Subchondral bone thickness, hardness and remodelling are influenced by short‐term exercise in a site‐specific manner

Abstract

It was hypothesised that subchondral bone thickness, hardness and remodelling are influenced by exercise intensity, and by location within a joint. Dorsal carpal osteochondral injury is a major cause of lameness in horses undergoing high intensity training. This project aimed to determine the subchondral bone thickness, formation, resorption and hardness at sites with high and low incidence of pathology in 2 year-old horses undergoing 19 weeks high intensity treadmill training or low intensity exercise, and to compare these factors between exercise groups. Dorsal and palmar test sites were identified on radial, intermediate and third carpal articular surfaces after euthanasia. Adjacent osteochondral samples from each test site underwent histomorphometric analysis (for subchondral bone thickness, osteoid perimeter, osteoid seam width, eroded cavity area and eroded cement line surface length) and microhardness testing. Bone from horses undergoing high intensity training was thicker with a greater osteoid perimeter, and at individual sites had a smaller osteoid seam width and eroded cavity. Exercise-related differences were most marked at dorsal locations. Maximal differences in bone formation indices were observed at dorsal radial and medial third carpal locations. Overall subchondral bone from dorsal sites was thicker with a greater osteoid perimeter. Subchondral bone from dorsal sites was approximately 35% harder than bone from palmar sites. These results show topographical variations in subchondral bone structure, formation, resorption and material properties and a site-specific response to exercise. The maximal response to exercise was at high load sites with a clinical predisposition to injury. These findings indicate that the combined effect of exercise and local load variations within a joint may lead to maxiinal adaptive responses or overload of these responses at sites predisposed to injury. 0 3001

Differential limb loading in miniature pigs (Sus scrofa domesticus): a test of chondral modeling theory

“…Chondral modeling theory predicts that growing joints subjected to elevated mechanical stresses exhibit an adaptive response, including elevated chondrocyte mitosis and hypertrophy, which results in increased cartilage formation and larger joints (Frost, 1979;Frost, 1999;Hamrick, 1999;Murray et al, 2001;Carter and Wong, 2003;Plochocki et al, 2009). This hypothesis was investigated in two ways in a sample of growing pigs subjected to different loading regimes: (1) the effects of exercise vs sedentary locomotion on cartilage plasticity in the proximal humerus; and (2) behaviorcontrolled comparisons of cartilage histomorphometry between the proximal humerus and proximal femur.…”

“…Chondral modeling is defined as the adaptive ontogenetic response of cartilage to regional variation in hydrostatic pressure, resulting in increased chondrocyte mitosis and synthesis of the extracellular matrix (ECM), influencing overall joint topography, congruence and size (Frost, 1979;Frost, 1999;Hamrick, 1999;Murray et al, 2001;Carter and Wong, 2003;Plochocki et al, 2009). Such chondrogenic changes are believed to facilitate normal joint movement and minimize dangerously high regional contact stresses (Frost, 1979).…”

“…Following the expectations of chondral modeling theory, it was hypothesized that an increase in mechanical loading of the proximal humerus would result in chondrocyte hypertrophy and proliferation, with corresponding increases in cartilage height (Frost, 1979;Frost, 1999;Hamrick, 1999;Murray et al, 2001;Carter and Wong, 2003;Plochocki et al, 2009). As pig forelimbs are known to be loaded more heavily than their hindlimbs (Thorup et al, 2007;Von Wachenfelt et al, 2009a;Von Wachenfelt et al, 2009b;Von Wachenfelt et al, 2010), chondral modeling was further examined via cohort-controlled analyses of the proximal humerus and proximal femur.…”

Animal Models for Cartilage Regeneration and Repair

“…Due to their weight and physiology, equine jointloading conditions and the consequent hardness of equine subchondral bone are of some concern. 89 Consequently, any potential treatment applied over the cartilage defect will be subjected to greater loading than in humans. Additionally, the horse is unable to maintain protected weight-bearing protocols that are typical following human cartilage repair procedures.…”

Knee Posture Predicted from Subchondral Apparent Density in the Distal Femur: An Experimental Validation

“…Because of its position at this interface, it may serve to transmit and distribute loads to the trabeculae and may also have some load attenuating function (Radin et al, 1970a;Radin and Paul, 1971;Simon et al, 1972;Hoshino and Wallace, 1987). The responses of subchondral bone to joint loading are not completely understood, but it appears to respond in a manner similar to other bony tissues (Radin and Paul, 1971;Simon et al, 1972;Eckstein et al, 1995;Murray et al, 2001;Burr and Radin, 2003), and while bone mineral density is largely influenced by heredity (Krall and DawsonHughes, 1993), other environmental factors such as exercise play significant roles (e.g., Forwood and Burr, 1993;Magkos et al, 2007). Increasing bone density confers several advantages, such as increased strength in compression, compressive modulus, fatigue life, resistance to crack initiation, and tensile strength (Carter and Hayes, 1977;Wright and Hayes, 1977;Wall et al, 1979;Currey, 1988Currey, , 2002Rice et al, 1988).…”