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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. [ABSTRACT FROM AUTHOR]

Background: The collagen ultrastructure of the discoid lateral meniscus (DLM) has not been precisely defined. Purpose: To investigate the ultrastructure of the DLM, focusing on its collagen fibers, and to compare the collagen net architecture between intact and torn DLMs using the Collagen Meniscal Architecture (CMA) scoring system. Study Design: Descriptive laboratory study. Methods: Thirty specimens were taken from 30 patients with a diagnosis of a complete DLM using a 1-piece technique. The collagen ultrastructure of the DLMs was assessed with transmission electron microscopy. To evaluate the meniscal ultrastructure, the degree of collagen disruption, intrafibrillar edema, loss of banding, degree of collagen packing, and fibril size variability were assessed and graded from 1 (normal) to 3 (severe disarray) according to the CMA scoring system. The DLM specimens were divided into 3 groups according to the intrasubstance tear: the intact group (group I) had no tear; the simple tear group (group S) had a radial, longitudinal, or horizontal tear; and the complicated tear group (group C) had a complicated horizontal tear. Intact normal meniscus specimens (group N) were used as the control group. Results: There were 10 specimens in group I, 8 in group S, 12 in group C, and 13 in group N. In group I, there were 5 grade 1 and 5 grade 2 menisci; group S had 2 grade 1, 3 grade 2, and 3 grade 3 menisci; group C had 1 grade 1, 4 grade 2, and 7 grade 3 menisci; and group N had 4 grade 1, 7 grade 2, and 2 grade 3 menisci. A significant difference in the CMA score was observed between the 4 groups (P = .009). The median CMA score was significantly lower in group I (2; range, 1-4) than in group S (4; range, 2-7) (P = .041) and group C (4.25; range, 1.5-7) (P = .018). No significant difference was found between groups S, C, and N. Conclusion: Variability existed in the collagen ultrastructure of the DLM, and some DLMs showed a nearly normal ultrastructural pattern. The degree of density and disorganization of the collagen architecture in the DLM was related to the tear. Clinical Relevance: The study results might provide a histological background for partial meniscectomy in the treatment of a symptomatic DLM. [ABSTRACT FROM AUTHOR]

Background: In vivo length change behavior of native medial patellofemoral ligament (MPFL) fibers throughout the range of knee motion has not been reported in vivo. Purpose: To measure the length changes of various fibers of the MPFL and to determine their length change patterns during in vivo passive knee flexion. Study Design: Descriptive laboratory study. Methods: The right knees of 11 living subjects were scanned with a high-resolution computed tomography scanner at 0, 30, 60, 90, and 120 of knee flexion, and 3-dimensional (3D) models were constructed using customized software. Five patellar points were determined: 20% (point 20), 30% (point 30), 40% (point 40), 50% (point 50), and 60% (point 60) from the superior pole of the patella. The Schöttle femoral point (point F) was marked on a translucent 3D model of a true lateral view. Five virtual fibers connecting these points on the 3D knee model were created, and the lengths of various fibers were digitally measured. Results: The average length changes were 9.1 6 2.5 mm in F20, 9.1 6 2.5 mm in F30, 8.1 6 2.6 mm in F40, 6.9 6 2.4 mm in F50, and 6.9 6 1.7 mm in F60. There were significant differences in length changes of these 5 fibers (P\.001). The lengths of 2 superior fibers (F20 and F30) increased as the knee flexed from 0 to 30 and decreased as the knee flexed over 30. The lengths of a middle fiber (F40) and an inferior fiber (F50) increased from 0 to 30, reached a plateau from 30 to 60, and then decreased from 60 to 120. F60 showed an increase from 0 to 30, and then a plateau pattern from 30 to 90, followed by a decrease during further flexion. Conclusion: Superior fibers exhibited their maximum lengths at low flexion angles, and inferior fibers exhibited their maximum lengths at midflexion angles. The MPFL is a complex of functionally various fibers with some taut and others slack over the whole range of knee motion. Clinical Relevance: The results for lengths and length change patterns of various MPFL fibers are expected to serve as a theoretical background for anatomic double-bundle MPFL reconstruction. [ABSTRACT FROM AUTHOR]