Shoulder Stabilizers and Their Function - Clinical Tests

INTRODUCTION

A. STATIC STABILIZERS

1. Bony Anatomy

• The humeral head has an inclination of 125° and retroversion of 25°
• The glenoid has a slight retrotilt that contributes to posterior containment
• The humeral head surface area is larger than the glenoid - only ~25-30% contact at any time
• Bony articulation provides minimal inherent stability

2. Glenoid Labrum

• Fibrocartilaginous rim around the glenoid
• Deepens the socket by 50% and increases surface area
• Acts as a "bumper" against translation of the humeral head
• Anatomic variants: sublabral foramen (anterosuperior) and Buford complex (absent anterosuperior labrum + cord-like MGHL)

3. Glenohumeral Ligaments (Capsule)

4. Negative Intra-articular Pressure

• Vacuum seal of the closed capsule generates negative pressure
• Enhances the stabilizing effect of capsuloligamentous structures
• Loss of this vacuum (capsule venting) produces significant inferior translation - the basis of the sulcus sign

B. DYNAMIC STABILIZERS

1. Rotator Cuff Muscles

2. Biceps Tendon (Long Head)

• Runs through the bicipital groove within the rotator interval
• Dynamic stabilizer against anterior and inferior translation
• The transverse humeral ligament stabilizes the biceps tendon in the groove

3. Periscapular / Scapulothoracic Muscles

• Serratus anterior, trapezius, rhomboids, levator scapulae
• Position the scapula (and therefore the glenoid) optimally under the humeral head
• Scapulothoracic dyskinesia impairs glenohumeral stability - important in MDI

4. Deltoid

• Works synergistically with the rotator cuff
• The rotator cuff must fix the fulcrum (humeral head against glenoid) for the deltoid to effectively elevate the arm

5. Proprioception

• Mechanoreceptors in the capsule and ligaments provide proprioceptive feedback
• Failure of proprioception contributes to instability, especially in MDI
• Patients with MDI have reduced proprioception compared to normal controls

C. CLINICAL TESTS FOR SHOULDER INSTABILITY

1. Apprehension Test (Crank Test)

• Technique: Patient supine; arm abducted 90°, elbow at 90°; examiner slowly externally rotates the arm
• Positive: Patient experiences a sense of apprehension (fear of dislocation), not merely pain
• Tests: Anterior capsulolabral complex and IGHL anterior band
• Significance: Anterior glenohumeral instability

2. Relocation Test (Fowler / Jobe Test)

• Technique: Immediately after apprehension test; examiner applies a posteriorly directed force on the proximal humerus
• Positive: Relief of apprehension
• Significance: Confirms anterior instability; most sensitive test for anterior instability (positive predictive value 96%)
• Together, apprehension + relocation tests are the most diagnostic combination for anterior shoulder instability

3. Load-and-Shift Test

• Technique: Patient supine; arm abducted 90°, elbow bent; examiner loads (compresses) the humeral head into glenoid, then applies anterior and posterior translatory force
• Grading:
  • 1+: Translation up to the glenoid rim (0-1 cm)
  • 2+: Translation over the glenoid rim and reduces (1-2 cm)
  • 3+: Translation over the glenoid rim, does not reduce (>2 cm) = frank dislocation
• Significance: Quantifies degree of instability; can assess anterior, posterior, and inferior laxity

4. Sulcus Sign (Inferior Instability)

• Technique: Patient seated, arm at side; examiner applies inferior traction to the arm
• Positive: A sulcus (dimple) appears below the acromion; graded by gap in cm (1+: <1 cm; 2+: 1-2 cm; 3+: >2 cm)
• Clinical pearl: If the sulcus sign persists with the arm in >45° ER, it indicates incompetency of the rotator interval (SGHL + CHL)
• Significance: Inferior laxity; multidirectional instability (MDI)

5. Posterior Jerk Test

• Technique: Patient seated; arm abducted 90° and maximally internally rotated; examiner applies axial compressive force and then horizontally adducts the arm across the body
• Positive: A "clunk" or "jerk" felt as the humeral head subluxates posteriorly, then spontaneously reduces
• Significance: Posterior glenohumeral instability

6. Kim Test

• Technique: Patient seated; arm abducted 90°; examiner applies axial compression and superiorly directed force while simultaneously adducting and depressing the arm
• Positive: Sudden pain or jerk
• Significance: Posteroinferior labral tear; posterior instability

7. Bony Apprehension Test

• Technique: Arm placed at below 45° abduction and 45° ER (below the classic apprehension position)
• Positive: Apprehension or pain at this low angle of abduction
• Significance: Suggests significant bony Bankart lesion or moderate-to-severe anterior glenoid bone loss (as opposed to soft-tissue Bankart)

8. Gagey Test (Hyperabduction Test)

• Technique: Examiner stabilizes the scapula and passively abducts the arm
• Positive: Hyperabduction >105° (or >15° asymmetric increase compared to contralateral)
• Significance: Incompetency of the IGHL complex; MDI

D. KEY SUMMARY TABLE (Miller's Table 4.7)

CLINICAL CORRELATIONS (DNB High-Yield Points)