Tibial Nerve

TIBIAL NERVE

This is the larger and medial terminal branch of the sciatic nerve. Its fibers are derived from the anterior divisions of the anterior rami of the fourth and fifth lumbar and the first, second and third sacral nerves. In the distal thigh, after its origin from the sciatic bifurcation, the tibial nerve is overlapped by the semimembranosus and biceps femoris muscles, becoming more superficial in the popliteal fossa; proceeding into the leg beneath the heads of the gastrocnemius lateral (L5, S1) and medial (S1, 2) and plantaris muscles; and descending to be above the popliteus muscle and under the soleus (S1, 2), to travel between the gastrocnemius medial and lateral heads of the tibialis posterior and, subsequently, between the flexor digitorum longus (L5, S1) and flexor hallucis longus muscles, innervating each of these muscles as well as plantaris and popliteus muscles. Distally, the nerve lies superficially, descending to the ankle, medial to the Achilles tendon; curving anteroinferiorly and posteriorly to the medial malleolus. Here it enters the tarsal tunnel, proceeding into the foot deep to the flexor retinaculum between the flexor hallucis longus and flexor digitorum longus tendons. Here it terminates, dividing into the medial and lateral plantar nerves that innervate all intrinsic foot muscles (S1, 2) and provide the sensation for the plantar surface of the foot.

The sural nerve, a cutaneous branch, arises from the tibial nerve at the popliteal fossa, descends between the gastrocnemius heads, pierces the deep fascia, gives off a small medial sural cutaneous nerve (it may be larger and arise directly from the tibial nerve), and is joined by the fibular communicating branch of the lateral sural cutaneous nerve, next passing over and lateral to the Achilles tendon. It provides cutaneous innervation to the posterior lateral lower leg, the lateral ankle, and heel. The terminal portion courses forward as the lateral dorsal cutaneous nerve of the foot.

The medial plantar nerve can be compared with the median nerve in the hand. It originates under the flexor retinaculum, traveling deep to the abductor hallucis, innervating it and subsequently the flexor digitorum brevis and flexor hallucis brevis muscles all (S1, 2). At the tarsometatarsal joints, this nerve ends by dividing into a proper plantar digital nerve that supplies the medial great toe and three common plantar digital nerves in a fashion similar to the median nerve of the hand.

The lateral plantar nerve is homologous with the ulnar nerve in the hand, arising deep to the flexor retinaculum; passing outward to innervate the lateral sole, the flexor digitorum brevis, the quadratus plantae, and the abductor digiti minimi all (S1, 2); and ending near the fifth metatarsal bone. Lastly, it divides into two branches: the superficial branch that splits into proper and common plantar digital nerves that innervate the plantar lateral small toe and the flexor digiti minimi and interossei muscles (S1, 2) of the fourth intermetatarsal space. The common plantar digital nerve divides into two proper plantar digital nerves supplying the fourth and fifth toes. A deep branch supplies the adductor hallucis, the second to fourth lumbricals, and the medial three interossei muscles (S1, 2).

Clinical. Isolated tibial neuropathies are very uncommon. This nerve is very well protected within the entirety of its course from the sciatic notch, through the thigh, within the popliteal fossa, and deep within the calf. It is not at risk for compression or entrapment. However, various traumas, such as localized lacerations, fractures, and hematomas, may involve the tibial nerve. A Baker cyst within the knee joint or a ganglion within the tibiofibular joint occasionally compromises this nerve. Intrinsic nerve tumors may affect the tibial nerve anywhere along its course. Depending on the site of involvement, there can be calf and/or foot muscle weakness and atrophy, as well as sensory loss appropriate to the lesion site. Other sites of involvement can lead to a painful or numb foot, as seen in the very uncommon tarsal tunnel syndrome or distal Morton neuroma.

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