Chapter 15: The thigh and knee

Fascia of thigh

The thigh is encased by superficial and deep fascia. The superficial fascia covers the saphenous opening (where it is termed the cribriform fascia) and fuses with the fascia lata inferior to, and parallel with the inguinal ligament, thereby preventing any fluid that might collect deep to the subcutaneous tissue of the abdomen from entering the thigh. The fascia of the thigh, known as the fascia lata, is attached posterolaterally to the iliac crest and anteriorly to the inguinal ligament. It sends lateral and medial intermuscular septa inward to the femur (fig. 15-2). That part of the fascia lata overlying the vastus lateralis is the iliotibial tract (figs. 15-1 and 15-2). It is attached superiorly to the iliac crest, where it forms the gluteal aponeurosis, and it receives the insertions of the gluteus maximus and the tensor muscle of the fasciae lata. This fan-shaped arrangement of muscle attachment (which resembles the deltoid in the upper limb) is important in maintaining posture and in locomotion.

The saphenous opening (figs. 13-1 and 15-3) is a gap in the fascia lata inferolateral to the pubic tubercle and overlying the femoral vein. It transmits the great saphenous vein, which joins the femoral vein. The fascia forms a sharp, falciform margin lateral to the great saphenous vein. The saphenous opening is covered by the cribriform fascia, which is pierced by the saphenous vein and some tributaries.

The superiormost parts of the femoral artery and vein lie in a vascular compartment posterior to the inguinal ligament and between the iliopsoas and pectineus muscles. The femoral nerve, together with the iliopsoas muscle, lies more laterally. The femoral artery and vein, together with the more medially placed femoral canal, are enclosed in a fascial funnel known as the femoral sheath (fig. 15-4). The sheath is formed anteriorly by the transverslis fascia of the abdomen (pierced by the femoral branch of the genitofemoral nerve and the great saphenous vein) and posteriorly by the iliac fascia. After a few centimeters, the sheath tapers inferiorly and fuses with the adventitia of the blood vessels. The femoral canal, situated in front of the pectineus, contains fat and a few lymphatic vessels. Its upper end or base, termed the femoral ring, is closed by extraperitoneal tissue known as the femoral septum. The medial boundary of the ring is sharp and ligamentous. The femoral canal is important surgically: a femoral hernia is a protrusion of extraperitoneal tissue, with or without an abdominal viscus, through the femoral ring. It may pass down the femoral canal and through the femoral sheath and saphenous opening. * Clinically, the neck of a femoral hernia is found immediately inferolateral to the pubic tubercle (see fig. 25-7). (An inguinal hernia is more medial.) The hernial sac is formed by parietal peritoneum, but the external coverings of the hernia are frequently fused.

The femoral triangle.

The femoral triangle (fig. 15-5), which contains the femoral nerve and vessels, is situated in the upper third of the anterior thigh. It is bounded laterally by the medial border of the sartorius, medially by the medial (Continental authors use lateral) border of the adductor longus, and by the inguinal ligament on the superior side. Its roof is formed by the fascia lata and the cribriform fascia. Its floor is formed by the iliopsoas, pectineus, and adductor longus (fig. 15-6).

The adductor canal.

which contains the femoral vessels and the saphenous nerve, is situated in the middle third of the medial part of the thigh. It is bounded laterally by the vastus medialis, medially by the adductor longus (and frequently magnus), and superficially by the sartorius and sub sartorial fascia. The adductor canal was described in the eighteenth century by John Hunter, who ligated the femoral artery in it to treat popliteal aneurysm.

Posterior thigh (table 15-1)

The muscles.

The muscles on the posterior thigh (biceps, semitendinosus, and semimembranosus) are known collectively as the hamstrings (see fig. 15-2). They are the main extensors of the thigh and flexors of the leg, especially during walking. Mostly they arise from the ischial tuberosity, cross both the hip and knee joints, have fascial and ligamentous as well as bony insertions, and are supplied by the tibial part of the sciatic nerve. The biceps and semitendinosus tendons, which are palpable and visible, form, respectively, the lateral and medial boundaries of the popliteal fossa (see fig. 15-9). The lower half of the semitendinosus is tendinous; hence its name. The tendons of origin and insertion of the semimembranosus together make up almost half of the length of the muscle. The short head of the biceps femoris is different in that it arises from the femur and is innervated by the fibular division of the sciatic nerve.

The sciatic nerve.

The sciatic nerve (see figs. 14-1, 14-2, 14-3 and 15-8) descends under cover of the gluteus maximus and passes down the middle of the thigh, where it is crossed from posterior by the long head of the biceps. Separation of the sciatic into the tibial and common fibular (peroneal) nerves may occur at any level in the gluteal region or thigh but usually takes place in the lower third of the thigh. Most of the branches arise from the medial side. Tibial twigs supply the semitendinosus, semimembranosus, long head of biceps, and adductor magnus. Common peroneal twigs supply the short head of biceps.

Damage to the sciatic nerve causes paralysis of the hamstrings (compensated for by the sartorius) and the muscles of the leg and foot, with loss of movement inferior to the knee. Sensation is also lost inferior to the knee except medially (saphenous nerve). In incomplete lesions of the sciatic nerve, the fibular component is usually more severely damaged than the tibial one.

Medial side of thigh (table 15-2)

The muscles.

The muscles on the medial side of the thigh (pectineus, adductor longus, brevis, magnus, and gracilis) are mostly adductors of the thigh, and are innervated by the obturator nerve (see figs. 15-2 and 15-7). The three named adductors are used in all movements in which the thighs are pressed together. The adductor magnus, however, consists of an adductor part anterosuperiorly and an extensor part medially. The adductor longus is the medial boundary of the femoral triangle. Ossification may occur in its tendon due to repeated trauma ("rider's bone"). The adductor brevis is sandwiched between the anterior and posterior branches of the obturator nerve. The lower end of the adductor magnus allows the passage of the femoral vessels into the popliteal fossa, forming the adductor hiatus.

The obturator nerve.

The obturator nerve (L[2],3,4,[5]) (see figs. 15-7 and 30-7) arises from the lumbar plexus in the substance of the psoas major muscle. It emerges at the medial margin of the psoas and accompanies the obturator vessels to the obturator groove, where it divides into anterior and posterior branches. These pass through the obturator foramen to reach the thigh, where they are separated by the adductor brevis. The anterior branch, which lies posterior to the pectineus and adductor longus, supplies these two (not always the pectineus) as well as the gracilis, adductor brevis, and skin on the medial side of the thigh. The posterior branch pierces and supplies the obturator externus, and gives twigs to the adductor magnus (and sometimes brevis). An accessory obturator nerve (L3,4 or L2,3), when present, communicates with the anterior branch of the obturator and supplies the pectineus.

The obturator artery.

The obturator artery (see fig. 13-5), a branch of the internal iliac, sends anterior and posterior branches around the margin of the obturator foramen. The posterior branch gives off an acetabular branch, which passes through the acetabular notch and is an important vascular source for the head of the femur.

Anterior thigh (table 15-3)

The muscles.

The chief muscles of the anterior thigh are the iliopsoas, quadriceps femoris, and sartorius. The iliopsoas (see figs. 15-4 and 15-6) consists of a lateral part, the iliacus, and a medial portion, the psoas major. It arises from the iliac fossa and the anterolateral portions of the lumbar vertebral bodies, enters the thigh posterior to the inguinal ligament, and is inserted into the lesser trochanter of the femur. The iliopsoas is the chief flexor of the thigh and, when the thigh is fixed, of the trunk. It flexes the hip when walking and is a postural muscle, being active during standing. It can also bend the vertebral column to one side. A psoas abscess originating in the spine may descend posterior to the inguinal ligament and simulate a femoral hernia.

The quadriceps femoris comprises the rectus femoris, which extends from the hip bone to the tibia, and three vasti (lateralis, medialis, and intermedius), which pass from the femur to the tibia (see fig. 15-2). The tendon of insertion of the quadriceps contains a large sesamoid bone, the patella, and its terminal portion from the patealla to the tibial tuberosity is known as the patellar ligament. The rectus femoris, which has been termed the "kicking muscle," aids the iliopsoas in hip flexion. The vastus medialis, which superficially appears to be fused with the intermedius, usually forms a characteristic medial bulge in the lower part of the thigh (see fig. 15-1). The quadriceps extends the leg at the knee and is important in climbing, running, jumping, rising from sitting, and walking up and down stairs.

The knee jerk (patellar reflex) is elicited by tapping the patellar ligament, which causes sudden stretching of the quadriceps (and its contained neuromuscular spindles). This elicits a rapid contraction of the muscle. The reflex center is in the L3-4 segment of the spinal cord.

The sartorius muscle forms the lateral boundary of the femoral triangle (see fig. 15-5) and covers the adductor canal, thereby serving as a surgical guide to the femoral artery. It flexes the hip and knee and assists in producing the crossed-leg position of tailors; hence its name (cf. sartorial).

The femoral nerve.

The femoral nerve (L2 to 4) (see figs. 15-7 and 30-7), the largest branch of the lumbar plexus, descends between the iliacus and psoas major and enters the thigh posterior to the middle of the inguinal ligament. The femoral nerve, arising external to the iliac fascia, remains outside the femoral sheath. In the femoral triangle, lateral to the femoral artery, it divides into terminal branches. The femoral nerve supplies the iliacus and pectineus muscles as well as the hip joint. The terminal branches include intermediate and medial cutaneous nerves of the thigh, muscular twigs to the sartorius, quadriceps femoris, and articularis genus muscles, and the saphenous nerve. The saphenous nerve, which may be regarded as the termination of the femoral nerve, descends with the femoral vessels through the femoral triangle and adductor canal and then becomes cutaneous. In the leg, it accompanies the great saphenous vein and ends on the medial side of the foot. An accessory femoral nerve from the lumbar plexus is not uncommon. The saphenous and other cutaneous nerves form subsartorial (beneath the sartorius) and patellar plexuses. The lateral femoral cutaneous nerve, a branch of the femoral nerve or of the lumbar plexus, supplies skin on the anterolateral aspect of the thigh and is liable to compression in the region of the inguinal ligament and produces paresthesia (meralgia paresthetica).

The femoral artery.

The femoral artery, the continuation of the external iliac artery, enters the femoral triangle by passing posterior to the inguinal ligament (see fig. 15-5). It then enters the adductor canal and passes posteriorward to reach the popliteal fossa by traversing a gap (the adductor hiatus) between the insertions of the adductor magnus muscle and the femur. There it changes its name to popliteal (see figs. 13-5 and 15-10). The femoral artery can be represented by the upper two thirds of a line from the midinguinal point (midpoint between the anterior superior iliac spine and the pubic symphysis) to the adductor tubercle of the femur (see fig. 14-4). Its pulsations can be felt at the midpoint of the inguinal ligament when the thigh is flexed, abducted, and rotated laterally. The femoral artery can be compressed, palpated or cannulated at the midinguinal point. The femoro-popliteal artery supplies the muscles of the calf, and obstruction interferes with their blood supply, producing symptoms on exertion (intermittent claudication). Proximally, the femoral artery gives off the superficial epigastric (which proceeds toward the umbilicus), superficial circumflex iliac (which runs toward the anterior superior iliac spine), and superficial and deep external pudendal arteries (to the inguinal and pudendal regions). The most important branch of the femoral artery is the deep femoral (profunda femoris) artery (see fig. 15-15), which arises in the femoral triangle and gives lateral and medial circumflex branches (one or both of which may arise directly from the femoral artery. The deep femoral artery descends along the medial side of the femur, gives origin to about three perforating arteries (which supply nearby muscles), and ends by passing through the adductor magnus as the last (fourth) perforating artery. The perforating arteries form an extensive anastomosis, and the first one meets transverse branches of the circumflex and also the inferior gluteal artery (collectively termed the cruciate anastomosis). The circumflex arteries supply the head and neck of the femur through branches that enter near the trochanters and traverse the neck to reach the head of the femur. Therefore, fractures of the neck can compromise the circulation of the head of the femur resulting in "avascular necrosis" if the artery of the head of the femur is not adequate. Distally, the femoral artery gives origin to the descending genicular artery, which supplies the knee joint. The femoral vein, which may be double below, accompanies the artery and finally lies medial to it in the femoral triangle. It receives the great saphenous vein and becomes the external iliac vein.

Popliteal fossa

The popliteal fossa (figs. 15-9 and 15-10) is a diamond-shaped area at the posterior knee. Its upper boundaries are the biceps laterally, and the semitendinosus and semimembranosus medially. Its lower boundaries are the lateral and medial heads of the gastrocnemius. The fascial roof is stretched on extension. The floor is formed, from superior to inferior, by the popliteal surface of the femur, the oblique popliteal ligament (an expansion of the semimembranosus tendon), and fascia overlying the popliteus muscle. The popliteal fossa contains the common fibular and tibial nerves, popliteal vessels, small saphenous vein, lymph nodes, bursae, and fat.

The common fibular nerve.

The common fibular nerve (L4 to S2) (fig. 15-10) arises from the sciatic nerve. It follows closely the medial edge of the biceps femoris tendon (fig. 15-9). The common fibular nerve winds around the neck of the fibula, where it can be felt and where it is liable to injury. Under cover of the peroneus longus muscle, it divides into the superficial and deep peroneal nerves (see fig. 15-7). The common peroneal nerve, while still a part of the sciatic nerve, supplies the short head of the biceps femoris muscle. In the popliteal fossa, it gives branches to the knee joint and to skin (lateral sural cutaneous nerve) and a communication to the medial sural cutaneous nerve. It sometimes supplies the fibularis longus, tibialis anterior, and extensor digitorum longus muscles. Injury to the common fibular nerve results in loss of eversion and of dorsiflexion of the foot (foot-drop) and in a sensory loss on the lateral side of the leg and on the dorsum of the foot.

The tibial nerve.

The tibial nerve (L4 to S3) (fig. 15-9) arises from the sciatic nerve at or suprior to the popliteal fossa. It exits the fossa by passing deep to the gastrocnemius, where it lies on the popliteus muscle. At the lower border of the popliteus muscle, it passes deep to the fibrous arch of the soleus. The tibial nerve, while still a part of the sciatic nerve, supplies the semitendinosus, semimembranosus, long head of the biceps, and adductor magnus muscles. In the popliteal fossa, it gives branches to the knee joint and to the gastrocnemius, soleus, plantaris, popliteus, and tibialis posterior muscles. The branch to the popliteus provides the interosseous nerve of the leg. The tibial nerve gives rise to the medial sural cutaneous nerve, which descends superficially between the heads of the gastrocnemius and usually joins a communication from the common peroneal nerve to form the sural nerve.

The sural nerve.

The sural nerve, which usually arises from both tibial and common peroneal components, lies on the calcaneal tendon, accompanies the small saphenous vein posterior to the lateral malleolus, and supplies the skin of the posterior leg and the lateral part of the foot, including the heel and at least the lateral side of the little toe.

Sensation from the sole of the foot is important in posture and locomotion, and damage to the tibial nerve results in a significant sensory loss on the sole and on the plantar aspects of the toes.

A simple scheme (fig. 15-11) shows the basic arrangement of the segmental innervation (dermatomes) of the skin of the lower limb, which is supplied successively down the pre-axial border and then up the postaxial border of the lower limb. Table 15-4 shows the segmental innervation of the muscles of the lower limb.

Hip joint

The hip joint is a ball-and-socket articulation between the acetabulum of the hip bone and the head of the femur (see figs. 12-7 and 12-8). The angle between the head and neck of the femur and the shaft may be abnormally diminished (coxa vara) or increased (coxa valga). More than half of the head of the femur is within the acetabulum, which is deepened by the fibrous or fibrocartilaginous acetabular labrum and completed on its inferior aspect by the transverse ligament that bridges the acetabular notch (figs. 15-12 and 15-13). The fibrous joint capsule is attached to the margin of the acetabulum and to the intertrochanteric line of the femur (fig. 15-14). The capsule is thickened anteriorly, to form the V-shaped iliofemoral ligament, and also inferiorly (pubofemoral ligament) and posteriorly (ischiofemoral ligament, which encircles the neck of the femur as the zona orbicularis). The posterior capsule is arranged so that the lateral one third to one half of the posterior neck of the femur is extracapsular (see fig. 12-18). Capsular fibers attached to the femur tend to be reflected along the neck as retinacula that carry vessels to the head of the femur. The ligament of the head (formerly known as the ligamentum teres) extends from the acetabular notch and transverse ligament to a pit on the head of the femur (see fig. 12-12), and it transmits vessels (fig. 15-15). The hip joint may be approached surgically from the anterior, posterior, or lateral sides, but it is surrounded by powerful muscles. The iliopsoas, pectineus, and femoral vessels are anterior relations. The hip joint may be tapped by a needle inserted anteriorly (halfway between the mid inguinal point and the greater trochanter) or laterally superior to the greater trochanter). The hip joint is supplied by branches of the femoral, sciatic, and obturator nerves, which also supply the knee joint. Hip disease is an important cause of pain referred to the knee.

The movements of the thigh at the hip joint are flexion and extension, abduction and adduction, and rotation and circumduction. The movements of the trunk at the hip joint are equally important, as when one lifts the trunk from the supine position. Flexion of the thigh is usually combined with flexion of the vertebral column, the chief flexor being the iliopsoas muscle. The joint capsule becomes taut during hip extension, with the iliofemoral ligament restricting this motion. The chief extensor muscles are the hamstrings, with assistance of the gluteus maximus muscle. The abductors are the glutei medius and minimus, and the main adductors are the adductor longus, brevis, and magnus. In rotation of the hip joint, the axis extends from the head of the femur to the medial condyle of the femur (not the long axis of the femur). The lateral rotators at the hip are the short muscles of the gluteal region. The chief medial rotators are the tensor fasciae latae and the glutei medius and minimus.

Knee joint

The knee joint is a condylar articulation between the condyles of the femur, those of the tibia, and the patella (figs. 15-16, 15-17, 15-18 and 15-19). The articular surfaces are large, complicated, and incongruent. The angle between the vertical axes of the femur and tibia is exaggerated in knock-knee (genu valgum), whereas the knees appear more separated in bowlegs (genu varum). The knee joint capsule, thin and partly deficient, is attached to the margins of the condyles of the femur, to the patella and patellar ligament, and to the condyles of the tibia. The capsule is strengthened by retinacula derived from the vasti and by an expansion (oblique popliteal ligament) from the semimembranosus tendon.

A strong extracapsular ligament is present on each side (fig. 15-16). The fibular collateral ligament extends from the lateral epicondyle of the femur to the head of the fibula, and its stabilizing function is aided by the biceps and popliteus tendons. The tibial collateral ligament extends from the medial epicondyle of the femur to the medial surface of the tibia, and it is attached to the medial meniscus.

The intra-articular ligaments are the cruciate ligaments and the menisci (fig. 15-16). The anterior and posterior cruciate ligaments limit, respectively, anterior and posterior slippage of the tibia on the femur. These ligaments are named for their tibial attachments, and they extend, respectively, anterior and posterior to the intercondylar eminence, from the proximity of the intercondylar fossa of the femur to the tibia (fig. 15-17). The ligaments cross each other; hence the name cruciate. You can "represent the ligaments by your lower limbs while standing, i.e., cross your right leg (right anterior cruciate ligament) in front of your left. Rotate your trunk to right and left" (Mainland). The lateral and medial menisci are fibrocartilagenous crescents that lie on the superior surface of the tibia. They act as cushions or shock absorbers and facilitate lubrication. Each meniscus is wedge-shaped in section, being thick externally and having a thin, free internal border. The ends, or horns, of the menisci are anchored to the tibia anterior to and posterior to the intercondylar eminence, and they may be connected anteriorly by a transverse ligament (see fig. 15-17). The lateral meniscus is almost circular, is anchored to the popliteus tendon (which probably pulls it posteriorward in flexion), and is freer to move. The medial meniscus is C-shaped, is anchored to the tibial collateral ligament, and is much more frequently torn by twisting injuries of the flexed knee.

The synovial membrane is extensive, and it lines the infrapatellar fat pad between the patella and tibia. About a dozen bursae are situated near the knee (fig. 15-19). The most important is the suprapatellar bursa or pouch, an extension of the joint cavity several centimeters above the patella, between the quadriceps and the anterior aspect of the femur. Hence, when the cavity of the knee joint is distended with fluid, e.g., after trauma, the swelling presents itself superior to, and at the sides of the patella (a site from which joint fluid can be drained. Other bursae that sometimes communicate with the joint cavity are related to the popliteus, medial head of the gastrocnemius (this bursa may form a cyst), semimembranosus, and lateral head of the gastrocnemius. A subcutaneous prepatellar bursa is situated between the skin and the lower part of the patella and may become inflamed ("housemaid's knee"). A subcutaneous infrapatellar bursa is found over the lower part of the tuberosity of the tibia and may become inflamed ("clergyman's knee"). There is also a deep infrapatellar bursa between the patellar ligament and the tibia.

The knee joint is supplied by various nerves of the thigh and leg, e.g., the femoral, obturator, and sciatic nerves, and pain may be referred to the knee from hip disease.

The knee joint is very complicated and is best regarded as a condylar rather than a hinge joint. This is because the shapes and curvatures of the articular surfaces are such that hinge movements are combined with gliding, rolling, and rotation about a vertical axis. Flexion of the thigh at the knee is first accompanied by lateral rotation of the thigh (contributed to by the popliteus), and the femur then rolls posteriorward on the tibia. Conversely, the last part of extension is accompanied by medial rotation of the thigh, and the ligaments are then taut and the joint is most stable. The quadriceps femoris extends the leg, and the hamstrings flex it. The biceps rotates the leg laterally, and the semitendinosus rotates it medially. The popliteus muscle, acting from a fixed tibia, is believed to be significant in rotating the femur laterally. The muscles around the knee are very important in providing stability for the joint.

Tibiofibular joint

The tibiofibular joint is a small, plane articulation between the posterior aspect of the lateral condyle of the tibia and the head of the fibula. The joint cavity may communicate with that of the knee.


15-1 What are the main compartments of the thigh?

15-1 The compartments of the thigh are the anterior, for the quadriceps (femoral nerve); the medial, for the adductors (obturator nerve); and the posterior, for the hamstrings (sciatic nerve). See figure 15-2.

15-2 What is the iliotibial tract?

15-2 The iliotibial tract is an important thickening of the fascia lata laterally. It extends from the iliac crest to the lateral condyle of the tibia, it receives the insertions of the gluteus maximus and tensor fasciae latae, and it stabilizes the knee. The combination of tensor, tract, and gluteus maximus may be thought of as the deltoid of the thigh, i.e., comparable to the anterior, middle, and posterior fibers, respectively, in the upper limb.

15-3 What is the clinical importance of the femoral canal?

15-3 The femoral ring and canal are the site of femoral hernia. The neck of a femoral hernia is found immediately inferolateral to the pubic tubercle.

15-4 What are the chief contents of (a) the femoral triangle and (b) the adductor canal?

15-4 The femoral triangle contains the femoral nerve and vessels; the adductor canal contains the femoral vessels and saphenous nerve. John Hunter, who proposed ligature of an artery well proximal to an aneurysm, ligated the femoral artery in the adductor (Hunter's) canal in 1785. See J. Dobson, John Hunter, Livingstone, Edinburgh, 1969, p. 260.

15-5 What is the chief action of the quadriceps?

15-5 All four parts of the quadriceps extend the knee. The muscle is involved in many movements, e.g., rising from a chair and walking. In quadriceps paralysis, a patient can stand erect, because the body weight tends to hyperextend the knee. Walking, however, is then performed in short steps that avoid extending the hip and flexing the knee, and such a patient may press the knee posteriorward with the hand.

15-6 Where is the reflex center for the knee jerk?

15-6 The center for the knee jerk is chiefly in the L3-4 segment of the spinal cord. The quadriceps is innervated by L2 to 4 (see table 15-4).

15-7 How far distally does the cutaneous territory of the saphenous nerve extend?

15-7 The saphenous nerve, which may be regarded as the termination of the femoral nerve (L2 to 4), generally supplies skin as far as the medial side of the foot. 15-8 The deep femoral artery is the most important branch of the femoral artery. Sudden occlusion of the femoral artery above the origin of the deep femoral almost always causes gangrene; blockage below the deep femoral origin seldom does so.

15-8 Which is the most important branch of the femoral artery?

15-8 The deep femoral artery is the most important branch of the femoral artery. Sudden occlusion of the femoral artery above the origin of the deep femoral almost always causes gangrene; blockage below the deep femoral origin seldom does so.

15-9 What is the guide to the location of the common fibular nerve and what is the chief effect of injury to the nerve?

15-9 The tendon of the biceps is the guide to the common peroneal nerve. Injury to the nerve, e.g., from a fracture or from a tight plaster cast, results characteristically in footdrop (loss of both dorsiflexion and eversion of the foot). In walking, the foot tends to slap the ground ("steppage" gait). The superficial peroneal nerve supplies skin on the lateral side of the leg and a variable amount of the dorsum of the foot. The deep peroneal nerve supplies the skin between the first and second toes dorsally.

15-10 On what does the stability of the hip joint depend?

15-10 The stability of the hip joint depends on the shape of the articular surfaces, the capsule, ligaments, and muscles. In dislocation of the hip, the head of the femur is usually displaced posteriorly. Congenital dislocation of the hip is an important but obscure condition.

15-11 What is the innervation of the hip and knee joints?

15-11 Both hip and knee joints are supplied ultimately by branches of the femoral, sciatic, and obturator nerves. Hip disease is an important cause of pain referred to the knee.

15-12 Compare the knee with the elbow joint.

15-12 In the knee joint (as compared with the elbow), the fibula is excluded (cf. the ulna), the soft tissues (rather than the bony structure) limit extension, and rotation occurs.

15-13 On what basis is the knee joint condylar and not a true hinge?

15-13 The knee joint is condylar rather than a hinge because the axis of flexion and extension shifts anteriorward during extension, and extension is associated with medial rotation of the femur.

15-14 When is the knee joint "locked?"

15-14 In full extension of the knee, the articular surfaces are in maximal contact, the ligaments are taut, and the joint is "locked" or "screwed home.

15-15 Which bursae communicate with the cavity of the knee joint?

15-15 Usually the suprapatellar pouch and bursae related to the popliteus, gastrocnemius, and semimembranosus communicate with the cavity of the knee joint.

Figure legends

Figure 15-1 Surface landmarks of the lower limb. (From Royce, J., Surface Anatomy, Davis, Philadelphia, 1965.)

Figure 15-2 Horizontal section through the middle of the thigh. In A, the nerves and vessels are identified. B shows the quadriceps (supplied by the femoral nerve) anteriorly, the adductors (supplied mostly by the obturator nerve) medially, and the hamstrings (supplied mostly by the sciatic nerve) posteriorly. The adductor longus is shown immediately anterior to the adductor magnus. The sartorius (5) has descended in a spiral from the anterior group and hence is supplied by the femoral nerve. The femoral vessels are situated subsartorially in the adductor canal. Although not shown here, the adductor magnus, in addition to its adductor part (supplied by the obturator nerve), has an extensor component supplied by the sciatic nerve. Ad.M., adductor magnus; B.F., biceps femoris; Gr., gracilis; R.F., rectus femoris; S., sartorius; S-m., semimebranosus; S-t., semitendinosus; V.I., vastus intermedius; V.L., vastus lateral is; V.M., vastus medialis.

Figure 15-3 Schematic representation of the anterior abdominal wall, inguinal ligament, and saphenous opening in a sagittal plane. The saphenous opening is in the fascia lata, and it transmits the great saphenous vein. It is covered by the cribriform fascia (interrupted line).

Figure 15-4 The structures that descend posterior to the inguinal ligament.

Figure 15-5 The femoral triangle: sartorius, adductor longus, and inguinal ligament.

Figure 15-6 The floor of the femoral triangle. The adductor longus, which also forms a part of the floor, is not shown.

Figure 15-7 Diagram of the muscular (and some cutaneous) branches of the femoral, obturator, and peroneal (from the sciatic) nerves.

Figure 15-8 Diagram of the muscular branches of the gluteal and sciatic nerves. The branches of the common fibular nerve are shown in the previous figure.

Figure 15-9 The right popliteal fossa.

Figure 15-10 Structures in the right popliteal fossa (popliteal veins omitted). Note the relationship of the tibial nerve first to the popliteal and then to the posterior tibial artery. Note also that the anterior tibial artery passes laterally, not anteriorly, through an arch in the interosseous membrane.

Figure 15-11 A, The basic arrangement of the segmental innervation (dermatomes) of the skin of the lower limb, which is supplied successively down the pre-axial border and then up the postaxial border. Note that the first toe is supplied by the fifth nerve and that the fifth toe is supplied by the first nerve. 8, An embryo of 7 weeks (measuring 17 mm between the small arrows) showing the longitudinal axes (A) of the upper and lower limbs. The parts of the limbs rostral to the axes are termed postaxial. The sequence of dermatomes from pre-axial to postaxial is shown on each limb. Cf. fig. 8-10.

Figure 15-12 The acetabulum and capsule of the hip joint after removal of the femur. Note how the capsule varies in thickness. The line indicates the plane and position of the section in the figure 15-13.

Figure 15-13 A coronal section of the hip joint in the plane indicated in the previous figure.

Figure 15-14 The capsule of the hip joint. Note that circular fibers form the zona orbicularis and that the neck of the femur is not completely covered on the posterior side.

Figure 15-15 The blood supply to the head and neck of the femur. Apart from a small branch of the obturator artery that enters through the ligament of the head, most of the epiphysis of the head is supplied by diaphysial branches from the lateral and medial circumflex arteries of the femoral artery. These branches travel in retinacula, i.e., reflections of the capsule along the neck toward the head. The vessels may be damaged in fractures of the neck of the femur, which may result in avascular necrosis of the head of the bone. (Based on von Lanz and Wachsmuth.)

Figure 15-16 Anterior view of a flexed right knee joint in which the transverse ligament is absent. In the posterior view of the right knee joint, note that the popliteus arises in part from the lateral meniscus. The attachments of the collateral ligaments to the menisci are omitted.

Figure 15-17 A, The cruciate ligaments and the menisci from above. Note the differences in the size and shape of the menisci. B, The right tibia from above, showing the attachments of the menisci and cruciate ligaments.

Figure 15-18 A coronal section of the knee joint.

Figure 15-19 A sagittal section of the knee joint. The width of the articular and bursal cavities is exaggerated.

* Based on his extensive experience in hernial surgery, W. J. Lytle disagrees with the traditional account and maintains that a femoral hernia must pass through two openings, namely the femoral ring and the lower end of the femoral canal (the "femoral hernial orifice") bounded medially by the curved edge of the lacunar ligament (Ann. R. Coll. Surg. Engl., 21:244-262, 1957).

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