Cadaveric study of 11 fresh-frozen shoulders testing how scapular inclination affects inferior glenohumeral stability. Investigators varied scapular tilt during simulated sulcus and abduction inferior stability tests. The question: does the position of the scapula itself, not just the humerus, govern inferior stability?
When you assess a patient for inferior or multidirectional instability, remember that stability is not just about the humerus and glenoid. The position of the scapula on the thorax matters.
This study gives the biomechanical basis for the bony cam effect: as the head drops inferiorly it slides laterally on the glenoid slope, tightening the superior capsule and stopping further descent. Increasing scapular inclination amplifies that tightening.
This explains why pectoralis major transfer to the inferior scapula, which increases scapular inclination, helps patients with inferior instability who present with a poorly inclined scapula during elevation.
The concept of a patient-specific critical angle is the practical takeaway. When planning an inclination-altering procedure, consider both the severity of instability and where that individual's critical angle sits.
Cadaveric study of 11 fresh-frozen shoulders testing how scapular inclination affects inferior glenohumeral stability. Investigators varied scapular tilt during simulated sulcus and abduction inferior stability tests. The question: does the position of the scapula itself, not just the humerus, govern inferior stability?
When you assess a patient for inferior or multidirectional instability, remember that stability is not just about the humerus and glenoid. The position of the scapula on the thorax matters.
This study gives the biomechanical basis for the bony cam effect: as the head drops inferiorly it slides laterally on the glenoid slope, tightening the superior capsule and stopping further descent. Increasing scapular inclination amplifies that tightening.
This explains why pectoralis major transfer to the inferior scapula, which increases scapular inclination, helps patients with inferior instability who present with a poorly inclined scapula during elevation.
The concept of a patient-specific critical angle is the practical takeaway. When planning an inclination-altering procedure, consider both the severity of instability and where that individual's critical angle sits.