Incomplete Histologic Healing and Diminished Biomechanical Strength of Meniscus-Bone Interface After Medial Meniscus Posterior Root Transosseous Repair in a Goat Model.

Purpose: To enhance the understanding of histologic healing after repairing medial meniscal posterior root tears (MMPRTs) at an early stage, utilizing a goat model.

Methods: Eighteen adult goats, totaling 36 knee joints, were allocated into 3 groups (n = 12): sham group (Sham), root tear group (RT), and root tear with transosseous suture group (RTS). At 12- and 24-week intervals postsurgery, all the knees were harvested for imaging, macroscopic, histologic, and biomechanical assessments.

Results: The intact root served as a meniscus-bone interface that connected the tibial and circular fibers of the meniscus with a bony insertion and a root-meniscus transition. A direct fibrous connection was displayed at the bony insertion proximal to the synovium in the RTS group, while the remaining regions of the root displayed indirect fibrous healing. The healing in the RT group was disjointed and reminiscent of scar tissue. The RTS group exhibited a more pronounced coronal extrusion compared to the Sham group (0.42 ± 0.09 vs 0.19 ± 0.02, P = .0012) but was improved relative to that of the RT group (0.49 ± 0.02, P = .0028). The failure load and stiffness of the RTS group were notably higher than those of the RT group, with a strength of 42.67% and a stiffness of 83.75% of the intact root. All the samples ruptured at the root-meniscus transitions.

Conclusions: The incomplete healing may be attributed to the histologic factors underlying the low healing rate and persistent medial meniscal extrusion. Notably, the region attached to the posterior cruciate ligament exhibited superior healing compared to other regions of the bony insertion in the repaired group. Conversely, the root-meniscus transition displayed discontinuity, representing a mechanical weakness in the healing process.

Clinical relevance: Modifications of bone tunnel positioning and suture placement could be undertaken in subsequent studies to enhance the healing of the root-meniscus transition.