Piriformis Syndrome

Piriformis syndrome is a clinical condition of sciatic nerve entrapment at the level of the ischial tuberosity.  While there are multiple factors potentially contributing to piriformis syndrome, the clinical presentation is fairly consistent, with patients often reporting pain in the gluteal/buttock region that may "shoot," burn or ache down the back of the leg (i.e. "sciatic"-like pain).  In addition, numbness in the buttocks and tingling sensations along the distribution of the sciatic nerve is not uncommon. 

The sciatic nerve runs just adjacent to the piriformis muscle, which functions as an external rotator of the hip. Hence, whenever the piriformis muscle is irritated or inflamed, it also affects the sciatic nerve, which then results in sciatica-like pain. The diagnosis of piriformis syndrome is not easy and is based on clinical history and presentation. Other conditions that can also mimic the symptoms of piriformis syndrome include lumbar canal stenosis, disc inflammation, or pelvic causes.[1][2]

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Etiology

Sciatic nerve entrapment occurs anterior to the piriformis muscle or posterior to the gemelli-obturator internus complex at the level of the ischial tuberosity. The piriformis can be stressed due to poor body mechanics in a chronic condition or an acute injury with the forceful internal rotation of the hip. There are also anatomic anomalies that may contribute to compression, including a bipartite piriformis, direct invasion by a tumor, anatomical variations of the course of the sciatic nerve course, direct tumor invasion, or an inferior gluteal artery aneurysm that may compress the nerve.

Causes of piriformis syndrome include the following:[2]

• Trauma to the hip or buttock area

• Piriformis muscle hypertrophy (often seen in athletes during periods of increased weightlifting requirements or pre-season conditioning)

• Sitting for prolonged periods (taxi drivers, office workers, bicycle riders)

• Anatomic anomalies:

  • Bipartite piriformis muscle

  • Sciatic nerve course/branching variations with respect to the piriformis muscle

    • In >80% of the population, the sciatic nerve courses deep to and exits inferiorly to the piriformis muscle belly/tendon[3]

    • Early (proximal) divisions of the sciatic nerve into its tibial and common peroneal components can predispose patients to piriformis syndrome, with these branches passing through and below the piriformis muscle or above and below the muscle

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