Poster 237: Menisco-Tibial Ligament Complex Anatomy and Biomechanics – Implications for Meniscus Repairs, Ramp Lesions and Transplants

Objectives: Meniscal injuries are among the most common orthopedic injuries in the United States. Meniscus repairs frequently achieve stability via capsular based repair techniques. Recent studies on meniscal ramp lesions, postero-lateral tears, and meniscus transplants demonstrate some shortcomings of meniscus suture techniques that incorporate menisco-capsular complex (MCC) repair. 1-3 Meniscus extrusion may also be affected by the function and integrity of the meniscus/menisco-tibial ligament complex (MTLC). 4 Inclusion of the MTLC in some repair/transplant constructs may produce more normal anatomic and biomechanical meniscus function, including the prevention of meniscus extrusion. However, the biomechanical properties of the MTCL in pediatric tissue has not been studied. Our objective was to evaluate the anatomy and biomechanical strength of the MTLC of the medial and lateral meniscus of pediatric knees. We hypothesized: 1) posterior anatomy of the medial and lateral knee would demonstrate a consistent recess or space between the posterior meniscus/MTLC complex and the MCC; and 2) the MTLC would demonstrate unique biomechanical characteristics between the posterior, middle, and anterior 1/3 zones of the medial and lateral meniscus. Methods: 14 fresh-frozen pediatric human knees from 10 donors (mean 7.5 years, range 5-10 years) were used in this study. The distance between the mensico-tibial ligament at the joint capsule and the height of the meniscus was measured with a depth gauge and digital caliper. We define this distance as the depth of the recess between MTLC and MCC (Fig. 1). Subsequently, the medial and lateral menisci were divided into approximate thirds with radial cuts extending through the menisco-tibial ligaments, creating anterior, central, and posterior testing zones for each meniscus (Fig. 2A). The posterior and anterior roots of each meniscus were released from the tibial attachment. Sandpaper was glued to each meniscus segment. Each tibial specimen was potted in fiberglass resin and mounted on an Instron 5944 test frame with a 2 kN load cell. Each meniscus/MTLC complex underwent 10 cycles of preconditioning from 3-5N at 10 mm/min followed by monotonic load to failure testing (Fig. 2B). The depth of recess, load-to-failure, and stiffness (maximum slope of load-displacement curve) were analyzed using linear mixed models with donor and limb as random factors and compartment (M/L) and position as fixed factors. Significance was at p<0.05 and pairwise comparisons used Bonferroni’s test. Results are reported as mean ± s.d. Results: A clear separation of the posterior 1/3 of each meniscus/MTLC and the posterior MCC was seen for each specimen, with a less obvious separation in anterior and central thirds. The depth of recess was significantly larger (p=0.049) in the posterior region (5.41 ± 2.05 mm) than in the anterior region (3.40 ± 2.00 mm), with no significant difference between medial and lateral menisci (Fig. 3). This confirms a distinct separation between the MTLC and the MCC. The load to failure in the anterior region (66.8 ± 31.3 N) was significantly lower than that in the central (91.7 ± 28.0 N, p=0.014) or posterior (93.5 ± 36.5 N, p=0.005) regions, with no significant difference between medial and lateral menisci (Fig. 4A). The stiffness of the central MTLC complex was significantly lower (p=0.014) in lateral menisci (10.0 ± 4.2 N/m) than in medial menisci (18.8 ± 9.4 N/m), with no other significant differences between regions (Fig. 4B). Conclusions: This study defines a clear space in the posterior 1/3 of the medial and lateral meniscus, in which the MTLC complex is distinct from the posterior MCC of the knee joint. This anatomic finding may suggest alternative techniques of meniscus repair/transplant fixation that include direct repair of some meniscus regions to the menisco-tibial ligament instead of meniscus repair to the capsular layer or MCC. This may be of particular importance to Ramp meniscus lesions, other posterior meniscus tear patterns, and meniscus transplant fixation techniques. Our results demonstrate that the central and posterior region of the MTLC can withstand higher loads than the anterior region, indicating that meniscus repairs in the central/posterior region may be of particular importance. These findings support continued development and evaluation of MTLC repair techniques that seek to reproduce the biomechanical and anatomic function of the MTLC, the MCC, and posterior meniscus. Future studies will need to evaluate the impact of MTLC repair on meniscus repair/transplant outcomes and meniscus extrusion. Abrams GD, Frank RM, Gupta AK, Harris JD, McCormick FM, Cole BJ. 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