Mechanics of the healed meniscus in a canine model.

The mechanical behavior of the intact canine stifle joint was studied, using a surgical model of meniscal injury and repair. Thirty-eight animals were divided into five study groups: Group S received only a sham arthrotomy (without a meniscal incision), Groups P13 and P26 received peripheral medial meniscal incisions, and Groups R13 and R26 received radial medial meniscus incisions. All meniscal incisions were repaired anatomically with absorbable suture. Groups P13 and R13 were sacrificed at 13 weeks following surgery and Groups P26 and R26 at 26 weeks. Following sacrifice, the joints were subjected to gross and histologic examination, and structural and material properties testing. All meniscal repairs healed, and the peripheral repairs were virtually invisible, with no articular damage. The radial repairs healed with 3 to 5 mm wide fibrovascular scars, and several joints demonstrated articular erosions. The radial repair tissue contained unorganized collagen bundles and ground substance deficient in mucopolysaccharides. Groups S, P13 and P26 demonstrated no statistically significant differences between test and control limbs in compressive force-displacement behavior, input energy (EI), and ratio of dissipated to input energy (ED/EI). There were significant test-control differences in the load-displacement characteristics of Groups R13 (P less than 0.05) and R26 (P less than 0.05), with the repaired joint stiffer than the control. EI decreased 26% in Group R13 (not significant) and 34% in Group R26 (P less than 0.05), while the ratio ED/EI increased from 27% to 44% in Group R13 (not significant) and from 31% to 38% in Group R26 (P less than 0.05). Medial compartment contact area did not change significantly in either peripheral repair group, but decreased by 25% in Group R13 (P less than 0.05) and by 13% in Group R26 (P less than 0.05). Yield stress, maximum stress, and Young's modulus decreased significantly (P less than 0.05) relative to the controls in tensile tests of the radial repair tissue. There were no significant changes in these properties from 13 to 26 weeks. We concluded that in this animal model, the mechanical function of the meniscus is restored following repair of peripheral longitudinal lesions; however, it appears that in the radial repairs, progressive spreading at the repair site (filled by a fibrovascular scar) altered normal meniscal geometry and structure, adversely influencing mechanical function. Future studies may document whether protective measures (immobilization, limited weightbearing, etc.) can preserve normal mechanical function following repair of radial lesions.