The Accuracy And Safety of Trans Pedicular Screw Fixation of The Sub-axial Cervical Spine Using A Triad- Dependent Technique (TDT)

The use of the pedicle screw system has become increasingly popular for treating an unstable cervical spine resulting from traumatic, degenerative, inflammatory, and neoplastic conditions. Because the cervical pedicle screw (CPS) has superior bio mechanical stability as the lateral mass screw or trans articular screw , pedicle screws allow for shorter instrumentation with improved spinal alignment. However, CPS insertion is technically demanding because of the anatomical variations in cervical pedicle size, lack of anatomical landmarks, small pedicle diameter, and the large transverse angle of cervical pedicles . The potential risk of injury to neurovascular structures, such as the vertebral artery, spinal cord, or nerve roots, caused by CPS remains a great concern. Therefore, accurate and safe CPS insertion techniques are necessary.

Although a number of studies have evaluated the morphometric of cervical pedicles to support accurate placement of pedicle screws , the results are inconclusive. Therefore, several techniques using lateral fluoroscopy , pedicle axis view by oblique fluoroscopy , laminoframinotomy and computer-assisted navigation systems for CPS insertion have been advocated. Determining an appropriate entry point for screw insertion as well as a proper trajectory angle of the screw on the axial plane is important for successful pedicle screw placement. Here, we present our method using a fashioned triad- dependent technique (TDT) which is a combination of three methods 1-preoperative planning of the selected pedicle using 3-diamentional multi-slice CT to measure pedicle transverse angle (PTA) , pedicle outer diameter(POD)and pedicle trajectory -contralateral lamina angle 2-AP and oblique fluoroscopy to determine pedicle entry point (PEP), parallelism to vertebral end plate and 4 direction cortical violation (medial, lateral, superior, inferior) 3-interlaminar confirmatory key hole for tactile cue of medial ,superior, and inferior borders of the pedicle and related nerve root to evaluate the accuracy and safety of pedicle screw placement in patients with sub axial cervical spine disorders treated using our method.