Surgical excision of heterotopic ossification of hip in a rare case of Moyamoya disease with extra articular ankylosis
A 27-year-old girl presented to us with ankylosis of the left hip following an acute onset of left-sided hemiplegia 9 months back. She had an angiogram of the cerebral blood vessels and she was diagnosed to have Moyamoya disease []. She had an indirect bypass procedure called encephalo-duro-arterio-myo-synangiosis which involves transposition of a segment of a scalp artery to supply the surface of the brain to improve collateral blood flow. The patient gradually recovered motor power but had difficulty in walking and sitting with mild spasticity of the left upper and lower limbs. On presentation, her left hip was ankylosed in 20° of external rotation, neutral abduction, and 10° flexion. Ectopic bone was palpable anterior to the left hip. There was no local warmth. Her alkaline phosphatase level was normal and radiograph showed HO in the iliopsoas muscles, extending from the ilium to the lesser trochanter with cortical delineation implying maturity []. Hip joint appeared normal. 3D CT scan of the hip and pelvis demonstrated that the mass was extra articular, lying anterior to the hip and also its proximal and distal extension [].\nSurgical excision was planned to restore hip joint motion as the mass was fully mature and the patient had good neurological recovery. The heterotopic bone was exposed through the anterior iliofemoral approach. The femoral neurovascular bundle was situated just medial to the mass and there was a risk of injury to the femoral nerve, femoral artery, or the profunda femoris artery. Dissection was done subperiosteally with careful medial dissection and minimal medial retraction. The mass was exposed from the level of lesser trochanter inferiorly to the level of the anterior inferior iliac spine superiorly. But it was extending into the iliac fossa along the iliopsoas muscle plane []. Anterior wedge resection was done with an osteotome after making multiple drill holes proximally and distally, and the hip joint capsule could be identified by gently rotating the hip []. Usually the capsule is uninvolved and there is a layer of tissue separating the hip joint from the mass []. A part of anterior wall of acetabulum was broken during the excision of the proximal part of the mass and this was fixed with a cancellous screw []. After excision of the heterotopic bone, the hip moved easily from 0° to 90° of flexion. The wound was closed over large suction drain.\nPostoperatively, the patient was mobilized nonweight bearing initially with the help of a walking aid because of the acetabular wall fracture and was on above knee skin traction as there was mild spasticity of the muscles and a detachable derotation boot for 4 weeks to prevent external rotation. She was allowed to sit up and the hip was gently mobilized with continuous passive motion machine to prevent stiffness of the hip. She was prescribed oral indomethacin 25 mg TID for 3 months. At 5 years followup, the patient is now able to drive a two wheeler, sit on the floor, and there is no evidence of recurrence of the HO []. The flexion in the hip is from 0° to 110° [].