P A Glazer1, M R Heilmann, J C Lotz, D S Bradford. 1. Department of Orthopaedic Surgery, Beth Israel-Deaconess Medical Center, Harvard University, Boston, Massachusetts, USA.
Abstract
STUDY DESIGN: The biomechanical and histologic characteristics of posterolateral spinal fusion in a rabbit model with and without the application of low-intensity ultrasound were analyzed. OBJECTIVES: To evaluate the use of ultrasound to improve the spinal fusion rate and biomechanical characteristics of the fusion mass in a rabbit model. SUMMARY OF BACKGROUND DATA: This is the first study in which the benefits of ultrasound in spinal fusion have been assessed. Posterolateral intertransverse process fusion in the rabbit has a pseudarthrosis rate similar to that recorded in humans (5-40%). METHODS: Fourteen New Zealand White rabbits were randomly assigned to each of two groups to undergo spinal fusion using autologous bone with ultrasound or autologous bone without ultrasound. A specially designed plastic constraint was used to focus the ultrasound over the rabbits' lumbar spine 20 minutes per day. Animals were killed at 6 weeks for biomechanical and histologic testing. RESULTS: The rate of pseudarthrosis, evaluated radiographically and manually in a blinded fashion, decreased at a statistically significant rate (from 35% to 7%) with ultrasound. Biomechanical analysis of the fusion mass showed that ultrasound resulted in statistically significant increases in stiffness (33%; P = 0.03), area under the load displacement curve (25%; P = 0.05), and load to failure of the fusion mass (24%; P = 0.04). Qualitative histologic assessment showed increased bone formation in those fusions exposed to ultrasound. CONCLUSIONS: Lumbar spinal fusion is a complex biologic process. The results of the current study demonstrate the reproducibility of a rabbit fusion model and the ability of ultrasound to induce a statistically significant increase in fusion rate, stiffness, area under the load displacement curve, and load to failure of the fusion mass. These results provide a basis for continued evaluation of biologic improvement of spinal arthrodesis with the use of ultrasound.
STUDY DESIGN: The biomechanical and histologic characteristics of posterolateral spinal fusion in a rabbit model with and without the application of low-intensity ultrasound were analyzed. OBJECTIVES: To evaluate the use of ultrasound to improve the spinal fusion rate and biomechanical characteristics of the fusion mass in a rabbit model. SUMMARY OF BACKGROUND DATA: This is the first study in which the benefits of ultrasound in spinal fusion have been assessed. Posterolateral intertransverse process fusion in the rabbit has a pseudarthrosis rate similar to that recorded in humans (5-40%). METHODS: Fourteen New Zealand White rabbits were randomly assigned to each of two groups to undergo spinal fusion using autologous bone with ultrasound or autologous bone without ultrasound. A specially designed plastic constraint was used to focus the ultrasound over the rabbits' lumbar spine 20 minutes per day. Animals were killed at 6 weeks for biomechanical and histologic testing. RESULTS: The rate of pseudarthrosis, evaluated radiographically and manually in a blinded fashion, decreased at a statistically significant rate (from 35% to 7%) with ultrasound. Biomechanical analysis of the fusion mass showed that ultrasound resulted in statistically significant increases in stiffness (33%; P = 0.03), area under the load displacement curve (25%; P = 0.05), and load to failure of the fusion mass (24%; P = 0.04). Qualitative histologic assessment showed increased bone formation in those fusions exposed to ultrasound. CONCLUSIONS: Lumbar spinal fusion is a complex biologic process. The results of the current study demonstrate the reproducibility of a rabbit fusion model and the ability of ultrasound to induce a statistically significant increase in fusion rate, stiffness, area under the load displacement curve, and load to failure of the fusion mass. These results provide a basis for continued evaluation of biologic improvement of spinal arthrodesis with the use of ultrasound.
Authors: William R Walsh; Andreas Loefler; Sean Nicklin; Doug Arm; Ralph E Stanford; Yan Yu; Richard Harris; R M Gillies Journal: Eur Spine J Date: 2004-03-18 Impact factor: 3.134