Radiographic Union Assessment in Surgically Treated Distal Femur Fractures: A Systematic Review

Background: Distal femur fractures are known to have challenging nonunion rates. Despite various available treatment methods aimed to improve union, optimal interventions are yet to be determined. Importantly, there remains no standard agreement on what defines radiographic union. Although various proposed criteria of defining radiographic union exist in the literature, there is no clear consensus on which criteria provide the most precise measurement. The use of inconsistent measures of fracture healing between studies can be problematic and limits their generalizability. Therefore, this systematic review aims to identify how fracture union is defined based on radiographic parameters for surgically treated distal femur fractures in current literature. Methods: In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, Medline, EMBASE, Cochrane Central Register of Controlled Trials, and Web of Science Core Collection databases were searched from inception to October 2022. Studies that addressed surgically treated distal femur fractures with reported radiographic union assessment were included. Outcomes extracted included radiographic definition of union; any testing of validity, reliability, or responsiveness; reported union rate; reported time to fracture union; and any functional outcomes correlated with radiographic union. Results: Sixty articles with 3,050 operatively treated distal femur fractures were included. Operative interventions included lateral locked plate (42 studies), intramedullary nail (15 studies), dynamic condylar screw or blade plate (7 studies), dual plate or plate and nail construct (5 studies), distal anterior-posterior/posterior-anterior screws (1 study), and external fixation with a circular frame (1 study). The range of mean follow-up time reported was 4.3 to 44 months. The most common definitions of fracture union included "bridging or callus formation across 3 of 4 cortices" in 26 (43%) studies, "bony bridging of cortices" in 21 (35%) studies, and "complete bridging of cortices" in 9 (15%) studies. Two studies included additional assessment of radiographic union using the Radiographic Union Scale in Tibial fracture (RUST) or modified Radiographic Union Scale in Tibial fracture (mRUST) scores. One study included description of validity, and the other study included reliability testing. The reported mean union rate of distal femur fractures was 89% (range 58%-100%). The mean time to fracture union was documented in 49 studies and found to be 18 weeks (range 12-36 weeks) in 2,441 cases. No studies reported correlations between functional outcomes and radiographic parameters. Conclusion: The current literature evaluating surgically treated distal femur fractures lacks consistent definition of radiographic fracture union, and the appropriate time point to make this judgement is unclear. To advance surgical optimization, it is necessary that future research uses validated, reliable, and continuous measures of radiographic bone healing and correlation with functional outcomes.