ULTRASONOGRAPHIC CROSS-SECTIONAL AREA AND MEAN ECHOGENICITY OF THE SUPERFICIAL AND DEEP DIGITAL FLEXOR TENDONS IN 50 TRAINED THOROUGHBRED RACEHORSES

Fifty Thoroughbred horses were examined. All horses had been in race t raining for a minimum of 4 months before examination and had worked at racing speed; 24 horses had raced. All horses were clinically sound a t the time of examination. Ultrasonography was performed, using a 7.5- MHz transducer with built-in fluid offset. Videotaped images of the pa lmar soft tissue structures were obtained at 4, 8, 12, 16, 20, and 24 cm distal to the base of the accessory carpal bone (DACB). Images were digitized, and each image was calibrated. Values for cross-sectional area (CSA) and mean echogenicity (ME) were then determined from the cr oss-sectional images of the superficial digital flexor (SDF) and the d eep digital flexor (DDF) tendons, using an image-analysis program. The SDF tendons were compared between right and left forelimbs at each le vel, and from proximad to distad on each limb, as were the DDF tendons . The relation between the SDF and DDF tendons for the same forelimb w as determined at each level. There were no significant differences in CSA or ME at equivalent levels of the left and right SDF tendons. Mean (+/- SD) CSA was 1.01 (+/- 0.12) cm(2) at 4 cm DACB, 0.95 (+/- 0.14) cm(2) at 12 cm DACB, and 1.12 (+/- 0.15) cm(2) at 24 cm DACB. Adjusted ME was 2.34 (+/- 0.34) at 4 cm DACB, 2.03 (+/- 0.38) at 12 cm DACB, a nd 2.04 (+/- 0.35) at 24 cm DACB. The left and right DDF tendons did n ot have significant differences in CSA or ME at any level. Cross-secti onal area was 1.13 (+/- 0.18) cm(2) at 4 cm DACB, 1.01 (+/- 0.12) cm(2 ) at 12 cm DACB, and 1.75 (+/- 0.29) cm(2) at 24 cm DACB. Adjusted ME was 2.60 (+/- 0.46) at 4 cm DACB, 2.49 (+/- 0.49) at 12 cm DACB, and 2 .50 (+/- 0.44) at 24 cm DACB. At all levels, the left and right SDF te ndons were smaller and less echoic than the DDF tendons of the same li mb. The SDF and DDF tendons had an hour-glass shape, with smallest CSA at 12 cm DACB. Mean echogenicity generally decreased for the SDF and DDF tendons from proximad to distad on the limb. These results indicat e that for clinically normal trained Thoroughbred racehorses, there sh ould be no significant difference in CSA or echogenicity between the l eft and right SDF tendons at equivalent distances DACB. There should b e no significant differences in the left and right DDF tendons at equi valent levels DACB. The SDF tendon is usually smaller and less echoic than the corresponding DDF tendon at each level.