Mammalian Limb Loading and Chondral Modeling During Ontogeny

Abstract

The adaptive growth response of cartilage, or chondral modeling, can result in changes in joint and limb proportions during ontogeny and ultimately contribute to the adult form. Despite Hamrick's (1999) reevaluation of the mechanisms of chondral modeling, the process of chondral modeling remains poorly studied in animal models. Here, we characterize the macro-and microanatomical responses of the femoral growth plate, articular cartilage, and bone in 15 juvenile Sus scrofa domestica subjected to different locomotor activity patterns. The exercised animals exhibit thinner cartilage zones, greater cellularity and larger proliferative chondrocyte areas in the growth plate, as well as larger femoral dimensions and a more elongate femoral head compared with sedentary controls. In general, the growth plate demonstrates greater adaptive changes than articular cartilage. Moreover, chondrocyte hypertrophy and proliferation were found to be responsive to locomotor loading and thus more important factors in chondral modeling than the extracellular matrix variables that were examined herein. In sum, the underlying mechanisms of adaptive chondrogenesis and bone plasticity are key to informing evolutionary and translational studies regarding determinants of variation in joint form and function. Given the disparity between the predictions of chondral modeling theory and our experimental findings, this suggests a need for further evaluation of chondral modeling responses during ontogeny. Anat Rec,

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

“…In this regard, a recent study found dissimilar results regarding the plasticity responses of articular and physeal cartilage to altered limb loading (Hammond et al, 2010). In particular, support for the predictions of chondral modeling theory, including increased cell proliferation and cartilage height, was observed only for the physeal cartilage.…”

“…Chondral modeling theory predicts regional or widespread thickening of cartilage, changes in cellular and extracellular cartilage composition, and differential mineralization and ossification of hyaline tissue, thereby directly influencing bony morphology through increased bone deposition. There is evidence that chondral modeling occurs at articular and physeal cartilage surfaces (Hammond et al, 2010) and it is hypothesized to occur at sites of fascial, tendinous and ligamentous insertion (Frost, 1979).…”

“…Postnatal variation in mechanical loading has been shown to yield changes in chondrocyte proliferation and metabolism, as well as changes in the synthesis and proteoglycan content of the ECM, ultimately influencing adult form (Eggli et al, 1988;Kiviranta et al, 1988;Wu and Chen, 2000;Liu et al, 2001;Carter and Wong, 2003;Ravosa et al, 2007;Ravosa et al, 2008a;Ravosa et al, 2008b;Hammond et al, 2010). Chondrocytes, in various stages of development, are the only cells located in cartilage.…”

“…While neither cartilage height nor cellularity discriminated well between the articular cartilage in the proximal femur of exercise vs sedentary pigs, both parameters in the physeal cartilage were highly successful in discriminating between loading cohorts. Such dissimilarities in the response of different cartilage types highlight the possibility of site-specific variability in chondrogenesis and, ultimately, variation in cartilage proportions within the same joint of members of a given loading cohort (Hammond et al, 2010). Additional in vivo data on load-induced responses of the ECM as well as chondrocyte proliferation and hypertrophy would be invaluable for further illuminating issues regarding intralimb variation in chondrogenesis as it relates to altered loading regimes.…”

Life history as a constraint on plasticity: developmental timing is correlated with phenotypic variation in birds

“…For example, fish reared on different diet types develop entirely different jaw morphologies (Meyer, 1987;Wainwright et al, 1991;Adams et al, 2003;Muschick et al, 2011), which adaptively affects their feeding performance on locally abundant resources (Bouton et al, 2002;Parsons and Robinson, 2007). Similarly, rabbits reared on different diets develop entirely different jaw, palate and cranial structures (Menegaz et al, 2009;Menegaz et al, 2010), whereas pigs reared in different locomotor environments differ in joint and bone structure (Hammond et al, 2010;Congdon et al, 2012). We focus on avian bills because variation in the length, depth and width of the bill has been tied to functional variation in avian foraging, both within and between species (Grant, 1979;Smith, 1987;Benkman et al, 2001;Herrel et al, 2005).…”