Risk Factors for Nonunion After Lateral Locked Plating of Periprosthetic Distal Femur Fractures

OBJECTIVES: To determine the rate of and risk factors for reoperation to promote fracture union of periprosthetic distal femur fractures treated with lateral locked plating. METHODS: Design : Retrospective cohort study. Setting: Two Level 1 Trauma Centers. Patient Selection Criteria: Adult patients undergoing operative treatment for a periprosthetic distal femur fracture (OTA/AO 33A or 33C) between 2006 and 2023 with a minimum follow-up of 3 months. Outcome Measures and Comparisons: Reoperation to promote fracture union compared across patient, fracture, and treatment characteristics. RESULTS: 218 patients (mean age 72 years [range: 52–84], 77% female) were included. There were 133 (61%) Su type 2 fractures, 10 (4.6%) open injuries, and 118 (54%) fractures with multifragmentary comminution of the metaphysis. Twenty (9.2%) patients required reoperation to promote fracture union, including 15 (6.9%) patients who presented with nonunion with implant failure. In multivariable logistic regression analysis, BMI (5-point increase; OR: 1.37 [95% CI: 1.00–1.86], p = 0.047), multifragmentary metaphyseal comminution (OR: 5.17 [95% CI: 1.47–18.3], p = 0.011), and varus malalignment (OR: 5.88 [95% CI: 1.29–26.8], p = 0.023) were associated with increased odds of reoperation for nonunion; whereas the use of titanium plates was protective (OR: 0.21 [95% CI: 0.07–0.63], p = 0.005). CONCLUSIONS: In this study of 218 patients undergoing lateral locked plating for a periprosthetic distal femur fracture, 9 out of 10 patients did not undergo reoperation to promote fracture union. Factors associated with reoperation included increased BMI, the presence of multifragmentary metaphyseal comminution, and varus malalignment with a lateral distal femoral angle of ≥84 degrees. The use of titanium plates was associated with decreased odds of reoperation although this finding should be interpreted in the context of varying plate designs and configurations. These results may help delineate indications for the selection of specific fixation constructs when treating periprosthetic distal femur fractures.