18th IAA Humans in Space Symposium (2011)
2150.pdf
Musculoskeletal Modeling – Bone Loss in Microgravity
J. A. Pennline
NASA Glenn Research Center, 21000 Brook Park Road, MS 49-7, Cleveland, Ohio 44135,
James.A.Pennline@nasa.gov
ABSTRACT
A mathematical model of bone remodeling in the human adult is described for a representative volume of trabecular
bone in the lower extremities. Results of time simulations of the changes in bone mass under conditions of changes
in load environment and biochemical changes are illustrated. As a continuation of an investigation into the ability of
a mathematical model to simulate bone loss in microgravity (which concentrated on intracortical remodeling) [1],
this work concentrates on trabecular remodeling and has improvements in the initial model which translate into
improved theoretical results. The key elements of the model are as follows. Using the geometry of trabecular
remodeling units, the rate of change of bone area is derived as a function of area resorbed by active resorbing
remodeling units, area formed by active forming remodeling units, activation frequency, osteoclast population, and
osteoblast population. A theoretical stress controlled biomechanical stimulus is replaced with a strain controlled
stimulus according to the well known adaptive response theory of Frost. Within the expressions for rates of changes
of the cellular populations, assumptions for the ligand and receptor expressions are altered in accordance with the
American Society of Bone and Mineral Research (ASBMR) educational literature. Due to the similarity in the
biomechanical element of the model, values of parameters in the model of Nyman et al, [2] are used.
REFERENCES
[1] Pennline J.A. (2009) NASA/TM – 2009-215824. [2] Nyman J.S. et al (2004) Bone 35, 296-305.