Differences in the repair process of longitudinal and transverse injuries of cartilage in the rat knee

Abstract

Objective: To clarify the relationship between type or direction of cartilage injury and its repair process, we investigated defects produced in rat knees histologically, immunohistochemically, and histomorphometrically. Methods: A full-thickness cartilage injury (1 mm wide and 5 mm long) was produced on the patellar groove of one knee (L-injury) and transversely on the other knee (T-injury) in 42 male Wistar rats. Six rats each were sacrificed at 1, 2, 3, 4, 6 and 8 weeks after surgery, and cartilage tissues were obtained, prepared into 4 μm-thick histologic specimens, and stained with hematoxylin and eosin. Cartilage thickness, cartilage area, and surface roughness were measured using a computer system. Localization of S-100 proteins was evaluated with immunohistochemistry. Results: Grossly, there were no difference in repair process between L- and T-injuries. However, histological and histomorphometric differences became apparent after the third week: cartilage thickness, repair area, and surface roughness showed better recovery in L-injury than in T-injury. Appearance of S-100-positive protein preceded the appearance of chondrocytes, and L-injury presented S- 100 in the entire defect while S-100 in T-injury appeared mainly on the margins of the defect. Conclusions: Repair mechanism of cartilage injury differs according to injury direction. Better repair can be obtained in the injury which is parallel to the direction of joint motion.