1. Shoulder Instability Basic Science • Upper Extremity Rounds • Dec 9, 2011

2. Definitions • Laxity: asymptomatic, passive translation of humeral head on glenoid • Instability: pathologic condition pain/discomfort associated w/ excessive translation of humeral head on glenoid

3. Anatomic Control • Static: ligaments and tendons • Dynamic: muscular contraction (rotator cuff, biceps, scapulothoracic motion) • Interaction between the two (proprioception mediated)

5. Static Stabilizers

6. Version • Glenoid • 30º anteverted (relative coronal plane) • 7º retroverted (relative to scapular plane) • 3-5º superior tilt • Humerus • neck/shaft 130-140º • 30º retroversion (relative to TE axis)

7. Conformity • Glenoid/Humeral Head • highly congruent-difference in radii 3mm • 25-35% head contact at a given time • glenoid peripheral cartilage thicker

8. Labrum • labrum-extension of glenoid • ↑ surface area GH articulation • anchor for capsuloligamentous structures • more tightly attached below glenoid equator

9. Capsuloligamentous Structures

10. Superior GHL+Coracohumeral ligament • ‘rotator interval region’ • CHL w/ SS and SC tendon edges • SGHL deep to CHL • origin superior glenoid tubercle inferior to biceps • parallel to CHL • inserts superior LT • Adducted arm: limit inferior translation and ER • Fl/Ad/IR: limit posterior translation • Role anteroinferior instability/MDI (contracture scarring adhesive capsulitis)

11. Middle GHL • originates supraglenoid tubercle/anterosuperior labrum, inserts anterior to LT, blends with posterior SC • absent/poorly defined in 40% • variable morphology: • a) cord like b) sheet like • abduction (60-90)/ER: passive restraint anterior and posterior translation • adduction: restrains inferior translation

12. Inferior GHL • O: anteroinferior labrum/glenoid neck • I: inferior to MGHL • 3 components: • anterior band • posterior band • axillary pouch • in abduction:hammock like function limit inferior translation • IGHLC: most important factor anterior instability*

13. Posterior Capsule • thinnest region of joint capsule • no direct ligamentous reinforcements • FF/AD/IF: limits posterior translation

14. Dynamic Stabilizers

15. Joint Compression • Rotator Cuff • enhances conformity • ↑ load necessary to translate head • more important than static stabilizers • dislocation association w rotator cuff tear >age 40 • overhead athletes/asynchronous rotator cuff = subtle forms instability

16. Ligament Dynamization • direct connections cuff tendons->capsuloligamentous structures • ‘dynamize’ capsule/ligaments • esp midranges of rotation • ?biceps->SGHL/MGHL (through labrum) • ?triceps-> axillary pouch (IGHLC) • SS/SC-> CHL

17. Biceps Long Head • intraarticular • helps in all directions • depend on IR/ER • compensates for failed primary restraints • instability rehab-->>directed at biceps

18. Scapular Rotators • trapezius,rhomboids latissimus dorsi, serratus anterior, levator scapulae • normal rhythm -> GH:ST = 2:1 • function = stable platform =must rehab scapular rotators

19. Proprioception • Mechanoreceptors =specialized nerve endings • (pacinian corpuscles, Ruffini endings, Golgi tendon-like endings) • mechanical deformation -> electric signals • capsule/ligaments/?labrum Vangsness et al, Arthroscopy, 1995

20. Pathoanatomy

21. Bankart • originally ‘essential lesion’-detachment capsulolabral complex from anterior joint • now + capsular plastic deformation/stretch • succesful surgery requires larger imbrication of the capsule

22. Capsular Injury • Traumatic intrasubstance • Humeral Avulsion (HAGL) • only 20% seen radiographically (BHAGL) • Repetitive Injury • overhead athletes • repetitive subfailure strain

23. Capsular Laxity • Intrinsic • unclear if risk factor for clinical instability • Inherited Collagen Disorders • Ehlers-Danlos common • surgery ineffective

24. Bone Loss • Humeral • Hill-Sachs/Reverse Hill-Sachs • present 80% anterior dislocations • >30% articular surface-> recurrent instability post repair • Glenoid: bone loss-> inverted pear • Laterjet, ICBG

25. Version abnormalities • excessive glenoid retroversion • excessive articular surface wear • dysplasia? • Glenoid/Humeral osteotomy • not common in North America

27. Take Home Points • laxity vs instability • static restraints vs dynamic restraint • common pathoanatomy • labrum, capsular injury/laxity, bony

28. Case • 48 yo F homemaker • R shoulder multiple subluxations/dislocations per week

30. april 19, 2010

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