The effect of medial meniscectomy and coronal plane angulation on in vitro load transmission in the canine stifle joint

Abstract

The purpose of this study was to determine the in vitro load transmission characteristics of the canine stifle joint, paying particular attention to the positioning effect of the meniscus in the coronal plane. The intact joint was first loaded, and then tested under two different loading conditions after a complete medial meniscectomy. The first set of test conditions attempted to simulate those used by previous investigators, by ignoring the spacer effect of the meniscus and not repositioning the joint after its removal. The second set of tests was carried out after the joint was repositioned in the coronal plane to allow initial contact to occur in both tibiofemoral compartments. It is presumed that this occurs subsequent to a meniscectomy in vivo, following the application of any weight-bearing load. As with previous investigators, it was found that after meniscectomy the joints produced slightly larger displacements and lower stiffnesses than when intact (no significant differences from intact). However, repositioning the meniscectomized joint produced markedly smaller displacements (35–49%, p < 0.01) and greater stiffnesses (47–123%, p < 0.05) over the range of forces analyzed, compared with the intact joint. The ratio of dissipated to input energy was 42% for the intact joint, and rose following meniscectomy to 54% (p < 0.05) with repositioning and 55% (p < 0.05) without repositioning. Measured contact area decreased by 17% (p < 0.05) following meniscectomy alone, and by 12% (p < 0.05) following meniscectomy with repositioning. Since repositioning of the joint subsequent to meniscectomy (accounting for the loss of the meniscal spacer) resulted in an increse in structural stiffness, it was concluded that the medial meniscus decreases the structural stiffness of the intact stifle joint. In addition, the meniscus has a role in elastic energy storage and increasing contact area. This study is intended to serve as a baseline comparison for future in vivo studies on meniscetomy, meniscal repair, and meniscal replacement, in addition to more fully elucidating the mechanism of load transmission. A model is presented to explain both the decrease in stiffness after meniscectomy without repositioning and the increase in stiffness after meniscectomy with repositioning, employing linear springs of unequal length and different stiffnesses. After removal of the softer meniscal element and allowing joint approximation to occur, loading of the stiffer articular element results in an initially stiffer preparation.