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Ultrasound‐Guided Dry Needling of the Healthy Rat Supraspinatus Tendon Elicits Early Healing Without Causing Permanent Damage

Overuse‐induced tendinopathy is highly prevalent in the general population. Percutaneous fenestration, or dry needling, techniques have been increasing in popularity, but despite their current use, there are no controlled laboratory studies to provide fundamental support for this practice. The objective of this study was to establish a model for percutaneous needling of the rat supraspinatus tendon using ultrasound guidance and to evaluate the biological response of needling healthy tendon. A total of 44 male Sprague–Dawley rats (477 ± 39 g) were used to evaluate the effect of dry needling on healthy supraspinatus tendon properties. Ten rats were reserved as un‐needled control animals, and the remaining animals underwent either mild or moderate bilateral needling protocols and were sacrificed at 1 or 6 weeks post‐needling (n = 8–10/group). Color Doppler ultrasound imaging was performed to analyze blood flow within the tendon. Histological and immunohistochemical analyses were used to determine cellular, inflammatory, and extracellular matrix properties of the tissue. Finally, quasi‐static tensile mechanical analysis was performed to obtain viscoelastic, structural, and material properties to evaluate the tendon healing outcome. Data were tested for normality, and then two‐way analysis of variance tests were performed followed by post hoc tests for multiple comparisons. Both the mild and moderate needling groups caused a transient healing response at early time points as shown by a statistically significant (p < 0.05) reduction in mechanical properties, and increase in blood flow, inflammation, and production of collagen III and glycosaminoglycans as compared to the control. Furthermore, mild needling properties returned to or exceeded pre‐needling values at the 6‐week time point. Clinical significance: Needling the rat supraspinatus tendon is a feasible technique that causes a transient healing response followed by a return to, or improvement of, normal tendon properties, indicating potential applicability in understanding the effects of current practices utilizing dry needling of tendons in humans. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2035–2042, 2019