Biomechanics of the Shoulder Complex-1.pptx

Shoulder complex

1. Shoulder Complex Team Ortho

2. Arthrokinematics of GH It is a incongruent joint Movements occur as a combination of rolling and gliding Flexion- posterior and inferior glide Extension- anterior and superior glide Abduction- inferior glide Adduction- superior glide Ext rotation- anterior glide Int rotation- posterior glide

3. Scapulo -humeral Rhythm It was previously believed that 2:1 ratio exists throughout the shoulder elevation Recent studies suggest it to be false Scapulohumeral rhythm is divided into following phases Setting phase (initial 30-60 degree) Scapula seeking positional stability in relation to humerous As arm elevates the weight acting causes a winging of scapula Trapezius and serratus contract together generating a force couple to avoid this winging and causes an upward rotation of scapula

4. Scapulo -humeral Rhythm Elevation phase (middle 60 degree) In this phase glenohumeral motion is in same proportion of scapulothorasic motion (1:1) Last 60 degree Glenohumeral motion is greater than scapulothorasic (5:1) Final scapular motion is caused by clavicular rotation and acromioclavicular joint

5. Muscle Contraction Deltiod Causes joint compression during humerous elevation In plane of scapula Anterior and middle fibres produce force for elevation Posterior fibres cause joint compression

6. Muscle contraction Supraspinatus Performs abduction and external rotation Maximum effort at 30 degree abduction Secondary function is to compress GHJ to provide stability to humerous Infraspinatus, Teres minor, Subscapularis Depresses humeral head Prevents superior impaction of humeral head into acromian

7. Muscle Contraction Lattisimus dorsi, pectoralis major, teres major Depresses humeral head Stabilizes anterior capsule Upper and lower trapezius and serratus Forms force couple and drives scapula into upward rotation

8. Shoulder Impingement Multiple theories exist as primary etiology of shoulder impingement Anatomic abnormalities of the coracoacromial arch Humeral head “tension overload” Ischemia Degeneration of the rotator cuff tendons Shoulder kinematic abnormalities

9. Stages of shoulder impingement Stage 1 Reversible lesions with edema and hemorrhage Most patients younger than 25 years Stage 2 Chronic inflammation or repeated episodes of impingement Histomorphological changes such as fibrosis and thickening of the supraspinatus, the long biceps tendon and subacromial bursae seen Patients usually between 25- 40 years

10. Stages of shoulder impingement Stage 3 Tears of the rotator cuff, rupture of the biceps tendon, and bony changes observed Significant tendon degeneration following a longhistory of refractory tendinitis Most patients more than 40 years of age

11. Pathomechanics R educed ST posterior tilting R educed ST upward rotation I ncreased ST internal rotation, or increased clavicular elevation relative to the thorax T hese alterations increase proximity of the rotator cuff tendons to coracoacromial arch Increased humeral head superior or anterior translation found in subjects with impingement These directions of humeral head motion reduce the subacromial space and increase impingement risk

12. Pathomechanics Various angles of shoulder elevation in different plane alters subacromial space The subacromial space is typically described as minimized at 90 degree of humeral elevation in all planes The rotator cuff tendons are in closest proximity to the acromion near 45 degree of humeral abduction By angles past 60 degree humeral abduction, the attachment sites of the cuff tendons on the greater tuberosity have rotated past the lateral acromial undersurface Patients may still have a painful arc of motion near 90 degree of humeral elevation in any plane, since this is where rotator cuff muscle forces are highest

13. Pathomechanics E vidence of increased upper trapezius activation and reduced serratus anterior activation seen in subjects who have demonstrated reduced ST posterior tilting, increased internal rotation, and reduced upward rotation Glenohumeral internal rotation deficit and experimentally induced posterior capsule tightness have also been shown to increase ST anterior tilting and humeral anterior translations Slouched sitting, thoracic kyphosis, and increased age have also been related to increased ST anterior tilting and internal rotation and reduced ST upward rotation O ther factors includ reduced rotator cuff activation and pectoralis major tightness can be biomechanically theorized to impact ST or glenohumeral kinematics in ways that increase impingement risk

14. Frozen Shoulder F rozen shoulder results in decreased external rotation and abduction compared to the contralateral side of the arm C apsular stiffness can compromise normal glenohumeral and scapulothoracic movement Movement Structure involved external rotation at 0° abduction coracohumeral ligament external rotation at 30–60°abduction superior glenohumeral ligament external rotation at 90°abduction anterior- inferior capsule decrease in internal rotation decrease in internal rotation

15. Pathomechanics N o consistent pattern of limitation on motion by the severity of capsular contracure because other factors including scapular stiffness and scapulohumeral muscular imbalance are linked with the restriction of glenohumeral joint motion E arly and significant increase in scapular upward rotation have been noticed in frozen shoulder and have been attributed to increased upper trapezius and reduced serratus anterior activation T he medial rotation, posterior tilt and downward rotation of the scapula in the affected shoulder is decreased compared to contralateral scapula in the same degree of glenohumeral angle.

16. Shoulder subluxation associated with paresis Most common type of subluxation associated with paresis is in inferior direction Inferior subluxations occur when muscle weakness leads to a downward rotation of the scapula The labrum and inferior portion of the glenoid fossa can no longer provide sufficient support to secure the humeral head into the glenoid In addition to the faulty mechanics at the scapula deltoid is no longer able to support the weight of the arm Gravitational forces applied to the weakened arm stretches the inert and non-inert structures to the point that the humeral head migrates distally below the glenoid fossa

17. Reference Pathomechanics of Frozen Shoulder: A Basic Research Perspective ,Yon- Sik Yoo Anatomy, Kinesiology, Pathomechanics , and Diagnosis of Shoulder Impingement Symptom , Tirza Z. Tamin An Orthopedic Approach to the Hemiparetic Upper Limb: Understanding the Biomechanics and Pathoanatomy of the Shoulder, Henry Hoffman

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