Biomechanical Analysis of Tibial Insert Under Varus Tilt After Medial Unicompartmental Knee Arthroplasy

The development of artificial joints is now considered to be quite mature, and is the main treatment for osteoarthritis. However, in recent unicompartmental knee arthroplasty clinical follow-ups, complications due to the wearing of polyethylene (PE) tibial components still exist. Therefore, the purpose of this study was to analyze the relation between insert wearing and components alignment in unicompartmental knee prostheses (UKP) by finite element analysis. This study evaluates the angles after correction of varus deformity and posterior tibial slope (PTS), the results show that the varus tilt should be less than 10deg, the excessive posterior tibial slope should be avoided, too. Otherwise the wear of the PE tibial components will increase and thus shorten the expectancy of joint prostheses.

I. Introduction

Unicompartmental knee arthroplasty (UKA) has been developing since the early 1970s. Much early literature indicates that results were not ideal. The main reasons inlcuded poorly designed implant, inappropriate patient selection, and doctors' misconceptions regarding the surgery [1]–[3]. UKA results and evaluations have greatly improved, thanks to improved implant design, precise patient selection, refined surgical techniques, and accumulated expertise in related techniques. However, recent reports of UKA clinical followups continue to show failed operations due to wearing PE tibial components [1], [4]. PE tibial component wear mainly comes from excess stress, mainly related to faulty component positioning [5], [6]. And, the main reason usually stems from the corrected angle in coronal plane and PTS [2], [6], [7]. Overcorrection may cause the damage of the opposite tibiofemoral cartilage, while undercorrection may cause the wear of PE tibial components. This implicitly signifies that the final angle corrected for knee deformity is a crucial factor of a successful UKA. Hernigou and Deschamps [8] further reported that the greater PTS would cause an increasing number of cases requiring secondary replacement due to PE tibial component damage.