which supplies skin and fascia lata over the front of the thigh down to the knee. The medial femoral cutaneous nerve supplies the medial side of the thigh, and an anterior branch reaches the front of the knee.
The nerve to rectus femoris is usually double, and the upper branch also supplies the hip joint. The nerve to vastus lateralis runs down with the descending branch of the lateral femoral circumflex artery between rectus femoris and vastus intermedius. The nerve to vastus intermedius sinks into the anterior surface of that muscle. The nerve to vastus medialis enters the upper part of the subsartorial canal and sinks into the muscle. The nerves to all three vasti also supply the knee joint.
The saphenous nerve crosses in front of the femoral artery in the subsartorial canal, and emerges from behind the posterior border of sartorius. Its infrapatellar branch pierces sartorius to run into the patellar plexus. The saphenous nerve pierces the fascia lata between the tendons of sartorius and gracilis and descends to supply skin and periosteum over the subcutaneous surface of the tibia. It runs with the great saphenous vein in front of the medial malleolus and ends on the medial side of the foot just short of the big toe.
Obturator nerve (L2, 3, 4—anterior divisions)
Emerging from the medial side of psoas the nerve lies on the ala of the sacrum lateral to the lumbosacral trunk. It slants down to the side wall of the pelvis between the origin of the internal iliac artery and the ilium. From the angle between external and internal iliac vessels it runs straight to the obturator foramen, supplying the parietal peritoneum of the side wall of the pelvis (in the female the ovary lies here). As it emerges from the obturator foramen it splits into anterior and posterior divisions.
The posterior division supplies obturator externus, then pierces the upper part of that muscle and runs into the thigh deep to adductor brevis. It runs down on adductor magnus, whose pubic part it supplies.
A slender branch accompanies the femoral artery into the popliteal fossa to supply the knee joint.
The anterior division passes over obturator externus and, emerging into the thigh, it supplies the hip joint. It runs down over adductor brevis, deep to pectineus and adductor longus. It supplies these two adductors and may supply pectineus. It also supplies gracilis. It supplies the medial side of the thigh by a cutaneous branch which runs through the subsartorial plexus.
The accessory obturator nerve, when occasionally present, passes over the superior pubic ramus to supply pectineus.
Sacral plexus
This is a flat, triangular formation on the front of piriformis muscle. It is formed out of the lumbosacral trunk (L4, 5) and the upper four anterior sacral rami (Fig. 5.76). These rami divide and unite as they converge to the greater sciatic foramen, forming the branches of the sacral plexus.
Figure 5.76 Left sacral plexus. The branches from its anterior surface (three Ps) are shown.
The nerves to piriformis (S1, 2) are twigs that pass back from the upper sacral nerves into the muscle.
The perforating cutaneous nerve (S2, 3) pierces the sacrotuberous ligament and the fibres of gluteus maximus that arise there, and supplies a small area of skin on the lower medial side of the buttock.
The posterior femoral cutaneous nerve (S1, 2, 3) has a wide distribution. It runs down below piriformis on the sciatic nerve. From the lower border of gluteus maximus it runs down the posterior midline beneath the fascia as far as the lower ends of the gastrocnemius bellies. It supplies a strip of deep fascia and skin, between anterior and posterior axial lines, from the buttock to the midcalf by a series of branches which pierce the deep fascia.
Gluteal branches wind around gluteus maximus to supply skin over the convexity of the buttock. The long perineal branch winds around the hamstrings and gracilis origins and pierces the fascia lata at the medial convexity of the upper thigh. It supplies the lateral part of the posterior two-thirds of the scrotum (labium majus).
The pelvic splanchnic nerves (S2, 3, 4) constitute the sacral parasympathetic outflow and the fibres join the inferior hypogastric plexus. They are motor to the bladder and to the large intestine from the splenic flexure downwards, and cause penile (clitoral) erection. Their afferent fibres include those for distension and pain from the bladder, lower cervix, lower colon and rectum. Referred pain may be felt in the distribution of the posterior femoral cutaneous nerve.
The pudendal nerve (S2, 3, 4) runs down and curls around the gluteal surface of the sacrospinous ligament to enter the pudendal canal. It is the nerve of the perineum.
At the posterior end of the canal it gives the inferior rectal nerve which arches through the fat of the ischioanal fossa; its branches supply the external anal sphincter, anal canal and perianal skin.
The perineal nerve emerges from the anterior end of the canal as a terminal branch of the pudendal. It runs forward and breaks up to supply skin of the posterior two-thirds of the scrotum and vulva, and the mucous membrane of the urethra and vagina. It is motor to the perineal muscles, namely, ischiocavernosus, bulbospongiosus, superficial and deep transversus perinei and the sphincter urethrae.
The dorsal nerve of the penis (clitoris) is the other terminal branch of the pudendal. It runs forward deep to the perineal membrane, which it pierces just below the symphysis pubis to supply the skin of the penis (clitoris).
Muscular branches of S3 and S4 supply levator ani and coccygeus on their upper (pelvic) surfaces.
The perineal branch of S4 passes between levator ani and coccygeus to supply the puborectalis, pubourethralis and pubovaginalis parts of levator ani from below, and the skin over the ischioanal fossa.
The nerve to quadratus femoris (L4, 5, S1) lies on the ischium deep to the sciatic nerve and runs down deep to obturator internus to sink into the deep surface of quadratus femoris. It also supplies the inferior gemellus and gives a branch to the hip joint.
The nerve to obturator internus (L5, S1, 2) passes below piriformis, curls around the base of the ischial spine and sinks into obturator internus. It also supplies the superior gemellus.
T h e superior gluteal nerve (L4, 5, S1) passes back through the greater sciatic notch above piriformis, runs in the plane between glutei medius and minimus, supplies both, and ends in the tensor fasciae latae.
The inferior gluteal nerve (L5, S1, 2) passes back below piriformis and sinks into the deep surface of gluteus maximus.
Sciatic nerve
The sciatic nerve is the largest branch of the sacral plexus from which it is formed at the lower margin of piriformis by union of its tibial and common peroneal parts. It passes into the buttock lying on the posterior surface of the ischium. Here the nerve to quadratus femoris is deep to it and the posterior femoral cutaneous nerve lies superficial. From midway between the greater trochanter and the ischial tuberosity, the sciatic nerve passes vertically downwards into the hamstring compartment.
It lies on obturator internus and gemelli, quadratus femoris and then on adductor magnus. It is overlaid by the long head of biceps. The main trunk of the sciatic nerve supplies all the hamstrings and the ischial fibres of adductor magnus and it then divides, usually at the upper angle of the popliteal fossa, into the tibial and common peroneal nerves. The branches for the long head of biceps, the two ‘semi-’
muscles and adductor magnus are from the tibial part, but the branch to the short head of biceps comes from the common peroneal part.
Common peroneal (fibular) nerve (L4, 5, S1, 2)
The common peroneal nerve supplies the extensor and peroneal compartments of the leg and the dorsum of the foot. It enters the apex of the popliteal fossa and runs medial to the biceps tendon just beneath the deep fascia. It crosses plantaris, lateral head of gastrocnemius and curves around the neck of the fibula, through peroneus longus, where it divides into two terminal branches, the deep and superficial peroneal (fibular) nerves. It can be palpated on the neck of the fibula, where it can be rolled on the bone. It is the nerve most commonly injured in the lower limb.
The common peroneal nerve itself supplies no muscles. Three articular branches, the upper and lower lateral and recurrent genicular nerves, supply the knee joint; the lateral genicular nerves accompany
the arteries, the recurrent supplies the superior tibiofibular joint as well.
There are two cutaneous branches. The sural communicating nerve joins the sural nerve below the gastrocnemius heads. The lateral cutaneous nerve of the calf supplies skin and deep fascia over the upper half of the peroneal compartment.
The deep peroneal nerve is formed in the substance of peroneus longus, spirals down over the fibula deep to extensor digitorum longus and reaches the interosseous membrane. It runs down lateral to the vessels, crosses the lower end of the tibia and the dorsum of the foot, and ends by supplying the skin of the first interdigital cleft.
It supplies the muscles of the extensor compartment of the leg: extensor digitorum longus, tibialis anterior, extensor hallucis longus and peroneus tertius. On the dorsum of the foot it gives a lateral branch which supplies extensor digitorum brevis.
The superficial peroneal nerve is formed in the substance of peroneus longus and runs down in the muscle, emerging from its anterior border about a third of the way down the leg. It supplies peroneus longus and brevis, then perforates the fascia to supply the skin over the peronei and extensor muscles in the lower third of the leg. Above the ankle it divides into a medial and a lateral branch which supply skin and deep fascia on the dorsum of the foot. The medial branch breaks up to supply the medial side of the big toe and the second interdigital cleft, while the lateral branch breaks up to supply the third and fourth clefts.
Tibial nerve (L4, 5, S1, 2, 3)
The tibial nerve supplies the calf and the sole of the foot around to the toenails. The nerve enters the apex of the popliteal fossa and, in the midline of the limb, passes vertically down deep to the heads of gastrocnemius behind the knee joint and across the popliteus muscle, to run beneath the fibrous arch in soleus.
Branches in the popliteal fossa. Three genicular nerves, upper and lower medial and a middle, accompany the arteries and supply the knee joint. Five muscular branches supply the muscles of the fossa: plantaris, both heads of gastrocnemius, soleus and popliteus. The last-named branch recurves around the lower border of the muscle to enter its deep (anterior) surface. A single cutaneous branch, the sural nerve, lies in the groove between the two heads of gastrocnemius and pierces the deep fascia halfway down the leg. Here it is joined by the sural communicating nerve. The sural nerve runs down alongside the small saphenous vein behind the lateral malleolus and ends on the lateral side of the little toe.
From the fibrous arch the nerve runs down with the posterior tibial vessels deep to the soleus muscle.
The neurovascular bundle lies in the groove between the bellies of flexor hallucis longus and flexor digitorum longus. Behind the medial malleolus, beneath the flexor retinaculum, the nerve divides into its terminal medial and lateral plantar branches.
Branches in the calf. Four muscular branches supply soleus, tibialis posterior and the flexors hallucis and digitorum longus. Medial calcanean branches pierce the flexor retinaculum and supply the weight-bearing skin of the heel.
The medial and lateral plantar nerves correspond approximately to the median and ulnar nerves in the hand as far as skin and muscle supplies are concerned. The medial plantar supplies the medial part of the sole and plantar surface of the medial three and a half digits, and innervates flexor digitorum brevis, abductor hallucis, flexor hallucis brevis and the first lumbrical, with the lateral plantar supplying the rest of the sole and the other small muscles of the foot.