Biomechanics of the shoulder

Bio-mechanics of shoulder joint for DPT students & Physical Therapists

1. Biomechanics the Shoulder Complex Dr. Abid Ullah PT Lecturer FIMS Abbottabad Email: [email protected]

2. Objective At the end of this lecture, you must be able to To identify the structure of the shoulder girdle, including joint types, articular space, and the surrounding tissues To describe joint motion occurring at the shoulder complex , including Osteokinematics and Arthrokinematics movements , muscle action, and factors checking shoulder motions To understand the stability mechanism of the shoulder complex and the possible mechanism of injury To distinguish the three degree of freedom joint from the one or two degree of freedom joint To understand the effect of the muscle synergies and the influence of weakness or paralysis of one single muscle in coupled muscle muscle motion

3. The Shoulder complex Function of shoulder complex Structure of shoulder complex Kinematic of shoulder complex Muscle at the shoulder complex Shoulder Stability Mechanism of injury at the shoulder

4. Function of shoulder complex To link the upper extremity to the trunk Dependent arm position Control of rotator cuff muscle To provide extension mobility of the arm in space To provide stability for elbow and hand skillful or forceful movements

5. Joints at Shoulder Complex Glenohumeral joint ( shoulder joint) Sternoclavicular joint Acromioclavicular joint Scapulothoracic articulation : muscle-bone articulation

6. Classified by smith et al 1996 Bony articulation Glenohumeral joint ( GH jt) Sternoclavicular joint (SC jt) Acromioclavicular joint (AC jt) Functional joints Scapulothoracic articulation Suprahumeral articulation (Subacromial articulation): The articulation b/w coracoacromial ligament and the humerus Bicipital groove : the groove b/w the greater & lesser tuberosity of the humerus

7. Glenohumeral joint ( GH jt) Proximal component : Scapula Concave glenoid cavity covered with glenoid labrum that is a fibrocartilage to deepen the glenoid cavity Distal component: Humerus Convex humeral head Retroversion of the humeral head about 30 deg posterior to the frontal axis of the elbow joint Joint type : ball & socket

8. Motion : convex on concave Shoulder flexion/extension with posterior/anterior glide of the humeral head on the glenoid cavity Shoulder abduction/adduction with inferior/superior glide of the humeral head on the glenoid cavity Shoulder internal/external rotation with posterior /anterior glide of the humeral head on the glenoid cavity Shoulder horizontal abduction/adduction with anterior/posterior glide on the humeral head on the glenoid cavity

9. Cont… DOF =3 Neutral Position : Anatomical Position Resting Position: 70 degree of shoulder abduction and 30 degree of flexion ( horizontal adduction) Closed packed position: 90 of shoulder abduction and full external rotation

10. Sternoclavicular joint ( SC jt) Proximal component: Sternum Saddle-shaped sternal manubrum Distal component: Clavicle Saddle-shaped medial end of the clavicle Disk b/w 2 articular surfaces Joint type: Saddle joint Motion: Shoulder girdle motion Clavicle elevation/depression Clavicle protraction/depression Clavicle posterior rotation DOF =3

11. Cont… Note: Clavicle Convex forward medially & concave forward laterally Quadripedal animals do not have clavicle Isokinetic strength of shoulder flexion and abduction decreases 50% if clavicle is removed

12. Acromioclavicular joint ( AC Joint) Proximal component: Convex lateral end of clavicle Distal component: Concave acromion process of the scapula Joint type: nearly plane joint/ synovial joint Motion: shoulder girdle motion Scapula wining: medial boarder of the scapula moves back wards Scapular tipping: inferior angle of the scapula moves back wards Scapular upward/downward rotation: inferior angle of the scapula rotates upward/downwards DOF = 3

13. Acromioclavicular joint ( AC Joint)

14. Scapulothoracic articulation (ST) Proximal component: convex rib cage Distal component: concave anterior surface of the scapula Note: an articulation b/w bone & muscle; not a synovial joint Motion: shoulder girdle motion; convex on concave Scapular elevation/depression: whole scapula moves upward /downwards Scapular abduction/adduction: medial boarder of the scapula moves away from/towards the spine scapular upward/downward rotation: inferior angle of the scapula rotates upward/downwards DOF =3

15. Cont…

16. Functions of the ST articulation To provide movement base for the humerus To maintain length –tension relationship for the deltoid muscle to function above 90 degree of arm elevation To provide stability of the glenohumeral joint working overhead To absorb the shock for forces applied to the outstretched arm To permit push-up during crutch walking

17. Suprahumeral articulation Synonym: subacromial joint Coracoacromial arch: composed of the coracoacromial ligament Supraspinatus tendon passing underneath this arch Not for joint stability Shoulder impingement occurs if the subacromial space is insufficient Insufficient inferior glide of the humeral head during arm elevation Insufficient external rotation of the humerus during arm elevation Inflammation of the tendon of the supraspinatus Hypertrophy of the tendon of the supraspinatus Subacromial ( subdeltoid) bursa

18. Cont…

19. Bicipital groove Groove b/w greater & lesser tuberosities of the humerus covered with the transverse humeral ligament Passing tendon of long head of biceps brachii Intra –articular but extra-synovial Plane of scapula the plane at the angle of 30 degree anterior to frontal plane Not parallel to the frontal plane Capsule in the loose packed position No impingement in the Suprahumeral joint if shoulder motion occur in the plane of scapula

20. Cont…

21. Kinematic of shoulder complex Shoulder flexion/extension Joint involved Glenohumeral joint Sternoclavicular joint Acromioclavicular joint Plane of motion: sagittal plane Axis of rotation: transverse axis through the center of the humeral head

22. Cont… Osteokinematic movements Range of motion Glenohumeral joint : 0-90 degree for shoulder flexion & 0-45 degree or 60 degree for shoulder extension Closed kinematic chain motion Pull-up Push-up Rowing Upper extremity cycling on an ergometer

23. Cont… Arthokinematic movements Posterolateral glide of the humeral head on the glenoid cavity with shoulder flexion Anteromedial glide of the humeral head on the glenoid cavity with shoulder extension Factors limiting shoulder flexion Inferior glenohumeral ligament Tightness of the posterior joint capsule Factors limiting shoulder extension Superior & middle glenohumeral ligament

24. Shoulder abduction & adduction Arm elevation = shoulder abduction or flexion Joint involved Glenohumeral joint Sternoclavicular joint Acromioclavicular joint Scapulothoracic articulation Plane of motion: frontal plane Axis of rotation GH joint: sagittal axis through the center of the humeral head SC joint: sagittal axis through the center of the medial end of the clavicle

25. Cont… Osteokinematic movement Range of motion Total range: 0-165-170 degree GH joint: 0-120 degree of shoulder abduction 0-60 degree with full internal rotation of humerus 0-90 degree with full external rotation of humerus SC joint: 0-30 -45 degree Most occurring in 1 st 90 degree of arm elevation

26. Cont… Arthokinematic movements Shoulder abduction Inferior glide of the humeral head on the glenoid cavity Inferior glide of the clavicle on the sternum in most people Factors limiting shoulder abduction: Inferior glenohumeral ligament Tightness of inferior joint capsule of the glenohumeral joint Tightness of costoclavicular & interclavicular ligament & subclavicius muscle at the SC joint Factors limiting shoulder adduction: trunk

27. Shoulder internal/external rotation Joint involved GH joint SC joint AC joint ST articulation Plane of motion: Transverse plane Axis of rotation: vertical axis through the center of the humeral head

28. Cont… Osteokinematic movements Range of motion ( ROM) Shoulder inter rotation: 0-70 degree as the arm at 90 degree of shoulder abduction & 90 degree elbow flexion Shoulder external rotation: 0-90 degree as the arm at 90 degree of shoulder abduction & 90 degree elbow flexion Note: if the elbow is extended, shoulder rotation occurs simultaneously with forearm rotation

29. Cont… Arthrokinematic movements Posterolateral glide of the humeral head on the glenoid cavity with shoulder internal rotation Anteromedial glide of the humeral head on the glenoid cavity with shoulder external rotation Factors limiting shoulder internal rotation Posterior capsule Factors limiting shoulder external rotation Coracohumeral ligament 3 glenohumeral ligament

30. Cont…

31. Shoulder horizontal abduction/adduction Synonym: horizontal extension/flexion Shoulder flexion/extension at 90 degree of shoulder abduction Horizontal abduction: arm moves backward as the arm is at 90 degree of shoulder abduction Horizontal adduction: arm moves forward as the arm is at 90 degree of shoulder abduction Joint involved GH joint SC joint AC joint ST articulation

32. Cont… Plane of motion: transverse plane Axis of rotation: vertical axis through the center of the humeral head Arthrokinematic movements Anteromedial glide of the humeral head on the glenoid cavity with shoulder horizontal abduction Posterolateral glide of the humeral head on the glenoid cavity with shoulder horizontal adduction

33. Frontal plane motion at shoulder girdle Shoulder girdle elevation Definition: ST joint elevation associated with SC elevation & AC tipping Joint involved ST articulation SC joint AC joint Arthrokinematic movement Elevation of the scapula on the rib cage Inferior glide of the clavicle on the sternum in most people Limited by the costoclavicular & interclavicular ligament & subclavicius muscle

34. Cont… Shoulder girdle depression Definition: ST joint depression associated with SC depression Joint involved ST articulation SC joint AC joint Range: 10-15 cm from maximum scapular elevated position Arthroinokinematic movements Depression of the scapula on the rib cage Superior glide of the clavicle in most people Limited by 1 st rib

35. Transverse plane motion at shoulder girdle Protraction Definition : ST joint abduction associated with SC protraction Joint involved ST articulation SC joint Axis of rotation: vertical axis passing through the center of the medial head of the clavicle Range 0-15 degree Abduction of scapula : 13-15 cm Arthrokinematic movements Abduction of scapula Protraction of scapula Limited by posterior sternoclavicular & costoclavicular ligamints

36. Cont… Retraction Definition: ST joint adduction associated with Sc retraction Joint involved ST articulation SC joint Axis of rotation: vertical axis passing through the center of the medial head of the clavicle Range: 0-15 degree Arthrokinematic movements Adduction of the scapula Retraction of the clavicle Limited by anterior Sternoclavicular ligament Total range: 25 degree totally

37. Circumduction motion at the SC joint A combination of elevation, protraction, depression & retraction or in reverse sequence Tip of the shoulder ( acromion process of the scapula) moves in a circle path

38. Cont…

39. Scapulothoracic rotation Upward rotation Definition: glenoid fossa facing upward with inferior angle of scapula sliding laterally & anteriorlly Osteokinematic movements First 30 degree: elevation of the clavicle through the axis at the base of the spine of scapula Last 30 degree: posterior rotation of the clavicle & scapular rotation around AC joint

40. Cont… Downward rotation Definition: glenoid fossa facing downwards with inferior angle of scapula sliding medially & posteriorlly

41. Transverse rotation of clavicle Axis of rotation: longitudinal axis of clavicle Total range: 40 degree Occurring after 90 degree of arm elevation due to tightening of the coracoclavicular ligament Arm elevation limited to 110 degree of this posterior rotation is not taken place

42. Muscle for glenohumeral (shoulder) motions Motion Prime movers Shoulder flexion Deltoid, anterior fiber of coracobrchialis , bicep brachii, long head of pectoralis major, clavicular head Shoulder extension Latissimus dorsi, teres major, tricep brachii, long head of deltoid, posterior fiber Shoulder abduction Deltoid, supraspinatus, bicep brachii; long head Shoulder adduction Pectoralis major, latissimus dorsi, teres major, bicep brachi long head, deltoid postrior fiber Shoulder external rotation Infraspinatus, teres major, deltoid posterior fiber Shoulder internal rotation Subscapularis, teres major, pectoralis major, latssimus dorsi, deltoid anterior fiber

43. Muscles for Scapulothoracic ( shoulder girdle) motion Motion Prim movers Scapular elevation Upper trapezius, levator scapulae, romboid major, romboid minor Scapular depression Pectoralis minor, lower trapezius, latssimus dorsi, subclavis Scapular protraction Serratus anterior, pectoralis major, pectoralis minor Scapular retraction Trapezius, romboid major, romboid minor Scapular upward rotation Trapezius, serratus anterior Scapular downward rotation Levator scapula, romboid major, romboid minor

44. Serratus anterior Origin: rib 1- 9 Insertion: medial border of the scapula Motion: protraction and upward rotation

45. Rotator cuff Supraspinatus Infraspinatus Teres minor Subscapularis Abduct and rotate the humerus Act as glenohumeral stabilizer

46. Pectoralis minor Origin: rib 2-5 Insertion: coracoid process of the scapula Depression & downward rotation Agonist Depressor Downward rotators Antagonist elevation + upward rotation

47. Shoulder complex stability Factors affecting stability of glenohumeral joint: primarily depend on muscles & ligaments Bony configuration 0-5 degree of superior inclination ( upward tilt) of the glenoid cavity Shape of the cartilage Depend glenoid labrum

48. Cont… Tension of ligaments Superior glenohumeral ligament Middle glenohumeral ligament Inferior glenohumeral ligament Coracohumeral ligament

49. Cont… Muscular arrangement : rotator cuff Supraspinatus Infraspinatus Teres minor Subscapularis capsule

50. Mechanism of injury at the shoulder Direct stress Direct stress Ac joint separation Anterior stress anterioinferior dislocation of the humeral head Repeated stress Repeated shoulder rotation motion as the shoulder is placed at 90 degree of abduction Repeated tensile stress on rotator cuff Rotator cuff tendinitis

51. Assignments What are the movements of the scapula? What is Scapular Elevation? What plane does elevation and depression occur in? Why is the Scapulothoracic joint not a true joint? What muscles upwardly rotate the scapula? What are the muscles that elevate the scapula? What muscles cause depression of scapula? What muscles move the scapula?

52. Thanks