Achieving Validated Thresholds for Clinically Meaningful Change on the Knee Injury and Osteoarthritis Outcome Score After Total Knee Arthroplasty: Findings From a University-based Orthopaedic Tertiary Care Safety Net Practice

A lack of knowledge exists about which patient characteristics predict failure to meet validated thresholds for clinically meaningful change on the Knee Injury and Osteoarthritis Outcome Score (KOOS) after total knee arthroplasty (TKA). METHODS: A retrospective chart review was performed on patients who underwent primary TKA by a single surgeon between January 2013 and June 2018. Variables included demographics (age, sex, race, and insurance type), comorbidities, body mass index, and preoperative KOOS subscale scores. Multivariate logistic regression was performed to identify characteristics associated with failing to meet or exceed the minimal clinically important difference (MCID) and substantial clinical benefit (SCB) on each KOOS subscale 6 months after TKA. RESULTS: A total of 159 patients were included. At 6 months after TKA, approximately one-third of patients (21% to 32%) failed to meet or exceed the MCID and 27% to 39% failed to meet or exceed the SCB on all KOOS subscales. Better preoperative KOOS Symptoms, quality of life, and activities of daily living subscale scores were statistically significantly associated with failing to meet the MCID and SCB on each respective subscale. Demographics, comorbidities, and body mass index were not notable predictors of either outcome for any of the KOOS subscales. DISCUSSION: About one-third of TKA patients in this single-site, single-surgeon sample failed to achieve a clinically meaningful outcome, and up to 4 in 10 patients had a less-than-ideal outcome 6 months after surgery. Surgeons should take care to set realistic expectations for patients with the least severe knee problems before TKA because this subgroup is especially at a high risk of failing to achieve a satisfactory outcome.