What is Piriformis Syndrome?
It is a neuritis of the sciatic nerve due to irritation or compression
by the piriformis muscle. The piriformis muscle is one of the external
rotators of the hip joint that crosses over the sciatic nerve in the buttock.
Other names for this condition are pseudosciatica, wallet sciatica, hip
socket neuropathy and deep gluteal syndrome. It is a poorly understood
condition that is often overlooked in patients suffering from sciatica.
Occasionally piriformis syndrome presents as an acute injury following
a twisting injury of one leg while the patient is carrying or lifting
in an awkward position. It can also result from direct and prolonged pressure
over the muscle as in sitting with a hard object in the back pocket of
a trouser (wallet sciatica). The most common presentation however is that
of chronic leg pain unrelated to any specific injury, with the duration
of symptoms ranging from months to years. Pain is the predominant symptom,
commonly extending from the buttock only as far as the knee, ankle or
heel. When sensory disturbances are present these usually involve multiple
dermatomes, rather than specific dermatomes as seen in a radiculopathy.
Actual numbness and weakness are however rare findings on examination.
The SLR test is generally negative. Pain may be reproduced by resisted
abduction or adduction of the flexed and internally rotated hip joint.
Tenderness over the sciatic is usually present and most patients report
that sitting exacerbates their pain and that it is relieved by walking.
On rectal or vaginal examination pressure with the finger tip over the
muscle just medial to the ischial spine may be intensely painful. The
symptom patterns and physical examination findings therefore differ significantly
from those in patients with spinal causes for their symptoms.
The MRI is the most useful diagnostic tool available to make the diagnosis
when a soft tissue pelvic MRI is performed. Typical MRI findings are hypertrophy
and edema of the piriformis muscle as well as edema or hyperintensity
in the sciatic nerve at that level. The MRI is also important to exclude
other more serious conditions, such as tumours of the sciatic nerve itself
, that can mimic piriformis syndrome. Where MRI is not available hypertrophy
of the piriformis muscle can also be identified with a high quality CT
scan of the pelvis.
Conservative treatment consists of rest, physiotherapy with stretching
exercises and anti- inflamatories. These measures are more likely to be
useful where piriformis syndrome is as a result of an acute injury. Other
measures include injections of cortisone and local anaesthetic into the
piriformis muscle itself under CT or open MRI guidance. Where these injections
relieve the symptoms they also confirm the diagnosis. Botox injections
have also been used to treat this condition. Surgery is indicated in patients
who show an initial response to the injection of cortisone and local anaesthetic
into the piriformis muscle but then have a recurrence of their symptoms.
During surgery an incision is made in the buttock and a section of the
piriformis muscle is excised thereby relieving the pressure on the sciatic
nerve. Where the diagnosis has been correctly established pre-operatively,
the outcomes after surgery are generally good
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