Abstract
Introduction
Knee joint should be aligned for reconstruction of the function in Total Knee Replacement(TKR). Although a surgeon try to correct the alignment of a knee joint, sometimes varus/valgus alignment has been tried in order to reconstruct function of knee joint. As a result, the varus or valgus alignment affects to ligaments and soft tissue, and the contact condition is changed between femoral component and tibial insert. One of important factor, wear characteristics of an implant can be changed due to the contact condition. In this study, we performed static contact tests from extension to flexion in varus and valgus to define the effect to contact condition when the alignment is varus or valgus.
Methods
LOSPA TKR femoral component #6 and Tibial insert #5 manufactured by Corentec Co., Ltd. were used as test specimens. The tests have performed with adapting ASTM F2777–10 ‘Standard Test Method for Evaluating Knee Bearing (Tibial Insert) Endurance and Deformation under High Flexion’. The test set like as Fig. 1. The load is applied at 7:3 ratio of lateral-medial by adapting gait analysis. The 5° of jig is used to compare the result in neutral, varus and valgus. The fuji films were used in tests were scanned, and the results were analyzed the compressed area and contact stress as angles of flexion in neutral stance and varus/valgus from scanning. The tests were performed 5 times per each for a reliability.
Results
The results of compressed area became decreasing as the angle of flexion was increased. The compressed areas in varus alignment was little smaller than the results in varus. The compressed areas in neutral stance were the greatest in all results. (Fig. 2.) There were little differences between the results in varus and valgus in view point of peak contact stress. (Fig. 3)
Discussion
Because the neutral stance makes the compressed area become more increasing than varus/valgus alignment, so that the lowest contact stress is induced between femoral component and Tibial insert. There is little difference between varus and valgus in viewpoint of peak contact stress if the varus/valgus alignment is not excess. It is considered that the alignment is tried to correct because low contact stress makes wear improve.
