Individual items versus summary scores in comparing patient outcomes among different types of total hip and knee arthroplasty designs

Purpose This study aimed to evaluate the discriminative ability of summary scores and individual items in comparing patient reported outcomes (PROs) across two total hip arthroplasty (THA) and two total knee arthroplasty (TKA) designs. Methods Primary elective THAs and TKAs performed between January 2012 and June 2022 from the Geneva Arthroplasty Registry were included. Two cup-stem combinations in THA and two prostheses with different stability designs in TKA were compared using WOMAC Pain and Function summary scores and individual items one year after surgery. Linear and ordinal logistic regression models were used to compare the ability of summary scores and items in differentiating between prostheses. Results A total of 773 THA and 624 TKA patients were included. Overall, differences between prostheses were detected using either WOMAC summary scores or items. Nevertheless, analyses revealed variability in the discriminative ability of WOMAC summary scores and items, with variations depending on the population. Additionally, in both THA and TKA, differences between prostheses were larger in the function domain than in the pain domain. Conclusion PRO summary scores are valuable for evaluating and comparing prostheses performance in THA and TKA. In addition, individual items may, in certain contexts, provide enhanced sensitivity to identify implant-related differences and offer a more detailed understanding of these differences.