Abstract
Introduction: The meniscus plays an important role in protecting the articular surfaces of the tibia and femur from excessive wear due to aberrant forces across the knee joint. While the biochemical changes associated with cartilage and meniscal wear have been well documented, little data exists in the literature describing the ultrastructural events associated with such a degenerative process.
Aim: To develop an in vivo model to evaluate the effects of joint incongruity on meniscal wear.
Materials and Methods: Six New Zealand White rabbits underwent an arthrotomy of the right knee joint. A sagittal osteotomy of the medial femoral condyle was then performed on four of these animals while the remaining two served as controls. Post operatively all animals were allowed to mobilise ad librium and were sacrificed after 20 weeks. The medial meniscus was harvested and processed for electron microscopy by routine methods. Survey light microscopy sections (1um) were examined and adjacent ultra-thin sections (50nm) were assessed in an electron microscope at magnifications from 1,500 to 30,000.
Results: On gross examination of the menisci there was no evidence of any significant wear. Neither was there noticeable damage on light microscopy. There was no significant difference in the numbers of chondrocytes and fibroblasts in the superior and inferior surfaces of both control and test samples, indicating a lack of cellular response in the test specimens. On electron microscopy, the superficial electron dense layer was markedly attenuated in test subjects (control 246 – 305 nm, test 109 – 167nm). The superior surfaces of two test samples were markedly roughened, while chondral fragments were noted in craters on the surface. Numerous cystic lesions were present within the superficial collagen stroma of test subjects. Interestingly cleavage planes were noted in the superior and inferior aspects of one of the four test subjects. No difference in collagen fibril diameter was observed between control and test subjects.
Discussion: These results represent the early stages of meniscal degeneration. The process appears to one of microfibrillation, with degeneration occurring within the bundles of collagen fibrils rather than within the substance of the fibrils themselves. The absence of a healing response suggests that this is an intractable process, a finding which accords well with findings in the clinical setting.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
