'ebook (11).pdf

Chia-Hsiung Cheng, OT, Ph.D.
Associate Professor
Department of Occupational Therapy
Graduate Institute of Behavioral Sciences
Chang Gung University
Feb. 22, Mar. 1, & Mar. 8, 2022
Shoulder Complex
1

Kinesiology and Biomechanics for OT
權重代號權重項目權重比例%
OTA01 醫學與行為科學相關知識。 10
OTA02 職能治療生理/長照領域相關知識。 60
OTA03 職能治療心理/社區領域相關知識。 0
OTA04 職能治療兒童/早療領域相關知識。 0
OTA05 研究方法概念。 0
OTA06 專業倫理、素養與終身學習能力。 0
OTA07 臨床專業技能。 30
核心能力

• Shoulder complex is composed of
– 4 bones
– 20 muscles
– 3 bony articulations
– 1 false articulation
Shoulder complex
- Introduction

4
Shoulder complex
- Introduction
• The purpose of shoulder complex
– Stabilizes the UE for hand motions, lifts and pushes objects, etc.
• The only bony attachment of the UE to the trunk is at the
sternoclavicular joint
– Stabilizations of the shoulder are primarily dependent on muscles
and ligaments
– Muscles in this region act in concert with other muscles to provide
its smooth function (synergist)
• Shoulder joint (glenohumeral joint) is only one element of the
shoulder complex

5
• Bones
• Joints
• Muscles of the shoulder complex
• Function of muscles of shoulder complex
• Functional deficiency applications
Outline

• Bones
– Manubrium, clavicle, scapula, humerus
• The manubrium with the left and right clavicles and scapulae
form an incomplete girdle, called shoulder girdle
– A true girdle completely surrounds a structure, but the shoulder
girdle does not have a bony connection posteriorly
Bones
6

• The most cephalic aspect of sternum
• The superior aspect of the manubrium
contains a shallow depression
– Sternoclavicular joint
• Jugular notch
– A prominent concavity that is easily
palpated
• Inferior aspect of the manubrium also
contains a shallow depression
– Attachment for the 1st rib
Manubrium
7

• An S-shaped structure, with the long axis is slightly above the horizontal
plane, resting 20° to the frontal plane
– Forward convexity at the sternal end
• Facets at the medial end
– Articulations with manubrium and first rib
Clavicle

• Costal tuberosity
– Attachment of costoclavicular
ligament
• Facets at the lateral end
– Articulations with scapula’s
acromion process
– There is no connection between
clavicle and humerus
 Animal that stand and run in a
quadruped position do not have
clavicle
 For human, clavicle increases
glenohumeral mobility
Clavicle

• A flat, triangular-shaped bone against the posterior thorax
– Between T2-T7
– Provide a stable base for the glenohemeral joint in more positions
• Inferior and superior angle
• Medial and lateral border
• Acromion
• Glenoid fossa (cavity)
• Spine of scapula (palpated at T3 medially to acromion laterally)
– Supraspinatus fossa
– Infraspinatus fossa
• Subscapular fossa
• Coracoid process
Scapula

Scapula
Coracoid
process Coracoid
process
Superior angle

• Acromion
– The acromion process sits over the
glenohumeral joint to protect it from
overhead force applied down
toward the shoulder
– Acromioclavicular joint (AC joint)
Scapula
- Acromion

• A shallow socket that receives
humeral head
• Two tubercles
– Supraglenoid tubercle
 Attachment site for long head of biceps
– Infraglenoid tubercle
 Attachment site of long head of triceps
• The fossa is narrower at its superior
aspect and broadens at its inferior border
• The glenoid labrum expands the depth
(50%) of glenoid fossa to increase the
joint congruence
Scapula
- Glenoid fossa

• The scapula does not lie in a pure frontal plane
– It rests 30°-45° to the frontal plane
• Because of the position of upper thorax and ribs, the scapula sits
tipped in the sagittal plane about 10°-20° so the superior aspect
of the scapula lies more anterior
Scapula
- Plane of scapula (Scapular plane)

• Head
– 1/3 to 1/2 of a sphere positioned superiorly and rotated posteriorly
– Glenohumeral joint
• Anatomical neck
• Surgical neck
• Greater tubercle
• lesser tubercle
• Intertubercular groove
– Also called “bicipital groove”
– The long head of biceps runs through
Humerus

16
• Bones
• Joints
Outline

• Three synovial joints in the shoulder complex
– Sternoclavicular (SC) joint
– Acromioclavicular (AC) joint
– Glenohumeral (GH) joint
• The scapula also slides on the thorax
• Scapulothoracic (ST) joint (although it is not a joint in the
technical sense of word)
Joints

• “Shoulder girdle” refers to the scapula, clavicle, and manubrium
• Motions at the AC and SC joints produce movement of the
scapula on the thorax (coupling movement)
– If there is deficiency on any of these three joints, the other two are
also affected
– The SC joint is responsible for the majority of scapular movement,
whereas AC joint acts more as a fine tuner of scapula motion
18
Definition of shoulder girdle movements

• Elevation and depression is a motion primarily to describe
the scapula
- Shoulder girdle elevation and depression
Elevation
(10 cm)
Depression
(2 cm)

• Both scapula and clavicle play important roles in this motion
– Protraction: scapular abduction
– Retraction: scapular adduction
- Shoulder girdle protraction and retraction
Protraction
(10 cm)
Retraction
(5 cm)

• Maximum range of upward rotation occurs with the full shoulder flexion
• Complete range of downward rotation occurs when the hand is placed
in the small of the back or when the shoulder is in maximum extension
- Shoulder girdle upward and downward rotation
Upward rotation
Downward rotation

• Anterior-posterior tilting
– Rotation of a scapula along a
medial-lateral axis
– During the shoulder flexion, the
scapula posteriorly tilt
 When the arm is elevated in the
scapular plane, a combination of
__upward_(external)__rotation,
and__posterior__tilting
- Scapular tilting

• SC joint is the only joint that
connects the UE directly to
the axial skeleton
• Saddle joint
– Elevation and depression
– Protraction and retraction
Sternoclavicular (SC) joint
23

• This joint has a disc and 3
strong stabilizing ligaments
– Articular disc
– Interclavicular ligament
– Sternoclavicular ligament
– Costoclavicular ligament
24
- Joint ligaments

• Sternoclavicular ligament
– Anterior and posterior
– Blend with capsule to protect against
anterior-posterior joint stress
• Interclavicular ligament
– Prevent upward clavicular displacement
• Costoclavicular ligament
– Two heads
– Restrict clavicular elevation, rotation,
medial and lateral movement
• The capsule and ligaments are
reinforced by the tendinous attachment
of sternocleidomastoid muscles
- Joint ligaments

• Elevation and depression
– Occurs in the frontal plane and A-P axis
– Elevation of this joint is 30°-45°, with most of the motion occurring
in the first 90° of shoulder elevation
– Elevation of this joint is limited by the costoclavicular ligament
– Depression of SC joint is 5°-10°, until the clavicle is stopped by the
interclavicular ligament, superior capsule, and 1st rib
26
- Joint kinematics

• Protraction and retraction
– Occurs in the transverse plane and nearly vertical axis
– 15°-30° for protraction and retraction
– Posterior SC ligament and costoclavicular ligament limit
protraction, and anterior SC ligament limit retraction
27
- Joint kinematics

• Rotation
– Posterior (backward) rotation about 40°-50° along its long axis
– It occurs after shoulder 90° elevation
– If the rotation of clavicle is prevented, arm elevation is limited to 110°
– Posterior rotation is tightened caused by the trapezoid and conoid
ligaments
– These two ligaments also function to prevent the separation of
clavicle from scapula
- Joint kinematics

- Joint kinematics
The S shape of the clavicle improves the scapula’s elevation motion
The scapula and clavicle
in the anatomical position
As shoulder elevated, scapula
begins upward rotation as
clavicle rotates posteriorly,
making the coracoclavicular
ligament taut
The higher the shoulder
elevates, the tautness of
coracoclavicular ligament
provides greater elevation of
the shoulder

- Joint arthrokinematics

• AC joint
– The acromial end faces medially and slightly superiorly while the
clavicular end faces laterally and inferiorly to for a wedge-like surface
• Superior and inferior acromioclavicular ligaments reinforce the
joint capsule
Acromioclavicular (AC) joint
- Joint ligaments

• SC joint provides for extensive clavicular motion and guides the
general path of the scapula, but AC joint motions are more subtle
and provide key but small adjustments of the scapula
Acromioclavicular (AC) joint
- Joint kinematics

Scapulothoracic (ST) joint
• It is a false, pseudo, or functional joint
– There are no bony articulations
– Separating scapula from thorax are soft tissue structures,
including a large subscapular bursa
– Serratus anterior attaches to the medial border of scapula and
connects to the first 9 ribs
33

• This joint is essential for the mobility and stability of the UE
– Increasing the range of motion to provide greater reach
– Providing glenohumeral stability through maintained glenoid
and humeral head alignment for work in the overhead position
– Providing for injury prevention through shock absorption of
force applied to the outstretched arm
– Permitting elevation of body in activities such as walking with
crutches or performing seated push-ups during transfers by
persons with a disability such as paraplegia
34

- Kinematics (Figs. 5-8 and 5-9)
• ST joint motion is a direct result of motion within the SC and
AC joints (elevation/depression, protraction/retraction…)
• ST joint provides 60° of total shoulder elevation
Practice Point
Total arm elevation is 180°. Since 60° of the motion is provided by the ST
joint, then 120° actually occurs in the glenohumeral (GH) joint itself.
These numbers provide the shoulder complex with a 2:1 ratio of GH
motion to ST motion.
Clinicians must remember this concept when rehabilitating individuals with
shoulder injury. It is important to begin rehabilitation exercise in the
lower 1/3 shoulder elevation before allowing the patient to move the
arm into higher elevation. This procedure allows the scapular muscles to
gain strength sufficiently to stabilize the scapula before increased stresses
are applied to them in higher levels of shoulder positions.

Glenohumeral (GH) joint
- Type of joint
• GH joint
– Ball-and-socket joint
– 3 degrees of freedom
– Little bony stability
– The convex head of humerus head
rests on the small, shallow, and
inclined glenoid fossa
– The humeral head faces a medial,
posterior, and superior direction

- Capsular reinforcement (Table 5-1)
• GH joint relies on surrounding soft tissue supports for its stability
– Coracohumeral ligament (a tunnel for long head of biceps brachii)
– Capsular (superior, middle and inferior glenohumeral) ligaments
– Foramen of Weitbrecht
 A frequent site of anterior dislocations of this joint

• Coracohumeral ligament
– The primary force against gravity’s downward pull on the joint
– Limit lateral rotation
Deep muscles also provide
intimate reinforcement
 Biceps brachii
 Triceps brachii
 Rotator cuff
Subscapularis
Supraspinatus
Infraspinatus
Teres minor

• Rotator cuff tendons can be injured when they move against the
acromion, coracoid process, or the strong connecting coracoacromial
ligament under the coracoacromial arch (impingement syndrome !!!)
• Injuries to these tendons often occur with elevation activities of the arm,
such as working overhead or in throwing sports

- Coracoacromial arch
• Coracoacromial arch is formed by the coracoacromial ligament
• Subacromial space (also called supraspinatus outlet)
– Between the arch and superior humeral head
– It contains supraspinatus muscles and tendon, long head of biceps
tendon, subacromial bursae, superior capsule
– It also protects GH joint from superior dislocations
– If pathologies exist in the soft tissue or bony structure, this space
may become narrower, threatening soft tissue injury (shoulder pain)
 Structural causes: enlarged tendon, angled acromion
 Biomechanical causes: muscle imbalances (or fatigue), poor posture
 e.g., competitive swimmers, people with poliomyelitis and paraplegia
Narrowing of the supraspinatus outlet is the most frequent cause of shoulder injuries

42
- Bursae
• A bursae reduces friction between two structures
– Although there are 8 bursae in the shoulder area, some of them
actually extended from the synovial lining of capsule or are
continuous with each other
– Two to most important: subacromial bursae and subdeltoid bursae

43
- Bursae
• Subacromial bursae
– Between supraspinatus tendon and coracoacromial arch
– It protects the supraspinatus tendon and allows for smooth tendon
movement during shoulder motion
• Subdeltoid bursae
– Continuous with the subacromial bursae and located between
deltoid muscle and supraspinatus tendon and humeral head

44
- Bursae
• If bursae become irritated and inflamed, the amount of fluid
increases (swollen bursae)
– Volumetric increase in subacromial bursae is problematic because
the narrower space will limit available space
– Inflamed GH bursae are usually the secondary conditions that are
caused by other existing injuries
 Supraspinatus tendon bursae narrowing the space and
impingement of soft tissue

45
- Joint kinematics (without scapula)
• Three degrees of freedom
– Flexion-extension, abduction-adduction, medial-lateral rotation
• Abduction and adduction
– The amount of abduction depends on the rotation of GH joint
– When GH joint medial rotation, the abduction is limited to 60°
(greater tubercle strikes acromion process)
– With 90° lateral rotation, greater tubercle rotates behind the
acromion so active abduction increases to 90° (limited by the active
insufficiency of deltoid muscle)
– Abduction can be continued passively to 120°, where it is then
limited by tension of inferior GH ligament

46
• Medial and lateral GH rotation
– GH rotation is isolated from supination and pronation of forearm by
elbow 90° flexion
– When the arm is 90° abduction, the total rotation is about 160°
– When the arm is fully elevated, it reduced to 90° (twisting and
tightening of coracohumeral and GH ligaments)
– When the shoulder is 90° abduction with forearm 90° flexion, the GH
lateral rotation is 90°, and medial rotation is about 70°

47
• Elevation of GH joint includes either flexion or abduction
– GH joint flexion is up to 120° (full flexion to 180° is due to the motion
of scapulothoracic joint)
– Achievement of maximum GH elevation requires lateral rotation of
GH in abduction
– The range of hyperextension is 40 to 60°, and limited by the
superior and middle GH ligaments
• Horizontal abduction and adduction
– These motions occur from a starting position of 90° abduction
• All normal limitations of motion on GH joint are due to ligaments and
passive muscle tightening. Thus, the end feel are all firm.

48
- Joint arthrokinematic motions
• Shoulder joint flexion and extension
– Humeral head spins in the glenoid fossa (no slide and rolling)
– However, slide of humeral head on glenoid fossa occurs when
shoulder reaches higher level of elevation or hyperextension
• Shoulder abduction
– Humeral head rolls superiorly as it slides inferiorly

49
- Joint arthrokinematic motions
• Lateral rotation
– Humeral head rolls posteriorly and slides anteriorly on the glenoid
fossa
• Medial rotation

- Shoulder abduction in the scapular plane (scaption)
• Scaption
– Defined by Perry to describe this plane of motion (scapular plane)
– GH abduction occurs 30° to 40° anterior to the frontal plane
– This position is recommend for evaluation of GH joint because
capsule is in a loose-packed position and is less likelihood of
impingement on the coracoacromial structure
• Most functional shoulder abduction motions in daily and sport
activities occur in the scapular plane

Resting and close-packed positions of shoulder complex
• The resting position of GH joint
– 20° to 30° horizontal abduction, and
– 55° flexion
• The closed-pack position of GH joint
– Full abduction with full lateral rotation
– Improper sleeping position is frequently a source of shoulder pain
and injury
• The closed-packed position of
– Sternoclavicular joint: when the arm is fully elevated
– Acromioclavicular joint: when the arm is 90° abduction

Scapulohumeral rhythm (P. 183)

53
• Bones
• Joints
Outline

Muscles of the shoulder complex
• Shoulder region muscles are divided into three groups
– Scapular stabilizers (Table 5-4)
Serratus anterior, trapezius, rhomboid major and minor,
pectoralis minor, levator scapulae
– GH stabilizers (Table 5-5)
Supraspinatus, infraspinatus, teres minor, subscapularis, biceps
brachii, triceps brachii
– Large movers of the shoulder (Table 5-6)
Deltoid, latissimus dorsi, teres major, pectoralis major,
coracobrachialis
54

• It is the primary scapular protractor
– Without it, the arm cannot be raised
to overhead
– The lowest 5 digitations is the
strongest portion
• Palpation
– Lower digitations may be seen and
palpated near the rib when the arm
is overhead
• “Winging” scapula
– When this muscle is paralyzed, the
scapula fails to protract on the rib
cage or to remain in contact with it
Scapular stabilizers
- Serratus anterior (“saw muscle”)
Origin: ribs 1-9
Insertion: vertebral border of scapula
55

• Upper trapezius
– Scapula: elevation, upward rotation
– Neck: extension, lateral flexion
• Lower trapezius
– Scapula: upward rotation,
depression, adduction
• Middle trapezius
– Scapula: adduction
• It is a superficial muscle of neck and
upper back, and easy to palpate
• In complete paralysis of this muscle,
shoulder elevation is limited to
120°…….why?
- Trapezius (“shawl muscle”)
Origin: occipital bone, spinous
processes from C7-T12
Insertion: acromion, spine of scapula
56

• They connect scapula with vertebral
column (lie under trapezius)
– Cranial portion: rhomboid minor
– Caudal portion: rhomboid major
• The rhomboids are made up of
parallel fibers
– The direction is almost
perpendicular to lower trapezius
• Action includes downward rotation
(rhomboid major), adduction, and
elevation of scapula
- Rhomboid major and minor
Origin: spinous processes from C6-T4
Insertion: medial border of scapula
57

• This muscle is entirely covered by
pectoralis major
• Weakness of this muscle
– Reduced strength during
depression of scapula against
resistance
- Pectoralis minor
Origin: ribs 2-5
Insertion: coracoid process 58

• It is covered by upper trapezius and
sternocleidomastoid muscle
– Scapula elevation
– Downward rotation (different from
upper trapezius)
- Levator scapulae
Origin: transverse processes of upper
cervical vertebrae
Insertion: medial border of scapula,
above the spine
59

• These muscles include rotator cuff group
– Provide GH stability and motion
• Rotator cuff sometimes refer to “SITS” muscles
– This label refers to their arrangement around GH joint
Glenohumeral stabilizers
60

• It is located above the spine and
covered by trapezius and deltoid
• Action
– Total motion of humeral abduction
without assistance of deltoid
- Supraspinatus
Origin: supraspinous fossa
Insertion: upper facet of greater tubercle
61

• Infraspinatus
– It occupies most of the infraspinatus
fossa
– Lateral rotation and adduction of GH
joint
• Teres minor
– Lateral rotation and adduction of GH
joint
- Infraspinatus and teres minor
Infraspinatus
Origin: infraspinatus fossa
Insertion: middle faucet of greater
tubercle
Teres minor
Origin: lateral border of scapula
Insertion: lower faucet of greater
tubercle

• It is located in the anterior scapula
 Primary function: medial rotation
- Subscapularis
Origin: costal surface of scapula
Insertion: lesser tubercle
63

• Two heads of biceps and long head of triceps cross the shoulder
joint and act on it
– Long head of biceps: attach to supraglenoid tubercle
– Short head of biceps: attach to coracoid process
– Triceps: attach to infraglenoid tubercle
• Biceps is an important stabilizer for GH joint during elevation, abduction,
and lateral rotation
• The long head of triceps also provides stability to GH joint during
elevation, abduction, and weight-bearing activities
- Biceps brachii and triceps brachii
Flexor
Abductor
Extensor and adductor

• This superficial muscle covers the
GH joint on all side exception for
inferior axillary area
• Although all 3 heads of deltoid
work together to produce
abduction as a common motion
– Anterior deltoid: flexion, horizontal
adduction, medial rotation
– Posterior deltoid: extension,
horizontal abduction, lateral
rotation
Large movers of the shoulder
- Deltoid
Origin: clavicle, acromion process,
spine of scapula
Insertion: deltoid tuberosity of humerus
65

• In normal condition, supraspinatus initiates GH abduction
– With supraspinatus paralysis, the deltoid is able to perform this
motion in full range (less strength)
• When the arm abduct to 50° or higher, it allows deltoid to work
synergistically with the rotator cuff to be a prime mover in
shoulder elevation after the initial range of motion
- Deltoid
66

• The largest part is thin and sheet-
like on the posterior thorax
• If the arms are stabilized, as in a
seated press down, the distal
attachment aids to lift the pelvis
– In crutch walking: this muscle
allows the foot to clear the ground
– In seated push-up: minimize the
likelihood to develop pressure sore
• It serves a vital function for divers,
gymnasts, wrestles, etc.
– Support their body with their UE
– Coughing muscle, swimmer’s muscle
- Latissimus dorsi (the broadest muscle)
Origin: spinous processes
Action: medial rotation, extension,
and adduction of GH joint
67

• It is round like the minor, but larger
– Extension and adduction of GH
joint
– This muscle acts in most pulling
activities (its function is closely
aligned with that of latissimus dorsi)
- Teres major
Origin: inferior angle of scapula
68

- Pectoralis major
• Two segments based on its fiber directions and function
– Clavicular head: flexes GH joint
– Sternocostal head: extends GH joint from fully flexed position
• The tendon appears to be twisted at the distal attachment
Origin: clavicle, sternum, ribs 2-6
Insertion: greater tubercle
Action: GH adduction, medial
rotation and horizontal adduction
69

• Parts of this muscle is covered by
deltoid, pectoralis major, and
biceps brachii
• It is considered a mover rather a
stabilizer of GH joint
– Since its line of pull is sufficiently
distant from the joint axis of motion
– Flexion and adduction of GH joint
- Coracobrachialis
Origin: coracoid process of scapula
Insertion: middle of shaft of humerus
70

71
• Bones
• Joints
Outline

• Passive (static) stabilization
– Capsule
– ligaments
• Dynamic stabilization
– Muscles
 Rotator cuff
 Biceps brachii
 Deltoid
 Trapezius
Passive and dynamic stabilization of GH joint
72

• Motions at the SC and AC joints are limited by strong ligaments,
and bony configuration, but GH and ST joints have little
ligamentous or bony stability
• There is no muscle contraction of shoulder girdle during relaxed
sitting or standing
– What structure prevent the humerus from subluxation?...Textbook
- Passive stabilization
73

• Trapezius
– Its activity is related to head posture because the upper fiber are
neck extensors and scapula elevators
– Source of tension and neck pain in people who work at a desk or
who have poor posture
– Trapezius paralysis is accompanied by scapular dropping and
downward rotation
- Dynamic stabilization

• Rotator cuff stabilization
– The most important function is to provide stability by compressing
humeral head into glenoid fossa during elevation of GH joint
– Not only pulls the humerus to the glenoid, but also moves the
humeral head into lower portion of glenoid fossa (allowing sufficient
space under coracoacromial arch)
75

• Biceps brachii
– The tendon of long head of biceps courses over the humeral head
and descends in the intertubercular groove
– Tension is produced when the muscle contracts to compress the
humeral head against the glenoid fossa (prevent subluxation of GH
joint when the elbow flexes with a weight in hand)
76

• Deltoid and rotator cuff
– With its main function of GH abduction, deltoid has a small rotary
component to its muscle force vector during arm elevation
– In the early part of elevation, deltoid bring the humeral head to the
glenoid, causing humeral head move upward to hit coracoacromial arch
– This movement is prevented by the horizontal and downward pull of
rotator cuff muscles

• Deltoid and rotator cuff (cont.)
– When arm elevates, rotator cuff pulls the humerus into the larger
inferior area, due to the factors of
1) The surface between glenoid and humeral head is greater,
providing more stability
2) With the humeral head depressed in the socket, the
subacromial soft tissues have optimal room and less risk of
impingement
Elevation with inadequate rotator cuff strength to
maintain the humeral head in the lower glenoid fossa

– As elevation progresses, most of the
force generated by deltoid is directed
to the stabilizing component
– In full shoulder elevation
 Serratus anterior and trapezius
(black) stabilize the scapula
 Then the scapular stability by rotator
cuff (green) allows the glenoid to be
stable in overhead motion
 At the same time, the humeral head
is held in a secure position by
rotator cuff
(Scapular rotator)
79

– Either or by combination of scapular rotators imbalance with
weakness of rotator cuff causes subacromial impingement
– Subacromial impingement during elevation
1) Deltoid overpowers the rotator cuff to pull humeral head into the
superior head of glenoid socket
2) Scapula shrugs upward rather than rotating upward
With lower trapezius and serratus anterior
weakness, the upper trapezius overpowers
these scapular upward rotators to cause the
scapula to elevate rather than rotate, leading
to impingement !!

• Definition: many muscles work together during any motion,
because of larger ROM and the absence of structural stability
• Sometimes the muscles work synergistically to produce a desired
motion; at other times, they are antagonist to each other
– Elevation of scapula: upper trapezius and levator scapulae (synergy)
– Upward rotation of scapula: serratus anterior, upper trapezius, and
lower trapezius
– Downward rotation of scapula: pectoralis minor, levator scapula,
rhomboid
Synergist muscle action (Table 5-7)

• Definition
– Two forces whose points of application occur on opposite sides of an axis
and in opposite directions to produce rotation
• During shoulder elevation, there are two primary force couples
– Scapulothoracic force couple: upper and lower trapezius, and serratus
anterior to produce upper rotation (What about downward rotation?)
– Glenohumeral force couple: deltoid and supraspinatus produce elevation,
while infraspinatus, teres minor and subscapularis pull the humeral head
down into the socket, producing rotation of the joint
Synergist muscle action
- Force couple

84
• Bones
• Joints
Outline

Functional deficiency applications
• At the GH joint, 3 to 5 muscles can perform each motion
– Other muscles can compensate for the paralyzed muscle
– Only with reduced strength
• At the scapula, each muscle perform very specific motion
– A deficiency of a single muscle can seriously affect the use of arm
• Scapular dyskinesis (肩胛運動障礙)
– Definition: an abnormal position and pattern of motion in the scapula
– Scapular dyskinesis may lead to many conditions, such as
subacromial impingement, GH instability, Superior Labrum Anterior
to Posterior (SLAP) lesions
85

• SLAP lesion (tear)
– Overhead and contact sports pose a greater risk
– Prevention: strong shoulder muscles remain the best defence
against shoulder injury; adequate warm-up before activities
86

- Serratus anterior
• With the deficiency of serratus anterior
– Scapula is not held against the rib cage and the medial border is
winged
– Scapulohumeral rhythm is abnormal (unable to fully elevate the arm)
– Unable to push on doors or drawers (without the stabilization by
serratus anterior, the pressure cause scapula to move posteriorly)
Dysfunction of serratus anterior produces
winging of the scapula’s medial border!
87

- Trapezius
• With the deficiency of trapezius
– Depression and downward rotation of the scapula
– The downward rotation of scapula in turn cause the likelihood of GH
subluxation and pain in the sternoclavicular joint
Weakness in the trapezius causes instability
of the scapula with positioning in downward
rotation and protraction!
88

- Trapezius and serratus anterior
• With the deficiency of both trapezius and serratus anterior
– Destroys scapular stability and its ability to upwardly rotate
– If this happens, deltoid cannot achieve an appropriate position that
will allow it to elevate the arm
– Imbalance of these muscles’ strength will lead to impingement (with
the existence of rotator cuff weakness)

Application in ADL (self reading, chapter 13 and 14)
90

92

93

Any question ??
• Contact information
 Email: ch.cheng@mail.cgu.edu.tw
 Office phone: 03-2118800 #3854

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