We aimed to determine whether extracorporeal shock waves of varying intensity would damage the intact tendo Achillis and paratenon in a rabbit model. We used 42 female New Zealand white rabbits randomly divided into four groups as follows: group a received 1000 shock-wave impulses of an energy flux density of 0.08 mJ/mm², group b 1000 impulses of 0.28 mJ/mm², group c 1000 impulses of 0.60 mJ/mm², and group d was a control group.

Sonographic and histological evaluation showed no changes in group a, and transient swelling of the tendon with a minor inflammatory reaction in group b. Group c had formation of paratendinous fluid with a significant increase in the anteroposterior diameter of the tendon. In this group there were marked histological changes with increased eosin staining, fibrinoid necrosis, fibrosis in the paratenon and infiltration of inflammatory cells.

We conclude that there are dose-dependent changes in the tendon and paratenon after extracorporeal shock-wave therapy and that energy flux densities of over 0.28 mJ/mm² should not be used clinically in the treatment of tendon disorders.