抄録
The glenoid bare spot commonly is observed in the adult shoulder. Carter et al. proposed that cartilage thickness was affected by normal homeostatic loads. The purpose of this study was to measure glenohumeral translation during shoulder abduction in order to explore development of the glenoid bare spot. 10 healthy shoulders (average 31.1 years old) were studied. 3D models of the scapula and humerus were created from CT scans. Motions were recorded with fluoroscopy during active abduction in neutral rotation for unloaded and a 3kg loaded trial. 3D motions were determined using model-based 3D-to-2D registration. Humeral translation was referenced in the superior/inferior direction to the assumed location of the bare spot (center of the circle described by the bony margins of the inferior glenoid). The bare spot location averaged 4.3mm inferior to the superior/inferior midpoint of the glenoid. Glenohumeral contact was 2.6 and 3.1mm superior to the bare spot for unloaded and loaded conditions with the arm at the side. The humeral head moved upward gradually with abduction to 4mm above the bare spot above 70° abduction (p>0.05, 0 vs 3kg). The glenoid surface stabilizes humeral head translation. Carter et al. suggested that cartilage grew thickest with high mechanical demands (compression and sliding) and thinner where demands were low. Humeral translation away from the bare spot with abduction suggests that lower loads were experienced when the humeral head was near the bare spot and larger loads were experienced with humeral translation away from the bare spot. These kinematic observations were consistent with Carter's framework for cartilage growth and provided a plausible explanation for the development of the glenoid bare spot.
