Poster 134: Biomechanical Analysis of Meniscotibial Ligament Tenodesis to Treat Meniscal Extrusion in the Setting of Posterior Medial Meniscal Root Repair

OBJECTIVES: There has been an increased focus on the significance of meniscal extrusion in medial meniscal root repairs, as meniscal extrusion is often still present following a successful medial meniscal root repair. If the meniscus is extruded, the function of the meniscus as a shock absorber and secondary knee stabilizer can be compromised. Recently, greater attention has been placed on the meniscotibial ligament (MTL) as a restraint to meniscus extrusion, with suggestions that disruption to the MTL is responsible for residual extrusion after root repair. However, there is no literature evaluating injury and tenodesis of the MTL to the tibia in the setting of root injury or root repair. The objective of this study was to evaluate an MTL tenodesis for treating meniscal extrusion in the setting of medial meniscal root tears and repair. We hypothesized that tenodesing the medial tibial capsule to the tibia will decrease meniscal extrusion in the setting of a medial meniscal root tear and repair along with improving the medial cartilage contact pressures in a cadaveric model. METHODS: Ten fresh-frozen cadaveric knees (Average age: 50.5 years) were tested in five conditions (Intact, MTL Tear, MTL + Root Tear, Root Repair + MTL Tear, Root Repair + MTL Tenodesis). Tekscan pressure sensors were inserted submeniscally between the femoral condyles and the superior surface of the medial and lateral tibial compartments. Specimens were mounted in full extension to a materials testing machine (Instron) which applied a 1000 N axial load to the specimen over a ten second period (Figure 1). With the specimen loaded, a contact map from the Tekscan pressure sensor was captured, and medial meniscal extrusion was measured from reproducible ultrasound images (Canon I-series, 18MHz transducer). Medial meniscal extrusion was defined as the maximum distance between the medial margin of the meniscus and the line connecting the medial margin of the distal femur to the medial margin of the proximal tibia. This testing procedure was repeated for each state. The MTL Tear state was reproduced by making a minimal incision to the medial MTL with a 10-blade scalpel. The MTL + Root Tear state was reproduced by cutting the posterior medial meniscal root within 10 mm from its enthesis. For the Root Repair + MTL Tear state, a standard transtibial tunnel was drilled under the posterior medial meniscal root footprint and anchored to the anterior tibial cortex with the meniscus tacked down using a horizontal mattress pattern. For the Root Repair + MTL Tenodesis state, a two anchor MTL tenodesis technique was used on the medial aspect of the tibial plateau. Each 2.6mm knotless FiberTak (Arthrex) was placed on either side of the medial collateral ligament and secured the MTL to anatomical position with a horizontal mattress pattern. Average contact pressure, peak contact pressure, contact area, and extrusion were compared across states using linear regression modelling and Tukey’s method. RESULTS: The Root Tear state alone yielded significantly elevated average (p = 0.0423) and peak contact pressures (p = 0.0028) and reduced contact area (p = 0.0044) in the medial compartment compared to the intact state. Notably, meniscotibial ligament disruption (MTL Tear state) had no effect on medial contact pressure or contact area. Medial meniscal extrusion significantly increased from the intact state with both an MTL tear (p = 0.035) and root tear (p < 0.0001). Root repair alone was able to restore extrusion (p < 0.0001), average pressure (p = 0.0276), and peak pressure (p = 0.0169) to the intact state. MTL tenodesis did not significantly improve the extrusion, contact pressures, or contact area from the root repair state. CONCLUSIONS: There are two key findings of this study. First, MTL disruption increased medial meniscal extrusion but did not change contact pressures or contact area, which supports prior clinical and biomechanical observations. Meniscal root tear alone increased contact pressures and decreased contact area. Secondly, meniscal root repair alone restored meniscal extrusion and contact pressures back to native. Further, we found that the addition of the meniscotibial tenodesis maintained this result, and restored pressure mapping closest to the intact state. Further clinical studies are needed to evaluate post operative clinical outcomes as well as measurable meniscus extrusion following MTL tenodesis. This study is limited in that the posterior and anterior sides of the MTL were cut to install the pressure sensors submeniscally, which may have affected true values of extrusion. While the utilization of ultrasound to measure meniscal extrusion introduced observer-dependent errors, the authors utilized a custom-made fixture that ensured repeatable placement of the transducer and minimize these errors. Finally, this is a time-zero evaluation only, and cannot assess the in vivo mechanics which likely result in late extrusion seen in clinical studies on this topic. This is one of the first studies to measure extrusion by ultrasound and the first study to measure extrusion both in the setting of root tear and meniscotibial ligament disruption. This study supports findings that MTL disruption may serve as a precursor to meniscal root injury and establishes a viable tenodesis treatment to address residual extrusion in the setting of meniscal root repair.