Torsional strength of double- versus single-screw fixation in a pig model of unstable slipped capital femoral epiphysis.

Slipped capital femoral epiphysis was produced in 9 matched pairs of fresh-frozen pig femurs (1-year-old pigs) by twisting the femoral head about the femoral neck axis. Each matched pair was fixed with a single steel cannulated screw on one side and 2 screws contralaterally, after which the perichondrium was removed before retesting. Double-screw fixation without the perichondrium provided 43% of the stiffness and 74% of the strength of the intact physis in torsion and approximately double the stiffness and strength of single-screw fixation (P<0.004). This information may be of use to the surgeon concerned about rotational stability in unstable slipped capital femoral epiphysis.