Reliability of current classification systems for periprosthetic distal femur fractures

Introduction: This study aims to determine which Periprosthetic Distal Femur Fracture (PDFF) classifica-tion system is the most reliable. The secondary aim was to determine which classification system corre-lated most accurately with the surgical management recommended and delivered. Methods: Between 2011 and 2019, 83 patients with 83 PDFFs that extended to the femoral component of a total knee arthroplasty (TKA) were retrospectively identified from a trauma database. Minimum follow-up was 1 year. Age, BMI, time from TKA, operative management, and Nottingham Hip Fracture Scores were collected, and AP and lateral radiographs used to classify all fractures using seven established clas-sification systems by two observers blinded to management. In patients treated operatively ( n = 69), preoperative radiographs were reviewed by two surgeons with expertise in trauma and knee revision who recommended fixation or distal femoral replacement (DFR) requirement. Results: Mean age was 80.7 years (SD9.4) and 50 (84.7%) were female. PDFFs occurred at a mean 9.5 years (SD5.2) after primary TKA. Mean follow-up was 3.8 years (SD2.9). Management was fixation in 47, DFR in 22 and non-operative for 14. The Fakler classification demonstrated highest interobserver reliabil-ity (ICC = 0.948), followed by the Rorabeck (ICC = 0.903), UCS (ICC = 0.850) and Chen (ICC = 0.906). The Neer classification demonstrated weakest agreement (ICC = 0.633). Overall accuracy of predicting DFR require-ment (as determined by two experts) was highest for the Fakler system (83.9%). Compared with actual management delivered the Rorabeck system was most accurate (94.1%). Multivariate regression demon-strated that the ultimate need for DFR ( n = 22) was independently associated with medial comminution (HR 2.66 (1.12-6.35 95%CI), p = 0.027) and fractures distal to the anterior flange and posterior condyle of the femoral component (HR 2.45 (1.13-5.31), p = 0.024). Conclusion: The Fakler classification showed highest interobserver agreement and was most accurately predictive of the management recommended by two experts. No classification system accurately pre-dicted the fractures that required DFR, and none included medial comminution which was independently associated with DFR requirement. There remains a need for a PDFF classification system that reliably guides operative management of PDFFs. (c) 2022 Elsevier Ltd. All rights reserved.