Larger animals have thicker bones, but their this does not hold true for their cartilage. This could point to increased risk of joint wear in larger animals like humans.
The cartilage research was published very recently in the journal PLoS ONE. In a joint study by UMC Utrecht and the Faculty of Veterinary Medicine at Utrecht University, knee cartilage of 121 animals from 58 different mammal species – including humans – was analysed. Measurements were taken of the cartilage thickness and composition from the knees of very diverse species: the weights of these adult animals varied from 25 grams (mouse) to 4000 kg (African elephant). Results demonstrated that the increase in cartilage thickness does not keep pace with the increase in body weight. Although the cartilage composition, and thus the tissue strength, remains constant across species, larger animals have proportionally thinner cartilage. This could make the cartilage of larger animals more vulnerable, which could partly account for these animals’ relatively high prevalence of joint wear, or arthrosis – a malady rarely seen in small animals. It follows, according to the investigators, that small mammals such as mice and rats are not appropriate models for human health.

The report does offer an explanation for the thinner cartilage. This tissue type is not supplied with blood vessels, receiving its nutrients instead via diffusion. When the distance over which the diffusion takes place is too great, sufficient nutrients do not reach the cells in the deepest layers.