Paper 02: Tibiofemoral load sharing and lateral meniscus function after type 3 lateral meniscus oblique radial tear (lmort) treatment: tibia-based suture anchor repair, capsular-based repair, and debridement

Objectives: The purpose of this study was to compare the biomechanical performance of tibia-based repair, capsular-based repair and debridement for type 3 LMORTs. The authors hypothesized that 1) type 3 LMORTs would alter lateral compartment contact mechanics and meniscal function compared to the intact state, and 2) tibia-based suture anchor repair would more effectively restore these metrics to intact levels compared to capsular-based repair techniques.
Methods: Eight unpaired fresh-frozen human cadaveric knees (mean age: 57, age range: 46 - 62, 2F:6M) were utilized. Each specimen was tested via a repeated-measures design across 5 states in the following order: 1) intact lateral meniscus, 2) LMORT type 3 tear created 12 mm lateral to the root attachment, 3) tibia-based suture anchor fixation, 4) capsular-based side-to-side repair, and 5) debridement. For each state, four knee flexion angles were tested in random order: 0°, 30°, 60°, and 90°. Pressure sensors were installed in the lateral compartment of the knee, and a three-axis sensor was installed inferior to the anterior lateral mensicus root to assess meniscus force transmission via measurement of root forces. The specimens were mounted onto a testing machine where a 500 N compressive load was applied to each specimen. An image of the lateral side of the knee was captured via ultrasound (Canon Aplio i800), and lateral extrusion was measured from the resulting image. Average pressure and peak pressure were captured from the pressure sensors, and 3D root forces were captured from the three-axis force sensor. Two-way repeated measures ANOVAs with a pairwise Bonferroni analysis were performed to assess differences in means of extrusion, average pressure, peak pressure, and forces along all three dimensions across all flexion angles between all testing states.
Results: Graphical display of the results can be found in Figure 1. Type 3 LMORTs significantly increased average pressure (0°: p=0.007, 30°: p=0.028, 60°: p=0.006, and 90°: p=0.043) by at least 37%, increased peak pressure (0°: p=0.046, 30°: p=0.013, 60°: p=0.011, and 90°: p=0.040) by at least 45%, increased extrusion (30°: p=0.001, 60°: p=0.001, and 90°: p<0.001) by 75% at higher flexion angles and 140% at lower flexion angles, and decreased lateral anterolateral root force (0°: p=0.004, 30°: p=0.018, 60°: p=0.011, and 90°: p=0.001) by at least 40% at all flexion angles compared to the intact state. Both tibia-based suture anchor and capsular-based side-to-side repair restored contact pressures, extrusion, and anterior root forces to the intact state (p>0.05) across all flexion angles, with no significant difference between the two repair conditions (p>0.05). Contact pressures, extrusion, and anterior root forces were not significantly different in the debridement state compared to the tear state alone (p>0.05) across flexion angles.
Conclusions: The most important findings were threefold. First, type 3 LMORTs significantly altered tibiofemoral joint mechanics, lateral meniscus force transmission, and extrusion, confirming the primary component of our hypothesis. Second, repair of these tears restores the intact state, regardless of repair construct, which rejects our secondary component of the hypothesis. Third, debridement of the tear offered no biomechanical benefit to the tear state itself, which corroborates results from with prior biomechanical studies on LMORT tears and repair. Both capsular-based side-to-side and tibia-based suture anchor repairs effectively restored intact mechanics, suggesting surgeon preference should guide repair choice. These biomechanical observations, however, are contrasted by clinical outcomes studies that report lateral tears left in situ have minimal impact on long term patient outcomes. Despite this controversy, there is a gap in clinical literature that reports outcomes of LMORT-specific treatment in the setting of an ACL-R. Our study provides unique data regarding the effects of type 3 LMORTs and LMORT repair on contact mechanics and meniscal function at time-zero, providing additional biomechanical justification for type 3 LMORT repair at the time of ACL reconstruction.