Loss of hip motion in slipped capital femoral epiphysis: a calculation from the slipping angle and the slope.

Abstract

The range of hip motion in 128 hips of 108 patients was measured at an average of 32.7 years after slipping of the capital femoral epiphysis (SCFE). Only hips without signs of osteoarthrosis were selected for the study. The hips were divided into three groups depending on treatment (i.e., fixation in situ, no treatment, osteotomy) and compared with those of a group with no slipping (normal hip). The slipping angle (SA) between the basis of the epiphysis and the perpendicular to the anteversion plane on lateral radiographs and the slope (S) between the basis of the epiphysis and the perpendicular to the axis of the femur on anteroposterior (AP) radiographs were measured. The only significant loss of hip motion evident in comparison of normal hips and hips with previous SCFE, was loss of external rotation in hips treated with osteotomy. Hips with no treatment and hips treated with fixation in situ showed no significant loss of hip motion as compared with normal hips. The greatest loss of hip motion in hips treated with fixation in situ was loss of internal rotation (LIR), which can be calculated using the radiographs as sin LIR = sin SA * sin S. The average difference between clinically established and calculated LIR was 1.15 degrees. We conclude that the loss of hip motion after SCFE is slight and in most patients not clinically relevant. Therefore, early surgical intervention, e.g., femoral osteotomy, due to expected loss of hip motion cannot be justified.