Abnormal mechanical stress due to excessive femoral torsion is associated with dysplasia of the distal femoral epiphyseal plate and trochlea.

Aims: The distal femoral epiphysis and epiphyseal plate are essential for skeletal morphogenesis during development. However, it is unclear how these growth mechanisms are affected by distal femoral torsion (DFT) and patellar instability. This study aimed to investigate how DFT development affects epiphyseal plate growth mechanisms. Methods: This study evaluated CT-based 3D reconstructed images of the distal femoral epiphyseal plates in 98 knees exhibiting trochlear dysplasia (50 patients). Morphological parameters including femoral anteversion, DFT, and the anatomical epicondylar axis-posterior condylar line (AEA-PCL) angle were measured to determine their relationship with epiphyseal plate development. Finite element modelling was then performed to evaluate how patellar displacement and distal femoral rotation influence epiphyseal stress in juvenile knees. A rat model that had undergone femoral rotational osteotomy was established (n = 12), and trochlear morphology (groove angle and depth) and trabecular microarchitecture (bone volume fraction, thickness, number, and separation) were compared with control specimens by micro-CT analysis at skeletal maturity. Results: Underdeveloped medial femoral epiphyseal plates were associated with excessive DFT and a large AEA-PCL angle. The medial-to-lateral epiphyseal plate ratio was inversely correlated with DFT and the AEA-PCL angle, suggesting mechanical influences on growth plate morphology. Finite element analysis revealed that medial patellar displacement and femoral external rotation decreased overall epiphyseal stress and shifted its distribution medially. Compared with control specimens, the experimental rats had significantly increased trochlear angles accompanied by reduced trochlear depth and subchondral bone loss in the medial femoral condyles and anterior medial epiphyses. Conclusion: DFT alters stress distribution across the epiphysis and epiphyseal plate, which modifies the trabecular microarchitecture in both medial femoral condyles and anterior medial epiphyses, and results in different medial-to-lateral ratio of the distal femoral epiphyseal plate which indicates the severity of trochlear dysplasia, although genetic investigations are needed to establish its causality.