The biomechanical effects of low-intensity ultrasound on healing tendons.

The effect of low-intensity ultrasound on the healing strength of tendons was studied in experimentally tenotomized, repaired and immobilized right tendo calcaneus (Achilles tendon) of 24 rabbits. Ten tendons were sonicated in continuous waves at a space-averaged intensity of 0.5 W cm-2 for 5 min every day. The remaining 14 tendons were mock-sonicated as controls. After nine consecutive treatments, the tendons were excised under anesthesia and compared for differences in tensile strength, tensile stress and energy absorption capacity. Sonication at 0.5 W cm-2 induced a significant increase in the tensile strength (p less than .02), tensile stress (p less than .005) and energy absorption capacity (p less than .001) of the tendons. These findings suggest that high-intensity sonication may not be necessary to augment the healing strength of tendons and that sonication at similarly low intensities may enhance the healing process of surgically repaired human tendo calcaneus.