BIOMECHANICAL COMPARISON OF 1-SCREW AND 2-DIVERGENT PIN INTERNAL FIXATIONS FOR TREATMENT OF SLIPPED CAPITAL FEMORAL EPIPHYSIS, USING SPECIMENS OBTAINED FROM IMMATURE DOGS

Biomechanical strength and stiffness of 2 fixation treatments used to repair acute slipped capital femoral epiphysis were evaluated in bone specimens from immature dogs. A servohydraulic testing machine was use d to create slipped capital femoral epiphysis in 7 pairs of femurs by shearing the capital femoral epiphysis along the physis in a craniocau dal direction. The slip was reduced and repaired with one 3.5-mm-diame ter screw placed in lag fashion or 2 double-pointed, 1.6-mm (0.062 inc h)-diameter smooth pins and retested. Strength and stiffness of each i ntact femur (which served as the control) and repaired femur were comp ared. Results of the study indicated that the failure strength of 2-pi n fixation was significantly (P < 0.05) weaker than its control and th e 1-screw fixation. There was no significant difference between failur e strength of the 1-screw fixation and its control. The stiffness of 1 -screw and 2-pin fixations was not significantly different, compared w ith each other, but was significantly (P < 0.05) less, compared with t heir respective controls.