Determination of a reference system for the three-dimensional study of the glenohumeral relationship.

OBJECTIVE: Knowledge of the normal and pathological three-dimensional glenohumeral relationship is imperative when planning and performing a total shoulder arthroplasty. There is, however, no consensus on which references should be used when studying this relationship. The purpose of the present study was to define the most suitable glenoid plane with normally distributed parameters, narrowest variability, and best reproducibility.
MATERIALS AND METHODS: Three-dimensional reconstruction CT scans were performed on 152 healthy shoulders. Four glenoid planes, each determined by three surgically accessible bony reference points, were determined. Two planes were triangular, with the same base defined by the most anterior and posterior point of the glenoid. The most inferior and the most superior point of the glenoid, respectively, define the top of Saller's inferior plane and the Saller's superior plane. The two other planes are formed by best-fitting circles. The circular max plane is defined by the superior tubercle, and two points at the distal third of the glenoid. The circular inferior plane is defined by three points at the rim of the inferior quadrants of the glenoid.
RESULTS: The parameters of all four planes behave normally. The humeral center of rotation is identically positioned for both the circular max and circular inferior plane (X = 91.71°/X = 91.66° p = 0.907 and Y = 90.83°/Y = 91.7° p = 0.054, respectively) and different for the Saller's inferior and Saller's superior plane (p ≤ 0.001). The circular inferior plane has the lowest variability to the coronal scapular plane (p < 0.001).
CONCLUSIONS: This study provides arguments to use the circular inferior glenoid plane as preferred reference plane of the glenoid.