21 - Articular Cartilage Becomes Thicker Under Load: A Rodent Model of Cartilage Response to Bipedalism

Poster Board Number: 21
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Co-authors:

David Komatsu - Department of Orthopedics and Rehabilitation - Stony Brook University; Christopher Percival, PhD - Assistant Professor, Anthropology, Stony Brook University

Abstract Body : Long femurs, femoral obliquity, and lateral femoral condyle ellipticity are all bony features hypothesized to be functionally related to bipedalism in humans and fossil hominins. However, the degree to which these morphologies might appear as a direct mechanical result of bipedal locomotion during an organism’s life, as opposed to an evolutionary change over many generations, is important to understanding the early context of the hominin shift to bipedalism. Analysis of children has shown that femoral obliquity and condylar ellipticity develop in conjunction with the acquisition of bipedal walking, indicating that bipedal locomotion itself may contribute to these morphologies. In animal models, rats subjected to bipedal exercise developed longer lower-limb bones and larger epiphyses than their quadrupedal or unexercised counterparts. Similarly, the fact that humans display thicker femoral articular cartilage than quadrupedal primate relatives may be the direct result of growth responses triggered by higher loading magnitudes experienced during bipedalism. To evaluate if articular cartilage thickness can be increased by plastic developmental responses to higher loads, we compared the tissue morphology of rats that exercised bipedally to quadrupedal controls. We collected histological slices from the right lateral femoral condyles of 4 rats (2 control and 2 biped). The slices were stained using Hematoxylin and Eosin. Multiple linear distance thicknesses of the anterior, middle, and posterior thirds of condylar articular cartilage were measured for each specimen. Averages and standard deviations were calculated for all thicknesses collected from single experimental groups for the anterior (biped: 16.99um + 1.51, control: 15.42um + 3.50), middle (biped: 17.58um + 1.84, control: 12.84um + 1.34), and posterior (biped: 19.04um + 2.16, control: 12.81um + 0.813) areas. Our results reveal that there is an average increase of ~1.5um in the anterior aspect of the condyle, ~4.7um in the middle aspect of the condyle, and ~6.2um in the posterior aspect of the condyle. Although the sample size is currently not large enough for statistical analysis, our results suggest that developmental plasticity may contribute to producing thicker articular cartilage in the human knee. Further work is planned to validate this result. This work was supported by start-up funds from Stony Brook University to CJP.