Menisci are crescent-shaped, fibrocartilaginous wedges that play an important role in complex knee mechanics and function. The menisci are primarily responsible for distributing loads through the tibiofemoral joint, joint stabilization, and congruency. The circumferential collagen fibers in the meniscus body continue into the anterior and posterior root insertional ligaments that attach to the tibial plateau. Continuity of the circumferential fibers between the meniscus body and its insertions enables proper fixation into bone and facilitates the distribution of axial tibiofemoral stresses to circumferential hoop stresses.
Meniscal root tears (MRTs) are complete radial tears or avulsion injuries of the meniscal root insertions from the tibial plateau and are a subset of injuries that cause the meniscus to inadequately distribute loads and protect the underlying articular cartilage. Untreated MRTs are becoming increasingly recognized to induce articular cartilage degradation over time; therefore, proper understanding of injury and progression of degeneration is essential.
Previously, studies on meniscal release, or destabilization of the medial meniscus (DMM), have been used to induce and analyze degeneration of knee joint tissues in murine, lapine, canine, and ovine models over time. These models all demonstrate measurable degeneration within the knee joint tissues. Despite the wide use of these models for osteoarthritis research, however, the authors are not aware of any studies assessing the degeneration of several tissues within the knee joint after release of the anterior insertions for both the lateral and medial menisci. Cadavers have also been used to investigate MRTs; however, these studies primarily focus on changes in knee biomechanics to the posteromedial and posterolateral meniscal insertions.
Although tears of the anterior meniscal root insertions may be less common than posterior tears, a recent study reported that iatrogenic injury occurs at the anterior insertions of the lateral and medial menisci while reaming tibial tunnels for anterior cruciate ligament (ACL) reconstruction. Currently, literature on anterior MRTs is limited to reports of case studies and anatomic analysis of the relationship between the ACL and anterior meniscal root insertions. Since the anterior meniscal insertions are susceptible to damage during ACL reconstructions, increasing the risk for MRTs, it is important to understand how these injuries affect the joint tissues. Additionally, since clinical samples of articular cartilage and menisci are usually salvaged from advanced stages of osteoarthritis after total knee reconstructions, animal models are commonly used to experimentally induce injury and assess early degeneration.
Therefore, the purpose of this study was to measure characteristics of early degeneration in the rabbit knee after untreated anterior MRTs for major sites of earliest discernible joint involvement seen in osteoarthritis. The amount and type of inflammatory cells present in the synovial fluid, the compressive material properties of the menisci and tibial articular cartilage, the subchondral bone morphology of the tibial plateau, the coverage and content of glycosaminoglycans (GAGs) of menisci and tibial articular cartilage, the total content of intact DNA, and the relative gene expression of matrix-degrading enzymes were measured after anterolateral MRTs (ALMRTs) and antero-medial MRTs (AMMRTs). It was hypothesized that if anterior MRTs of either the medial or lateral menisci were left untreated after injury, early osteoarthritic change would occur within the joint tissues.