Abstract
Introduction: Arthrodesis of the shoulder joint is appropriate for several conditions, including paralysis, degenerative disease, infection, and salvage of failed arthroplasty. Two common complications of shoulder fusion, non-union and unacceptable arm position, may reflect failure to achieve rigid fixation during the surgical procedure. Numerous fixation techniques have been described, including plate fixation, external fixation, and screw fixation.
Aim: To compare the biomechanics of five fixation techniques of shoulder fusion in a human cadaveric model.
Methods: Twenty-five shoulder fusions were carried out in fresh-frozen human cadaveric specimens with the following five techniques: screw fixation alone (n=5), external fixation alone (n=5), external fixation supplemented with screw fixation (n=5), single plate fixation (n=5), and double plate fixation (n=5). Each specimen was tested on a servo-hydraulic machine under repeated physiologic loads to determine the bending and torsional stiffness.
Results: There was a statistically significant difference in bending and torsional stiffness between all five fixation techniques (ANOVA, p< 0.05). Normalised bending (B) and torsional (T) stiffness, in descending order, were: double plate (B=1.0, T=1.0), single plate (B=0.77, T=0.89), external-fixation with screws (B=0.68, T=0.74), external-fixation alone (B=0.40, T=0.53), and screws alone (B=0.13, T=0.26).
Discussion & Conclusion: Statistically significant differences in bending and torsional stiffness have been identified using five different techniques of shoulder fusion. The risk of the most common complications of this surgical procedure, non-union and unacceptable arm position, may be minimised if these biomechanical findings are applied to surgical decision-making.
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
