title: [Stiffness of the AO spinal external fixator. Experimental results of stiffness of the AO spinal external fixator with 3 different pedicle screw systems].
abstract: The stiffness of the AO external pedicular fixator was analysed in an experimental laboratory study using three different sets of pedicle screws and different configurations of the implant. The experiments were performed with a wooden model as well as with bi-segmental human lumbar spine specimens with disc and ligaments intact. The capacity of the AO external pedicular fixator to compensate axial load, transversal- and torsion forces was compared to physiological requirements. Of particular interest was the effect of preload on the axial stiffness. It is demonstrated that the axial stiffness of the AO external pedicular fixator is so low that the axial load on the lumbar spine level in humans cannot be influenced by the fixator even when preloaded. However the resistance against torsion and transversal slipping is probably higher than required in vivo. No significant differences were found between the three types of pedicular screws. The effect of the triangular counter nuts of the AO external pedicular fixator on the transversal- and torsion stability was important. The presented results suggest that the AO external pedicular fixator can be of significant value in segmental rotation- and translocation pathologies of the lumbar spine and that the effect of isolated segmental distraction has probably been overestimated.
authors.affiliation: Orthopädische Universitätsklinik BALGRIST, Zürich.
authors.forename: H
authors.initials: H
authors.lastname: Stalder
authors.forename: H A
authors.initials: HA
authors.lastname: Jacob
authors.forename: H J
authors.initials: HJ
authors.lastname: Leu
mesh_terms: D001863:Bone Screws; D004548:Elasticity; D004867:Equipment Design; D016267:External Fixators; D006801:Humans; D013123:Spinal Fusion / Q000295:instrumentation*; D013718:Tensile Strength
vernacular_title: Steifigkeit des AO-Wirbelfixateur externe.Experimentelle Ergebnisse zur Steifigkeit des AO Wirbelfixateur externe mit drei verschiedenen Pedikelschraubensystemen.