# Sports-Related Shoulder Instability

## Overview
Shoulder is the most commonly dislocated joint due to inherent mobility-stability tradeoff. Glenohumeral joint: ball-and-socket with shallow glenoid (only 25-30% of humeral head covered). Anterior instability accounts for 95% of shoulder dislocations. Peak incidence: males 15-29 years, contact sport athletes. Recurrence rates after first dislocation: up to 90% in patients under 20 years.

## Anatomy and Stabilizers

### Static Stabilizers
**Glenoid labrum**: fibrocartilaginous rim that deepens glenoid socket by 50%. **Glenohumeral ligaments**: Superior GHL: limits inferior translation in adduction. Middle GHL: limits anterior translation in mid-range abduction (45-60 degrees).

Inferior GHL (IGHL) complex: most important; limits anterior translation in abduction and external rotation (90 degrees abduction). Anterior band: primary restraint in apprehension position. Posterior band: limits posterior translation in flexion/internal rotation. **Glenoid concavity-compression**: congruent articular surfaces compressed by rotator cuff.

**Joint capsule**: provides static restraint at end-range. **Negative intra-articular pressure**: contributes to joint stability.

### Dynamic Stabilizers
**Rotator cuff**: supraspinatus, infraspinatus, teres minor, subscapularis. Concavity-compression mechanism. Dynamic centering of humeral head. **Long head of biceps**: anterior stabilizer.

**Scapular stabilizers**: serratus anterior, trapezius, rhomboids. Scapular dyskinesis impairs dynamic stability. **Deltoid**: provides compressive force.

<image>Glenohumeral joint anatomy showing labrum, glenohumeral ligaments, and rotator cuff as static and dynamic stabilizers</image>

## Spectrum of Instability

### Traumatic Instability (TUBS)
**T**raumatic etiology. **U**nidirectional (typically anterior). **B**ankart lesion. **S**urgery often required. Classic first-time dislocation in sports.

### Atraumatic Instability (AMBRI)
**A**traumatic onset. **M**ultidirectional. **B**ilateral predisposition. **R**ehabilitation is primary treatment. **I**nferior capsular shift if surgery needed. Associated with generalized ligament laxity (Beighton score).

### Microinstability
Subtle instability without frank dislocation. Common in overhead athletes (swimmers, throwers, volleyball). Repetitive microtrauma leads to capsular stretching. Presents as pain and apprehension rather than dislocation. "Dead arm" sensation with throwing.

| Feature | TUBS (Traumatic) | AMBRI (Atraumatic) |
|---------|-----------------|-------------------|
| Etiology | Traumatic event | Atraumatic/repetitive |
| Direction | Unidirectional (anterior) | Multidirectional |
| Bilaterality | Unilateral | Often bilateral |
| Key pathology | Bankart lesion | Capsular redundancy |
| Primary treatment | Surgery often required | Rehabilitation first |
| Surgical option | Bankart repair | Inferior capsular shift |

## Pathoanatomy of Instability Lesions

### Bankart Lesion
Detachment of anteroinferior labrum from glenoid. Most common lesion in traumatic anterior instability. Variants: soft tissue Bankart (labrum only), bony Bankart (labrum + glenoid bone fragment). Critical glenoid bone loss: >20-25% of glenoid face (inverted pear glenoid).

### Hill-Sachs Lesion
Posterolateral humeral head compression fracture. Results from impaction against anterior glenoid rim during dislocation. Present in 40-90% of anterior dislocations. "Engaging" Hill-Sachs: large enough to engage glenoid rim during functional ROM (increases recurrence risk). "Non-engaging" Hill-Sachs: smaller, does not catch on glenoid.

### SLAP Lesion (Superior Labrum Anterior to Posterior)
Tear of superior labrum at biceps anchor. Common in overhead athletes. Types I-IV (Type II most common and clinically significant). Mechanism: traction (follow-through phase), compression (fall on outstretched hand).

### HAGL Lesion (Humeral Avulsion of Glenohumeral Ligament)
Avulsion of IGHL from humeral neck. Easily missed on arthroscopy and MRI. Requires specific repair technique.

### Other
Capsular redundancy/patulousness. Rotator interval lesions. Glenoid rim fractures. Kim lesion (incomplete posterior labral tear).

## Clinical Assessment

### History
Mechanism: arm position at time of dislocation (abduction + external rotation = anterior). Number of dislocations/subluxations. Direction of instability. Activities provoking symptoms. History of reduction (self-reduced vs. ED). Generalized laxity symptoms.

### Physical Examination
**Apprehension test**: abduction + external rotation at 90 degrees. Positive: patient feels impending dislocation (apprehension, not just pain). **Relocation test**: posterior force on humeral head reduces apprehension. Confirms anterior instability.

**Load and shift test**: anteroposterior translation grading. Grade I: increased translation without subluxation. Grade II: subluxation over glenoid rim with spontaneous reduction. Grade III: dislocation without spontaneous reduction.

**Sulcus sign**: inferior traction with arm at side. Positive: visible dimple below acromion. Grading: Grade I <1 cm, Grade II 1-2 cm, Grade III >2 cm. Tests inferior instability; if positive with external rotation = rotator interval incompetence.

**Kim test**: posteroinferior instability. **Jerk test**: posterior labral pathology. **O'Brien test**: SLAP lesion screening. **Beighton score**: generalized hypermobility (≥4/9 = hypermobile).

<image>Clinical examination tests for shoulder instability including apprehension, relocation, load and shift, and sulcus sign</image>

### Imaging
**Radiographs**: AP, axillary lateral, Stryker notch view. Bankart fracture, Hill-Sachs lesion, glenoid bone loss. West Point view: anteroinferior glenoid rim. **MRI**: labral tears, capsular pathology, rotator cuff integrity.

**MR arthrography**: gold standard for labral pathology (sensitivity 89-95%). Especially important for detecting subtle labral tears, HAGL lesions. **CT with 3D reconstruction**: quantify glenoid bone loss (critical for surgical planning). Best circle method or Pico method for glenoid bone loss measurement.

## Non-Operative Management

### Acute Dislocation Management
Reduction as soon as possible (less muscle spasm = easier reduction). Techniques: external rotation method, Stimson technique, traction-countertraction, Cunningham technique. Post-reduction radiographs to confirm concentric reduction and assess for fractures. Immobilization: traditional internal rotation sling vs. external rotation brace.

External rotation immobilization may reduce recurrence (controversial, variable evidence). Duration: 1-3 weeks (shorter is acceptable in older patients).

### Rehabilitation Program (Non-Operative or Pre-Operative)

#### Phase 1: Protection and Pain Control (Weeks 0-3)
Sling immobilization. Gentle pendulum exercises. Scapular isometrics (retraction, depression). Avoid combined abduction + external rotation.

#### Phase 2: Early ROM and Activation (Weeks 3-6)
Progressive passive then active-assisted ROM. Rotator cuff isometrics progressing to isotonics. Scapular stabilization exercises (serratus anterior, lower trapezius). Closed kinetic chain exercises.

#### Phase 3: Strengthening (Weeks 6-12)
Progressive rotator cuff strengthening (internal/external rotation). Emphasis on posterior cuff and scapular muscles. Proprioception and neuromuscular training. Core and kinetic chain integration.

#### Phase 4: Return-to-Sport (Weeks 12-16+)
Sport-specific training. Plyometric shoulder exercises. Contact confidence and apprehension resolution. Functional testing.

## Surgical Management

### Indications
Recurrent instability despite rehabilitation. First-time dislocation in young (<25 years) contact sport athletes (consider early surgery). Significant bone loss (Bankart fracture >20%, engaging Hill-Sachs). Associated repairable pathology (rotator cuff tear, SLAP tear). In-season athletes requiring reliable stability for return to play.

### Surgical Options
**Arthroscopic Bankart repair**: standard for soft tissue Bankart without significant bone loss. Suture anchor fixation of labrum to glenoid rim. Success rate: 85-95% in appropriate candidates. Risk factors for failure: young age, contact sports, bone loss, hyperlaxity.

**Latarjet procedure (coracoid transfer)**: for significant glenoid bone loss or high-risk patients. Transfers coracoid with attached conjoint tendon to anterior glenoid. Triple stabilization: bone augmentation, sling effect, capsular repair. Lower recurrence rates than Bankart in high-risk patients.

**Remplissage**: filling Hill-Sachs defect with infraspinatus tendon/capsule. Used in combination with Bankart repair for engaging Hill-Sachs. **Open Bankart repair**: lower recurrence than arthroscopic in some studies, more tissue trauma. **Capsular shift**: for multidirectional instability (AMBRI pattern).

## Return-to-Sport Considerations
After arthroscopic Bankart repair: 4-6 months for non-contact sports, 6-9 months for contact sports. After Latarjet: 4-6 months. Must have: full ROM, strength ≥ 90% of contralateral, no apprehension, sport-specific testing passed. Bracing: shoulder stabilization braces limit extremes of abduction/ER in contact sports. May reduce recurrence risk during return to sport.

<image>Surgical options for shoulder instability: arthroscopic Bankart repair, Latarjet coracoid transfer, and remplissage</image>

## Clinical Pearls
Recurrence risk after first-time anterior dislocation in patients under 20 is up to 90% - early surgical consultation is warranted in this population. The apprehension test is positive when the patient feels the shoulder is about to dislocate (apprehension), NOT when it causes pain - pain alone is nonspecific. Quantify glenoid bone loss with CT 3D reconstruction before deciding on arthroscopic Bankart vs. Latarjet - >20% bone loss generally requires a bone block procedure. In the overhead athlete with "dead arm" symptoms, think microinstability and SLAP tear rather than frank instability - MR arthrography is the imaging study of choice. Rehabilitation for atraumatic multidirectional instability should emphasize rotator cuff and scapular stabilizer strengthening for a minimum of 3-6 months before considering surgery.

## References
- Kuhn JE. A new classification system for shoulder instability. Br J Sports Med. 2010;44(5):341-346.
- Dickens JF, et al. Return to play and recurrent instability after in-season anterior shoulder instability in athletes. Am J Sports Med. 2014;42(12):2842-2850.
- Hurley ET, et al. Arthroscopic Bankart repair versus Latarjet procedure for recurrent shoulder instability: a systematic review and meta-analysis. Am J Sports Med. 2019;47(6):1529-1538.
- Wilk KE, et al. Rehabilitation after shoulder instability surgery. J Am Acad Orthop Surg. 2021;29(3):e119-e130.
- Provencher MT, et al. Glenoid bone loss in anterior instability: treatment options. J Am Acad Orthop Surg. 2018;26(19):e405-e415.