The effects of cracks on the quantification of the cancellous bone fabric tensor in fossil and archaeological specimens: a simulation study

Abstract

Cancellous bone is very sensitive to its prevailing mechanical environment, and study of its architecture has previously aided interpretations of locomotor biomechanics in extinct animals or archaeological populations. However, quantification of architectural features may be compromised by poor preservation in fossil and archaeological specimens, such as post mortem cracking or fracturing. In this study, the effects of post mortem cracks on the quantification of cancellous bone fabric were investigated through the simulation of cracks in otherwise undamaged modern bone samples. The effect on both scalar (degree of fabric anisotropy, fabric elongation index) and vector (principal fabric directions) variables was assessed through comparing the results of architectural analyses of cracked vs. non-cracked samples. Error was found to decrease as the relative size of the crack decreased, and as the orientation of the crack approached the orientation of the primary fabric direction. However, even in the best-case scenario simulated, error remained substantial, with at least 18% of simulations showing a > 10% error when scalar variables were considered, and at least 6.7% of simulations showing a > 10° error when vector variables were considered. As a 10% (scalar) or 10° (vector) difference is probably too large for reliable interpretation of a fossil or archaeological specimen, these results suggest that cracks should be avoided if possible when analysing cancellous bone architecture in such specimens.

Human-like hip joint loading in Australopithecus africanus and Paranthropus robustus

“…For both SK 82 and La Ferrassie 1, internal damage and cracks were present in the center of the femoral head. Because cracks can have significant effects on quantification of degree of anisotropy (DA) (Bishop et al, 2017), we translated the SK 82 VOI laterally approximately 3.5 mm and the La Ferrassie 1 VOI approximately 3 mm in the lateral, posterior, and superior directions to avoid damaged regions. The translation of these VOIs, although small relative to the overall size of the femoral head, may affect our ability to effectively compare these individuals with others in the sample due to documented effects of VOI position and size on quantification of trabecular bone (Kivell et al, 2011).…”

“…Due to the nature of preservation in some of the fossils, the articular surfaces were not always complete, so the precise position of the VOI may not have been homologous with the position in the extant species. In addition, in the case of SK82 and La Ferrassie 1, the VOI was translated several millimeters to avoid internal cracks through the trabecular bone, a phenomenon that may have a significant impact on quantification of anisotropy (Bishop et al, 2017). This translation of the VOIs, although small relative to the overall size of the femoral head, may affect the quantified fabric structure results for these individuals (Kivell et al, 2011), which is potentially reflected in the results of these individuals relative to the rest of the hominin sample.…”

Cancellous bone and theropod dinosaur locomotion. Part I—an examination of cancellous bone architecture in the hindlimb bones of theropods

“…In the fossil specimens, cracks or other regions of obvious deformation (e.g. twisting, bending, flattening) were avoided ( Bishop et al, 2017 ); they were identified and their geometry subsequently mapped out in the CT scans using Mimics, and the resulting geometry was used to remove VOIs from analysis in Rhinoceros ( Fig. 11 ).…”

Peer Review #2 of "Cancellous bone and theropod dinosaur locomotion. Part I—an examination of cancellous bone architecture in the hindlimb bones of theropods (v0.1)"

“…Post-analysis inspection revealed that inadvertently including small amounts of cortical bone or medullary cavity did not alter the overall results. In the fossil specimens, cracks or other regions of obvious deformation (e.g., Manuscript to be reviewed twisting, bending, flattening) were avoided (Bishop et al 2017); they were identified and their geometry subsequently mapped out in the CT scans using Mimics, and the resulting geometry was used to remove VOIs from analysis in Rhinoceros (Fig. 11).…”