shoulder biomechanics

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

2. Shoulder Motion
• Flexion - 150 - 1800
• Extension - 50 - 600
• Abduction - 150 - 1800
• External rotation - 900
• Internal rotation - 70 - 900
• Horizontal abduction
• Horizontal adduction
Combined Movements:

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

4. Glenohumeral Motion
• Passive restraints
• Active restraints
Controlled by:

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

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

7. Capsuloligamentous Structures
Glenohumeral ligaments:

8. Capsuloligamentous
Structures
• Coracohumeral ligament
• anterior band
• posterior band

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

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

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

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

13. Arthrokinematics of
Glenohumeral Joint

14. Glenohumeral Motion
Convex - Concave Rule:

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

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. Glenohumeral Motion
Results in Abnormal
Arthrokinematics
Capsular Tightness:

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

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

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

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

24. Subscapularis
• 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
• 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
• Essential force
couples maintained
• Normal strength &
function possible
Supraspinatus:

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

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

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
• 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
Clinical Relevance:

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

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
• Axial rotation of clavicle
(spin)
• Angulation between scapula
& clavicle
Movements:

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

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

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

48. Scapular Rotation
• 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
Phase I

49. Scapular Rotation
• 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
Phase II

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