CONTACT STRESS-ANALYSIS IN MENISCAL BEARING TOTAL KNEE ARTHROPLASTY

The effect of a mobile meniscal bearing on tibiofemoral contact stress was tested with a standard fixed tibial component and with movable ti bial components (anteroposterior sliding, rotationally sliding, and an teroposterior and rotationally sliding). A digital electronic sensor w as used to detect tibiofemoral contact location in five cadaver knees, then the location was reproduced while peak and mean stresses were me asured under compressive load at 0 degrees, 30 degrees, 60 degrees, an d 90 degrees of flexion. Stresses were measured when the tibial compon ent was normally aligned and at 15 degrees internal and 15 degrees ext ernal rotation. To evaluate the effect of excessive overhang of the po lyethylene articular surface, undersurface stress of the relationally sliding component was also measured with a 30 degrees and a 45 degrees malrotated tibial tray. Uppersurface stresses of the fixed-bearing co mponents were significantly higher at full extension than those record ed in components with rotational mobility. Undersurface stresses were always lower than uppersurface stresses, but correlated with uppersurf ace stresses. Undersurface stresses of the rotationally sliding compon ent gradually increased as the malrotation angle of the tray increased . A mobile meniscal bearing surface appears to offer an advantage over a standard fixed component when rotational malalignment of the tibial component occurs. However, with severe rotational malalignment, edge contact markedly increases undersurface stresses, which could cause de formity and subluxation.