Revision Surgery Is the Most Common Definition of Failure in Studies Evaluating Knee Cartilage Restoration Outcomes: A Systematic Review.

Purpose: To assess the definitions of "failure" of knee chondral restoration surgery in the current literature and to provide a recommendation on what should define failure. Methods: By use of Preferred Reporting Items for Systematic Reviews and Meta-analyses criteria, a systematic search of the PubMed, Embase, Ovid, and Cochrane Library databases was conducted to identify studies published between January 1, 2017, and May 1, 2021. The inclusion criteria consisted of studies containing patients who underwent knee cartilage surgery that included a definition of failure. We excluded animal studies; articles comparing alternative medical treatments, such as rehabilitation, anti-inflammatory medications, and physical therapy; studies enrolling patients with diseases other than those of the knee, and non-English-language studies. Failure data were extracted and categorized as surgical, graft related, or based on patient-reported outcomes (PROs). This information was analyzed to develop a recommendation for a standardized definition of failure of knee cartilage restoration. Results: A total of 61 studies met the inclusion criteria. The most common definition of knee chondral restoration failure was the need for any revision surgery (52 of 61 studies, 85.3%), with failure rates ranging from 3.22% to 75%. Graft failure, defined as delamination and/or graft inadequacy (39 of 61, 63.9%), with failure rates ranging from 2.10% to 47%, and conversion to knee arthroplasty (34 of 61, 55.7%) were also used as definitions. Failure to return to sport and/or regular activity (4 of 61, 6.6%), presence of symptoms (21 of 61, 34.4%), removal of graft or implant (14 of 61, 22.9%), and other unclassified follow-up revisions (8 of 61, 13.1%) were additional definitions of failure documented. Subjective PROs were used in 54.1% of the studies (33 of 61), with failure rates ranging from 3.45% to 59%. Conclusions: A variety of definitions of failure are used to evaluate knee chondral restorative surgery outcomes in the orthopaedic literature. Any unplanned revision surgery and graft failure, defined as delamination and/or graft inadequacy, were the most common criteria defining knee chondral restoration failure. Patients' functionality and quality of life, determined by PROs, were also used to define knee chondral restoration failure in multiple studies. Higher rates of failure were observed after knee chondral restorative procedures when using multiple definitions of failure that were more inclusive. To account for heterogeneity in definitions, procedures, and patient circumstances, we recommend using multiple outcomes, including unplanned surgical procedures, PROs, and the ability to return to the desired level of function, as factors to define failure. Level of Evidence: Level IV, systematic review of Level II to IV studies.