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Tendon pathologies are among the most common musculoskeletal disorders in horses. Some tendons are more prone to injury than others, and the superficial digital flexor tendon (SDFT) is one of the most commonly affected structures. After damage the tendon repairs by forming disorganized scar tissue that is of inferior functional quality, leading to high re-injury rates. Many of the currently available treatment modalities cannot significantly reduce this high recurrence rate, urging a continuing quest for improved therapies. Autologous Conditioned Plasma ® (ACP) has been described in the literature as a leukocyte-reduced platelet concentrate. This blood product has been used in equines and humans for the treatment of tendon and ligament injuries. It has been recently claimed that this preparation might be superior improving tendon healing than other platelet concentrates. However, the effect of this therapeutical approach on tendon healing is unknown. Therefore the first objective of this study was to evaluate the effects of intra-lesional treatment of tendon injuries with ACP. Additionally, even though equine multi-limb tendinopathy models have been previously reported, it is unknown if fore- and hindlimb tendon healing behave similarly. Therefore, the second aim of this study was to compare the healing process of surgically induced, placebo treated, SDFT core lesions of fore- and hindlimbs in horses.
Tendon core lesions were surgically induced in the SDFT of both fore- and hindlimbs in eight healthy horses. At days 7 and 15 after lesion induction, one randomly assigned fore- and hindlimb was treated with ACP and the contralateral one with placebo. Tendon healing was monitored clinically and using plain and color Doppler ultrasonography (CDU). After 24 weeks, the tendons were harvested for the evaluation of biochemical, biomechanical and histological parameters.
Twenty-three weeks after treatment, the ACP treated tendons presented a significantly lower concentration of glycosaminoglycans (GAGs) (p=0.05) when compared to placebo. Twenty-four weeks post-surgery, forelimb SDFT lesions presented a significantly higher CDU vascularization score (p=0.02) and GAGs concentration (p=0.04) and a significantly lower hydroxylysylpyridinoline (HP) content (p=0.03) when compared to the hindlimbs.
In conclusion, our results indicate that 2 intra-tendinous ACP treatments, without anticoagulant, during the proliferative phase of healing, in surgically induced tendon core lesions, have a limited effect on tendon healing, when comparing ultrasonographic, biochemical, biomechanical and histological parameters with the control treatment. Nevertheless, the significant decrease of sulphated GAGs in the ACP treated tendons can be interpreted as a possible, but apparently limited, beneficial effect on tendon healing. Long-term placebo controlled clinical trials with a more horses are warranted to determine if this effect is clinically significant. Moreover, our results suggest that fore- and hindlimb SDFT surgically induced lesions exhibit significant differences in several important parameters of tendon healing 24 weeks post-surgery. These differences create significant challenges in using all 4 limbs and accurately interpreting the results that one might generate. Therefore these findings do not support the use of four limb models for study of tendon injury, until the reasons for these differences are much better understood.