Epiphyseal distraction for bony bridges: a biomechanical and morphologic study.

Partial physeal bridges were produced by resecting part of the lower femoral physis in 8-week-old rabbits. After 4 weeks, an external fixator, strain-gauged to measure distraction forces, was applied across the physis. Distraction was performed for 15 days: 1.0 mm/day medially and 0.5 mm/day laterally. Weekly radiographs were obtained. Animals were killed at 0, 3, and 6 weeks after distraction. Characteristic force patterns were evident if the bridge fractured. Medial fixator forces just before bridge fracture were very high (mean 89 N, SD 28 N), although forces in the lateral fixator were low (mean 25 N, SD 15 N). All animals killed 3 and 6 weeks after distraction ceased showed complete physeal closure. Results suggest that distraction epiphysiolysis may have high potential for producing premature physeal fusion.