Biomechanics of shoulder complex

1. BIOMEHANICS

2. CONTENTS
*Introduction/Components of the Shoulder Complex
*Sternoclavicular Joint
*Acromioclavicular Joint
*Scapulothoracic Joint
*Glenohumeral Joint
-Static Stabilization
-Dynamic Stabilization
*Integrated Function of the Shoulder Complex
-Scapulohumeral Rhythm

3. INTRODUCTION
*Shoulder Complex composed of
the CLAVICLE, SCAPULA + HUMERUS
-links the UE  THORAX - Sternum
*Articular structural design – indicate
Primary Function : Wide ROM mobility
Dynamic Stabilization

4. DYNAMIC STABILIZATION
Exists when a moving segment/ set of segments is limited very
little by passive forces :
articular surface configuration, capsule /ligaments
and
instead relies heavily on active forces / dynamic muscular control
Example – Shoulder Joint

6. COMPONENTS OF SHOULDER COMPLEX
1. Sternoclacicular joint
2. Acromioclavicular joint
3. Glenohumeral joint
4. Scapulothoracic joint – Functional joint
5. Suprahumeral joint – Functional joint

7. ELEVATION: OF THE UPPER EXTREMTY
The Combination of Scapular, Clavicular and Humeral motion
that occurs when arm is raises forward/ to the side
*Sagittal plane flexion
*Frontal plane abduction
*All motion in between
Total Shoulder Complex Motion – Total Elevation
= Motion of the scapula on Thorax [ 1/3 of total motion]
+Motion of the GH joint [2/3 of total motion]
INTEGRATED SHOUDLER COMPLEX FUNCTION:
SCAPULOHUMERAL RHYTHM

8. 1. STERNOCLAVICULAR JOINT
*Connects UE to Axial Skeleton
*Type: Plane Synovial joint /3 DOF
*Has Joint capsule & Disc
*Articular Surfaces
-2 shallow saddle shaped surfaces
Medial end of clavicle
Notch of Manubrium sternum & 1st Costal cartilage

10. Sternoclavicular Disc –
Fibrocartilage disc
*Increases congruence b/w the
articulating surfaces
*Improve joint stability
*Absorb forces transmitted
from lateral end of clavicle to
SC joint

11. Sternoclavicular Joint Ligaments
1. Strong Fibrous capsule – Fairly strong
2. Anterior Sternoclavicular ligament
3. Posterior Sternoclavicular ligament
-Check Anterior & posterior translation of medial end of clavicle
4. Costoclavicular ligament – Bilaminar : Anterior/Posterior
-Limits the elevation of lateral end of clavicle
5. Interclavicular ligament
– Limits excessive depression of the distal clavicle and
Superior gliding of the medial clavicle on the manubrium

13. Sternoclavicular Motions:
Movements of Clavicle
*Elevation & Depression (48/15)
*Protraction & Retraction(15-20/30)
*Anterior & Posterior Rotation (10/50)

14. ELEVATION & DEPRESSION OF THE CLAVICLE

15. PROTRECTION & RETRACTION OF THE CLAVICLE

16. ANTERIOR & POSTERIOR ROTATION OF CLAVICLE

17. 2. ACROMIOCLAVICULAR JOINT
-Attaches Scapula to Clavicle
Type: Plane synovial joint /3 DOF
Articular Surfaces:
Lateral end of Clavicle & Small facet on acromion of the Scapula

19. Acromioclavicular Joint – Ligaments
1.Joint Capsule - weak
2. Acromioclavicular Ligaments – Superior & Inferior
3. Coraco-clavicular ligaments
Limits Superior/Inferior & Anterior / posterior Stability

21. Acromioclavicular Motions
*Internal & External Rotation (30-60)
*Anterior & Posterior Tilting /Tipping (60)
*Upward & Downward Rotation(30/15)

22. INTERNAL & EXTERNAL ROTATION

23. Protraction & Retraction of the Scapula require Internal & External Rotation

24. ANTERIOR & POSTERIOR TILTING/ TIPPING

25. UPWARD & DOWNWARD ROTATION

26. 3. SCAPULOTHORACIC JOINT
-Formed by the articulation of the scapula with the thorax
-Not true anatomic joint
-The SC joint + AC joint : interdependent with ST
Movement at ST joint
 AC joint movement /SC joint movement/Both

27. RESTING POSITION OF THE SCAPULA

28. Motions of the Scapula
1. Upward & Downward Rotation (50-60)
2. Elevation & Depression
3. Protraction & Retraction
4. Internal & External Rotation
5. Anterior & Posterior Tilting

29. UPWARD & DOWNWARD ROTATION

30. ELEVATION & DEPRESSION

31. PROTRACTION & RETRACTION

32. Scapular Elevation coupled
with Anterior tilting
Scapular Depression coupled
with posterior tilting
To follow the Convex Thorax

33. 4. GLENOHUMERUAL JOINT
Most Mobile / Unstable Joint of the human body
Type: Ball-and-Socket Synovial Joint / 3 DOF
Articular Surfaces: The large head of humerus - Distal
The smaller Glenoid fossa – Proximal
Less Articular Congruency  less Joint Stability
More susceptible to Degeneration / Instability

34. GLENOID FOSSA
*Orientation of Glenoid Fossa-
Slightly upward & anterior/posterior
Anteversion – GF faces anterior (10)
Retroversion – GF faces posterior (10)
*Vertical curve > Horizontal curve
*Concavity increased by
articular cartilage + GL

35. HEAD OF THE HUMERUS
– Anatomical resting position
Head faces medially
+
superiorly
+
posteriorly
In relation to the shaft of the humerus & the humeral condyles
When the arms hang at the side – the inferior surface of the
humeral head rests on only a small inferior portion of the
Glenoid fossa

36. HEAD OF THE HUMERUS – Angle of inclination
Formed by an axis through the humeral head and neck in relation
to a longitudinal axis through the shaft of the humerus (N=130-
150 in frontal plane)

37. HEAD OF THE HUMERUS – Angle of Torsion
Formed by an axis through the humeral head and neck in
relation to an axis through the humeral condyles(N= 30
posterior)
Posterior Torsion
Retrotorsion
Retroversion

38. Normal Retroversion of Head of Humerus

39. Reduced Retroversion / Anteversion of head of humerus

40. Increased Retroversion of head of humerus

41. GLENOID LABRUM
-Increases the total articular surface of the Glenoid fossa by
increasing the depth / concavity of the fossa by approx. 50%
FUNCTIONS
*Provides resistance to
humeral head translation
*Protects Bony edges
*Reduces joint friction
*Dissipation/spreading
of joint contact forces
*Provides attachment site for
GH ligaments & Long Head -Biceps

42. Shoulder Joint - Anatomy

43. Shoulder Joint - Anatomy

44. GLENOHUMERAL LIGAMENTS & JOINT CAPSULE
When arm dependent at the side
Joint Capsule - Loose
Taut superiorly
Slack anteriorly & inferiorly
---------------------------------
Tightens with
Humeral abduction + ER
(Closed packed Positon)

45. GLENOHUMERAL LIGAMENTS:
1. Superior Glenohumeral Ligament
2. Middle Glenohumeral Ligament
3. Inferior Glenohumeral Ligament Complex [Anterior band +
posterior band]
4. Coracohumeral Ligament

46. Gleno Humeral Ligaments- At Rest

47. GHL – At 45 Humeral Abduction + Neutral rotation

48. GHL – At 90 Humeral Abduction + Neutral rotation

49. GHL – At 90 Humeral Abduction + External rotation

50. GHL – 90 Humeral Abduction + Medial rotation

51. ROTATOR INTERVAL CAPSULE

52. CORACOACROMIAL ARCH
The coracoacromial/suprahumeral arch is formed by the coracoid
process, the acromion, and the coracoacromial ligament that
spans the two bony projections

53. BURSAE
A fluid filled sac / thin cushions/tiny water balloon, located at
points of friction between a bone and the surrounding soft tissue
such as skin, muscles, ligaments & tendons for lubrication / to
reduce the friction
1. Subacromial Bursa
2. Subdeltoid Bursa
3. Subcoracoid Bursa
4. Subscapular Bursa

54. Glenohumeral Motions: Osteokinematics & Arthrokinematics
OSTEOKINEMATICS
3 DOF
Flexion /Extension [120/50]
Abduction/ Adduction [ 90-120]
Medial Rotation/Lateral Rotation
Scaption: Abduction in the plane of the scapula

55. ARTHROKINEMATICS

56. STATIC STABILIZATION

57. In the dependent arm
*Bony geometry - articular surfaces alone can not maintain
joint stability
*With the humeral head rest on the GF:
Gravity acts caudally/downwards
*To maintain equilibrium  Cranially directed force needed
-Active contraction / passive tension in
Deltoid/ Supraspinatus/ Long head of Biceps ???- Relaxed
-RIC: Rotator Interval Capsule
*Superior Capsule
*Superior Gleno Humeral ligament
*Coracohumeral ligament
-Glenoid Inclination: Anatomical

58. Inadequate Static stabilization : heavily loaded arm
Supraspinatus Activation
Paralysis of Supraspinatus
 Gradual subluxation of GH joint

59. DYNAMIC STABILIZATION
Muscles of Shoulder Complex- Dynamic stabilizers
*Deltoid
*Supraspinatus
*Infraspinatus
*Teres Minor
*Subscapularis
*Long Head of Biceps brachii

60. Shoulder Complex Anatomy - Attachments and Actions

65. DELTOID

66. *Deltoid – a prime mover for GH Abduction [+ Supraspinatus]
*Anterior Fibers  GH - Flexion
Middle Fibers  GH - Abduction
Posterior Fibers  GH – Extension
*Resolution of Deltoid muscle force vector :
-Fx Component :Parallel to long axis of the humerus
 Larger
 Stabilizer
-Fy Component: Perpendicular to long axis of the humerus
 Smaller
Mobilizer

67. *Fx – Parallel muscle force component of Deltoid – if unopposed
Cause the humeral head to impact the coracoacromial arch
before much abduction occurs
*Fy – perpendicular muscle force component of Deltoid
– Not effective
Not be able to cause much abduction
Until the equilibrium of the translatory forces are achieved

68. *Theoretically: 1
Inferiorly directed contact force of the arch
=
Fx component of the Deltoid
Impingement of Subacromial structures  PAIN
Prevent much motion

69. *Theoretically: 2
The Inferior pull of the Gravity
Can not offset the Fx component of the Deltoid
The Resultant Force [ Effort Force]
>>
The Gravitational Force [ Resistance Force]
Rotation

70. HOW ARM ELEVATION IS BEEN ACHIVED???
The Deltoid can’t independently ELEVATE the Arm
Another Force / Set of Forces – to work synergistically with the
Deltoid
For the Deltoid to work effectively
To Produce the desires ROTATION
?????

71. ROTATOR CUFF

72. Rotator Cuff – Muscle force vectors

73. Resolution of RCM Force Vectors

74. *Fy ITS – Perpendicular force component
Cause some Humeral rotation
Compresses the head of the humerus into the Glenoid fossa
*Fx ITS – Parallel force component
Critical :
The Inferior translatory pull of ITS
Nearly Offsets
The Superior translatory pull of the Deltoid
Additional:
Teres Minor + Infraspinatus – Lateral Rotation of Humerus
Subscapularis - Medial Rotation of Humerus

75. The action of the deltoid
and
the combined actions of
the Infraspinatus, Teres minor, and Subscapularis muscles
approximate a force couple
The nearly equal and opposite forces for the deltoid and these
three rotator cuff muscles acting on the humerus approximate an
almost perfect rotation of the humeral head around a relatively
stable axis of rotation

76. *Supraspinatus:
Fx – Parallel force component – Superior translatory
Not able to offset the upward dislocating Deltoid action
Fy – Perpendicular force component - Compressive
Effective Stabilizer of GH joint
Independent Abductor : Larger Moment Arm
Gravity : Stabilizing Synergist

77. *Long head of the Biceps Brachii
Force of Flexion – Neutral Humerus
Force of Abduction – Humerus LR
Reinforce Superior & Middle Glenohumeral ligaments

78. Summary : Dynamic Stabilization
*FOG
*Force of the prime movers - Dynamic
*Force of the muscle stabilizers
*Articular Surface Geometry
*Passive Capsule + Ligaments Forces
*Force of Friction
*Joint Reaction Forces
9-10 Times the Weight of the UE

79. INTEGRATED FUNCTION OF THE SHOULDER
COMPLEX
-
SCAPULOHUMERAL RHYTHM

80. *The Shoulder Complex acts in a coordinated manner to provide
the smoothest & greatest ROM possible to the UE
*The GH motion alone can not achieve full range of elevation of
the humerus
*The remainder of the range is contributed by the scapula on the
thorax through the SC & AC joint motions

81. Significance of Scapulo-Humeral Rhythm
1. Distributes the motions b/w the joints
Allow a large ROM with less compromise of stability
2. Maintains joint congruency
3. Maintains good muscle length - tension relationship
Prevent Active Insufficiency

82. DEFINITION – Scapulo-Humeral Rhythm
An overall ratio of 2 degree of Glenohumeral motion to 1 degree
of Scapulothoracic motion during arm elevation
[ Flexion/Abduction/Scaption]
This Combination of concomitant Glenohumeral &
Scapulothoracic motion is commonly referred to as
SCAPULOHUMERAL RHYTHM

84. PHASES OF SCAPULO-HUMERAL RHYTHM
PHASE – 1:[0- 30] Degree Elevation
GH Joint – 30 Degree
ST Joint [ Clavicular Motion] – Minimal 0-5 Degree
PHASE – 2: [30-90] Degree Elevation
GH Joint – 40 Degree
ST Joint – 20 Degree
PHASE – 3: [90-180] Degree Elevation
GH Joint – 50-60 Degree
ST Joint – 30-40 Degree

85. Scapulo Thoracic Contribution:
to ELEVATION of the Humerus
-By upward rotation of the Glenoid fossa 50-60 degree from its
resting position
Gleno-Humeral Contribution:
to ELEVATION of the Humerus
-100-120 of Flexion / 90-120 of Abduction
Maximum Range of ELEVATION : 150-180
Lateral Rotation – 50

86. Sternoclavicular + Acromioclavicular Contributions
ST upward Rotation
Coupled with
Clavicular Posterior Rotation
+
Clavicular Elevation
At SC joint

87. ST upward rotation
Coupled with
Scapula – Posterior Tilting [20-30]
+
Initially-Scapular Int. Rotation
&
End Range – Scapular Ext. Rotation [25]
At AC Joint

88. Integrated
movement
during
elevation

89. 50% From SC Joint : 20 30 Degree of ST upward Rotation
50% From AC Joint : 20-30 Degree of ST upward Rotation
-------------------------------------------------
Variations in Scapulohumeral Rhythm
GH Motion : ST Motion Ratio -- 1.25:1  2.69:1

90. Upward Rotators of the Scapula
The motions of the scapula are primarily produced by a balance of
the forces between the trapezius and Serratus anterior muscles

91. MUSCLES
OF
ELEVATION & DEPRESSION

96. ELEVATORS
*Deltoid
*Supraspinatus
*Infraspinatus
*Teres Minor
*Subscapularis
*Upper & Lower trapezius
*Serratus Anterior
*Rhomboids – Minor & Major

97. DELTOID
*Scapular plane abduction- anterior and middle deltoid
*Posterior deltoid has smaller MA
and
thus less effective in frontal plane abduction
*Maintenance of appropriate length-tension relationship of
deltoid is dependent on scapular position/movement and
stabilization.
For example:
when scapula cannot rotate, there is more shortening of deltoid
and thus loss of tension, which causes elevation to up to 90
degrees only.

98. Supraspinatus
*Primary function - to produce abduction with deltoid muscle.
[MOBILIZER]
*Secondary function: acts as a ‘steerer’ of humeral head
and
helps to maintain stability of dependent arm.
[STABILIZER]

99. Infraspinatus + Teres minor + Subscapularis
* These muscle function gradually increases from- 0-115 degrees of
elevation after which (115-180 degrees) it dropped.
*In the initial range of elevation, [I +T]
work to pull the humeral head down,
and
during the middle range,
act to externally rotate for clearing greater tubercle
under coracoacromial arch.
* Subscapularis helps as internal rotator when arm is at side and
during initial range and
With more abduction, its inter rot capacity decreases.

100. UPPER AND LOWER TRAPEZIUS + SERRATUS ANTERIOR
*This force couple produces upward rotation of scapula.
*When the trapezius is intact and the Serratus anterior muscle is paralyzed
active abduction of the arm can occur through its full range,
although it is weakened.
*When the trapezius is paralyzed
(even though the Serratus anterior muscle may be intact),
active abduction of the arm is both weakened and limited in range
with remaining range occurring exclusively at the GH joint.
*Without the trapezius (with or without the Serratus anterior muscle),
the scapula rests in a downwardly rotated position
as a result of the unopposed effect of gravity on the scapula.

101. How SA and trap work with deltoid??
The Serratus anterior and trapezius muscles are prime movers
for upward rotation of the scapula.
These two muscles are also synergists for the deltoid during
abduction at the GH joint.
The trapezius and Serratus anterior muscles,
as upward scapular rotators,
prevent the undesired downward rotatory movement of the
scapula by the middle and posterior deltoid segments that are
attached to the scapula.

102. Rhomboid
It works eccentrically to control upward rotation of the scapula
produced by the trapezius and the Serratus anterior muscles.
It adducts the scapula with lower traps to offset the lateral
translation component of the Serratus anterior muscle.

103. DEPRESSORS
*Latissimus Dorsi
*Pectorals – Major & Minor
*Teres Major

104. CLINICAL CONNECTION:
PATHOMECHANICS
*RCI – Rotator Cuff Injury
-Stain /tear of RC muscles
-Common in baseball pitcher/swimmers/racket sports
-Degeneration/improper lifting
*Shoulder Dislocation
*Glenoid Labrum Tear  Shoulder Dislocation