Posterior Approach to the Acetabulum (Kocher-Langenbeck)

DISCUSSION: In Figure A, the arrow labeled A is pointing to the Gluteus minimus muscle, B is pointing to the tendon of the piriformis muscle, and C is pointing to the sacrotuberous ligament (Illustration A). These are all important landmarks and points of identification during a posterior approach to the hip.

Illustrations B and C demonstrate the relationship of the ischial spine and ischial tuberosity in relation to the hip joint and the associated ligaments. The superior gemellus originates from the ischial spine.

DISCUSSION: The arrow points to the ischial spine and is the site of attachment of the sacrospinous ligament which anatomically divides the greater and lesser sciatic notches. The contents of the greater sciatic notch include the piriformis, the superior and inferior gluteal vessels and nerves, the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, and the nerves to the obturator internus and quadratus femoris. The lesser sciatic notch is home to the tendon of the obturator internus, the nerve which supplies that muscle, and the internal pudendal vessels and nerve that course back through the lesser notch after having exited the greater notch.

DISCUSSION: The pudendal nerve, sciatic nerve, inferior gluteal nerve, and inferior gluteal artery all exit the sciatic foramen. The obturator nerve does not exit the sciatic foramen. The greater sciatic foramen is bounded as follows: anterolaterally by the greater sciatic notch of the illium, posteromedially by the sacrotuberous ligament, inferiorly by the sacrospinous ligament and ischial spine, and superiorly by the anterior sacroiliac ligament. It is partially filled up by the piriformis which leaves the pelvis through it. The following structures make their exit from the pelvis through the greater sciatic foramen above the piriformis: superior gluteal vessels and superior gluteal nerve. Below the piriformis the following structures exit: inferior gluteal vessels, inferior gluteal nerve, internal pudendal vessels, pudendal nerve, sciatic nerve, posterior femoral cutaneous nerve, nerve to obturator internus, and nerve to quadratus femoris. The obturator nerve originates from the L2, L3, and L4 nerve roots, exits the pelvis through the obturator foramen, innervates the gracilis, adductors (longus, brevis, magnus), and provides sensation to the inferomedial thigh.