12 Anterior Shoulder Instability



Alexander E. Loeb and Uma Srikumaran


Summary


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




  1. Laxity: Physiologic translation of the humeral head on glenoid



  2. Instability: Pathologic translation of the humeral head on the glenoid causing pain or dysfunction



  3. Anteroinferior stability most common



  4. Static and dynamic stabilizers responsible for stability.



II. Anatomy (▶Fig. 12.1)




  1. Glenohumeral joint resembles a ball on tee:




    1. Articulating surface of humeral head is 3× larger than the surface of the glenoid.



  2. Glenoid:




    1. Glenoid is pear-shaped, broader inferiorly than superiorly



    2. Provides 50% of the depth of the glenohumeral joint:




      1. Labrum provides the other 50% of depth.



    3. Slightly concave:




      1. Cartilage thicker at the periphery, bare spot centrally.



    4. Retroversion and inclination varies widely, approximately 0–5 degrees retroverted, 5 degrees inclined.



  3. Humerus:




    1. Greater and lesser tuberosities are sites of rotator cuff insertion



    2. Retroverted 30 degrees from the transepicondylar axis, 130 degrees neck–shaft angle.



  4. Labrum:




    1. Provides 50% of the depth of glenohumeral joint



    2. Increases glenohumeral contact



    3. Provides conforming seal:




      1. Negative intra-articular pressure.

        Fig. 12.1 Shoulder anatomy. (Source: Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)


  5. Ligaments:




    1. Inferior glenohumeral ligament:




      1. Anterior band is primary restraint to anterior translation with the shoulder in 90 degrees abduction and external rotation.



    2. Superior glenohumeral ligament:




      1. Primary restraint to inferior translation with the arm in adduction.



    3. Middle glenohumeral ligament:




      1. Primary restraint to anterior translation with the arm in adduction as well as 45 degrees abduction and external rotation.



  6. Musculature:




    1. Provide dynamic stabilization by compression into the glenoid concavity:




      1. Rotator cuff provides dynamic stabilization against anteroinferior translation:




        • i. Supraspinatus



        • ii. Infraspinatus



        • iii. Teres minor



        • iv. Subscapularis.



      2. Other contributors: Teres major, latissimus dorsi, long head of biceps brachii, pectoralis major, and deltoid.



III. Pathogenesis




  1. Instability can be traumatic, acquired, or atraumatic:




    1. Trauma involves direct impact or anterior directed force with the arm abducted and externally rotated:




      1. Typically young, athletic population



      2. Male to female ratio in this population is 9:1.



    2. Acquired instability through multiple microtrauma events, for example, in overhead athletes



    3. Atraumatic, typically involves congenital anatomic deformities, connective tissue disorders, and multidirectional instability.



  2. Bankart lesion:




    1. Detachment of the anteroinferior labrum from the glenoid at its inferior glenohumeral ligament attachment



    2. Pathognomonic for anteroinferior instability



    3. Present in 90% of glenohumeral dislocations.

      Fig. 12.2 Anteroposterior radiograph with bony Bankart lesion.


  3. Bony Bankart lesion (▶ Fig. 12.2 ):




    1. Anteroinferior glenoid avulsion/shear fracture in association with above findings



    2. Present in half of recurrent dislocators



    3. Should be addressed at time of surgery or will remain at risk for instability



    4. Bony defect >20% is highly unstable, requires fixation/Bristow/Latarjet.



  4. Humeral avulsion of glenohumeral ligament (HAGL) lesion:




    1. Results from avulsion of inferior glenohumeral ligament from its insertion on the humerus.



  5. Glenoid labral articular defect (GLAD) lesion:




    1. Articular cartilage sheared off with labrum.



  6. Anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion (▶ Fig. 12.3 ):




    1. Labrum is avulsed with anterior glenoid neck periosteum



    2. At risk for scarring down more medially, resulting in recurrent instability.



  7. Hill-Sachs lesion (▶ Fig. 12.4 ):




    1. Impaction fracture in the posterosuperior humeral head



    2. Head impaction results from contact with glenoid rim



    3. Pathognomonic for anterior dislocation



    4. Present in 80% of traumatic dislocations



    5. May engage the glenoid and cause catching, recurrent dislocation or subluxation, or irreducibility.

      Fig. 12.3 Magnetic resonance imaging (MRI) arthrogram of anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion.


  8. Laxity:




    1. Recurrent subluxations and dislocations lead to attenuation and lengthening of the middle and inferior glenohumeral ligaments



    2. Less static stabilization results in more instability events, a vicious cycle



    3. Teenagers have 90% chance of recurrent dislocation.



  9. Other injuries:




    1. Greater tuberosity fractures associated with dislocations in the elderly



    2. Axillary nerve transient neurapraxia in 5% of traumatic dislocations



    3. Rotator cuff tears in 30% of patients younger than 40 years, more common in elderly.

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Feb 6, 2021 | Posted by in ORTHOPEDIC | Comments Off on 12 Anterior Shoulder Instability
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