1. Anatomy & Biomechanics of the Shoulder
James J. Irrgang, Ph.D., PT, ATC
Department of Physical Therapy
University of Pittsburgh

2. Shoulder Motion Combined Movements: Flexion - 150 - 1800
Extension
Abduction
External rotation - 900
Internal rotation
Horizontal abduction
Horizontal adduction

3. Shoulder Girdle Includes: G-H joint A-C joint S-C joint S-T joint
Subacromial space

4. Glenohumeral Motion Controlled by: Passive restraints
Active restraints

5. Glenohumeral Motion Passive Restraints: Bony geometry Labrum
Capsuloligamentous structures
Negative intra-articular pressure

6. Capsuloligamentous Structures
Glenohumeral ligaments:
SGHL
MGHL
IGHL complex
anterior band
posterior band
axillary pouch

7. Capsuloligamentous Structures
Glenohumeral ligaments:

8. Capsuloligamentous Structures
Coracohumeral ligament
anterior band
posterior band

9. Restraints to External Rotation
Dependent on arm position:
00 - SGHL, C-H & subscapularis
450 - SGHL & MGHL
900 - anterior band IGHLC

10. Restraints to Internal Rotation
Dependent on arm position:
00 - posterior band IGHLC
450 - anterior & posterior band IGHLC
900 - anterior & posterior band IGHLC

11. Restraints to Inferior Translation
Dependent on arm position:
00 - SGHL & C-H
900 - IGHLC

12. Glenohumeral Motion Scapular Plane: Flexion/extension - 1200
Abduction/adduction
External/internal rotation
Horizontal abduction/ adduction

13. Arthrokinematics of Glenohumeral Joint

14. Glenohumeral Motion
Convex - Concave Rule:

15. Glenohumeral Motion Arthrokinematics: Abduction Flexion Extension
External rotation
Internal rotation

16. Glenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990

17. Glenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990

18. Glenohumeral Motion
Arthrokinematics:
Harryman et. al. 1990

19. Results in Abnormal Arthrokinematics
Glenohumeral Motion
Capsular Tightness:
Results in Abnormal Arthrokinematics

20. Glenohumeral Motion
Normal Arthrokinematics:
Combines rotation & translation to keep humeral head centered on glenoid

21. Scapulohumeral Muscles
Prime Movers:
Deltoid
Pectoralis major
Latissimus dorsi
Teres major
Biceps
Coracobrachialis
Triceps

22. Scapulohumeral Muscles
Rotator Cuff:
Subscapularis
Supraspinatus
Infraspinatus
Teres Minor

23. Rotator Cuff Function Approximates humerus to function
Supraspinatus assists deltoid in abduction
Subscapularis, infraspinatus & teres minor depress humeral head

24. Subscapularis Turkel et. al. JBJS 1981
Effective restraint to ER with arm at side
Ineffective restraint to ER with arm abducted to 900
Turkel et. al. JBJS 1981

25. Infraspinatus/Teres Minor
Reduces strain on anterior band of IGHLC
“Hamstrings” of glenohumeral joint
Cain et. al. AJSM 1987

26. Long Head of Biceps Rodosky et. al. AJSM 1994
Biceps tendon force increases torsional rigidity to ER
No effect on strain of IGHLC
Effect lost with SLAP lesion
Rodosky et. al. AJSM 1994

27. Biceps Becomes More Important Anterior Stabilizer as Capsuloligamentous Stability Decreases
Itoi et. al. JBJS 1994 &
Glousman et. al. 1988

28. Force Couples Acting on Glenohumeral Joint
Transverse plane - anterior vs. posterior RC
Coronal plane - deltoid vs. inferior RC

29. Rotator Cuff Tear Supraspinatus: Essential force couples maintained
Normal strength & function possible

30. Rotator Cuff Tear Supraspinatus/Posterior Cuff:
Essential force couples disrupted
Weakness with external rotation
Little active elevation possible

31. Rotator Cuff Tear Massive Tear : Essential force couples disrupted
Weakness with internal & external rotation
Little active elevation possible

32. Subacromial Space

33. 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

34. 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

35. Subacromial Space Clinical Relevance: Primary impingement:
structural stenosis of subacromial space
Secondary impingement:
functional stenosis of subacromial space due to abnormal arthrokinematics

36. Scapulothoracic Joint

37. Scapulothoracic Muscles
Trapezius
Serratus anterior
Rhomboids
Levator scapulae
Pectoralis minor
Subclavius

38. Scapulothoracic Motion
Elevation/depression
Protraction/retraction
Upward/downward rotation

39. Force Couple at Scapulothoracic Joint
Serratus anterior produces anterio-lateral movement of inferior angle
Upper trapezius pulls scapula medially

40. Scapulohumeral Rhythm
Total elevation:
1200 at G-H joint
600 at S-T joint

41. Force Couple at Scapulothoracic Joint
Serratus anterior produces anterio-lateral movement of inferior angle
Upper trapezius pulls scapula medially

42. Acromioclavicular Joint

43. Acromioclavicular Joint
Joint capsule
A-C ligaments
Intra-articular disc
Coracoclavicular ligaments
conoid (medial)
trapezoid (lateral)

44. Acromioclavicular Joint
Movements:
Axial rotation of clavicle (spin)
Angulation between scapula & clavicle

45. Sternoclavicular Joint
Joint capsule
Anterior & posterior S-C ligaments
Intra-articular disc
Interclavicular ligament
Costoclavicular ligament

46. Sternoclavicular Joint
Motions:
Protraction/retraction
Elevation/depression
Axial rotation (spin)

47. Biomechanics of Scapular Rotation
Scapulothoracic motion occurs as part of closed kinetic chain involving:
A-C joint
S-C joint

48. 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

49. 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

50. Scapular Rotation Necessary to: Enhance glenohumeral stability
Elevate acromion to avoid impingement
Maintain effective length tension relationship of scapulohumeral muscles
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