The Shoulder A Balance Of Mobility and Stability

1. The ShoulderA Balance Of Mobility and Stability

2. Glenohumeral Joint Stability • Static stabilizing structures: • Bony geometry • Glenoid labrum • Capsulo-ligamentous complex • Intra-articular pressure • Dynamic stabilizing structures: • Musculo-tendinous influences

3. Static Stabilizing Structures • Bony Geometry • Sacrifices joint stability for great mobility • “Golf ball sitting on a tee” • 2 mechanisms for providing stability • Glenoidfossa/Humeral head contact area • 25-30% of humeral head contacts glenoid • Articular surface congruency • Glenoidfossa orientation • Humeral head orientation

5. Static Stabilizing Structures • Glenoid Labrum • Most effective in mid-ROM • Fibrous rim that deepens the glenoidfossa •  depth ~50% or 2.5-5.0 mm •  total surface contact area • intra-articular pressure

7. Capsulo-Ligamentous • Joint capsule • Predominantly type I collagen • Less than 5 mm thick • Primary role – maintaining negative intra-articular pressure

8. Capsulo-Ligamentous • Coracohumeral ligament • Tight during shld ER & elevation (0-60°) • Prevents inferior translation in shld ADD • Superior Glenohumeral ligament • Prevents inferior translation in shld ADD

9. Capsulo-Ligamentous • Middle Glenohumeral Ligament • Prevents anterior translation • Limits shld ER between 0-90° of arm elevation • Inferior Glenohumeral Ligament Complex

10. Inferior Glenohumeral Ligament • Anterior band and axillary pouch – anterior stability in upper ranges of elevation • Posterior band – inferior stability during arm elevation • In shld elevation: • Anterior band becomes taut w/ shld ER • Posterior band becomes taut w/ shld IR

11. Capsulo-Ligamentous Structures

12. Dynamic Stabilizing Structures Primary StabilizersSecondary Stabilizers SupraspinatusTeres Major InfraspinatusLatissimusDorsi Teres Minor Pectoralis Major Subscapularis Long Head of Biceps Deltoid*

14. Primary Stabilizers • Concavity-compression mechanism • Dynamic ligament tension – helps reinforce the joint capsule • Initiation of movement, forces for acceleration and deceleration • Neutralize the superior pull of the deltoid

15. Primary Stabilizers • External rotation controlled by infra and teres minor – reduces strain on anteroinferiorcapsuloligamentous structures • Subscapularis – anterior stability w/ arm in abd and neutral rotation • Posterior cuff muscles – anterior stability w/ arm in abd and ER

16. Primary Stabilizers • Supraspinatus – compression, abd, & generates a small ER torque, peaks at 30°-60°, generates most force in scapular plane • Infraspinatus/Teres Minor – compression, generates inferoposterior force, provides great ER torque, generates most force at 0° abd • Subscapularis – compression, ant stability, generates IR torque, generates most force at 0° abd, primary IR at 90° abd

17. Secondary Stabilizers • Long Head of Biceps – dynamic restrain to ER in the abducted shld; large role in dynamic stability when capsuloligamentous structures are compromised • Deltoid – dynamic stability w/ arm in scapular plane; decreases the stability of the shldw/ arm in coronal plane