The reliability and validity of the Unified Classification System of periprosthetic femoral fractures after hip arthroplasty

The Unified Classification System has expanded and updated the Vancouver Classification System and applied treatment principles to all periprosthetic fractures. This study assessed the reliability and validity of the Unified Classification System for femur fractures after hip arthroplasty. Thirty-eight radiographs were finally evaluated by 6 observers, 3 consultants and 3 trainees. Each observer read the radiographs on 2 separate occasions, independently, at least 2 weeks apart. Interobserver and intraobserver agreement and validity were analyzed, using weightedκ statistics. The mean κ value for interobserver agreement was found to be 0.849 (0.838-0.871) for consultants (almost perfect agreement) and 0.761 (0.707-0.836) for the trainees (substantial agreement). Intraobserver κvalues ranged from 0.740 to 0.903, showing substantial to almost perfect agreement. Validity analysis of 23 type B cases revealed 79.710% agreement within B1, B2, and B3 subgroups with a mean κ value of 0.694 (0.670-0.741)（substantial agreement）