Postoperative sagittal alignment and reoperation predict late outcomes after plate fixation of AO/OTA 33C distal femur fractures: a retrospective cohort study

Background: Intra-articular distal femoral fractures are associated with high complication rates and variable late outcomes. Although the AO Foundation/Orthopaedic Trauma Association (AO/OTA) classification system is useful for describing injury severity and anticipating complications, whether fracture subtype alone determines clinically relevant late outcomes remains unclear. This study aimed to evaluate postoperative complications and late outcomes following plate fixation of intra-articular distal femoral fractures and to identify factors independently associated with final clinical outcomes.Methods: This retrospective cohort study was conducted at a regional Level I trauma center. Patients with AO/OTA 33C intra-articular distal femoral fractures who underwent plate fixation and were followed for at least 12 months were included. Radiographic parameters reflecting coronal and sagittal alignment were assessed using standardized measurement methods. Postoperative complications and reoperation were recorded as intermediate events. Clinically relevant late outcomes included final knee range of motion (ROM), leg length discrepancy, and radiographic osteoarthritis severity, assessed as the difference in Kellgren-Lawrence grade. Multivariable linear regression analyses were performed to identify factors independently associated with late outcomes.Results: The 33C3 group (n=33) had significantly higher rates of open fracture (54.5%), nonunion (39.4%), and reoperation (45.5%) than the 33C1–2 group (n=49). At the final follow-up, 33C3 fractures were associated with lower mean ROM (P<0.001) and greater osteoarthritis progression (P<0.001). However, multivariable analysis showed that sagittal malalignment (Δ anatomical posterior distal femoral angle: β=−2.35, P=0.001) and reoperation (β=−17.5, P=0.001), rather than AO/OTA subtype itself, were independent predictors of final ROM.Conclusions: Although fracture subtype according to the AO/OTA classification was associated with predictable complication patterns, clinically relevant late outcomes following intra-articular distal femoral fractures were more closely associated with postoperative alignment quality and the treatment course than with fracture classification alone. These findings highlight the importance of optimizing radiographic alignment and preventing complications that lead to reoperation to improve long-term outcomes after plate fixation.Level of evidence: III.