The relation of the distal femoral physis and the medial patellofemoral ligament

Purpose The purpose of this study was to analyse true lateral radiographs of children and adolescents to determine the relation of the origin of the MPFL and the distal femoral physis considering the complex anatomy of the physis. The hypothesis was that the femoral insertion of the MPFL is distal to the growth plate. Methods Antero-posterior and true lateral radiographs from PACS computer records of 27 patients with a history of patellofemoral instability were assessed. To determine the femoral origin of the MPFL, the method by Scho¨ ttle et al. and the method by Redfern et al. were applied independently. On the anteroposterior radiograph, the distance between the medial most part of the physis and the central part of the physis was measured to quantify the concave curvature of the physis. To cross-reference the femoral insertion of the MPFL onto an ap view, the projected MPFL origin–physis distance was subtracted from the distance between the most medial part of the physis and the central part of the physis. Results The projected median origin of the MPFL as measured on a lateral radiograph was located 3.2 mm (1.2–5.8 mm) proximal to the physis. The median distance between the most medial part of the physis and the physeal line on the anteroposterior radiograph was 9.9 mm (4.1–12.0 mm). Subtracting the two measured values, the median origin of the MPFL as seen on the ap view was 6.4 mm (2.9–8.5 mm) distal to the femoral physis. Conclusion Considering the concave curvature of the distal femoral physis, it can be assumed that the femoral insertion of the MPFL is distal to the femoral physis. As a too proximal insertion of the graft can cause unintentional tightening of the MPFL in knee flexion, these results have to be considered when performing reconstruction of the MPFL in children and adolescents with open growth plates. Levels of evidence Diagnostic study, Level II.