Biomechanical analysis of single- versus double-screw fixation in slipped capital femoral epiphysis at physiological load levels.

Slipped capital femoral epiphyses in 12 pairs of bovine femora were pinned with a single screw on one side and two screws on the other. The specimens were subjected to physiological shear loads across the epiphysis (100 cycles at 1.1 Hz; 400 N for slow walking, and 900 N for fast walking). The rates of creep were decreased 23% with double screws compared to single screws at slow walking, and 30% at fast walking; this was not statistically significant. Single-screw fixation in slipped epiphyses is thus recommended, because the small gains in resistance to cyclic creep at physiological loading were not statistically different, and did not offset the increased risks of complications with multiple screws.