Shoulder complex Biomechanics

SHOULDER COMPLEX
BIOMECHANICS
Prepared By: Dr.Krupa Soni (MPT Ortho)

 The shoulder complex, composed of the clavicle,
scapula, and humerus, is an intricately designed
combination of three joints linking the upper
extremity to the thorax.
2 Dr.Krupa Soni (MPT Ortho)

 The articular structures of the shoulder complex are
designed primarily for mobility, allowing us to move
and position the hand through a wide range of
space.
 The glenohumeral (GH) joint, linking the humerus
and scapula, has greater mobility than any other joint
in the body.

Components of the
Shoulder Complex

 The osseous segments of the shoulder complex are
the clavicle, scapula, and humerus.
 These three segments are joined by three
interdependent linkages:
 The Sterno Clavicular joint,
 The Acromioclavicular (AC) joint
 The Gleno humeral joint.
 The Scapulothoracic (ST) joint

 The joints that compose the shoulder complex in
combination with trunk motion can contribute as
much as 180º of elevation to the upper extremity.
 Motion of the scapula on the thorax normally
contributes about one third of the total motion
necessary for elevation of the arm through the linked
SC and AC joint motions, whereas the GH joint
contributes about two thirds of the total motion.

Sternoclavicular Joint
 The SC joint serves as the only structural attachment
of the clavicle, scapula, and upper extremity to the
axial skeleton.
 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.

 The SC joint is a
 Plane synovial joint
 Three rotatory and three translatory degrees of freedom.
 This joint has a synovial capsule, a joint disk, and three
major ligaments.

Sternoclavicular Articulating Surfaces
 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

 The sternal end of the clavicle and the manubrium
are incongruent; that is, there is little contact
between their articular surfaces.
 Movements of the clavicle in relation to the
manubrium result in changes to the areas of contact
between the clavicle, the SC joint disk, and the
manubriocostal cartilage.

Sternoclavicular Disk
 it is generally true at an incongruent joint, the SC joint
has a fibrocartilage joint disk, or meniscus, that increases
congruence between joint surfaces.
 The SC disk serves an important stability function by
increasing joint congruence and absorbing forces that
may be transmitted along the clavicle from its lateral end.
 Upper portion- Posterosuperior clavicle
 Lower portion- manubrium and first costal cartilage ,
fibrous capsule.
 The disk diagonally transects the SC joint space and
divides the joint into two separate cavities

 In elevation and depression of the clavicle, the
medial end of the clavicle rolls and slides on the
relatively stationary disk, with the upper attachment
of the disk serving as a pivot point.
 The disk, therefore, is considered part of the
manubrium in elevation/depression.

 In protraction/retraction of the clavicle, the SC disk
and medial clavicle roll and slide together on the
manubrial facet, with the lower attachment of the
disk serving as a pivot point.
 The disk, therefore, is considered part of the clavicle
in protraction/ retraction.

Sternoclavicular Joint Capsule and
Ligaments
 The SC joint is surrounded by a fairly strong fibrous
capsule but must depend on three ligaments for the
majority of its support.
 Sternoclavicular ligaments(Anterior, posterior)
 Costoclavicular ligament,
 Interclavicular ligament

 The anterior and posterior SC ligaments reinforce
the capsule and function primarily to check anterior
and posterior translatory movement of the medial
end of the clavicle.

 The costo-clavicular ligament is a very strong
ligament found between the clavicle and the first rib.
The costoclavicular ligament has two segments or
laminae.
 The anterior lamina has fibers directed laterally from
the first rib to the clavicle, whereas the fibers of the
posterior lamina are directed medially from the rib to
the clavicle.
 Both segments check elevation of the lateral end of
the clavicle

 The interclavicular ligament resists excessive
depression of the distal clavicle and superior glide of
the medial end of the clavicle.

Sternoclavicular Motions
 The three rotatory degrees of freedom at the SC joint
are most commonly described as
 elevation/depression,
 protraction/retraction, and
 anterior/posterior rotation of the clavicle.
 Motions of any joint are typically described by
identifying the direction of movement of the portion
of the lever that is farthest from the joint.

 The motions of elevation/depression and protraction/
retraction should be visualized by referencing
movement of the lateral end of the clavicle.
 Clavicular anterior/posterior rotation are long axis
rolling motions of the entire clavicle.

Elevation and Depression of the Clavicle
 The motions of elevation and depression occur
around an approximately anteroposterior (A-P) axis
between convex clavicular surface and a concave
surface formed by the manubrium and the first costal
cartilage.
 With elevation, the lateral clavicle rotates upward,
and with depression, the lateral clavicle rotates
downward.

Protraction and Retraction of the
Clavicle
 Protraction and retraction of the clavicle occur at the
SC joint around an approximately vertical
(superoinferior) axis that also appears to lie at the
costoclavicular ligament.
 With protraction, the lateral clavicle rotates anteriorly,
and with retraction, the lateral clavicle rotates
posteriorly.

 During protraction, the medial clavicle is expected to
slide anteriorly on the manubrium and first costal
cartilage.

Anterior and Posterior Rotation of the
Clavicle
 Anterior/posterior, or long axis, rotation of the clavicle
occurs as a spin between the saddle shaped surfaces of
the medial clavicle and manubrio costal facet.
 Unlike many joints that can rotate in either direction from
resting position of the joint, the clavicle rotates primarily
in only one direction from its resting position.
 The clavicle rotates posteriorly from neutral, bringing the
inferior surface of the clavicle to face anteriorly.
 This has also been referred to as backward or upward
rotation rather than posterior rotation. From its fully
rotated position, the clavicle can rotate anteriorly again to
return to neutral.

Sternoclavicular Stress Tolerance
 The SC joint serves its purposes of joining the upper
limb to the axial skeleton, contributing to upper limb
mobility, and withstanding imposed stresses.
 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.

Acromioclavicular Joint

Contains..
 Introduction
 Articulating surfaces
 Joint disc
 Capsule & ligaments
 Motions
 AC joint stress

 The AC joint attaches the scapula to the clavicle.
 It is generally described as a plane synovial joint
with three rotational and three translational degrees
of freedom.
 It has
 Joint capsule and
 Two major ligaments
 Joint disk (may or may not be present)

 The primary function of the AC joint is
 To allow the scapula to rotate during arm movement. Also
provide additional range of rotation and allow for
adjustments of the scapula on the thorax.
 In addition, the joint allows transmission of forces from the
upper extremity to the clavicle.

WHY GLENOID IS PLACED BENEATH THE
HUMERAL HEAD????
 SCAPULA REMAINS CONGRUENT & STABLE ON
THE THORAX

Acromioclavicular Articulating Surfaces
 The AC joint consists of the
articulation between the lateral
end of the clavicle and a small
facet on the acromion of the
scapula.
 The articular facets,
considered to be incongruent,
vary in configuration.
 They may be flat, reciprocally
concave-convex, or reversed
(reciprocally convex-concave).
 The vertical orientation of the
articulating surfaces varies
from individual to individual.

Acromioclavicular Joint Disk
 The disk of the AC joint is variable in size between
individuals, at various ages within an individual, and
between sides of the same individual.

Acromioclavicular Capsule and
Ligaments
 The capsule of the AC joint is weak and cannot
maintain integrity of the joint without reinforcement of
the
 Superior and inferior acromio-clavicular ligament
 Coraco-clavicular ligament

Superior & Inferior Acromio-clavicular
Ligament
 The superior
acromio-clavicular
ligament assists the
capsule in apposing
articular surfaces and
in controlling A-P joint
stability.

 The fibers of the
superior AC ligament
are reinforced by
aponeurotic fibers of the
trapezius and deltoid
muscles, which makes
the superior joint
support stronger than
the inferior.

Coraco-clavicular ligament
 The coracoclavicular
ligament, although not
belonging directly to the
anatomic structure of
the AC joint, firmly
unites the clavicle and
scapula and provides
much of the joint’s
stability.

 This ligament is divided
into two portion,
 Trapezoid
ligament(Lateral),
 Conoid
ligament(Medial)

 The trapezoid ligament
is
 quadrilateral in shape
and
 is nearly horizontal in
orientation.
 Provides the majority of
resistance to posterior
translatory forces
applied to the distal
clavicle.

 The conoid ligament,
 medial and
 slightly posterior to the
trapezoid,
 is more triangular and
 vertically oriented.
 Primary restraint to
translatory motions
caused by the superior
directed forces to distal
clavicle.

 Both the portions of the coraco clavicular ligament
limit upward rotation of the scapula at AC joint.
 The medial directed forces on the humerus are
transferred to the glenoid fossa of the scapula ,
medial displacement of the scapula on the clavicle is
prevented by the coracoclavicular
ligament(Perticular the horizontal trapezoid portion).
 Both the portion (Trapezoid & Conoid) are separated
by adipose tissues & a large bursa.

 One of the most critical roles played by the
coracoclavicular ligament in integrated shoulder
function is to couple the posterior rotation of the
clavicle to scapula rotation during arm elevation.

Acromioclavicular Motions
 The articular facets of the AC joint are small, afford
limited motion, and have a wide range of individual
differences.
 The primary rotatory motions that take place at the
AC joint are
 Internal/external rotation
 Anterior/ posterior tipping or tilting
 Upward/downward rotation

 These motions occur around axis that are oriented to
the plane of the scapula rather than to the cardinal
planes.

1. Internal/external rotation (Shoulder protraction &
retraction) - occurs around vertical axis
2. Anterior/posterior tilting (Shoulder elevation &
depression)- occurs around an oblique “coronal”
axis
3. Upward/downward rotation – occurs around an
oblique “A-P” axis

Internal and External Rotation (Shoulder
protraction & retraction)
 Internal/external rotation of the scapula in relation to
the clavicle occurs around an approximately vertical
axis through the AC joint.
 Internal and external rotation at the AC joint can best
be visualized as bringing the glenoid fossa of the
scapula anteromedially and posterolaterally,
respectively.

 These motions occur in part to maintain contact of
the scapula with the horizontal curvature of the
thorax as the clavicle protracts and retracts , sliding
the scapula around the thorax in scapular protraction
and retraction.
 The orientation of the glenoid fossa is important to
maintain congruency with the humeral head;
maximize the function of GH muscles, capsule, and
ligaments; maximize stability of the GH joint; and
maximize available motion of the arm.

 The available range of motion (ROM) at the AC joint
is difficult to measure.
 The available ROM Of Internal & external
rotation at Acromio clavicular joint.

Anterior and Posterior Tilting(Shoulder
elevation & depression)
 The second AC motion is anterior/posterior tipping or
tilting of the scapula in relation to the clavicle around
an oblique “coronal” axis through the joint.
 Anterior tipping will result in the acromion tilting
forward and the inferior angle tilting backward.
 Posterior tipping will rotate the acromion backward
and the inferior angle forward.

 Scapular tipping, like internal/ external rotation of the
scapula, occurs to maintain the contact of the scapula
with the contour of the rib cage and orient the glenoid
fossa.
 As the scapula moves upward or downward on the rib
cage in elevation or depression, the scapula must adjust
its position to maintain full contact with the vertical
curvature of the ribs.
 Elevation of the scapula on the thorax, such as occurs
with a shoulder shrug, can result in anterior tilting.
 The scapula does not always follow the curvature of the
thorax precisely.53 Dr.Krupa Soni (MPT Ortho)

 During normal flexion or abduction of the arm, the
scapula posteriorly tilt on the thorax as the scapula is
upwardly rotating.

 As the scapula moves upward or downward on the
rib cage in elevation or depression, the scapula must
adjust its position to maintain full contact with the
vertical curvature of the ribs.

Upward/Downward Rotation
 Upward/downward rotation of the scapula in relation
to the clavicle about an oblique “A-P” axis
approximately perpendicular to the plane of the
scapula, passing midway between the joint surfaces
of the AC joint.
 Upward rotation tilts the glenoid fossa upward , and
downward rotation is the opposite motion.

 The amount of available passive motion into
upward/downward rotation specifically at the AC joint
is limited by the attachment of the coracoclavicular
ligament.
 Posterior rotation at the SC joint releases tension on
the coracoclavicular ligaments and “opens up” the
AC joint, allowing upward rotation to occur

Acromioclavicular Stress Tolerance
 Unlike the stronger SC joint, the AC joint is extremely
susceptible to both trauma and degenerative
change.
 This is likely to be due to its small and incongruent
surfaces that result in large forces per unit area.
 Trauma to the AC joint most often occurs in during
first three decades of life, during either contact
sports or a fall on the shoulder.
 The trauma results in AC joint disruption ranging
from sprain & subluxation to dislocation.

 Treatment of sprains, subluxations, and dislocations
of this joint occupies a large amount of the literature
on the shoulder complex.
 Controversy exists on description and classification
of AC subluxations and dislocations, as well as on
nonsurgical and surgical management.

Scapulothoracic Joint

Contains…
 Introduction
 Resting position of scapula
 Scapulothoracic motions
 Scapulothoracic stability

 The ST “joint” is formed by the articulation of the
scapula with the thorax.
 It is not a true anatomic joint because it has none of
the usual joint characteristics.

 By contrast , the articulation of the scapula with
thorax depends on the integrity of the anatomic AC
and SC joints.
 The SC and AC joints are interdependent with the
ST joint because the scapula is attached by its
acromion process to the lateral end of the clavicle
through the AC joint; the clavicle, in turn, is attached
to the axial skeleton at the manubrium of the
sternum through the SC joint.

 Any movement of the scapula on the thorax must
result in movement at either the AC joint, the SC
joint, or both; that is, the functional ST joint is part of
a true closed chain with the AC and SC joints and
the thorax.

Resting Position of the Scapula
 Normally, the scapula rests at a position on the
posterior thorax approximately 5 inches from the
midline, between the second through seventh ribs.

 The scapula also is internally rotated 30º to 45º from
the coronal plane , is tipped anteriorly approximately
10º to 20º from vertical, and is upwardly rotated 5º to
10º from vertical.

Motions of the Scapula

 The motions of the scapula from this resting or
reference position include three rotations that were
already described because they occur at the AC
joint.
 These are
 Upward/downward rotation,
 Internal/external rotation, and
 Anterior/posterior tilting/tipping.

 Of these three AC joint rotations, only
upward/downward rotation is readily observable at
the ST, and it is therefore considered for our
purposes to be a “Primary” scapular motion.
 Internal/external rotation and anterior/posterior tilting
are normally difficult to observe and are therefore
considered for our purposes to be “Secondary”
scapular motions.

 The scapula presumably also has available the
translatory motions of the scapular
 Elevation/depression &
 Protraction/retraction.
 These “primary” scapular motions are typically
described as if they occur independently of each
other.

 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.
 Instead, scapular motions on the thorax must occur
in combinations, such as the simultaneous upward
rotation, external rotation, and posterior tipping that
occur when the arm is abducted.

Upward/Downward Rotation
 Upward rotation of the scapula on the thorax is the
principal motion of the scapula observed during
active elevation of the arm and plays a significant
role in increasing the range of elevation of the arm
overhead.
 Approximately 60º of upward rotation of the scapula
on the thorax is typically available.

 Upward/downward rotation of the scapula are
contributed by
 SC joint elevation/ depression, posterior/anterior
rotation,
 AC joint upward/downward rotation.
 Most often, scapular upward/downward rotation
results from a combination of these SC and AC
motions.

Elevation/Depression
 Scapular elevation and depression can be isolated
(relatively speaking) by shrugging the shoulder up
and depressing the shoulder downward.
 Elevation and depression of the scapula on the
thorax are commonly described as translatory
motions in which the scapula moves upward
(cephalad) or downward (caudally) along the rib
cage from its resting position.

 Scapular elevation, however, occurs through
 SC joint - Elevation of the clavicle
 AC joint - Anterior/posterior tilting & internal/external
rotation at the to maintain the scapula in contact with the
thorax.

Protraction/Retraction
 Protraction and retraction of the scapula on the
thorax are often described as translatory motions of
the scapula away from or toward the vertebral
column, respectively.
 However, if protraction of the ST joint occurred as a
pure translatory movement, the scapula would move
directly away from the vertebral column, and the
glenoid fossa would face laterally.
 Only the vertebral column would remain in contact
with the ribcage.

 In reality full scapular protraction results in glenoid
fossa facing anteriorly, with the scapula in contact
with the rib cage.

 Scapular protraction/retraction , however, occurs
through
 SC joint - clavicular protraction and retraction
 AC joint - internal/external rotation at the to maintain the
scapula in contact with the thorax

Internal/External Rotation
 The scapular motions of internal and external rotation are
normally not overtly identifiable on physical observation
but are critical to its movement along the curved rib cage.
 Approximately 15º to 16º of internal rotation occurs at the
acromio clavicular joint during normal elevation of arm.
 A larger amount of internal rotation of the scapula on the
thorax that is isolated to (or occurs excessively at) the AC
joint results in prominence of the vertebral border of the
scapula as a result of loss of contact with the thorax.
 This is often referred to clinically as scapular “winging”.

 Internal/external rotation of the scapula on the thorax
should normally accompany
 SC joint - protraction/ retraction of the clavicle.

Anterior/Posterior Tilting
 The scapular motions of are anterior/ posterior tilting
normally not overtly identifiable on physical
observation but are critical to its movement along the
curved rib cage.
 Internal/external rotation of the scapula on the thorax
should normally accompany protraction/ retraction of
the clavicle at the SC joint.
 Anterior tilting beyond resting values will result in
prominence of the inferior angle of the scapula.

 Anterior/posterior tilting of the scapula on the thorax
should normally accompany
 SC joint - Elevation/ Depression of the clavicle at the,
anterior/posterior rotation of the clavicle
 AC joint - Anterior/posterior tilting

Scapulothoracic Stability
 Stability of the scapula on the thorax is provided by the
structures that maintain integrity of the linked AC and SC
joints.
 The muscles that attach to both the thorax and scapula
maintain contact between these surfaces while producing
the movements of the scapula.
 In addition, stabilization is provided through the ST
musculature by pulling or compressing the scapula to the
thorax.
 The scapula with its associated muscles and linkages,
can perform stability & mobility functions and also serves
dynamic stabilization in the human body.

Glenohumeral Joint

 The GH joint is a ball-and-socket synovial joint with
three rotational and three translational degrees of
freedom.
 It has a capsule and several associated ligaments
and bursae.
 The articulation is composed of the large head of the
humerus and the smaller glenoid fossa.

Glenohumeral Articulating Surfaces
 The glenoid fossa of the scapula serves as the
proximal articular surface for this joint.
 Because the glenoid fossa of the scapula is proximal
segment of the gleohumeral joint, any motion of the
scapula will influence gleno humeral joint function.
 The orientation of shallow concavity of glenoid fossa
varies with resting position of scapula on thorax &
with motions.

 The fossa also does not always lie in a plane
perpendicular to the plane of the scapula; it may be
anteverted or retroverted up to 10º, with 6º to 7º of
retroversion most typical.
 Retroversion: With anteversion, the glenoid fossa
faces slightly anterior in relation to the plane or body
of the scapula and, with retroversion, slightly
posterior.

 The glenoid fossa may be tilted slightly upward or
downward when the arm is at the side, although
representations most commonly show a slight
upward tilt.
 Glenohumeral joint has sacrificed the articular
congruency to increase the mobility of UE & hand.
 It is therefore susceptible to degenerative changes,
instability, and derangement.

 The humerus is the distal segment of the GH joint.
 The humeral head has an articular surface that is
larger than that of the proximal glenoid articular
surface, forming one third to one half of a sphere.

 As a general rule, the head faces medially,
superiorly, and posteriorly with regard to the shaft of
the humerus and the humeral condyles.

 Angle of inclination of the humerus - An axis
through the humeral head and neck in relation to a
longitudinal axis through the shaft of the humerus
forms an angle of 130º to 150º in the frontal plane.

 Angle of torsion: In the transverse plane, the axis
through the humeral head and neck in relation to the
axis through the humeral condyles forms an angle
that varies far more than other parameters but is
usually described as approximately 30º posteriorly.

 The normal posterior position of the humeral head
with regard to the humeral condyles may be termed
posterior torsion, retrotorsion, or retroversion of
the humerus.

 Because of the internally rotated resting position of
the scapula on the thorax, retroversion of the
humeral head increases congruence of the GH joint
by “turning” the humeral head back toward the
glenoid fossa of the scapula.
 Reduced retroversion (or anteversion) results in a
more anterior position of the humeral head on the
glenoid surface when the arm is in an anatomically
neutral position.

Glenoid Labrum
 When the arms hang dependently at the side, the two
articular surfaces of the GH joint have little contact.
 The majority of the time, the inferior surface of the
humeral head rests on only a small inferior portion of the
fossa.
 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%.

 The labrum superiorly is loosely attached, whereas
the inferior portion is firmly attached and relatively
immobile.
 The labrum is composed of densly packed fibrous
connective tissues.
 The glenoid labrum also serves as the attachment
site for the glenohumeral ligaments and the tendon
of the long head of the biceps brachii.

 Functions:
 Resistance to humeral head traslation
 Protection of the bony edges of labrum
 Reduction joint friction
 Dissipation of joint contact forces

Glenohumeral Capsule and Ligaments
 The entire GH joint is surrounded by a large, loose
capsule that is taut superiorly and slack anteriorly
and inferiorly in the resting position (arm dependent
at the side).
 The capsular surface area is twice that of the
humeral head.
 When the humerus is abducted and laterally rotated
on the glenoid fossa, the capsule twists on itself and
tightens, making abduction and lateral rotation the
close-packed position for the GH joint.

 Superior GH ligaments
 Middle GH ligaments
 Inferior GH ligaments
 Coracohumeral ligament

Superior GH ligaments
 Externally, the superior GH ligament passes from the
superior glenoid labrum to the upper neck of the
humerus deep to the coracohumeral ligament.
 Superior GH ligament, superior capsule &
coracohumeral ligament are interconnected
structures also known as rotator interval
capsule(RIC).

 The middle GH ligament runs obliquely from the
superior anterior labrum to the anterior aspect of the
proximal humerus below the superior GH ligament
attachment.
 It may absent in 30% subjects.
 The middle GH ligament contributes primarily to
anterior stability by limiting anterior humeral
translation with the arm at the side and up to 45º of
abduction.

 The inferior GH ligament has been described as
having at least three portions and thus has been
termed the inferior GH ligament complex (IGHLC).
 The three components of the complex are the
anterior and posterior bands and the axillary
pouch in between.
 With abduction beyond 45º or with combined
abduction and rotation, the IGHLC plays the major
role of stabilization

 The coracohumeral ligament originates from the
base of the coracoid process and may be defined as
having two bands.
 The first inserts into the edge of the supraspinatus
and onto the greater tubercle, where it joins the
superior GH ligament; the other band inserts into the
subscapularis and lesser tubercle.
 The two bands form a tunnel through which the
tendon of the long head of the biceps brachii passes.

 In addition, the coracohumeral ligament is usually
reported as resisting humeral external rotation with
the arm adducted.

Coracoacromial Arch

 The coracoacromial (or suprahumeral) arch is
formed by the coracoid process, the acromion, and
the coracoacromial ligament and the inferior surface
of the acromioclavicular joint.
 The coracoacromial arch forms an osteoligamentous
vault over the humeral head and the region between
the arch & the humeral head is called the
“subacromial space”
 The subacromial bursa, the rotator cuff tendons, and
a portion of the tendon of the long head of the biceps
brachii lie with in the subacromial space.

 The coraco acromial arch protects the structures
beneath it from direct trauma from above.
 Such trauma is relatively common and can occur
through such simple daily tasks as carrying a heavy
bag over the shoulder.
 The arch also prevents the head of the humerus
from dislocating superiorly, because an unopposed
upward translatory force on the humerus would
cause the head of the humerus to hit the
coracoacromial arch.

 The supraspinatus tendon is particularly vulnerable
because of its location beneath all of the potentially
impinging superior structures except the coracoid.
 The subacromial space, or area between the
humeral head and coracoacromial arch, is also
referred to as the suprahumeral space or
supraspinatus outlet.

116
 The subacromial space or supraspinatus outlet, has
been quantified by measuring the superior to inferior
acromio humeral interval on radiographs.
 This interval averages 10 mm in healthy subjects
with the arm adducted at the side. During elevation
of the arm, this space decreases to about 5 mm.
Dr.Krupa Soni (MPT Ortho)

 When the subacromial space is narrowed, the
likelihood of impingement of the rotator cuff tendons
and subacromial bursa during elevation of the arm
increases.
 When the sub acromial space decreases even more
than what has been measured in healthy subjects,
the likelihood of impingement of the rotator cuff
tendons and sub acromial bursa during elevation of
the arm increases.

Narrowing of the space can be caused by
anatomic factors such as
 Changes in the shape of the acromion inferiorly,
 Changes in the slope of the acromion,
 AC joint osteophytes,
 Large coracoacromial ligament,
 Abnormal scapular or humeral motions can also functionally
reduce the size of the suprahumeral space.
 Inadequate posterior tipping or upward rotation of the scapula
during arm elevation or abnormal superior or anterior translation
of the humeral head on the glenoid fossa brings the humeral head
and rotator cuff tendons in closer proximity to the humerus and
increases the risk of impingement.
 Inflammation, fibrosis and thickening of the soft tissues can occur
with repetitive impingement, further reducing the available
subacromial space for clearance of the soft tissues during arm
elevation.

Bursae
 In part because of the confined nature and proximity
of structures in the subacromial space, several
bursae are associated with the shoulder complex in
general and with the GH joint specifically.
 The presence of bursae are indicative of the
potential for frictional forces between structures.
 Although all bursae contribute to function, the most
important are the subacromial and subdeltoid
bursae.

 These bursae separate the supraspinatus tendon
and head of the humerus from the acromion,
coracoid process, coracoacromial ligament, and
deltoid muscle.
 The bursae may be separate but are commonly
continuous with each other.

 The subacromial bursa permits smooth gliding
between the humerus and supraspinatus tendon and
surrounding structures.
 Interruption or failure of this gliding mechanism is a
common cause of pain and limitation of GH motion,
although it rarely occurs as a primary problem.

 Subacromial bursitis is most commonly secondary to
inflammation or degeneration of the supraspinatus
tendon.
 When inflamed, the space occupied by the bursa
increases.
 With an intact rotator cuff, the subacromial bursa
does not communicate with the GH joint space.

Glenohumeral Motions

 The GH joint is usually described as having three
rotational degrees of freedom: flexion/extension,
abduction/adduction, and medial/lateral rotation.
 Flexion and extension occur about a coronal axis
passing through the center of the humeral head. The
GH joint is often considered to have 120º of flexion
and about 50º of extension.

 Medial and lateral rotation occur about a long axis
parallel to the shaft of the humerus and passing
though the center of the humeral head.
 The range of medial/lateral rotation of the humerus
varies with position.
 With the arm at the side, medial and lateral rotation
may be limited to as little as 60º of combined motion.
 Abducting the humerus to 90º frees the arc of
rotation.

 The restricted arc of medial/lateral rotation when the
arm is at the side may be related to different
alignment of the greater and lesser tubercles, which
creates a mechanical block, or to different areas of
capsular or muscular tightness when the arm is
adducted versus abducted.

 Abduction/adduction of the GH joint occur around an
A-P axis passing through the humeral head center.
 The restriction to abduction in medial or neutral
rotation is commonly attributed to impingement of
the greater tubercle on the coracoacromial arch.
 When the humerus is laterally rotated 35º to 40º the
greater tubercle will pass under or behind the arch
so that abduction can continue.

 The ROMs for abduction of the GH joint (if impact of the
greater tubercle is avoided) are reported to be anywhere
from 90º to 120º.
 When the humerus is elevated in the plane of the scapula
(referred to as abduction in the plane of the scapula,
scapular abduction, or scaption), there is presumably
less restriction to motion because the capsule is less
twisted than when the humerus is brought further back
into the frontal plane.
 During active arm elevation in all planes of elevation,
glenohumeral lateral rotation is observed.

Intra-articular Contribution to
Glenohumeral Motions
 Full ROM of the GH joint is, to a reasonable degree,
a function of the intra-articular movement of the
incongruent articular surfaces.
 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.

 Elevation of the humerus requires that the articular
surface of the humeral head slide inferiorly (caudally) in a
direction opposite to movement of the shaft of the
humerus.
 Failure of the humeral articular surface to slide
downwardly in abduction of the humerus would cause
superior (cephalad) rolling of the humeral head surface
on the fossa.
 The large humeral head would soon run out of glenoid
surface, and the head of the humerus would impinge
upon the overhanging coracoacromial arch.
 If, as it should, the articular surface of the head of the
humerus slides inferiorly while the head rolls up the
fossa, full ROM can be achieved.132 Dr.Krupa Soni (MPT Ortho)

134
 There is consensus that inferior sliding of the
humeral head’s articular surface is necessary to
minimize upward rolling of the humeral head.
 However, it appears that the humeral head as a
whole (its center of rotation) still moves somewhat
superiorly (translates upwardly) on the glenoid fossa
inspite of the downward sliding.

135
 The humeral head’s center is believed to move
slightly superior (1 to 2 mm of translation) until about
60 of active elevation motion.
 With further elevation, the humeral head’s center is
believed to remain relatively stable and centered on
the glenoid fossa.
 Less agreement exists with regard to anterior and
posterior translations of the humeral head’s center.
 Slight anterior positioning and translation (1 to 2 mm)
has been reported during active elevation.

Static Stabilization of the
Glenohumeral
Joint in the Dependent Arm

137
 Given the incongruence of the GH articular surfaces,
the bony surfaces alone cannot maintain joint
contact in the dependent position (arm hanging at
the side).
 As the humeral head rests on the fossa, gravity acts
on the humerus parallel to the shaft in a downward
direction (caudally directed translatory force).
 This appears to require a vertical upward pull to
maintain equilibrium.

138
 Such a vertical force could be supplied by muscles
such as the deltoid, supraspinatus, or the long heads
of the biceps brachii and triceps brachii.
 The line of gravity (LOG) acting on the upper
extremity (and extended through the humerus)
creates a downward force on the humerus (and an
inferiorly directed force on the humeral head).

139
 Given the magnitude of passive tension in the
structures of the rotator interval capsule (superior
capsule, superior GH ligament, and coracohumeral
ligament) that are taut when the arm is at the side,
the resultant pull of both the LoG and the rotator
interval capsule creates a line of force that
compresses the humeral head into the lower portion
of the glenoid fossa , where the humeral head
commonly sits when the arm is at the side.

141
 In addition to the passive tension in the rotator
interval capsule, two other mechanisms help provide
static stability of the glenohumeral joint with the arm
at the side.
 In a healthy GH joint, the capsule has an airtight
seal, which produces negative intra-articular
pressure.
 This pressure creates a relative vacuum that resists
inferior humeral translation caused by the force of
gravity.

142
 Loss of intra articular pressure by venting the
capsule or tears in the glenoid labrum , results in
large increase in inferior humeral translation.
 A slight upward tilt of glenoid the glenoid fossa will
also block inferior humeral translation.
 When these available passive forces are inadequate
for static stabilization, as may occur in the heavily
loaded arm, activity of the supraspinatus is recruited.

143
 In fact , the role of the suprspinatus may be more
critical than its activity as mesured by EMG indicates
because of paralysis or dysfunction in the
supraspinatus may lead to gradual inferior
subluxation og GH joint.
 Without the reinforcing passive tension of the intact
supraspinatus muscle, the sustained load on the
structures of the rotator interval capsule apparently
causes these structures to gradually stretch (become
plastic), which results in a loss of joint stability.

144
 Inferior GH subluxation is commonly encountered in
patients with diminished rotator cuff function caused
by stroke or other brain injury.

Dynamic Stabilization of the
Glenohumeral Joint

146
 The Deltoid and Glenohumeral Stabilization
 The Rotator Cuff and Glenohumeral Stabilization
 The Supraspinatus and Glenohumeral
Stabilization
 The Long Head of the Biceps Brachii and
Glenohumeral Stabilization
 Costs of Dynamic Stabilization of the
Glenohumeral Joint

The Deltoid and Glenohumeral Stabilization
148
 It is generally accepted that the deltoid muscle is a
prime mover (along with the supraspinatus) for GH
abduction.
 The anterior deltoid is also considered the prime
mover in GH flexion.
 The resultant action line of action of the deltoid
muscle in abduction can be used to highlight the
stabilization needs of the GH joint in elevation
activities.

Line of action of deltoid when the arm at the
side

150
 The action lines of the three segments of the deltoid
acting together coincide with the fibers of the middle
deltoid.
 When the muscle action line (FD) is resolved into its
parallel (Fx) and perpendicular (Fy) components in
relation to the long axis of the humerus, the parallel
component directly cephalad (superiorly) is by far the
larger of the two components.
 That is, 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.Dr.Krupa Soni (MPT Ortho)

151
 At many other joints, a force component parallel to
the long bone has a stabilizing effect because the
parallel component contributes to joint compression.

152
 Consequently, the force (Fx) applied parallel to the
long axis of the bone creates a shear force
(approximately parallel to the contacting articular
surfaces) rather than a stabilizing (compressive)
effect.

153
 The large superiorly directed force of the deltoid, if
unopposed, would cause the humeral head to impact
the coracoacromial arch before much abduction had
occurred.
 The rotatory torque produced by the relatively small
perpendicular component of the deltoid (Fy) will not
be particularly effective until the translatory forces
are in equilibrium.

154
 If the humeral head migrated upward into the coracoacromial
arch, the inferiorly directed contact force of the arch would
offset the Fx component of the deltoid, theoretically permitting
rotation of the humeral head to continue.
 However, pain from impinged structures in the subacromial
space is likely to prevent much motion.
 The inferior pull of gravity cannot offset the Fx component of
the deltoid, because the resultant force of the deltoid must
exceed that of gravity before any rotation can occur.
 That is, 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. Dr.Krupa Soni (MPT Ortho)

The Rotator Cuff and Glenohumeral Stabilization
155
 The supraspinatus, infraspinatus, teres minor, and
subscapularis muscles compose the rotator or
musculotendinous cuff (also referred to by the
acronym SITS muscles).
 These muscles are considered to be part of a “cuff”
because the inserting tendons of each muscle of the
cuff blend with and reinforce the GH capsule.

157
 If any one or all three of the vector pulls of the
infraspinatus, teres minor, or subscapularis muscles
is resolved into its components , it can be seen that
the rotatory force component (Fy) not only tends to
cause at least some rotation of the humerus, given
its orientation to the long axis of the bone, but Fy
also compresses the head into the glenoid fossa.
This is an example of creating joint stabilization.

158
 Although the infraspinatus, teres minor, and
subscapularis muscles of the rotator cuff are
important GH joint compressors, equally (or perhaps
more) critical to the stabilizing function of these
particular muscles is the inferior (caudal) translatory
pull (Fx) of the muscles.

159
 The sum of the three
negative (inferior)
translatory components
of these three muscles of
the rotator cuff nearly
offsets the superior
translatory force of the
deltoid muscle.

160
 The teres minor and infraspinatus muscles, in addition
to their stabilizing role, contribute to abduction of the
arm by providing the external rotation that typically
occurs with elevation of the humerus to help clear the
greater tubercle from beneath the acromion.
 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 spinning of the humeral
head around a relatively stable axis of rotation.

The Supraspinatus and Glenohumeral
Stabilization
161
 Although the supraspinatus muscle is part of the
rotator cuff, the action line of the supraspinatus
muscle, unlike the action lines of the other three
rotator cuff muscles, has a superior (cephalad)
translatory component, rather than the inferior
(caudal) component found in the other muscles of
the cuff.

162
 The more superior location of the supraspinatus
results in an action line that lies farther from the GH
joint axis than the action lines of the cuff muscles.
 The supraspinatus has a large enough moment arm
(MA) that it is capable of independently producing a
full or nearly full range of GH joint abduction while
simultaneously stabilizing the joint.
 Gravity acts as a stabilizing synergist to the
supraspinatus by offsetting the small upward
translatory pull of the muscle.

The Long Head of the Biceps Brachii
and Glenohumeral Stabilization
163
 The long head of the
biceps brachii runs
superiorly from the
anterior shaft of the
humerus through the
bicipital groove between
the greater and lesser
tubercles to attach to
the supraglenoid
tubercle and superior
labrum.

164
 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

165
 Although elbow and shoulder position may influence
its function, the long head appears to contribute to
GH stabilization by centering the head in the fossa
and by reducing vertical (superior and inferior) and
anterior translations.

Costs of Dynamic Stabilization of the
Glenohumeral Joint
166
 When all stabilization factors are intact, the head of the
humerus rotates into flexion or abduction around a
relatively stable axis with minimal translation.
 Over time, however, even normal stresses resulting from
the complex dynamic stabilization process may lead to
degenerative changes or dysfunction at the GH joint.
 The supraspinatus muscle is a particularly key structure
in dynamic stabilization. The supraspinatus is either
passively stretched or actively contracting when the arm
is at the side (depending on load); it also participates in
humeral elevation throughout the ROM.

167
 Mechanical compression and impingement of the
stressed supraspinatus tendon can occur
 When the subacromial space is reduced by
osteoligamentous factors,
 When there is increased superior or anterior translation of
the humeral head center with less favorable GH
mechanics,
 When the scapula does not posteriorly tip or upwardly
rotate adequately during humeral elevation,
 When occupational factors require heavy lifting or
sustained overhead arm postures.
 The supraspinatus tendon is the most vulnerable of
the cuff muscles. However, the overuse and potential
impingement issues also apply to the other cuff
muscles. Dr.Krupa Soni (MPT Ortho)

168
 Symptomatic and asymptomatic rotator cuff tears are
seen in almost all people over the age of 70º, with
the supraspinatus likely to show lesions before the
other tendons of the cuff.
 Rotator cuff tendinitis or tears typically produce pain
between 60º and 120º of humeral elevation in
relation to the trunk. This range constitutes what is
known as the painful arc. It is within this ROM that
the tendons of the rotator cuff are passing beneath
the coracoacromial arch.

169
 The long head of the biceps brachii similarly can
produce pain in the anterosuperior shoulder.
Because the long head of the biceps tendon also
passes directly beneath the impinging structures of
the coracoacromial arch, it is subject to some of the
same degenerative changes and the same trauma
seen in the tendons of the rotator cuff.
 If the bicipital tendon sheath is worn or inflamed, or if
the tendon is hypertrophied (as often seen with
rotator cuff tears), the gliding mechanism may be
interrupted and pain produced.

Integrated Function of
the Shoulder Complex

171
 The shoulder complex acts in a coordinated manner
to provide the smoothest and greatest ROM possible
to the upper limb.
 Motion available to the GH joint alone would not
account for the full range of elevation (abduction or
flexion) available to the humerus.
 The remainder of the range is contributed by the
scapula on the thorax through its SC and AC
linkages.

172
 Combined scapulohumeral motion
 Distributes the motion between the joints, permitting a
large ROM with less compromise of stability than would
occur if the same range occurred at one joint;
 Maintains the glenoid fossa in an optimal position in
relation to the head of the humerus, increasing joint
congruency while decreasing shear forces; and
 Permits muscles acting on the humerus to maintain a
good length-tension relation while minimizing or
preventing active insufficiency of the GH muscles.

Scapulothoracic and
Glenohumeral Contributions

174
 The scapula on the thorax contributes to elevation (flexion and
abduction) of the humerus by upwardly rotating the glenoid
fossa 50º to 60º from its resting position.
 It has long been recognized that the upward rotation of the
scapula and the flexion or abduction of the humerus occur
synchronously throughout arm–trunk elevation in healthy
individuals.
 If the humerus were (immobile) fixed to the fossa, this alone
would result in up to 60º of elevation of the humerus. The
humerus, of course, is not fixed (immobile) but can move
independently on the glenoid fossa.
 The GH joint contributes 100º to 120º of flexion and 90º to
120º of abduction.

175
 The combination of scapular and humeral movement
results in a maximum range of elevation of 150º to
180º.
 The overall ratio of 2º of GH to 1º 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.
 According to the 2-to-1 ratio framework, flexion or
abduction of 90º in relation to the thorax would be
accomplished through approximately 60º of GH and
30º of ST motion.

176
 For every 2° of glenohumeral joint abduction or
flexion there is 1° of upward rotation at the
scapulothoracic joint, resulting in a 2:1 ratio of
glenohumeral to scapulothoracic joint movement in
both flexion and abduction.
 The glenohumeral joint contributes approximately
120° of flexion or abduction and the scapulothoracic
joint contributes approximately 60° of upward
rotation of the scapula, yielding a total of about 180°
of arm–trunk elevation.

178
 The authors state that the ratio of glenohumeral to
scapulothoracic motion becomes apparent and
remains constant after approximately 30° of
abduction and approximately 60° of flexion.

179
 It must also be recognized, however, that elevation of the
arm is often accompanied not only by elevation of the
humerus but also by lateral rotation of the humerus in
relation to the scapula.
 During abduction of the humerus in the plane of the
scapula, an average of 43º of lateral rotation from the
resting position has been reported, with peak lateral
rotation generally occurring between 90º and 120º of
humeral elevation.
 During flexion, an average of 51º of lateral rotation has
been reported.

180
 The scapula contributes to elevation of the arm not
only by upwardly rotating on the thorax but also
through other ST motions.

181
 The general patterns of scapular motions, however,
are relatively consistent.
 As the arm is elevated into flexion, scapular plane
abduction, or frontal plane abduction, the scapula
posteriorly tips on the thorax.
 As the arm moves from the side to 150º of elevation,
the magnitude of this motion is about 20º to 30º.

182
 This posterior tilting allows the inferior angle of the
scapula to move anteriorly and stay in contact with
the thorax as it rotates upward and around the rib
cage.
 Posterior tilting of the scapula also has the effect of
bringing the anterior acromion up and back.
 This may serve to minimize reduction in the
subacromial space as the humerus elevates.

184
 In general, at the end ranges of elevation, the scapula is,
in general, externally rotating on the thorax.
 External rotation of the scapula is important to
maintaining the scapula, particularly the medial border, in
contact with the thorax as the scapula upwardly rotates
during arm elevation.
 The magnitude of external rotation during scapular plane
abduction of the humerus, however, may be less.
 McClure and colleagues reported about 25º of external
rotation of the scapula during abduction of the humerus
in the plane of the scapula, most of which occurs at more
than 90º of motion.

185
 In flexion, the scapula initially protracts and internally
rotates to orient the glenoid fossa anteriorly (in the
sagittal plane).

186
 Structural limitations or
inability of muscles to
appropriately stabilize
the scapula may result
in anterior tipping,
internal rotation, and
downward rotation of
the scapula with
attempted flexion of the
arm.

Sternoclavicular and
Acromioclavicular Contributions

188
 Elevation of the arm in any plane involves motion of
the SC and AC joints to produce ST joint motion,
because the ST joint is part of a closed chain.
 Given the complexity of the linkages, there is no
consensus on the relative contribution of the SC and
AC joints to the 60º arc of upward rotation of the
scapula as the scapula moves through its full ROM.
 The initiation of ST upward rotation as the arm is
flexed or abducted appears to couple with clavicular
posterior rotation and elevation at the SC joint.

189
 This scapular upward
rotation occurs around
an approximately A-P
axis, passing through
the costo clavicular
ligament (SC motion)
and projecting
backward through the
root of the scapular
spine (ST motion).

190
 As elevation of the arm
progresses, the ST axis of
rotation gradually shifts
laterally, reaching the AC
joint in the final range of
scapular upward rotation.
 This major shift in the axis
of rotation happens
because the ST joint
motion can occur only
through a combination of
motions at the SC and AC
joints.

191
 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; and when the axis of scapular
upward rotation is in an intermediate position, both
the SC and AC joints are contributing to ST motion.

192
 Inman and coworkers in 1944 described relative
contributions of the SC and AC joint to ST upward
rotation during arm elevation to be about 50% from
SC elevation and 50% from AC upward rotation (20º
to 30º each to obtain 50º to 60º upward rotation).
 However, current three-dimensional descriptions of
clavicular motion show only about 10º or less of
clavicular elevation during arm elevation.

193
 In order for additional upward rotation of the scapula
is to occur at the AC joint, the limitation to AC motion
imposed by the coracoclavicular ligament must be
overcome.
 Tension in the coracoclavicular ligament (especially
the conoid portion) is produced as the coracoid
process of the scapula gets pulled downward, with
muscle forces attempting to upwardly rotate the
scapula at the AC joint.

195
 The tightened conoid ligament pulls its
posteroinferior clavicular attachment forward and
causing the clavicle to posteriorly rotate.
 Posterior rotation of the clavicle around its
longitudinal axis will result in additional ST upward
rotation.

196
 The ST upward rotation occurs both as the lateral
end of the S-shaped clavicle flips up and as the
tension in the coracoclavicular ligament is reduced,
to permit upward rotation at the AC joint.
 The magnitude of posterior rotation of the clavicle
may be anywhere from 30º to 50º contributing 20º or
more ST upward rotation.
 For the clavicle to rotate about its longitudinal axis, it
appears to require mobility of both the SC and the
AC joints.

197
 Throughout elevation of the arm (flexion, scapular
plane abduction, or frontal plane abduction), the
clavicle also retracts at the SC joint, typically 20º to
25º, contributing to external rotation of the scapula
on the thorax.
 As the scapula adjusts to the differing contour of the
rib cage, the AC joint allows varying amounts of
anterior/posterior tipping and internal/external
rotation, contributing to the overall ST motions
previously described.

198
 The AC joint is internally rotated through out arm
elevation.
 The magnitude of AC joint internal rotation is slightly
greater in flexion and less in frontal plane abduction.
 As a result AC joint internal rotation offset the large
portion of ST joint external rotation that would occur
because of SC joint retraction.

199
 The final component motion of the scapula on the
thoracic occurring during arm elevation in all plane is
posterior tilting.

Upward Rotators of the Scapula

201
 There is agreement that
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.

Trapezius
202
 The upper portion of the
trapezius muscle is
attached to the clavicle
and positioned to
contribute directly to the
initial elevation of the
clavicle.

Serratus anterior
203
 The serratus anterior muscle makes its contribution
to the combined clavicular and scapular motion
through its action on the scapula.
 When the location of the axis for upward rotation is
at the AC joint , the lower trapezius may contribute to
upward rotation, although the lower serratus anterior
muscle has a much greater moment arm.

205
 There are substantial implication for the large shift in
axis of rotation for scapular upward rotation with
regard to muscle function.
 As the axis of rotation shifts laterally towards the AC
joint , the serratus anterior muscle maintains the
large moment arm for ST Joint upward rotation
throughout the entire range of elevation.

206
 Despite lines of action and moment arms that are not as
effective for producing ST upward rotation ,the trapezius
is clearly active during arm elevation and plays role in the
balance of forces that move & control the scapula on
thorax. (Trapezius)
 If the serratus anterior muscle acted in isolation, the
lateral line of action would result in substantial lateral
translation and less effective upward rotation of scapula.
 The medial translatory action of the trapezius offsets the
lateral translatory action of the serratus anterior and
results in more effective upward rotation by serratus
anterior.

209
 The serratus anterior muscle, with its insertions into the
inferior angle and medial border of the scapula, plays a
primary role in stabilizing the scapula to the thorax.
 Although the function of the serratus anterior muscle is
classically considered to be production of scapular
protraction, its line of action is capable of producing AC
joint external rotation as it pulls the scapula laterally on
the thorax.
 Any scapular protaction the serratus anterior might help
to produce would be through ST protraction.
 In fact, paralysis of the serratus anterior muscle is
classically characterized by scapular “winging.”

Structural Dysfunction
210
 Disruption of movement in any of the participating
joints will result in a loss of ROM.
 Once restrictions to function are introduced, the
concept of scapulohumeral rhythm is altered; that is,
a reduction in GH joint range will not result in a
proportional decrease in ST range.

Muscles of Elevation

212
 Deltiod muscle
 Supraspinatus muscle
 Infraspinatus , Teres minor and subscapularis
muscle
 Upper & Lower trapezius and Serratus Anterior
muscle function
 Rhomboid muscle function

Deltiod muscle
213
 The deltoid is at resting length (optimal length
tension) when the arm is at the side.
 When at resting length, the deltoid’s angle of pull will
result in a predominance of superior translatory pull
on the humerus with an active contraction.
 With an appropriate synergistic inferior pull from the
infraspinatus, teres minor, and subscapularis
muscles, the rotatory components of the deltoid
muscle are an effective primary mover for flexion and
abduction.

214
 While the anterior deltoid is the prime mover for
flexion, the anterior deltoid can assist with abduction
after 15º of GH motion.
 The action line of the posterior deltoid has too small
a MA (and too small a rotatory component) to
contribute effectively to frontal plane abduction; it
serves primarily as a joint compressor and in
functions such as horizontal abduction.

215
 If the scapular upward rotators are absent, the
middle and posterior fibers of the activate deltoid will
act not on the heavier arm but on the lighter scapula;
that is, without the stabilizing tension in the upward
rotators, the middle and posterior deltoid will
downwardly rotate the scapula.

Supraspinatus muscle
216
 The supraspinatus
muscle is considered an
abductor of the
humerus.
 The MA of the
supraspinatus is fairly
constant throughout the
ROM and is larger than
that of the deltoid for the
first 60º of shoulder
abduction.

217
 When the deltoid is paralyzed, the supraspinatus
alone can bring the arm through most if not all of the
GH range, but the motion will be weaker.
 The secondary functions of the supraspinatus are to
compress the GH joint, to act as a “steerer” for the
humeral head, and to assist in maintaining the
stability of the dependent arm.
 Isolated paralysis of the supraspinatus is unusual,
however, because its innervation is the same as the
infraspinatus and related to that of the teres minor
muscle.

218
 With a suprascapular
nerve block that
paralyzes the
supraspinatus and the
infraspinatus, the
strength of elevation in
the plane of the scapula
is reduced by 35% at 0º
and by 60% to 80% at
150º.

Infraspinatus , Teres minor and
subscapularis muscle
219
 When Inman and coworkers assessed the combined
actions of the infraspinatus, teres minor, and
subscapularis muscles, EMG activity indicated a
nearly linear rise in action potentials from 0º to 115º
elevation.
 Activity dropped slightly between 115º and 180º.
 Total activity in flexion was slightly greater than that
in abduction.

Upper & Lower trapezius and Serratus Anterior
muscle function
220
 The trapezius is
composed of three
distinct bellies: upper,
middle, and lower.
 The muscle’s
attachments on both the
clavicle and scapula
indicate that it acts at
both the
sternoclavicular and
scapulothoracic joints.

221
 The upper trapezius and
upper serratus anterior
muscles form one
segment of a balance of
forces that drives the
scapula in elevation of the
arm.
 These two muscle
segments, along with the
levator scapula muscle,
also support the shoulder
girdle against the
downward pull of gravity Dr.Krupa Soni (MPT Ortho)

222
 In active abduction of the arm, the force of the trapezius
seems more critical than the force of the serratus anterior
muscle to ST motion.
 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
& flexion will be both diminished in strength and limited in
range to 130 or 140 of flexion.

223
 Although the trapezius seems to be more critical to
upward rotation of the scapula in abduction, the
serratus anterior muscle seems to be the more
critical of the two muscles in producing scapular
upward rotation during flexion of the arm.
 Serratus anterior is the only muscle capable of
producing simultaneous scapular upward rotation,
posterior tipping, and external rotation, the three
component motions of the scapula that have been
identified as occurring during elevation of the arm.

224
 The serratus is the primary stabilizer of the inferior
angle and medial border of the scapula to the thorax.
 Finally, reductions of serratus anterior muscle
activation have been identified in patients with
shoulder impingement, which is further suggestive
of the importance of this muscle to normal shoulder
function.

225
 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.

Rhomboid muscle function
226
 The rhomboid major and
minor muscles are
active in elevation of the
arm, especially in
abduction.
 If the rhomboids,
downward rotators of the
scapula, are active during
upward rotation of the
scapula, these muscles
must be working
eccentrically to control the
change in position of the
scapula produced by the
trapezius and the serratus
anterior muscles.

227
 Paralysis of these muscles causes disruption of the
normal scapulohumeral rhythm and may result in
diminished ROM.
 Like the lower trapezius, the rhomboid muscles act
primarily to offset the lateral translation component of
the serratus anterior muscle.

Muscles of Depression

229
 Latissimus dorsi & pectoral muscle function
 Teres major & Rhomboid muscle function

Latissimus dorsi & pectoral muscle function
230
 When the upper extremity is free to move in space,
the latissimus dorsi muscle may produce
adduction, extension, or medial rotation of the
humerus.
 Its activity may contribute to GH joint stability
because the latissimus dorsi causes compression of
the joint when the arm is above the horizontal.

231
 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.

232
 When the hands are
bearing weight on the
handles of a pair of
crutches, a contraction
of the latissimus dorsi
will unweight the feet as
the trunk rises beneath
the fixed scapula,
allowing the legs to
swing forward through
the crutches.

233
 The clavicular portion
of the pectoralis major
muscle can assist the
deltoid in flexion of the
GH joint, but the sternal
and abdominal
portions are primary
depressors of the
shoulder complex.

234
 In activities involving
weight-bearing on the
hands, the pectoralis
major and the latissimus
dorsi muscles in
combination can
depress the shoulder
complex, while
synergistically offsetting
anterior/posterior
movement of the
humerus and
protraction/retraction of
the scapula.

Teres major & Rhomboid muscle function
235
 The teres major
muscle, like the
latissimus dorsi,
adducts, medially
rotates, and extends the
humerus.
 The teres major muscle
is active primarily during
resisted activities but
may also be active
during unresisted
extension and
adduction activities
behind the back. Dr.Krupa Soni (MPT Ortho)

236
 Without stabilization, the teres
major muscle would upwardly
rotate the lighter scapula rather
than move the heavier
humerus.
 The rhomboid muscles, as
downward rotators of the
scapula, offset the undesired
upward rotatory force of the
teres major muscle.
 By fixing the scapula as the
teres major muscle contracts,
the rhomboids allow the teres
major muscle to move the
heavier humerus. Dr.Krupa Soni (MPT Ortho)

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