ULTRASONOGRAPHY AS A METHOD TO DETERMINE TENDON CROSS-SECTIONAL AREA

Ultrasonographic cross-sectional area (CSA) measurements of equine sup erficial digital flexor (SDF) tendon were obtained to determine the fe asibility of ultrasonography for CSA measurement of tendon in vivo and in vitro. Ultrasonographic measurements were compared with a more tra ditional CSA measurement method, ink-blot analysis. In addition, value s for ultrasonographic SDF tendon mean echogenicity were obtained in v ivo and in vitro. The left forelimb SDF tendons of 23 horses were eval uated ultrasonographically. Cross-sectional images were acquired at 4- cm intervals distal to the base of the accessory carpal bone (DACB) to the level of the proximal sesamoid bones while horses were standing s quarely. After euthanasia, the left forelimbs were mounted in a materi als testing system (MTS) and loaded under tension to standing load. Ul trasonographic images were again acquired at the same locations. The u ltrasonographic images were digitized, and values for ultrasonographic CSA and mean echogenicity were obtained for each level. Immediately a fter mechanical testing, a 1-cm-thick transverse section of SDF tendon at 12 cm DACB was removed. Three ink blots were prepared from each en d of the removed tendon section and digitized. The 6 CSA values were a veraged to generate a value for morphologic CSA for each DF tendon at 12 cm DACB. Standing ultrasonographic tendon CSA at 12 cm DACB was con sistently smallest (mean +/- SD CSA = 86 +/- 11 mm(2)), followed by MT S ultrasonographic CSA (mean, 95 +/- 12 mm(2)), with ink-blot morpholo gic CSA being largest (mean, 99 +/- 15 mm(2)). Comparison of standing and MTS ultrasonographic CSA values at 12 cm DACB revealed a strong po sitive linear correlation between methods (R(2) = 0.74, P = 0.001). Co mparison of ink-blot CSA at 12 cm DACB with standing and MTS ultrasono graphic CSA revealed strong positive linear correlations (R(2) = 0.64, P = 0.001 and R(2) = 0.72, P = 0.001, respectively). For ultrasonogra phic mean echogenicity, standing values insignificantly exceeded MTS v alues at each level. The authors conclude that ultrasonography is a us eful technique for the noninvasive assessment of SDF tendon CSA that c an be applied in vivo and in vitro.