Anterior Shoulder Instability

Definition
• Stabilizing Factors
• Tests - LAXITY TESTS, INSTABILITY TESTS
• Imaging – Radiographs, CT, MRI, MR arthrography
• Classification, Matsen’s TUBS & AMBRII
• Surgical options: Anatomic Reconstruction (Bankart Repair and Montgomery and Jobe modification);
• Non-Anatomic Reconstruction (Bristow Latarjet Procedure, Putti- Platt Procedure, Magnuson Stack Procedure, Neer’s, O’Brien)
• Current Recommendations
• Clinical Scenarios

Definition of Shoulder Instability:- Abnormal symptomatic motion of the humeral head relative to the glenoid during active shoulder motion.


Stabilizing Factors:
• The mechanisms providing stability can be categorized as ‘static’ and ‘dynamic’.
• The rotator cuff muscles form the ‘dynamic’ stabilizers whereas the articular anatomy and the capsuloligamentous complex form the ‘static’ stabilizers.
• In all, the glenohumeral joint is stabilized by following key elements:
1. Concavity of the glenoid
2. The muscles that compress the humeral head into the glenoid.
3. The coracoacromial arch
4. The capsuloligamentous restraints
5. Adhesion-cohesion of the articular surfaces
• The above mentioned elements function inter-dependently to keep the humeral head stable in the glenoid cup. Deficiencies or defects in any of these structures or incoordination between the structures can lead to instability.

Factors influencing probability of recurrent dislocation:
1. Age,
2. return to contact/collision sports,
3. bony defect (glenoid /humeral head)
Glenoid Concavity
The glenoid concavity is formed by three components:
1. the osseous glenoid - slightly concave
2. the articular cartilage - thicker at the periphery and thinner in the center making the concavity deeper and
3. the glenoid labrum - further deepens the glenoid concavity by 50%
• The concavity of the glenoid provides stability to the humeral head similar to a ball which sits at the centre of a concave surface.
• The adequacy of the glenoid concavity in different directions can be assessed clinically by the ‘load-and-shift test’.


Muscles that compress the humeral head
• The humeral head is compressed into the glenoid by the muscles of the rotator cuff and other scapulohumeral and thoracohumeral muscles.
Subscapularis - primary anterior compressor
Supraspinatus - primary superior compressor
Infraspinatus – primary posterior compressor (assisted by teres minor)
• The rotator cuff muscles function as head compressors in almost any position of the glenohumeral joint, except the terminal range.
• Other muscles, such as deltoid, long head of the biceps, pectoralis, latissimus, teres major and pectoralis major contribute to humeroglenoid compression in certain other positions. For example, deltoid becomes a strong compressor of the head into the glenoid when the arm is abducted 90°.
• Paralysis, detachment, or dysfunction of any of the rotator cuff muscles results in loss of humeral head compression.


The Glenohumeral Ligaments and Capsule
• During rotation of the arm, the glenohumeral ligaments and capsule tighten and loosen reciprocally, thus limiting translations and rotations in a load-sharing fashion.
• The glenohumeral capsule and its associated ligaments are lax and do not exert a centering effect in mid-range positions (Compare muscular stabilizers). However at the extremes of motion, these structures become important contributors to humeral centering. They prevent humeral rotation beyond the point where the muscles are effective.

Adhesion-Cohesion
• The surfaces of the humeral and glenoid cartilage and the surfaces of the coracoacromial arch and the proximal humeral convexity adhere to each other because of the adhesive and cohesive properties of water molecules giving a smooth glide for the surfaces while simultaneously preventing them from separating.

The Suction Cup Mechanism
• The negative intra-articular pressure in the joint makes the pliable labrum centered by a non-compliant osseous glenoid stick to the humeral head like a suction cup.
• Both the adhesion-cohesion and the suction-cup mechanism are non-energy- consuming.
• Conditions where these mechanisms are lost: 1) fracture of the glenoid lip, 2) when the joint surfaces are not covered with smooth wettable hyaline cartilage eg. Glenohumeral arthritis or following total shoulder replacement, 3) both are also lost when there is joint effusion or hemarthrosis.

Evaluation of Glenohumeral Instability:
Patient History
• Age of 1st dislocation event or instability- Younger the age, higher is the chance of recurrent instability. <20yrs->40yrs 10%,but more tendency to fracture with dislocation
• Onset- Traumatic or Atraumatic
o History of trauma?
o Frank dislocation that required manual reduction or a subjective feeling of instability of the shoulder (subluxation)?
• Position of the arm at the time of instability- To know if the dislocation was anterior or posterior
• Any particular position or movement exaggerating the pain or produces sense of instability?
• The number of discrete instability events and the degree of disability?
• The ability to voluntarily dislocate the joint? Surgical management of instability in this patient population may result in high rates of recurrence.

Physical examination
Physical examination for shoulder instability can be divided into two main groups:
(1) tests for glenohumeral laxity and
(2) tests for glenohumeral instability.
(3) tests for generalized ligamentous laxity

Laxity Tests:
Anterior Drawer Test
• Quantifies the amount of anterior translation.
• Patient lying supine, examiner stands at the ipsilateral side of the affected extremity. The patient’s hand is positioned in the examiner’s axilla. The shoulder is in 80o to 120o of abduction, 0o to 20o of forward flexion, and 0o to 30o of external rotation. The scapula is stabilized with one hand. The other hand grasps the proximal humeral shaft and exerts an anterior force. The amount of translation is quantified.
Posterior Drawer
• Patient in supine position. For left shoulder, the patient’s left wrist and forearm is held with the elbow flexed to 120o. With the shoulder in 80o to 120o of abduction and 60o to 80o of forward flexion and internal rotation, a posterior force is applied on the arm. The amount of posterior translation is assessed by the hand stabilizing the scapula.
Lachman test
Patient supine, extremity in various degrees of abduction and external rotation in the plane of the scapula. Anterior stress is applied to proximal humerus. The amount of translation and the end point are evaluated.
Anterior and Posterior Load and Shift Test
• Supine position with arm in 20o of abduction, 20o of forward flexion and neutral rotation or upright position with arm by the side of torso.
• The examiner grasps upper arm and applies an axial load perpendicular to the articular surface of the glenoid. Anterior or posterior-directed forces are then applied the humeral head and translation relative to the glenoid is measured.
Gage Hyperabduction Test
• It is a measure of laxity of the inferior glenohumeral ligament complex.
• The test is performed with the patient sitting and the examiner standing behind. With one hand stabilizing the scapula, the other hand is used to abduct the affected shoulder.
• The amount of abduction measured before the initiation of scapula motion is recorded.
• The amount of abduction where glenohumeral motion ends and scapulothoracic motion begins is the passive motion of the shoulder in abduction.
• A value greater than 105o is suggestive of inferior glenohumeral ligament laxity.
Sulcus Sign
• It is positive when there is increased inferior translation of the humeral head relative to the glenoid with applied downward traction in patients with inferior and multidirectional instability.
• The sulcus should be measured at both neutral and 30o of external rotation. Elimination of the sulcus sign with external rotation suggests competency of the rotator interval; persistence of sulcus sign at 30o of external rotation suggests a lax rotator interval.

Grading of Humeral Translation
• grade 0 - Minimal inferior translation
• grade I – 0 to 1 cm translation (or) greater than the opposite uninvolved extremity
• grade II - 1 to 2 cm translation (or) humeral head translation to the glenoid rim
• grade III - greater than 2.0 cm translation (or) translation over the glenoid rim
• grade IV - indicates dislocation during testing

Instability Tests:
Apprehension Test• Patient in supine or upright position.
Anterior apprehension test:
• Affected shoulder is passively moved to abduction and maximum external rotation and a gentle anterior force is placed on the posterior humeral head. Test is positive when the patient becomes apprehensive and experiences pain.
Posterior apprehension test
• The affected shoulder is adducted and internally rotated.
Apprehension-Relocation Test:
• After apprehension test, a posterior-directed force is applied to the anterior humeral head. There is relief of apprehension. This is also called “Fowler’s sign”.

Anterior Release and Surprise Test
• The patient is in the supine position. The affected shoulder is held over the edge of the examiner’s table. The arm is positioned in 90o of abduction. A posterior directed force is applied to the anterior humeral head while simultaneously moving the shoulder to maximum external rotation. The posterior force is then released.
• The test is positive when the patient experiences pain and apprehension.

Imaging:
Radiographs:
Basic Views
• True anteroposterior (AP) view of the G-H joint
• Supraspinatous Outlet View (SSOV) also called lateral or Y view in the scapular plane and an Axillary view
Special Views
Stryker-notch view:
• For Hillsach’s Lesion
• Patient lying supine with the cassette placed posterior to the shoulder. The hand of the affected extremity is placed on top of the head with the elbow pointing straight upward. The radiograph beam is directed 10o cephalad and centered over the coracoid process.
West Point axillary view:
• For Bony Bankart or Glenoid fracture.
• Patient lying prone with the affected shoulder resting on a pad. The radiograph beam is aimed 25o from the horizontal plane (angled toward the table surface) and 25o toward the patient’s midline.

CT scan
• Useful for assessing bone defects on humeral or glenoid side.
• CT scan should be considered if patient reports instability at low abduction angles or has marked apprehension at low abduction/external rotation during provocative testing
• To determine the percentage of defect, the area of bone loss is divided by the area of a circle based on the inferior glenoid and the quotient is multiplied by 100%

MRI and MR arthrography
• Gold standard for evaluating the capsulolabral structures especially the Bankart’s lesion (Detachment of anterioinferior glenoid labrum and the inferior gleno-humeral ligament from the glenoid).
• The addition of contrast can improve the ability of MRI to show rotator cuff pathology, humeral avulsion of glenohumeral ligament(HAGL), capsular tears
Examination under anesthesia confirms laxity but not instability.
Arthroscopy is an excellent technique for confirming shoulder instability.

Classification:
Shoulder instability can be classified based on the direction, degree, and duration of symptoms and direction of instability should be categorized as unidirectional, bidirectional, or multidirectional.
Matsen’s Classification
TUBS: Traumatic, Unidirectional , with a Bankart’s lesion, requires Surgery and
AMBRII: Atraumatic, Multidirectional and Bilateral, responds to Rehabilitation, occasionally requires an Inferior capsular shift and Internal closure.
Surgical options:
Checklist for treating Shoulder Instability
1. Unidirectional/ Multidirectional.
2. Status of Dynamic stabilizers (Rotator cuff and Long head of Biceps).
3. Status of Capsuloligamentous structures (Glenohumeral ligaments/ Capsule).
4. Status of articulating bones (Humeral head defect/ Glenoid bone deficiency).

Anatomic Reconstruction
Bankart Repair

Principle: Reattachment of the antero-inferior glenoid labrum and the IGHL back to the glenoid anatomically.
Procedure: Open/ Arthroscopic
Subscapularis and anterior capsule are opened vertically. Lateral leaf of capsule is attached to anterior glenoid rim. Medial leaf is imbricated and subscapularis is approximated.
Adv: Corrects labral defect, no metallic internal fixation device required.
Disadv: Technical difficulty, restriction of external rotation.
Modified Bankart repair: Modified by Montgomery and Jobe. Anterior capsule imbricated in north-south direction. Hence external rotation not lost.

Keys to success of Bankart surgery
1. Abrading the scapular neck
2. Restoring glenoid concavity
3. Anatomical capsular fixation at the edge of glenoid
4. Superior and inferior capsular advancement and imbrication
5. Goal oriented rehabilitation

Non-Anatomic Reconstruction
• Bristow Latarjet Procedure- Transfer of coracoid to anterior glenoid rim
• Putti- Platt Procedure- Reefing the subscapularis and anterior capsule of the shoulder joint.
• Magnuson Stack Procedure- Lateral transfer of the subscapularis tendon attachment.
• Inferior Capsular Shift (Neer’s procedure)- Described for Multidirectional instability to reduce the volume of the joint. T shaped incision starting from the glenoid neck. Obliterates the capsular redundancy on the side of surgery and also on the opposite side.
• O’Brien modification of Neer procedure: Capsular shift procedure with the T portion of the incision starting adjacent to the glenoid. Allows much easier repair of a detached glenoid labrum if present.
- Weber osteotomy: Subcapital rotational osteotomy of proximal humerus for large humeral defects. The procedure rotates the defect to a more posterolateral position to avoid levering of the humeral head on the glenoid at the Hill-Sachs lesion.

• Anterior instability without bony defect - Anatomic reconstruction (Bankart repair)
• Anterior instability with humeral head defect of
<20% - Reduction + Immobilisation/ Bankart anterior stabilisation
20-30%: Acute-Disimpaction; Old-Bankart repair
30-45% - As above/ Bone graft/ Weber osteotomy
>45% - Prosthetic replacement
• Anterior instability with anteroinferior glenoid defect of
<20% - Bankart repair
>20% - Bone graft/ Corocoid transfer



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