Mineralization of equine proximal sesamoid bones precedes articular cartilage and fibrocartilaginous enthesis maturation in early postgestational development.

This research article studies the development and maturation of a specific bone in horses known as the proximal sesamoid bone. The researchers found that the bone undergoes mineralization before the maturation of the adjacent cartilage, and suggest this may influence the occurrence of certain bone lesions in young horses.

Methodology

• The research team studied forelimb proximal sesamoid bones (PSBs) from 12 equines, ranging in age from 105 days of gestation to 540 days postgestation.
• These PSBs were analyzed through radiography, which was used to initially assess joint and PSB mineralization.
• This was followed by microcomputed (micro)-CT imaging, offering a more detailed inspection of the mineralized PSBs.
• Through the micro-CT sections, the researchers quantified the tissue volume, bone volume fraction, height, width, depth, trabecular thickness, and anisotropy of the PSBs.
• The team then took histologic sections of the PSBs, staining them to assess the ratio of the ossification center to the cartilage template size and to describe the development of the cartilage template, ossification center, spherical growth plate, articular cartilage, and entheses.

Findings

• The study discovered that PSBs in horses mineralize around cartilage canals and a spherical growth plate during the late gestational to early postgestational period.
• The apical, flexor, basilar, and articular ossification frontages showed considerable variations in their morphology.
• As the articular cartilage and entheses developed its structural organization, so too did an underlying plate of compact bone at the same time.
• However, even after 540 days postgestation, the fibrocartilaginous entheses of the flexor cortex of the PSB remained immature.

Conclusion and Implications

• Overall, the research demonstrated that equine PSBs predominantly mineralize by endochondral ossification during late gestation to early postgestational period, preceding the maturation of the articular cartilage and fibrocartilaginous entheses.
• The authors suggest that this earlier mineralization of the PSB, prior to complete maturation of its surrounding tissues, could predispose young horses to developing lesions at these sites.
• While such lesions, such as apical avulsion fractures, weren’t directly studied in this paper, the authors note their presence as a noteworthy avenue for future research.