Meeting Abstract
83.2 Friday, Jan. 7 Locomotor Loading of the Femur in Opossums: Safety Factors, Loading Regimes, and an Explanation for Mediolateral Bending BLOB, R.W.*; BUTCHER, M.T.; GOSNELL, W.C.; MAIE, T.; PARRISH, J.H.A.; Clemson Univ.; Youngstown State Univ.; Clemson Univ.; Clemson Univ.; Clemson Univ. rblob@clemson.edu
Terrestrial locomotion exposes vertebrate limb bones to significant loads that must be resisted to avoid injury. Sprawling amphibians and reptiles exhibit different loading patterns than upright, cursorial mammals, including higher limb bone safety factors and greater torsion. To help evaluate whether non-cursorial mammals might show loading patterns more similar to those of sprawling lineages, we have used implanted strain gauges and force platform recordings to measure loads on the femur in the Virginia opossum (Didelphis virginiana) during terrestrial locomotion. This species uses more crouched limb posture than cursorial mammals and, as a marsupial, belongs to a clade phylogenetically between reptiles and previously studied eutherian mammals. Femoral safety factors for opossums were higher than those for other mammals. In addition, both strain and force platform studies indicated the presence of moderate torsional loading in opossum femora, though bending was predominant. Surprisingly, both strain and force plate data indicate the primary direction of bending in opossum femora is mediolateral, rather than anteroposterior as would be expected for a mammal running with parasagittal limb motion. Force platform data allow us to model muscular contributions to femoral stress, and indicate that mediolateral bending of the femur results because bending imposed by knee extensors on the anterior surface and limb retractors on the posterior surface essentially cancel out, while no lateral muscles are active to counter the compression placed on the medial surface by limb adductors. These results highlight the reciprocal insights to be gained from these experimental techniques. NSF IOS-0517340.
