Drehmann sign and femoro-acetabular impingement in SCFE.

BACKGROUND: Drehmann sign is a characteristic clinical feature in slipped capital femoral epiphysis (SCFE). The presence of SCFE indicates an anatomic change of the proximal femur, which induces obligatory hip external rotation with hip flexion. In contrast, a cam-type femoro-acetabular impingement (FAI) is well known as sequelae of SCFE. The purpose of this study was to clarify the relationship between Drehmann sign and radiologic FAI.

METHODS: We studied 92 hips of 80 SCFE patients who had been treated with in situ fixation. The occurrence rate of Drehmann sign was analyzed according to the degree of remodeling (the Jones classification) and the radiologic α-angle measured in each class at the final follow-up. At a mean 12.2 years after the final follow-up, the patients' present condition was clinically investigated with a questionnaire using a part of the Harris Hip Rating Scale (HHRS). In addition, 3-dimensional computed tomography analysis was performed to clarify the anatomic relationship between the femoral head and the acetabulum during testing for Drehmann sign.

RESULTS: Among the 92 hips in the study, 60 were well remodeled (Jones type A), 24 were type B, and 8 were type C, with 6.5 years of mean follow-up. The mean of the modified α-angles for the 3 groups (A, B, and C) were 61.8, 84.7, and 119.4, respectively (P < 0.05); 25%, 75%, and 100% of the hips in the 3 groups, respectively, exhibited Drehmann sign. The set of hips (n = 41) with a positive Drehmann sign had a mean α-angle of 85.6 versus 63.0 degrees for the set of hips (n = 51) with a negative Drehmann sign (P < 0.05). Seven (13.5%) of 52 patients responding to the questionnaire reported hip pain and/or limp in the positive Drehmann sign group, but no patient in the negative sign group complained of either. Three-dimensional computed tomography delineated FAI at 2 different positions during testing for Drehmann sign.

CONCLUSIONS: Drehmann sign is highly valuable for clinically evaluating the existence of FAI and for following up with observation or realignment to prevent early osteoarthritis.