Piriformis syndrome is one of the important causes of sciatica. In this neuromuscular disorder, the sciatic nerve is compressed or irritated by the piriformis muscle.
The symptoms are pain, tingling and numbness in the buttocks and along the path of the sciatic nerve descending down the lower thigh and into the leg.
The syndrome may occur due to anatomical variations in the muscle-nerve relationship, or from overuse or strain.
Piriformis syndrome should be considered as a possible diagnosis when sciatica occurs without a clear spinal cause.
Pathophysiology of Piriformis Syndrome
The basic event is compression or irritation of the sciatic nerve. It is a kind of entrapment neuropathy.
Usually the sciatic nerve underneath the piriformis muscle. However, in 15-30% of the population, the sciatic nerve passes through the substance of piriformis muscle. These people have a greater incidence of piriformis syndrome than does the general population.
Normally, piriformis acts as an external rotator of the femur. It causes rotation at the hip so as to turn foot pointing outward.
Overuse injury resulting in piriformis syndrome can result from activities performed in the sitting position that involves the strenuous use of the legs as in rowing/sculling and bicycling.
Runners, bicyclists and other athletes engaging in forward-moving activities are particularly susceptible to developing piriformis syndrome.
Disproportionately weak hip abductors/gluteus medius muscles, combined with very tight adductor muscles, can cause the piriformis muscle to shorten and severely contract.
Piriformis muscle spasm can result in impingement of not only the sciatic nerve but also the pudendal nerve (a nerve that controls the muscles of the bowels and bladder) and can lead to urinary and fecal incontinence.
Other proposed causes for piriformis syndrome are stiffness of the sacroiliac joints and overpronation of the foot or injury.
Piriformis syndrome is also known as wallet sciatica or fat wallet syndrome, as the condition can be caused or aggravated by sitting with a large wallet in the affected side’s rear pocket.
Diagnosis of Piriformis Syndrome
Symptoms include radiating pain in the buttock, posterior thigh and lower leg. The pain is exacerbated with activity, prolonged sitting or walking.
A physical examination would reveal tenderness in the area of the sciatic notch.
The diagnosis is largely clinical and is one of exclusion. Other causes of sciatica should be ruled out.
CT, MRI, ultrasound, and electromyography are useful in excluding other conditions and help in reaching a diagnosis.
Magnetic resonance neurography
It is a medical imaging technique that can show the presence of irritation of the sciatic nerve at the level of the sciatic notch where the nerve passes under the piriformis muscle.
Neurography can also determine whether or not a patient has a split sciatic nerve or a split piriformis muscle – this may be important in getting a good result from injections or surgery.
Treatment of Piriformis Syndrome
- Non-steroidal anti-inflammatory drugs and/or muscle relaxants for pain relief
- Stretching exercises and massage,
- Avoidance of contributory activities as noted before
- Stretching exercises
- Local ice/heat
- Custom foot orthotics
- Gait correction
- Ultrasound to provide deeper heat
- Injections – steroids, botulinum toxin, lidocaine