Osirix 64 bit workstation

Post-operative CT images were co-registered to pre-operative CT using an iterative closest point (ICP) algorithm. The location of the cranial screw was determined as the point where the center of the screw comes into contact with the skull. The screw location recorded by the OTI system was compared to the location of the centre of the screw on post-operative CT. The post-operative actual screw location was located using an OSIRIX 64 bit workstation (Version 10.9.5, PIXMEO SARL, Switzerland).

Pre- and post-operative CT images were resliced to 0.3 mm thickness and dynamically resliced using multiplanar reconstruction corresponding to the axial and sagittal co-ordinates of the intra-operative and post-operative screw trajectories. For benchmark spine screws, the corresponding axial and sagittal co-ordinates were localized manually using distinct anatomical landmarks. The entry point of the screw was determined as the point where the center of the screw comes into contact with the vertebral body. The distance from the axis of symmetry perpendicular to the point of entry, as well as the angle between the screw trajectory and the perpendicular distance of the entry point, were recorded on the pre- and post-operative axial and sagittal multiplanar reconstructions. All measurements were performed using an OSIRIX 64-bit workstation (Version 10.9.5, PIXMEO SARL, Switzerland) (Fig. 5).