Six-Month Outcomes of Clinically Relevant Meniscal Injury in a Large-Animal Model

Abstract

Background: The corrective procedures for meniscal injury are dependent on tear type, severity, and location. Vertical longitudinal tears are common in young and active individuals, but their natural progression and impact on osteoarthritis (OA) development are not known. Root tears are challenging and they often indicate poor outcomes, although the timing and mechanisms of initiation of joint dysfunction are poorly understood, particularly in large-animal and human models. Purpose/Hypothesis: In this study, vertical longitudinal and root tears were made in a large-animal model to determine the progression of joint-wide dysfunction. We hypothesized that OA onset and progression would depend on the extent of injury-based load disruption in the tissue, such that root tears would cause earlier and more severe changes to the joint. Study Design: Controlled laboratory study. Methods: Sham surgeries and procedures to create either vertical longitudinal or root tears were performed in juvenile Yucatan mini pigs through randomized and bilateral arthroscopic procedures. Animals were sacrificed at 1, 3, or 6 months after injury and assessed at the joint and tissue level for evidence of OA. Functional measures of joint load transfer, cartilage indentation mechanics, and meniscal tensile properties were performed, as well as histological evaluation of the cartilage, meniscus, and synovium. Results: Outcomes suggested a progressive and sustained degeneration of the knee joint and meniscus after root tear, as evidenced by histological analysis of the cartilage and meniscus. This occurred in spite of spontaneous reattachment of the root, suggesting that this reattachment did not fully restore the function of the native attachment. In contrast, the vertical longitudinal tear did not cause significant changes to the joint, with only mild differences compared with sham surgery at the 6-month time point. Conclusion: Given that the root tear, which severs circumferential connectivity and load transfer, caused more intense OA compared with the circumferentially stable vertical longitudinal tear, our findings suggest that without timely and mechanically competent fixation, root tears may cause irreversible joint damage. Clinical Relevance: More generally, this new model can serve as a test bed for experimental surgical, scaffold-based, and small molecule–driven interventions after injury to prevent OA progression.

Acute repair of meniscus root tear partially restores joint displacements as measured with MRI and loading in a porcine knee

“…Studies using pressure sensors placed into the joint space showed that the femoral contact point shifts medially after meniscus injury [2]- [4], [16], similar to our meniscus and femur results.…”

“…Seven fresh-frozen Yucatan minipig hindlimbs, harvested from 12-18 month-old castrated males, were obtained (Sierra Medical for Sciences, Whittier, CA, sierra-medical.com). We chose this age range because the animals are skeletally mature and it matches the age of pigs that we have previously used in our live animal model [3], [4]. After thawing, all skin and musculature were removed from the stifle joint, with special care taken to preserve the joint capsule, lateral collateral ligament, and medial collateral ligament.…”

“…The Intact case was an intact joint, where the joint capsule and lateral and medial collateral ligaments were preserved and the musculature removed, prepared as described above. In the Tear case, a medial meniscus root tear was created by transection of the anterior attachment (destabilization of the medial meniscus, DMM, a frequently used model) using a minimally invasive anterior approach to limit the size of the incision in the joint capsule [3], [4], [10]. The attachment was severed via a horizontal cut along the bone insertion.…”

“…Previous work has shown that there is a relation between greater meniscal extrusion and joint degeneration [13]- [15]. Some studies have shown, using pressure sensors (e.g., Tek-Scan) inserted into the joint space, that meniscus injury leads to larger peak forces and smaller contact areas on the tibial plateau; however, these studies required transecting the joint capsule and sometimes the LCL or MCL to make the measurement [2]- [4], [16], [17]. Therefore, developing non-invasive measurement of joint and meniscus kinematics is critical to understanding the impact of meniscus injury and repair on joint loading and chondroprotection.…”

“…We hypothesized that a root tear would cause meniscus extrusion and medial displacements of the femur, and that a suture anchor repair would restore the meniscus to its near intact position and kinematics. This in vitro work used a Yucatan minipig stifle joint model, similar to our established animal model [3], [4].…”