Glycosaminoglycan depletion lowers the crack resistance of articular cartilage under impact loading

Osteoarthritis is a degenerative and debilitating disorder affecting diarthrodial joints, where articular cartilage degeneration occurs due to simultaneous, enzymatic degradation and mechanical damage through crack initiation and propagation. Healthy cartilage is effective in absorbing impact loads and resists cracking but physical impact beyond a certain high energy is considered as the critical reason for initiation and propagation of cracks. Enzymatic degradation destroys the molecular structure of cartilage affecting its biomechanical properties and is bound to affect its crack resistance. This research aims to explore the conditions associated with crack initiation in healthy bovine cartilage through indirect assessment of absorbed impact energy, and to determine the influence of enzymatic degradation on cartilage cracking. Cartilage cracks are characterized by length, number of branches and endpoints. Bovine cartilage enzymatic degradation was achieved through treatment with chondroitinase ABC, which reduces the cartilage glucosamine glycan (GAG) content. A drop tower impact test (stainless steel ball-bovine cartilage plug) was applied to evaluate the absolute energy absorption capacity of the cartilage. In contrast, the pendulum test was designed to better replicate a physiological scenario—specifically, cartilage-on-cartilage contact from a massive collision. The absorbed impacting energy by both sides together was obtained in this case. Due to the depletion of GAGs by chondroitinase ABC, the digested cartilage showed more severe cracks under the same impact energy as healthy cartilage. Also single cracks formed from parallel to 45° to perpendicular to the collagen fibers orientation on both cartilage groups.