Subfracture insult to a knee joint causes alterations in the bone and in the functional stiffness of overlying cartilage

Abstract

The current criteria used by the automotive industry for predicting joint injury are based on fracture of bone, but clinical studies suggest that chronic diseases such as osteoarthrosis can occur from a single blunt insult without bone fracture. In the current study, blunt insults were delivered to the patellofemoral joints of rabbits without producing bone fractures. Biomechanical and histological studies were performed on joint tissues at various times after insult. The functional integrity of the retropatellar cartilage on the lateral facet was measured with mechanical indentation experiments, and the thickness of the subchondral bone was measured from histological sections. Impacts produced surface lesions on the retropatellar cartilage. The thickness of the subchondral bone in representative animals tended to increase with time after insult, and the bone exhibited significant thickening at 12 months. The overlying cartilage showed signs of degeneration. However, the mechanical stiffness of the cartilage did not change until 12 months after the insult.

Enforced exercise after blunt trauma significantly affects biomechanical and histological changes in rabbit retro-patellar cartilage

“…One explanation for this result may be related to the significant change documented in the histological character of the impacted cartilage in the cage-activity group between years 1 and 2. Histological sections of retro-patellar tissue in the earlier study at 1 year (Newberry et al, 1997) did not show significant ossification/calcification, erosion and extensive loss of surface integrity in the impacted versus non-impacted limbs, in contrast to that shown in the current study. The histology of impacted cartilage after 1 year of cageactivity was described as being more similar to that of the exercise group in the current study, in which the impacted cartilage was also softer than that of the nonimpacted limb.…”

“…In a previous study from this laboratory 12 months of cage activity following a 6 J impact on the PF joint resulted in a statistically significant softening of the retro-patellar cartilage, based on G U from the Hayes et al (1972) solution (Newberry et al, 1997). A comparison with the current study would suggest that an additional year of cage activity must have resulted in a stiffening of the impacted cartilage with respect to the non-impacted limb.…”

Cell death after cartilage impact occurs around matrix cracks

“…Cracking ofGartilage seen in animal models of OA [17,19,20] have been shown to be co-localized with acellularity in the cracked tissue [ 191, and regions of chondrocyte apoptosis [l]. Since simple cuts in cartilage do not lead to progression [26] it is likely cell death and tissue disruption is needed for progression.…”

“…Post-traumatic cracking of cartilage has been seen in human joints in vivo, and increased cracking was associated with higher histological damage scores indicating cell death or injury [14]. So the spatial relationship between matrix cracks and non-viable cells may be of clinical importance [20] and it is easy to imagine progression to full-depth cracks, even with normal joint loading [25,28].…”

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.…”