Background: The three-dimensional vault geometry beneath the glenoid face reduces to a narrow width in many individuals, creating a risk of perforation of the glenoid component pegs or keel in total shoulder arthroplasty. The purpose of this study was to introduce the concept of a centerline of the glenoid vault determined by computed optimization and to compare this centerline geometry against two existing surgical methods for orienting the glenoid component. Methods: Thirty-four subject-specific computer models of three-dimensional scapular geometry were created from computed tomography scans. The glenoid vault centerline was calculated by slicing the vault into a series of cross sections, determining the center of each section, and fitting a centerline with use of optimization. Vault centerline orientations were compared with the drill-line orientations determined by two surgical techniques, the face plane technique, which drills perpendicular to the glenoid face, and the neutralization technique, which drills parallel to the scapular body resulting in 0° of glenoid version. Distances between the drill lines and the vault wall, throughout the vault depth, were also calculated. Results: The vault centerline intersected the articular surface of the glenoid at an intersubject average (and standard deviation) of 1.1 ± 0.8 mm posterior to the glenoid face center point. In comparison with the neutralization direction, the centerline was oriented an average of 9.4° ± 5.1° posteriorly and the face plane perpendicular direction was oriented an average of 7.3° ± 4.0° posteriorly. Minimum distances between the centerline and the vault wall averaged 5.1 mm (minimum, 2.6 mm), whereas they averaged 4.4 mm (minimum, 1.0 to 1.4 mm) for the center peg drill lines of both surgical techniques. Conclusions: The normal glenoid vault centerline is directed from lateral-posterior to medial-anterior, and it crosses, on the average, close to the glenoid face center. The neutralization direction, on the average, anteverts the glenoid relative to the vault centerline and the face plane perpendicular. Relationships between these directions vary across the subjects. Clinical Relevance: The vault centerline represents optimal containment of the glenoid central peg within the vault. This study provides an understanding of the location of this centerline relative to scapular landmarks and relative to the drill directions from two existing surgical techniques.
All Science Journal Classification (ASJC) codes
- Orthopedics and Sports Medicine