The cross‐sectional areas of normal equine digital flexor tendons determined ultrasonographically

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Abstract
Fifty-two animals, comprising 22 Irish Draught crosses (Group A), 15 Thoroughbreds (Group B) and 15 ponies (Group C) were examined ultrasonographically using a 7.5 mHz linear array probe and stand-off pad. All animals were free of tendon disease as determined from clinical and ultrasonographical examination. The superficial (SDFT) and deep (DDFT) digital flexor tendons were scanned at 7 transverse (axial) levels between the carpus and metacarpophalangeal joint. Each transverse image was digitised using a commercially available frame grabber and the cross-sectional areas of each tendon at each level measured using a dedicated software application. Excellent accuracy (averaging less than 5%) was demonstrated between the ultrasound generated areas and those measured from the tendons post mortem in 12 limbs. The mean, s.d. and tolerance intervals of both SDFT and DDFT cross-sectional areas at each level were determined for each group of horses. There was no statistically significant difference between Groups A and B and these 2 groups were, therefore, combined for further analysis. The cross-sectional areas of both tendons were statistically smaller for Group C when compared to Groups A and B. The ratio of SDFT to DDFT cross-sectional areas was calculated for each level and this demonstrated less variation between groups. The difference in measurements between limbs of the same horse was analysed. The mean differences for all groups were 9.13 mm2 for the SDFT and 11.64 mm2 for the DDFT. Upper limits (95% of the population) were 22.67 mm2 (SDFT) and 29.22 mm2 (DDFT). Weight (Groups A and C), height and mid-metacarpal circumference (all groups) were measured and these physical parameters related to the tendon size at each level for Groups A and B combined and Group C. Tolerance limits and normograms were calculated. No significant regression was found for the horse group over the range of physical parameters measured while regression was shown for the ponies. The cross-sectional areas measured in this study may be useful for determining increased tendon size in cases of bilateral tendonitis or where there is minimal disruption to the internal ultrasonographic architecture of the tendon.