An anterior shoulder dislocation commonly presents as an acute shoulder injury from direct trauma. Young, active males and patients with glenoid bone loss are at highest risk of recurrent dislocation. First-time dislocators without significant risk factors can be managed with reduction, immobilization, and physical therapy, while high-risk patients and recurrent dislocators may be treated with surgery.
12 Anterior Shoulder Instability
I. General overview
Laxity: Physiologic translation of the humeral head on glenoid
Instability: Pathologic translation of the humeral head on the glenoid causing pain or dysfunction
Anteroinferior stability most common
Static and dynamic stabilizers responsible for stability.
II. Anatomy (▶Fig. 12.1)
Glenohumeral joint resembles a ball on tee:
Articulating surface of humeral head is 3× larger than the surface of the glenoid.
Glenoid is pear-shaped, broader inferiorly than superiorly
Provides 50% of the depth of the glenohumeral joint:
Labrum provides the other 50% of depth.
Cartilage thicker at the periphery, bare spot centrally.
Retroversion and inclination varies widely, approximately 0–5 degrees retroverted, 5 degrees inclined.
Greater and lesser tuberosities are sites of rotator cuff insertion
Retroverted 30 degrees from the transepicondylar axis, 130 degrees neck–shaft angle.
Provides 50% of the depth of glenohumeral joint
Increases glenohumeral contact
Provides conforming seal:
Inferior glenohumeral ligament:
Anterior band is primary restraint to anterior translation with the shoulder in 90 degrees abduction and external rotation.
Superior glenohumeral ligament:
Primary restraint to inferior translation with the arm in adduction.
Middle glenohumeral ligament:
Primary restraint to anterior translation with the arm in adduction as well as 45 degrees abduction and external rotation.
Provide dynamic stabilization by compression into the glenoid concavity:
Rotator cuff provides dynamic stabilization against anteroinferior translation:
iii. Teres minor
Other contributors: Teres major, latissimus dorsi, long head of biceps brachii, pectoralis major, and deltoid.
Instability can be traumatic, acquired, or atraumatic:
Trauma involves direct impact or anterior directed force with the arm abducted and externally rotated:
Typically young, athletic population
Male to female ratio in this population is 9:1.
Acquired instability through multiple microtrauma events, for example, in overhead athletes
Atraumatic, typically involves congenital anatomic deformities, connective tissue disorders, and multidirectional instability.
Detachment of the anteroinferior labrum from the glenoid at its inferior glenohumeral ligament attachment
Pathognomonic for anteroinferior instability
Present in 90% of glenohumeral dislocations.
Bony Bankart lesion (▶ Fig. 12.2 ):
Anteroinferior glenoid avulsion/shear fracture in association with above findings
Present in half of recurrent dislocators
Should be addressed at time of surgery or will remain at risk for instability
Bony defect >20% is highly unstable, requires fixation/Bristow/Latarjet.
Humeral avulsion of glenohumeral ligament (HAGL) lesion:
Results from avulsion of inferior glenohumeral ligament from its insertion on the humerus.
Glenoid labral articular defect (GLAD) lesion:
Articular cartilage sheared off with labrum.
Anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion (▶ Fig. 12.3 ):
Labrum is avulsed with anterior glenoid neck periosteum
At risk for scarring down more medially, resulting in recurrent instability.
Hill-Sachs lesion (▶ Fig. 12.4 ):
Impaction fracture in the posterosuperior humeral head
Head impaction results from contact with glenoid rim
Pathognomonic for anterior dislocation
Present in 80% of traumatic dislocations
May engage the glenoid and cause catching, recurrent dislocation or subluxation, or irreducibility.
Recurrent subluxations and dislocations lead to attenuation and lengthening of the middle and inferior glenohumeral ligaments
Less static stabilization results in more instability events, a vicious cycle
Teenagers have 90% chance of recurrent dislocation.
Greater tuberosity fractures associated with dislocations in the elderly
Axillary nerve transient neurapraxia in 5% of traumatic dislocations
Rotator cuff tears in 30% of patients younger than 40 years, more common in elderly.