Piriformis muscle: clinical anatomy and consideration of the piriformis Syndrome

Patients with lumbosacral and buttock pain provide tacit support for recognizing the piriformis muscle as a contributing factor to the pain (piriformis syndrome). One hundred and twelve cadaveric specimens were observed to elucidate the anatomical variations of the piriformis muscle referred to the diagnostic and treatment of the piriformis syndrome. The distance between the musculotendinous junction and the insertion was measured and the piriformis categorized into three types: Type A (71, 63.39%): long upper and short lower muscle belly; Type B (40, 35.71%): short upper and long lower muscle belly; Type C (1, 0.9%): fusion of both muscle bellies at the same level. The diameter of the piriformis tendon at the level of the musculotendinous junction ranged from 3 to 9 mm (mean: 6.3 mm). The piriformis showed the following possible fusions with adjacent tendons. In type one (60, 53.57%) a rounded tendon of the piriformis reached the upper border of the greater trochanter. In type two (33, 29.46%) it first joined into the gemellus superior tendon and at last both fused with the obturator internus tendon and inserted into the medial surface of the greater trochanter. A fusion of the piriformis, obturator internus and gluteus medius tendon with the same insertion area as above was observed in type three (15, 13.39%) and finally in type four (4, 3.57%) the tendon fused with the gluteus medius to reach the upper surface of the greater trochanter. Based on this survey anatomical causes for the piriformis syndrome are rare and a more precise workup is necessary to rule out more common diagnosis.