The document provides an in-depth analysis of the shoulder joint complex, emphasizing its structural components like the clavicle, humerus, and scapula, and their interdependent linkages. It details the mechanics and movements of the sternoclavicular and acromioclavicular joints, as well as the glenohumeral joint dynamics, including various motions and stabilization mechanisms. Additionally, it outlines the roles of ligaments, muscular contributions, and implications for shoulder injuries and joint stress tolerance.

3. Introduction
 Shoulder joint (GH joint) has more mobility
than stability.
 Only SC joint connects the components of
shoulder joint to the axial skeleton. This puts
greater demands on the muscles for securing
the shoulder girdle on thorax during static and
dynamic conditions (dynamic stabilization).

4. Components of shoulder complex
 Clavicle, humerus and scapula are linked
with 3 interdependent linkages: SC joint, AC
joint & GH joint.
 Additionally a functional joint called
scapulothoracic joint ( ST joint) is considered as
a part oh shoulder complex.

5. Components of shoulder complex

6. MOVEMENTS
 Elevation: Sagittal plane flexion and frontal
plane abduction and all the motions in
between.
1/
3
ST
GH
2/
3

8. STERNOCLAVICULAR JOINT
 Movement of the clavicle at the SC joint
inevitably produces movement of the scapula
under conditions of normal function, because
the scapula is attached to the lateral end of the
clavicle.
 SC joint is a plane synovial joint, with 3
rotatory and 3 translatory degrees of
freedom.

9. SC articulating surface:
 The SC articulation consists of two saddle-
shaped surfaces, one at the sternal or medial
end of the clavicle and one at the notch
formed by the manubrium of the sternum and
first costal cartilage.
 It is a plane synovial joint.
 The articulating surfaces are incongruent.
 The superior portion of the clavicle does not
makes any contact with the manubrium,
instead it serves as an attachment site for SC
disk and interclavicular ligaments.

12. Sternoclavicular disk
 It is a fibrocartilaginous disk to increase
the congruency b/w incongruent articular
surfaces.
 Attachment: upper portion is attached to the
postero- superior clavicle and the lower portion
is attached to the manubrium and first
costal cartilage.
 The disk diagonally transects the SC joint
space
and divides the joint into 2 separate cavities.

13.  The disk is considered part of the manubrium
in elevation/depression and thus the upper
attachment of the disk serves as pivot point and
the disk acts as the part of the clavicle in
protraction/ retraction with lower attachment
serving as pivot point.
 The axis of motions of SC joint
elevation/depression and protraction/retraction
is located lateral to the SC joint, on the
costoclavicular ligament.
 The disk functions to absorb the medially
directed force transmitted along the clavicle
from its lateral end.

14. Sternoclavicular joint capsule and
ligaments
 Sc joint is supported by fibrous
capsule
 3 ligaments:
 Sternoclavicular
ligament
 Costoclavicular
ligament
 Interclavicular
ligaments
ANTERIOR
POSTERIOR
ANTERIOR
LAMINA
POSTERIOR
LAMINA

16. Sternoclavicular motions
 3 rotatory degrees of freedom:
 Elevation/depression
 Protraction/retraction
 Anterior/posterior rotation of clavicle
 3 degrees of translatory motion at the SC
joint (very small in magnitude):
 Anterior/posterior
 Medial/lateral
 Superior/inferior

17. Elevation/depression of clavicle

18.  Clavicular elevation= upto 48 degrees
 Passive clavicular depression= less than 15
degrees

19. Protraction/retraction of clavicle

20.  protraction= 15-20
degrees
 Retraction= 20-30
degrees

21. Anterior and Posterior Rotation of
the Clavicle

22.  Posterior rotation= 50 degrees
 Anterior rotation= less than 10
degrees

23. Sternoclavicular stress tolerence
 Although the SC joint is considered
incongruent, the joint does not undergo the
degree of degenerative change common to the
other joints of the shoulder complex.
 Strong force-dissipating structures such as
the SC disk and the costoclavicular ligament
minimize articular stresses and also prevent
excessive intra- articular motion that might
lead to subluxation or dislocation.

25. AC JOINT
 Plane synovial joint
 3 rotational and 3 translational degrees of
freedom
 The primary function of the AC joint is to allow
the scapula additional range of rotation on
the thorax and allow for adjustments of the
scapula (tipping and internal/external rotation)
outside the initial plane of the scapula in order
to follow the changing shape of the thorax as
arm movement occurs.
 In addition, the joint allows transmission of

26. AC articulating surface
 Incongruent surfaces
 Variation in
inclination of
articulating surface:
flat, reciprocally
concave-convex, or
reversed
(reciprocally
convex-concave).

27. AC joint disk
 Through 2 years of age, the AC joint is
actually a fibrocartilaginous union.
 With use of UE progressively, a joint space
develops on each articulating surface that may
leave a meniscoid fibrocartilage remnant
within the joint.

28. AC joint capsule and ligaments
 Superior acromioclavicular
ligament
 Inferior acromioclavicular
ligament
 Coracoclavicular
ligament
TRAPEZOID
(LATERAL)
CONOID
(MEDIAL
)

30.  The capsule of the AC joint is weak and cannot
maintain integrity of the joint without
reinforcement of the superior and inferior
acromioclavicular and the coracoclavicular
ligaments.
 Superior AC ligament is reinforced by
aponeurotic extensions from deltoid and
trapezius.

31.  Trapezoid portion: oriented more
horizontally. It resists posterior forces on
distal clavicle
 Conoid portion: oriented more vertically. It
resists superior and inferior forces
 Both limit upward rotation of scapula on AC
joint.
 Prevents medial displacement of
acromion on clavicle when leaning on 1
hand
 CC lig helps in coupling post clavicular rot

33. AC motions
 3 rotatory motions:
 Internal/external rotation
 Anterior and posterior
tipping
 Upward and downward
rotation
 3 translatory motions:
 Anterior/posterior
 Medial/lateral
 Superior/inferior

34. Axis and planes for AC joint
motions

35. Internal/external rotation

36. While elevating the arm
 Protraction and
retraction of the
scapula require
internal and external
rotation, respectively,
for the scapula to
follow the convex
thorax and orient the
glenoid fossa with the
plane of elevation.

37.  Smaller values (20 to 35 degrees) have been
reported during arm motions, although up to
40 to 60 degrees may be possible with full-
range motions reaching forward and across
the body.

38. Anterior and posterior tipping

39. While elevating the arm
 The scapula posteriorly tips on thorax as the
scapula is upwardly rotating.

40.  The magnitude of anterior/posterior tipping
during elevation of arm is approx 30 degrees.
 Although in maximal flexion and extension,
ant/post tipping can reach up to 40 degrees or
more

41. Upward and downward rotation

42.  Upward rotation=30
degrees
 Downward rotation=17
degrees

43. Acromioclavicular stress tolerence
 AC joint is susceptible to trauma and
degenerative changes because of Smaller and
incongruent surfaces.
 It is commonly found in 2nd decade to 6th
decade of life.

45. ST JOINT
 It is not a true anatomic joint.
 The functional ST joint is part of a true closed
chain with the AC and SC joints and the
thorax.

46. RESTING POSITION OF SCAPULA

47. Resting position of scapula
 2 inches from midline
b/w
2nd and 7th rib.
 Internally rot -30-
45 degrees from
coronal plane.
 Ant tipped -10-
20degrees from
frontal plane
 Upward rotated - 10-
20 degrees from
sagittal plane

48.  The linkage of the scapula to the AC and SC joints,
however, actually prevents scapular motions
both from occurring in isolation and from
occurring as true translatory motions.
 Eg. When the arm is abducted, scapula
undergoes upward rotation, external
rotation and posterior tipping (all movts in
combination).

49. MOTIONS OF THE SCAPULA
 Upward rotation
 Elevation/depression
 Protraction/retraction
 Internal /external
rotation

50. UPWARD ROTATION
 Approx. 60 degrees
of upward rotation
of the scapula on the
thorax is typically
available.
 Upward rotation of
the scapula is
produced by
clavicular elevation
and posterior
rotation at the SC
joint and by
rotations at the AC

51. ELEVATION/DEPRESSION
 Elevation and depression
of the scapula are
produced by
elevation/depression of
the clavicle at the SC
joint and requires subtle
adjustments in
anterior/posterior
tipping and
internal/external
rotation at the AC joint to
maintain the scapula in
contact with the thorax.

52. PROTRACTION/RETRACTION
 Protraction and
retraction of the
scapula are produced
by
protraction/retractio
n of the clavicle at
the SC joint, and by
rotations at the AC
joint to produce
internal rot & ant
tipping.

53. Internal/external rotation
 Internal/external rotation
of the scapula on the
thorax should normally
accompany protraction/
retraction of the clavicle
at the SC joint.
 Internal rotation of the
scapula on thorax which
occurs only at the AC
joint, will result in the
prominence of the
vertebral border of
scapula. (WINGING OF
SCAPULA-suggestive of
impaired
neuromuscular control
of ST muscles ).

55. GH ARTICULATING SURFACE
 Scapula-
 Glenoid fossa is oriented/facing upwards
and 6-7 degrees retroverted.
 The radius of curvature of the fossa is increased
by articular cartilage that is thinner in the
middle and thicker on the periphery, which
improves congruence with the much larger
radius of curvature of the humeral head.

56.  Humerus-
 The head faces medially, superiorly, and
posteriorly with regard to the shaft of the
humerus and the humeral condyles.
 ANGLES:
 Angle of inclination=130-150 degrees
 Angle of torsion=30 degrees posteriorly

57. Angle of
inclinatio
n
Angle
of
torsio
n

58.  Because of the internally rotated resting position
of the scapula on the thorax, retroversion of the
humeral head increases congruence of the GH
joint.
 Reduced retroversion of humeral head
(anteversion)- increases ROM for internal
rotation and decreases ROM for external rotation
and has a tendency to produce anterior GH
subluxation.
 Vice versa for increased retroversion of humeral
head.

59. Subluxation of shoulder

60. GLENOID LABRUM
 Enhance the depth
or curvature of the
fossa by 50%.
 It is a redundant fold
of dense fibrous
connective tissue
with little
fibrocartilage.
 It is attached to
glenohumeral
ligament and long
head of biceps
brachii.

61. GH CAPSULE & LIGAMENTS
 GH Capsule laxity is
required for large
excursions of
shoulder joint.
 But capsule gives
less stability alone
and its work has
to be reinforced
by GH ligaments.

62. GH ligament
 Superior
 Middle
 Inferior
 Coracohumeral
lig
 Foramen of
weitbrecht- area
of weakness in
the capsule.

63. Rotator interval capsule
 superior GH ligament,
the superior capsule,
and the
coracohumeral
ligament are
interconnected
structures that bridge
the space between the
supraspinatus and
subscapularis muscle
tendons- rotator
interval capsule.

64. Inferior GH ligament complex
 Inferior GH ligament
has 3 parts:
 Anterior bands
 Axillary pouch
 Posterior bands

65. Function of GH ligament
• Limits ant and inf translation in
arm at 0 degrees of abduction
Superior GH
Lig
• Limits anterior translation at
arm 45 degrees abduction
Middle GH
Lig
• Limits ant translation beyond 45
degrees abduction + external
rotation
Anterior band
of IGHLC
• Limits posterior translation with
arm 45 degrees abd+ internal
rotation
Posterior
band of
IGHLC

66. Coracoacromial arch

67. Coracoacromial arch
 Contents under coracoacromial arch:
subacromial bursae, rotator cuff tendons
and portion of long head of biceps brachii.
 Also called as supraspinatus outlet/
subacromial space
 Normally, it is 10 mm wide, but reduces to
5mm on elevation of arm.
 Repetitive overhead activity can cause
painful impingement syndrome.

68. Bursae
 Subacromi
al
 Subdeltoi
d
Subacromi
al
bursae

69. Glenohumeral motions.
MOTIONS ROM available
Flexion 120
Extension 50
Abduction 90-120
Adduction
External rotation 60 degrees of combined motions
(arm
at side)
120 degrees of combined
motions ( arm at 90 degrees
abducted)
Internal rotation -

70.  For complete range of abduction to occur, there
must be 35-40 degrees of lateral rotation, for
the clearance of greater tubercle under the
Coracoacromial arch.
 MAXIMUM ABDUCTION IS FOUND TO OCCUR IN
SCAPULAR PLANE, i.e 30-40 degrees anterior to
frontal plane. This is due to lack of capsular
tension in scapular plane.

71. Intra-articular Contribution to
Glenohumeral Motions
 The convex humeral head is a substantially
larger surface and may have a different
radius of curvature than the shallow concave
fossa.
 Given this incongruence, rotations of the joint
around its three axes do not occur as pure
spins but have changing centers of rotation and
shifting contact patterns within the joint.

72.  Without downward sliding of the articular
surface of the humeral head, the humeral
head will roll up the glenoid fossa and
impinge upon the coracoacromial arch.

73.  Slight superior translation of the center of
the humeral head can still occur during
humeral
abduction despite inferior sliding of the
head’s articular surface. (1-2mm)

74. Static Stabilization of the GH Joint in the
Dependent Arm- UNLOADED ARM
 PASSIVE TENSION IN THE ROTATOR
INTERVAL CAPSULE
 AIR-TIGHT CAPSULE PRODUCING
NEGATIVE INTRAARTICULAR PRESSURE
 GLENOID INCLINATION-THERE IS SLIGHT
UPWARD TILT OF GLENOID FOSSA EITHER
DUE TO ANATOMICALLY OR DUE TO UPWARD
ROTATION OF THE SCAPULA.

75. UNLOADED ARM

76. LOADED ARM-STATIC STABILIZATION
 SUPRASPINATUS ACTIVITY STARTS WHEN
THE PASSIVE TENSION IN ROTATOR INTERVAL
CAPSULE IS INSUFFICIENT AS IN LOADED
ARM.

77. DYNAMIC STABILIZATION OF THE
GH JOINT
 The Deltoid and Glenohumeral Stabilization
 The majority of the force of contraction of the
deltoid causes the humerus and humeral head to
translate superiorly; only a small proportion of
force is applied perpendicular to the humerus and
directly contributes to rotation (abduction) of the
humerus.
 It also produces a shear force rather than a
compressive force
 The deltoid cannot independently abduct (elevate)
the arm. Another force or set of forces must be
introduced to work synergistically with the deltoid
for the deltoid to work effectively.

78. EFFECT OF DELTOID (ALONE) ON
ABDUCTION

79. The Rotator Cuff and
Glenohumeral Stabilization
 ROTATOR OR MUSCULOTENDINOUS CUFF
MUSCLES ARE:
 Supraspinatus (S)
 Infraspinatus (I)
 Teres minor(T)
 Subscapularis(S)

80.  The infraspinatus,
teres minor, and
subscapularis muscles
individually or together
have a similar line of
pull.
 The rotatory
component (Fy)
compresses as well as
rotates, and the
translatory
component (Fx) helps
offset the superior
translatory pull of the

81. The Supraspinatus and
Glenohumeral Stabilization
 The supraspinatus has
a superiorly directed
translatory
component (Fx) and
a rotatory
component (Fy) that
is more compressive
than that of the other
rotator cuff muscles
and can
independently abduct
the humerus.

82. The Long Head of the
BicepsBrachii
and Glenohumeral
Stabilization
 The long head of
biceps may produce
its effect by
tightening the
relatively loose
superior labrum and
transmitting
increased tension to
the superior and
middle GH ligaments.

83.  The long head of the biceps brachii, because of
its position at the superior capsule and its
connections to structures of the rotator interval
capsule, is sometimes considered to be part of
the reinforcing cuff of the GH joint.
 The biceps muscle is capable of contributing
to the force of flexion and can, if the
humerus is laterally rotated, contribute to
the force of abduction and anterior
stabilization.

84. Costs of Dynamic Stabilization of
the Glenohumeral Joint
 Supraspinatus tendon tears
 Supraspinatus impingement in subacromial
arch
 Rotator cuff tear
 AC joint degenerative changes
 Bicipital tendinitis
 Dislocation of shoulder

86. AC joint degenerative changes

87. Bicipital tendinitis

89. Scapulothoracic and
Glenohumeral Contributions
 SCAPULAR UPWARD ROT = 60 DEGREES
 SCAPULA not only upwardly rotates but
also posteriorly tips to 30 degrees.
 GLENO-HUMERAL CONTRIBUTION = 100 to
120 of flexion and 90 to 120 of abduction.
 TOTAL MOVEMENT IN ELEVATION= OF 150-
180 DEGREES

90.  The overall ratio of 2 of GH to 1 of ST motion
during arm elevation is commonly used, and the
combination of concomitant GH and ST motion
most commonly referred to as scapulohumeral
rhythm.

91. Sternoclavicular and
Acromioclavicular Contributions

92. Sternoclavicular and
Acromioclavicular Contributions
 The major shift in the axis of rotation( for scapular
upward rotation) happens because the ST joint
motion can occur only through a combination of
motions at the SC and AC joints.
 When the axis of scapular upward rotation is
near the root of the scapular spine, ST motion is
primarily a function of SC joint motion;
 when the axis of scapular upward rotation is at
the AC joint, AC joint motions predominate;
 when the axis of scapular upward rotation is in
an intermediate position, both the SC and AC
joints are contributing to ST motion.

93.  50 % of contribution from AC and SC joint is
required to produce a total of 60 degrees of
scapular upward rotation.
 Any additional degrees of upward rotation
is accomplished by posterior rotation of
clavicle.

94. Integrated
movemen
t during
elevation

95. 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
through their attachments on the clavicle and
the scapula.

96.  TRAPEZIUS WITH SERRATUS Anterior-
forms a force couple for scapular upward
rotation
 INITIATION Of scapular rotation- upper
trap + middle traps
 AT THE END RANGE= Lower traps

98. 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 upto
90 degrees only.

99. Supraspinatus
 Primary function is to produce abduction
with deltoid muscle.
 It has a fairly constant MA throughout the
range of motion of abduction
 Secondary function: acts as a ‘steerer’ of
humeral head and helps to maintain stability
of dependent arm.

100. Infraspinatus, teres minor and
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, these muscles
(infrasp and t.minor) work to pull the humeral
head down, and during the middle range, these
muscles act to externally rotate for clearing
greater tubercle under coracoacromial arch.
 Subscapularis helps as internal rot when arm is at
side and during initial range
 With more abduction, its inter rot capacity decreases.
 Then it acts with other RC muscles to promote
stability by
compression.

101. 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 to 75, 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.

102.  Serratus anterior produces upward
rotation, posterior tipping and external
rotation of scapula, which is necessary for
upward elevation of arm.
 The serratus is the primary stabilizer of the
inferior angle and medial border of the
scapula to the thorax.

103. 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.
 The trapezius and serratus anterior muscles maintain
an optimal length-tension relationship with the deltoid
and permit the deltoid to carry its heavier distal lever
through full ROM.

104. 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.

106.  Depression involves the forceful
downward
movement of the arm in relation to the
trunk.

107. Latissimus Dorsi and
Pectoral Muscle Function
 When the upper extremity is free to move in
space, the latissimus dorsi muscle may produce
adduction, extension, or medial rotation of the
humerus. Through its attachment to both the
scapula and humerus, the latissimus dorsi
can also adduct and depress the scapula and
shoulder complex.
 When the hand and/or forearm is fixed in
weight- bearing, the latissimus dorsi muscle
will pull its caudal attachment on the pelvis
toward its cephalad attachment on the scapula
and humerus. This results in lifting the body
up as in a seated pushup.

108. Pectoralis major muscle
 Clavicular
portion
 Sternal portion
 Abdominal
portion
Flexion of
shoulder
Depression
of
shoulder
Depressor
function is
assisted by
pectoralis
minor

109. Teres Major and Rhomboid
Muscle Function
 In order for the teres
major muscle to
extend the heavier
humerus rather than
upwardly rotate the
lighter scapula, the
synergy of the
rhomboid muscles is
necessary to stabilize
the scapula.

110. REFERENCE:
joint structure and function. Lavangie and Norkin, 4th edition
Thankyo
u