An Investigation on the Correlation between the Mechanical Properties of Human Skull Bone, Its Geometry, Microarchitectural Properties, and Water Content

Abstract

With increasingly detailed imaging and mechanical analysis, modalities need arises to update methodology and assessment criteria for skull bone analysis to understand how bone microarchitecture and the presence of attached tissues may affect the response to mechanical load. The main aim was to analyze the effect of macroscopic and microstructural features, as well as periosteal attachment, on the mechanical properties of human skull bone. Fifty-six skull specimens from ethanol-phenoxyethanol-embalmed cadavers were prepared from two human cadavers. Assuming symmetry of the skull, all samples from one-half each were stripped of periosteum and dura mater, while the soft tissues were kept intact on the remaining samples on the contralateral side. The specimens were analyzed using microcomputed tomography to assess trabecular connectivity density, total surface area, and volume ratio. The specimens were loaded under three-point bend tests until fracture with optical co-registration. The bone fragments were then lyophilized to measure their water content. With increasingly detailed imaging and mechanical analysis modalities, there is a need to update methodology and assessment criteria for skull bone analysis to understand how the bone microarchitecture and the presence of attached tissues may affect the response to mechanical load. The mechanical properties were negatively correlated to bone thickness and water content. Conversely, most microarchitectural features did not influence either mechanical parameter. The correlation between mechanical response data and morphologic properties remains similar between the results of embalmed tissues presented here and fresh osseous tissue from literature data. The findings presented here add to the existing methodology to assess human skull for research purposes. The interaction between most microarchitectural features in ethanol-phenoxyethanol-embalmed embalmed skull samples and bending stress appear to be minute.

Figure 1

Diagram of sampling sites of specimens mapped on a skull.

Figure 2

A skull specimen on the three-point bending rig, with loading beam radius 2 mm and support beams 30 mm apart. Measurements were taken from the mid distance of the diploë layers at the horizontal orientation of the upper and the lower anvils.

Figure 3

Scattered plots and corresponding regression lines with 95% confidence intervals depicting the association of specimen thickness and bending modulus (see Table 3 for p values). (a) Specimen 1; (b) specimen 2.

Figure 4

Scattered plots and corresponding regression lines with 95% confidence intervals depicting the association of bending modulus (a) and bending strength (b) with the water content of the bone specimens (see Table 3 for p values).

Figure 5

Scattered plots and corresponding regression lines with 95% confidence intervals depicting the association of bending modulus (a) and bending strength (b) with the surface area of the bone specimens (see Table 3 for p values).