Tibial nerve

The tibial nerve is a major branch of the sciatic nerve and is located in the lower limb. It arises in the popliteal fossa at the back of the knee, after the sciatic nerve bifurcates into the tibial and common peroneal nerves. The tibial nerve travels down the posterior compartment of the leg, passing deep to the gastrocnemius and soleus muscles. It runs alongside the posterior tibial artery and continues behind the medial malleolus (inside ankle bone) through the tarsal tunnel. In the foot, it divides into the medial and lateral plantar nerves, providing both motor and sensory innervation to the leg and foot.

Structure and Anatomy

The tibial nerve is one of the two terminal branches of the sciatic nerve and is a major nerve of the lower limb, supplying both motor and sensory functions to the posterior leg and foot. Below is a detailed description of its anatomy, including its origin, course, branches, and relationship with surrounding structures.

Origin

The tibial nerve originates from the sciatic nerve, which arises from the lumbosacral plexus (nerve roots L4–S3). The sciatic nerve descends through the posterior thigh, where it bifurcates into the tibial nerve and the common peroneal nerve in the popliteal fossa. This bifurcation typically occurs near the superior angle of the popliteal fossa, located at the back of the knee.

Course and Pathway

• Popliteal Fossa: After its origin from the sciatic nerve, the tibial nerve descends through the popliteal fossa, a diamond-shaped depression located behind the knee. In this region, the nerve is positioned between the semimembranosus and biceps femoris muscles superiorly and the gastrocnemius muscle heads inferiorly. It runs close to the popliteal artery and popliteal vein, lying slightly medial and superficial to these vessels.
• Posterior Compartment of the Leg: The tibial nerve enters the posterior compartment of the leg, passing deep to the gastrocnemius muscle and the soleus muscle. It continues its descent along the posterior aspect of the leg, running between the deep and superficial muscles of the posterior compartment. The nerve lies on the posterior surface of the tibialis posterior muscle and is accompanied by the posterior tibial artery and veins.
• Ankle (Tarsal Tunnel): As it approaches the ankle, the tibial nerve passes posterior to the medial malleolus (the bony prominence on the inner side of the ankle) through a fibrous passage called the tarsal tunnel, formed by the flexor retinaculum. The tarsal tunnel is an important anatomical landmark, as the nerve is relatively superficial here and vulnerable to compression or injury.
• Foot: After passing through the tarsal tunnel, the tibial nerve divides into its terminal branches: the medial plantar nerve and the lateral plantar nerve. These branches provide motor and sensory innervation to various structures in the sole of the foot.

Branches

The tibial nerve gives off several important branches along its course, which serve both motor and sensory functions.

• Muscular Branches in the Popliteal Fossa: These branches supply the gastrocnemius, plantaris, soleus, and popliteus muscles in the posterior compartment of the leg.
• Medial Sural Cutaneous Nerve: The medial sural cutaneous nerve arises from the tibial nerve in the popliteal fossa and provides sensory innervation to the posterior aspect of the lower leg. It typically joins with the peroneal communicating branch from the common peroneal nerve to form the sural nerve, which continues to supply sensation to the lateral foot and ankle.
• Motor Branches to Deep Posterior Compartment Muscles: In the leg, the tibial nerve supplies motor innervation to the deep muscles of the posterior compartment, including the tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles. These muscles play key roles in plantar flexion of the foot and toe movements.
• Medial and Lateral Plantar Nerves: After passing through the tarsal tunnel, the tibial nerve bifurcates into the medial plantar nerve and the lateral plantar nerve. These branches provide sensory and motor innervation to the sole of the foot, including the intrinsic muscles that control toe movements and the skin of the sole.

Relationship to Neighboring Structures

• Popliteal Artery and Vein: In the popliteal fossa, the tibial nerve is closely associated with the popliteal artery and vein, lying superficial and medial to these vessels. The close proximity of the nerve and the popliteal artery is important in surgical interventions around the knee, as injury to either structure can lead to significant complications.
• Gastrocnemius and Soleus Muscles: As the tibial nerve descends through the posterior compartment of the leg, it travels deep to the gastrocnemius and soleus muscles, both of which receive motor branches from the nerve. The nerve runs between the superficial and deep muscles of the posterior leg, providing innervation to the deeper muscles like the tibialis posterior.
• Posterior Tibial Artery: The tibial nerve runs alongside the posterior tibial artery in the posterior compartment of the leg. This artery provides blood supply to the muscles and tissues of the posterior leg and foot, and both the nerve and artery pass through the tarsal tunnel together.
• Tarsal Tunnel: The tibial nerve passes through the tarsal tunnel, a fibro-osseous passage located posterior to the medial malleolus. The tarsal tunnel contains the tibial nerve, the posterior tibial artery, and the tendons of several muscles, including the flexor hallucis longus, flexor digitorum longus, and tibialis posterior. Compression of the tibial nerve in this region can lead to tarsal tunnel syndrome, a condition characterized by pain and sensory disturbances in the foot.

Terminal Branches

• Medial Plantar Nerve: This nerve is the larger of the two terminal branches of the tibial nerve. It travels along the medial aspect of the sole and supplies motor innervation to muscles like the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and the first lumbrical. It also provides sensory innervation to the medial three and a half toes and the adjacent part of the sole.
• Lateral Plantar Nerve: The lateral plantar nerve is the smaller terminal branch of the tibial nerve and courses along the lateral side of the sole. It innervates muscles such as the abductor digiti minimi, flexor digiti minimi brevis, and adductor hallucis, among others. It also supplies sensory innervation to the lateral one and a half toes and the adjacent part of the sole.

Anatomical Variations

• Bifurcation Level: The point at which the tibial nerve bifurcates into the medial and lateral plantar nerves can vary slightly among individuals. In some cases, the bifurcation may occur higher or lower within the tarsal tunnel.
• Additional Branches: In some individuals, additional small branches may arise from the tibial nerve along its course in the leg or foot. These variations can influence the distribution of sensory and motor innervation in the foot.

Blood Supply

The blood supply to the tibial nerve comes from branches of the posterior tibial artery, which runs alongside the nerve in the posterior compartment of the leg. Small arterial branches provide blood flow to the nerve, ensuring its function and health.

Function

The tibial nerve plays a crucial role in providing both motor and sensory innervation to the posterior compartment of the leg, the plantar surface of the foot, and various muscles and skin in these areas. Its functions can be categorized into motor and sensory roles, both of which are essential for movements like walking, running, and balance, as well as for sensory feedback from the foot and leg. Below is a detailed explanation of the tibial nerve’s functions.

Motor Function

The tibial nerve supplies motor innervation to a wide array of muscles in the posterior leg and foot, contributing to movements such as plantarflexion, toe flexion, and stabilization of the foot and ankle. These motor functions are essential for walking, running, jumping, and maintaining balance.

• Gastrocnemius Muscle: The tibial nerve innervates the gastrocnemius, the large superficial muscle of the calf. This muscle is responsible for plantarflexion of the foot (pointing the toes downward) and assists in knee flexion. Gastrocnemius activation is crucial during walking, running, and jumping, especially during the push-off phase when the heel lifts off the ground.
• Soleus Muscle: The tibial nerve innervates the soleus, a deeper muscle beneath the gastrocnemius. The soleus also contributes to plantarflexion of the foot and plays an important role in maintaining postural stability during standing, as it helps to counterbalance the forward sway of the body.
• Plantaris Muscle: The tibial nerve innervates the plantaris, a small muscle located between the gastrocnemius and soleus. The plantaris assists in plantarflexion and knee flexion, although its contribution is minor compared to the gastrocnemius and soleus.
• Popliteus Muscle: The tibial nerve supplies the popliteus, a muscle located at the back of the knee. The popliteus is responsible for unlocking the knee joint by laterally rotating the femur on the tibia during the initial phase of knee flexion. It also stabilizes the knee, particularly when the leg is fully extended.
• Tibialis Posterior Muscle: The tibialis posterior, innervated by the tibial nerve, is the primary muscle responsible for inversion (turning the sole inward) and plantarflexion of the foot. This muscle also plays a key role in maintaining the medial longitudinal arch of the foot, which is important for walking and running.
• Flexor Digitorum Longus Muscle: The tibial nerve innervates the flexor digitorum longus, which is responsible for flexing the lateral four toes (second to fifth toes). Flexion of the toes is critical for gripping the ground during the stance phase of walking and for maintaining balance.
• Flexor Hallucis Longus Muscle: The flexor hallucis longus, also innervated by the tibial nerve, is responsible for flexing the big toe (hallux). This muscle plays a key role in the push-off phase of walking and running, as the big toe provides the final point of contact with the ground before the foot lifts off.
• Intrinsic Foot Muscles (via Medial and Lateral Plantar Nerves): After the tibial nerve divides into the medial and lateral plantar nerves in the foot, it supplies the intrinsic muscles of the sole of the foot. These muscles include the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, lumbricals, and interossei, which are involved in toe flexion, abduction, and adduction. These movements help with fine motor control of the toes, balance, and foot stabilization.

Sensory Function

The tibial nerve provides sensory innervation to the skin of the posterior leg, plantar surface of the foot, and lateral aspect of the ankle and foot. Sensory feedback from these areas is essential for detecting touch, pressure, pain, and temperature, which help regulate posture, balance, and protective reflexes.

• Posterior Leg Sensation: The tibial nerve, through its branches such as the medial sural cutaneous nerve, provides sensory innervation to the posterior aspect of the leg. Sensory information from this area helps the body detect pressure and pain, particularly when standing or engaging in physical activities. This feedback is essential for adjusting posture and preventing injuries to the lower leg.
• Plantar Surface of the Foot (Sole): The tibial nerve’s medial plantar and lateral plantar branches provide sensory innervation to the plantar surface of the foot. The medial plantar nerve supplies sensation to the medial three and a half toes and the adjacent portion of the sole, while the lateral plantar nerve supplies the lateral one and a half toes and the lateral sole. Sensory feedback from the sole of the foot is critical for balance, proprioception, and protection from potentially harmful stimuli (e.g., sharp objects or hot surfaces).
• Lateral Ankle and Foot Sensation: The sural nerve, formed partly by the tibial nerve’s medial sural cutaneous branch, provides sensory innervation to the lateral side of the foot, the lateral ankle, and the fifth toe. Sensory information from this area is important for adjusting foot posture and pressure distribution, especially during lateral movements or when walking on uneven surfaces.
• Tarsal Tunnel Sensation: As the tibial nerve passes through the tarsal tunnel, it supplies the medial side of the ankle and heel. Compression of the tibial nerve in this area can lead to tarsal tunnel syndrome, causing pain, numbness, or tingling in the sole and ankle.

Role in Gait and Balance

The tibial nerve plays a fundamental role in gait and balance by innervating the muscles responsible for plantarflexion, toe flexion, and foot stabilization. These motor functions allow for efficient movement during walking, running, and jumping. Additionally, sensory feedback from the plantar surface of the foot and the posterior leg helps the body maintain balance and adjust posture based on changes in foot pressure and surface texture.

• Push-Off Phase of Gait: The tibial nerve innervates muscles such as the gastrocnemius, soleus, flexor digitorum longus, and flexor hallucis longus, which are responsible for plantarflexing the foot and flexing the toes during the push-off phase of gait. This action propels the body forward and helps lift the foot off the ground, allowing for smooth and efficient walking and running.
• Balance and Foot Stabilization: Sensory input from the sole of the foot, provided by the medial and lateral plantar nerves, helps the body detect changes in pressure and surface texture. This feedback allows the nervous system to make rapid adjustments to foot positioning and muscle activity, ensuring balance and stability during walking, standing, and running.
• Postural Adjustments: The tibial nerve’s sensory and motor functions are essential for postural adjustments when standing on uneven surfaces or during quick changes in movement. For example, when standing on a sloped surface, sensory input from the foot allows the body to adjust muscle tension and weight distribution to maintain balance.

Reflexive Functions

The tibial nerve is involved in several reflexive actions that help protect the body from injury and maintain stability.

Withdrawal Reflexes: Sensory input from the posterior leg and plantar surface of the foot allows for quick withdrawal reflexes in response to painful stimuli, such as stepping on a sharp object or encountering extreme heat. These reflexes help prevent further injury by causing the foot or leg to pull away from the source of harm.

Clinical Significance

The tibial nerve plays a crucial role in both motor and sensory functions of the posterior leg and foot, making it clinically significant in several conditions. Injury to the tibial nerve can lead to weakness in plantarflexion, loss of toe flexion, and difficulty in walking, as it innervates the muscles responsible for these movements. Damage or compression of the tibial nerve, particularly in the tarsal tunnel (tarsal tunnel syndrome), can cause numbness, tingling, and pain in the sole of the foot and toes, affecting mobility and balance.

In cases of trauma, such as fractures of the tibia or ankle, the tibial nerve is at risk due to its location near bone structures. Surgical interventions, such as nerve grafting, may involve the tibial nerve, and its sensory branches, particularly the sural nerve, are often used for nerve repair. Overall, the tibial nerve’s health is essential for maintaining normal foot function and walking ability.