Association Between Body Weight and Clinical Characteristics of Slipped Capital Femoral Epiphysis in Switzerland: A 21-Year Single-Centre Retrospective Analysis (2005-2025)

Background: Epidemiological patterns vary across populations and treatment centres worldwide, with obesity consistently reported as the main risk factor. The primary aim of this study was to characterise age- and sex-adjusted body mass index (BMI) z-scores in children with slipped capital femoral epiphysis (SCFE) treated in Bern, as well as to investigate their association with clinical characteristics. A secondary aim was to compare the observed characteristics with those reported internationally. Methods: This is a single-centre, retrospective cohort study conducted at the Department of Pediatric Surgery, University Children's Hospital, Inselspital, University of Bern, and included patients under the age of 18 who were treated for SCFE between 2005 and 2025. Demographic, clinical, and anthropometric data were collected for all patients, including sex, age at the time of surgery, slip severity using the Southwick angle, intraoperative slip stability, symptom duration, as classified by Fahey/O'Brien, affected side of the hip, as well as height and weight at the time of surgery. The primary outcome was the age- and sex-adjusted BMI z-score at the time of surgery. Analyses stratified by sex, age, and slip severity were prespecified as secondary analyses. All other subgroup analyses were exploratory and hypothesis-generating. Results: The final cohort included 90 males (69.23%) and 40 females (30.77%). BMI data were available for 114 of the 130 patients. Two-thirds of the patients (62.3%) were overweight or obese. The median BMI z-score was 1.43 (interquartile range 0.72-2.19; mean 1.31 ± 1.11) and was significantly higher than the expected reference value of 0 (p < 0.001). There was no statistically significant difference in BMI z-scores between females and males (p = 0.288). A statistically significant association was observed between age at surgery and BMI z-score. Higher age at surgery was associated with lower BMI z-scores (p = 0.007). There was a trend towards lower BMI z-scores with increasing slip severity. However, this difference did not reach statistical significance (p = 0.158). In an exploratory, hypothesis-generating analysis, patients with stable slips had significantly higher BMI z-scores than those with unstable slips (p = 0.008). This association persisted after adjustment for age and after correction for multiple testing (p_adj = 0.032). A further exploratory, hypothesis-generating analysis showed that BMI z-scores also differed significantly across symptom duration, as classified by Fahey/O'Brien (p = 0.026). The lowest values were observed in the acute-on-chronic group. However, these differences just missed the threshold for statistical significance after adjustment for age and after correction for multiple testing (p_adj = 0.052). Conclusions: In Switzerland, children diagnosed with SCFE had a significantly higher BMI compared to the reference population. Our study revealed that two-thirds of the children were classified as overweight or obese, with obesity being approximately ten times more prevalent among this group compared to the overall Swiss paediatric population. A higher relative body weight was found to be independently associated with a younger age at surgery, consistent with obesity accelerating skeletal maturation and advancing the manifestation of SCFE. We identified a trend towards lower BMI z-scores with increasing slip severity; however, this finding did not reach statistical significance. Consequently, elevated body weight should be regarded as a marker of predisposition and earlier disease onset rather than of slip severity. Childhood obesity prevention may be relevant to SCFE prevention in Switzerland.