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Post Traumatic Myositis Ossificans of The Iliacus Muscle
J Jagiasi, H Argekar, PD Samant, CJ Thakkar, AB Goregaonkar
A case of traumatic myositis ossificans of the iliopsoas muscle in 30 year old farmer is presented. A history of fall from a tree one year ago with blunt trauma to the region of the left hip in addition to the radiographic appearance of calcification were indicative of ectopic bone formation. The lesion was explored surgically to excise the tumour. Histological examination demonstrated the zoning effect of myositis ossificans with patterns varying from a cellular central zone to a peripheral one of fairly well oriented bone. The patient remained symptom-free and no radiographic evidence of recurrence was observed one year postoperatively.

A thirty year old male farmer presented with restricted left hip movements since one year. Patient had a history of fall from tree following which he was treated by a local bonesetter with massage. He started walking within a week and complained of restricted range of movements within a month. He was unable to squat to sit cross-legged. His stiffness gradually increased over six-month period and at the time of presentation he had an immobile hip.

On Examination
Left lower limb was in an attitude of external rotation. Wasting of the left quadriceps and calf muscles. No obvious swelling seen in iliac fossa or the femoral triangle. Palpation revealed a well localized bony swelling in the left femoral triangle extending below the inguinal ligament into the iliac fossa. There was no rise in temperature over the swelling, no tenderness. The mass was fixed to underlying bone and was about 15 cms X 6 cms X bone deep below the femoral vessels and nerve. Left hip had a ten degree flexion rotation deformity and a fifteen degree external rotation deformity. No further movement at the hip. Ipsilateral knee contralateral hip and knee were normal in all respects.

X-ray pelvis with both hips (Figs. 1 and 2) showed calcification of the iliacus muscle. This was confirmed on CT scan (Figs. 3,4). Alkaline phosphatase was normal. All other haematological investigations were within normal range. Needle biopsy was unsuccessful.

Surgical excision of the mass was done through a Smith Peterson’s approach. Adequate mass of bone was resected so as to get a full range of movement intraoperatively (Figs. 5 and 6). Histopathology of the excised tissue confirmed myositis ossificans. Indwelling epidural catheter was kept for 1 week post op. Patient was put on continuous passive movements under epidural analgesia immediately post op. Patient was given indomethacin 100 mg per day for six weeks. Patient regained ninety degree of left hip flexion and thirty degree of rotations at the end of two months and was able to squat and sit cross-legged at the end of one year.

Heterotopic bone formation was first described in 1692 when Guy Patin described myositis ossificans progressiva in children.1 Descriptions of HO in children have been described following ilio-psoas release11-13, and femoral osteotomy,10 spinal cord injury,4 and spinal fusion4,12 in recent literature. Heterotopic ossification (HO) is the formation of lamellar bone (which may mature with time) where bone does not usually form in soft tissues. Myositis ossificans is a condition in which HO occurs in muscles and other soft tissue.14 There are three types of myositis ossificans circumscripta, myositis ossificans progressiva, and localized traumatic myositis ossificans.17 Ectopic calcification is mineralization of soft tissue structures usually due to physical or chemical trauma such as calcific tendonitis-histologically the deposits are not bone forming.4 Aetiologies of HO include trauma, neurogenic, and myositis ossificans progressiva. Traumatic aetiologies include after spinal fusions, total hip arthroplasty, ORIF of acetabular fractures, soft tissue releases about the hips and burns. Myositis ossificans progressiva is a rare autosomal dominant disease, which begins in early infancy which initially, involves the muscles of the back, neck, and shoulders and then progresses to immobilize the patient in early life.4 Pathophysiology of HO is unclear. Histologic studies of heterotopic bone reveal the percentage of osteoblasts is typically double that of normal bone indicating that the bone being formed is metabolically active.14 One distinguishing feature is that the new bone and mature bone lacks periosteum.15 Heterotopic bone is often diffuse and does not always follow anatomic planes of tissue. Bone morphogenic protein is a potential inducer of undifferentiated mesenchymal cells, which are precursors of cartilage and bone forming elements. It has been theorized that BMP may induce inappropriate differentiation of pluripotential cells, mesenchymal cells or fibroblasts into osteoprogenitor cells.5

Evaluation of a patient includes an adequate physical exam. The initial clinical finding is decreased range of motion. There may be localized tissue hyperaemia, swelling and tenderness to palpation. Initial onset is usually 4-16 weeks but ranges from two to fifty-two weeks.14 Differential diagnosis is infection,14,9 tumour, thrombophlebitis14,9 reflex sympathetic dystrophy, and many patients will have multiple and complex problems.14 Traumatic type of HO is found near focus of trauma. Radiographic findings of HO on plain films is evident at 4-6 weeks, usually trabeculation is absent. Payne and DeLuca10 define HO in soft tissues as radiodensity 5 mm from the femoral shaft and not initially adjacent to the femur which is periosteal callus and HO is usually a flocculent pattern. Computed tomography can differentiate native vs. ectopic bone by revealing the osseous architecture.14 Computed tomography may also be useful in planning surgical approach. Magnetic resonance imaging can demonstrate soft tissue swelling but receives only limited signal from calcified tissue.14 Ultrasound has been shown to detect HO earlier than plain radiographs in eight consecutive patients by Thomas and Amstutz.17

Surgical treatment should not be considered until the HO has matured. Many researchers feel that six months after initial trauma (without neural injuries) that HO can be resected. It should not be resected until it is considered mature bone.13 Surgery is usually delayed at least one year, but should be performed at 1.5 to 2 years in young males with anklyosis or near ankylosis of the hip, radiographic evidence of progression of HO longer than six months, greater than moderate amounts of HO.

Myositis of the iliacus muscle is relatively rare and presenting symptom is ankylosis of hip. On excision of the myositis mass the patient can get a functional range of hip movement. Before excision, the possibility of a tumour should be kept in mind and a CT scan, biopsy and haematological investigations should be done.

We thank the Dean, LTMGH and the Head of Department of Orthopaedics, LTMGH, Sion Hospital for giving us permission to publish the above data.

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