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

Abstract

Purpose of the study: Attempts to control growth of the spine without provoking epiphysiodesis is a promising area of investigation. The purpose of our experimentation was to achieve localized interruption of vertebral body growth without damaging the adjacent disc and ligament structures.

Material and methods: Two Yucatan micropigs weighing 7 and 9 kg were used for this study. Before initiating the experiment, a complete imaging work-up (x-ray, computed tomography, magnetic resonance imaging) of the spine of the two pigs was obtained. The animals were anesthetized for thoracotomy and a 810 nm 30W laser diode (Diomed Ltd) was implanted in the superolateral part of nine vertebral bodies (3 mm under the cartilage endplate and 3 mm in depth) in order to apply a certain quantity of heat. The nine vertebrae were divided into three groups of three vertebrae. Each group received 2W for 200, 300, or 400s (groups 1, 2 and 3 repectively). The temperature generated by the thermal delivery was recorded in the growth cartilage and in the disc using thermal probes. A complete imaging series of the spine was again obtained four months later, before sacrifice. The results presented correspond to the CT-scan findings used to analyze the effect on vertebral growth and to the MRI findings used to check for discal injury. Each vertebral level was sampled for a histological examination and (in the second part of the study) a biomechanical analysis was undertaken.

Results: Among the 18 vertebral levels studied (two micropigs), 11 levels exhibited localized interruption of growth without any alteration of the adjacent discs. We were unable to observe any significant correlation between the temperature recorded in the disc and the discal structure observed at sacrifice, although above 52°C, there appeared to be a greater risk of definitive discal damage. As disc growth can be controlled (as demonstrated in this study) without damaging the adjacent disc (which will require further study to demonstrate) is would be possible to use this technique as an alternative to treatment by corset for progressive idiopathic scoliosis in growing children.