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

Abstract

SUMMARYVariation in mechanical loading is known to influence chondrogenesis during joint formation. However, the interaction among chondrocyte behavior and variation in activity patterns is incompletely understood, hindering our knowledge of limb ontogeny and function. Here, the role of endurance exercise in the development of articular and physeal cartilage in the humeral head was examined in 14 miniature swine (Sus scrofa domesticus). One group was subjected to graded treadmill running over a period of 17 weeks. A matched sedentary group was confined to individual pens. Hematoxylin and eosin staining was performed for histomorphometry of cartilage zone thickness, chondrocyte count and cell area, with these parameters compared multivariately between exercised and sedentary groups. Comparisons were also made with femora from the same sample, focusing on humerus-femur differences between exercised and sedentary groups, within-cohort comparisons of humerus-femur responses and correlated changes within and across joints. This study shows conflicting support for the chondral modeling theory. The humeral articular cartilage of exercised pigs was thinner than that of sedentary pigs, but their physeal cartilage was thicker. While articular and physeal cartilage demonstrated between-cohort differences, humeral physeal cartilage exhibited load-induced responses of greater magnitude than humeral articular cartilage. Controlling for cohort, the humerus showed increased chondrocyte mitosis and cell area, presumably due to relatively greater loading than the femur. This represents the first known effort to evaluate chondral modeling across multiple joints from the same individuals. Our findings suggest the chondral response to elevated loading is complex, varying within and among joints. This has important implications for understanding joint biomechanics and development.

The analysis of knee joint loading during drop landing from different heights and under different instruction sets in healthy males

“…This study examined transient knee joint loads during the drop-landing response and the effect of drop height and instruction cues on knee joint loads. Further, this study took steps toward a development of standardized exercise task to examine the effect of acute bouts of mechanical loading on bone and cartilage metabolism in humans, since previous research has been focused on animal models [15, 16]. Consistent with previous literature [24, 30], we found that the knee joint compression force increased with drop height and the instruction to land stiffly.…”

“…Short-term and acute responses of skeletal and articular cartilage metabolism to physical activity have been reported [12–14]; however, findings across studies are difficult to compare because the types of activities and research methodology are not standardized [14]. Traditionally, animal models have been used to examine the effects of mechanical loading on bone and articular cartilage [15, 16]; however, a comparable and standardized model to assess the acute response of bone and cartilage turnover to various levels of mechanical loading has not yet been clearly defined in humans [17]. To improve clinical utility of exercise that may result in a net formation of bone and cartilage in humans, it is important to have a standardized approach that allows researchers to examine responses, to quantify doses of mechanical loads, and to determine if a dose-response exists [14].…”

Teaching an old jaw new tricks: Diet-induced plasticity in a model organism, from weaning to adulthood

“…Indeed, Ravosa et al (Ravosa et al, 2008) found that symphyseal hard tissues in older rabbits maintain a level of plasticity unlike that of the TMJ, which exhibits decreased biomineralization and apparent increases in porosity. The notion that tissue plasticity might be site-specific is supported by comparisons of proximal limb joints in growing pigs subjected to exercise-induced dynamic loading, where differences in bone and cartilage responses were noted between the proximal femur and proximal humerus in the same experimental subjects (Congdon et al, 2012). Osteogenic responses of cortical bone to exercise may also vary along the length of a limb element, with distal regions exhibiting more pronounced morphological changes to altered mechanical stimuli (Hamrick et al, 2006; see also Hsieh et al, 2001).…”

Mouse Shoulder Morphology Responds to Locomotor Activity and the Kinematic Differences of Climbing and Running

“…Different regions of the musculoskeleton do not always respond to mechanical load regimes in the same manner (Biewener and Gillis, '99;Pearson and Lieberman, 2004;Plochocki et al, 2008;Congdon et al, 2012). In this study, we investigated how different locomotor regimes-climbing and running exercise-influence scapular development and the anatomical locations most strongly affected.…”