There is no clinically important difference in the Oxford knee scores between one and two years after total knee arthroplasty: The one-year score could be used as the benchmark timepoint to assess outcome.
BACKGROUND
The aim was to assess the whether there was a clinically important change in the Oxford knee score (OKS) between one and two years after total knee arthroplasty (TKA), and to identify predictors associated with a clinically important change.


METHODS
A retrospective cohort study was undertaken using an established arthroplasty database of 5857 primary TKA. Patient demographics, body mass index, social deprivation, OKS and EuroQoL five-domain (EQ-5D) score were collected preoperatively and at one and two years postoperatively. A clinically important change in the OKS was defined as ≥5 points.


RESULTS
There was a 0.2 point increase in the OKS between one and two years, which was statistically significant (95% confidence interval (CI) 0.1 to 0.4, p < .0001), but not clinically important. A better preoperative OKS (p < .001) and in contrast a worse one year OKS (p < .001) were independently associated with a greater improvement from one to two years. There were 1006 (17.3%) patients that had a clinically important improvement in the OKS between one and two years. Receiver operating characteristic curve analysis showed that a one year OKS of less than 35 was a reliable predictor of a clinically important improvement between one and two years (area under the curve 0.77, 95% CI 0.76 to 0.78, p < .001).


CONCLUSION
There was not a clinically important change in the OKS from one to two years after TKA when assessed as a group. However, individual patients with a one year OKS of less than 35 may demonstrate a clinically important improvement at two years.


LEVEL OF EVIDENCE
Retrospective diagnostic study, Level III.
['Clement|N D|ND|', 'Afzal|I|I|', 'Demetriou|C|C|', 'Deehan|David J|DJ|', 'Field|R E|RE|', 'Kader|D|D|']
D000328:Adult D000368:Aged D000369:Aged, 80 and over D019645:Arthroplasty, Replacement, Knee D019985:Benchmarking D005260:Female D005500:Follow-Up Studies D006801:Humans D008297:Male D008875:Middle Aged D020370:Osteoarthritis, Knee D011184:Postoperative Period D012372:ROC Curve D012189:Retrospective Studies D013997:Time Factors D016896:Treatment Outcome
Difference Oxford knee score Total knee arthroplasty Outcome Change Follow-up