TO RUST OR TO MRUST? RELIABILITY OF RADIOLOGICAL HEALING EVALUATION IN PATIENTS WITH DISTAL FEMUR FRACTURES DURING THE COURSE OF RECOVERY

Definition of radiographic distal femur fracture union is heterogeneous, largely non-specific, and not standardized. The purpose of this study was to evaluate the interobserver and intraobserver reliability of the standard radiographic union score for tibial (RUST) and modified RUST (mRUST) for distal femoral fractures over multiple consecutive time points. A prospective cohort of 196 patients who sustained a distal femur fracture (OTA 33-A, B, C) and underwent open reduction and internal fixation with a plate (NCB Zimmer) as part of an international, multicentre, randomized controlled trial (“Far Cortical Locking Versus Standard Constructs for Distal Femur Fractures (FCL)”) were retrospectively reviewed by four fellowship-trained orthopaedic trauma surgeons. Radiographs at standardized intervals (6 weeks, 3 months, 6 months, and 12 months) were blinded for treatment, timepoint and subject IDand were presented to readers in random order during 2 sessions 3 months apart Agreement was measured by intraclass correlation coefficient (ICC) The inter-observer ICC for the mRUST was slightly higher than the standard RUST in distal femur fractures, and had consistent good agreement at every time point. Reliability improved over time from ICC 0.61 at 6 weeks to 0.73 at 12 months. The Intra-observer reliability was good to excellent for both scores at all time points, and all cortices (ICC 0.71–0.82). The least reliable components of the RUST and mRUST scores were early in recovery the lateral and anterior components as they were often obscured by the plate (6 week ICC, mRust lateral (0.37, 0.45) anterior 0.45, 0.50). For assessment of healing in distal femur fractures, mRUST is more reliable throughout the first year of recovery, although neither functions optimally at time point critical for clinical decision making (6 weeks and 3 months). Lateral plates limit the reproducibility of specific cortical measurements, as such alterations in interpretation of scores may be warranted.