IN-DEPTH: THE RELATIONSHIP BETWEEN IMAGING FINDINGS AND LAMENESS


Fig. 1. Doppler ultrasound examination of a substantial lesion of the dorsal aspect of the lateral lobe of the deep digital flexor tendon at level B in the pastern. Examination at the time of presentation and 2 months after presentation revealed increased vascularity of the lesion (white arrow) as expected during the proliferation and reparative phases of healing (A and B) which was resolved by 6 months post-presentation (C). For all images, lateral is on the left side of the image. Red represents blood flow toward the ultrasound probe while blue represents blood flow away from the ultrasound probe.


for the differentiation of active versus inactive ten- don and ligament injuries.5–11 In terms of monitor- ing tendon healing, Doppler is especially useful for identifying the progression of a tendon lesion out of the inflammation and proliferation/reparative phases in which hypervascular granulation tissue exists (Fig. 1, A and B) and into the remodeling phase in which hypovascular scar tissue predomi- nates (Fig. 1C). Such information is helpful for determining lesion resolution, or lack thereof in some cases, and for appropriately guiding increases in levels of controlled exercise. Doppler is also very useful for assessing re-injury or even setbacks dur- ing the initial rehabilitation period in which a lesion that was hypovascular on a previous examination suddenly becomes vascular again. While little in- formation is available regarding the use of Doppler for assessing ligament healing, a descriptive study examining the suspensory branches of 13 horses did find Doppler signal in all branches that were abnor- mal on gray-scale ultrasound and did not find Dopp- ler signal in any branches that were normal on gray- scale ultrasound.10 While these results were not able to be correlated to soundness, they provide justification for further investigation of the use of Doppler for the assessment of ligament injuries.10 Elastography is another ultrasound technique


now used in both equine and human sports medicine to assess the quality of healing tendon tissue.3,12–14 Elastography allows for determination of tissue stiffness through application of compression with the ultrasound probe which results in tissue defor-


mation (strain) and alteration of sound waves as they travel through that tissue. Normal tendon tis- sue is stiffer than injured tendon and therefore elas- tography can be used to monitor tendon healing over time from “soft” to “hard” tissue as commonly re- ported with a color scale on most ultrasound pro- grams (Fig. 2). In a prospective longitudinal study on the healing of naturally occurring superficial dig- ital flexor tendon injuries in 7 racing Thorough- breds, an important finding was that gray-scale ultrasonography scores improved over the initial 3 months but then became static while elastography scores and strain ratios continued to improve with healing over the full 9 months that the horses were monitored.3 Similar to as described above for Dopp- ler, such information can be very useful for guiding informed decisions on increases in exercise intensity during rehabilitation as well as to monitor for any potential setbacks or re-injuries in which a previously stiff or “hard” tendon lesion suddenly becomes less stiff or “soft” again. Finally, both methods can be used to identify chronic tendon lesions that remain hypervascular and “soft” despite treatment and, therefore have a poor prognosis. Again, similar to as described above for Doppler, much less is known regarding the utility of elastography for ligaments as compared to tendons. In a study examining 33 suspensory branches, however, elastography corre- lated well with gray-scale ultrasound, MRI, and clinical examination findings, suggesting that it is a useful technique for monitoring lesions at this site.12


Fig. 2. Gray-scale (A) and elastography images (B and C) of the same lesion of the dorsal aspect of lateral lobe of the deep digital flexor tendon as shown in Fig. 1. The lesion was diffusely “soft” (red) at the time of presentation (B) but markedly improved by 6 months post-presentation as shown in the split screen gray-scale and elastography image of the lateral lobe (C).


AAEP PROCEEDINGS  Vol. 66  2020 31


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