Focused ultrasound as an alternative to dry needling for the treatment of tendinopathies: A murine model

Abstract

Tendinopathies account for 30% of 102 million annual musculoskeletal injuries occurring annually in the United States. Current treatments, like dry needling, induce microdamage to promote healing but produce mixed success rates. Previously, we showed focused ultrasound can noninvasively create microdamage while preserving mechanical properties in ex vivo murine tendons. This present study compared growth factor, histological, and mechanical effects after focused ultrasound or dry needling treatments in an in vivo murine tendon injury model. Partial Achilles tenotomy was performed in 26 rats. One-week postsurgery, tendons were treated with focused ultrasound (1.5 MHz, 1-ms pulses at 10 Hz for 106 s, p₊ = 49 MPa, p_- = 19 MPa) or dry needling (30 G needle, 5 fenestrations over 20 s) and survived for 1 additional week. Blood was collected immediately before and after treatment and before euthanasia; plasma was assayed for growth factors. Treated tendons and contralateral controls were harvested for histology or mechanical testing. No differences were found between treatments in release of insulin growth factor 1 and transforming growth factor beta; vascular endothelial growth factor A concentrations were too low for detection. Histologically, focused ultrasound and dry needling tendons displayed localized fibroblast infiltration without collagen proliferation with no detectable differences between treatments. Mechanically, stiffness and percent relaxation of dry needling tendons were lower than controls (p = 0.0041, p = 0.0441, respectively), whereas stiffness and percent relaxation of focused ultrasound tendons were not different from controls. These results suggest focused ultrasound should be studied further to determine how this modality can be leveraged as a therapy for tendinopathies.

Keywords: dry needling (DN); focused ultrasound (fUS); growth factors; histology; mechanical testing.

Figure 1.

Murine Achilles tendons were targeted with fUS while partially submerged in a degassed, deionized water tank. The fUS transducer was aligned and monitored with co-axial B-mode ultrasound. Inset: Approximate focal dimensions in relation to the tendon diameter and injured sites.

Figure 2.

(left) IGF-1 and (right) TGF-β concentrations measured before, after, and 1-week from fUS and DN interventions. (Note: Before = before intervention; After = after intervention; 1-week = 1-week post-intervention)

Figure 3.

Representative H&E sections for (a) focused ultrasound (fUS); (b) dry needling (DN); and (c) control tendons. Fibroblast migration, which appears as scattered basophilic (purple-stained) cytoplasm and nuclei, was found in fUS- and DN-treated sections. Conversely, untreated areas and control tendons displayed long fibrous cells with sparse basophilic nuclei. Of note, the upper right area in image (a) is an artifact from the histological adhering process.

Figure 4.

Representative picrosirius red sections for (a) focused ultrasound (fUS); (b) dry needling (DN); and (c) control tendons. Fibroblast migration areas did not contain collagen, or bright yellow stain. Conversely, untreated areas and control tendons displayed bright yellow collagen content.

Figure 5.

(a) Elastic modulus; (b) stiffness; (c) ultimate tensile stress; (d) maximum load; and (e) percent relaxation of Achilles tendons exposed to dry needling (DN) and focused ultrasound (fUS).