Slipped capital femoral epiphysis is an important orthopaedic problem of early adolescence. Many hypotheses about its etiology have been proposed; still the underlying mechanisms are not clearly understood. The aim of our paper is to examine radiographic characteristics of hips at risk for slipped capital epiphysis.

Two groups of hips were compared: a group of 100 asymptomatic hips contralateral to the slipped ones and a group of 70 age- and gender-matched healthy hips. The hips contralateral to the slipped ones were assumed to have identical morphology to the preslip-page morphology of the slipped hips. In each hip the following radiographic parameters were measured: the inter-hip distance, the femoral neck length/width, the pelvic height, the pelvic width, the femoral head radius, the coordinates of the abductor muscles trochanteric attachment, the inclination of the femoral epiphyseal growth plate, the femoral neck-shaft angle and the Wiberg center-edge angle.

Subjects with hips at risk for slipping had significantly higher body weight (590 vs. 500 N; p < 0.001), larger diameter of the femoral neck (38.6 vs 37.3 mm; p = 0.027), higher (138.9 vs. 134.6 mm; p = 0.022) and wider pelvis (53.8 vs. 48.7 mm; p < 0.001) and more laterally placed abductor muscles trochanteric attachment. There were no significant differences in the inter-hip distance, the femoral head radius, the femoral neck length and the femoral neck-shaft angle angle. Hips contralateral to the slipped ones had a more vertically inclined physeal angle (55.4 vs. 63.2 degrees; p < 0.001) in comparison to the healthy hips. The Wiberg centre-edge angle of the hips contralateral to the slipped ones was on average 7% larger from the healthy group (34.7 vs. 32.2 degrees; p = 0.003).

Children with hips at risk for slipping had larger pelvices and femora with more vertically inclined femoral epiphyseal growth plate. In addition, one cannot overlook the significant difference in the body weight between the age- and gender-matched groups of our study, confirming previous findings on the role of body weight in SCFE. It is therefore possible that anatomical changes may be a downstream effect of bone remodelling caused by altered loading during growth and development. This may suggest that the predisposition of the hip to slipping occurs earlier in the patient’s lifetime and that targeted radiographic examinations in obese individuals could reveal changes in pelvic geometry even before adolescence. Considering the high rates of bilateral involvement, our results could be used to predict the need for preventive fixation of asymptomatic hips after the capital femoral epiphysis has slipped in the contralateral hip.

Background: Slipped capital femoral epiphysis (SCFE) is an important orthopaedic problem which emerges in early adolescence. Not clearly identified factors in the growth zone of proximal femur produce slip in which the femoral head remains in the acetabulum and femoral shaft rotates outwards and backwards. This occurs usually in one but occasionally in both hips. As we assumed that in Department of orthopaedic surgery in Ljubljana half of Slovenian adolescent population with SCFE was treated, we could calculate epidemiological data for SCFE for whole Slovenian population.

Patients and Methods: In retrospectively study we analysed patients treated operatively at Department of orthopaedic surgery in Ljubljana between 1.1.1970 and 31.12.2006. The data about sex, age and side of the slips were collected. We calculated average age at occurance, ratio boys to girls, and predominance of left or right side. For determination of SCFE incidence in Slovenia, we used the attack rate method which is the sum of annual incidences of SCFE in age interval when the slips occur calculated for each one-year group.

Results: There were 224 patients, 126 boys and 98 girls presenting with SCFE between 1970 and 2006 treated in Department of orthopaedic surgery in Ljubljana. The average age of boys was 12.9 and the age of girls 11.6 years (range: 8–16 years). On the average the age was 11.3 years. Slipped capital femoral epiphysis appeared more frequently on the left side (58%) than on the right side (31%). In 11% of cases the slips were bilateral. Incidence per 1000 adolescents extrapolated to Slovenian population (attack rate method) was 0,796 ‰ for boys, 0,667 ‰ for girls and 0,734 ‰ for entire endangered population. Yearly incidence of SCFE was thus 0,089 ‰ for boys and 0,073 ‰ for girls.

Discussion: Epidemiological data for SCFE in Slovenia are comparable to those found in Sweden and is difficult to compare with other countries, where different statistical methods were used. Risk of getting SCFE in critical period for boys is 1:1265 and for girls: 1:1499. Risk for whole critical population is 1:1362. It is interesting that our study showed marked increase in the number of boys with SCFE in recent years. Boys to girls ratio has changed from 1:1 in years 1970 to 1994 (Zupanc in sod. 2002) to 1,29:1 in our study.