Anatomy and Biomechanics of the Shoulder. Part I II

Anatomy & Biomechanics of the Shoulder James J. Irrgang, Ph.D., PT, ATC Department of Physical Therapy University of Pittsburgh Shoulder Motion Combined Movements: • • • • • • • Flexion - 150 - 1800 Extension - 50 - 600 Abduction - 150 - 1800 External rotation - 900 Internal rotation - 70 - 900 Horizontal abduction Horizontal adduction Shoulder Girdle Includes: • • • • • G-H joint A-C joint S-C joint S-T joint Subacromial space Glenohumeral Motion Controlled by: • • Passive restraints Active restraints Glenohumeral Motion Passive Restraints: • • • • Bony geometry Labrum Capsuloligamen tous structures Negative intraarticular pressure Capsuloligamentous Structures Glenohumeral ligaments: • • • SGHL MGHL IGHL complex • • • anterior band posterior band axillary pouch Capsuloligamentous Structures Glenohumeral ligaments: Capsuloligamentous Structures • Coracohumeral ligament • • anterior band posterior band Restraints to External Rotation Dependent on arm position: • • • 00 - SGHL, C-H & subscapularis 450 - SGHL & MGHL 900 - anterior band IGHLC Restraints to Internal Rotation Dependent on arm position: • • • 00 - posterior band IGHLC 450 - anterior & posterior band IGHLC 900 - anterior & posterior band IGHLC Restraints to Inferior Translation Dependent on arm position: • • 00 - SGHL & C-H 900 - IGHLC Glenohumeral Motion Scapular Plane: • • • • Flexion/extension - 1200 Abduction/adduction - 1200 External/internal rotation Horizontal abduction/ adduction Arthrokinematics of Glenohumeral Joint Glenohumeral Motion Convex - Concave Rule: Glenohumeral Motion Arthrokinematics: • • • • • Abduction Flexion Extension External rotation Internal rotation Glenohumeral Motion Arthrokinematics: Harryman et. al. 1990 Glenohumeral Motion Arthrokinematics: Harryman et. al. 1990 Glenohumeral Motion Arthrokinematics: Harryman et. al. 1990 Glenohumeral Motion Capsular Tightness: Results in Abnormal Arthrokinematics Glenohumeral Motion Normal Arthrokinematics: rotation & translation to keep humeral head centered on glenoid •Combines Scapulohumeral Muscles Prime Movers: • • • • • • • Deltoid Pectoralis major Latissimus dorsi Teres major Biceps Coracobrachialis Triceps Scapulohumeral Muscles Rotator Cuff: • • • • Subscapularis Supraspinatus Infraspinatus Teres Minor Rotator Cuff Function • • • Approximates humerus to function Supraspinatus assists deltoid in abduction Subscapularis, infraspinatus & teres minor depress humeral head Subscapularis • • Effective restraint to ER with arm at side Ineffective restraint to ER with arm abducted to 900 Turkel et. al. JBJS 1981 Infraspinatus/Teres Minor • • Reduces strain on anterior band of IGHLC “Hamstrings” of glenohumeral joint Cain et. al. AJSM 1987 Long Head of Biceps • • • Biceps tendon force increases torsional rigidity to ER No effect on strain of IGHLC Effect lost with SLAP lesion Rodosky et. al. AJSM 1994 Biceps Becomes More Important Anterior Stabilizer as Capsuloligamentous Stability Decreases Itoi et. al. JBJS 1994 & Glousman et. al. 1988 Force Couples Acting on Glenohumeral Joint • • Transverse plane anterior vs. posterior RC Coronal plane deltoid vs. inferior RC Rotator Cuff Tear Supraspinatus: • • Essential force couples maintained Normal strength & function possible Rotator Cuff Tear Supraspinatus/Posterior Cuff: • • • Essential force couples disrupted Weakness with external rotation Little active elevation possible Rotator Cuff Tear Massive Tear : • • • Essential force couples disrupted Weakness with internal & external rotation Little active elevation possible Subacromial Space Structures Within Suprahumeral Space • • • • • • Long head of biceps Superior capsule Supraspinatus tendon Upper margins of subscapularis & infraspinatus tendons Subacromial bursa Inferior surface of A-C joint Subacromial Space Clinical Relevance: • Avoidance of impingement during elevation of arm requires: • • external rotation of humerus to clear greater tuberosity upward rotation of scapula to elevate lateral end of acromion Subacromial Space Clinical Relevance: • • Primary impingement: • structural stenosis of subacromial space Secondary impingement: • functional stenosis of subacromial space due to abnormal arthrokinematics Scapulothoracic Joint Scapulothoracic Muscles • • • • • • Trapezius Serratus anterior Rhomboids Levator scapulae Pectoralis minor Subclavius Scapulothoracic Motion • • • Elevation/depression Protraction/retraction Upward/downward rotation Force Couple at Scapulothoracic Joint • • Serratus anterior produces anterio-lateral movement of inferior angle Upper trapezius pulls scapula medially Scapulohumeral Rhythm • Total elevation: • • 1200 at G-H joint 600 at S-T joint Force Couple at Scapulothoracic Joint • • Serratus anterior produces anterio-lateral movement of inferior angle Upper trapezius pulls scapula medially Acromioclavicular Joint Acromioclavicular Joint • • • • Joint capsule A-C ligaments Intra-articular disc Coracoclavicular ligaments • • conoid (medial) trapezoid (lateral) Acromioclavicular Joint Movements: • • Axial rotation of clavicle (spin) Angulation between scapula & clavicle Sternoclavicular Joint • • • • • Joint capsule Anterior & posterior SC ligaments Intra-articular disc Interclavicular ligament Costoclavicular ligament Sternoclavicular Joint Motions: • • • Protraction/retraction Elevation/depression Axial rotation (spin) Biomechanics of Scapular Rotation • Scapulothoracic motion occurs as part of closed kinetic chain involving: • • A-C joint S-C joint Scapular Rotation Phase I • • • Upper & lower portions of trapezius & serratus anterior produce upward rotatory force on scapula Motion at A-C joint prevented by coracoclavicular ligament Rotation of scapula occurs as elevation of clavicle at S-C joint Scapular Rotation Phase II • • • Further motion at S-C joint prevented by costoclavicular ligament Continued upward rotation of scapula pulls on costoclavicular ligament causing posterior rotation of clavicle Posterior rotation of clavicle allows further upward rotation of scapula Scapular Rotation Necessary to: • • • Enhance glenohumeral stability Elevate acromion to avoid impingement Maintain effective length tension relationship of scapulohumeral muscles Review this lecture