Use of ultrasound in spinal arthrodesis. A rabbit model.
METHODS
The biomechanical and histologic characteristics of posterolateral spinal fusion in a rabbit model with and without the application of low-intensity ultrasound were analyzed.


OBJECTIVE
To evaluate the use of ultrasound to improve the spinal fusion rate and biomechanical characteristics of the fusion mass in a rabbit model.


BACKGROUND
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.
Glazer
P A
PA
Department of Orthopaedic Surgery, Beth Israel-Deaconess Medical Center, Harvard University, Boston, Massachusetts, USA.
Heilmann
M R
MR
Lotz
J C
JC
Bradford
D S
DS
D000818:Animals; D001696:Biomechanical Phenomena; D016025:Bone Transplantation; D004195:Disease Models, Animal; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000473:pathology; D011542:Pseudarthrosis / Q000000981:diagnostic imaging / Q000473:pathology / Q000628:therapy*; D011817:Rabbits; D011859:Radiography; D013123:Spinal Fusion / Q000379:methods*; D014464:Ultrasonic Therapy; D014463:Ultrasonography; D014945:Wound Healing