What Are the Substantial Clinical Benefit Thresholds for KOOS Pain, Physical Function, and Joint Replacement Scores After Primary TKA?
Khaled A. Elmenawi, Ignacio Pasqualini, Shujaa T. Khan, Matthew J. Hadad, , Nicolas S. PiuzziBackground
The Centers for Medicare & Medicaid Services (CMS) have mandated the collection of patient-reported outcome measures (PROMs) for inpatient TKA with a submission deadline of September 2025. Not achieving a 20-point improvement in substantial clinical benefit (SCB) on the Knee Injury and Osteoarthritis Outcome Score (KOOS) for joint replacement (JR) will negatively impact hospital reimbursement. However, SCB thresholds for KOOS subscales and factors associated with not achieving SCB remain poorly defined.
Questions/purposes
We retrospectively analyzed a large TKA database at a multisite tertiary healthcare system and asked: (1) What are the SCB thresholds for the KOOS pain, physical function short form (PS), and JR subscales at 1 year after primary TKA? (2) What patient factors are associated with failure to achieve the SCB on these KOOS subscales?
Methods
This was a retrospective analysis of a longitudinally maintained institutional registry, which evaluated the results of 15,638 patients who underwent primary TKA from 2016 to 2022. Of these, 89% (13,850) of patients completed baseline PROMs, and 79% (10,988 of 13,850) of patients completed 1-year follow-up; data from those patients were used in this analysis. Demographics, comorbidities, as well as baseline and 1-year KOOS scores were recorded. The median (IQR) age of these patients was 67 years (61 to 73), 60% (6615 of 10,988) of patients were women, and the median (IQR) BMI was 31.0 kg/m 2 (27.2 to 35.5). The SCB thresholds were calculated using anchor-based methodology, utilizing item 8 from the Veterans RAND 12-Item Health Survey at 1 year postoperatively as an anchor question: “Compared to one year ago, how would you rate your physical health in general now?” The optimal threshold, defined as the value that maximized the Youden index, was used as the SCB threshold to distinguish patients who had substantially improved in terms of end point versus those who had not. Multivariable logistic regression identified factors that were associated with not achieving the SCB. It should be noted that race was identified by self-report and grouped as White and non-White per our database.
Results
The SCB thresholds were 33 of 100 for KOOS pain (sensitivity 0.80, specificity 0.53, area under the receiver operating characteristic curve [AUC] 0.72), 16 of 100 for KOOS PS (sensitivity 0.82, specificity 0.47, AUC 0.69), and 23 of 100 for KOOS JR (sensitivity 0.82, specificity 0.51, AUC 0.72), achieved by 59% (6483) of patients for each subscale. For KOOS pain, factors associated with not achieving the SCB included older age (OR 0.84 [95% confidence interval (CI) 0.78 to 0.9]; p < 0.001), non-White race compared with White race (OR 1.7 [95% CI 1.59 to 1.93]; p < 0.001), a higher Charlson comorbidity index (CCI) (OR 1.11 [95% CI 1.05 to 1.17]; p < 0.001), and commercial insurance (OR 0.80 [95% CI 0.72 to 0.89]; p < 0.001). For KOOS PS, factors associated with not achieving the SCB included older age (OR 0.82 [95% CI 0.76 to 0.89]; p < 0.001), non-White race (OR 1.82 [95% CI 1.59 to 2.1]; p < 0.001), a higher CCI (OR 1.08 [95% CI 1.02 to 1.15]; p < 0.01), commercial insurance (OR 0.77 [95% CI 0.68 to 0.87]; p < 0.001), and lower education level (OR 0.89 [95% CI 0.83 to 0.96]; p < 0.01). For KOOS JR, factors associated with not achieving the SCB included older age (OR 0.84 [95% CI 0.78 to 0.90]; p < 0.001), non-White race (OR 1.77 [95% CI 1.56 to 2.01]; p < 0.001), a higher CCI (OR 1.07 [95% CI 1.01 to 1.12]; p = 0.01), commercial insurance (OR 0.8 [95% CI 0.72 to 0.90]; p < 0.001), and lower education level (OR 0.92 [95% CI 0.86 to 0.98]; p < 0.01).
Conclusion
As TKA outcomes are increasingly judged by achievement of the 20-point SCB threshold on the KOOS JR under new CMS policies, determining SCB thresholds is of utmost importance. This study found SCB thresholds of 33 for KOOS pain, 16 for KOOS PS, and 23 for KOOS JR, with only 59% (6483) of patients achieving these thresholds 1 year after TKA. More at-risk populations, including older, non-White, less educated, and patients with medically complex conditions, were at higher risk of not achieving the SCB. These results suggest that SCB nonattainment after TKA is likely found in a meaningful subset of patients—especially those with greater baseline symptom burden and medical complexity. These findings can guide perioperative support to increase the likelihood that all patients achieve the reduction in pain and improvement in function that they seek from arthroplasty, as healthcare systems prepare for the implementation of the new PROM policy for TKA from the CMS.
Level of Evidence
Level III, Therapeutic study.