Tibial shape and size predicts the risk of tibial plateau fracture after cementless unicompartmental knee arthroplasty in Japanese patients.

AIMS: Cementless unicompartmental knee arthroplasty (UKA) has advantages over cemented UKA, including improved fixation, but has a higher risk of tibial plateau fracture, particularly in Japanese patients. The aim of this multicentre study was to determine when cementless tibial components could safely be used in Japanese patients based on the size and shape of the tibia. METHODS: The study involved 212 cementless Oxford UKAs which were undertaken in 174 patients in six hospitals. The medial eminence line (MEL), which is a line parallel to the tibial axis passing through the tip of medial intercondylar eminence, was drawn on preoperative radiographs. Knees were classified as having a very overhanging medial tibial condyle if this line passed medial to the medial tibial cortex. They were also classified as very small if a size A/AA tibial component was used. RESULTS: The overall rate of fracture was 8% (17 out of 212 knees). The rate was higher in knees with very overhanging condyles (Odds ratio (OR) 13; p < 0.001) and with very small components (OR 7; p < 0.001). The OR was 21 (p < 0.001) in those with both very overhanging condyles and very small components. In all, 69% of knees (147) had neither very overhanging nor very small components, and the fracture rate in these patients was 1.4% (2 out of 147 knees). Males had a significantly reduced risk of fracture (OR 0.13; p = 0.002), probably because no males required very small components and females were more likely to have very overhanging condyles (OR 3; p = 0.013). 31% of knees (66) were in males and in these the rate of fracture was 1.5% (1 out of 66 knees). CONCLUSION: The rate of tibial plateau fracture in Japanese patients undergoing cementless UKA is high. We recommend that cemented tibial fixation should be used in Japanese patients who require very small components or have very overhanging condyles, as identified from preoperative radiographs. In the remaining 69% of knees cementless fixation can be used. This approach should result in a low rate of fracture. Cite this article: Bone Joint J 2020;102-B(7):861-867.

Oxford phase 3 unicompartmental knee arthroplasty in Japan--clinical results in greater than one thousand cases over ten years.

There are few reports of the Oxford unicompartmental knee arthroplasty (UKA) survival rate in Asia. This study describes outcomes of 1279 Oxford UKAs for Japanese patients. The mean follow-up was 5.2 years. We divided patients into two groups based on preoperative indications (extended indications group and strict indications group). The Oxford knee score improved from 22.3 to 40.8 (P=0.041). The 10-year survival rate using revision was 95%. A total of 25 UKAs (2.0%) required revision. The most common reason was subsidence of tibial component. The 5-year cumulative survival rate of the strict indications group was significantly higher than that of the extended indications group (99.1% vs. 93.8%, P<0.001). When we followed inclusion criteria strictly, good clinical results were achieved in Asia.