The Ontogeny of the Human Calcaneus: Insights From Morphological and Trabecular Changes During Postnatal Growth

Objectives: To investigate the developmental changes in the human calcaneal internal and external morphology linked to the acquisition of mature bipedal locomotion. Methods: Seventy seven micro-CT scans of modern juvenile calcanei (from perinates to 15 years old) are employed. The chronological period spans from the Middle/Late Neolithic (4800-4500 BCE) to the 20th century. Through a comprehensive approach that comprises geometric morphometric methods and whole-bone trabecular analysis, the calcaneal growing morphology has been explored. Results: Morphological changes reflect the development of bipedal locomotion, showing its potential when tracking the major locomotor milestones. The calcaneal shape is immature and almost featureless during the first year of life. The internal architecture is dense and isotropic with numerous thin trabeculae closely packed together. The internal architecture changes to better adapt to variations in load stimulated by a more mature gait by increasing bone mass and alignment, with fewer and thicker struts. The external morphology shows its plasticity by increasing the surface area where greater strain is expected and changing the orientation of the articular facets. Conclusions: Analysis of morphological changes in the growing calcaneus highlights the importance of an integrative methodology when exploring developmental bone plasticity. The changes in calcaneal internal and external morphologies reflect the different loading patterns experienced during growth, gradually shifting from a more generalized morphology to a more adult-like one, reflecting major locomotor achievement. Our research shows that although initially genetically driven, calcaneal plasticity may display mechanical influences and provide precious information on tracking the main locomotor milestones.