Malpositioning of Prosthesis: Patient-specific Total Knee Arthroplasty Versus Standard Off-the-Shelf Total Knee Arthroplasty

INTRODUCTION: A recent study has challenged the premise that a patient-specific (PS)–designed total knee arthroplasty (TKA) component has better clinical survival than an off-the-shelf (OTS) prosthesis. METHODS: We developed the finite element models for PS TKA and OTS TKA with 5° varus and valgus malalignment and 5° internal and external malrotations. RESULTS: Contact stress on the medial side of the insert increased with internal femoral malrotation and varus tibial malalignment, but it decreased with external femoral malrotation and varus tibial malalignment in both PS TKA and OTS TKA. An increase in ligament force occurred in valgus malalignment and external malrotation, and in particular, the force exerted on the medial collateral ligament increased. However, PS TKA provided better biomechanical effects than did the standard OTS TKA with malpositioning in TKA. DISCUSSION: These results emphasize the importance of precise surgical preservation in regard to the TKA position.