Piriformis syndrome refers to a condition in which the sciatic nerve is compressed in the gluteal region. It is one of the most common causes of chronic nerve injury in the lower limbs.
Anatomical Overview
The piriformis muscle is the uppermost muscle of the external rotator group of the hip joint. Approximately 85% of sciatic nerves exit the pelvis below the lower border of the piriformis muscle, passing between the superior gemellus, obturator internus, inferior gemellus, quadratus femoris, and gluteus maximus muscles. The sciatic nerve then runs along the posterior thigh and provides motor and sensory innervation to regions below the knee.
Etiology
Compression of the sciatic nerve in the region of the piriformis muscle may result from trauma to the gluteal area causing hematoma, adhesions, or scar formation. Medications injected into the gluteal region may lead to degenerative changes, fibrosis, or contracture of the piriformis muscle. A posterior-superior acetabular fracture with displacement or excessive callus formation can also compress the sciatic nerve near the piriformis muscle. In rare cases, anatomical variations in the path of the sciatic nerve, where it passes through the piriformis muscle, can result in compression. Chronic nerve injury may occur over time due to excessive pressure on the sciatic nerve during strong contraction of the piriformis muscle, especially during external rotation of the hip.
Clinical Features
The primary symptom of piriformis syndrome is sciatica, with pain radiating from the gluteal region to the posterior thigh, and further into the lower leg and foot. The pain is often severe, leading to difficulty in walking. Patients frequently present with painful limping, mild calf muscle atrophy, and sensory disturbances in the skin below the calf. Palpation of the gluteal region may reveal cord-like structures (fibrotic scars) or masses (callus). The Patrick's test, when resisted with external force, can exacerbate or provoke sciatic pain. Tinel’s sign may be positive at the site of tenderness in the gluteal region. In cases with a history of acetabular fractures, X-ray imaging may reveal displaced bone fragments or callus formation.
Differential Diagnosis
Lumbar Disc Herniation
Piriformis syndrome can easily be confused with sciatica caused by lumbar disc herniation. However, lumbar disc herniation typically presents with low back pain accompanied by compensatory lumbar scoliosis. Activities that increase abdominal pressure can worsen or trigger sciatic pain. The extent of sciatic nerve involvement corresponds to the location of disc herniation. A positive straight leg raise test and a positive Lasegue's test are often present, while the Patrick's test is usually negative.
Neurilemmoma
High-level sciatic nerve neurilemmomas are relatively rare. Symptoms progressively worsen over time and are unrelated to physical activity or rest. Tinel’s sign in the gluteal region is often pronounced, although a palpable cord-like tumor along the sciatic nerve is typically absent. Occasionally, ultrasonographic imaging may identify a uniformly thickened hypoechoic band along the surface of the sciatic nerve. Surgical intervention and pathological examination are the definitive diagnostic methods.
Treatment
Mild cases of piriformis syndrome in the early stages may respond to conservative treatment. However, when the underlying cause cannot be resolved and significant scar adhesion, callus compression, or anatomical nerve pathway variations are present, surgical intervention is required. The effectiveness of surgical treatment is closely related to the duration of the condition.