The minimal clinically important difference for Knee Society Clinical Rating System after total knee arthroplasty for primary osteoarthritis.
OBJECTIVE
The Knee Society Clinical Rating System (KS) is one of the most popular tools used to assess patient outcome after total knee arthroplasty (TKA), but its minimal clinically important difference (MCID) has not been identified. This study aims to identify the MCID of KS function score (KS-FS) and knee score (KS-KS) after TKA in patients with primary knee osteoarthritis.


METHODS
The authors retrospectively analysed patients who underwent TKA for primary knee osteoarthritis between 2005 and 2015 in a single institution. KS-FS, KS-KS, and Oxford Knee Score (OKS) were collected pre-operatively and 2 years post-operatively. Patient satisfaction with TKA at 2 years was also collected. Anchor-based approach with 2 external indicators was used. The MCID for KS-FS and KS-KS was determined using simple linear regression according to patient satisfaction with TKA and the MCID of OKS.


RESULTS
The mean age of the 550 subjects studied was 66 ± 8 years. There were 373 (67.8 %) female subjects. The KS-FS improved by 22.8 (95 % CI 20.9-24.6) points, and the KS-KS improved by 44.4 (95 % CI 42.6-46.3) points. The MCID identified for KS-FS is between 6.1 (95 % CI 5.1-7.1) and 6.4 (95 % CI 4.4-8.4) and between 5.3 (95 % CI 4.3-6.3) and 5.9 (95 % CI 3.9-7.8) for KS-KS.


CONCLUSIONS
This is the first study, to the knowledge of the authors, to identify the MCID of KS. This will allow future trials to have an accurate prediction of sample size. Clinically, physicians will be able to better interpret outcomes of TKA studies to guide a treatment option.


METHODS
IV.
Department of Orthopaedic Surgery, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore. leewuchean@yahoo.com.
Wu Chean
http://orcid.org/0000-0002-7524-9404
WC
Lee
Program in Health Services and Systems Research, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore.|Centre of Quantitative Medicine, Office of Clinical Sciences, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore.|Department of Pharmacy, Khoo Teck Puat Hospital, 90 Yishun Central, Singapore, 768828, Singapore.
Yu Heng
YH
Kwan
Orthopaedic Diagnostic Centre, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
Hwei Chi
HC
Chong
Department of Orthopaedic Surgery, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
Seng Jin
SJ
Yeo
D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000534:rehabilitation*; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D000071081:Minimal Clinically Important Difference; D020370:Osteoarthritis, Knee / Q000601:surgery*; D017060:Patient Satisfaction; D012189:Retrospective Studies
Knee Society Clinical Rating System; Minimal clinical important difference; Total knee arthroplasty