Developmental dysplasia of the hip alters fracture patterns in femoral neck fractures.

Femoral neck fractures are commonly classified using Pauwels' system, which reflects fracture-line inclination and mechanical stability. However, anatomical factors influencing fracture configuration remain unclear. This multicenter prospective cohort study investigated whether pelvic morphology, particularly developmental dysplasia of the hip (DDH), is associated with variations in Pauwels classification. Between April and December 2023, 254 surgically treated femoral neck fractures from nine hospitals were analyzed. Radiological parameters, including center-edge angle, sharp angle, acetabular roof obliquity, acetabular version (AV), and acetabular and femoral head diameters, were measured. DDH was diagnosed using established radiographic criteria. Logistic regression analyses were performed to identify independent predictors of Pauwels type I and III fractures. DDH was present in 23.6% of patients and was significantly associated with a higher proportion of Pauwels type I fractures, whereas absence of DDH and reduced AV were associated with Pauwels type III fractures. Multivariate analysis confirmed DDH as an independent predictor of Pauwels type I fractures and decreased AV as an independent predictor of Pauwels type III fractures. These findings suggest that pelvic morphology, including mild dysplasia and acetabular retroversion, contributes to fracture configuration in femoral neck fractures and may provide insight into the biomechanical mechanisms underlying fracture patterns.