KOOS vs. KS-F after TKA
Page A1
Knee Society Function Score versus Knee Injury and Osteoarthritis Outcome Score after Total Knee Arthroplasty
Appendix A
Responsiveness characterizes the ability of a measure to change over a pre-specified time frame or as it relates to a corresponding change in a reference measure (i.e pre- and post-operation). Thus, when evaluating different outcome tools for responsiveness, the “bigger is better” rule applies. Highly responsive scales are preferred as fewer patients are needed to have high statistical power in clinical trials and smaller changes in outcomes can be detected more easily [3,6,7,16].
Responsiveness is widely measured using Standardized Response Mean (SRM), which is calculated as the mean change in scores divided by the standard deviation of the change in scores (SRM = mean(Δ scores)/SD(Δ scores)). A higher SRM indicates a more responsive outcome tool. The range of SRM for validated orthopedic instruments is 0.9-1.9 [9]. Newer studies have further stratified effect size, with 1.2-2.0 being a large effect, 2.0-4.0 very large, and greater than 4.0 “nearly perfect” [11].Pain response SRMs up to 0.5 have been seen in placebo groups. Large responses (SRMs ≥1.0) would be expected for surgical interventions such as a TKA[8].Because there is typically a large improvement in patient function after TKA, using an outcome tool that has a higher responsiveness allows for a more accurate comparison of outcome tools when evaluating different implants or surgical techniques. Responsiveness is designed to evaluate change and if a patient does not improve the evaluation of a tool’s responsiveness will be inaccurate [9], therefore patients who had scores that did not change or who had scores that decreased should be removed from the cohort when evaluating an outcome tool’s responsiveness.
The ceiling effect means that the variance in an independent variable is not measured or estimated above a certain level (i.e. the maximum possible score). If a ceiling effect is present in an outcome tool, a difference in outcomes between patients may not be able to be measured. If more than one-third of the patients achieve the top score after an intervention, either the intervention is extremely effective or the tool for measuring the intervention does not fully evaluate the patient’s outcome. Thus, an outcome tool that has one-third or more of the patients reaching the top score is undesirable [1].
Validity is the extent to which an outcome tool accurately measures the intended outcome (i.e. does the study scientifically answer the questions it intended to answer). The KS-F and KOOS have been validated to measure outcomes after TKA in several previous studies [5, 10, 12-14].The KOOS is also validated to measure outcomes after ACL reconstruction and cartilage repair [2, 4, 15], and has been used for evaluation in patients with tibial osteotomy and menisectomy as well [13].
KOOS vs. KS-F after TKA
Page A1
References
1.Barber-Westin SD, Noyes FR, McCloskey JW. Rigorous statistical reliability, validity, and responsiveness testing of the Cincinnati knee rating system in 350 subjects with uninjured, injured, or anterior cruciate ligament-reconstructed knees. Am J Sports Med. Jul-Aug 1999;27(4):402-416.
2.Bekkers JE, de Windt TS, Raijmakers NJ, Dhert WJ, Saris DB. Validation of the Knee Injury and Osteoarthritis Outcome Score (KOOS) for the treatment of focal cartilage lesions. Osteoarthritis Cartilage. Nov 2009;17(11):1434-1439.
3.Deyo RA, Centor RM. Assessing the responsiveness of functional scales to clinical change: an analogy to diagnostic test performance. J Chronic Dis. 1986;39(11):897-906.
4.Engelhart L, Nelson L, Lewis S, et al. Validation of the Knee Injury and Osteoarthritis Outcome Score subscales for patients with articular cartilage lesions of the knee. Am J Sports Med. Oct 2012;40(10):2264-2272.
5.Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res. Nov 1989(248):13-14.
6.Kazis LE, Anderson JJ, Meenan RF. Effect sizes for interpreting changes in health status. Med Care. Mar 1989;27(3 Suppl):S178-189.
7.Kreibich DN, Vaz M, Bourne RB, et al. What is the best way of assessing outcome after total knee replacement? Clin Orthop Relat Res. Oct 1996(331):221-225.
8.Liang MH, Fossel AH, Larson MG. Comparisons of five health status instruments for orthopedic evaluation. Med Care. Jul 1990;28(7):632-642.
9.Marx RG, Jones EC, Allen AA, et al. Reliability, validity, and responsiveness of four knee outcome scales for athletic patients. J Bone Joint Surg Am. Oct 2001;83-A(10):1459-1469.
10.Medalla GA, Moonot P, Peel T, Kalairajah Y, Field RE. Cost-benefit comparison of the Oxford Knee score and the American Knee Society score in measuring outcome of total knee arthroplasty. J Arthroplasty. Jun 2009;24(4):652-656.
11.Middel B, van Sonderen E. Statistical significant change versus relevant or important change in (quasi) experimental design: some conceptual and methodological problems in estimating magnitude of intervention-related change in health services research. Int J Integr Care. 2002;2:e15.
12.Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. Knee Injury and Osteoarthritis Outcome Score (KOOS)--development of a self-administered outcome measure. J Orthop Sports Phys Ther. Aug 1998;28(2):88-96.
13.Roos EM, Lohmander LS. The Knee injury and Osteoarthritis Outcome Score (KOOS): from joint injury to osteoarthritis. Health Qual Life Outcomes. 2003;1:64.
14.Roos EM, Toksvig-Larsen S. Knee injury and Osteoarthritis Outcome Score (KOOS) - validation and comparison to the WOMAC in total knee replacement. Health Qual Life Outcomes. 2003;1:17.
15.Salavati M, Akhbari B, Mohammadi F, Mazaheri M, Khorrami M. Knee injury and Osteoarthritis Outcome Score (KOOS); reliability and validity in competitive athletes after anterior cruciate ligament reconstruction. Osteoarthritis Cartilage. Apr 2011;19(4):406-410.
16.Wright JG, Young NL. A comparison of different indices of responsiveness. J Clin Epidemiol. Mar 1997;50(3):239-246.