BACKGROUND CONTEXT: There is no universal consensus regarding the biomechanical aspects and relevance on the primary stability of misplaced pedicle screws. PURPOSE: The study is aimed to the determination of the correlation between axial pullout forces of pedicle screws with the possible screw misplacement, including mild and severe cortical violations. METHODS: Eighty-eight monoaxial pedicle screws were implanted into 44 porcine lumbar vertebral bodies, paying attention on trying to obtain a wide range of placement accuracy. After screw implantation, all specimens underwent a spiral computed tomography scan, and the screw placements were graded following the scales of Laine et al. and Abul Kasim et al. Axial pullout tests were then performed on a servohydraulic material testing system. RESULTS: Decreasing pullout forces were determined for screws implanted with increasing cortical violation. A smaller influence of cortical violations in the medial direction with respect to the lateral direction was observed. Screws implanted with a large cortical violation and misplacement in the craniocaudal direction were found to be significantly less stable than screws having comparable cortical violation but in a centered sagittal position. CONCLUSIONS: These results provide adjunctive criteria to evaluate more accurately the fate of a spine instrumentation. Particular care should be placed in the screw evaluation regarding the craniocaudal positioning and alignment.
BACKGROUND CONTEXT: There is no universal consensus regarding the biomechanical aspects and relevance on the primary stability of misplaced pedicle screws. PURPOSE: The study is aimed to the determination of the correlation between axial pullout forces of pedicle screws with the possible screw misplacement, including mild and severe cortical violations. METHODS: Eighty-eight monoaxial pedicle screws were implanted into 44 porcine lumbar vertebral bodies, paying attention on trying to obtain a wide range of placement accuracy. After screw implantation, all specimens underwent a spiral computed tomography scan, and the screw placements were graded following the scales of Laine et al. and Abul Kasim et al. Axial pullout tests were then performed on a servohydraulic material testing system. RESULTS: Decreasing pullout forces were determined for screws implanted with increasing cortical violation. A smaller influence of cortical violations in the medial direction with respect to the lateral direction was observed. Screws implanted with a large cortical violation and misplacement in the craniocaudal direction were found to be significantly less stable than screws having comparable cortical violation but in a centered sagittal position. CONCLUSIONS: These results provide adjunctive criteria to evaluate more accurately the fate of a spine instrumentation. Particular care should be placed in the screw evaluation regarding the craniocaudal positioning and alignment.
Authors: Sophie Le Cann; Thibaut Cachon; Eric Viguier; Lotfi Miladi; Thierry Odent; Jean-Marie Rossi; Patrick Chabrand Journal: PLoS One Date: 2015-10-09 Impact factor: 3.240
Authors: D Kubosch; E J Kubosch; B Gueorguiev; I Zderic; M Windolf; K Izadpanah; N P Südkamp; P C Strohm Journal: BMC Musculoskelet Disord Date: 2016-03-22 Impact factor: 2.362