Validation of the KOOS, JR: A Short-form Knee Arthroplasty Outcomes Survey

Background Medicare is rapidly moving toward using patient-reported outcome measures (PROMs) for outcomes assessment and justification of orthopaedic and other procedures. Numerous measures have been developed to study knee osteoarthritis (OA); however, many of these surveys are long, disruptive to clinic flow, and result in incomplete data capture and/or low followup rates. The Knee injury and Osteoarthritis Outcome (KOOS) physical function short-form (KOOS-PS), while shorter, ignores pain, which is a primary concern of patients with advanced knee OA.

Questions/purposes Our objective was to derive and validate a short-form survey focused on the patient with end-stage knee OA undergoing TKA.

Methods Using our hospital’s knee replacement registry, we retrospectively identified 2291 patients with knee OA who underwent primary unilateral TKA and had completed preoperative and 2-year postoperative PROMs. We assessed 30 items from the 42-item KOOS that were quantitatively most difficult for patients to perform before TKA and qualitatively most relevant to patients with end-stage knee OA. Rasch analysis identified the KOOS, JR, a seven-item instrument, representing a single dimension, which we define as “knee health” because it reflects aspects of pain, symptom severity, and activities of daily living (ADL) including movements or activities that are directly relevant and difficult for patients with advanced knee OA. We assessed the internal consistency, external validity (versus KOOS and WOMAC domains), responsiveness, and floor and ceiling effects of the KOOS, JR. External validation was performed using calculated KOOS, JR scores in collaboration with a nationally representative joint replacement registry, the Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement (FORCE-TJR).

Results Internal consistency for the KOOS, JR was high (Person Separation Index, 0.84; and 0.85 [FORCE]), external validity against other validated knee surveys was excellent (Spearman correlation coefficient, ρ 0.54-0.91), particularly for the KOOS pain (ρ 0.89 [95% CI, 0.88-0.91] Hospital for Special Surgery [HSS]; and 0.91 [95% CI, 0.90-0.93] [FORCE]) and KOOS ADL (ρ 0.87 [95% CI, 0.85-0.88] [HSS]; and 0.84 [95% CI, 0.81-0.87] [FORCE]). The KOOS, JR responsiveness (standardized response means, 1.79 [95% CI, 1.70-1.88] [HSS]; and 1.70 [95% CI, 1.54-1.86] [FORCE]) was high and floor 0.4-1.2%) and ceiling (18.8-21.8%) effects were favorable.

Conclusions The new short knee PROM, the KOOS, JR, provides a single score representing “knee health” as it combines pain, symptoms, and functional limitations in a single score. This short-form PROM is patient-relevant and efficient.

Level of Evidence Level III, diagnostic study.