Dear Editor:
Recently, Sgroi and coauthors4 published a study in the Orthopaedic Journal of Sports Medicine with the intent to “compare the capability of 3 commonly used knee assessment tools to measure the impact of meniscal tears on knee function and quality of life: the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the Knee injury and Osteoarthritis Outcome Score (KOOS), and the Western Ontario Meniscal Evaluation Tool (WOMET).”4 The authors concluded that the WOMET can be recommended for the evaluation of knee function and quality-of-life impairment of patients with meniscal tears.
The comparative analyses performed are based on total scores of the respective instruments, a procedure recommended against in the user guide accompanying the KOOS.3 Hence, the scoring method used in the study by Sgroi et al4 is not validated, and data cannot be interpreted as presented. As a consequence, the current article should be retracted, and data should be reanalyzed, reinterpreted, and published with validated scoring methods.
For the KOOS, the 5-subscale scores for pain, other symptoms, activities of daily living, sport and recreation function, and knee-related quality of life should be calculated and reported separately on a scale of 0 (worst) to 100 (best).3 Although calculating a total KOOS score is not recommended,3 a total KOOS score has been reported in many orthopaedic papers.4 The KOOS subscales hold from 4 to 17 items each, and summing all items across the subscales will give very different weights to the 5 subscales. As an example, 40% of the contribution to a total score would originate from items related to difficulty with activities of daily living. Reporting a total score threatens the validity of the KOOS for many patient groups, including younger individuals with knee injury, for whom function during sport and recreation and knee-related quality of life are subscales of greater relevance, and older subjects with knee osteoarthritis, for whom the pain subscale is of equal or greater relevance as compared with difficulty with function during daily activities.1,2
Ewa M. Roos, PhD
Odense, Denmark
Footnotes
One or more of the authors has declared the following potential conflict of interest or source of funding: E.M.R. is the developer of the KOOS, KOOS-Child, HOOS, HAGOS, FAOS, RAOS, and NOOS. These instruments were developed in an academic context and are freely available. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
References
- 1. Collins NJ, Prinsen CA, Christensen R, et al. Knee injury and Osteoarthritis Outcome Score (KOOS): systematic review and meta-analysis of measurement properties. Osteoarthritis Cartilage. 2016;24(8):1317–1329. [DOI] [PubMed] [Google Scholar]
- 2. Roos EM. 3 steps to improve reporting and interpretation of patient-reported outcome scores in orthopedic studies. Acta Orthop. 2018;89(1):1–2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3. Roos EM. KOOS user’s guide. http://www.koos.nu. Published 2012. Accessed January 31, 2018.
- 4. Sgroi M, Kocak S, Reichel H, Kappe T. Comparison of 3 knee-specific quality-of-life instruments for patients with meniscal tears. Orthop J Sports Med. 2018;6(1):2325967117750082. [DOI] [PMC free article] [PubMed] [Google Scholar]