Evidence Supporting Intralesional Stem Cell Therapy to Improve Equine Flexor Tendon Healing

This Knowledge Summary addresses the published information supporting intralesional administration of cell-based therapies for the treatment of flexor tendinitis/tendinopathy in horses. The current body of evidence supports intralesional stem cell therapy to improve quality of repair tissue during equine SDFT healing, based on histological and histomorphometric analyses and, in some studies, tensile load testing. Accepting this, comparative analyses to determine relative efficacies of specific cell sources are inadequate to draw any firm conclusions on this issue and any informative meta-analysis of the existing studies is confounded by inconsistencies in cell sources, injury models and clinical case selections, times after injury when cells were injected, number of cells administered, delivery vehicles used, the outcomes used to assess utility and timing of outcomes after administration. Further, in none of the experimental studies were the horses subject to training and/or racing stresses, and it is still unclear how closely the existing experimental models reflect the clinical condition following repetitive strain injury. Further, single-cycle tensile testing does not necessarily model the high-frequency, recurrent, and (to be hoped) submaximal tensile loading that flexor tendons experience during high speed exercise.