The ShoulderA Balance Of Mobility and

Stability

Glenohumeral Joint Stability Static stabilizing structures:

Bony geometry Glenoid labrum Capsulo-ligamentous complex Intra-articular pressure

Dynamic stabilizing structures: Musculo-tendinous influences

Static Stabilizing Structures Bony Geometry

Sacrifices joint stability for great mobility“Golf ball sitting on a tee”

2 mechanisms for providing stabilityGlenoid fossa/Humeral head contact area

25-30% of humeral head contacts glenoidArticular surface congruency

Glenoid fossa orientationHumeral head orientation

Static Stabilizing Structures Glenoid Labrum

Most effective in mid-ROM Fibrous rim that deepens the glenoid fossa

depth ~50% or 2.5-5.0 mm total surface contact areaintra-articular pressure

Capsulo-Ligamentous Joint capsule

Predominantly type I collagen Less than 5 mm thick Primary role – maintaining negative intra-articular

pressure

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

Capsulo-Ligamentous Middle Glenohumeral Ligament

Prevents anterior translation Limits shld ER between 0-90° of arm elevation

Inferior Glenohumeral Ligament Complex

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

Capsulo-Ligamentous Structures

Dynamic Stabilizing StructuresPrimary Stabilizers Secondary

StabilizersSupraspinatus Teres

MajorInfraspinatus

Latissimus DorsiTeres Minor

Pectoralis MajorSubscapularis

Long Head of Biceps

Deltoid*

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

Primary Stabilizers External rotation controlled by infra and teres

minor – reduces strain on anteroinferior capsuloligamentous structures

Subscapularis – anterior stability w/ arm in abd and neutral rotation

Posterior cuff muscles – anterior stability w/ arm in abd and ER

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

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 shld w/ arm in coronal plane