The tibial nerve is one of the two main divisions of the sciatic nerve, the largest nerve in the human body. Originating in the lower spine, it extends downward to control movement and sensation in the lower leg and foot. The nerve controls most of the muscles in the back of the leg and the sole of the foot. Its function is important for walking, balance, and the ability to feel sensations on the bottom of the foot. Damage or compression along its path can lead to changes in mobility and sensation.
Anatomy: Tracing the Tibial Nerve’s Course
The tibial nerve begins in the thigh, separating from the common fibular nerve as one of the two terminal branches of the sciatic nerve. It descends through the popliteal fossa, the space located behind the knee joint. In this region, the nerve lies posterior to the popliteal artery and vein.
From the popliteal fossa, the nerve moves downward into the posterior compartment of the leg, passing deep to the arch of the soleus muscle. It continues along the midline of the calf, positioned between the superficial and deep muscle layers of the posterior compartment. The nerve runs alongside the posterior tibial artery and vein.
The nerve then travels toward the ankle, passing posterior to the medial malleolus, the bony prominence on the inner side of the ankle. Here, it enters the tarsal tunnel, a narrow passageway formed by bone and the flexor retinaculum. This confined location makes the nerve susceptible to compression before it divides into its final branches.
Motor and Sensory Functions
The tibial nerve is responsible for innervating the muscles that facilitate plantarflexion, the movement that points the foot downward. It supplies all the muscles in the posterior compartment of the leg, including the gastrocnemius, soleus, and plantaris muscles. These muscles are responsible for the pushing motion needed for propulsion during walking and running.
The nerve also controls the tibialis posterior muscle, which is involved in foot inversion (turning the sole inward). Furthermore, it innervates the long flexors, such as the flexor digitorum longus and flexor hallucis longus, which allow for the curling and bending of the toes. Loss of function above the ankle can limit the ability to push off the ground and maintain balance.
The sensory component provides feeling to a portion of the posterior leg and foot through its branches. The nerve contributes fibers to the sural nerve, which transmits sensation from the posterolateral skin of the lower leg. It also gives off the medial calcaneal branches, which provide sensation to the skin over the heel area.
The Terminal Branches in the Foot
As the tibial nerve passes through the tarsal tunnel, it divides into its two terminal branches: the medial plantar nerve and the lateral plantar nerve. This division occurs just distal to the medial malleolus, where the nerve enters the sole of the foot. These two branches control movement and sensation within the foot.
The medial plantar nerve is the larger branch, comparable in distribution to the median nerve in the hand. It supplies motor function to four intrinsic foot muscles, including the abductor hallucis and the flexor digitorum brevis. This nerve provides sensation to the medial sole of the foot and the plantar surface of the inner three-and-a-half toes.
The lateral plantar nerve is the smaller branch and travels obliquely across the sole, deep to the foot muscles. It innervates most of the remaining intrinsic muscles, such as the quadratus plantae, the interossei, and the muscles that move the fifth toe. Its sensory domain covers the skin of the lateral sole and the plantar surface of the outer one-and-a-half toes.
Common Disorders Affecting the Tibial Nerve
Tarsal Tunnel Syndrome (TTS) occurs when the nerve or its branches are compressed within the narrow tarsal tunnel near the ankle. This compression often results in a pattern of symptoms in the foot and ankle. Causes of compression can include swelling from an injury like a sprain or fracture, bone spurs, ganglion cysts, or biomechanical issues like flat feet or a high arch.
Symptoms of TTS typically involve neuropathic pain, described as a burning sensation, tingling, or numbness, particularly on the bottom of the foot and toes. If the compression is severe or long-standing, it can lead to weakness and muscle wasting in the small, intrinsic muscles of the foot. In severe cases, the inability to move the toes correctly can lead to foot deformities.
The tibial nerve can also be affected by generalized conditions like diabetic neuropathy, where long-term high blood sugar levels cause widespread nerve damage. Direct trauma, such as deep lacerations or fractures to the leg, can also cause acute injury to the nerve. Furthermore, compartment syndrome, where excessive pressure builds up in the posterior compartment of the leg, can compromise the nerve’s blood supply and function.