Ultrasonography is an established technique to follow up injured tendons, although the lesions' echogenicity tends to become normal before the tendon is ready to sustain the stresses imposed by exercise. Normalized axial speed of sound (SOS) has been found to correlate with an injured tendon's stiffness; therefore, the purpose of this study was to establish whether SOS would be a useful tool in tendon injury follow-up. Axial SOS was measured in 11 equine superficial digital flexor tendons during a 15-week follow-up period and compared with an ultrasonographic grading system. SOS significantly decreased 2 weeks after the surgical induction of a core lesion, showing a minimum between 7 and 10 weeks; ultrasonographic grade showed a minimum at 3 weeks and increased thereafter. The ultrasonographic grading at 15 weeks was correlated to normalized SOS. These results suggest that axial SOS provides complementary information to ultrasonography that could be of clinical interest.
