Piriformis Syndrome Piriformis
syndrome is a syndrome of low back and leg pain thought to be due to
chronic contracture of the piriformis muscle that causes irritation of
the sciatic nerve. The syndrome involves gluteal pain often accompanied
by pain radiating down the affected leg in the distribution of the
sciatic. It is commonly called “hip pocket neuropathy” or “wallet
neuritis”. Two most common theories are 1)
compression of the nerve between the inflamed muscle and the bony
pelvis 2) compression of the nerve between the two inflamed fascicles
of the piriformis muscle. Robinson observed that any inflammation or
spasm of the piriformis muscle will compress the sciatic nerve whenever
the leg is raised, producing the sciatica. Pace proposed
that focal hyper-irritability of the piriformis muscle resulted in a
trigger-point syndrome. Sciatic neuritis is believed to result from
irritation of the sciatic nerve sheath, which is caused by biochemical
agents released from an inflamed piriformis muscle where the two
structures meet at the greater sciatic foramen. In a series of biopsies
of myofascial trigger points, Awad documented the pathologic findings
of metachromatic ground substance (mucopolysaccharide), extravasated
platelets, degranulating mast cells, and giant myofilaments. Based on
these findings, he hypothesized the probable mechanism of “interstitial
myofibrositis” to be as follows: trauma to the muscle results in
extravasation of blood, release of serotonin from extravasated
platelets, and degranulation of mast cells releasing histamine and
heparin. Serotonin and histamine are vasoactive amines that produce
vasodilation and increased vascular permeability. Anatomy The
piriformis muscle is a flat, pyramidal-shaped muscle that originates
from the anterior surface of the sacrum from S2 to S4 and sacrotuberous
ligament, passes through the upper part of the greater sciatic notch,
and inserts on the superior surface of the greater trochanter. The
piriformis is innervated by the nerve of L5, S1, and S2 segmental
origin. The sciatic nerve emerges from the greater sciatic notch, very
close to the inferior border of the piriformis muscle. The function of
the piriformis muscle is to externally rotate the leg and abduct the
thigh when the hip is flexed. The sciatic nerve
originates from the L4, L5, S1, and S2 nerve roots. It arises from the
lumbosacral plexus and leaves the pelvis through the greater sciatic
notch. It is composed of two trunks, the peroneal division and the
tibial division. The sciatic nerve divides into the common peroneal and
tibieal nerves at the midthigh to distal thigh region. All the
hamstring muscles except the short head of the biceps femoris are
innervated by the tibial division. All the muscles below the knee are
innervated by the sciatic nerve. All sensory nerves except the
saphenous nerve are derived from the sciatic nerve. The
location of the sciatic nerve in relationship to the muscle makes it
vulnerable to irritation and entrapment secondarily to pathology
involving the piriformis muscle. In about 20%, the piriformis muscle is split and one or both parts of the sciatic nerve pass through the muscle belly, and in 10% of the population, the tibial and peroneal portions of the sciatic nerve are not enclosed in a common sheath and one portion may pierce the muscle. Six possible anatomic variations of the relationship between the sciatic nerve and piriformis muscle have been described. The first four have been confirmed, the last two are hypothetical. 1) the sciatic nerve passing below the piriformis muscle 2) a divided nerve passing through and below the piriformis 3) a divided nerve above and below the muscle 4) an undivided nerve passing through the piriformis 5) a divided nerve passing through and above the muscle 6) an undivided nerve passing above the muscle Diagnosis Piriformis
syndrome was mostly a diagnosis of exclusion with the symptoms of
sciatica and pain in the buttock. There have been studies of diagnostic
tests which may aid in identifying piriformis syndrome. The common
findings on history and physical will be reviewed. History
of trauma to the buttock is commonly reported. In Durrani and Winnie's
study, 92% of their patients reported either direct or indirect trauma.
Direct trauma may be to the low back or buttocks. Indirect truama may
be due to unusual stretching of the lumbosacral and/or hip muscles
through athletic or other strenuous activities. Women
often complain of pain with sexual intercourse, dyspareunia, men may
complain of rectal pain. There is pain with walking, limping, and
squatting. Pain with stooping or lifting, intolerance to sitting,
taking long automobile rides, and complaint of pain in the buttock. The treatment for the sciatic pain may not yield results. History of failed laminectomy, discetomy, and chemonucleolysis, or a series of epidural steroid injections with no change in sciatica may indicate piriformis syndrome. Robinson described six classic findings for piriformis syndrome: 1) a history of trauma to the sacroiliac and gluteal regions 2) pain in the region of the sacroiliac joint, greater sciatic notch, and piriformis muscle that usually extends down the limb and causes difficulty with walking 3) acute exacerbation of pain caused by stooping or lifting 4) a palpable sausage-shaped mass, tender to palpation, over the piriformis muscle 5) a positive Lasegue sign 6) gluteal atrophy Durrani and Winnie used the following physical examination tests to diagnose piriformis syndrome: 1) digital palpation of the piriformis muscle for reproducing sciatica 2) rectal or pelvic examination to rule out lateral pelvic wall tenderness and reproduce sciatica 3) Freiberg’s and Pace’s signs 4) Tonic external rotation of the affected lower extremity They
found that 26/26 people had moderate to severe tenderness of the
lateral pelvic wall along with reproduction of their sciatica during
pelvic or rectal examination, 24/26 had reproduction of pain with deep
digital palpation of the piriformis muscle. Lasegue’s
sign is pain in the vicinity of the greater sciatic notch with
extension of the knee with the hip flexed to 90 degrees and tenderness
to palpation of the greater sciatic notch also involving pain on
voluntary adduction, flexion, and internal rotation. Freiberg’s sign is
pain with passive internal rotation of the hip. Pace’s sign is pain and
weakness in association with resisted abduction and external rotation
of the affected thigh, different source says internal rotation of hip.
The piriformis sign is pain with tonic external rotation of the
affected lower extremity. A diagnostic
maneuver for piriformis syndrome was described by Robert A. Beatty. It
is performed with the patient lying with the painful side up, the
painful leg flexed, and the knee resting on the table. Buttock pain is
produced when the patient lifts and holds the knee several inches off
the table. It relies on contraction of the muscle, rather than
stretching which reproduces one of the proposed mechanisms for
piriformis syndrome. A modification to this maneuver was proposed by
Robert M. Titelman. Hold the patient’s affected thigh and leg slightly
above the other so it is slightly medially rotated. The patient relaxes
the lower membrane, while being held in the same position. Have the
patient laterally rotate against your resistance, but while still
holding the leg to keep the abductors relaxed and the thigh from
abducting. This would eliminate the abduction and extension involved in
Beatty's diagnostic maneuver. Diagnostic Studies Imaging studies for piriformis syndrome may demonstrate inflammation or hypertrophy of the piriformis muscle. Bone scan may demonstrate abnormal uptake in the soft tissues of the pelvis in the distribution of the piriformis muscle. In a case report, computed tomography and magnetic resonance imaging showed an enlarged piriformis with normal and homogenous muscle signal intensity (demonstration of atrophy or fibrous tissue replacement of the piriformis muscle). Imaging may demonstrate other causes of sciatica such as herniated nucleus pulposa or extrinsic compression of the sciatic nerve by tumor or abscess. Myelography
can show the enlargement of the piriformis muscle and also demonstrate
the correct placement of the needle within the muscle. However, Durrani
and Winnie had 6 piriformis syndrome patients with myelograms, all of
which were negative. Electromyography has
been used to aid in the diagnosis of piriformis syndrome. Fishman and
Zybert have studied the use of the H-reflex in electrodiagnostic
studies. The H-reflex is an electrically stimulated version of the
Achilles reflex. Subjects were tested in the anatomically prone
position and then placed in a lateral decubitus position. H-reflex was
reexamined with the hip flexed, maximally adducted, the knee flexed,
and passive rotation of the thigh internally. They concluded that there
was significant delay in the H-reflex in the affected limb. Durrani and
Winnie had 8/18 patients which had electromyographic evidence of
radiculopathies. Relief of pain produced by infiltration of the piriformis muscle with local anesthetic is considered to be a diagnostic sign. Treatment Treatment
of piriformis syndrome should include correction of any abnormal
biomechanics caused by posture, pelvic obliquity, leg-length
inequality, or ankle/foot problems. Nonsteroidal
anti-inflammatory drugs, analgesics, and muscle relaxants may be
prescribed to reduce local prostaglandin-mediated inflammation, pain
and spasm. Piriformis stretching exercises with heat therapy may be
sufficient to relieve the pain. Other relatively conservative
treatments include ultrasound treatment, transrectal massage, rectal
diathermy, and transcutaneous electrical stimulation. Trigger
point injections could be considered diagnostic and therapeutic. Local
anesthetics and osteopathic manipulation work by reducing muscle spasm,
restoring joint motion, and keeping the patient ambulatory. The local
anesthetic apparently reverses the hyperirritability of the piriformis
muscle and produces relief that outlasts the duration of the
medication. Sarapin, an aqueous distillate of Sarracenia purpurea,
blocks C-fiber pain transmission without affecting motor or sensory
function and may be useful when used as part of the injectate.
Injection of Botulinum toxin type A into the piriformis muscle could
provide longer lasting relief than local anesthetics. Botulinum toxin
type A is a protein produced by the Clostridium botulinum bacteria. It
inhibits the release of the neurotransmitter acetylcholine thus causing
muscle relaxation. Caudal epidural steroid injection has
been used since it is a well established treatment for low back pain.
Solutions deposited in the caudal epidural space would be expected to
diffuse along the nerve root sleeves and hence along the proximal part
of the sciatic nerve. This was subsequently demonstrated with
computerized tomographic evidence. The sacral innervation of the
piriformis muscle may also have some bearing on its success. The caudal
epidural injection consisted of 60-80 mg of triamcinolone with 15 ml of
0.25% bupivicaine. This is believed to relieve sciatic nerve irritation
and piriformis muscle spasm. Perisciatic
injection of steroid have been successful in recalcitrant cases of
piriformis syndrome. Perineural injection of steroid has been shown to
reduce nerve swelling, reduce ectopic discharge, and facilitate
recovery of nerve conduction following nerve injury. The perisciatic
injection of steroid is thought to reduce swelling and irritation of
the sciatic nerve while piriformis muscle injections relax the muscle
and reduce nerve compression. Surgical release of the
piriformis muscle with exploration of the sciatic nerve is reserved
until more conservative treatments have failed. The piriformis muscle
may be thinned, elongated, divided, or excised. The obturator internus,
gemelli, and quadratus femoris share a common insertion at the greater
trochanter, these muscles will compensate for the loss of piriformis
muscle. Surgery was performed for piriformis syndrome caused by blunt
trauma to the buttock and is a result of hematoma formation and
subsequent scarring between the sciatic nerve and the short external
rotators. The gluteus maximus fascia and muscle are split. The
insertion of the piriformis tendon is palpated, exposed, and divided
from its insertion on the greater trochanter. It is dissected
proximally to its exit from the greater sciatic notch. The sciatic
nerve is identified and neurolysis performed by mobilizing the nerve
from the overlying piriformis muscle and other short rotators with use
of blunt dissection proximally into the greater sciatic foramen and
distally to the end of the wound. The results from Benson and Schutzer
were encouraging with few complications.
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