Radiological morphometric analysis of lower cervical and upper thoracic vertebrae pedicles

The cervicothoracic junction is a unique region with its own anatomical and biomechanical features due to the fact that it is the transition zone between the cervical and thoracic spine. Since it is the transition zone from the highly mobile cervical region to the thoracic region whose movement is restricted by the rib cage, the cervicothoracic junction is under heavy load both dynamically and statically. Trauma, tumors, spondylosis, infection and iatrogenic causes are the most common reason of instability in the cervicothoracic junction. Due to its complex anatomy, it is very difficult to detect injury in this region with direct radiographs. Similarly, evaluation with fluoroscopic imaging during pedicle screw application with the free-hand technique is difficult due to the overlapping and superposition of neighboring structures in the image. For this reason, the surgeon who will perform the operation should have a good grasp of the anatomy of the cervicothoracic junction, the variations in this region and the anatomical changes of the pedicle sizes according to the vertebrae levels, thus minimizing the possibility of the pedicle breach by following this information during the surgery. In this study, patients who applied to Mersin University Medical Faculty Hospital between May 2020 and May 2022 were evaluated. Patients whose cervicothoracic junction vertebrae could be clearly evaluated in contrast-enhanced computed tomography were included in the study. Our study is a retrospective descriptive study that aimed to examine the anatomical structures of the lower cervical and upper thoracic vertebrae. A total of 100 patients, 50 female and 50 male, aged between 19 and 83, whose cervicothoracic junction vertebrae could be evaluated clearly, were included in the study. In both genders, the vertebra thickest pedicle was found in T1 vertebra (8.78±1.15 mm at T1 level in males, 7.44±1.13 mm at T1 level in females), and the pedicle thickness gradually decreases until T4. The highest pedicle in both genders was found in T3 vertebra (13.04±2.29 mm at T3 level in males, 11.35±1.30 mm at T3 level in females) and the pedicle height gradually increases from C7 to T3. The longest pedicle axis was found in T2 vertebra (34.48±2.22 mm) in males, and in T4 vertebra (31.44±2.92 mm) in females, and there is no significant increase or decrease pattern among the vertebrae. In both genders, the pedicle with the highest axial angle was found in C7 vertebra (34.24±2.50⁰ at C7 level in males, 33.96±3.72⁰ at C7 level in females), and the axial angle of the pedicle gradually decreases until T4. In both genders, the pedicle with the highest sagittal angle was found in T4 vertebra (8.40±2.99⁰ caudally at T4 level in males, 9.06±5.22⁰ caudally at T4 level in females) and the pedicle sagittal angle gradually increases until T4. In our study, the thickness, height, length, sagittal and axial angles of the vertebral pedicles between C7-T4, as well as the entry point of the vertebral artery to the transverse foramen and the hypoplasia of the transverse foramen were evaluated. Our aim is to describe the diameter, length and angles of the screw for transpedicular fusion surgeries of cervicothoracic junction that will serve as a guide, and to minimize morbidity and mortality that may occur during surgery by investigating vascular variations. Keywords: cervicothoracic junction, lower cervical, pedicle, radiological anatomy, upper thoracic