Mechanical significance of femoral head trabecular bone structure inLorisandGalagoevaluated using micromechanical finite element models

Abstract

Work on the interspecific and intraspecific variation of trabecular bone in the proximal femur of primates demonstrates important architectural variation between animals with different locomotor behaviors. This variation is thought to be related to the processes of bone adaptation whereby bone structure is optimized to the mechanical environment. Micromechanical finite element models were created for the proximal femur of the leaping Galago senegalensis and the climbing and quadrupedal Loris tardigradus by converting bone voxels from high-resolution X-ray computed tomography scans of the femoral head to eight-noded brick elements. The resulting models had approximately 1.8 million elements each. Loading conditions representing takeoff phase of a leap and more generalized load orientations were applied to the models, and the models were solved using the iterative "row-by-row" matrix-vector multiplication algorithm. The principal strain and Von Mises stress results for the leaping model were similar for both species at each load orientation. Similar hip joint reaction forces in the range of 4.9 x to 12 x body weight were calculated for both species under each loading condition, but the hip reaction values estimated for Loris were higher than predicted based on locomotor behavior. These results suggest that functional adaptation to hip joint loading may not fully explain the differences in femoral head trabecular bone structure in Galago and Loris. The finite element method represents a unique and useful tool for analyzing the functional adaptation of trabecular bone in a diversity of animals and for reconstructing locomotor behavior in extinct taxa.

Finite element analysis in functional morphology

“…Laser scans can offer a high-resolution representation of the outer surface, but lack information about internal geometry (Kappelman, 1998). Computed tomography (CT) scan voxels (3D version of pixels, the unit volume resolution) can also be directly transformed into the elements of a high-resolution FE model (Ryan and van Rietbergen, 2005). The automation and high resolution make this method attractive, but it also involves complex issues in finding appropriate thresholding algorithms to demarcate the bone-air (or other) boundary reliably throughout a structure (e.g., skull) with varying bone thickness and density (Fajardo et al, 2002;Ryan and van Rietbergen, 2005).…”

“…Computed tomography (CT) scan voxels (3D version of pixels, the unit volume resolution) can also be directly transformed into the elements of a high-resolution FE model (Ryan and van Rietbergen, 2005). The automation and high resolution make this method attractive, but it also involves complex issues in finding appropriate thresholding algorithms to demarcate the bone-air (or other) boundary reliably throughout a structure (e.g., skull) with varying bone thickness and density (Fajardo et al, 2002;Ryan and van Rietbergen, 2005). It also currently results in models with so many elements that the models may require computational abilities beyond those available in many powerful desktop workstations.…”

“…Without such attempts at validation, it is often difficult to evaluate whether the results have any significance in the real world. Unfortunately, most FEA studies to date in functional morphology literature or in the large clinical FEA literature include little or no validation of their models (Spears and Crompton, 1996;Spears and Macho, 1998;Macho and Spears, 1999;Witzel and Preuschoft, 1999;Rayfield et al, 2001;Witzel et al, 2004;Ryan and van Rietbergen, 2005).…”

“…FEA may be used to compare the mechanical behavior of different skeletal designs of the same structure (Richmond, 1998;Ryan and van Rietbergen, 2005). In this way, FEA promises to be a powerful new tool for testing biomechanical hypotheses in extant and fossil taxa.…”

Structural Adaptation of Trabecular Bone Revealed by Position Resolved Analysis of Proximal Femora of Different Primates

“…Images obtained by HrCT can be directly used as input to microscopic mechanical analysis using microfinite element (l-FE) models (Van Rietbergen et al, 2003;Homminga et al, 2004). Application of this method to the proximal femur of two different primates led to the conclusion that the differences in the femoral head trabecular architecture may not be fully explainable by differences of the hip joint loading (Ryan and van Rietbergen, 2005).…”