Shoulder Biomechanics PDF

Shoulder: Clinical Anatomy & Biomechanics Dr.Bassem Khalifa  Shoulder Complex Glenohumeral Joint Acromioclavicular Joint Sternoclavicular Joint ScapulothoracicArticulation Subacromial Space  Anatomical Orientation of the Shoulder Complex  Stability Functions of Shoulder Girdle...

Shoulder: Clinical Anatomy & Biomechanics Dr.Bassem Khalifa  Shoulder Complex Glenohumeral Joint Acromioclavicular Joint Sternoclavicular Joint ScapulothoracicArticulation Subacromial Space  Anatomical Orientation of the Shoulder Complex  Stability Functions of Shoulder Girdle Provides stable base from which shoulder muscles can generate force Shoulder girdle muscles as stabilizers Maintain appropriate force-length relationship Maintain maximum congruence of shoulder joint  Mobility Functions of Shoulder Girdle Permits largest ROM of any complex in the body Shoulder girdle increases ROM with less compromise of stability (scapulohumeral rhythm) (4 joints vs.1 joint) Facilitatemovements of the upper extremity by positioning GH favorably Shoulder Girdle Motion Elevation Protraction (Abduction) Depression Retraction (Adduction) Shoulder Girdle Motion Upward rotation Upward tilt Downward rotation Reduction of Upward Tilt  Muscular Considerations Muscle Action on the Shoulder Girdle Shoulder Girdle Muscles Pectoralis Minor: scapular downward rotation, depression, protraction SerratusAnterior: scapular protraction, upward rotation Subclavius: stabilizes sternoclavicular joint Shoulder Girdle Muscles Levator Scapulae: elevation and downward rotation Rhomboids: downward rotation, retraction, elevation Shoulder Girdle Muscles Trapezius Upper: elevation, upward rotation of scapula Middle: retraction of scapula Lower: depression, retraction of scapula Shoulder Joint Muscles Pectoralis Major: flexion, horizontal adduction, internal rotation of humerus Deltoid: nearly all movements of arm from shoulder joint, internal rotation, abduction, hyperextension, flexion, horizontal adduction Shoulder Joint Muscles Coracobrachialis: forward movements of humerus Subscapularis: internal rotation of humerus, stabilizes glenohumeral joint Biceps brachii: flexion and adduction , horizontal adduction Shoulder Joint Muscles Supraspinatus: abduction of humerus Infraspinatus: external rotation, horizontal abduction, stabilize humerus during flexion Teres Minor: external rotation, horizonal abduction, stabilize humerus during flexion Shoulder Joint Muscles Latissimus Dorsi: extension and adduction of arm Teres Major: shoulder extension, adduction, medial rotation Triceps Brachii: adduction, extension, hyperextension of humerus Scapulothoracic Muscles Elevators – Upper trapezius, levator scapula, rhomboids Depressors – Lower trapezius, pectoralis minor Scapulothoracic Muscles Protractors – Serratus anterior, pectoralis minor Retractors – Mid & lower trapezius, rhomboids, levator scapulae Scapulothoracic Muscles Upward Rotators – Serratus anterior, upper trapezius Downward Rotators - Rhomboids, pectoralis minor, levator scapulae Glenohumeral Joint Muscles Abductors – deltoid, supraspinatus Adductors – pectoralis major, latissimus dorsi, teres major Internal Rotators – pectoralis major, subscapularis, anterior deltoid, latissimus dorsi, teres major External Rotators – infraspinatus, teres minor, posterior deltoid Flexors – biceps brachii, coracobrachialis, anterior deltoid Extensors – triceps brachii, posterior deltoid, latissimus dorsi, teres major Specific Joints Structure and Function  Sternoclavicular Joint Clavicle Sternum 1st Rib Sternoclavicular ligaments Costoclavicular ligament Articular disc Muscular attachments Sternoclavicular Joint Motions Elevation/Depression – 45/10 degrees Max Protraction/Retraction – 15 to 30 degrees in each direction Axial Rotation – 40 to 50 degrees Acromioclavicular Joint Gliding or planar joint Articular disc Acromioclavicular ligament Coracoclavicular ligament Acromioclavicular Joint Motions Upward & downward rotation Horizontal & sagittal plane adjustments Coracoclavicular Ligaments Conoid ligament (medial) andTrapezoid ligament (lateral) Maintenance of the acromioclavicular joint Support of the scapula Scapulothoracic Articulation Not a true joint Provide the movement base for the humerus ST motion = AC motion + SC motion  Primary Movements of the Scapulothoracic Articulation Scapulothoracic Elevation ST Elevation = SC joint elevation + downward rotation atAC joint Scapulothoracic Upward Rotation ST Upward Rotation = SC joint elevation + upward rotation atAC joint  Scapular Rotation Enhance glenohumeral stability Elevate acromion to avoid impingement Maintain effective length tension relationship of scapulohumeral muscles Glenohumeral Joint  Glenohumeral Joint Humeral Head Glenoid Fossa Glenoid Labrum Rotator Cuff Muscles (SITS) Capsuloligamentous complex Coracohumeral Ligament Long Head of Biceps Subacromial Space Glenohumeral Ligaments SGHL MGHL IGHL complex Anterior band Posterior band Axillary pouch Coracohumeral ligament Anterior band Posterior band Glenohumeral Joint Motions Flexion/Extension (120/45 deg) Abduction/Adduction (120 deg) Internal/External Rotations (80/70 deg) Cannot precisely be isolated from motion of other elements of the shoulder girdle Glenohumeral Joint Stability Static restraints Dynamic restraints Bony structures Rotator Cuff Labrum Biceps Capsuloligamentous Proprioceptive receptors structure Neuromotor coordination Negative joint pressure Kinematics and Biomechanics Convex Concave Rules Convex Stationary + concave moving = gliding in same direction as angular motion Concave stationary + convex moving = gliding in opposite direction of angular motion Glenohumeral Joint Motions Normal Arthrokinematics: Combines rotation & translation to keep humeral head centered on glenoid Glenohumeral Roll / Glide Glenohumeral Roll / Glide Glenohumeral Roll / Glide Glenohumeral Roll / Glide Glenohumeral Joint Motions AbnormalArthrokinematics: Capsular tightness Rotator cuff tears Glenohumeral Roll / No Glide Glenohumeral Roll / No Glide Glenohumeral Roll / No Glide Clinical Implication  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 Primary impingement: Structural stenosis of subacromial space Secondary impingement: Functional stenosis of subacromial space due to abnormal arthrokinematics Dynamic Stabilization Mechanisms Passive muscle tension Compressive forces from muscle contraction Joint motion that results in tightening of passive structures Redirection of joint force toward center of GH joint Dynamic Stabilization Mechanisms Force-length relationships quite variable due to multiple joints Tension development in agonist frequently requires tension development in antagonist to prevent dislocation of the humeral head Force couple – 2 forces equal in magnitude but opposite in direction Force Couples Acting on Glenohumeral Joint Transverse plane - anterior vs.posterior rotator cuff muscles Coronal plane - deltoid vs.inferior rotator cuff Force Couples Disruption Rotator Cuff Muscles Supraspinatus Teres Minor Infraspinatus Subscapularis Rotator Cuff – Dynamic GH Stabilizer Rotator Cuff Function Approximates humerus to function Supraspinatus assists deltoid in abduction Subscapularis, infraspinatus & teres minor depress humeral head Scapulohumera l Rhythm Scapulohumeral Rhythm Movement relationship between humerus and scapula during arm raising movements Scapulohumeral Rhythm Synergistic coordination of scapulothoracic musculature producing abduction Combined motion of GH, AC, SC & ST joints 2:1 ratio – for every 3 degrees of shoulder abduction, 2 degrees occur at GH joint, and 1 degree occurs at the ST joint (SC, AC) Scapulohumeral Rhythm 0 – 90 degrees of abduction : 60 deg of GH motion; 30 degrees of ST motion ST abduction: 20-25 degrees of clavicular elevation, 5-10 degrees of AC upward rotation 90-180 degrees of abduction : 60 deg of GH motion; 30 degrees of ST motion ST abduction: 5 degrees of clavicular elevation, 25 degrees of AC upward rotation Scapulohumeral Rhythm Preserves the length-tension relationships of the glenohumeral muscles sustain their force production through a larger portion of the range of motion Prevents impingement between the humerus and the acromion simultaneous movement limits relative movement between the two bones Scapulohumeral Rhythm Clinical Implications Rotator cuff pain in early phase of active abduction Impingement pain in mid phase of active abduction AC pain in late phase of active abduction Effects of Poor Scapular Stabilization Poor resting posture of scapula;slightly protracted position Loss of upward or optimal tilt of scapula Loss of static stability of GH joint Inferior translation and internal rotation of humeral head Traction ischemia of rotator cuff musculature, especially supraspinatus Capsular laxity; poor dynamic stabilization ThankYou