Mechanobiology of human pisiform formation as a model for endochondral ossification

The role of mechanical stimuli in promoting endochondral ossification during somatic growth and maturation remains an active area of research. This study employs a pisiform model of endochondral ossification to investigate the potential role of mechanobiological signals in the appearance and development of ossification centers and to develop theoretical applications to the primate basicranium. We constructed finite element models based on the structure of a human pisiform within the flexor carpi ulnaris tendon. The pisiform was assigned initial material properties of hyaline cartilage, and tendon properties were based on in situ observations drawn from the literature. A macaque growth model was used to simulate increased load over time as a function of body mass. A load case of uniaxial tension from the tendon was applied over 208 iterations, to simulate weekly growth over a 4-year span. The mechanical signal was defined as shear stress. Element stresses were evaluated in each iteration, with elements exceeding the yield threshold subsequently assigned a higher elastic modulus to mimic mechanically driven mineralization. Three unique mineralization rates were tested. Regardless of rate, all ossification simulations predict a pisiform with heterogeneous stiffness through alternating periods of material stasis and active mineralization/ossification. Assuming metabolic processes underlying endochondral ossification are similar throughout the body, our model suggests that a mechanical signal alone is an insufficient stimulus in the etiology of bone formation through endochondral ossification. Consequently, given the general validity of the simulation, endochondral ossification cannot be fully explained in terms of mechanical stimuli.