Pin placement in slipped capital femoral epiphysis.

Standard radiographs taken at right angles to each other during the pinning of a slipped capital femoral epiphysis may not demonstrate pins protruding into the joint. In this study roentgenograms of 110 patients (148 hips) with slipped capital femoral epiphyses were analysed by a three-dimensional mathematical model of the femoral head and pin position. A computer was used to determine the spatial distance between the tip of the pin and the subchondral bone of the femoral head. Pin protrusion was found in 41 hips. In 22, protrusion was sufficient to have transgressed the joint space. Pin protrusion did not, however, appear to increase the risk of chondrolysis.