Mechanical Responses of the Rabbit Patello-Femoral Joint to Blunt Impact

Abstract

Various studies suggest impact trauma may initially soften cartilage, damage subchondral bone, or a combination thereof. The initial damages are commonly thought due to excessive contact pressure generated on cartilage and the underlying bone. The objective of this research was to develop a small animal model for studying post-traumatic OA and to correlate contact pressure with tissue damage. Blunt insult was graded by dropping a rigid mass onto the hyperflexed hind limb of rabbits. Contact pressure in the patello-femoral joint was measured with pressure sensitive film. One, 3, 6, and 14 days later the animals were euthanized. Damage to cartilage and the underlying bone was assessed visually and in microscopic sections. Indentation experiments were performed on the patellar cartilage with a rigid, flat probe. Contact pressures were nonuniform over the articular surfaces and a high frequency of surface fissures were generated on the lateral facet in severe insults. The appearance of surface fissures correlated better with the magnitude of contact pressure gradients in the damage zone than the magnitude of contact pressures on the facet, per se. Blunt trauma causing surface fissures resulted in a measurable degree of softening in the patellar cartilage, especially close to the defects. Surgical intervention of the joint to insert pressure sensitive film, however, also resulted in significant softening of the cartilage.

Mechanical quality of tissue engineered cartilage: Results after 6 and 12 weeks in vivo

“…[2][3][4] Injuries or illnesses may furthermore lead to a softening of the cartilage composite structure. 5 In such instances, the cartilage composite structure may be irreversibly destroyed. Self-repair processes may not be adequately able to restore the articular joint surface and integrity.…”

Causes of mechanically induced collagen damage in articular cartilage

“…3 Several impact models have been used to study the processes leading to cartilage degeneration. The most common trauma caused by impact loading are fissures at the cartilage surface in the middle of the impacted zone, which extend downward at approximately 45 degrees into the superficial, [4][5][6][7][8] middle, 9,10 or deep 11,12 zones. Excessive shear stresses, 13 excessive tensile stresses, 14 or excessive principal strains, [15][16][17][18] might cause the formation of these cracks.…”

The limitation of acute necrosis in retro-patellar cartilage after a severe blunt impact to the in vivo rabbit patello-femoral joint

“…The blunr impact experiments have been described previously [14]. Briefly, a 1.33 kg mass with a flat 25 mm diameter aluminum impact interface was dropped from 0.46 m (6 J of impact energy) onto the right patello-femoral joint of anesthetized animals (2% isoflurane and oxygen).…”

“…A low speed bone saw (model# 11-1180-170, Buehler, Inc., Lake Bluff, IL) was used to remove trabecular bone from the overlying retro-patellar cartilage, leaving approximately 0.5 mm of subchondral bone. Full depth sections (0.5 mm thick) of retro-patellar cartilage and subchondral bone were cut using a specialized cutting device [8] from the area of known patello-femoral contact during blunt impact [14]. Sections were stained with Calcein AM and Ethidium Homodimer, according to the manufacturer's specifications (Live/Dead Cytotoxicity Kit, Molecular Probes, Eugene, OR).…”

“…We developed a model of post-traumatic OA using the Flemish Giant rabbit [14]. In a recent study using this model, a rigid impact mass was dropped with 6 J of energy onto the flexed patello-femoral joint, resulting retro-patellar surface cartilage, and thickening of underlying subchondral bone after 3 years [lo].…”