Departmental Bulletin Paper Coronal Instability after Total Knee Arthroplasty using Bi-Surface type 3 : An Averaged 10 Year Follow-up Study

金, 民大  ,  渡邊, 敏文  ,  宗田, 大  ,  大原, 敏之  ,  関矢, 一郎  ,  古賀, 英之

65 ( 2 )  , pp.51 - 58 , 2018-06 , Tokyo Medical and Dental University
The stability of the knee joint affects the outcome of total knee arthroplasty. Among the knees with Bi-Surface type 3 (BS3), some showed progressive mediolateral (ML) displacement in the tibiofemoral joint on the standing anteroposterior (AP) radiographs, which indicated ML instability. We aimed to clarify the coronal instability and related factors with it.We compared radiological and clinical outcomes of the 26 knees with BS3 and 38 knees with NexGen LPS (LPS). All surgeries were performed with the same surgical techniques at our institution. Radiological evaluation included the component shift ratio, which indicated coronal instability. Correlations of the component shift ratio at latest follow-up with radiological and clinical measurements were also assessed.Greater component shift ratios in the BS3 group were found, while clinical outcomes showed no significant differences in both groups. The component shift ratio increased with the posterior tibial slope, the femorotibial angle, the implant extension angle, and the knee extension at the latest follow-up.BS3 knees exhibited coronal instability on radiographs, although clinical outcomes were similar to LPS knees. Understanding the design characteristics of BS, avoiding excess posterior tibial slope, and paying attention to the soft tissue balance would be the keys to prevent the instability with this prosthesis.

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