The influence of different tibial stem designs in load sharing and stability at the cement-bone interface in revision TKA.

Total Knee Arthroplasty (TKA) changes mechanical loading of the knee joint. Bone loss in the tibia is commonly encountered at the time of the revision TKA. Restoration of lost bone support and joint stability are the primary challenges in revision TKA. Normally, these defects are treated with non-living structures like metallic augments or bone grafts (autografts or allografts). Alone, neither of these structures can provide the initial support and stability for revision implants. In the latter, the use of intramedullary stems can provide the necessary load sharing and protect the remaining host bone and graft from excessive stress, increasing component stability. The purpose of this study was to evaluate comparatively load sharing (cortical rim, cancellous bone and stem) and stability at the cement-bone interface under the tibial tray induced by the use of cemented and press-fit tibial component stem extensions. Furthermore the study of the desirable option in cases where the bone defect is cavitary (cancellous bone defect contained by an intact cortical rim) or uncontained bone defect (bone loss involving the supporting cortical rim) was carried out. Because in vitro evaluation of these biomechanical parameters is difficult we used finite element (FE) models to overcome this. The biomechanical results suggest an identical behaviour in case of cavitary defects for both types of stems assessed. In the case of uncontained defect treated with bulk allografts the cemented stem may be a prudent clinical option.