Sciatic Nerve Decompression

Sciatic nerve decompression is a treatment option for sciatic nerve pain that is caused by certain structural spinal conditions. ^[1]

Sciatic neuropathies can result from nerve compression and injury in the gluteal region or thigh. Sciatic neuropathy in the gluteal region is most often caused by trauma. The nerve can be directly injured during an intramuscular injection into the buttocks.

Because of the close anatomical relationship between the nerve and the hip joint, nerve injuries can result from posterior dislocation of the hip, pelvic fracture, and accidental injury during elective hip arthroplasty. Other causes of sciatic neuropathy in this region include prolonged external nerve compression (“toilet seat neuropathy”), compression from pelvic hematoma, tumors, and endometriosis. See the images below.

The relationship between the piriformis muscle and the sciatic nerve.

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The sciatic nerve and its area of entrapment in the buttocks.

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Anatomic variation of the piriformis muscle may also cause compression of the nerve as it exits the pelvis. Piriformis syndrome generally includes buttocks and leg pain (sciatica) made worse by prolonged sitting. This is caused by direct compression of the sciatic nerve by the piriformis muscle as it exits the pelvis. ^[2]  It may be relieved by standing or walking, which is associated with signs of progressive sciatic neuropathy in severe cases. Piriformis syndrome is often misdiagnosed as disc disease and therefore may be diagnosed late. ^[3]

Sciatic neuropathy in the thigh is less common. It can be caused by fractures of the femur, compression by popliteal aneurysm, penetrating trauma, and nerve sheath tumors.

The indications for surgical exploration, decompression, and repair of sciatic neuropathies should take into account both the mechanism and completeness of nerve injury.

Complete traumatic axonal sciatic nerve injuries are best addressed with immediate nerve exploration and repair.

Partial traumatic lesions are usually initially managed conservatively but are referred for surgical exploration and repair if there is limited or no recovery after 3–6 months.

Patients with suspected piriformis syndrome who present with pain without neurologic deficit should initially be managed conservatively with medication and physiotherapy. ^[4] Surgical exploration and decompression of the sciatic nerve is usually reserved for patients who are resistant to conservative management, ideally in the presence of MRI or neurographic confirmation of the diagnosis.

All nontraumatic progressive sciatic neuropathies with neurologic deficit should be referred for surgical exploration, even if results of imaging studies are normal, since compressive lesions, including nerve sheath tumors and piriformis syndrome, can be difficult to diagnose without direct examination of the nerve. ^{[5, 6]}

Anatomy

The sciatic nerve originates from the L4 through S3 nerve roots in the inner wall of the pelvis and then passes under the piriformis muscle, out of the pelvis into the buttock, and through the greater sciatic foramen (sciatic notch). The nerve continues under the gluteus maximus muscle, close to the posterior capsule of the hip joint, deep in the posterior thigh, where motor branches innervate the hamstring muscles. ^[7]

The sciatic nerve then divides into the common peroneal and tibial nerve branches in the distal thigh proximal to the popliteal fossa. The common peroneal nerve continues around the fibula head into the lateral calf, innervates the peroneal muscle group (ankle dorsiflexion and eversion), and provides sensation to the lateral calf and dorsum of the foot. The tibial nerve continues through the posterior calf and innervates the gastrocnemius and soleus muscles (ankle plantar flexion), posterior tibial muscle (ankle inversion), and toe flexors and provides sensation to the posterior calf and sole of the foot. See the image below.

Posterior view of the leg, showing the sciatic nerve and the bifurcation to form the tibial and peroneal nerves.

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Although the sciatic nerve branches in the distal thigh, the nerve fibers within the proximal main nerve trunk are arranged topographically. Those fibers are destined to become the common peroneal nerve arranged as a discrete fascicle on the outside (lateral) aspect of the sciatic nerve, where they are more predisposed to compression and injury. Consequently, proximal sciatic nerve injuries can be difficult to distinguish from common peroneal nerve injuries without detailed electrophysiological and radiological assessment. ^[8]

In addition to a careful clinical examination, patients with suspected sciatic nerve injury or compression usually require electrodiagnostic testing and imaging studies prior to surgical management.

Electrophysiological assessment of nerve injuries is beyond the scope of this topic. However, these studies can be critical for differentiating complete and partial lesions, lateral sciatic nerve and common peroneal nerve injuries, and sciatic nerve injuries in the gluteal and thigh regions. Preoperative imaging may include radiographs of the hip and pelvis, EMG of the sciatic nerve, MRI of the lumbar spine and pelvis, and MR neurography.

Imaging of the pelvis can be used to identify a pelvic mass or hematoma, as well anatomic variations in the piriformis muscle that can cause sciatic nerve compression. See the images below.

Unenhanced computed tomography scan of the pelvis in a patient with sciatic nerve compression from pelvic hematoma. The arrow indicates edema and hematoma in the left gluteus medius muscle.

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Axial T1-weighted magnetic resonance imaging of the pelvis of a patient with left piriformis syndrome. The image shows asymmetric enlargement of the piriformis muscle belly (arrow), which compresses the sciatic nerve.

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Magnetic resonance neurography uses a high-resolution fast-spin echo T2 imaging technique to demonstrate abnormal signal within nerve trunks at sites of major nerve injuries and compression. It can be particularly useful for identifying piriformis syndrome, even when results of conventional imaging studies are normal.

There are two basic classifications of complications: systemic complications and complications specific to the procedure. Deep venous thrombosis can be prevented with serial compression devices, which may need to be placed on the upper extremities when both legs need to be approached to harvest the sural nerves for grafting. Pharmacologic prophylaxis can be used, but caution should be exercised when a complex and potentially bloody dissection is anticipated. As with any surgery, complication prophylaxis needs to be individualized per patient and for their particular medical, surgical, and pharmacologic history.

Prone positioning can be fraught with hazards, particularly with regard to pressure sores, neurapraxia, and airway issues. The airway should be well stabilized. Changes in position should not result in right main stem bronchus intubation and concomitant atelectasis. All potential neurovascular pressure points should be well padded or free floating.

Complications specific to the procedure revolve mainly around nerve injury and bleeding. There are numerous short perforating blood vessels in and around the buttocks. Bleeding may be troublesome in two ways: It may be hemodynamically significant and/or may obscure the surgical field, which can lead to inadvertent nerve injury.

Epinephrine-laden irrigation fluid can help to mitigate intraoperative bleeding. Very proximal dissection of the nerve can lead to an intrapelvic injury of the sacral venous plexus, which can easily lead to exsanguination. Bleeding of the sacral plexus is difficult to control even during open laparotomy. It is even more difficult when a prone patient needs to be emergently repositioned supine and then laparotomy performed.

Nerve injury can result from numerous factors. Difficulty in controlling bleeding and inadvertent cautery injury and/or hemostatic sutures can easily injure nerves. Overly vigorous dissection and misidentification of structures can also lead to injury. This is especially possible in light of difficult dissections at reoperative surgery. Intraoperative nerve monitoring can be very helpful in discerning structures, but there is no substitute for a good working knowledge of normal anatomy and common variations.

It is especially important to note that the area around the piriformis muscle is especially subject to variability in nerve anatomy, as compared to other nerve variants. The superior gluteal, sciatic, and inferior gluteal nerves can vary in their relationship to the piriformis muscle. They frequently pierce the substance of the muscle.

The area around the buttocks is not particularly sterile and difficult to dress properly, so infection avoidance is also important.

Careful selection of patients for surgery is necessary to obtain optimal outcomes. Three of the largest cohort studies published on sciatic nerve decompression reported that patient outcomes varied from 68.8% of patients achieving >50% relief to two-thirds of patients experiencing improvement to 100% of patients reporting excellent or good results. In a study by Ilizaliturri et al., the authors report the outcomes of 15 patients who underwent endoscopic sciatic nerve decompression. Average pain scores were estimated using a visual analog scale (VAS); decreasing from 7.4 (preoperatively) to 1.86 at 24-month follow-up. All cases demonstrated statistically significant postoperative improvement in pain and were able to return to work and perform daily activities without limitations. ^[9]