Turkel and colleagues examined how much the subscapularis and each glenohumeral ligament limit external rotation and prevent anterior dislocation at 0°, 45° and 90° of abduction.
Cadaver study: dissection of 36 embalmed shoulders, plus radiographic marker and cutting studies in 10 unembalmed shoulders.
Methods
Model
36 embalmed cadaver shoulders for dissection
10 unembalmed cadaver shoulders for radiographic and cutting studies
Constructs
Group I (5 shoulders): subscapularis cut first, then the superior, middle and inferior glenohumeral ligaments
Group II (5 shoulders): the same structures cut in reverse order, inferior glenohumeral ligament first
Loading
External rotation at 0°, 45° and 90° of abduction
Outcome measures
Added external rotation after each cut
Frank anterior dislocation
Radiopaque marker position, tightness and laxity
Key Findings
With every other structure left intact, cutting the inferior glenohumeral ligament through its superior band dislocated all 5 shoulders at 45° and 90°.
None of the 5 Group II shoulders dislocated at 0° after the same inferior ligament cuts, because the anterior capsule and subscapularis gave primary stability in that position.
In Group I, once the posterior axillary pouch was also divided, external rotation dislocated all 5 shoulders at every abduction angle.
The authors suggested these findings may allow the defect in recurrent dislocation to be located more precisely and repaired more selectively.
Board pearl
The superior band of the inferior glenohumeral ligament is its thickened anterosuperior edge, identified in 36 of 46 specimens.
Authors' conclusion
The conclusions from these experiments were that at zero degrees of abduction, the subscapularis muscle stabilizes the joint to a large extent; at 45 degrees of abduction, the subscapularis, middle glenohumeral ligament, and anterosuperior fibers of the inferior glenohumeral ligament provide the stability; and as the shoulder approaches 90 degrees of abduction, the inferior glenohumeral ligament prevents dislocation during external rotation.
Turkel and colleagues examined how much the subscapularis and each glenohumeral ligament limit external rotation and prevent anterior dislocation at 0°, 45° and 90° of abduction.
Cadaver study: dissection of 36 embalmed shoulders, plus radiographic marker and cutting studies in 10 unembalmed shoulders.
Methods
Model
36 embalmed cadaver shoulders for dissection
10 unembalmed cadaver shoulders for radiographic and cutting studies
Constructs
Group I (5 shoulders): subscapularis cut first, then the superior, middle and inferior glenohumeral ligaments
Group II (5 shoulders): the same structures cut in reverse order, inferior glenohumeral ligament first
Loading
External rotation at 0°, 45° and 90° of abduction
Outcome measures
Added external rotation after each cut
Frank anterior dislocation
Radiopaque marker position, tightness and laxity
Key Findings
With every other structure left intact, cutting the inferior glenohumeral ligament through its superior band dislocated all 5 shoulders at 45° and 90°.
None of the 5 Group II shoulders dislocated at 0° after the same inferior ligament cuts, because the anterior capsule and subscapularis gave primary stability in that position.
In Group I, once the posterior axillary pouch was also divided, external rotation dislocated all 5 shoulders at every abduction angle.
The authors suggested these findings may allow the defect in recurrent dislocation to be located more precisely and repaired more selectively.
Board pearl
The superior band of the inferior glenohumeral ligament is its thickened anterosuperior edge, identified in 36 of 46 specimens.
Authors' conclusion
The conclusions from these experiments were that at zero degrees of abduction, the subscapularis muscle stabilizes the joint to a large extent; at 45 degrees of abduction, the subscapularis, middle glenohumeral ligament, and anterosuperior fibers of the inferior glenohumeral ligament provide the stability; and as the shoulder approaches 90 degrees of abduction, the inferior glenohumeral ligament prevents dislocation during external rotation.