Screening Horses at Risk of Tendon Injury Using Power Doppler Ultrasound

Injuries to the superficial digital flexor tendon (SDFT) are devastating and career-ending for some horses. The presence of hypervascularity (increased blood flow) in the SDFT detected by power Doppler ultrasound (PDU) during screening of apparently healthy, injury-free horses is a risk factor for future injury to the SDFT. In fact, researchers found horses with a positive PDU signal are three times more likely to develop an SDFT injury than horses without.^*

Because SDFT injuries are time-consuming and expensive to heal and associated with a high reinjury rate even following extended layups, preventing injury is extremely important. Screening tools capable of identifying early SDFT injury to reduce the occurrence of clinically severe SDFT injuries would be invaluable. Researchers from the Japan Racing Association hypothesized that PDU could have prognostic value in identifying SDFT tendons at risk of injury.

“Tendons are typically poorly vascularized, and vascularization usually only occurs when there is acute injury and inflammation. Studies in humans show that PDU can detect vascularity in the Achilles tendon even without the presence of pain and swelling,” explained Ashley Fowler, Ph.D., a nutritionist for Kentucky Equine Research.

To determine if PDU was a clinically useful means of assessing hypervascularity in tendons that appear normal on grayscale ultrasonography, the researchers conducted a trial. Ninety-seven racing Thoroughbreds had a baseline ultrasound examination, both grayscale and PDU. Those horses were followed for one year and follow-up ultrasound examinations were performed on horses that suffered SDFT injury.

In that year, twenty-nine horses (30%) developed injury to the SDFT, and PDU signal in the SDFT at baseline was identified as a risk factor for injury. Horses with a positive PDU in the SDFT at baseline, prior to evidence of clinical injury, were over three times more likely to suffer injury of the SDFT than horses without baseline PDU signal.

“These results suggest that frequent PDU examinations of apparently healthy, injury-free horses may be useful for early detection of SDFT injury based on the presence of hypervascularity,” Fowler said. “In cases with positive PDU signals, training programs may be modified and training intensity decreased to limit damage to the SDFT.”

In cases of SDFT injury, management could include long layups with a strict, controlled-exercise rehabilitation program and application of regenerative therapies.

“During layups and stall rest, bone can demineralize due to lower forces being exerted on the skeleton. Providing nutritional support helps maintain bone density by preventing bone loss during periods of inactivity. This leads to denser bone that is better prepared to withstand the return to exercise,” advised Fowler.

 ^*Tamura, N., E. Yoshihara, K. Seki, N. Mae, K. Kodaira, M. Iimori, Y. Yamazaki, H. Mita, S. Urayama, T. Kuroda, M. Ohta, and Y. Kasashima. 2024. Prognostic value of power doppler ultrasonography for equine superficial digital flexor tendon injury in Thoroughbred racehorses. Veterinary Journal: doi: 10.1016/j.tvjl.2024.106179.