Regional Alterations of Macroscopy and Histology in Meniscus in an ACL Transection Rabbit Model

Background: Although meniscal injury is common after anterior cruciate ligament (ACL) injury, the underlying process in different meniscal regions remains unclear. Purpose: To investigate macroscopic and histological alterations in different meniscal regions in an ACL transection (ACLT) rabbit model. Study Design: Controlled laboratory study. Methods: ACLT was performed on New Zealand White rabbits. Both the medial meniscus (MM) and the lateral meniscus (LM) of the ACLT knees were obtained at 8 (n = 6) and 26 (n = 6) weeks postoperatively. MM and LM collected from nonoperated knees were considered 0 weeks (n = 6) postoperatively. Menisci were then divided into posterior, central, and anterior regions for macroscopic (width) and histological (hematoxylin and eosin, safranin O/fast green, collagen type 2 [COL2]) analysis. Results: The macroscopic widths of MM and LM increased and then decreased over 26 weeks postoperatively, with all 3 MM widths at 8 weeks significantly wider than at 0 weeks (posterior: P < .01; central: P < .05; anterior: P <.05). In the MM, chondrocyte-like cell density increased and then decreased postoperatively, whereas in the LM, it decreased and then remained almost unchanged. Cell density was significantly higher in the central MM region at 8 weeks than at 0 weeks (P < .05). Glycosaminoglycan (GAG) and COL2 percentages of MM and LM decreased from 0 to 8 weeks and then returned to nearly normal levels at 26 weeks postoperatively. In the MM, the GAG percentage in the posterior (P <.05) and central (P < .01) regions and the COL2 percentage in the posterior region (P < .05) was significantly lower at 8 weeks than at 0 weeks. Conclusion: After ACLT in rabbit meniscus, the extracellular matrix (ECM) initially decreased and then increased to almost normal. Additionally, there were significant differences in the ECM percentage in the posterior and central regions of the MM in comparison with other meniscal regions between 0 and 8 weeks postoperatively.