STABILITY OF EXTERNAL CIRCULAR FIXATION - A MULTIVARIABLE BIOMECHANICAL ANALYSIS

Objective. To determine how the manipulation of the parameters of fixa tion and components of the circular external frame could improve and m aintain optimal stability of bone fragments. Design. We performed a mu lti-parametric biomechanical analysis of the extrinsic parameters effe cting bone fragment stabiliza tion. Results of testing are presented a s a percent change in stiffness due to the manipulation of frame compo nents and their interaction with other fixation parameters. Background . Although there have been investigations of the biomechanical charact eristics of circular external fixation, they have been limited to eith er individual frame components or full frame comparisons. Therefore, t hese studies did not provide a comprehensive understanding of how the manipulation of circular fixator components influences bone fragment s tability. Methods. Mechanical testing was performed in three phases ex amining the effect of numerous components including ring diameter, wir e angle, ring separation, etc. on axial, torsional and bending stiffne ss. Results. For phase I (single ring) and phase II (double-ring block ), ring diameter was the most significant factor affecting axial and t orsional stiffness, while wire angle, ring separation. and their inter action had the most influence on bending stiffness. Phase III (two dou ble-ring blocks) showed that ring positioning with respect to the oste otomy site had the most affect on bending and torsional stiffness whil e axial stiffness was non-linear and dependent upon the applied load. Conclusions. The stability of bone fragments within a circular externa l fixator is affected by manipulation of the parameters of fixation or individual components of the frame. The contribution of each componen t to overall bone fragment stability is dependent upon the mode of loa ding. The changes in overall stability of bone fragments are dependent not only on the individual frame components but also upon their inter action with other parameters of fixation. Relevance Understanding how the manipulation of individual frame components will affect overall bo ne fragment stabilization will allow the surgeon to better control the stability of bone fragments for each clinical situation. (C) 1998 Els evier Science Ltd. All rights reserved.