Background Case-mix adjustment is an established method to take account of variations across cohorts in baseline patient factors, when comparing health outcomes. Although commonplace, there is a lack of evidence as to the most appropriate case-mix adjustment model to use to enable fair comparisons of PROM data in musculoskeletal services. Objectives To conduct a systematic review summarising evidence of the development, validation, and performance of musculoskeletal case-mix adjustment models, and to make recommendations for future methods. Data Sources Searches included; AMED, CINAHL, EMBASE, HMIC, MEDLINE, and grey literature. Eligibility Criteria Studies; from January 1992-May 2017, English language, musculoskeletal adult population, developing or validating a case-mix adjustment model, using a relevant PROM, and using patient factors feasible for clinical collection. Data Synthesis Two reviewers evaluated selected papers. The CASP Cohort Tool was used to assess quality. Results Fourteen studies were included; eight US studies on the Focus on Therapeutic Outcomes model (pooled n = 546,726 patients (with pre/post treatment data)) and six UK studies related to the UK National PROMs Programme model (pooled n = 282,424 patients (with pre/post treatment data)). The majority used retrospective data, restricted to complete datasets. Both US and UK models showed good predictive ability (R2 18-42%). Common model variables were; baseline PROM score, age, sex, comorbidities, symptom duration, and surgical history. Reduced quality scores were mainly due to acceptability of patient recruitment, and completeness and length of patient follow up. Conclusion Significant methodological crossover was found. Further studies are however needed to externally validate and develop models across musculoskeletal settings. (C) 2018 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.
