Morphometric study of the equine navicular bone: comparisons between fore and rear limbs.

The study analyzed the anatomical characteristics of the navicular bones in horses. The research found that most dimensions of this bone are larger in the forelimbs than in the rear limbs, which is likely an adaptation to handle greater forces experienced by the forelimbs.

Objective of the Study

• The researchers aimed to analyze and compare the morphometry – the quantitative measurement of the form- of the equine navicular bones present in the forelimbs and the rear limbs. They utilized navicular bones collected from sound, or healthy, horses.

Procedure

• The team collected navicular bones from the four limbs of 95 sound horses and conducted an in-depth anatomical analysis.
• Their study took into account differences due to morphological types, gender, weight, size, and age.

Findings

• All dimensions (height, width, etc) of the navicular bone, excluding thickness, were found to be larger in the forelimbs of the horses.
• This finding is believed to be a biological adaptation to counter the higher forces to which the forelimbs are subjected, both during exercise and rest.
• The group also studied the bones of 61 horses and described the anatomical bases for histomorphometry (the study of the microscopic structure of tissues) of the fore and rear navicular bones.
• Contrary to expectations, the fore navicular bones had less cortical (hard outer layer of bone) at the articular (joint) surface, the flexor surface, and proximal border, but more cancellous bone (spongy bone).
• Notably, the fore navicular bone showed greater mineralized cartilage and higher porosity in the cortical bone.

Significant Observations

• A unique finding from the research is the identification of two previously unreported zones in the flexor surface cortex (the outer layer).
• The first, the external zone, is primarily composed of poorly remodelled lamellar bone (mature, strong bone) with a disto-proximal oblique (from bottom to top at an angle) direction.
• The second, the internal zone, has a significant portion of secondary bone (new bone formed during the repair process), with a latero-medial (from side to side) direction of Haversian canals (central channel in bone that houses blood vessels and nerves).

Discussion

• The researchers theorize that the distinct bone architecture could correlate with the mechanical load the bone experiences during locomotion. However, further research is required to explore this possibility.