Morphometric Study of C1 Pedicle and Feasibility Evaluation of C1 Pedicle Screw Placement with a Novel Clinically Relevant Radiological Classification in an Indian Population

STUDY DESIGN: A retrospective computed tomography (CT)-based morphometric study of 84 C1pedicles in an Indian population focusing on critical morphometric dimensions vis-a-vis C1 pedicle screw placement. PURPOSE: To determine the feasibility of C1 pedicle screw placement in an Indian population and propose a novel classification system for the same. OVERVIEW OF LITERATURE: At present, C1 pedicle screws are rarely used, and very few studies have focused on the feasibility of pedicle screw placement in terms of racial, gender, and ethnic variations in anatomical structures. There are no CT-based data on C1 pedicles that assess the feasibility of pedicle screw placement in the Indian population. METHODS: We measured C1 pedicle diameter on CT coronal scan images of 42 adult patients. Extramedullary height (EMH) and intramedullary height (IMH) were measured. We examined the differences between the right and left atlas pedicles and compared measures between males and females. These data were analyzed using significance tests. Based on the results, we propose a novel classification system, which we believe will help in determining the feasibility of C1 pedicle screw placement. RESULTS: Forty-two adult patients (84 pedicles) were examined. Average EMH and IMH were 4.48±0.91 and 0.86±0.77, respectively. Approximately, 32% of the C1 pedicles had bone thicknesses of <4 mm, 49% had IMH of <1 mm, and 38% had no pedicles. The average thickness in women was 4.21±0.93 mm, which was significantly thinner than that in men (4.73±0.81 mm, p=0.004). Right and left pedicles were not significantly different. CONCLUSIONS: Our data indicate that approximately one-third of the Indian population may not be suitable candidates for C1 pedicle screw placement. Caution should be exercised while placing type 1B and type 2 pedicles based on our proposed classification system.