Paper 49: Weight bearing after novel onlay medial meniscus root repair: a cadaveric study analyzing the integrity of meniscal root repairs subjected to physiologic cyclic loading with an intraosseous all-suture anchor device

Objectives: Meniscal root tears characterize an important variant of meniscal pathology, and if mistreated, can lead to rapid osteoarthritic changes. The meniscal root plays an important role in overall meniscal integrity and function. A meniscal root tear causes increased tibiofemoral contact pressures secondary to meniscal extrusion due to loss of hoop stress function. Most post-operative repair protocols call for a period of non-weight bearing to protect the repair from immediate stresses. The purpose of this study is to evaluate the feasibility of weightbearing postoperatively after medial meniscus root repair. We hypothesized that medial meniscus root repairs performed using an onlay intraosseous all-suture anchor device could withstand over twice the physiologic force of weightbearing and cyclic loading in full extension. This scenario would simulate a postoperative state that a patient who is weight bearing as tolerated in a knee immobilizer may experience.The purpose of this study was to evaluate the integrity of medial meniscus root repairs performed using an onlay intraosseous all-suture anchor device. By simulating a repair and cyclic weight bearing scenario, we hope to demonstrate that in a cadaver model, allowing weight bearing in the immediate post-operative period after meniscal root repairs using this novel technique is safe and effective, without causing undesired meniscal root displacement.
Methods: 7 cadaveric fresh frozen whole knee specimens with intact collateral ligaments, cruciate ligaments, and meniscocapsular attachments were utilized for the study. All specimens underwent diagnostic knee arthroscopy to confirm that the medial menisci (MM) were intact. 7 cadaveric knee specimens had intact MM. Metallic tracers (Arthrex Mini Corkscrew Anchors 2.5 mm x 7 mm fully threaded anchors) were placed into the medial tibial spines and another into the midsubstance of the posterior horns of the medial menisci in all tested specimens. The metallic anchor in the tibial spine was placed to be a static tracer, while the anchor within the meniscus would be used to represent meniscal displacement. Marker distance was measured on each image with ImageJ software (National Institute of Health, USA) and expressed as a percentage of medial tibial plateau width, to account for differences in mini C-arm fluoroscopy orientation and distance. Data were compared using a Friedman test, with Conover's post-hoc test using Bonferroni-Hom corrections. The tracer distance was measured while a 1700N static force was applied to a neutrally (0 degrees) extended knee in four separate states - 1. Intact meniscus with 1700N static load. 2. Detached/cut root simulating a tear 3. Repaired root and 4. Repaired root after 250 weight bearing cycles in full extension. The force of 1700N was chosen as it represents roughly 2.5x body weight for a 75 kg patient). The intact MM roots were detached in radial fashion using arthroscopic scissors, and root repair was performed using an onlay technique with an intraosseous all-suture anchor device (Arthrex SutureLoc anchor). For simulated weight bearing, the knee specimens were attached to a proprietary jig and loaded in full extension using an Instron machine. Mini C-arm fluoroscopic AP views were obtained to document the posterior horn and medial tibial spine metallic tracer spatial relationships. The knee specimens underwent repeat knee arthroscopy after cycling in order to assess the clinical integrity of the MM root repairs. Post hoc measurements were performed between the medial tibial spine/posterior horn metallic tracers in order to calculate meniscal displacement in the different loading scenarios.
Results: The intact menisci during loading displayed metallic tracers with a mean 0.601 tibial plateau widths apart. With the meniscal roots cut and statically loaded, this distance increased to a mean of 0.658. After repair and a single static load, the distance was 0.622. After 250 cyclic loads, this distance remained intact with a mean of 0.621. This shows that meniscal markers were further apart for the cut condition compared to intact (P=0.003), repaired (P=0.027) and repaired and cycled (P=0.018) conditions. Neither repaired condition was different from the intact meniscus (both P=0.840).
Conclusions: The outcomes of our study demonstrate that in a human cadaveric study, cyclical weight bearing in the fully extended knee following meniscal root repair using an intraosseous all-suture anchor onlay device does not lead to meniscal displacement. This evidence suggests that it may be biomechanically safe to allow for post-operative weight bearing with a knee immobilizer in extension following meniscal root repair using this novel technique. We hope that this advanced rehabilitation protocol would expedite patient recovery after these injuries and subsequent repairs.