Articular cartilage superficial zone collagen birefringence reduced and cartilage thickness increased before surface fibrillation in experimental osteoarthritis

Abstract

Objectives-To investigate articular cartilage collagen network, thickness of birefringent cartilage zones, and glycosaminoglycan concentration in macroscopically normal looking knee joint cartilage of young beagles subjected to experimental slowly progressive osteoarthritis (OA). Methods-OA was induced by a tibial 30°v algus osteotomy in 15 female beagles at the age of 3 months. Fifteen sisters were controls. Cartilage specimens were collected seven (Group 1) and 18 months (Group 2) postoperatively. Collagen induced optical path diVerence and cartilage zone thickness measurements were determined from histological sections of articular cartilage with smooth and intact surface by computer assisted quantitative polarised light microscopy. Volume density of cartilage collagen fibrils was determined by image analysis from transmission electron micrographs and content of glycosaminoglycans by quantitative digital densitometry from histological sections. Results-In the superficial zone of the lateral tibial and femoral cartilage, the collagen induced optical path diVerence (birefringence) decreased by 19 to 71% (p < 0.05) seven months postoperatively. This suggests that severe superficial collagen fibril network deterioration took place, as 18 months postoperatively, macroscopic and microscopic OA was present in many cartilage areas. Thickness of the uncalcified cartilage increased while the superficial zone became thinner in the same sites. In operated dogs, glycosaminoglycan content first increased (Group 1) in the lateral tibial condyle and then decreased (Group 2) (p < 0.05). Conclusion-In this OA model, derangement of the superficial zone collagen network was the probable reason for birefringence reduction. This change occurred well before macroscopic OA.

Causes of mechanically induced collagen damage in articular cartilage

“…19,21,22 Indeed, several studies showed that fibrillation, clefts, and disintegration of the collagenous fibril network in the tangential zone occur in early in degeneration. [23][24][25][26][27] Lewis et al 28 found broken collagen fibrils at the tips of cracks, but most fibrils were partially peeled apart. This peeling process suggests that the fibrils are normally ''tied'' together in a parallel fashion [29][30][31] and that crack propagation starts by fibrils being peeled apart as a result of failure of the collagen fibril bonding.…”

Vibrational spectroscopy of articular cartilage

“…Degenerative changes occur in AC tissue during OA. Typically, the first changes are seen in the superficial layer of AC: the amount of proteoglycans decreases (8) and fibrillation of the collagen network occurs (9). AC has a limited intrinsic capability of healing injuries.…”

Study on the damage mechanism of articular cartilage based on the fluid–solid coupled particle model

“…The early degradation, crack, and damage of collagen network in articular cartilage usually occur in the tangential section. 3,4 Most previous researches on articular cartilage have treated it as porous materials composed of a porous fluid phase and a solid phase (collagen, proteoglycans, and chondrocytes immiscible solid matrix and pore fluid. Namely, collagen, proteoglycans, and chondrocytes were considered as a linear elastic solid, whereas water and electrolyte were considered as an ideal fluid.…”