Summary

Of three short form versions of the KOOS that are currently available (KOOS-12, KOOS-Global and KOOS-ACL) KOOS-Global is the preferred measure to detect changes beyond the initial return to sport phase following ACL reconstruction.

Abstract

Background

The Knee injury and Osteoarthritis Outcome Score (KOOS) is a commonly used patient reported outcome measure following anterior cruciate ligament (ACL) reconstruction surgery. To minimize responder burden various short forms of the KOOS are now available, however they have not been extensively used following ACL reconstruction.

Purpose

To compare a variety of KOOS short forms with each other and determine their responsiveness in patients who have undergone ACL reconstruction surgery.

Methods

In part A, the KOOS was administered between 2 and 6 years (mean 3 years) following ACL reconstruction surgery to a cohort of 832 (489M, 343F) patients. From the full KOOS the following three short form versions were calculated: KOOS-12 Short form, KOOS-Global and KOOS-ACL. Descriptive statistics were calculated for all three measures and associations between them were explored using nonparametric (Spearman rho) correlations. Floor or ceiling effects were considered present if >15% of patients reported the worst (floor effect) or best (ceiling effect) possible score. In part B, the KOOS and a measure of overall knee function were administered at both 2- and 5-years following ACL reconstruction surgery to a cohort of 276 (149M, 127F) patients. The same 3 short forms were derived, and responsiveness was assessed using several distribution and anchor-based methods. From distribution statistics, the standardized response mean (SRM) and smallest detectable change (SDC) score was calculated. Using the anchor-based method, the minimally important change (MIC) score that was associated with an improvement in knee function was determined using receiver operating characteristic (ROC) analysis.

Results

Ceiling effects were present for all KOOS short form versions. They were only marginally above threshold for the KOOS-12 and KOOS-Global (both 16%) but clearly above for the KOOS-ACL (26%). KOOS-12 and KOOS-Global were very highly correlated (rho = 0.98). The correlation between both these short forms and KOOS-ACL was also substantial (rho = 0.9). Only KOOS-Global scores significantly increased over time, whereas KOOS-12 and KOOS-ACL did not change. The increase in KOOS-Global was associated with a small (0.2-0.3) SRM. MIC scores ranged from 3.2 to 5.2 points, and for all measures MIC scores were larger than the SDC score at a group level. KOOS-Global was the only measure for which the mean difference between the two assessments exceeded both the SDC (group level) and MIC.

Conclusion

Of the three short form versions of the KOOS that are currently available there was little to differentiate between KOOS-Global and KOOS-12, and both had superior psychometric properties compared to KOOS-ACL when used at a single timepoint 2-6 years following ACL reconstruction surgery. However, KOOS-Global had the greatest responsiveness to change between 2- and 5-years post ACL reconstruction surgery. It would therefore be the preferred measure to detect changes beyond the initial return to sport phase following ACL reconstruction.