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.
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 microns-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.
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.
Repair mechanisms 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.