Piriformis Syndrome is the compression of the sciatic nerve by the piriformis muscle.
Conditions affecting the sciatic nerve that refer pain down the posterior thigh are often referred to by the general public as sciatica. This term is not specific, because it may refer to inflammation of the nerve or compression of the nerve in the lumbar spine, in the gluteals or at another distal point along the pathway of the nerve. It may even refer to the symptoms common to piriformis trigger points.
The sciatic nerve supplies sensory and motor function to the skin and muscles of the posterior thigh, most of the leg and foot. It is composed of nerve roots L4 to S2/S3, with sources differing to the later (Omer, Spinner 1980, Dawson et al 1990). The sciatic nerve is comprised of two peripheral nerves, common peroneal and tibial which travel as one to the knee.
The piriformis muscle interts on the anterior surface of the sacrum (S1 to S4) and runs horizontal to attach at the medial superior aspect of the greater trochanter of the femur. Deep to gluteus maximus, the pirirformis and upper lateral rotators spread out from the greater trochanter like a fan. The broader portion of the muscle emerges from the foramen and the muscle narrows at the greater trochanter.
Function of the Piriformis;
- Restrain rapid/vigorous internal rotation of the hop, such as occurs with running or in the stance phase of walking.
- Externally rotate the femur when the hip is extended or in neutral.
- Horizontally abduct the thigh when the hip is flexed to 90 degrees.
- Internally rotate the femur when the hip is fully flexed.
- Anomalies in the course of the nerve.
- Direct/indirect trauma.
- Postural and positional.
- Usually unilateral – Pain from a variety of sources results in pain/paresthesia in posterior thigh to calf and foot, numbness.
- Pudendal nerve compression causes perineal and inguinal pain.
- Compression of the gluteal nerve causes buttock pain.
- Active trigger points can result in low back pain, buttocks, hip and posterior thigh.
- Pain can decrease with external rotation of the hip.
- Weakness in performing abduction, flexion and internal rotatlon of affected hip.
- SIJ dysfunction may be present due to shortening and tension in piriformis.
- Pace abduction is positive.
- Piriformis length is positive – short piriformis on affected side.
- SIJ motion palpation – may reveal restricted movement.
Differentiating sources of radiating glue pain;
- Lumbar spine stenosis results in progressive pain, usually bilateral in the calf and foot.
- Facet Joint irritation positive Kemp’s test.
- Inflammatory arthrides, ankylosing spondylitis, x-ray.
- Compression of nerve at lumbar spine from a herniated disc.
- Which location is common for compression – lumbar or piriformis. Symptoms – numbness and tingling to lateral foot and small toe – S1, or to dorsum of the foot – L5, or to medial calf – L4.