Treatment of racehorse superficial digital flexor tendonitis: A comparison of stem cell treatments to controlled exercise rehabilitation in 213 cases

Overstrain of the superficial digital flexor tendon (SDFT) is a common Thoroughbred racehorse limb injury requiring treatment.To determine whether treatment of SDFT lesions in flat Thoroughbred racehorses with autologous bone marrow-derived mesenchymal stem cells (BM-MSCs) or allogenic adipose-derived mesenchymal stem cells (A-MSCs) is associated with improved likelihood of returning to racing, when compared to racehorses managed with a controlled exercise rehabilitation program (CERP) alone.Retrospective cohort study combining clinical treatment records with race records.A total of 213 Thoroughbred racehorses were identified. All were prescribed the same 12-month CERP and 66 also received intralesional BM-MSC and 17 A-MSC treatment. Follow-up was a minimum of 2 years after return to full race training. Multivariable logistic regression models were used to investigate associations between the treatments and the likelihood of returning to racing and completing five or more (C5+) races post-injury.Compared to CERP alone, BM-MSC treatment was associated with increased odds of returning to racing (OR 3.19; 95% CI 1.55-6.81) and C5+ races post-injury (OR 2.64; 95% CI 1.32-5.33). Older age and increasing lesion length were associated with a reduced likelihood of returning to racing. Male sex and increased number of pre-injury starts were associated with increased odds of returning to racing. There was no observed increased likelihood of return to racing or C5+ races associated with treatment with A-MSCs compared to CERP alone.Due to the retrospective nature of the study it was not possible to ascertain how strictly the CERP was followed. Due to the novelty of the method, the A-MSC treatment group included a limited number of horses.In the study population, intralesional BM-MSC treatment was significantly associated with an increased likelihood of returning to racing and C5+ races post-injury compared to CERP alone. Intralesional A-MSC showed no significant association between treatment and the two investigated outcomes.