Abstract
Introduction
Total knee arthroplasty (TKA) is an excellent treatment for end-stage osteoarthritis of the knee. In Asian countries, the number of TKA performed has rapidly increased, and is expected to continue so with its 4.4 billion population and increasing life expectancy. Asians' knees are known to be kinematically different to Caucasians after TKA. Controversy exists as to whether multi-radius (MR) or the newer single-radius (SR) TKA has superior outcome. Studies regarding this have been largely based on Caucasian data with few small sample Asian data.
Methods
This is a retrospective analysis of prospectively collected institutional registry data between 2004 and 2015. Outcomes of 133 single-radius (SR) (Scorpio NRG, Stryker) and 363 multi-radius (MR) (Nexgen LPS, Zimmer) primary TKA for primary osteoarthritis were compared. All TKA was performed or directly supervised by the senior author. Range of motion (ROM), Oxford Knee Score (OKS), SF-36 physical component score (SF36-PCS), SF-36 mental component score (SF36-MCS), Knee Society Function Score (KS-FS) and Knee Score (KS-KS) were recorded preoperatively and at 2 years post-operation.
Results
The mean age in both groups were similar at 66 ± 8 years (p=0.66). Both groups were in majority female (71% and 70% females in SR and MR respectively, p=0.10) and ethnic Chinese (79% and 84% in SR and MR respectively, p=0.53). The preoperative ROM and outcome scores in both groups were similar.
MR-TKA achieved significantly greater improvement over 2 years in terms of ROM (7.5º ± 18.2º vs. 3.5º ± 19.3º, p=0.04), KS-KS (49.0 ± 20.9 vs. 42.7 ± 21.1, p=0.01), OKS (17.4 ± 18.4, p=0.03), and SF36-PCS (17.1 ± 12.5, p=0.02).
At 2-years follow up, MR-TKA group fared slightly better for SF36-PCS (48 ± 10 vs. 46 ± 10, p=0.032), but the absolute difference was only 2 points. There were no significant differences between SR-TKA and MR-TKA for ROM (115º ± 16º vs. 117º ± 16º, p=0.218), KS-KS (81 ± 16 vs. 85 ± 12, p=0.795), KS-FS (74 ± 21 vs. 75 ± 20, p=0.627), OKS (20 ± 7 vs. 18 ± 6, p=0.099), and SF36-MCS (56 ± 10 vs. 55 ± 10, p=0.324).
There were larger proportions of MR-TKA patients who achieved the minimum clinically important difference (MCID) for OKS (95% vs. 82%, p<0.001) and SF36-PCS (67% vs. 55%, p=0.011) at 2-years follow-up. Logistic regression, controlling for all preoperative variables, showed SR-TKA is less likely to achieve MCID for OKS with an odds ratio of 0.275 (95% confidence interval: 0.114 – 0.663, p=0.004), and SF36-PCS with an odds ration of 0.547 (0.316 – 0.946, p=0.031).
Discussion and conclusion
SR-TKA and MR-TKA produced similar outcomes, in concordance with current literature. However, SR-TKA has lower odds of achieving MCID in OKS and SF36-PCS, possibly due to its smaller improvement in flexion over 2 years. This subtle difference has a greater impact in the context of Asian patients due to the cultural practice of kneeling and/or squating.
