One-year Oxford knee scores should be used in preference to 6-month scores when assessing the outcome of total knee arthroplasty

N D Clement,D Macdonald,N Ng,C E H Scott,C R Howie

doi:10.1186/s43019-020-00060-5

N D Clement, D Macdonald + Show 3 more

Open Access

https://doi.org/10.1186/s43019-020-00060-5

Copy DOI

Abstract

PurposeThe primary aim of this study was to assess whether there was a clinically significant difference in the mean Oxford knee score (OKS) between 6 and 12 months after total knee arthroplasty (TKA). The secondary aim was to identify variables associated with a clinically significant change in the OKS between 6 and 12 months.MethodsA retrospective cohort study was undertaken using an established arthroplasty database of 1574 primary TKA procedures. Patient demographics, body mass index (BMI), comorbidities, OKS and EuroQoL 5-domain (EQ-5D) score were collected preoperatively and at 6 and 12 months postoperatively. A clinically significant change in the OKS was defined as 5 points or more.ResultsThere was a 1.1-point increase in the OKS between 6 and 12 months postoperatively, which was statistically significant (95% confidence (CI) 0.8–1.3, p < 0.0001). There were 381 (24.2%) patients who had a clinically significant improvement in their OKS from 6 to 12 months. After adjusting for confounding, patients with a lower BMI (p = 0.028), without diabetes mellitus (p < 0.001), a better preoperative OKS (p < 0.001) or a worse 6-month OKS (p < 0.001) were more likely to have a clinically significant improvement. A 6-month OKS < 36 points was a reliable predictor of a clinically significant improvement in the 6-month to 12-month OKS (area under the curve 0.73, 95% CI 0.70–0.75, p < 0.001).ConclusionOverall, there was no clinically significant change in the OKS from 6 to 12 months; however, a clinically significant improvement was observed in approximately a quarter of patients and was more likely in those scoring less than 36 points at 6 months. Level of evidence: retrospective diagnostic study, level III.

Highlights

Patient reported outcome measures (PROMs) are valuable tools that are commonly used to assess the outcome of total knee arthroplasty (TKA) [1]
Patients excluded were slightly younger (70.3 versus 69.1 years, difference 1.2, 95% confidence intervals (CI) 0.5–1.9, p = 0.002), but there was no difference in gender (p = 0.13) or body mass index (BMI) (p = 0.18)
The mean preoperative Oxford knee score (OKS) was 21.3 (SD 7.8), which by 6 months postoperatively had increased to a mean of 35.2 (SD 9.0); the 13.9point improvement was significant (95% confidence interval (CI) 13.4–14.4, p < 0.0001 paired t test)

Summary

Introduction

Patient reported outcome measures (PROMs) are valuable tools that are commonly used to assess the outcome of total knee arthroplasty (TKA) [1]. The Oxford knee score (OKS) [2] is a joint-specific PROM and is the outcome measure of choice in England and Wales to evaluate the functional outcome of TKA [3]. The OKS is a validated assessment tool and has been shown to be reliable, reproducible and capable of measuring a clinical change after TKA [2, 4]. There may be a 2-point improvement in the OKS from 6 to 12 months after TKA, it is not known whether this is statistically and clinically significant or which patients are more likely to experience OKS improvement

Objectives

Methods

Results

Discussion

Conclusion