Anterior Shoulder Instability

Shoulder instability can be divided as unidirectional and multidirectional with an acronyms TUBS and AMBRI as mnemonics.

TUBS: Traumatic unilateral dislocations with a Bankart lesion often necessitate surgery (Anterior Shoulder Instability).

AMBRI: Atraumatic multidirectional shoulder instability often responds to rehabilitation, and sometimes an inferior capsular shift or plication is required.

Anterior Shoulder Instability is a pathologic state characterized by abnormal translation of the humeral head on or over the glenoid, leading to frank anterior dislocation, functional impairments, or pain. It is the most common type of shoulder instability.

Related Anatomy

Glenohumeral joint has dynamic and static constraints.

Dynamic constraints include:

• Rotator cuff muscles.
• Long head of biceps tendon.

Static Constraints include:

1. Bony anatomy.
2. Joint capsule.
3. Joint labrum.
4. Negative intraarticular pressure
5. Glenohumeral ligaments:
   • Superior glenohumeral ligament (SGHL).
   • Middle glenohumeral ligament (MGHL).
   • Inferior glenohumeral ligament (IGHL).
   • Coracohumeral ligament (CHL).

See Also: Rotator Cuff of the Shoulder

Anterior Shoulder Instability AMBRI VS TUBS

	Shoulder Instability	Traumatic Anterior Dislocation
History	Feeling of shoulder slippage with pain Feeling of insecurity when doing specific activities No history of injury	Arm elevated and laterally rotated relative to body Feeling of insecurity when in specific position (of dislocation) Recurrent episodes of apprehension
Observation	Normal	Normal (if reduced; if not, loss of rounding of deltoid caused by anterior dislocation)
Active movement	Normal ROM May be abnormal or painful at activity speed	Apprehension and decreased ROM in abduction and lateral rotation
Passive movement	Normal ROM Pain at extreme of ROM possible	Muscle guarding and decreased ROM in apprehension position
Resisted isometric movement	Normal in test position May be weak in provocative position	Pain into abduction and lateral rotation
Special tests	Load and shift test positive	Apprehension positive Augmentation positive Relocation positive
Reflexes and cutaneous distribution	Normal reflexes and sensation	Reflexes normal Sensation normal, unless axillary or musculocutaneous nerve is injured
Palpation	Normal	Anterior shoulder is tender
Diagnostic imaging	Normal	Normal, unless still dislocated; defect possible

Pathoanatomy

The pathoanatomy of the anterior shoulder instability can be capsulo-labral, osseous, or both.

Capsulo-labral pathoanatomy

Bankart lesion:

Bankart lesion is an avulsion of the anterior-inferior capsulo-labral complex with extension into the scapular periosteum and rupture of the periosteal tissue.

The weakest region of the capsule is generally anteriorly and inferiorly in the interval between the lower border of the subscapularis and the long head of the triceps muscle. It’s found to occur in 90% of patients with recurrent dislocation of shoulder.

HAGL:

Humeral avulsion of the glenohumeral ligaments (HAGL) lesion is an avulsion of glenohumeral ligaments from their humeral-sided attachment.

ALPSA:

ALPSA stands for Anterior labro-ligamentous periosteal sleeve avulsion lesion, it’s an avulsion of anterior-inferior gleno-labral complex with stripping of medial scapular neck periosteum but preservation of a medial hinge, loose fragment subsequently scars medially down scapular neck.

Perthes lesion:

It’s an avulsion of anterior-inferior gleno-labral complex with preservation of medial scapular neck periosteum.

See Also: What is SLAP Lesion?

Osseous pathoanatomy

Bony Bankart lesion:

Osseous avulsion fracture of anterior-inferior glenolabral complex. It is usually present in 40% in the first-time dislocations, and in 85% in the recurrent dislocations. The bone fragment in a bony Bankart lesion undergoes rapid absorption within 1 year of the primary injury.

Hill-Sachs lesion:

It’s a bone injury typically occurs to the posterior superior humeral head with Anterior Shoulder Instability.

A Hill-Sachs lesion can be found in:

• 40% of patients with recurrent subluxations,
• 90% of first-time dislocations,
• Almost 100% of recurrent anterior shoulder instability.

The most important factor in predicting anterior shoulder instability recurrence is the age at first dislocation:

1. Almost 100% in persons with open growth plates.
2. 70% to 95% of persons younger than 20 years.
3. 60% to 80% in persons aged 20 to 30 years.
4. 15% to 20% in persons older than 40 years.

Associated Injuries in Anterior Shoulder Instability

Up to 40% of patients with anterior shoulder instability have an associated injury that could include:

• Greater tuberosity fracture: it is associated with anterior dislocation in patients > 50 years of age.
• Lesser tuberosity fracture: it is associated with posterior dislocations.
• Axillary nerve injury: occurs in 5% of patients, it’s most often a transient neurapraxia.
• Rotator cuff tears:
  • Occurs in 30% of patients > 40 years of age.
  • Occurs in 80% of patients > 60 years of age.

Clinical Evaluation

There is a history of trauma prior to anterior shoulder instability. The patient feels the instability in addition to shoulder pain.

Shoulder examination to evaluate anterior shoulder instability includes:

• The apprehension and relocation test.
• Sulcus sign.
• The anterior load and shift test can be used to classify degrees of anterior shoulder instability based on distance of humeral head translation:
  • 1+: 0 to 1 cm of translation to before glenoid rim.
  • 2+: 1 to 2 cm of translation to glenoid rim.
  • 3+: more than 2 cm translation or over glenoid rim.

Imaging Evaluation

Radiographic imaging includes the following views:

Views	Conditions
True Anterior-posterior view	Shoulder dislocation
Axillary view	Shoulder dislocation direction.
West Point view	Bony Bankart lesion seen with instability
Apical oblique (Garth) view	Bony Bankart lesion – Hill-Sachs defect
Stryker notch	Hill-Sachs impression fracture
Anteroposterior internal rotation	Hill-Sachs defect

CT scan:

Accurately identify of glenoid bone loss. Three-dimensional reconstructions are more reliable for measurement purposes.

MRI:

MRI is helpful in detecting capsular or labral damage and detecting humeral avulsion of the inferior glenohumeral ligament (HAGL) lesions, which require repair. An ABduction-External Rotation (ABER) view further increases sensitivity.

Anterior Shoulder Instability Treatment

Non-operative treatment:

Reduction, sling immobilization and follow up physical therapy is used in acute dislocations.

Reduction techniques include:

• Traction-countertraction is most commonly employed.
• The Milch maneuver (slow abduction and external rotation) has some evidence suggesting increased success rates.

Meta-analyses suggest no difference between immobilization in internal or external immobilization. Also, immobilization period for more than 1 week did not improve recurrence rates.

Physical therapy for shoulder instability should begin after the immobilization period. It’s aimed to strengthen the dynamic stabilizers of the shoulder (rotator cuff and periscapular musculature).

Operative treatment:

Open surgery include:

Bankart repair:

In Bankart repair, reattach labrum and IGHL to anterior glenoid, often combined with capsular shift. Gold standard when glenoid bone loss < 20 %. It’s ocasionally preferred in contact athletes.

Latarjet coracoid transfer (Bristow Procedures):

The distal 2 cm of coracoid is transferred to anterior glenoid neck with two-screw fixation and reattachment of Coracoacromial (AC) ligament to anterior glenohumeral capsule.

It’s the primary procedure in patients with > 25% glenoid bone loss.

Anterior capsulo-labral reconstruction:

Glenoid-based capsular shift. It’s designed for overhead athletes; may be performed as adjunct to Bankart.

Arthroscopic surgery include:

Bankart repair: Reattach labrum and IGHL to anterior glenoid with use of suture anchors. It’s the most common operation for anterior instability.

Coracoid transfer (hybrid Bristow-Latarjet): Distal 2 cm of coracoid transferred to anterior glenoid neck. The coracoacromial (CA) ligament is preserved.

Supplementary Procedures:

Remplissage: Arthroscopic infraspinatus and posterior capsule fixation into Hill-Sachs lesion using suture anchors. It’s performed in moderate to large Hill-Sachs lesions. Medialized sutures limit external rotation

Humeral head allograft: Osteoarticular allograft inserted into HillSachs lesion. It’s performed in large Hill-Sachs lesions.

Partial humeral head resurfacing: Cobalt-chrome component inserted into Hill-Sachs lesions. Typically performed with Latarjet procedure. Alternative to humeral head allograft

Rotator interval closure: Open or arthroscopic superior capsular shift of middle glenohumeral ligament (MGHL) to superior glenohumeral ligament (SGHL). This procedure limits external rotation.

Revision Procedures:

1. Allograft bone grafting of glenoid:
   • Iliac crest or distal tibia secured to anterior glenoid neck with screws.
   • Performed in severe glenoid bone loss.
2. Humeral hemiarthroplasty:
   • Humeral component retroverted 50 degrees to achieve stability.
   • Indicated in older patients with > 45% of humeral head bone loss and glenohumeral arthritis.
3. Rotational humeral osteotomy:
   • Subcapital external rotational osteotomy to rotate Hill-Sachs lesion outside glenoid track.
   • Performed in severe Hill-Sachs lesions.
4. Allograft anterior capsulolabral reconstruction:
   • Allograft tendon used to reconstruct anterior band of inferior glenohumeral ligament (IGHL) and middle glenohumeral ligament (MGHL).
   • Performed in severe capsular deficiency due to systemic soft tissue disorders, electrothermal capsular necrosis, or repeated surgical procedures without bone loss.

Historical Procedures:

Bristow coracoid transfer: Distal 1 cm of coracoid transferred and secured with 1 screw. The coracoacromial CA ligament is preserved. It has higher rate of recurrence.

Caspari technique: Arthroscopic transglenoid suture repair of glenoid labrum. It has higher rate of recurrence and injury to suprascapular nerve.

Staple capsulorrhaphy: Reattachment of capsule to glenoid neck with a staple. High rate of pain, recurrence, reduced internal and external rotation and staple migration.

Putti-Platt: Subscapularis advancement and shortening. Reduced external rotation. posterior glenoid arthritis

Magnusson-Stack: Subscapularis transfer to greater tuberosity. Reduced external rotation.

Thermal capsular shrinkage: Use of thermal energy to reduce capsular volume. Higher rate of recurrence. Can result in capsular deficiency and chondral damage.

Instability Severity Index Score

Instability Severity Index Score is a simple preoperative score to select patients for arthroscopic or open shoulder stabilization. It’s Based on a Preoperative Questionnaire, Clinical Examination, and Radiographs.

If score < 6 points: An acceptable recurrence risk of 10% with arthroscopic stabilization.

If score > 6 points: A score of > 6 points has an unacceptable recurrence risk of 70% and should be advised to undergo open surgery (i.e. Laterjet procedure).

Prognostic Factors	Description	Points
Age	– < 20 years – > 20 years	2 0
Degree of sport participation	– Competitive – Recreational or none	2 0
Type of sport	– Contact or forced overhead. – Other	1 0
Shoulder hyperlaxity	– Shoulder hyperlaxity (anterior or inferior). – Normal laxity	1 0
Hill-Sachs lesion on AP radiograph	– Visible in external rotation – Not visible in external rotation	2 0
Glenoid loss of contour on AP radiographs	– Loss of contour – No lesion	2 0
Total Points		10

References & More

1. Campbel’s Operative Orthopaedics 12th edition Book.
2. Millers Review of Orthopaedics -7th Edition Book.
3. Whelan DB, Kletke SN, Schemitsch G, Chahal J. Immobilization in External Rotation Versus Internal Rotation After Primary Anterior Shoulder Dislocation: A Meta-analysis of Randomized Controlled Trials. Am J Sports Med. 2016 Feb;44(2):521-32. doi: 10.1177/0363546515585119. Epub 2015 Jun 26. PMID: 26116355.
4. Smith BI, Bliven KC, Morway GR, Hurbanek JG. Management of primary anterior shoulder dislocations using immobilization. J Athl Train. 2015 May;50(5):550-2. doi: 10.4085/1062-6050-50.1.08. Epub 2015 Mar 5. PMID: 25742466; PMCID: PMC4560007.