AJSM - 2026-04-14 - Journal Article
Establishment of a Rat Pull-Out Repair Model Demonstrating Fibrous Meniscus-Bone Healing and Suppression of Meniscal Extrusion After Medial Meniscus Posterior Root Tear.
Katsumata T, Nakagawa Y, Yoshida R, Matsuda J, Nakamura T, Miyatake K, Katagiri H, Seki R, Tokumoto Y, Hagiwara R, Sekiya I, Tsuji K, Koga H
Topics
Key Takeaway
A rat pull-out repair model for MMPRT demonstrates significantly lower meniscal extrusion ratio versus unrepaired controls at all time points, with tensile load-to-failure equivalent to the contralateral healthy limb by 4 weeks, but healing proceeds via fibrovascular indirect insertion rather than direct fibrocartilaginous regeneration at 12 weeks.
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Summary
This controlled laboratory study created a rat MMPRT pull-out repair model using external fixation to assess biomechanical, histological, and radiographic healing outcomes at 4 and 12 weeks. The repair group demonstrated significantly lower meniscal extrusion ratio than the nonrepair group at all time points, and maximum load to failure did not differ from the contralateral healthy knee at either time point. Histology at 12 weeks revealed predominantly fibrovascular indirect insertion-like healing with collagen type 3 matrix at the meniscus-bone interface, with direct healing observed in only 2 of 50 specimens.
Key Limitation
Healing was assessed only at 2 discrete time points with no intermediate intervals, leaving the temporal sequence of fibrovascular-to-fibrocartilaginous transition—and whether it occurs at all—uncharacterized.
Original Abstract
BACKGROUND
Medial meniscus posterior root tear (MMPRT) disrupts meniscal hoop tension and is associated with osteoarthritis progression. Although pull-out repair is a standard surgical technique for MMPRT, its precise healing process remains unclear.
PURPOSE/HYPOTHESIS
This study aimed to establish a rat model for MMPRT pull-out repair, investigating its biomechanical and histological healing and its effect on medial meniscus extrusion (MME). It was hypothesized that pull-out repair would show reduced MME and restore biomechanical property toward normal.
STUDY DESIGN
Controlled laboratory study.
METHODS
A total of 100 male Wistar rats were assigned to the repair (MMPRT pull-out repair with external fixation) or nonrepair (unrepaired MMPRT with external fixation) group. Contralateral knees served as controls. Operated knees were immobilized with an external fixator for 2 weeks. Evaluations at 4 and 12 weeks included micro-computed tomography to quantify MME using the meniscal extrusion ratio (MER), biomechanical testing for tensile strength, and macroscopic/microscopic assessments.
RESULTS
The repair group showed a significantly lower MER than the nonrepair group at all time points. No difference in maximum load to failure was found between 4 and 12 weeks. At both time points, there was no significant difference between the repair group and the healthy leg. Histological analysis at 12 weeks in the repair group showed ongoing meniscus-bone healing, characterized mainly by fibrovascular interface tissue resembling indirect insertion-like healing, although direct healing was observed in 2 specimens. Immunohistochemically, a collagen type 3-positive matrix was observed along the meniscus-bone interface, indicating persistent remodeling of the fibrous tissue. In the nonrepair group, no spontaneous healing at the posterior root attachment was observed, and scar adhesions to surrounding tissues were present at 12 weeks.
CONCLUSION
The authors established a rat model for pull-out repair of the MMPRT combined with external fixation. In this model, the process of meniscus-bone healing was elucidated, showing an indirect healing pattern characterized by fibrovascular interface formation. This model may serve as a preclinical platform to test strategies aimed at enhancing repair stability and promoting meniscus-bone healing.
CLINICAL RELEVANCE
This model provides a valuable tool for comprehensively investigating the biological and biomechanical aspects of MMPRT repair. It may serve as a preclinical platform to investigate the healing mechanism and test future modifications of the surgical procedure and postoperative loading/rehabilitation conditions.