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Collagenous Ultrastructure of the Torn Medial Meniscus Posterior Root: A Transmission Electron Microscopy Study

Background: The collagen ultrastructure of torn medial meniscus posterior roots (MMPRs) has not been precisely defined. Purpose: To investigate the ultrastructure of torn MMPRs, focusing on their collagen fibers, and to compare the collagen net architecture between intact and torn MMPRs using the Collagen Meniscal Architecture (CMA) scoring system. Study Design: Descriptive laboratory study. Methods: Forty-three human meniscal specimens were obtained from 32 patients with osteoarthritis during total knee arthroplasty between January 2018 and November 2018. There were 23 specimens taken from patients with an MMPR tear and 20 taken from patients without an MMPR tear served as a control group. The presence of an MMPR tear was defined as a complete radial tear within 9 mm of the posterior root attachment. The collagen ultrastructure of the meniscal specimens was assessed with transmission electron microscopy using the CMA scoring system. Patient demographics included sex, age, and body mass index, and radiographic assessments included the Kellgren-Lawrence (K-L) grading system and the mechanical axis angle. Results: The median CMA score was significantly higher in torn MMPRs (5.5 [interquartile range, 3.5-6.0]) than in intact MMPRs (2.0 [interquartile range, 1.5-3.8]) (P < .001). When the CMA scores were converted to CMA grading, 23 torn MMPRs had 1 grade I, 9 grade II, and 13 grade III menisci. In 20 intact MMPRs, there were 12 grade I, 7 grade II, and 1 grade III menisci. No significant differences in sex, age, body mass index, K-L grade, or mechanical axis angle were found between groups. Conclusion: This study showed that torn MMPRs had decreased numbers and disorganized courses of collagen fibers. The structural problem of torn MMPRs can negatively affect meniscal healing, function, and long-term survival after root repair. Clinical Relevance: These results might provide a histopathological reason for the low healing rate after MMPR repair.