Surgical Exposure of Peripheral Nerves of the Lower Extremity. I. Sciatic Nerve and Its Branches (Peroneal and Posterior Tibial Nerves)

Clinical Anatomy of the Sciatic Nerve

The sciatic nerve is the largest nerve of the body, originating from the L4–S3 nerve roots. The nerve is formed from the lumbosacral and sacral plexuses in the pelvis and quickly exits this region through the greater sciatic notch. It then descends into the posterior thigh to the popliteal fossa. Here the nerve divides into its branches: the peroneal and tibial nerves. The tibial nerve continues down the leg, supplying the calf muscles, and enters the medial foot, supplying sensation to the weight-bearing portion of the foot as well as innervating the toe flexors. The common peroneal continues around the neck of the fibula and splits into deep and superficial branches. The deep branch innervates muscles in the anterior compartment of the leg (e.g., anterior tibialis, extensor hallucis, and toe extensors). The superficial branch supplies the peroneus muscles and sensation to the anterior surface of the foot.

Pathological conditions of the sciatic nerve that may require neurosurgical intervention include entrapment, iatrogenic injury, tumor, and trauma. Exposure of the nerve from the pelvis to its distal branches may be required for the treatment of these various pathologies. For lesions of the pelvis, general surgical, colorectal, or gynecologic assistance may be required for exposure.

Detailed history and physical examination are critical for the diagnosis of pathologies of the sciatic nerve and its branches. Differential diagnoses include lumbar radiculopathies and abdominal or pelvic masses. Fractures and dislocations of the hip or knee must be excluded. Imaging of these regions may be required. Detailed, high-quality magnetic resonance imaging of the sciatic nerve and its branches is possible. Potential sources of entrapment or tumor may be visualized and used in the decision-making process. Electromyographic and nerve conduction studies are paramount for the diagnosis and localization of pathology.

Surgical exposure of the sciatic nerve and its branches are utilized for nerve exploration and repair. For the purposes of this chapter, exposure of the nerve is divided into the gluteal region and thigh. Exposure of the major branches, tibial and peroneal, in the leg and ankle is also included.

70.1.2 Preoperative Preparation and Operative Procedure

Surgical Exposure of the Sciatic Nerve in the Gluteal Region

The sciatic nerve in the gluteal region may be involved with trauma (i.e., stretch injury), hip dislocation, tumor, or entrapment, among others. Iatrogenic injuries are the most common injuries to the sciatic nerve in the gluteal region with injections and total hip arthroplasties being the most common causes. The nerve may be entrapped by the piriformis muscle leading to the piriformis syndrome. Exposure is performed with the patient in the prone position with the knees slightly bent. All pressure points are padded, and the legs and ankles are slightly elevated. The entire buttock and leg are prepared for potential sural nerve harvest. The incision begins near the posterior–inferior iliac spine, curves laterally toward the greater trochanter, and again medially into the gluteal fold ( ▶ Fig. 70.1). This incision may be carried into the posterior thigh for a greater exposure of the nerve.

Fig. 70.1 Surgical exposure of the sciatic nerve in the extrapelvic gluteal region. A question mark incision is made with the curve surrounding the gluteus maximus muscle laterally, connecting with a straight line in the proximal dorsal thigh.

After incision of the skin and subcutaneous tissue, the gluteus maximus muscle is encountered. This muscle inserts on the femur and iliotibial tract laterally and the iliac crest rostrally. The sciatic nerve may be palpated in the upper thigh between the hamstring muscles and a finger placed superficial to the nerve under the inferior border of the gluteus maximus. The gluteus maximus is then split superiorly, leaving a cuff at its lateral attachment to aid in closing. A portion of the rostral aspect of the muscle should also be divided from the iliac crest to aid in a more medial exposure. Edges of the cut muscle should be marked with suture to aid with reapproximation during closure. The posterior cutaneous nerve of the thigh should be protected and medially displaced. The muscle flap may then be reflected medially, with care to avoid injury to the inferior gluteal nerve (supplies the gluteus maximus) and artery, which should be displaced medially with the muscle. The sciatic nerve is then visualized, emerging from the greater sciatic notch. The nerve passes over the piriformis, superior gemellus, obturator internus, inferior gemellus, and quadratus femoris ( ▶ Fig. 70.2). The nerve may lie dorsal or ventral or may be split by the piriformis muscle. This muscle is attached to the ventral sacrum and passes through the greater sciatic notch to insert on the femur. It may be a site of potential entrapment. In this region, the posterior femoral cutaneous nerve lies medial to the sciatic nerve. It must be identified and protected.

Fig. 70.2 The sciatic nerve is identified in the caudal aspect of the exposure after gentle retraction of the head of the biceps femoris and the semitendinous muscles. The gluteus maximus muscle may be mobilized medially by dividing its fascial attachment laterally, without dissecting or incising muscle fibers. It also facilitates the closure. The nerve is followed proximally to where it comes under the piriformis muscle. This is a commonly described site of entrapment of the sciatic nerve. The cause of the entrapment may be inflammation of the piriformis muscle or an abnormal course of the sciatic nerve through this muscle.

In the gluteal region, only one division of the nerve may be affected. It is possible to separate the sciatic nerve into its divisions ( ▶ Fig. 70.3). Often a septum is visualized or palpated and permits safe division. As previously noted, the piriformis muscle may split the two divisions, with the peroneal division usually superior in orientation.

Fig. 70.3 The sciatic nerve proximal to the popliteal fossa is a single nerve. Often pathology affects only one of its divisions. The sciatic may be split into its tibial and peroneal divisions if necessary. A septum may be seen and/or palpated. A scalpel may then be used to separate the divisions.

In certain instances, it may be possible to expose the nerve in a very proximal location (i.e., some distance into the true pelvis). This is accomplished by removing some of the bone and ligament around the sciatic notch. The piriformis muscle is divided to gain exposure of the notch.

Entrapment of the Sciatic Nerve (Piriformis Syndrome)

Entrapment of the sciatic nerve by the piriformis muscle is known as the piriformis syndrome. It may be secondary to piriformis muscle inflammation or an abnormal course of the sciatic nerve through this muscle. Affected patients may complain of sciatic nerve distribution pain or pain in the buttocks secondary to superior gluteal nerve involvement.

Surgical Exposure of the Sciatic Nerve in the Thigh

The patient is positioned prone. The entire leg is prepped for potential sural graft harvest; the contralateral leg is prepared as well. A midline posterior incision is recommended. The incision is begun laterally in the gluteal crease and extends down the midline of the thigh, in a medial-to-lateral orientation into the popliteal fossa. The incision then continues laterally over the fibular head ( ▶ Fig. 70.4). The semitendinosus muscle medially and biceps femoris muscle laterally are identified and separated. The sciatic nerve is readily identified in this upper thigh region between these muscles ( ▶ Fig. 70.5). The nerve runs superficial to the adductor magnus muscle. The nerve may be followed distally into the popliteal fossa. Care should be taken to preserve the branches to the hamstring muscles during exposure in this region. As in the gluteal region, the nerve may be split into its two divisions.

Fig. 70.4 The sciatic nerve may be exposed in the posterior thigh. An incision is begun laterally in the gluteal crease and extends down the midline thigh in a medial-to-lateral orientation into the popliteal fossa and continues laterally over the fibular head.

Only gold members can continue reading. Log In or Register to continue