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. 2024 Oct 10;10(10):1665-1675.
doi: 10.3390/tomography10100122.

The Correlation between the Elastic Modulus of the Achilles Tendon Enthesis and Bone Microstructure in the Calcaneal Crescent

Kenichiro Doi  1   2 , Dina Moazamian  1 , Behnam Namiranian  1 , Sheronda Statum  1   3 , Amir Masoud Afsahi  1 , Takuaki Yamamoto  2 , Karen Y Cheng  1 , Christine B Chung  1   3 , Saeed Jerban  1   3
Affiliations

The Correlation between the Elastic Modulus of the Achilles Tendon Enthesis and Bone Microstructure in the Calcaneal Crescent

Kenichiro Doi et al. Tomography. .

Abstract

Background: The calcaneal enthesis, an osseous footprint where the Achilles tendon seamlessly integrates with the bone, represents a complex interface crucial for effective force transmission. Bone adapts to mechanical stress and remodels based on the applied internal and external forces. This study explores the relationship between the elasticity of the Achilles tendon enthesis and the bone microstructure in the calcaneal crescent.

Methods: In total, 19 calcaneal-enthesis sections, harvested from 10 fresh-frozen human cadaveric foot-ankle specimens (73.8 ± 6.0 years old, seven female), were used in this study. Indentation tests were performed at the enthesis region, and Hayes' elastic modulus was calculated for each specimen. Micro-CT scanning was performed at 50-micron voxel size to assess trabecular bone microstructure within six regions of interest (ROIs) and the cortical bone thickness along the calcaneal crescent.

Results: Significant Spearman correlations were observed between the enthesis elastic modulus and trabecular bone thickness in the distal entheseal (ROI 3) and proximal plantar (ROI 4) regions (R = 0.786 and 0.518, respectively).

Conclusion: This study highlights the potential impacts of Achilles tendon enthesis on calcaneal bone microstructure, which was pronounced in the distal calcaneal enthesis, suggesting regional differences in load transfer mechanism that require further investigation.

Keywords: achilles tendon; bone microstructure; calcaneal crescent; elastic modulus; enthesis; micro-computed tomography.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Flowchart illustrating the overall study design, including sample preparation, mechanical indentation testing, micro-CT imaging, bone microstructure analysis, and statistical correlation evaluation.
Figure 2
Figure 2
(a) Experimental setup for indentation test on a representative Achilles tendon-enthesis specimen using a commercial biomechanical testing system (MACH-1, Biomentum, QC, Canada). A flat-end cylindrical indenter with a 1.0 mm diameter was placed perpendicular to the specimen’s cut surface. (b) Load-displacement curve of a typical indentation test to determine the maximum load (Pmax) required to calculate the Hayes’ elastic modulus (E).
Figure 3
Figure 3
(a) A representative Achilles tendon-calcaneus specimen sagittal image using micro-CT at 50-micron voxel size. (b) The observation areas of the calcaneal bone selected over a cropped image with increased contracts. ROIs 1, 2, and 3 divided the trabecular bone into three areas beneath the enthesis, and ROIs 4, 5, and 6 divided the trabecular bone into three areas in the plantar region distal to the enthesis. ROIs 7 and 8 divided the cortical bone into two areas: the entheseal and plantar regions. (c) The segmented bone image and (d) the local thickness map was calculated using MATLAB.
Figure 4
Figure 4
Bar charts illustrating the mean values of (a) Bone Volume to Total Volume (BV/TV), (b) Trabecular Thickness (Tb.Th), (c) Bone radiodensity in Hounsfield Units (HU), and (d) Trabecular Separation (Tb.Sp) for six Regions of Interest (ROIs). Error bars in red represent standard deviations. ** indicated a statistically significant difference.
Figure 5
Figure 5
Scatter plots and linear trend lines for the average Hayes’ elastic modulus within the enthesis of Achilles tendon against the average trabecular bone microstructural parameters within ROI 1 to ROI 6 in calcaneal crescent. abbreviations: Bone Volume to Total Volume (BV/TV), Trabecular Thickness (Tb.Th), Bone Radiodensity in Hounsfield Units (HU), Trabecular Separation (Tb.Sp), and Region of Interest (ROI).
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