Up to 40% of kids who experience a slipped capital femoral epiphysis (SCFE) in one hip develop a slip in the contralateral hip. Recent research in pediatric orthopaedics has attempted to identify risk factors for a second SCFE in patients who have had a first. A retrospective study by Maranho et al. in the February 6, 2019 issue of JBJS provides additional evidence about one particular risk factor.
The authors radiographically measured the epiphyseal tilt, epiphyseal extension ratio, alpha angle, and epiphyseal angle of the uninvolved, contralateral hip among 318 patients (mean age of 12.4 years) who presented for treatment of a unilateral SCFE between 2000 and 2017. After adjusting for triradiate cartilage status, Maranho et al. found that, over a minimum follow-up of 18 months:
- Increased posterior epiphyseal tilt was associated with an increased risk of contralateral SCFE, which corroborates recent findings. Specifically, an epiphyseal tilt of >10° corresponded to a 54% predicted probability of a contralateral slip in patients with open triradiate cartilage.
- Increased epiphyseal extension around the metaphysis in the superior plane had a protective effect against a contralateral SCFE. For each 0.01 increase in superior epiphyseal extension ratio, the odds of a contralateral slip decreased by 6%.
- The alpha angle and epiphyseal angle were not independently associated with a contralateral slip.
Clinically, the authors suggest that the tilt findings may be more useful than the extension-ratio findings, especially when it comes to the difficult decision around whether to perform prophylactic percutaneous pinning of the contralateral hip. They write that “prophylactic fixation may be discussed with the families of patients presenting with unilateral SCFE who have a tilt angle of >10°,” noting that this threshold “would result in a low proportion of patients undergoing unnecessary prophylactic pinning.” Maranho et al. are quick to add that even contralateral hips with epiphyseal tilt angles <10° are at risk of SCFE and should be closely monitored.