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The minimal clinically important difference for Knee Society Clinical Rating System after total knee arthroplasty for primary osteoarthritis

  • Knee
  • Published:
Knee Surgery, Sports Traumatology, Arthroscopy Aims and scope

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Abstract

Purpose

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.

Level of evidence

IV.

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Acknowledgments

The authors would like to thank all the surgeons for giving the permission for the usage of their data, and the staff at Orthopaedic Diagnostic Centre for assisting in the collation of the data presented in this study.

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Authors and Affiliations

  1. Department of Orthopaedic Surgery, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore

    Wu Chean Lee & Seng Jin Yeo

  2. Program in Health Services and Systems Research, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore

    Yu Heng Kwan

  3. Centre of Quantitative Medicine, Office of Clinical Sciences, Duke-NUS Medical School, 8 College Road, Singapore, 169857, Singapore

    Yu Heng Kwan

  4. Department of Pharmacy, Khoo Teck Puat Hospital, 90 Yishun Central, Singapore, 768828, Singapore

    Yu Heng Kwan

  5. Orthopaedic Diagnostic Centre, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore

    Hwei Chi Chong

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  1. Wu Chean Lee
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Correspondence to Wu Chean Lee.

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Lee, W.C., Kwan, Y.H., Chong, H.C. et al. The minimal clinically important difference for Knee Society Clinical Rating System after total knee arthroplasty for primary osteoarthritis. Knee Surg Sports Traumatol Arthrosc 25, 3354–3359 (2017). https://doi.org/10.1007/s00167-016-4208-9

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