Change of vertebral orientation, between the supine position and the prone position.

PURPOSE: Our aim was to assess the change of vertebral orientation, expressed in the sagittal plane, in the transversal plane and in the frontal plane, at each level from T1 to S1 between the supine position (like in in a CT scan) and the prone position lying on bolsters like in an OR. METHODS: Thirty-six patients were selected and included for a total number of one hundred and forty-eight vertebral levels. There were 30 females and 6 males. The mean age was 15 years and 9 months. A semi-automatic image processing technique and software (3D slicer), with a custom-made python script add-on, was used for each patient: paired preoperative CT scan and intraoperative cone beam computed tomography (CBCT) scan were processed to acquire complete spinal reconstructions in a consistent 3D coordinate system. The aim was to automatically compute a set of sagittal, transversal, and frontal rotations of each vertebral level of the same patient describing the 3D vertebral rotation between the supine position and the prone position lying on bolsters. RESULTS: For sagittal analysis, the results showed a behavior in the evolution of rotation depending on the level. Between T01 and T10, the rotation was between - 14° and - 8°. Between T10 and L05, the sagittal rotation increased from - 10° up to + 10°. For frontal and transversal analysis, the rotations were under 6.5°. CONCLUSION: These results could be valuable to perform a safe virtual templating: the information given by the virtual templating seems to be more accurate in the transversal plane than in the sagittal plane.

Sliding on cortical shell: Biomechanical characterization of the vertebral cannulation for pedicle screw insertion.

BACKGROUND: Pedicular screws pull-out has been well studied unlike their insertion. A need for characterizing cannulation before pedicle screw implantation is highlighted in literature and offers promising prospects for future intra-operation instrumentation. A reliable cannulation protocol for ex-vivo testing in swine and cadaver vertebrae is presented in this work to predict extra pedicular perforation. METHODS: An MTS Acumen 3 A/T electrodynamic device, with a tri-axis 3 kN Kistler load cell mounted on a surgical tool was used to reproduce surgeon's gesture by moving at a constant rotational speed of 10°/mm and performing a three-section test. Perforation of the pedicle's cortical shell was planned through a design of experiment on the surgical tool angle at the entry point. Samples were scanned before and after mechanical tests and reproducibility of the protocol was tested on synthetic foam. Computation of the angle between cannulation tool and pedicle cortical shell was performed as well as cannulation coefficient of each perforation section. FINDINGS: A total of 68 pedicles were tested: 19 perforated and 21 non-perforated human pedicles, 17 perforated and 16 non-perforated swine pedicles. The reproducibility of the protocol for cannulation coefficient computation resulted in an intraclass correlation coefficient of 0.979. Cannulation coefficients results presented variability within spinal levels as well as between swine and human model. Correlation between bone density and cannulation coefficient was found significant (p < 0.005). Torque measurement was found to be the best predictor of perforation. Threshold of angle for prediction of perforation was found to be 21.7°. INTERPRETATION: Characterizing pedicle cannulation enables to predict extra pedicular perforation. Influence of bone mineral density and patient-specific morphology on pedicle cannulation has been highlighted together with a comparison of swine and cadaver models.