Effect of extracorporeal shock wave therapy on the biochemical composition and metabolic activity of tenocytes in normal tendinous structures in ponies

Reasons for performing study: Extracorporeal shockwave therapy (ESWT) has recently been introduced as a new therapy for tendon injuries in horses, but little is known about the basic mechanism of action of this therapy. Objectives: To study the effect of ESWT on biochemical parameters and tenocyte metabolism of normal tendinous structures in ponies. Methods: Six Shetland ponies, free of lameness and with ultrasonographically normal flexor and extensor tendons and suspensory ligaments (SL), were used. ESWT was applied at the origin of the suspensory ligament and the midmetacarpal region of the superficial digital flexor tendon (SDFT) 6 weeks prior to sample taking, and at the midmetacarpal region (ET) and the insertion on the extensor process of the distal phalanx (EP) of the common digital extensor tendon 3 h prior to tendon sampling. In all animals one front leg was treated and the other front leg was used as control. After euthanasia, tendon explants were harvested aseptically for in vitro cell culture experiments and additional samples were taken for biochemical analyses. Results: In the explants harvested 3 h after treatment, glycosaminoglycan (GAG) and protein syntheses were increased (P<0.05). The synthesis of all measured parameters was decreased 6 weeks after ESWT treatment. Biochemically, the level of degraded collagen was increased 3 h after treatment (P<0.05). Six weeks after treatment, there was a decrease of degraded collagen and GAG contents. DNA content had not changed in either tendon samples or explants after culturing. Conclusions: ESWT causes a transient stimulation of metabolism in tendinous structures of ponies shortly after treatment. After 6 weeks metabolism has decreased significantly and GAG levels are lower than in untreated control limbs. Potential relevance: The stimulating short-term effect of ESWT might accelerate the initiation of the healing process in injured tendons. The long-term effect seems less beneficial. Further research should aim at determining the duration of this effect and at assessing its relevance for end-stage tendon quality.