Abstract
Aim: To examine the effect of the low intensity ultrasound stimulation (SAFHS, Exogen) on new bone formation and stress shielding in a distraction osteogenesis model in New Zealand white rabbits.
Methods: Thirty male rabbits underwent a right tibial osteotomy at eight weeks of age. Distraction of the osteotomy by 0.75mm/day was performed for two weeks. Ultrasound stimulation commenced on the seventh day after wound healing. The ‘active’ group was stimulated for 20 minutes daily. The controls had identical dummy stimulators applied. Half of the animals were culled at four weeks and half at six weeks. Dual-energy x-ray absorptiometry scans evaluated BMC and BMD. Quantitative computerised tomography measured the cross-sectional areas. Four-point bend testing of distracted and non-operated tibiae was performed in a standardised fashion.
Results: No differences were identified between the active and control groups at four or six weeks with respect to BMD, BMC or cross-sectional area of the regenerated bone. Stress shielding osteopaenia was unaffected by ultrasound stimulation. No significant improvement in strength of the regenerate was identified in either group – there was a trend towards improved strength at four weeks.
Discussion: Low intensity pulsed ultrasound accelerates fracture healing in humans when immobilised by plaster of Paris. One published study purporting to show improvement in distraction osteogenesis is fatally flawed. We believe the intensity of the ultrasound may need to be increased to stimulate mechanically a bone rigidly fixed by an external fixator. Other interventions such as the use of growth factors or bisphosphonates provide much greater improvements in experimental animals and are much more convenient to apply.
The abstracts were prepared by Professor A. J. Thurston. Correspondence should be addressed to him at the Department of Surgery, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand
