Morphological findings of the sub-axial cervical spine among different populations and its implication on cervical screw placement: a systematic review and metanalysis

Introduction: Cervical pedicle screws (CPS) were first introduced by Abumi in 1994. They were used in traumatic cases with good rates of neurological recovery and correction of deformities reported by the authors. The use and indications were extrapolated for other cases a few years later.
The anatomy of the sub-axial cervical vertebrae can present significant variations and offer limitations during surgical instrumentation. In this systematic review, the authors evaluate the main measures for the sub-axial spine pedicles among different populations from distinct continents.

Methods: A comprehensive search was conducted using PubMed, Google Scholar, and EMBASE. The authors included anatomical studies with computed tomography (CT) measurements, cohort studies, and case series. Participants included adult populations from diverse countries on different continents. Four key measurements were analyzed in the studies: Pedicle Width (PW), Pedicle Height (PH), Main Maximal Screw Length (MSL), and Pedicle Transverse Angle (PTA).
The authors grouped the studies based on geographic location and ethnic characteristics.

Results: The cervical spine Computed Tomography (CT) measurements of more than 4153 patients/cadavers from different countries and locations grouped by geographic/ethnicity were obtained. A total of 48 studies using CT measurements were included.
A total of 18.702 measurements of PW were analyzed across various studies. Significant differences were observed among the groups for the C3, C5, C6, and C7 vertebrae, with p-values of 0.02, 0.03, 0.01, and 0.02, respectively. The main PW progressively increased from C3 to C7. The PW was largest in Subgroup 1 (Japan, China, and South Korea), followed by the Southeastern Asia Subgroup, and it was significantly smaller in the Southern Asia group.
PTA was reported in 40 studies. A total of 16.227 measurements were analyzed from C3 to C7. The test for subgroup differences was significant only for C7.
No significant differences were found in PH and MSL among the groups.

Conclusion : Understanding the pedicle anatomy and orientation in different populations may enrich the safety of the CPS technique and help select the best candidates for it. Our findings can explain the reason CPS is more diffusely used in the Asian population.