The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Unexpected regional differences in collagen fiber orientation heterogeneity (CFO-Het) between chimpanzee and human proximal femoral shafts: is CFO-Het still a useful characteristic for corroborating load history data?


Dept. of Orthopaedics, University of Utah School of Medicine

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Gray levels (GLs) in circularly polarized light (CPL) images reflect predominant collagen fiber orientation (CFO) (Skedros et al., 2011 J. Anatomy). CFO-Het, measured as the full-width at half-maximum (FWHM) of a GL/CFO profile, has been shown to corroborate the bending load history in the chimpanzee proximal femoral shaft (Keenan et al., 2011 AAPA). Based on this previous chimpanzee study, greater CFO-Het in compression “cortices” was also expected in the human femur. Twenty-four sections from 12 adult human proximal femoral shafts were embedded in methacrylate, ultramilled, and imaged in CPL. FWHM was measured from CFO profiles (larger FWHM = greater CFO-Het). Statistical analysis was based on the: 1) left peak (LP), 2) right peak (RP), and 3) average of both peaks (AvgP) of the CFO profile of each image. Results show highest CFO-Het in the medial “compression” cortex when considering the LP (p<0.05), but is unexpectedly highest in the lateral “tension” cortex when considering the RP and AvgP (p<0.05). Although CFO-Het correlates moderately with CFO for the RP and LP (RP: r=0.5, p<0.001, LP: r= -0.6, p<0.001), there is no correlation with AvgP data (r= -0.1). While CFO-Het clearly corroborates CFO-based load history data in chimpanzee femora (greater CFO-Het in “compression” cortices), CFO-Het does not clearly reflect this load history in human proximal femora. This may reflect difficulties in quantifying CFO-Het based on the presence of two CFO peaks in human femora (chimpanzees = one peak). Consequently, CFO-Het does not appear useful for predicting a history of bending in these bones.

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