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Introduction: To describe a case series of congenital metacarpal synostosis treated with longitudinal osteotomy and bone graft substitute interposition and propose a reproducible method of measuring deformity on plain radiographs.

Materials & Methods: We retrospectively reviewed charts of all patients with metacarpal synostosis treated with a longitudinal osteotomy and bone graft substitute interposition at 2 institutions. Radiographic and clinical appearance was analyzed at initial diagnosis, intra-operatively, and at last follow-up. For the ring-small metacarpal synostosis, the amount of abduction of the small finger proximal phalanx was measured with respect to the longitudinal axis of the third metacarpal. For middle-ring finger metacarpal involvement, the amount of deformity between the affected digits was calculated by measuring the angle between the longitudinal axis of both proximal phalanges. The goal for correction in this type of deformity was to have the 2 proximal phalanges lie parallel to each other.

Results: A total of 10 patients (14 hands) met the inclusion criteria. Six patients (8 hands) demonstrated ring-small metacarpal synostosis while 4 patients (6 hands) had a middle-ring metacarpal synostosis. The median age at operation was 5 years (range 2 – 16). Follow-up ranged from 1 to 14 years (average 3 years). Associated hand anomalies included polydactyly, symbrachydactyly, and clinodactyly.

Pre-operatively, the small finger proximal phalanx was angulated away from the middle metacarpal on average 46º (range 26º-60º), and angulation between middle and ring digits averaged 43º (range 26º-50º). Postoperative correction at 1 year was statistically significant (P< 0.05) for both ring-small metacarpal synostosis, average 23º (range 10º-30º) and middle-ring metacarpal synostosis, average 16º (range 5º-44º). Recurrence of digital abduction was evident in 2 patients who both had middle-ring finger metacarpal synostosis.

Conclusions: Congenital metacarpal synostosis may be effectively treated with a longitudinal osteotomy, realignment of component metacarpals, and interposition of bone graft substitute. In the most common form the ring and small finger metacarpals are associated with abduction of the small finger in an awkward position. Use of the described technique is safe and effective, yet concerns regarding mild persistent angulation and risk of recurrence remain. We recommend obtaining plain radiographs with all fingers maximally adducted, in order to provide more accurate measurements. When the procedure is performed at a young age, we recommend follow-up until skeletal maturity to identify recurrence of the deformity.