Sciatic nerve lesions
The sciatic nerve (L4–5, S1–3) is a branch of the lumbosacral plexus and the largest nerve in the body. It supplies most of the muscles and cutaneous sensation of the leg, so that sciatic nerve lesions cause serious disability.
Division of the sciatic nerve occurs occasionally in penetrating injuries. Traction injuries occur more commonly in association with fractures of the pelvis or hip dislocations. It is most frequently injured by badly placed intramuscular injections in the gluteal region (avoided by injecting into the upper outer quadrant of the but-tock). It supplies all the muscles of the lower leg, some of the hamstrings, and most of the sensation of the calf, as well as the skin on the sole and lateral side of the foot.
In most sciatic nerve lesions, the common peroneal nerve component is most affected, probably because its nerve fibres lie most superficial in the sciatic nerve trunk.
Flexion of the knee is markedly impaired and all the muscles below the knee are paralysed, causing drop foot. The calf is wasted. Sensation is absent in most of the skin below the knee.
In traumatic damage, exploration and repair of the nerve should be carried out. A footdrop splint is worn to keep the ankle in a safe position, but the lower leg is very vulnerable to neuropathic ulceration and development of Charcot’s joint, which may necessitate a below-knee amputation.