Location of the optimized centerline of the glenoid vault: a comparison of two operative techniques with use of three-dimensional computer modeling.

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 degrees 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 degrees +/- 5.1 degrees posteriorly and the face plane perpendicular direction was oriented an average of 7.3 degrees +/- 4.0 degrees 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.