128 - Sciatic Nerve Entrapment at the Knee

Abstract

The sciatic nerve provides innervation to the distal lower extremity and foot with the exception of the medial aspect of the calf and foot, which are subserved by the saphenous nerve. The largest nerve in the body, the sciatic nerve, is derived from the L4, L5, and S1–S3 nerve roots. The roots fuse in front of the anterior surface of the lateral sacrum on the anterior surface of the piriformis muscle. The nerve travels inferiorly and leaves the pelvis just below or through the piriformis muscle via the sciatic notch. Just beneath the nerve at this point is the obturator internus muscle. The sciatic nerve lies anterior to the gluteus maximus muscle; at this muscle’s lower border, the sciatic nerve lies halfway between the greater trochanter and the ischial tuberosity. The sciatic nerve courses downward past the lesser trochanter to lie posterior and medial to the femur. In the mid-thigh, the nerve gives off branches to the hamstring muscles and the adductor magnus muscle. In most patients, the nerve divides to form the tibial and common peroneal nerves in the upper portion of the popliteal fossa, although in some patients these nerves can remain separate through their entire course. The tibial nerve continues downward to provide innervation to the distal lower extremity, whereas the common peroneal nerve travels laterally to innervate a portion of the knee joint and, via its lateral cutaneous branch, provides sensory innervation to the back and lateral side of the upper calf.