Suspensory ligament branch injuries can cause severe lameness in horses, with affected animals typically needing extensive rehabilitation and time off from work. These injuries can be career-ending for some horses. Veterinarians might use orthobiologics, or natural substances such as stem cells and platelet-rich plasma, to treat such injuries. While practitioners have used mesenchymal stem cells (MSCs, a type of orthobiologic) since the early 2000s, this is a relatively new approach for injuries, and a recently published retrospective study by researchers from Purdue University and Rood & Riddle Equine Hospital shows promising results using MSCs.

Researchers reviewed the records and treatment of 69 Thoroughbred racehorses that had been diagnosed with suspensory ligament branch desmitis (SLBD) from 2010 to 2019. They noted SLBD is a common injury in young racehorses in training and during their racing careers. Even mild cases of desmitis have been shown to have a negative impact on future racing careers.

The researchers utilized each horse’s ultrasound and radiographic findings to categorize the degree of suspensory damage and sesamoiditis (inflammation of the sesamoid bone, which can be related to suspensory branch injury). They graded the suspensory ligament lesions found on ultrasound on a scale from 1 to 4, with Grade 4 being most severe, and the degree of sesamoiditis found on radiographs from 1 to 3, with 3 being most severe.

The cases reviewed in this study involved horses treated at the time of diagnosis with an injection of allogeneic (taken from different individuals of the same species) umbilical blood stem cells. The treating veterinarians also extracted bone marrow from the horses’ hip bones and used it to produce autologous (from the animal itself) stem cells. They then expanded the cells to form doses they administered as a series of three to four injections over a 10- to 12-week period into the suspensory ligament lesion area. Horses with more severe ultrasonographic lesions also underwent a procedure known as ligament splitting of the core lesion prior to MSC injections. “Using this procedure to remove fluid from within the lesion, in the more severely affected ligaments, allows for improved healing by decreasing swelling and improving blood flow,” said Larry Bramlage, DVM, MS, Dipl. ACVS, surgeon at Rood & Riddle in Lexington, Kentucky, who was a co-author on the study.

The treating veterinarians recommended a rehabilitation program of progressive hand walking, paddock turnout, and trotting based on each horse’s return to soundness and visible healing on ultrasound examination. After four weeks of trotting exercise, the horses returned to race training. They were not re-examined unless there was a concernthat the injury had recurred.

The researchers used a commercial racing database to determine the horses’ return to racing and racing success. Overall, the prognoses were similar between the more severe (Grades 3-4) and less severely injured horses (Grades 1-2). The researchers noted that 71% of the entire treatment group went on to race post-injury with an average racing career length of 29.5 months. Horses with previous racing history were more likely to return to racing (90%) than those horses that had not yet raced (63%). They also found that males were more likely to race after injury (79%) than females (52%). Owner and trainer behavior and decisions cannot be controlled, the researchers noted, so mares might be retired for broodmare use, creating some bias between sexes.

For the horses that had previously raced, researchers found no significant difference before and after injury in the number of races, earnings, and earnings per start.

Take-Home Message

This study supports MSCs as a successful treatment approach for SLBD, and Bramlage added that autologous stem cell injections are now his treatment of choice for these injuries, which were previously associated with negative outcomes. It also gives researchers a baseline to compare future studies on additional treatment options and return to soundness for SLBD injuries.

The study, “Racing performance of Thoroughbred racehorses with suspensory ligament branch desmitis treated with mesenchymal stem cells (2010–2019),” appeared in the Aug. 2023 Issue of Equine Veterinary Journal.