New Risk Factors Discovered for Slipped Capital Femoral Epiphysis
In this study, mechanical factors affecting slipped capital femoral epiphysis (SCFE) are investigated. SCFE is a condition that affects the hip in teenagers between the ages of 12 and 16 most often. In this condition, the growth center of the hip (the capital femoral epiphysis) actually slips backwards on the top of the femur (the thighbone).
What causes this and why it only affects some children is unknown. It's likely that there are endocrine, genetic, and mechanical factors. The effect of shear stress on SCFE is the subject of this study. The authors used X-rays of normal hips (control group) and compared them to hips with SCFE. They also looked at the opposite (uninvolved) hip in patients with SCFE.
A mathematical model was used to measure hip stress and force. The formula took into consideration the muscle attachment points around the hip and the interhip distance. The peak shear stress in the epiphyseal (growth) plate of the femoral neck was also measured. Body weight was taken into consideration.
They found that children with SCFE were much heavier in body weight than those in the control group. Hip shear stress was higher in both hips of children with SCFE compared with normal hips. The epiphyseal growth plate of the femoral neck in children with SCFE was more vertical in orientation than in the control group. This position was decidedly a risk factor for SCFE.
The shape of the pelvis and femoral heads helped normalize the hip stress at peak contact. But the added body weight negated the benefit of those anatomic differences. It appears that slipped hips and uninvolved hips in the same child have the same geometry. Based on anatomy and mechanics involved, if one hip slipped, the risk of the second one slipping is much greater than if the uninvolved hip had a more normal shape. The elevated shear stress is a risk factor for SCFE.
References: Oskar Zupanc, MD, PhD, et al. Shear Stress in Epiphyseal Growth Plate is a Risk Factor for Slipped Capital Femoral Epiphysis. In Journal of Pediatric Orthopaedics. June 2008. Vol. 28. No. 4. Pp. 444-451.
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