Therapeutic Ultrasound and Shockwave Therapy for Tendinopathy: A Narrative Review

Abstract

Tendon injury is prevalent and costly in the United States, comprising 45% of the 66 million musculoskeletal injuries and costing $114 billion annually. Surgical and therapeutic methods, such as arthroscopic surgery, dry needling, and physical therapy, produce mixed success in reintroducing a healing response in tendinopathy due in part to inconsistent dosing and monitoring. Ultrasound is one therapeutic modality that has been shown to noninvasively induce bioeffects in tendon that may help promote healing. However, results from this modality have also been mixed. This review compares the current state of the field in therapeutic ultrasound and shockwave therapy, including low-intensity therapeutic ultrasound, extracorporeal shockwave therapy, and radial shockwave therapy, and evaluates the efficacy in treating tendinopathies with ultrasound. We found that the mixed successes may be attributed to the wide variety of achievable parameters within each broader treatment type and the lack of standardization in measurements and reporting. Despite mixed outcomes, all three therapies show potential as an alternative therapy with lower-risk adverse effects than more invasive methods like surgery. There is currently insufficient evidence to conclude which ultrasound modality or settings are most effective. More research is needed to understand the healing effects of these different therapeutic ultrasound and shockwave modalities.

Figure 1

Therapeutic ultrasound can elicit various mechanisms. (a) Diagram showing that in general as acoustic intensity increases, mechanisms become more destructive and induce irreversible bioeffects. Multiple mechanisms, like periodic motion and forces from the displacement of the tissue from ultrasound propagation, thermal effects from acoustic absorption, and bubble effects (in brackets), can occur at the same intensity. The dotted outline indicates secondary mechanisms, like radiation forces, microstreaming, and microjets, can form from primary bubble mechanisms, which can elicit net motion of the tissue and/or surrounding fluids. (b) Summary table showing which bioeffects can occur from the therapeutic ultrasound mechanisms.

Figure 2

General characteristics of low-intensity therapeutic ultrasound (LITUS), extracorporeal shockwave therapy (ESWT), and radial shockwave therapy (RSWT). ESWT achieves nonlinear shock waves at the focus, while LITUS operates at much lower acoustic energy to produce linear waves. RSWT energy lies in between the other two therapies. (I_SATA = spatially-averaged temporally-averaged intensity; EFD = energy flux density)