The effect of maturation and aging on the biomechanical, ultrasonographic, and histomorphometric properties of equine superficial digital flexor tendon

hese studies were conducted to elucidate the structural and biomechanical characteristics of normal equine superficial digital flexor (SDF) tendons. Our objectives were to; (1) establish the sensitivity of ultrasonographic measurement of tendon cross-sectional area; (2) establish a normal range of values for ultrasonographic, biomechanical, histomorphometric and biochemical characteristics of equine SDF tendon and determine the relationship between these parameters; (3) determine if maturation and aging had an effect on these characteristics; and (4) evaluate the effect of training on the ultrasonographic characteristics of SDF tendon.;Histomorphometry revealed a significant decrease in SDF tendon fascicle CSA with increasing age from two to twenty-three years; two year old horses had tendons with significantly larger fascicles than horses aged three years and older. Quantitation of mature (non-reducible) collagen cross-links revealed a trend for an increase in hydroxypyridinium (OHP), the most prevalent mature cross-link in tendon, with increasing age. There were strong associations between decreasing fascicle size with increasing age and between increasing OHP levels and increasing age, leading to the conclusion that there is a structural component to increasing tendon elastic modulus with increasing age in addition to the effect of increasing mature collagen cross-links.;Fascicles in the central region of tendon cross-sections tended to be larger than fascicles from peripheral regions. There was a non-significant difference in vessel number per region, with central, medial and lateral regions containing greater numbers of vessels than dorsal and palmar regions; no significant differences were found in regional vessel CSA. Other studies have attributed the high incidence of central region damage in equine tendonitis to poor central vascularity; our study indicates that differences in central fascicle architecture, ie increased fascicle size, may have an important role in central region damage.;Ultrasonographic evaluation of both forelimb SDF and deep digital flexor (DDF) tendons of fifty Thoroughbred horses in active race training established a range of normal ultrasonographic measurements for each structure for both forelimbs. Average SDF tendon CSA at each level examined for this (trained) group was larger than the average SDF tendon CSA for the twenty-three normal SDF tendons from the untrained group used to determine the effect of aging on SDF tendon. A previous study of a small group of horses showed that SDF tendon ultrasonographic CSA increased over time in training. It appears that equine SDF tendon adapts to training stress by increasing in CSA, an effect that is not seen with maturation in unexercised horses. (Abstract shortened by UMI.).;Ultrasonographic measurements of tendon CSA and mean echogenicity did not change with increasing age from two to twenty-three years and were unaffected by gender or weight. Tendons with larger CSAs required greater loads to produce tendon strain equal to 3%. Average elastic modulus was 1.44 GPa for normal SDF tendon from horses not in athletic use. A significant increase in elastic modulus was found with increasing age from two to twenty-three years; two year old horses were also found to have tendons with significantly lower elastic moduli than horses aged three years and older. Energy conservation for normal SDF tendon averaged 94.3%. No age, gender or weight effect was observed on energy conservation. Static creep and stress relaxation for normal equine SDF tendon were negligible (0.04% and...