Low-intensity pulsed ultrasound improves spinal fusion.

BACKGROUND CONTEXT: Increasing the incidence of solid bony fusion is a primary goal in spine surgery. Daily low-intensity pulsed ultrasound therapy has been shown to improve and accelerate the bone healing process. PURPOSE: The purpose of this study was to evaluate the efficacy of daily low-intensity pulsed ultrasound therapy to improve the rate and quality of spinal fusion. STUDY DESIGN: Canine fusion model prospective study. PATIENT SAMPLE: Fourteen adult male dogs were used. OUTCOME MEASURES: Radiographic grading of plain films, computed tomography (CT) and magnetic resonance imaging (MRI), gross palpation, torsional stiffness and histologic grading were used to determine the presence or absence of fusion. METHODS: Posterior noninstrumented bilateral fusions were evaluated at the L2-L3 and L5-L6 levels. Treatment with low-intensity pulsed ultrasound for 20 minutes per day over the fusion site (stimulated) was compared with fusion sites that received no stimulation (nontreated controls) at 6 and 12 weeks after surgery. Plain film radiographs, CT and MRI, mechanical torsion testing and histologic examination were performed. RESULTS: At 6 weeks, ultrasound treated sites were more frequently fused compared with nontreated controls, although the difference in fusion rate was not statistically significant. At 12 weeks after surgery complete radiographic and histologic fusion occurred in 100% of ultrasound-treated sites. In the nontreated control sites 78% had achieved complete radiographic fusion and 44% had complete histologic fusion. Compared with control sites, the histological and mechanical fusion rate was significantly greater in ultrasound-treated sites (P<.05) at 12 weeks. A statistically significant increase in mechanical stiffness in ultrasound-treated sites was also found at 12 weeks after surgery. CONCLUSIONS: Low-intensity pulsed ultrasound therapy may be a useful means to ensure successful spine fusion.