Towards a staged evidence-based approach for the treatment of tendon injuries in the horse

Abstract

Healing of tendon lesions, a common disorder in the equine species, is slow and often inadequate because the resulting scar tissue cannot meet the functional demands posed by the everyday athletic activity of many horses, making re-injury the most common and often fatal complication after initial trauma. Many therapies have been tried over time, but none of them thus far has succeeded in significantly improving the functional recovery rate in horses after suffering from a tendon injury. The healing trajectory of tendon injuries can be divided in three partially overlapping phases: the inflammation phase, the proliferative phase and the maturation phase. These phases are charactersied by biological porcesses specific to the phase of healing. Up to now very little attempts have been made to distinguish between these phases when applying a therapy to an injured tendon. In this thesis a specific therapy for each of the stages was studied, although it is acknowledged that therapies might exhibit effects in more than one phase of the healing trajectory. During the inflammatory phase there is an initial enlargement of original the lesion due to proteolytic and biomechanical influences. In an in vitro mechanical study it was shown that this lesion propagation after tendon injury may be mitigated by immobilisation during the early phase of repair, although in vitro work remains necesarry to confirm these findings. The proliferative phase is characterised by cell proliferation and synthesis of extracellular matrix components, such as collagen and glycosaminoglycans. These processes can possibly be enhanced by treatment with platelet rich plasma (PRP), an autologous concentrate of growth factor containing platelets. PRP treatment was evaluated in a blinded placebo-controlled experimental study, in which artificially induced tendon lesions were treated with PRP or placebo and tissue was harvested after 24 weeks. PRP improevd biochemical, biomechanical and histological properies of the treated tendons. Doppler ultrasonography revealed large differences in vascularisation between treated and untreated tendons. Computerised Ultrasonography was used to monitor the healing process and appeared capable of predicting outcome at a relatively early stage of the healing process and revealed clues about some of the mechanisms of action. Extracorporeal Shock Wave Therapy (ESWT), a technique based on physical intervention, was used in vivo on healthy equine tendons. It could be shown that, after an initial boost of metabolic activity in the tendon tissue, there was a long-term (6 weeks after treatment) negative effect on cell-matabolism. Further, a rather severe disorganisation of the normal tendon architecture. Both findings warrant caution in the clinical use of this technique, but might also explain the positive effects ESWT appears to have on more chronic tendon lesions. The thesis concludes that a staged approach for the treatment of tendon injuries is likely to improve the final prognosis of horses that are recoverring from a tendon injury, although functional healing of tendon injuries will remain a problem in equestrian sports and additional research is necessary. Improvement of prognosis can be expected by a proactive approach including early immobilisation and application of novel intratendinous treatments.