The Terrible Triad as a Predictor of Nonunion in Distal Femur Fractures Treated With Lateral Locking Plates: A Retrospective Cohort Study

OBJECTIVES: To identify risk factors for nonunion in distal femur fractures (DFFs) treated with lateral locking plates (LLPs). METHODS: Design : Retrospective cohort study Setting: Single Level I Trauma Center Patient Selection Criteria: Adult patients with OTA/AO 33A and 33C DFFs treated with LLPs between 2014 and 2019 were included. Outcome Measures and Comparisons: Nonunion, defined as the need for a subsequent surgical procedure to promote bone healing, was assessed in relation to patient demographics, comorbidities, injury, and fixation characteristics. RESULTS: A total of 298 patients (75.5% male; mean age 43.1 ± 13.7 years) were included. Among these, 166 fractures were classified as OTA/AO type 33A and 132 fractures as type 33C. Open fractures were present in 47.7%, and 72.1% had comminuted fractures. Nonunion occurred at 19.1% (57/298). No significant differences in age, sex, BMI, smoking, or diabetes were observed between union and nonunion groups. Multivariable analysis identified open fracture (OR 3.25; 95% CI 2.10–5.02; p < 0.001), comminution (OR 2.85; 95% CI 1.89–4.31; p < 0.001), and medial void >1 cm (OR 4.50; 95% CI 2.80–7.30; p < 0.001) as independent predictors. Fixation characteristics, including plate material, length, screw configuration, and alignment, were not associated with nonunion. A post hoc composite variable, the “Terrible Triad,” combining open fracture, comminution, and medial void >1 cm, was associated with a 36.7% nonunion rate compared to 5.9% without the triad (p < 0.001) and remained an independent predictor (OR 6.5; 95% CI 3.3–12.9; p < 0.001). CONCLUSIONS: The distal femur fracture “Terrible Triad” (open fracture, comminution, and medial void >1 cm) was a strong independent predictor of nonunion after lateral locked plating. Lateral locked plating fixation characteristics of were not significantly associated with nonunion. Early recognition and targeted management of triad features may improve healing outcomes. LEVEL OF EVIDENCE: Prognostic Level III.