Deel 2 Anatomie PDF

**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.utrechtun...

**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) ).  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) ). Afbeelding met Medische beeldbewerking, röntgenfilm, radiologie, medisch Automatisch gegenereerde beschrijving 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. Afbeelding met skelet Beschrijving automatisch gegenereerd met gemiddelde betrouwbaarheid 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) ).  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).