anatomy of shoulder and biomechanics

1. Shoulder complex
SUNIL
C.P.R.S (JMI)

2. Introduction
• The shoulder complex is intricately designed
combination of three joints
• The shoulder complex is designed primarily for
mobilty
• The shoulder complex is one of the most
common peripheral joints to be treated in
physical therapy clinics
• The shoulder is capable of moving in more than
16,000 positions differentiated by 1 degree in
normal individual

3. Introduction

4. Osteology
• Sternum
• Clavicle
• Scapula
• Proximal to Mid Humerus

5. Sternum

6. Clavicle

7. Scapula

8. Humerus

9. Arthrology
• Four joints within the shoulder complex are
1. Sternoclavicular joint
2. Acromioclavicular joint
3. Scapulothoracic joint
4. Glenohumeral joint

10. Sternoclavicular Joint
Articular surfaces
 Medial end of clavicle
 Clavicular facet on
sternum
 Sup. Border of the
cartilage of first rib.

11. • SC joint is subjected to unique functional
demands that are met by a complex saddle
shaped articular surface.
• Tremendous individual difference exist across
people and the saddle shape of these surfaces
exist across people and the saddle shape of
these surfaces is very subtle, the SC joint is
often classified as plan synovial joint.
• Links axial skeletal with appendicular skeleton.

12. Tissues that stabilizes the SC joint

13. • The following tissues stabilizes the SC joint
1. Anterior and Posterior Sternoclavicular
ligament
2. Interclavicular ligament
3. Costoclavicular ligament
4. Articular Disc

14. Sternoclavicular Disk
• The articular disc at the SC joint separates the
joint into distinct medial and lateral joint
cavities
• The disc is flattened piece of fibrocartliage
that attaches inferiorly near the lateral edge of
clavicular facet and superiorly at the head of
clavicle and interclavicular ligament

15. • The remaining outer edge of the disc attaches
to the internal surface of the capsule
• The disc functions as shock absorber within
the joint by increasing the surface area of
joint

16. SC joint Ligaments
Sternoclavicular ligament
• The anterior and posterior sternoclavicular
ligaments reinforce the capsule
• They function primarily to check anterior and
posterior translatory movement of the medial
end of clavicle

17. Costoclavicular Ligament
• The ligament is a strong structure extending
from the cartilage of the first rib to the costal
tuberosity on the inferior surface of clavicle
• The ligament has two distinct fiber bundle
running perpendicular to each other
• The anterior bundle runs obliquely in a
superior and lateral direction, the posterior
bundle runs obliquely in superior and medial
direction
• This ligament firmly stabilizes the SC joint and
limits the extreme of all Clavicular motion

18. Interclavicular ligament
• The Interclavicular ligament spans the jugular
notch and connects the medial end of the
right and left clavicles
• The Interclavicular ligament resists excessive
depression of the distal clavicle and superior
glide of the medial end of the clavicle

19. Kinematics of SC joint
• The Osteokinematics of Sc joint are defined
for three degrees of freedom.
• Each degree of freedom is associated with one
of the three cardinal planes: Saggital, Frontal
and Horizontal
• Osteokinematics of SC joint includes
1. Elevation and Depression
2. Protraction and Retraction
3. Axial rotation of the clavicle

21. Arthrokinematics of SC joint
A. Elevation B. Depression

22. • Arthrokinematics during
retraction of Scapula
around the right SC
joint

23. Acromioclavicular Joint
A. Anterior view B. Posterior View

24. Acromioclavicular Joint
Articular surfaces
 Lateral end of clavicle
 Small facet on acromion
of scapula

25. Tissues that Stabilizes the AC joint

26. • The following Structres stabilizes the AC joint
1. Superior and Inferior AC joint capsule
2. Deltoid and Upper Trapezius
3. Coracoclavicular ligament
4. Articular disc

27. AC joint Ligaments
Superior and Inferior AC joint capsular
ligaments
• They together reinforce the capsule
• The superior AC ligament assists the capsule in
opposing articular surfaces and in controlling
A-P joint stability
• The superior capsular ligament is reinforced
through attachments from the deltoid and
trapezius

28. Coracoclavicular ligament
• The coracoclavicular ligament provides
additional stability to the AC joint
• This ligament firmly unites the clavicle and the
scapula providing joint stability
• The extensive ligament consists of trapezoid
and conoid ligaments
• The Trapezoid ligament extends in a superior
lateral direction from the superior surface of
the coracoid process to the trapezoid line on
the clavicle

29. • The conoid ligament extends almost vertically
from the proximal base of the coracoid
process to the conoid tubercle on the clavicle

30. Acromioclavicular Disc
• The articular surfaces at the AC joint are lined
with a layer of fibrocartilage and often
separated by a complete or incomplete
articular disc
• An extensive dissection of 223 sets of AC joint
revealed complete discs in only 10% of joints

31. A cross section of the AC joint shows the
disc

32. Kinematics of AC joint
• AC joint permits subtle and often slight
movement of the scapula
• The motion of the scapula at the AC joint are
described in three degrees of freedom
• The AC joint influences and is also influenced by
rotation of the clavicle around its long axis
• Osteokinematics of the AC joint includes
1. Upward and Downward rotation
2. Internal and External rotation
3. Anterior and Posterior tipping

33. The Acromioclavicular rotatory axes of
motion

34. Osteokinematics of AC joint

36. Scapulothoracic Joint
• The ST joint is an a typical joint which lacks all
the traditional characteristics of a joint except
one that is motion
• The primary role of this joint is to amplify the
motion of GH joint

37. Movements at the scapulothoracic joint
• Elevation and depression
• Protraction and retraction
• Upward and downward rotation

41. ST joint: A composite of the AC and SC
joint

44. Glenohumeral Joint
Articular Surfaces
 Large convex head of
the humerus
 Shallow concavity of the
glenoid fossa

45. • An axis through the humeral head and neck in
relation to a longitudinal axis through the
shaft of the humerus forms an angle of 130 to
150 degrees in the frontal plane. This is
commonly known as Angle of Inclination
• In transverse plane, the axis through the
humeral head and neck in relation to the axis
through the humeral condyles forms an angle
known as Angle of torsion
• Angle of torsion is usually described as
approximately 30degrees posteriorly

46. • The normal posterior position of the humeral
head with regard to humeral condyles may be
termed posterior torsion, retroversion or
retrotorsion of the humerus
• Humeral retroversion influences the range of
IR and ER

47. Angle of Inclination Angle of torsion

48. Tissues that Stabilizes the GH joint

49. • The following structres stabilizes the GH joint
1. Rotator cuff muscles
2. GH joint capsular ligaments
3. Coracohumeral ligament
4. Long head of Biceps
5. Glenoid labrum

50. Glenoid Labrum
• The total available articular surface of the
glenoid fossa is enhanced by an accessory
structure, the Glenoid Labrum
• This structure surrounds and is attached to
the periphery of the glenoid fossa enhancing
the depth or curvature of the fossa by
approximately 50%

51. • The labrum is superiorly is loosely attached
whereas the inferior portion is firmly attached
and relatively immobile
• The glenoid labrum also serves as the
attachment site for the glenohumeral
ligament and the tendon of the long head of
the biceps brachii

52. Glenohumeral Capsule and
Ligaments

54. Glenohumeral Capsule
• The entire GH joint is surrounded by a large,
loose capsule that is taut superiorly and slack
anteriorly and inferiorly in the resting position
of arm
• The capsule attaches along the rim of the
glenoid fossa and extends to the anatomic
neck of the humerus

55. • The potential volume of space within the GH
joint capsule is about twice the size of the
humeral head
• In anatomic or adducted position the inferior
portion of capsule appears as a slackened
recess called axillary pouch
• When the humerus is abducted and laterally
rotated on the glenoid fossa the capsule twists
on itself and tightens making it close-pack
position of the joint

56. Glenohumeral Ligaments

57. Coracoacromial Arch

58. • The coracoacromial arch is formed by the
coracoacromial ligament, coracoid process
and acromion process of the scapula
• The coracoacromial arch functions as the roof
of the GH joint
• The subacromial space contains the
supraspinatus muscle and tendon, the
subacromial bursa, the long head of the
biceps, and part of the superior capsule

59. Associated Bursa

60. Kinematics of GH joint
• The GH joint has three degrees of freedom
• Osteokinematics of the GH joint includes
1. Abduction and Adduction
2. Flexion and Extension
3. Internal and External rotation

62. Arthrokinematics
• Arthrokinematics during
right shoulder
abduction

63. • Arthrokinematics during
flexion of the GH joint

64. • Arthrokinematics during
active external rotation
of the GH joint

65. Importance of Roll and Slide
Arthrokinematics at the GH joint

67. Scapulohumeral Rhythm

68. • A natural kinematic rhythm or timing exists
between GH abduction and Scapulothoracic
upward rotation
• Inman reported this rhythm as constant
throughout abduction, occurring at a ratio of
2:1
• For every 3 degrees of shoulder abduction, 2
degrees by GH joint abduction and 1 degree by
ST joint upward rotation

70. Static Stability of GH joint
• When standing at rest with arms at side the
head of humerus remains stable against the
glenoid fossa. This stability is referred to as
static stability
• At rest superior capsular structures including
the coracohumeral ligament provide primary
stabilizing forces between humeral head and
glenoid fossa

71. • Electromyographic (EMG) data suggest that
the supraspinatus provides a secondary
source of static stability by generating active
forces that are directed nearly parallel to the
SCS force vector
• Basmajian and Bazant showed that vertically
running muscles such as the biceps, triceps
and middle deltoid are not actively involved in
providing static stability even significant
downward traction is applied to the arm

72. Static stability of GH joint
• The rope indicates a
muscular force that holds
the glenoid fossa in a
slightly upyward rotated
position
• The passive tension in the
taut superior capsular
structres(SCS) is added to
the force produced by
gravity (G) yeilding the
compression force (CF)

73. • With a loss of upward rotation
posture of the scapula, the
change in the angle between
the SCS and G vectors reduces
the magnitude of the
compressive force across the
GH joint
• As a result the head of the
humerus slides down the now
vertically oriented glenoid
fossa

74. Dynamic Stability of GH joint
• The contradictory requirements on the
shoulder complex for both mobility and
stability are met through active forces or
Dynamic Stabilization

75. The Deltoid and Glenohumeral
Stabilization
• The action lines of three segments of the
deltoid acting together coincide with the
fibers of the middle deltoid
• Majority of the force of contraction of the
deltoid causes the humerus head to translate
superiorly
• A force component parallel to the long bone
has a stabilizing effect

76. • The articular surface of the humerus is not
line with the shaft of humerus
• As a result the force applied parallel to the
long bone creates a shear force rather than
the stabilizing effect

77. The Rotator Cuff and GH
Stabilization

80. Muscles and Joint Interaction
• Muscles of Shoulder joint falls into two
categories
a) Proximal Stabilizers
b) Distal Mobilizers

81. Proximal Stabilizers
• The proximal Stabilizers
consist of muscles that
originate on the spine, ribs,
cranium, and insert on
clavicle and scapula.
• Examples are Trapezius and
Serratus anterior
Distal Mobilizers
• The Distal Stabilizers consist
of muscles that originate on
the scapula and clavicle and
insert on the humerus or
forearm
• Examples are deltoid and
biceps brachii

82. • Muscles of the Scapulothoracic Joint
A. Elevators of the SC joint
B. Depressors of the SC joint
C. Protractors of the SC joint
D. Retractors of the SC joint
• Muscles that elevate the arm

83. Elevators of the ST joint
• The muscles responsible for elevation of the
Scapula are the Upper trapezius, levator
scapulae, and to a lesser extent the
rhomboids

85. Depressors of the ST joint
• Depression of the ST joint is performed by the
lower trapezius, pectoralis minor, and the
subclavius

87. Protractors of the ST joint
• The serratus anterior is the prime protractor
of the ST joint
• The force of scapular protraction is usually
transferred across the GH joint and employed
for forward pushing and reaching activities

89. Retractors of the ST joint
• The middle trapezius muscle is the primary
retractor of the ST joint
• The rhomboids and the lower trapezius
muscles function as secondary retractors

91. Muscles that Elevate the Arm
• The term “elevation” of the arm describes the
active movement of bringing the arm
overhead without specifying the exact plane
of motion

92. • Elevation of the arm is performed by muscles
that fall into three groups
A. Muscles that elevate (i.e. abduct or flex) the
humerus at the GH joint
B. Scapular muscles that control the upward
rotation of the ST joint
C. Rotator cuff muscles that control the
dynamic stability of the GH joint

93. Muscles that elevate the arm at the
GH joint
• The prime muscles that abduct the GH joint
are Anterior deltoid, Middle deltoid,
Supraspinatus muscles
• Elevation of the arm through flexion is
performed primarily by Anterior deltoid,
Coracobrachialis, and long head of biceps

96. Upward Rotators at the ST joint
• Upward rotation is an essential component of
elevation of the arm
• To varying degrees Serratus anterior and all
parts of Trapezius cooperate during the
upward rotation

98. • The mechanics of the
upward rotation force
couple are similar to the
mechanics of three
people walking through
a revolving door

99. Function of Rotator Cuff muscles
during elevation of arm
• The RC group muscles include Subscapularis,
Supraspinatus, Infraspinatus, and Teres minor
• All these muscles show significant EMG
activity when the arm is raised
• The EMG reflects the function of these
muscles as
Regulators of the dynamic stability
Controllers of the arthrokinematics

100. Muscles that Adduct and Extend
the Shoulder
• The primary muscles for shoulder adduction
and extension are Teres major, Long head of
Triceps, Posterior Deltoid, Infraspinatus, Teres
minor, Latissimus dorsi, and Pectoralis major

103. Muscles that Internally and
Externally Rotate the Shoulder
Internal Rotator muscles
• The primary muscles that internally rotate the
GH joint are Subscapularis, Anterior deltoid,
Pectoralis major, Latissimus dorsi, and Teres
major
• The total mass of the shoulder’s Internal
rotators is much greater than the External
rotators

105. • External Rotator Muscles
• The primary muscles that externally rotate the
GH joint are Infraspinatus, Teres minor, and
Posterior deltoid
• The Supraspinatus can assist with ER provided
the GH joint is between neutral and full
external rotation
• The ER’s are a relatively small percentage of
the total muscle mass at the shoulder

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