this is a ppt made usually for bachelor of physiotherapy students and contains the basic biomechanics of shoulder complex

1. Debashree Roy

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 forces
from the upper extremity to the clavicle.

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 with
scapular upward rot during elevation of arm.

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
joint.

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/retraction
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
inclination
Angle of
torsion

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 abductionSuperior GH Lig
• Limits anterior translation at arm 45
degrees abductionMiddle 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
 Subacromial
 Subdeltoid
Subacromial
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 deltoid.

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
movement
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
Thankyou