In vitro load transmission in the canine knee: the effect of medial meniscectomy and varus rotation.

The purpose of this study was to determine the in vitro load-transmission characteristics of the canine knee, 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. The second set of tests were carried out following varus rotation of the joint (to account for the loss of the meniscal spacer) to assure initial contact in both tibiofemoral compartments at the start of test cycle. It is presumed that this varus realignment occurs during weight bearing following meniscectomy in vivo. As in previous studies, the joints experienced slightly larger displacements (although not statistically significant) and had lower stiffness values following medial meniscectomy than when intact. However, following varus realignment of the joint after meniscectomy, the displacement was markedly smaller (-35% to -49%; P < 0.01) and the structural stiffness was much greater (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 increased following meniscectomy to 54% (P < 0.05) with realignment and 55% (P < 0.05) without realignment. Measured contact area decreased by 17% (P < 0.05) following meniscectomy alone, and by 12% (P < 0.05) following meniscectomy with realignment.(ABSTRACT TRUNCATED AT 250 WORDS)