is attached by much of its deep surface to the underlying fibrous membrane. It is anchored superiorly to the medial femoral epicondyle just inferior to the adductor tubercle and descends anteriorly to attach to the medial margin and medial surface of the tibia above and behind the attachment of the sartorius, gracilis, and semitendinosus tendons. [Cruciate ligaments] The two cruciate ligaments are in the intercondylar region of the knee and interconnect the femur and tibia ( [Figs. 6.79D and 6.80](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0400) ). They are termed "cruciate" (Latin for "shaped like a cross") because they cross each other in the sagittal plane between their femoral and tibial attachments: - The **anterior cruciate ligament **attaches to a facet on the anterior part of the intercondylar area of the tibia and ascends posteriorly to attach to a facet at the back of the lateral wall of the intercondylar fossa of the femur. - The **posterior cruciate ligament **attaches to the posterior aspect of the intercondylar area of the tibia and ascends anteriorly to attach to the medial wall of the intercondylar fossa of the femur.   Fig. 6.80 Cruciate Ligaments of the Knee Joint. Superolateral view. The anterior cruciate ligament crosses lateral to the posterior cruciate ligament as they pass through the intercondylar region. The anterior cruciate ligament prevents anterior displacement of the tibia relative to the femur and the posterior cruciate ligament restricts posterior displacement (see [Fig. 6.80](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0405) ). [Locking mechanism] When standing, the knee joint is locked into position, thereby reducing the amount of muscle work needed to maintain the standing position ( [Fig. 6.81](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0410) ). Fig. 6.81 Knee "Locking" Mechanism. One component of the locking mechanism is a change in the shape and size of the femoral surfaces that articulate with the tibia: - In flexion, the surfaces are the curved and rounded areas on the posterior aspects of the femoral condyles. - As the knee is extended, the surfaces move to the broad and flat areas on the inferior aspects of the femoral condyles. Consequently the joint surfaces become larger and more stable in extension. Another component of the locking mechanism is medial rotation of the femur on the tibia during extension. Medial rotation and full extension tightens all the associated ligaments. Another feature that keeps the knee extended when standing is that the body's center of gravity is positioned along a vertical line that passes anterior to the knee joint. The popliteus muscle unlocks the knee by initiating lateral rotation of the femur on the tibia. [Vascular supply and innervation] Vascular supply to the knee joint is predominantly through descending and genicular branches from the femoral, popliteal, and lateral circumflex femoral arteries in the thigh and the circumflex fibular artery and recurrent branches from the anterior tibial artery in the leg. These vessels form an anastomotic network around the joint ( [Fig. 6.82](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0415) ).   Fig. 6.82 Anastomoses of Arteries Around the Knee. Anterior view. The knee joint is innervated by branches from the obturator, femoral, tibial, and common fibular nerves. **\ ** **In the clinic: Collateral ligament injuries** The collateral ligaments are responsible for stabilizing the knee joint, controlling its sideway movements, and protecting the knee from excessive motion. Injury to the fibular collateral ligament occurs when excessive outward force is applied to the medial side of the knee (varus force), and is less common than an injury to the tibial collateral ligament that is damaged when excessive force is applied inward to the lateral side of the joint (valgus force). Injuries to the tibial collateral ligament can be part of a so called "unhappy triad" that also involves tears of the medial meniscus and the anterior cruciate ligament. The spectrum of injuries to collateral ligaments of the knee range from minor sprains where the ligaments are slightly stretched, but still able to stabilize the knee joint, to full thickness tears where all fibers are torn and the ligaments lose their stabilizing function. **In the clinic: Cruciate ligament injuries** The anterior cruciate ligament (ACL) is most frequently injured during non-contact activities when there is a sudden change in the direction of movement (cutting or pivoting) ( [Fig. 6.83](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0420) ). Contact sports may also result in ACL injury due to sudden twisting, hyperextension, and valgus force related to direct collision. The injury usually affects the mid-portion of the ligament and manifests itself as a complete or partial discontinuity of the fibers or abnormal orientation and contour of the ligament. With an acute ACL tear, a sudden click or pop can be heard and the knee becomes rapidly swollen. Several tests are used to clinically assess the injury, and the diagnosis is usually confirmed by MRI. A full-thickness ACL tear causes instability of the knee joint. The treatment depends on the desired level of activity of the patient. In those with high activity levels, surgical reconstruction of the ligament is required. Those with low activity levels may opt for knee bracing and physiotherapy; however, in the long term the internal damage to the knee leads to the development of early osteoarthritis. Fig. 6.83 Sagittal MRI of Knee Joint Showing Rupture of the Anterior Cruciate Ligament *(ACL) *. A tear to the posterior cruciate ligament (PCL) requires significant force, so it rarely occurs in isolation. It usually occurs during hyperextension of the knee or as a result of a direct blow to a bent knee such as when striking the knee against the dashboard in a motor vehicle accident. Typically, the injury presents as posterior displacement of the tibia on physical examination (the so called tibial sag sign). Patients complain of knee pain and swelling, inability to bear weight, and instability. The diagnosis is confirmed on MRI. The management, as in ACL injury, depends on the degree of the injury (sprain, partial thickness, full thickness) and the level of desired activity. **In the clinic: Degenerative joint disease/osteoarthritis** Degenerative joint disease can occur in many joints of the body. Articular degeneration may result from an abnormal force across the joint with a normal cartilage or a normal force with abnormal cartilage. Typically degenerative joint disease occurs in synovial joints and the process is called osteoarthritis. In the joints where osteoarthritis occurs, the cartilage and bony tissues are usually involved, with limited change within the synovial membrane. The typical findings include reduction in the joint space, eburnation (joint sclerosis), osteophytosis (small bony outgrowths), and bony cyst formation. As the disease progresses the joint may become malaligned, its movement may become severely limited, and there may be significant pain. The commonest sites for osteoarthritis include the small joints of the hands and wrist, and in the lower limb, the hip and knee are typically affected, though the tarsometatarsal and metatarsophalangeal articulations may undergo similar changes. The etiology of degenerative joint disease is unclear, but there are some associations, including genetic predisposition, increasing age (males tend to be affected younger than females), overuse or underuse of joints, and nutritional and metabolic abnormalities. Further factors include joint trauma and preexisting articular disease or deformity. The histological findings of osteoarthritis consist of degenerative changes within the cartilage and the subchondral bone. Further articular damage worsens these changes, which promote further abnormal stresses upon the joint. As the disease progresses the typical finding is pain, which is usually worse on rising from bed and at the end of a day's activity. Commonly it is aggravated by the extremes of movement or unaccustomed exertion. Stiffness and limitation of movement may ensue. Treatment in the first instance includes alteration of lifestyle to prevent pain and simple analgesia. As symptoms progress a joint replacement may be necessary, but although joint replacement appears to be the panacea for degenerative joint disease, it is not without risks and complications, which include infection and failure in the short and long term. **In the clinic: Examination of the knee joint** It is important to establish the nature of the patient's complaint before any examination. The history should include information about the complaint, the signs and symptoms, and the patient's lifestyle (level of activity). This history may give a significant clue to the type of injury and the likely findings on clinical examination, for example, if the patient was kicked around the medial aspect of the knee, a valgus deformity injury to the tibial collateral ligament might be suspected. The examination should include assessment in the erect position, while walking, and on the couch. The affected side must be compared with the unaffected side. There are many tests and techniques for examining the knee joint, including the following. [Tests for anterior instability] - Lachman's test---the patient lies on the couch. The examiner places one hand around the distal femur and the other around the proximal tibia and then elevates the knee, producing 20 degrees of flexion. The patient's heel rests on the couch. The examiner's thumb must be on the tibial tuberosity. The hand on the tibia applies a brisk anteriorly directed force. If the movement of the tibia on the femur comes to a sudden stop, it is a firm endpoint. If it does not come to a sudden stop, the endpoint is described as soft and is associated with a tear of the anterior cruciate ligament. - Anterior drawer test---a positive anterior drawer test is when the proximal head of a patient's tibia can be pulled anteriorly on the femur. The patient lies supine on the couch. The knee is flexed to 90 degrees and the heel and sole of the foot are placed on the couch. The examiner sits gently on the patient's foot, which has been placed in a neutral position. The index fingers are used to check that the hamstrings are relaxed while the other fingers encircle the upper end of the tibia and pull the tibia. If the tibia moves forward, the anterior cruciate ligament is torn. Other peripheral structures, such as the medial meniscus or meniscotibial ligaments, must also be damaged to elicit this sign. - Pivot shift test---there are many variations of this test. The patient's foot is wedged between the examiner's body and elbow. The examiner places one hand flat under the tibia pushing it forward with the knee in extension. The other hand is placed against the patient's thigh pushing it the other way. The lower limb is taken into slight abduction by the examiner's elbow with the examiner's body acting as a fulcrum to produce the valgus. The examiner maintains the anterior tibial translation and the valgus and initiates flexion of the patient's knee. At about 20 to 30 degrees, the pivot shift will occur as the lateral tibial plateau reduces. This test demonstrates damage to the posterolateral corner of the knee joint and the anterior cruciate ligament. [Tests for posterior instability] - Posterior drawer test---a positive posterior drawer test occurs when the proximal head of a patient's tibia can be pushed posteriorly on the femur. The patient is placed in a supine position and the knee is flexed to approximately 90 degrees with the foot in the neutral position. The examiner sits gently on the patient's foot placing both thumbs on the tibial tuberosity and pushing the tibia backward. If the tibial plateau moves, the posterior cruciate ligament is torn. [Assessment of other structures of the knee] - Assessment of the tibial collateral ligament can be performed by placing a valgus stress on the knee. - Assessment of lateral and posterolateral knee structures requires more complex clinical testing. [The knee will also be assessed for:] - joint line tenderness, - patellofemoral movement and instability, - presence of an effusion, - muscle injury, and - popliteal fossa masses. [Further investigations] After the clinical examination has been carried out, further investigations usually include **plain radiography** and possibly **magnetic resonance imaging**, which allows the radiologist to assess the menisci, cruciate ligaments, collateral ligaments, bony and cartilaginous surfaces, and soft tissues. **Arthroscopy** may be carried out and damage to any internal structures repaired or trimmed. An arthroscope is a small camera that is placed into the knee joint through the anterolateral or anteromedial aspect of the knee joint. The joint is filled with a saline solution and the telescope is manipulated around the knee joint to assess the cruciate ligaments, menisci, and cartilaginous surfaces. **In the clinic: Anterolateral ligament of the knee** A ligament associated at its origin with the fibular collateral ligament of the knee has been described. This ligament (anterolateral ligament of the knee) courses from the lateral femoral epicondyle to the anterolateral region of the proximal end of the tibia and may control internal rotation of the tibia (*J Anat* 2013;223:321--328).  **Ankle joint** The ankle joint is synovial in type and involves the talus of the foot and the tibia and fibula of the leg ( [Fig. 6.104](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0525) ). Fig. 6.104 Ankle Joint. ( **A **) Anterior view with right foot plantarflexed. ( **B **) Schematic of joint, posterior view. ( **C **) Superior view of the talus to show the shape of the articular surface. The ankle joint mainly allows hinge-like dorsiflexion and plantarflexion of the foot on the leg. The distal end of the fibula is firmly anchored to the larger distal end of the tibia by strong ligaments. Together, the fibula and tibia create a deep bracket-shaped socket for the upper expanded part of the body of the talus: - The roof of the socket is formed by the inferior surface of the distal end of the tibia. - The medial side of the socket is formed by the medial malleolus of the tibia. - The longer lateral side of the socket is formed by the lateral malleolus of the fibula. The articular surfaces are covered by hyaline cartilage. The articular part of the talus is shaped like a short half-cylinder tipped onto its flat side with one end facing lateral and the other end facing medial. The curved upper surface of the half-cylinder and the two ends are covered by hyaline cartilage and fit into the bracket-shaped socket formed by the distal ends of the tibia and fibula. When viewed from above, the articular surface of the talus is much wider anteriorly than it is posteriorly. As a result, the bone fits tighter into its socket when the foot is dorsiflexed and the wider surface of the talus moves into the ankle joint than when the foot is plantarflexed and the narrower part of the talus is in the joint. The joint is therefore most stable when the foot is dorsiflexed. The articular cavity is enclosed by a synovial membrane, which attaches around the margins of the articular surfaces, and by a fibrous membrane, which covers the synovial membrane and is also attached to the adjacent bones. **In the clinic: Fracture of the talus** The talus is an unusual bone because it ossifies from a single primary ossification center, which initially appears in the neck. The posterior aspect of the talus appears to ossify last, normally after puberty. In up to 50% of people there is a small accessory ossicle (the os trigonum) posterior to the lateral tubercle of the posterior process. Articular cartilage covers approximately 60% of the talar surface and there are no direct tendon or muscle attachments to the bone. One of the problems with fractures of the talus is that the blood supply to the bone is vulnerable to damage. The main blood supply to the bone enters the talus through the tarsal sinus from a branch of the posterior tibial artery. This vessel supplies most of the neck and the body of the talus. Branches of the dorsalis pedis artery enter the superior aspect of the talar neck and supply the dorsal portion of the head and neck, and branches from the fibular artery supply a small portion of the lateral talus. Fractures of the neck of the talus often interrupt the blood supply to the talus, so making the body and posterior aspect of the talus susceptible to osteonecrosis, which may in turn lead to premature osteoarthritis and require extensive surgery. The ankle joint is stabilized by **medial** (deltoid) and **lateral ligaments** . **Medial ligament (deltoid ligament)** The medial (deltoid) ligament is large, strong ( [Fig. 6.105](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0530) ), and triangular in shape. Its apex is attached above to the medial malleolus and its broad base is attached below to a line that extends from the tuberosity of the navicular bone in front to the medial tubercle of the talus behind. Fig. 6.105 Medial Ligament of the Ankle Joint, Right Foot. The medial ligament is subdivided into four parts based on the inferior points of attachment: - The part that attaches in front to the tuberosity of the navicular and the associated margin of the plantar calcaneonavicular ligament (spring ligament), which connects the navicular bone to the sustentaculum tali of the calcaneus bone behind, is the **tibionavicular part **of the medial ligament. - The **tibiocalcaneal part**, which is more central, attaches to the sustentaculum tali of the calcaneus bone. - The **posterior tibiotalar part **attaches to the medial side and medial tubercle of the talus. - The fourth part (the **anterior tibiotalar part **) is deep to the tibionavicular and tibiocalcaneal parts of the medial ligament and attaches to the medial surface of the talus. **Lateral ligament** The lateral ligament of the ankle is composed of three separate ligaments, the anterior talofibular ligament, the posterior talofibular ligament, and the calcaneofibular ligament ( [Fig. 6.106](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0535) ): - The **anterior talofibular ligament **is a short ligament, and attaches the anterior margin of the lateral malleolus to the adjacent region of the talus. - The **posterior talofibular ligament **runs horizontally backward and medially from the malleolar fossa on the medial side of the lateral malleolus to the posterior process of the talus. - The **calcaneofibular ligament **is attached above to the malleolar fossa on the posteromedial side of the lateral malleolus and passes posteroinferiorly to attach below to a tubercle on the lateral surface of the calcaneus. Fig. 6.106 Lateral Ligament of the Ankle Joint. (**A**) Lateral view, right foot. (**B**) Posterior view, right foot. **Intertarsal joints** The numerous synovial joints between the individual tarsal bones mainly invert, evert, supinate, and pronate the foot: - Inversion and eversion is turning the whole sole of the foot inward and outward, respectively. - Pronation is rotating the front of the foot laterally relative to the back of the foot, and supination is the reverse movement. Pronation and supination allow the foot to maintain normal contact with the ground when in different stances or when standing on irregular surfaces. The major joints at which movements occur include the subtalar, talocalcaneonavicular, and calcaneocuboid joints ( [Fig. 6.107](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0540) ). The talocalcaneonavicular and calcaneocuboid joints together form what is often referred to as the **transverse tarsal joint**.  Fig. 6.107 Intertarsal Joints, Right Foot. Intertarsal joints between the cuneiforms and between the cuneiforms and the navicular allow only limited movement. The joint between the cuboid and navicular is normally fibrous. **\ ** **In the clinic: Ankle fractures** An appreciation of ankle anatomy is essential to understand the wide variety of fractures that may occur at and around the ankle joint. The ankle joint and related structures can be regarded as a fibro-osseous ring oriented in the coronal plane. - The upper part of the ring is formed by the joint between the distal ends of the fibula and tibia and by the ankle joint itself. - The sides of the ring are formed by the ligaments that connect the medial malleolus and lateral malleolus to the adjacent tarsal bones. - The bottom of the ring is not part of the ankle joint, but consists of the subtalar joint and the associated ligaments. Visualizing the ankle joint and surrounding structures as a fibro-osseous ring allows the physician to predict the type of damage likely to result from a particular type of injury. For example, an inversion injury may fracture the medial malleolus and tear ligaments anchoring the lateral malleolus to the tarsal bones. The ring may be disrupted not only by damage to the bones (which produces fractures) but also by damage to the ligaments. Unlike bone fractures, damage to ligaments is unlikely to be appreciated on plain radiographs. When a fracture is noted on a plain radiograph, the physician must always be aware that there may also be appreciable ligamentous disruption. Ottawa Ankle Rules The Ottawa ankle rules were developed to assist clinicians in deciding whether patients with acute ankle injuries require investigation with radiographs in order to avoid unnecessary studies. Named after the hospital where they were developed, the rules are highly sensitive and have reduced the utilization of unwarranted ankle radiographs since their implementation. An ankle X-ray series is required if there is ankle pain and any of the following: - Bone tenderness along the distal 6 cm of the posterior tibia or tip of the medial malleolus - Bone tenderness along the distal 6 cm of the posterior fibula or tip of the lateral malleolus - Inability to bear weight for four steps both immediately after the injury and in the emergency department A foot X-ray series is required if there is midfoot pain and any of the following: - Bone tenderness at the base of the fifth metatarsal bone - Bone tenderness at the navicular bone - Inability to bear weight for four steps both immediately after the injury and in the emergency department **Functions** Positioning the hand Unlike the lower limb, which is used for support, stability, and locomotion, the upper limb is highly mobile for positioning the hand in space. The shoulder is suspended from the trunk predominantly by muscles and can therefore be moved relative to the body. Sliding (protraction and retraction) and rotating the scapula on the thoracic wall changes the position of the **glenohumeral joint** (**shoulder joint**) and extends the reach of the hand ( [Fig. 7.3](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0020) ). The glenohumeral joint allows the arm to move around three axes with a wide range of motion. Movements of the arm at this joint are flexion, extension, abduction, adduction, medial rotation (internal rotation), lateral rotation (external rotation), and circumduction ( [Fig. 7.4](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0025) ). Fig. 7.3 Movements of the Scapula. (**A**) Rotation. (**B**) Protraction and retraction.  Fig. 7.4 Movements of the Arm at the Glenohumeral Joint. The major movements at the **elbow joint** are flexion and extension of the forearm ( [Fig. 7.5A](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0030) ). At the other end of the forearm, the distal end of the lateral bone, the radius, can be flipped over the adjacent head of the medial bone, the ulna. Because the hand is articulated with the radius, it can be efficiently moved from a palm-anterior position to a palm-posterior position simply by crossing the distal end of the radius over the ulna ( [Fig. 7.5B](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0030) ). This movement, termed pronation, occurs solely in the forearm. Supination returns the hand to the anatomical position. Afbeelding met joint, skelet Automatisch gegenereerde beschrijving Fig. 7.5 Movements of the Forearm. (**A**) Flexion and extension at the elbow joint. (**B**) Pronation and supination. At the **wrist joint** , the hand can be abducted, adducted, flexed, extended, and circumducted ( [Fig. 7.6](https://www-clinicalkey-com.utrechtuniversity.idm.oclc.org/f0035) ). These movements, combined with those of the shoulder, arm, and forearm, enable the hand to be placed in a wide range of positions relative to the body. Fig. 7.6 Movements of the Hand at the Wrist Joint. **The hand as a mechanical tool** One of the major functions of the hand is to grip and manipulate objects. Gripping objects generally involves flexing the fingers against the thumb. Depending on the type of grip, muscles in the hand act to: - modify the actions of long tendons that emerge from the forearm and insert into the digits of the hand, and - produce combinations of joint movements within each digit that cannot be generated by the long flexor and extensor tendons alone coming from the forearm. **The hand as a sensory tool** The hand is used to discriminate between objects on the basis of touch. The pads on the palmar aspect of the fingers contain a high density of somatic sensory receptors. Also, the sensory cortex of the brain devoted to interpreting information from the hand, particularly from the thumb, is disproportionately large relative to that for many other regions of skin.