Research Article Monoaxial Pedicle Screws Are Superior to Polyaxial Pedicle Screws and the Two Pin External Fixator for Subcutaneous Anterior Pelvic Fixation in a Biomechanical Analysis

Copyright © 2013 Rahul Vaidya et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Purpose. Comparison of monoaxial and polyaxial screws with the use of subcutaneous anterior pelvic fixation. Methods. Four different groups each having 5 constructs were tested in distractionwithin the elastic range. Once that was completed, 3 components were tested in torsion within the elastic range, 2 to torsional failure and 3 in distraction until failure. Results. The pedicle screw systems showed higher stiffness (4.008 ± 0.113Nmmmonoaxial, 3.638 ± 0.108Nmm Click-x; 3.634 ± 0.147Nmm Pangea) than the exfix system (2.882 ± 0.054Nmm) in distraction. In failure testing, monoaxial pedicle screw system was stronger (360N) than exfixes (160N) and polyaxial devices which failed if distracted greater than 4 cm (157N Click-x or 138N Pangea). The exfix had higher peak torque and torsional stiffness than all pedicle systems. In torsion, the yield strengths were the same for all constructs. Conclusion. The infix device constructed with polyaxial or monoaxial pedicle screws is stiffer than the 2 pin external fixator in distraction testing. In extreme cases, the use of reinforcement or monoaxial systems which do not fail even at 360N is a better option. In torsional testing, the 2 pin external fixator is stiffer than the pedicle screw systems. 1