Radiographic assessment of bone remodelling inslippedupper femoral epiphyses using Kleins line and the α angle of femoral-acetabular impingement

Background: Bone remodelling in patients with earlier slipped upper femoral epiphysis (SUFE) has been shown to have a generally positive effect on both clinical and radiologic parameters. This study aims to further assess the effect of bone remodelling on the femoral head-neck relationship in SUFE patients, with the aid of 2 radiographic measurements not earlier used for this assessment. Methods: A retrospective review of radiographs was performed on all patients surgically managed for SUFE at a tertiary institution between 2000 and 2006. The postoperative and the most recent review radiographs were used for analysis. Alpha angles of Notzli (generally used to measure cam-type femoral-acetabular impingement) and displacement from Kleins line were measured as markers of femoral head-neck relationship. Results: A total of 59 hips were evaluated with a median mean follow-up time of 17.7 months. Patients had mild-to-moderate SUFE. The postoperative α angle mean reduced by 17.7 degrees (95% confidence interval: 13.6-21.8, P<0.001) at follow up. The displacement from Kleins line improved by a mean of 4.8 mm (95% confidence interval: 3.9-5.8 mm, P<0.001), over the review period. Conclusions: The femoral head-neck relationship, measured by both the Notzli α angle and the displacement from Kleins line, becomes significantly closer to normal after in situ pinning of mild-to-moderate SUFE, compatible with favorable bone remodelling. Both of these indices show promise for use in prospective study and standardized clinical follow up of patients with SUFE, and could be especially useful in assessing for future femoral-acetabular impingement. Level of evidence: III.