Meeting Abstract

P1.164  Monday, Jan. 4  Ground reaction forces on the hindlimb of the opossum ( Didelphis virginiana ) during terrestrial locomotion: implications for femoral loading GOSNELL, W. C.*; BUTCHER, M. T.; MAIE, T.; BLOB, R. W.; Clemson Univ.; Youngstown State Univ.; Clemson Univ.; Clemson Univ. wgosnel@clemson.edu

Studies of limb bone loading in terrestrial mammals have typically found bending to be the primary loading regime, with torsion less significant. However, previous studies have focused on large and/or cursorial eutherian species in which the limbs are held essentially upright. Recent in vivo strain data from the Virginia opossum Didelphis virginiana, a marsupial that uses crouched rather than upright limb posture, have indicated that its femur experiences moderate torsion during locomotion. Though not as great as the torsion measured from the femora of non-avian reptiles, femoral torsion in opossums is greater than that seen in cursorial mammalian species. The elevated femoral torsion observed in opossums (compared to other mammals) might result from medial inclination of the ground reaction force (GRF), crouched limb posture, or a combination of these factors. To evaluate the mechanism underlying torsional loading in opossum femora, we filmed opossums running over a force platform, allowing us to measure the magnitude of the GRF and its three-dimensional orientation relative to the limb. Results indicate that at peak magnitude the GRF is oriented nearly vertically, with mediolateral inclination typically less than 5 degrees. These results are similar to those observed in other mammals, indicating that elevated torsional loads in opossum femora are likely correlated with their crouched limb posture, rather than differences in GRF orientation compared to other taxa. NSF IOB-0517340.