Nerves



Nerves


Molly E. Mounsey

Khushdeep S. Vig



NERVES

The innervation of the foot and ankle is complex, with lumbar and sacral nerve roots contributing to a multitude of nerves within the area. The foot and ankle broadly are supplied by the fourth and fifth lumbar and first, second, and third sacral nerve roots.


LUMBAR PLEXUS

The lumbar plexus is composed of the first through fourth lumbar ventral rami. The anterior division of the lumbar plexus does not provide any innervation to the foot and ankle. The posterior division of the lumbar plexus, however, provides innervation to components of the foot and ankle via the saphenous nerve, a branch of the femoral nerve.


FEMORAL NERVE

The femoral nerve is formed by the ventral rami of the second through fourth lumbar nerve roots. The femoral nerve runs laterally to the psoas major in the pelvis before traveling in between the psoas and iliacus muscles. It then enters the thigh in the femoral canal, underneath the inguinal ligament. The femoral nerve bifurcates into anterior and posterior divisions which are separated by the lateral femoral circumflex artery.


SAPHENOUS NERVE

The posterior division of the femoral nerve gives rise to the saphenous nerve, its largest branch, and the longest nerve within the body. The saphenous nerve is purely a sensory nerve. The saphenous nerve arises within the femoral canal and travels through the adductor canal where it divides. An infrapatellar branch is given off which contributes to the patellar plexus lying anterior to the patella. This branch supplies the skin overlying the patella and medial knee and continues into the leg running medially to the tibia. As the saphenous nerve travels along the medial leg, it provides sensation to the skin of the medial leg and foot. Distally, the saphenous nerve divides into a branch lying anterior to the ankle which provides sensation to the medial foot and a branch running to the ankle. Within the foot, the saphenous nerve connects with the superficial peroneal nerve.


SACRAL PLEXUS

The sacral plexus is composed of the lumbosacral trunk (ventral rami L4-5) and the first through fourth sacral ventral rami. The dorsal fibers contribute to the posterior division of the sacral plexus while the ventral fibers contribute to the anterior division.

The nerves of the sacral plexus initially converge into a band that becomes the sciatic nerve. The sciatic nerve is composed of nerve fibers from the fourth and fifth lumbar spinal nerves and the first through third sacral spinal nerves.
The nerve itself is composed of both an anterior and posterior division. The sciatic nerve divides at the popliteal fossa with the posterior division forming the common peroneal nerve and the anterior forming the tibial nerve.


ANTERIOR DIVISION


Tibial Nerve

The tibial nerve is responsible for innervating the posterior compartment of the leg. The tibial nerve is formed by divisions of the fourth and fifth lumbar and first through third sacral ventral rami. In the proximal leg, the tibial nerve runs through the popliteal fossa, covered by the junction of the heads of the gastrocnemius. The tibial nerve then descends into the posterior compartment of the leg with the posterior tibial vessels. The tibial nerve runs deep to the gastrocnemius and soleus, lying on the tibialis posterior and later tibia. In the leg, the tibial nerve supplies the gastrocnemius, soleus, posterior tibialis, and plantaris muscles. Muscular branches also supply the flexor digitorum longus and flexor hallucis longus muscles. The tibial nerve continues on as the posterior tibial nerve at the fibrous arch of the soleus, entering the foot between the heel and medial malleolus. As the tibial nerve enters the foot, it runs superficially, covered by skin and fascia. It then crosses laterally over the posterior tibial vessels and bifurcates into medial and lateral plantar nerves under the flexor retinaculum (lacinate ligament) in the tarsal tunnel on the medial aspect of the foot.

The tibial nerve also produces additional articular branches that innervate the knee and ankle joints. The knee joint is supplied via a plexus with the obturator nerve. These branches innervate the oblique popliteal ligament, medial capsule, posterior aspect of the superior tibiofibular joint. Additionally, an articular branch to the ankle is given off just before the bifurcation of the nerve.

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Sep 8, 2022 | Posted by in ORTHOPEDIC | Comments Off on Nerves
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