Quantitative evaluation of equine deep digital flexor tendon morphology using magnetic resonance imaging.

The researchers conducted a study to better understand the structure (morphology) and possible injury patterns of the deep digital flexor tendon (DDFT) in horses through the analysis of magnetic resonance (MR) images, and to examine whether injury alters these features. They found a predictable pattern in the size and symmetry of the DDFT and identified changes associated with injury.

Deep Digital Flexor Tendon Morphology

• The study used a retrospective analysis of magnetic resonance images to examine the deep digital flexor tendon’s structure in the limbs of live and cadaver horses, some without identified DDFT lesions, and others with observable abnormalities in the DDFT.
• Measurements of the DDFT’s cross-sectional area, width, and depth were obtained at six predetermined points.
• A consistent morphology was found in the distal aspect of the DDFT across all horses studied. Starting as a flat crescent shape at the point of attachment (the insertion), the shape transitioned to a more profound bilobed form higher up, with the mid-navicular area presenting the most substantial cross-sectional area.

Findings concerning Symmetry and Correlation>

• Deep digital flexor tendon showed strong symmetry both in medial-lateral (width-wise) dimensions and between the left and right limbs.
• There was a robust association between the cross-sectional area of the DDFT and a horse’s weight. Additionally, a strong correlation was noted between the widths of DDFT and the navicular bone, a distal limb bone in the horse’s foot.

Impact of Injury on DDFT

• The symmetry observed in healthy DDFTs was disrupted by unilateral lesions, with corresponding loss of correlation between a horse’s weight and the DDFT’s cross-sectional area.
• When damaged, primarily with central-area (“core”) lesions, the DDFT showed a consistent increase in cross-sectional area. However, other types of lesions did not significantly increase the DDFT size.
• The minimal increase in DDFT size upon injury could possibly be due to the restrictive structures of the horse’s hoof. This could explain the sustained pain often noticed in such lesions.

Conclusions

• The predictable pattern and symmetry in normal tendons could be related to individual mechanical demands placed on the different elements of the DDFT.
• Understanding the changes in morphology and size of the DDFT with injury provides potential insights into diagnosing and treating such injuries in horses because they have been identified as a common cause of lameness in the animals.