Symphalangism is a congenital hand anomaly where there is a longitudinal failure of bony differentiation. There is cartilaginous or bony fusion - synostosis - usually at the proximal interphalangeal joint (PIPJ) but sometimes at the distal interphalangeal joint or metacarpophalangeal joint. It is associated with symbrachydactyly, Apert's and Poland's Syndrome.
Pathologically, the joint may be replaced by bone or a spacer of solid cartilage.
Clinical features include stiff, slender and possibly short digits and an absence of normal flexion joint flexure creases. The digit is usually extended at the PIPJ. If the digits are short as well as stiff, this is described as brachysymphalangism.
Radiographically, the joint may appear normal due to the cartilaginous bar being radiolucent. However, with age the cartilage ossifies and anklyosis results.
The treatment of symphalangism is frustrating. Usually, splinting and physiotherapy have uniformly poor outcomes. Associated syndactyly may require a soft tissue release. Arthrodesis can be considered in an adult or chondrodesis is a child to preserve the growth plate.
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