Evidence for the validity of a patient-based instrument for assessment of outcome after revision knee arthroplasty

Journal article

Aims: To estimate the measurement properties for the Oxford Knee Score (OKS) in patients undergoing revision knee arthroplasty (responsiveness, minimal detectable change (MDC-90), minimal important change (MIC), minimal important difference (MID), internal consistency, construct validity, and interpretability).

Methods: Secondary data analysis was performed for 10,727 patients undergoing revision knee arthroplasty between 2013 to 2019 using a UK national patient-reported outcome measure (PROM) dataset. Outcome data were collected before revision and at six months postoperatively, using the OKS and EuroQol five-dimension score (EQ-5D). Measurement properties were assessed according to COnsensus-based Standards for the selection of health status Measurement Instruments (COSMIN) guidelines.

Results: A total of 9,219 patients had complete outcome data. Mean preoperative OKS was 16.7 points (SD 8.1), mean postoperative OKS 29.1 (SD 11.4), and mean change in OKS + 12.5 (SD 10.7). Median preoperative EQ-5D index was 0.260 (interquartile range (IQR) 0.055 to 0.691), median postoperative EQ-5D index 0.691 (IQR 0.516 to 0.796), and median change in EQ-5D index + 0.240 (IQR 0.000 to 0.567). Internal consistency was good with Cronbach’s α 0.88 (baseline) and 0.94 (post-revision). Construct validity found a high correlation of OKS total score with EQ-5D index (r = 0.76 (baseline), r = 0.83 (post-revision), p < 0.001). The OKS was responsive with standardized effect size (SES) 1.54 (95% confidence interval (CI) 1.51 to 1.57), compared to SES 0.83 (0.81 to 0.86) for the EQ-5D index. The MIC for the OKS was 7.5 points (95% CI 5.5 to 8.5) based on the optimal cut-off with specificity 0.72, sensitivity 0.60, and area under the curve 0.66. The MID for the OKS was 5.2 points. The MDC-90 was 3.9 points. The OKS did not demonstrate significant floor or ceiling effects.

Conclusion: This study found that the OKS was a useful and valid instrument for assessment of outcome following revision knee arthroplasty. The OKS was responsive to change and demonstrated good measurement properties.

Authors: Sabah, SA; Alvand, A; Beard, DJ; Price, AJ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: British Editorial Society of Bone and Joint Surgery
• Journal: Bone and Joint Journal
• Volume: 103-B
• Issue: 4
• Pages: 627-634
• Publication date: 2021-04-01
• Acceptance date: 2020-11-03
• DOI: 10.1302/0301-620x.103b4.bjj-2020-1560.r1
• EISSN: 2049-4408
• ISSN: 2049-4394
• Pmid: 33789485
• Language: English
• Keywords: reoperation; FFR; replacement; arthroplasty; quality of life; knee; Patient Reported Outcome Measures; osteoarthritis