Stress Analysis of the Proximal Tibia using Finite Element Method after Unicompartmental Knee Arthroplasty

BACKGROUND: Because the indications for UKA are limited, the number of patients who have undergone this procedure is small, and it is therefore difficult to decide the acceptable range of variation in the details of this surgical procedure on the basis of the available clinical data. The objective of the present study was to determine the factors affecting the stress distribution of the proximal tibia after UKA. METHODS: The two-dimensional finite element analysis in the proximal tibia was employed to assess the following four factors: 1) Two types of implants, all-ultra-high molecular weight polyethylene (UHMWPE) type and metal backed type, 2) post-operative alignment, 3) coverage of tibial bone, 4) level of the tibial osteotomy. RESULTS: In the cases of varus alignment, high stress and large deformation was observed on and beneath the implant. In the cases of valgus alignment, stress concentration was seen at the lateral portion of tibial tray. In comparison with the standard model, the stress concentration was observed at the medial edge of the medial condyle in a narrow coverage model. Comparing to the standard model, the stress distribution in a low osteotomy level model did not differ markedly from that in the standard model. Metal backed implants were shown to provide better stress distribution than UHMWPE implants in this study. CONCLUSIONS: The proper postoperative alignment must be achieved in UKA. The osteotomy level should be set at the cancellous bone close to the joint line, and maximum bone stock should be preserved.