Quantitative Anatomy of C7 Vertebra in Southern Chinese for Insertion of Lateral Mass Screws and Pedicle Screws

Abstract

Study DesignRetrospective study.PurposeTo analyze the quantitative anatomy of C7 vertebra for insertion of lateral mass screws and pedicle screws in Southern Chinese patients.Overview of LiteratureC7 lateral mass is smaller when compared to other subaxial cervical levels, which limits the length of lateral mass screws that can be used. Some studies have suggested pedicle screws for better fixation. But, this option is limited by the narrow pedicle width.MethodsWe have obtained computed tomography (CT) cervical spine data in 0.625 mm slices from our radiology department. The patients were adults. CTs were from May to August, 2015. The lateral mass screw length was measured using Margerl's technique and pedicle width and pedicle screw trajectory were determined in three-dimensional reformated images.ResultsCT scans of cervical spines of 94 patients were obtained and 188 lateral masses and pedicles of C7 vertebrae were measured. The mean lateral mass screw length was 13.2 mm (standard deviation [SD] 1.6 mm), mean outer pedicle width was 5.9 mm (SD 1.0 mm) and mean pedicle screw trajectory was 29.4 degrees (SD 3.6 degrees). Most (91.0%) of the pedicles had an outer diameter ≥4.5 mm.ConclusionsThe mean lateral mass screw length was longer when compared with other similar studies, while the mean outer pedicle width was narrower. Nearly 10% of the pedicles were unable to accommodate 3.5 mm screws. These findings favor the use of lateral mass screws to provide a safe and stable fixation for C7 vertebrae in Southern Chinese patients, while the final choice of fixation method should only be confirmed after careful preoperative planning with CT scan.

Comparison of Three Different Options for C7 Posterior Vertebral Anchor in the Indian Population—Lateral Mass, Pedicle, and Lamina: A Computed Tomography-Based Morphometric Analysis

“…The C7 vertebra is a transitional vertebra, and its anatomy is unique compared with the other subaxial vertebrae [ 2 , 3 ]. However, fixation at C7 is an important part of any construct spanning the cervicothoracic junction [ 7 ].…”

“…Careful preoperative planning with appropriate investigational modalities is of utmost importance before C7 fixation because of the peculiar, variable anatomy of lateral masses and pedicles at C7 and its inconsistent relationship to the vertebral artery [ 9 ]. However, understanding the general anatomic profile of C7 vertebral elements for any demographic patient population also provides us with the basic knowledge in these situations [ 2 ]. Currently, no studies have reported the morphometric analysis of C7 in the Indian population.…”

“…However, a good C7 lateral mass screw can preclude the need for extending cervical fusion to the T1 level [ 12 ]. It can also help the surgeon align the C7 screw well in relation to the C6 lateral mass screw compared with a C7 pedicle screw, which may require skipping a screw at the C6 level [ 2 , 3 ]. CT scans showed that unicortical lateral mass screws (using Magerl technique) longer than 10 mm and 12 mm could be safely accommodated in 92% and 48% of Indian patients, respectively.…”

“…Compared with the other six vertebrae, C7 is unique because of its peculiar anatomy of pedicles, laminae, and foramen transversarium; junctional location; resemblance to thoracic vertebrae; and inconsistent relationship to the vertebral artery [ 2 ]. Nevertheless, the inevitability of securing a stable anchor at the C7 level cannot be understated in cervicothoracic fusions; the current options of screw fixation at C7 include pedicles, laminae, and lateral masses [ 3 ].…”

“…Nevertheless, the inevitability of securing a stable anchor at the C7 level cannot be understated in cervicothoracic fusions; the current options of screw fixation at C7 include pedicles, laminae, and lateral masses [ 3 ]. Various reports have discussed the advantages and disadvantages of each of these options in the literature, including the preference for different fixation modalities based on the demographic profile of the patient population [ 2 - 4 ]. Reports comparing these three C7 stabilization modalities in the Indian population are currently not available.…”