Normal glenoid rim anatomy and the reliability of shoulder instability measurements based on intrasite correlation.

Purpose: To evaluate the glenoid shape and to evaluate if the contralateral glenoid can be used as size reference.

Methods: Two independent investigators prospectively analysed shoulder computer-tomographies of 90 patients. The glenoids were positioned in a true "en face" view and evaluated for size and shape. The intraindividual correlation of these parameters between left and right side were assessed.

Results: In the 90 computer tomographically evaluated shoulder pairs a significant intraindividual correlation of size and shape was seen (P < 0.001). The intraindividual difference in glenoid surface area averaged 1.8% of the total glenoid surface. The shape of the inferior hemisphere correlated 100%. We found all the inferior glenoids to be circular.

Conclusion: Our study clearly shows that the inferior glenoid in healthy individuals has the shape of a circle. The high side-to-side correlation of the glenoid surface area can be applied when measuring bony defects by evaluation of the contralateral side.