Histological and biochemical changes of experimental meniscus tear in the dog knee.

Background: When degeneration is noted in the meniscus, sutures should not be applied even for a tear of the vascularized region of the meniscus because the meniscus may rerupture after suturing. In this study, the degeneration process of bucket-handle tear of the meniscus was investigated using histological and biochemical markers.

Methods: A bucket-handle tear in the intercondylar notch was prepared in the dog knee. Eight animals each were killed at 2, 4, 12, 24, and 48 weeks; and changes in the articular cartilage were observed. The cell count and morphology in the meniscus were investigated by hematoxylin and eosin staining, and glycosaminoglycans in the matrix were investigated by toluidine blue staining. Glycosaminoglycans were also measured by high-performance liquid chromatography.

Results: Erosion was noted in the weight-bearing region of the articular cartilage after 12 weeks. The cell count in the meniscus was markedly decreased at 48 weeks. Regarding cell morphology, fibrochondrocytes remained in the meniscus until 12 weeks. The cell morphology varied at 24 weeks, but the number of cells was maintained. Cell proliferation, mainly fibroblasts, was noted from 2 weeks and 4 weeks after surgery in the periphery and body of the meniscus, respectively. Fibrochondrocyte-like cells proliferated from 12 weeks in the meniscal body, and metachromasia was detected by toluidine blue staining, indicating meniscal repair. A marked decrease in glycosaminoglycans was noted at 48 weeks, which was consistent with the decrease in the cell count in the meniscus.

Conclusions: Early application of sutures is desirable for bucket-handle tear of the meniscus because lesions appear in the cartilage within 12 weeks, but suturing may be performed until 24 weeks because of the absence of obvious meniscal degeneration. However, disorder of the meniscus progresses after 48 weeks and may affect the outcome of the meniscal suture.