The nerves of the lower limb include the femoral nerve anteriorly and the sciatic nerve posteriorly, along with their branches (the tibial nerve and common peroneal nerve).
Injury of the Femoral Nerve
The femoral nerve originates from the lumbar plexus (L2–L4) and descends along the surface of the iliacus muscle. It passes posterior to the inguinal ligament and branches approximately 3–4 cm below it, lateral to the femoral artery. It supplies the sartorius muscle, the quadriceps femoris, and the anterior skin of the thigh. Below the knee, it continues as the saphenous nerve, innervating the skin on the medial side of the leg.
Injuries to the femoral nerve are relatively uncommon. They typically result in paralysis of the quadriceps femoris, causing impaired knee extension, along with sensory deficits in the anterior thigh and medial leg. Closed traction injuries of the femoral nerve may be managed with observation. Sharp open injuries, such as those caused by penetrating trauma, often require primary surgical repair. In cases where knee extension does not recover, reconstructive procedures involving tendon transfer, such as relocating the biceps femoris and semitendinosus tendons, may be considered.
Injury of the Sciatic Nerve
The sciatic nerve originates from L4, L5, and S1–S3 nerve roots. It exits the pelvis through the greater sciatic notch, passes below the piriformis muscle, and enters the gluteal region beneath the gluteus maximus. It runs between the ischial tuberosity and greater trochanter and descends along the posterior thigh between the biceps femoris and semimembranosus muscles. At the apex of the popliteal fossa, it divides into the tibial and common peroneal nerves. Along its course, it also supplies the muscles of the posterior thigh, including the biceps femoris, semitendinosus, and semimembranosus.
The manifestations of sciatic nerve injury depend on the level of injury. High-level injuries may result from posterior hip dislocations, lacerations to the gluteal region, complications from gluteal muscle contracture surgeries, or intramuscular injections. Such injuries can cause paralysis of all posterior thigh muscles as well as the lower leg and foot muscles, leading to complete loss of knee flexion, ankle, and toe movements. Foot drop deformity is commonly observed. Sensory loss affects the posterolateral lower leg and the foot. For injuries occurring in the mid-to-lower thigh, the hamstring muscles retain function, preserving knee flexion, while dysfunction is limited to movements of the ankle and toes.
The prognosis of high-level sciatic nerve injuries is generally poor. Early surgical exploration, followed by neurolysis or repair based on the findings, is often necessary.
Injury of the Tibial Nerve
The tibial nerve enters the popliteal fossa alongside the popliteal artery and vein. It passes deep to the tendinous arch of the soleus muscle and runs through the posterior compartment of the leg. It descends between the posterior compartment muscles, exiting behind the medial malleolus, passing through the flexor retinaculum, and entering the sole of the foot. It innervates the flexor muscles of the posterior leg and provides sensory innervation to the sole.
Tibial nerve injuries can occur with supracondylar fractures of the femur or knee dislocations, resulting in paralysis of the posterior leg flexor muscles and intrinsic muscles of the sole. Typical functional deficits include impaired plantarflexion, foot adduction, and inversion, as well as inability to flex, abduct, and adduct the toes. Sensory loss commonly includes the posterior leg, lateral foot, heel, and the sole. Such injuries are often caused by contusions, and recovery is observed for 2–3 months. Surgical exploration is indicated if no recovery signs are seen within this period.
Injury of the Common Peroneal Nerve
The common peroneal nerve descends obliquely and laterally along the medial border of the biceps femoris in the popliteal fossa. It winds around the neck of the fibula, passing through the two heads of the fibularis (peroneus) longus muscle. At this point, it divides into the superficial peroneal and deep peroneal nerves. The superficial branch descends between the fibularis longus and brevis muscles before piercing the deep fascia at the lower third of the leg to supply the lateral and dorsal aspects of the foot. The deep branch descends between the extensor digitorum longus and the tibialis anterior, running with the anterior tibial vessels to reach the dorsum of the foot.
The common peroneal nerve supplies the extensor muscles in the anterior and lateral compartments of the leg and provides sensory innervation to the skin of the anterior and lateral leg, as well as the dorsum of the foot. Fractures of the fibular head or neck often cause common peroneal nerve injury. This results in paralysis of the anterior and lateral compartment muscles, causing deficits in ankle dorsiflexion and eversion. The typical deformity includes foot drop, with an inability to extend the toes and evert the foot, along with sensory loss over the anterolateral leg and dorsum of the foot.
Early surgical exploration may be required for common peroneal nerve injuries. In cases where motor recovery does not occur, late-stage tendon transfer procedures can be undertaken to correct foot drop deformity.