Remodelling After Percutaneous Pinning for Slipped Capital Femoral Epiphysis: The Influence of Transphyseal Screw Position

<b>Introduction:</b> Slipped capital femoral epiphysis (SCFE) is commonly treated using percutaneous in situ fixation. After screw fixation, remodelling of the proximal femur can occur; however, the factors influencing this process are poorly understood. This study aimed to measure the amount of remodelling after in situ SCFE fixation and determine the influence of the transphyseal screw position across the physis. <b>Methods:</b> In this retrospective study, all eligible patients with SCFE who had percutaneous screw fixation at Erasmus MC-Sophia Children's Hospital between 2012 and 2020 were included. The amount of remodelling was determined by measuring the Southwick angle, alpha angle and displacement from Klein's line directly after screw fixation and at final follow-up. Transphyseal screw position was measured through AP and frog-leg lateral radiographs by measuring the placement of the centre of the screw in relation to the centre of the epiphysis. A linear mixed model was used to determine factors influencing the amount of remodelling. <b>Results:</b> 86 patients with 96 affected hips were included; the mean age was 12.4 (±2.0) years at surgery, and the mean follow-up duration was 3.7 (±2.0) years. All measurements showed significant remodelling at follow-up compared to baseline. Over the follow-up period, the mean change in Southwick angle was 4.6° (95% CI: 2.5; 6.7, <i>p</i> < 0.001), the mean change in Alpha angle was 10.4° (95% CI: 7.3; 13.5, <i>p</i> < 0.001) and the mean change in displacement from Klein's line was -1.2 mm (95% CI: -1.7; -0.61, <i>p</i> < 0.001). Linear mixed model analyses showed that remodelling was significantly correlated with deformity at baseline for all measurements. Also, a more lateral screw position was significantly correlated with more improvement in displacement from Klein's line (estimate: -4.2, 95% CI: -8.0 to -0.5). However, the effect observed was relatively small. <b>Conclusions:</b> A statistically significant amount of remodelling was measured after percutaneous screw fixation for patients with SCFE. The amount of remodelling was relatively limited, but was shown to be influenced by the severity of the initial slip and a more lateral transphyseal screw position.