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The Journal of Bone & Joint Surgery, Volume 79, Issue 6

Case Reports | June 01, 1997

Myositis Ossificans of the Piriformis Muscle: An Unusual Cause of Piriformis Syndrome: A Case Report*

RICHARD P. BEAUCHESNE, M.D.†; STEVEN F. SCHUTZER, M.D.‡, HARTFORD, CONNECTICUT

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Investigation performed at Hartford Hospital, Hartford

The Journal of Bone & Joint Surgery. 1997; 79:906-10

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Introduction

Introduction | Case Report | Discussion | References

Piriformis syndrome is the result of entrapment of the sciatic nerve by the piriformis muscle as it passes through the sciatic notch. Because of its relative rarity, a high index of suspicion is necessary to make the diagnosis^4,15,22,24. Etiologies have included hypertrophy of the piriformis muscle^3,11,16; trauma^17,26; pseudoaneurysm of the inferior gluteal artery¹⁷; excessive exercise¹²; and inflammation and spasm of the piriformis muscle¹⁹, often in association with trauma^11,20, infection², and anatomical variations of the muscle^1,10,18. The syndrome also has been reported in association with dystonia musculorum deformans⁸. To our knowledge, traumatic myositis ossificans of the piriformis muscle has not been described previously as a cause of piriformis syndrome. We report the case of a patient in whom the sciatic nerve was compressed between the piriformis muscle and the roof of the sciatic notch; bone-scanning, computerized axial tomography, magnetic resonance imaging, and histopathological testing indicated that the compression was secondary to myositis ossificans of the piriformis muscle.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Mousam Valley Orthopaedics, 177 Main Street, Springvale, Maine 04083-1409.

‡Orthopaedic Associates of Hartford, 85 Seymour Street, Suite 607, Hartford, Connecticut 06106.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Mousam Valley Orthopaedics, 177 Main Street, Springvale, Maine 04083-1409.

‡Orthopaedic Associates of Hartford, 85 Seymour Street, Suite 607, Hartford, Connecticut 06106.

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Fig. 1 Posteroanterior bone scan demonstrating asymmetrical increased uptake in the left hemipelvis

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Fig. 2 Computerized axial tomograph of the pelvis, showing enlargement and ossification of the piriformis muscle (arrow).

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Figs. 3-A, 3-B, and 3-C: Magnetic resonance images demonstrating enlargement of the piriformis. Fig. 3-A: T1-weighted image demonstrating low signal intensity in the area of ossification (arrows).

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Fig. 3-B T2-weighted image demonstrating heterogeneous signal intensity in the area of ossification (arrow).

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Fig. 3-C Gadolinium-enhanced image showing enlargement and apparent ossification of piriformis muscle (arrow).

Case Report

Introduction | Case Report | Discussion | References

A thirty-two-year-old man who had a history of alcohol abuse fell down a flight of stairs while intoxicated and was not found until the following day. The injuries included a mild closed head injury, several fractures of the ribs, and a contusion of the right thigh and the left buttock. A few days later, he noted increasing pain that radiated from the left gluteal region to the posterior portions of the thigh and calf. Three weeks after the injury, he observed paresthesias and decreased sensation on the lateral border of the left foot as well as weakness in the left ankle. He did not have pain or spasm in the back.

He was admitted to the medical service one month after the injury for the treatment of delirium tremens and alcohol withdrawal. He was evaluated by the neurology and neurosurgery services because of progressive left lumbar root pain. He had no muscular atrophy in the left lower extremity and no tenderness or spasm in the back. There was no tenderness over the sciatic notch, and other diagnostic tests for piriformis syndrome apparently were not done. A neurological evaluation revealed decreased sensation to light touch on the lateral aspect of the left leg and foot. Manual motor-testing showed mild weakness of eversion of the foot and dorsiflexion of the ankle. The Achilles-tendon reflex was absent on the left. The result of the Lasègue test initially was reported to be negative; however, a later examination by the orthopaedic service showed the result to be positive. Gait analysis revealed an antalgic gait with a limp on the left as well as a slight foot drop.

Plain radiographs made six weeks after the injury revealed periosteal new-bone formation in the anterior and lateral aspects of the middle third of the right femur. These findings were thought to be post-traumatic in origin as a result of hematoma formation and subsequent myositis ossification. A radiograph of the chest that was made at the time of admission showed healing fractures of the ribs. The initial anteroposterior radiograph of the left hip was unremarkable. The consulting neurologist diagnosed a lesion of the left first sacral nerve; the cause of the lesion was unknown, but it probably was extraspinal. The results of electromyographic and nerve-conduction studies were non-specific but did show denervation potentials in the distributions of the left fifth lumbar and first sacral nerves. A follow-up evaluation was scheduled, and the patient was discharged. Computerized axial tomography of the lumbosacral spine revealed normal findings. Three weeks later, the patient was readmitted to the medical service because of increasing pain in the left lower extremity as well as depression and anxiety associated with alcohol withdrawal. A bone scan revealed a linear area of increased uptake in the left hemipelvis (Fig. 1). Computerized axial tomography (Fig. 2) and magnetic resonance imaging (Figs. 3-A, 3-B, and 3-C) of the pelvis demonstrated enlargement and apparent ossification of the piriformis muscle. Two computerized-axial-tomography-directed needle biopsies of the left piriformis muscle were done; the specimens had a calcified appearance that was compatible with a healing infection, a calcifying hematoma, or a sarcoma. The presumptive diagnosis was metastatic sarcoma of the piriformis muscle. An orthopaedic consultation then was obtained; on the basis of the information available, it was concluded that the patient had traumatic myositis ossificans of the piriformis muscle and secondary compression of the sciatic nerve. An operation was scheduled because of the neuropathy and severe chronic radicular pain, and the patient was released.

At the time of the operation, the patient was placed in the lateral decubitus position and the piriformis muscle was exposed through a posterior gluteus-maximus-splitting approach. The piriformis muscle contained an osseous mass. The sciatic nerve was intimately associated with the mass, being severely flattened and compressed between it and the roof of the sciatic notch. The area of myositis ossificans of the piriformis muscle was excised as far proximally into the pelvis as possible to decompress the sciatic nerve. Postoperatively, the patient had immediate relief of the pain in the lower extremity but had some residual numbness of the left foot as well as a limp. Both the numbness and the limp resolved in four weeks.

Discussion

Introduction | Case Report | Discussion | References

Piriformis syndrome is usually a diagnosis of exclusion once the more common causes of sciatica have been ruled out²⁸. Yoeman³¹ is credited as being the first author to have described entrapment of the sciatic nerve by the piriformis muscle. Freiberg and Vinke^6,7 further defined the condition and described what is known as the Freiberg sign (pain caused by passive internal rotation of the extended thigh). Beaton and Anson¹ described four anatomical variations in the relationship between the piriformis muscle and the sciatic nerve and implicated these variations as a cause of compression and inflammation of the sciatic nerve. The term piriformis syndrome apparently was first used by Robinson²⁰, in 1947. He listed six cardinal features: (1) a history of trauma to the sacro-iliac and gluteal regions; (2) pain in the region of the sacro-iliac joint, greater sciatic notch, and piriformis muscle, extending down the lower limb and causing difficulty in walking; (3) acute exacerbation of the symptoms by lifting or stooping; (4) a palpable, sausage-shaped mass over the piriformis muscle, during an exacerbation of symptoms, that is markedly tender to pressure (this feature is pathognomonic of the syndrome); (5) a positive result on the straight-leg-raising test; and (6) gluteal atrophy, depending on the duration of symptoms²⁸.

A number of patients were referred to us between 1987 and 1994 with a presumptive diagnosis of piriformis syndrome. Many of these patients did not have the syndrome, were not candidates for an operation, or had symptoms that were too mild to warrant operative intervention. Eight patients, however, were managed with a release of the piriformis tendon and neurolysis of the sciatic nerve after the failure of non-operative treatment; although these patients are not the subject of the present report, they represent our experience in the operative treatment of piriformis syndrome. All eight patients had complete relief of the radicular pain after the procedure or by the time of the two-week postoperative visit. All were managed with postoperative physical therapy. Seven patients were involved in Workers' Compensation or other liability claims. Three patients continued to have some residual pain in the low back and the buttock. All eight patients had sustained an injury of the pelvic or buttock region (for example, as a result of falling on ice, falling from a truck, slipping on a dock, or falling down stairs) that had led to localized swelling and ecchymosis in the buttock. It has been postulated that trauma leads to swelling and inflammation of muscle, adhesions, and subsequent entrapment of the sciatic nerve.

The diagnosis often can be made on the basis of a careful clinical evaluation^{10,15,22,24,28}. Physical findings that suggest compression of the sciatic nerve by the piriformis muscle include tenderness over the sciatic notch, isolated atrophy of the gluteus maximus, dysesthesia of the posterior aspect of the thigh, and tenderness of the rectal wall with or without a sausage-shaped mass that is felt laterally during a rectal examination¹¹. Additional findings that are indicative of such compression include the Freiberg sign^6,7 (pain with forced internal rotation of the extended thigh) and the sign of Pace and Nagle¹⁵ (pain with resistance to abduction and external rotation of the thigh). The innervations of the gluteus medius, gluteus minimus, and tensor fasciae latae often are spared as the superior gluteal nerve branches proximal to the piriformis muscle. The tibial division of the sciatic nerve is involved less often than is the peroneal division because the former is located more medially in the sciatic notch^9,10,16. Hypoesthesia in the distribution of the posterior cutaneous nerve of the thigh may be present¹⁰. A positive Lasègue sign has also been reported to be a clinical feature of piriformis syndrome^{10,11,20,22,28}. In our experience, most patients who have piriformis syndrome secondary to trauma involving the buttock will have a positive Lasègue sign. Back pain is uncommon, non-specific, and not related to piriformis syndrome.

The diagnosis of piriformis syndrome may be confirmed by additional studies. Hughes et al.¹⁰ suggested that the syndrome should be confirmed by neurophysiological testing before an operation is perfomed. Nerve-conduction studies may demonstrate delayed F waves and H reflexes^{5,16,23,25,29}. Plain radiographs are usually normal. However, computerized axial tomography and magnetic resonance imaging have been reported to show hypertrophy of the piriformis muscle in some instances^3,11,16. In our experience, eight patients who ultimately had an operation for the treatment of piriformis syndrome had asymmetry (hypertrophy or atrophy) of the piriformis muscles on computerized axial tomography. Karl et al.¹³ reported that a bone scan demonstrated abnormal uptake in the soft tissues of the pelvis in a patient who had piriformis syndrome.

The treatment of piriformis syndrome has included the administration of non-steroidal anti-inflammatory agents^12,28, physical therapy and stretching¹², the injection of local anesthetics and of corticosteroids^{1,2,8,9,11,12,15,18-21,26,27,30}, transrectal massage²⁷, and ultrasound⁹. The efficacy of these modalities in relieving the syndrome when entrapment has been proved is not clear. Early decompression is indicated when entrapment with neurological findings is confirmed. Operative release of the piriformis muscle has been recommended for syndromes refractory to other modalities^{7,10,14,20,22,28}. The procedure entails sectioning of the piriformis tendon at its insertion into the posterior aspect of the greater trochanter and dissection of the tendon and muscle back into the greater sciatic notch to release any fibrous bands or compressing vessels. Special care must be taken to ensure that the sciatic nerve does not pass through a bifid or aberrant piriformis muscle. External neurolysis of the sciatic nerve also has been recommended²⁸. Operative release of the piriformis tendon has been effective for the relief of the symptoms of compression of the sciatic nerve^{7,10,14,20,22,28}. The indications for the operation in our patient were increasing pain and neurological deficits due to compression of the sciatic nerve between the bone of the greater sciatic notch and the ossified piriformis muscle. Postoperatively, our patient had complete relief of pain and full recovery from all neurological deficits.

References

Introduction | Case Report | Discussion | References

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