With an aging population and increase in total knee arthroplasty, periprosthetic distal femur fractures (PDFFs) have increased. The differences between these fractures and native distal femur fractures (NDFF) have not been comprehensively investigated. The purpose of this study was to compare the demographic, fracture, and treatment details of PDFFs compared to NDFFs. A retrospective study of patients ≥ 18 years old who underwent surgical treatment for either a NDFF or a PDFF from 2010 to 2020 at a level 1 trauma center was performed. Demographics, AO/OTA fracture classification, quality of reduction, fixation constructs, and unplanned revision reoperation were compared between PDFF patients and NDFF patients using t-test and Fisher's exact test. 209 patients were identified with 70 patients having a PDFF and 139 patients having a NDFF. Of note, 48% of NDFF had a concomitant fracture of the ipsilateral knee (14%) or tibial plateau (15%). The most common AO/OTA classification for PDFFs was 33A3.3 (71%). NDFFs had two main AO/OTA classifications of 33C2.2 (28%) or 33A3.2. (25%). When controlling for patient age, bone quality, fracture classification, and fixation, the PDFF group had increased revision reoperation rate compared to NDFF (P < 0.05). PDFFs tend to occur in elderly patients with low bone quality, have complete metaphyseal comminution, and be isolated; whereas, NDFF tend to occur in younger patients, have less metaphyseal comminution, and be associated with other fractures. When controlling for variables, PDFF are at increased risk of unplanned revision reoperation. Surgeons should be aware of these increased risks in PDFFs and future research should focus on these unique fracture characteristics to improve outcomes

Introduction. Distal femur fractures around a total knee arthroplasty (TKA) are a growing problem for orthopaedic surgeons. The purpose of this study was to identify risks of reoperation for nonunion following open reduction and internal fixation of TKA periprosthetic distal femur fractures (PDFF). Method. Patients with PDFF (AO 33A-C[VB1, C1, D1], Su types 1-3) managed operatively with open reduction and internal fixation (ORIF) were retrospectively reviewed. Exclusion criteria were acute management with a distal femur replacement, less than 6 months of follow-up, and lack of injury or follow-up radiographs. The primary outcome measure was reoperation to achieve bony union. Comparisons were made between cases that did and did not require a reoperation to achieve union. Univariate analysis was used to identify factors to be analyzed in multivariate analysis to determine independent risk factors for the primary outcome. Result. A total of 77 patients met inclusion criteria. Union rate was 69/77 (89.6%). There were no differences between the groups for age, sex, BMI, comorbidities, Su classification, open injury, or mechanism of injury. Multivariate analysis identified risks for nonunion including post-operative malalignment (OR 1.41; CI 1.20-1.64; p<0.001), notching pre-operatively (OR 1.22; CI 1.04-1.42; p=0.012), presence of screws through fracture line (OR 1.28; CI 1.17-1.39; p<0.001), plate length <12 holes (OR 1.16; CI 1.02-1.33; p=0.024) and screw density greater than 0.4 (OR 2.18; CI 1.25-3.78; p=0.006). Conclusion. The reoperation rate to promote union was 10.4%. The study identified post-operative malalignment, notching pre-operatively, presence of screws through fracture line, plate length <12 holes, and proximal screw density greater than 40% as independent risk factors for nonunion