EXPERIMENTAL STUDY OF THE FEASIBILITY OF CONTROLLING VERTEBRAL GROWTH WITHOUT ARTHRODESIS (SECOND PART)

Abstract

Purpose of the study: In the growing pig, we have been able to achieve localized control of vertebral body growth by selective destruction ofhte physis using the thermal effect of a laser probe (first part of the study). The purpose of the second part of the study was to evaluate the mechanical effects in terms of 1) intersomatic disc mobility, and 2) bony resistance of the vertebral body and risk of fracture.

Material and methods: Thoracotomy was performed on two Yucatan micropigs (group A); a 510 nm 30W diode laser delivered heat applied to nine vertebral bodies. Four months later, the micropigs were sacrificed. Two normal micropigs (group B) served as controls. The specimens were dissected to the intersomatic disc-ligament complex. Three-level vertebral assemblies were thus obtained for mobility tests (flexion-extension, lateral inclination, right-left rotation). Destruction tests were pursued to fracture. Tests were performed with a Zebris 3D motion analyzer. Computed tomography images and histological findings were also assessed.

Results: Motion: In group A, when the discal space appeared normal on the specimen, no difference was noted in motion in comparison with group B. Conversely, when imaging demonstrated discal injury, joint stiffness was noted. The destruction tests showed that in group A specimens the fracture did not occur at the zone of lytic bone destruction caused by the heat delivery. Fractures observed were similar in the two groups, including epiphyseal detachements and sagittal fractures of the vertebral bodies.

Discussion: Applying laser-delivered heat to the vertebrae in micropigs enabled partial destruction of the physis without injuring the intervertebral disc. Heat delivery induced a modification in vertebral growth. When imaging showed an intact neighboring intervertebral disc, mechanical tests showed normal mobility and resistance. Bone resistance was not diminished. This result is important to consider for the treatment of vertebral osteoid osteomas with laser.

Conclusion: Laser application to vertebral bone is a reproducible method which can stop growth of the minipig vertebral bodies without injuring the intervertebral disc and without reducing bone resistance.