The propagation of induced tendon lesions in the equine superficial digital flexor tendon: an ex vivo study.

Reasons For Performing Study: Clinical tendon lesions usually enlarge during the first days to weeks after sustaining the injury due to enzymatic and biomechanical influences. Limiting this enlargement would positively influence prognosis related to lesion size.

Objectives: To investigate the effect of cyclic loading on the propagation of enzymatically and physically induced tendon lesions and to assess the effect of immobilisation thereon in an ex vivo model.

Methods: Equine cadaver limbs with either physically or collagenase-induced SDFT lesions were placed in a pneumatic loading device. Groups consisted of unloaded limbs, cyclically loaded limbs and cyclically loaded limbs with fibreglass cast immobilisation. Lesion size was evaluated ultrasonographically and macroscopically and load at failure was determined for groups where lesions enlarged.

Results: Physically induced lesions did not propagate after cyclical loading and were not further investigated. Collagenase-induced lesions propagated significantly more after cyclical loading compared to unloaded limbs. This propagation could effectively be reduced by immobilisation through a lower limb cast. Immobilisation did not influence load at failure.

Conclusions: The combination of enzymatic and mechanical stimulation caused the lesions to propagate most. Casting appeared effectively to reduce the enlargement of the original tendon lesions in this ex vivo model, while it did not affect ultimate tendon strength.

Potential Relevance: As prognosis of tendon injuries is related to lesion size, the outcome of this study warrants further investigations in vivo.