Piriformis Syndrome

PIRIFORMIS SYNDROME

Yeoman first described the relationship between the sciatic nerve and piriformis muscle and Robinson coined the term ‘piriformis syndrome’(1)
Various theories have been proposed for the aetiology of piriformis syndrome:-
Robinson attributed the spectrum of the symptoms to sciatic nerve entrapment by adhesions on the piriformis muscle caused by the initial injury, which is a fall on the buttock(2)
Pecina’s hypothesis: individuals with the sciatic nerve passing through the tendinous portion of the piriformis muscle are susceptible to compression of the nerve by the edge of the muscle or tendon with internal rotation of the hip joint, and accordingly nerve damage and symptoms(3)
Five variations of sciatic nerve exiting the greater sciatic notch have been described

sciatic nerve passing below the piriformis muscle
sciatic nerve passing through the muscle belly
a divided nerve above and through the muscle belly
a divided nerve through and below the muscle belly
undivided nerve passing above an undivided piriformis muscle(9)

Pace and Nagle’s hypothesis: focal irritability of the piriformis muscle, usually caused by trauma, results in myofascial pain syndrome that could be treated by trigger point injections(4)

Clinical Features:

buttock pain with or without radiation to the leg
Sitting on hard surfaces will exacerbate the pain
Occasional numbness and paraesthesias without definitive weakness
Since the piriformis muscle is related to the lateral pelvic wall, patients may experience pain with bowel movements and women may experience dysparenuia
Tenderness maybe present between the sacrum and the greater trochanter with the hip and knee flexed
A palpable taut band maybe present with pelvic and rectal examination since the piriformis rests on the pelvic floor
Freiberg’s sign: Pain on passive hip adduction and internal rotation
Pace’s sign: is an active contraction test, Resistance to active hip external rotation and abduction elicits pain due to contraction of the piriformis
A positive SLR maybe present

Diagnosis

Fishman’s clinical criteria:

1.Positive Lasegue sign at 45 degrees

2. Tenderness at sciatic notch

3. Increased pain in the sciatic distribution with the thigh in the FAIR (flexion, adduction and Internal rotation)

4, Electrodiagnostic studies that exclude neuropathy or myopathy

MRI and CT to rule out IVDP. MRI may show anatomic anomalies of sciatic or lumbosacral nerve, enlarged piriformis with enlargement and compression of sciatic nerve.
EMG/NCV: prolonged F waves and H reflex in findings in the distribution of the inferior gluteal nerve and the tibial and peroneal divisions of the sciatic nerve.(10)

DD:

L5/S1 radiculopathy
Superior and inferior gluteal artery aneurysm
Facet joint arthropathy
sacroilitis

Treatment

Analgesics, gabapentin, amitryptiline, soft cushions while sitting,
Ultrasound therapy
Stretching exercises: internal rotation and hip adduction and flexion
Correction of biomechanical abnormalities that initiate piriformis syndrome like leg length inequality, increased foot pronation and hamstring tightness
Recalcitrant cases may require a perisciatical injection of corticosteroid; alternatively a caudal epidural injection may be considered (5).
Recently, Botulinum toxin (BTX) is used to treat PS, it relieves sciatic nerve compression and inherent muscle pain from a tight piriformis.
Rarely, surgical release of the piriformis muscle may be necessary for unremitting pain (6). An additional sciatic nerve neurolysis maybe performed to release the nerve from the posterior pelvic column

REF:

1. Yeoman W. The relation of arthritis of the sacroiliac joint to sciatica, with an analysis of 100 cases. Lancet 1928;2:1119– 22

2. Robinson DR. Pyriformis syndrome in relation to sciatic pain. Am J Surg 1947; 73:335–58.

3. Pecina M. Contribution to the etiological explanation f the piriformis syndrome. Acta Anat Basel) 1979; 105:181–7.

4. Pace JB, Nagle D. Piriform syndrome. West J Med 1976; 124:435–9.

5. Mullin V, de Rosayro M. Caudal steroid injection for treatment of piriformis syndrome [see comments]. Anesth Analg 1990;71:705– 7.

6. Benson ER, Schutzer SF. Posttraumatic piriformis syndrome: diagnosis and results of operative treatment. J Bone Joint Surg [Am] 1999;81:941– 9.

7. Silver JK, Leadbetter WB: Piriformis syndrome: Assessment of current practice and literature review

8. Vandertop WB, Bosma NJ: The Piriformis Syndrome. JBJS 1991; 73: 1095-1096

9. Ozaki S, Hamabe T, Muro T: Piriformis syndrome resulting from an anomalous relationship between the sciatic nerve and the piriformis muscle. Orthopedics 1999:22; 771-772

10. Hughes SS, Goldstein MN, Hicks DG, Pellegrini Jr VD. Extrapelvic compression of the sciatic nerve. An unusual cause of pain about the hip: report of five cases .J Bone Joint Surg [Am] 1992;74: 1553– 9.

11. Kirschner JS, Foye PM, Cole JL. Piriformis syndrome, diagnosis and treatment. Muscle and Nerve 2009; 40: 10-18

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