Clinimetric quality of the new 2011 Knee Society Score: High validity, low completion rate

The demands of the younger and more active current total knee arthroplasty (TKA) patients are not in line with the current outcome assessments. Therefore, new questionnaires are developed or adjusted, as with the popular 1989 Knee Society Score (KSS). This study is the first to investigate the clinimetric parameters of the patient-reported outcome measurement (PROM) part of the 2011 KSS.

Four-hundred-fifteen primary Dutch TKA patients were scored using the PROM part of the 2011 KSS. The scale is subdivided into an Objective (not evaluated), Satisfaction, Expectation and Function subscales.

Clinimetric quality was evaluated by response and completion rate, test–retest reliability (n = 29, intraclass correlation coefficient), internal consistency (n = 172, Cronbach’s alpha), construct validity (Pearson’s correlations with 1989 KSS (n = 75) and KOOS-PS (n = 139)) and responsiveness (n = 20, paired-samples t-test, effect sizes and floor and ceiling effects).

A response rate of 96% and completion rate of 43% were found. Reliability and internal consistency proved excellent with ICCs ≥ 0.79 and Cronbach’s alpha ≥ 0.76 for all subscales. Strong correlations were found between the Function subscales of the 2011 KSS and KOOS-PS (r = − 0.60 to − 0.83). All subscales improved significantly after intervention, with exception of Walking & Standing and Discretionary Activities. 23% reached the maximum score postoperatively in Walking & Standing, indicating a ceiling effect.

The 2011 KSS is a reliable, internal consistent, construct valid and responsive questionnaire to assess the outcome of the Dutch TKA patients. Optimizations (e.g. shortening the scale, simplified design) are recommended to increase the disappointing completion rate.

The 2011 KSS is a reliable, internal consistent, construct valid and responsive questionnaire to assess the outcome of the Dutch TKA patients.