The surgeon is able to select the ideal screw diameter and length in the pre-operative planning phase; the computer provides a 3D view of the selected screw in the pre-operatively acquired image. It also provides a "target" window to facilitate screw insertion along the predetermined trajectory. In one of the earlier clinical studies in the use of image guidance for the insertion of lumbosacral pedicle screws , 137 out of a total of 150 screws were optimally placed. Only one screw was found to be in a significantly unsatisfactory position. No nerve root injuries were reported.
Image guidance is even more valuable in pedicle screw insertion into the thoracic spine . Compared with its lumbar counterpart, the thoracic pedicle is smaller, has a more complex 3D morphology and has a variable cross-section in the coronal plane. There is a high degree of variability in the diameter, shape and angle of the thoracic pedicle. Moreover, its proximity to the pleura, nerve roots and the relatively fixed spinal cord means that inappropriate insertion is less forgiving. From clinical and cadaveric studies, up to 25% of thoracic pedicle screws were found to violate the pedicular cortex when perioperative fluoroscopy alone was used. In a recent study using post-operative CT evaluation, only 5 out of 266 screws inserted at all levels of the thoracic spine in 65 patients showed a structurally significant (defined as more than 2 mm) inadvertent violation of the pedicular cortex. These tended to cluster in the mid-thoracic spine. The majority of these misplacements occurred in severe traumatic fracture subluxations, implying that the increased inter-segmental mobility in these situations interferes with the accuracy of registration of the imageguidance system. The authors also advocate an alternative screw trajectory through the rib head into the vertebral body if the pedicle is smaller than 4 mm in its widest coronal diameter, or scaphoid in shape, or laterally directed. This information can only be gleaned through pre-operative pedicle evaluation on the imageguidance system.
Image guidance is also useful when there is a concurrent anterior construct, such as a Kaneda system, for example. Pedicle screw insertion then allows a rigid parallelogram of fixation .
Applications to the cervical spine have included anterior cervical diskectomy and ver-tebrectomy, transoral odontoid resection, and the insertion of C1-C2 transarticular screws and lateral mass plates . In anterior cervical surgery, image guidance allows the identification of the lateral resection margins of osteo-phytes and their relationships to the transverse foramen, the vertebral artery and the nerve root foramen. The risks of vascular and neurological injury (to the nerve roots and spinal cord) for these procedures have been quoted as up to 5% and 1% respectively. Image guidance also reduces the risk of incomplete osteophyte excision.
Surgical difficulties in the C1-C2 region include the complexity of the anatomy, which may be distorted by inflammatory pannus or tumor, and a limited operative field. Image guidance allows the determination of the position of unexposed structures, minimizing the need for extensive exposures. Insertion of atlanto-axial transarticular screws can then be performed with a higher margin of safety and with increased confidence.
Was this article helpful?
The term vaginitis is one that is applied to any inflammation or infection of the vagina, and there are many different conditions that are categorized together under this ‘broad’ heading, including bacterial vaginosis, trichomoniasis and non-infectious vaginitis.