Shoulder Complex anatomy for medical .pdf

Anatomy

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3. SHOULDER COMPLEX

Dr/Mohamed Ahmed Raafat
Lecturer of Physical Therapy for
Neurology Disorders and it’s Surgery
South valley University

TADA Na

4. > AMO XA ASIN O SS

FOUR JOINTS & FOUR BONES WITHIN THE SHOULDER COMPLEX

Four joints:

+ Sternoclavicular joint

+ Acromioclavicular joint
+ Scapulothoracic joint

* Glenohumeral joint

Four bones:
+ Sternum,
+ Clavicle,
+ Scapula,
+ Proximal-to-Mid Humerus

[A

5. GENERAL FUNCTION

+ Provides very mobile, yet strong base for hand to perform its intricate
gross and skilled functions

+ Transmits loads from upper extremity to axial skeleton.
+ Clavicle:

V Acts a strut connecting upper extremity to thorax

V Protects brachial plexus & vascular structures

y Serves as attachment site for many shoulder muscles

6. Loe

Anterior view
Sternocleidomastoid

STERNUM

Osteologic Features of the Sternum
+ Manubrium
+ Clavicular facets
+ Costal facets
+ Jugular notch

+ costal facets located on the lateral edge of the manubrium
provide bilateral attachment sites for the first two ribs.

Xiphoid
process

7. CLAVICLE

Osteologic Features of the Clavicle
+ Shafe

+ Sternal end

+ Costal facer

= Costal tuberosity
= Acromial end
= Acromial facet
+ Conoid tubercle
+ Trapezoid line

+ Shaft: convex medially and concave lat

+ long axis of the clavicle is oriented slight
horizontal plane and about 20 degrees

the frontal plane.

. costal facet (inferior surface) rests again
rib.

+ costal tuberosity, an attachment for the
Ci ligament.

8. FIGURE 5-5. Posterior (A) and anterior (B) surfaces of the right scapula. Proximal attachments of muscles are
' shown in ved, dal anachments in gray. The dashed lies show the capsulas arachments around the geno-
umeral joint.

9. + Triangular-shaped scapula has three angles: inferior, superior,and lateral.

+ Palpation of the inferior angle provides a convenient method for following the
movement of the scapula during arm motion.

+ The scapula also has three borders.

* posterior surface of the scapula is separated into a supraspinous fossa and an
infraspinous fossa by the prominent spine. The depth of the supraspinous fossa is
filled by the supraspinatus muscle.

+ The medial end of the spine diminishes in height at the root of the spine.

* the lateral end of the spine gains considerable height and flattens into the broad
and prominent acromion.

+ The clavicular facet on the acromion forms part of the Geromioclavicular joint,

. En ‘à head of the humerus at the slightly concave g/enoid
»5sa

10. Superior view

SCAPULA

Lateral

Conoid ligament

Trapezoid ligament

Pectoralis minor

Short head biceps
and coracobrachialis.

FIGURE 5-6. A close-up view of the right coracoid process seen from
oe Proximal attachments of muscle are in red, distal attachments
amentous attachment is indicated by light blue outlined
by dica fide,

11. SCAPULA

+ The slope of the glenoid fossa is inclined upward about 4 degrees relative
to a horizontal axis through the body of the scapula.

+ (scapular plane) : At rest the scapula is normally positioned against the
posterior-lateral surface of the thorax, with the glenoid fossa facing about
30-40 degrees anterior to the frontal plane.

* coracoid process projects sharply from the scapula, providing multiple
attachments for ligaments and muscles. 22222222(mention)

12. FIGURE 5-4. Superior view of both shoulders in the anatomic position. Angle A: The orientation of the clavicle
deviated about 20 degrees posterior to the frontal plane. Angle B: The orientation of the scapula (scapular
plane) deviated about 35 degrees anterior to the frontal plane. Angle C: Retroversion of the humeral head
about 30 degrees posterior to the medial-lateral axis at the elbow. The right clavicle and acromion have been
removed to expose the top of the right glenohumeral joint.

13. of

PROXIMAL-TO-MID HUMERUS

Osteologic Features of the Proximal-to-Mid Humerus
+ Head of the humerus
+ Anatomic neck
+ Lesser tubercle and crest
+ Greater tubercle and crest
+ Upper, middle, and lower facets on the greater ubercle
+ Interrubercular (bicipital) groove
+ Deltoid tuberosity
+ Radial (spiral) groove

” FIGURE 5-7. Anterior (A) and superior (B) aspects ofthe right humerus. The dashed line in A shows the
capsula attachments around the glenohumeral joint. Dial atachment of muscles is shown in gay.

14. PROXIMAL-TO-MID HUMERUS
° Humeral head :
Y faces medially and superiorly,

V forming an approximate 135 degree angle of inclination with the long axis
of the humeral shaft.

Y normally rotated (or twisted) posteriorly about 30 degrees within the
horizontal plane.

= Humeral neck:
Y has prominent lesser and greater tubercles.

y greater tubercle has an upper, middle, and lower facet, marking the distal
attachment of the supraspinatus, infraspinatus, and teres minor, respectively

15. FIG. 5.8 The right humerus showing a 135-degrec “angle of inclination” between the shaft and head of the humerus
in the frontal plane (A) and the retroversion of the humeral head relative to the distal humerus (B).

16. PROXIMAL-TO-MID HUMERUS

+ Sharp crests extend distally from the anterior side of the greater and
lesser tubercles. These crests receive the distal attachments of the
pectoralis major and teres major.

» intertubercular (bicipital) groove:
V which houses the tendon of the long head of the biceps brachii.

V The latissimus dorsi muscle attaches to the floor of the intertubercular
groove, medial to the biceps tendon.

y Distal and lateral to the termination of the intertubercular groove is the
deltoid tuberosity.

17. PROXIMAL-TO-MID HUMERUS

+ radial (spiral) groove:

Y runs obliquely across the posterior surface of
the humerus.

y separates the proximal attachments of the
lateral and medial heads of the triceps

y Traveling distally, the radial nerve spirals
around the posterior side of the humerus in the
radial groove,

y The oblique path of the radial groove and its
contained nerve may be explained as a physical
remnant of the natural de-rotation of the
excessively retroverted humerus

Triceps
(medial head)

Posterior view

Infraspinatus

Middle facet

Teres minor

Lower facet

Triceps
(lateral head)

18. + As the shoulder girdle
composed of 4 joints , the
term “shoulder movement”
describes the combined
motions at both
(glenohumeral j +the
scapulothoracic j).

Terminology Describing the Primary Movements at the

Scapulothoracic Joint

Elevation—The scapula slides superiorly on the thorax, as when
“shrugging of the shoulders.”

Depression —From an elevated position, the scapula slides inferiorly
on the thorax.

Protraction—The medial border of the scapula slides anterior-
laterally on the thorax away from the midline, as when maximiz-
ing forward reach.

Retraction—The medial border of the scapula slides posterior-
medially on the thorax toward the midline, as when “pinching”
of the “shoulder blades” together.

Upward rotation—The inferior angle of the scapula rotates in a
superior-lateral direction, facing the glenoid fossa upward. This
rotation occurs as a natural component of raising the arm
upward.

Downward rotation —From an upward rotated position, the inferior
angle of the scapula rotates in an inferior-medial direction. This
motion occurs as a natural component of lowering the arm
down to the side.

19. o

Elevation and depression Protraction and retraction Upward and downward rotation

Cc

FIG. 5.10 Motions of the right scapulothoracic joint. (A) Elevation and depression. (B) Protraction and retraction.
(©) Upward and downward rotation.

20. STERNOCLAVICULAR JOINT

+ Irregular saddle-shaped articular joint
surface (medial end of the clavicle is
usually convex along its longitudinal
diameter and slightly concave along its
transverse diameter).

+ The remarkable stability at the SC joint is

due to the arrangement of the
periarticular connective tissues and
muscles, means Large forces through the
clavicle often cause # of the bone before
the SC joint dislocates.

21. STERNOCLAVICULAR JOINT

Manubrium

FIG. 5.11 The sternoclavicular joints. The capsule and lateral section of the anterior bundle of the costoclavicular liga-
ment have been removed on the left side.

Tissues That Stabilize the Sternoclavicular Joint

Anterior and posterior sternoclavicular joint ligaments
Interclavicular ligament

Costoclavicular ligament

Articular disc

Sternocleidomastoid, sternothyroid, sternohyoid, and subcla-
vius muscles

a

22. STERNOCLAVICULAR JOINT
OSTEOKINEMATIC

ProT/ReT]

ROM:
- Axial Rotation: 50°
-EL/DEP: 35°

- PROT/RET: 35°

23. STERNOCLAVICULAR JOINT
OSTEOKINEMATIC

* The osteokinematics of the clavicle rotate in all three degrees of
freedom (sagittal, frontal, and horizontal )

* clavicle elevates and depresses, protracts and retracts, and
rotates around the bone’s longitudinal axis

. = The primary purpose of these movements is to place the
scapula in an optimal position to accept the head of the humerus.

=> as the arm is raised overhead

24. o
STERNOCLAVICULAR JOINT

Superior view FABURE 514, Anterior ie fa mechanical
digan of the anbrokinematcs of ol and
slide during elevation (A) and depresion (B)
ofthe aide around the gt stemoce
calar joint, The ates of rotation ae shown
in the amerio-pesterior diction tea the
eu ofthe civil Suche cures ae
shown as thin elongated ao; sien
ces are shown a any row. Not in
A a the cho cosochavcula hgament
produce à dommmar fre in the direction
ofthe side, CCL cosocviular gament;
CL, inercial games; SC, superior
aprık.

fetures are shown as a wa
CL, costoclavicular liga

terior capsular ligameı

Retraction occurs as the concave articular Elevation of the clavicle occurs as its
surface of the clavicle rolls and slides convex articular surface rolls superiorly
posteriorly on the convex surface of the and simultaneously slides inferiorly on
sternum the concavity of the sternum

25. ACROMIOCLAVICULAR JOINT

+ The AC joint is a gliding or plane joint, EEE 'oll-cnd-slide arthrokinematics
are not described

+ The articular surfaces at the AC joint are lined with a layer of fibrocartilage
tissue, usually separated by an articular disc.7

Slave,

26. ACROMIOCLAVICULAR JOINT

Tissues That Stabilize the Acromioclavicular Joint
+ Superior and inferior actomioclavicular joint ligaments
+ Coracoclavicular ligament

+ Articular disc (when present)

+ Deltoid and upper trapezius

ligament
Coracoclavicular

Trapezoid Igament

ligament

27. ACROMIOCLAVICULAR JOINT
OSTEOKINEMATIC

Q The motions of the AC joint
are described by movement
of scapula relative to the
lateral end of the clavicle.

Q Motion has been defined for
3 degrees of freedom: oe

¥ upward (30) downward rotation
Y” Horizontal plane adjustments (IR+ER)

Y Sagittal plane adjustments (anterior

tilting + posterior tilting )
Q Difcult to measur ROM ... REFLECT
It SCAPULOTHORACIC Je

{ps oucobinematcs of the sty, croire (AC) join, The
donna rotation ar hows purple, Honcontal ad mapa plane au
shown

28. SCAPULOTHORACIC JOINT

OSTEOKINEMATIC
not a true joint per se but rather a point of contact between the anterior surface of the scapula

and the posterior-lateral wall of the thorax.

Utwo surfaces do not make direct contact; rather, they are separated by layers of muscle, such as the
subscapularis, serratus anterior, and erector spinae.

Oplane of the scapula:
>10 degrees of anterior tilt,
+5 to 10 degrees of upward rotation, and about

> 30-40 degrees of internal rotation

l. Scapulothoracic elevation & Depression
ll. Scapulothoracic Protraction and Retraction
Il. pulothoracic upward &downward Rotation

29. SCAPULOTHORACIC JOINT

30. SCAPULOTHORACIC JOINT

Posterior view

FIGURES-22. A, Scapulothoracc upward rotation shown asa summation of B (elevation atthe sternoclavicular
join) and C (upward rotation atthe acromioclaicular join)

31. GLENOHUMERAL JOINT

CGH) joint is the articulation formed between the
relatively large convex head of the humerus and the
shallow concavity of the glenoid fossa.

Qglenoid fossa is directed anterior-laterally in the scapular
plane.

Ohumeral head is directed medially and superiorly, as well
as posteriorly because of its natural retroversion.

AClose-packed position
+ ABD with LR

JOINT FIBROUS CAPSULE:

V Inherently lax

Y Surface area 2X head size

v Rrovides restraint for ABD, ADD, LR, MR
= extensive mobility GH joint.

[

32. o

GLENOHUMERAL JOINT

Fibrous capsule

Glenoid labrum

Transverse ligament

Articular

(cut) cartilage
Synovial sheath
for biceps tendon
Biceps brachli
tendon (ong head)

Axillary pouch

FIGURE 5-23. Anterior view ofa frontal section through the right glenohumeral joint. Note the fibrous capsule,
synovial membrane (blue), and the long head of the biceps tendon. The axillary pouch is shown as a recess in
A the inferior capsule.

33. GLENOHUMERAL JOINT

FIGURE 5-25. Anterior view of

Conoid
the right glenohumeral joint trang, 1 % jj soem

showing the primary ligaments." igament Z

Note the subacromial space Trapezoid
located between the top of the ligament

humeral head and the underside
of the acromion.

34. GLENOHUMERAL JOINT

Capsular Ligaments

TABLE tal Attachments and Primary Functions of the Glenohumeral Joint Capsular Ligaments
Superior glenohumeral Anatomic neck, above the lesser Adduction; inferior and anterior-posterior
ligament tubercle translations of the humeral head
Middle glenohumeral ligament Along the anterior aspect of the Anterior translation of the humeral head, especiall
anatomic neck; also blends with in about 45-60 degrees of abduction; external
the subscapularis tendon rotation
Inferior glenohumeral ligament As a broad sheet to the anterior Axillary pouch: 90 degrees of abduction, combine:
(three parts: anterior band, inferior and posterior-inferior with anterior-posterior and inferior translations
posterior band, and margins of the anatomic neck Anterior band: 90 degrees of abduction and full
connecting axillary pouch) external rotation; anterior translation of humera
head

Posterior band: 90 degrees of abduction and full
internal rotation
Coracohumeral ligament Anterior side of the greater tubercle; Adduction; inferior translation of the humeral
also blends with the superior head; external rotation
capsule and supraspinatus tendon

35. D

GLENOHUMERAL JOINT

Muscles and Long Head of the

eps Brachii

Coracoacromial arch

Supraspinatus Biceps brachii tendon (long head)

Coracoacromial ligament
Subacromial bursa Coracohumeral ligament

Coracoid process

‘Superior glenohumeral ligament
Rotator interval

Infraspinatus
Glenoid labrum

Glenoid fossa a
Teres minor Middle glenohumeral ligament

“Anterior band | inferior
Axillary pouch | glenohumeral
Posterior band | ligament

36. Coracoid process

Biceps brachii
tendon (long head)

FIG. 5.25 Side view of right glenohumeral joint with the joint opened
up to expose the articular surfaces. Note the extent of the subacromial
space under the coracoacromial arch. Normally this space is filled with
the supraspinatus muscle and its tendon, and the subacromial bursa.

37. GLENOHUMERAL JOINT

Rotator Cuff Muscles and Long Head of the Biceps Brachii

QOGH joint capsule receives significant structural reinforcement from the four
rotator cuff muscles

QThe subscapularis, the thickest of the four muscles, lies just anterior to the
capsule. The supraspinatus, infraspinatus, and teres minor lie superior and
posterior to the capsule.

OThese four muscles form a cuff that protects and actively stabilizes the GH
joint, especially during dynamic activities.

Qtendons of these muscles actually blend into the capsule. E> This unique
anatomic arrangement helps explain why the mechanical stability of the GH
joint is so dependent on the innervation, strength, and control of the rotator
cuff muscles.

38. GLENOHUMERAL JOINT
Rotator Cuff Muscles and Long Head of the Biceps Brachii

Orotator cuff fails to cover two regions of the capsule: inferiorly, and a
region between the supraspinatus and subscapularis known as the rotator

cuff) interval.

OThe rotator interval is typically reinforced by the tendon of the long head
of the biceps, the coracohumeral ligament, and by superior and (sometimes
upper parts of the) middle GH ligaments.

UThe rotator interval is a relatively common site for anterior dislocation of
the GH joint

39. GLENOHUMERAL JOINT

Doriginates off the supraglenoid tubercle of the scapula and adjacent rim of
connective tissue known as the glenoid labrum.

OF rom this proximal attachment, this intracapsular tendon crosses over the humeral
head as it courses distally toward the intertubercular groove on the anterior humerus.

OFunction:
> restricts anterior translation of thehumeral head.

> position of the tendon across the dome of the humeral head > resists superior
translation of the humeral head

40. GLENOHUMERAL JOINT

Úrim of the glenoid fossa is encircled by a triangular fibrocartilagenous
ring, or lip,

About 50% of the overall depth of the glenoid fossa has been
attributed to the glenoid labrum.

ÜBy deepening the concavity of the fossa, the labrum increases contact
area with the humeral head & therefore helps stabilize the joint.

41. GLENOHUMERAL JOINT

Tissues That Reinforce or Deepen the
Glenohumeral Joint

Joint capsule and associated GH capsular ligaments
Coracohumeral ligament

Rotator cuff muscles (subscapularis, supraspinatus, infraspina-
tus, and teres minor)

Long head of the biceps brachii

Glenoid labrum

42. SCAPULOTHORACIC POSTURE AND ITS EFFECT
ON STATIC STABILITY

+» (A) The rope indicates a muscular force that holds the glenoid fossa in
a slightly upward-rotated position. In this position. the passive tension
in the taut superior capsular structure (SCS) is added to the force
produced by gravity (G), yielding the compression force (CF). The
compression force applied against the slight incline of the glenoid
“locks” the joint.

(B) With a loss of upward rotation posture of the

scapula (indicated by the cut rope), the change in angle between the
SCS and G vectors reduces the magnitude of the compression force
across the GH joint. As a consequence, the head of the humerus may
slide down

the now vertically oriented glenoid fossa. The dashed lines indicate
the parallelogram method of adding force vectors.

+ SCS: superior capsular ligament +the
(+ Jacohumeral lig + the of the supraspinatus tendon

43. D

CORACOACROMIAL ARCH AND ASSOCIATED BURSA

Subacromial bursa

Supraspinatus |
and tendon Capsular ligament
Deltoid Synovial membrane

o Glenoid labrum
Subdeltoid

subacromial bursa
subscapular bursa,
subdeltoid bursa

44. GLENOHUMERAL JOINT
OSTEOKINEMATICS

[GH joint rotates in all 3 planes & possesses 3 degrees of
freedom.
> The primary rotational movements at GH joint are: flexion
and extension (60°),
> abduction (180°)

— 60° in max IR

> adduction, Hyperadduction (75°) pri
internal and external rotation (90°)

VW

(435°) & abduction (45°) |

45. ARTHROKINEMATICS

convex head of the humerus
rolling superiorly while
simultaneously sliding inferiorly
Y

a spinning motion of the humeral
head around the glenoid fossa.

v ER
‘humeral head simultaneously

rolls posteriorly + slides
anteriorly on the glenoid fossa

s

Subacromial

Supraspinatus
pull

FIG. 5.31 The arthrokinematics of the right glenohumeral joint during
active abduction. The supraspinatus is shown contracting to direct the
superior roll of the humeral head. The taut inferior capsular ligament
(ICL) is shown supporting the head of the humerus like a hammock (see
text). Note that the superior capsular ligament (SCL) remains relatively
taut because of the pull from the attached contracting supraspinatus.
Stretched tissues are depicted as long black arrows.

46. GLENOHUMERAL JOINT

* acromiohumeral distance (AHD)
naturally fluctuates from about 7.5 mm
at 20 degrees of abduction to its
smallest distance of 2.6 mm near 85
degrees of abduction. The AHD then
increases to about 5 mm at 150 degrees
of abduction.

V Recall that the longitudinal diameter
of the articular surface of the humeral
head is almost twice the size of the

longitudinal diameter on the glenoid 0 20 40 60 80 100 120 140 160
fossa Shoulder abduction angle (degrees)

4

E)

Acromiohumeral distance (mm)

9
8
7
6
5
4
3
2
1

o

47. Coracoacromial arch

BSSO} prova]

Subacromial bursa

N

Y

Supraspinatus pull

48. FIGURE 5-35. Posterior view of the
right shoulder complex after the
arm has abducted 180 degrees.
The 60 degrees of scapulothoraci
joint upward rotation and the 120
degrees of glenohumeral (GH) joint
abduction are shaded in purple.
Additional inserts contained in the
boxes depict superior and lateral
views of selected kinematics of the
clavicle and scapula, respective
All numeric values are chosen from
a wide range of estimates cited
across multiple literature sources
(see text). Actual kinematic values
vary considerably among persons
and studies.

49. Six Kinematic Principles Associated with Full Abduction of the Shoulder

Principle 1: Based on a generalized 2:1 scapulohumeral rhythm,
active shoulder abduction of about 180 degrees occurs as a
result of simultaneous 120 degrees of glenohumeral (GH)
joint abduction and 60 degrees of scapulothoracic upward
rotation.

Principle 2: The 60 degrees of upward rotation of the scapula during
full shoulder abduction is the result of a simultaneous elevation at

sternoclavicular (SC) joint combined with upward rotation at

e acromioclavicular (AC) joint.

Principle 3: The clavicle retracts at the SC joint during shoulder
abduction.

Principle 4: The upwardly rotating scapula posteriorly tilts and, less
consistently, externally rotates slightly during full shoulder
abduction.

Principle 5: The clavicle posteriorly rotates around its own axis during
shoulder abduction.

Principle 6: The GH joint externally rotates during shoulder
abduction.

50. ||
Clavicular

posterior
rotation

AC joint

Coracoclavicular
ligament

Coracoid

process
Serratus
anterior

pull

FIG. 5.38 The mechanics of posterior rotation of the right clavicle are shown. (A) At rest in the anatomic position,
the acromioclavicular (AC) and sternoclavicular (SC) joints are shown with the coracoclavicular ligament represented
by a slackened rope. (B) As the serratus anterior muscle rotates the scapula upward, the coracoclavicular ligament is
drawn taut. The tension created within the stretched ligament rotates the crank-shaped clavicle in a posterior direc-
tion, allowing the AC joint to allow full upward rotation.

52. SHOULDER MUSCLES KINITICS:

OTwo functional categories:

> Proximal stabilizers: originate on the spine, ribs, and cranium and
insert on the scapula and clavicle, such as trap. or SA.

> Distal mobilizers: originate on the scapula and clavicle and insert on
he humerus or the forearm, such as the deltoid or biceps brachii.

53. MUSCLES OF THE SCAPULOTHORACIC JOINT

Muscles with Significant Actions at the
Scapulothoracic Joint =
ELEVATORS RETRACTORS Upper trapezius Y Levator scapula
+ Upper trapezius + Middle trapezius Rhomboid minor
+ Levator scapulae + Rhomboids (major and minor) _-Rhomboid
+ Rhomboids (major + Lower trapezius cor
ud minds) UPWARD ROTATORS
DEPRESSORS + Serratus anterior
+ Lower trapezius + Upper and lower trapezius
. Latissimus dorsi DOWNWARD ROTATORS
+ Pectoralis minor E
A + Rhomboids
+ Subclavius .
+ Pectoralis minor
PROTRACTORS
+ Serratus anterior

en

54. ELEVATORS

paralysis of her left upper trapezius caused by the polio virus.
si

> Over time, a depressed clavicle has resulted in

> As the lateral end of the clavicle is lowered, the
medial end is forced upward because of the fulcrum

action of the underlying 1st rib.
+ The depressed shaft of the clavicle may compress f
the subclavian vessels and part of the brachial f a
| .
aS |
| » X
: |

plexus.

55. ELEVATORS

long-term paralysis of the upper trapezius is an
inferior dislocation (or subluxation) of the GH joint As
Flacid hemiplegia:

ÜHumeral head being held firmly against the inclined
plane of the glenoid fossa

O With long-term paralysis of the trapezius,the glenoid
fossa loses its upwardly rotated position, allowing the
humerus to slide inferiorly.

Udownward pull imposed by gravity on an unsupported
arm may strain the capsular ligaments at the GH joint
ad lead to an irreversible dislocation.

56. ELEVATORS

healthy young woman with the classic “rounded shoulder

y Both scapulae are slightly A
& À

Y both scapulae are also &
— postures hypothesized to predispose to
impingement of the tissues within the subacromial
space.

57. DEPRESSORS

+ Subclavius (acts indirectly on the scapula)
small amount of depression torque on the
clavicle compressing +stabilizing SC joint.

¢ lower trapezius and pectoralis minor act
directly on the scapula.

* latissimus dorsi, depresses the shoulder
girdle indirectly, primarily by pulling the
humerus inferiorly.

Subclavius

Pectoralis
minor

Anterior

58. + force generated by the depressor muscles
can be directed through scapula & UL&
applied against some object, such as the

action can increase

Lower
trapezius

Latissimus
dorsi

overall functional

Length of UL

59. persons with tetraplegia (quadriplegia) who lack sufficient triceps strength to lift
the body weight through elbow extension.

(With the arm firmly held against the armrest
of the wheelchair, contraction of the LT & LD
pulls the thorax and pelvis up toward the
fixed scapula relieve the contact
pressure in the tissues superficial to the ischial
tuberosities.

Lower trapezius

Latissimus dorsi

60. PROTRACTORS

« force of scapular protraction is usually transferred across the GH joint
and employed for forward pushing and reaching activities.

» Although the pectoralis minor has the ability to impart a protraction-
directed force on the scapula, its relative ability to generate this action is
small.

« its role in limiting scapular retraction when the muscle becomes overly
tight.

+ Amplify the fina/ phase of the standard prone push-up.

Y he early phase of a push-up is performed primarily by the triceps
and pectoralis major.

61. Superior view

Serratus

anterior

Sternoclavicular
Lag joint

/

Serratus
anterior.

B

+ A- SA passes anterior to the scapula to attach

along entire length of its medial border. The . oo
muscle's line of force is shown protracting the B- protraction torque is primarily the result of SA

scapula and arm in a forward pushing or force multiplied by the internal moment arm (IMA)
reaching motion. originating at the vertical axis of rotation at SC joint.

a

62. RETRACTORS

+ MT has the most optimal line of force for this
action.

> This A: an essential force
component required for pulling activities, such c
climbing $ rowing.

+ Rhomboids & LT are direct antagonists to one
another.

Rhomboids

Lower
> The lines of force of Rhomboids & LT combine,
however, to produce pure retraction.

| 1 trapezius
+ Complete paralysis of the trapezjus, and to a
lesser extent the rhomboids, =< reduces the
retraction potential oF scapula.

a

63. MUSCLES THAT ELEVATE THE ARM

Elevation of the arm is performed by muscles that typically fall into three groups:

a
Muscles Primarily Responsible for Elevation of the Arm

GLENOHUMERAL JOINT MUSCLES
* Anterior and middle deltoid
+ Supraspinatus
* Coracobrachialis
+ Biceps brachii
SCAPULOTHORACIC JOINT MUSCLES
+ Serratus anterior
+ Trapezius
ROTATOR CUFF MUSCLES
+ Supraspinatus
+ Infraspinatus
+ Teres minor
+ Subscapularis

Middle
deltoid

Anterior
deltoid

64. MUSCLES THAT ELEVATE THE ARM

MUSCLES THAT ELEVATE ARM AT GLENOHUMERAL JOINT
Oprime muscles abduct the GH joint are the anterior deltoid, middle

deltoid, & supraspinatus .

Oflexion is performed primarily by the anterior deltoid, coracobrachialis,
and the biceps brachii.

Olanterior and middle deltoid and supraspinatus muscles are activated at
the onset of abduction, reaching a maximum level of activation between
60 and 90 degrees of abduction—a point where the external torque
due to the weight of the arm approaches its greatest level.

65. MUSCLES THAT ELEVATE ARM

+ With the deltoid paralyzed, supraspinatus ms is generall;
capable of fully abducting the GH joint, although the abduction
torque is much reduced.

+ with the supraspinatus paralyzed or its tendon completely
ruptured, mm} full abduction is often difficult, albeit achievable.

+ muscles that actively abduct the shoulder > produce relatively
large compression forces across the GH joint. These joint forces reach
80% to 90% of body weight in a position of 90 degrees of

[ peductión.

66. MUSCLES THAT ELEVATE THE ARM
UPWARD ROTATORS AT THE SCAPULOTHORACIC JOINT
Oprimary upward rotator muscles are SA, UL &LL.

QaAxis of rotation for scapular upward rotation passing in an anterior-posterior direction through

scapula mu) axis allows a convenient way to analyze the force-couple formed between SA & UL
&LL.

This force-couple rotates the scapula in the same rotary direction as the abducting humerus.

mechanics of this force-couple assume that force of each of the 3 muscles acts
simultaneously.

OSA Em rotates the glenoid fossa upward and laterally.

(most effective upward rotators of the force-couple, primarily because of their larger moment arm for this action)

UT => upwardly rotates scapula indirectly by its superior & medial pull on
the clavicle.

upwardly rotates the scapula by its inferior & medial pull on
theo0 a the he of the scapula.

67. MUSCLES THAT ELEVATE THE ARM

1
FIG. 5.49 Posterior view of a healthy shoulder showing the muscular
interaction between the scapulothoracic upward rotators and the gleno-
humeral abductors, Shoulder abduction requires a muscular “kinetic arc”
between the humerus and the axial skeleton. Note two axes of rotation:
the scapular axis, located near the acromion; and the glenohumeral joint
axis, located at the humeral head. Internal moment arms for all muscles
are shown as dark black lines. DEL, Deltoid and supraspinatus; ZT, lower

trapezius; MT, middle trapezius; SA, serratus anterior; UT, upper
trapezius.

&
Crap
98 jessuinyoue\D

68. MUSCLES THAT ELEVATE THE ARM

The muscular force-couple formed by these
3 ms is analogous to mechanics of 3
people walking through a revolving door

69. MUSCLES THAT ELEVATE THE ARM

O(EMG) analysis of upward rotation of the scapula shows:
LL E particularly active during the later phase of shoulder abduction.

MT mm very active during shoulder abduction.

j j ith the rhomboid ms
tr neutralize the strong protraction effect ofS

> SA & parts of the trapezius function simultaneously as both agonists and
antagonists, acting synergistically in upward rotation but opposing, and
Utes partially limiting, each other’s strong protraction and retraction
effects.

> The net force dominance between the two muscles during elevation of the
arm helps determine the final retraction-protraction position of the upward
rotated scapula.

+ / During shoulder abduction (especially in the frontal plane), the scapular retractors typically
dominate, as evident by the fact that the clavicle (and linked scapula) retracts during shoulder abduction

70. MUSCLES THAT ELEVATE THE ARM
+ SA + MT + LL => post. tilting & ER the upwardly rotating scapula, most
evident as the shoulder approaches full abduction .

+ LT pulls inferiorly on the scapula, These simultaneous muscular
actions, coupled with their
moment arms, would have the

+ MT pulls medially on the scapula J = ability to ER

+ SA pull anterior-laterally on the scapula.

the upwardly rotating scapula.

This ER torque would also secure the medial

border of the scapula firmly against the

thorax.

71. B) SA &LT force-couple to

posteriorly tit scapula
relative to the axis of rotation
at the AC joint (indicated by

C) SA &MT Force-couple

to ER scapula relative to

the axis of rotation at the
AC joint

72. PARALYSIS OF THE UPWARD ROTATORS OF THE SCAPULOTHORACIC JOINT

Trapezius Muscle Weakness

+ During full abduction of the shoulder, the thoracic spine naturally extends
10-15 degrees. Weakness of the trapezius may reduce the magnitude of this
accompanying thoracic extension, and thereby indirectly distort overall
scapulothoracic kinematics.

* healthy person with paralysis of the trapezius has moderate to marked
difficulty in flexing the shoulder above the head.

(The action can usually be accomplished, however, as long as the SA is fully
innervated and relatively strong).

DElevation of the arm in the pure frontal plane lie. abduction) is usually
very difficult, and often not achievable, because this action requires that the
MT generates a strong retraction force on the scapula

n

73. PARALYSIS OF THE UPWARD ROTATORS OF THE

Serratus Anterior Muscle Weakness

Y complete paralysis of the SA have great difficulty actively elevating the arm
above the head, regardless of plane of motion.

y Attempts at shoulder abduction, especially against resistance, typically result in
limited elevation of the arm coupled with excessively downwardly rotated
scapula .

As middle deltoid & supraspintus overshorten rapidly As Predicted by the force-
velocity and length tension relationships of muscle producing a paradoxic (and

ineffective) downward rotation of the scapula.

- Normally, con: i ron tates the scapula, thus allowing
the contracting and to rotate the humerus in the
same rotary direction as the scapula.

74. Deltoid
N
a q

1 <=

\ \ fa \ Serratus anterior
B

A) paradoxic downwardly rotated B) Kinesiologic analysis of the extreme

position, which can be exaggerated by downward rotated position.

applying resistance against the
shoulder abduction effort. Note also
that the scapula is abnormally

anteriorly tilted + internally rotated.

75. PARALYSIS OF THE UPWARD ROTATORS OF THE SCAPULOTHORACIC JOINT

+ 2ND : scapula is also slightly anteriorly tilted & IR (evident by the “flaring”
of the scapula’s inferior angle and medial border, respectively). Such a
distorted posture is often referred to clinically as a

+ 3RD: described earlier in this chapter, the serratus anterior contributes a
subtle but important posterior tilting + external rotation torque to the
upwardly rotating scapula.

76. FUNCTION OF THE ROTATOR CUFF MUSCLES DURING ELEVATION OF THE ARM

A) Regulators of Dynamic Stability at the Glenohumeral Joint

An important function of the rotator cuff group is to compensate for the GH
joint’s natural laxity and propensity for instability.

OThe distal attachments of the rotator cuff muscles blend into the GH joint capsule
before attaching to the proximal humerus

OThis anatomic arrangement forms a protective cuff around the joint, becoming
rigid when activated by the nervous system.

Odynamic ilizi ion of the infraspinatus muscle during ER was
discussed.

OThis dynamic stabilization is an essential function of all members of the rotator
cuff. Forces produced primarily by the rotator cuff (and their attachments into the
capsule) not only actively rotate the humeral head but also compress and
centralize it against the glenoid fossa

77. BT

Y

FUNCTION OF THE ROTATOR CUFF MUSCLES DURING ELEVATION OF THE ARM

Regulators of Dynamic Stability at the Glenohumeral Joint

Infraspinatus
Superior view contraction

LE
2

FIG. 5.35 Superior view of roll-and-slide arthrokinematics during
active external rotation of the right glenohumeral joint. The infraspi-
natus is shown contracting (dark red), causing the posterior roll of the
humerus. The subscapularis muscle and anterior capsular ligament
(ACL) generate passive tension from being stretched. The posterior
capsule (PC) is pulled relatively taut because of the pull of the contract-
ing infraspinatus muscle. The two large bold black arrows represent
forces that centralize and thereby stabilize the humeral head during
external rotation. Stretched tissues are depicted as thin, elongated
arrows.

EXTERN,

Anterior

78. FUNCTION OF THE ROTATOR CUFF MUSCLES DURING ELEVATION OF THE ARM

horizontally oriented supraspinatus produces a compression force directly into the glenoid fossa; this
force stabilizes the humeral head firmly against the fossa during its superior roll into abduction.

>the remaining rotator cuff muscles (subscapularis, infraspinatus, and teres minor)+ long head of the
biceps have a line of force that can exert an inferiorly directed force on the humeral head during
abduction.

> During abduction, the muscle's contractile force rolls the humeral head superiorly while simultaneously
serving as a musculotendinous “spacer” that restricts an excessive and counterproductive superior
translation of the humeral head.

> All the aforementioned inferior-directed forces on the humerus are necessary to help neutralize the
contracting deltoid’s strong superior translation effect on the humerus, especially at low abduction
angles.

> passive forces from muscles being stretched during abduction, such as the latissimus dorsi and teres
major, can likely exert a useful inferior-directed force on the humeral head.

» Finally, during abduction, the infraspinatus and teres minor muscles can also externally rotate the
H lerus to varying degrees to increase the clearance between the greater tubercle and the acromion

79. Summary of the Functions of the Rotator Cuff Muscles
in Controlling the Arthrokinematics of Abduction at the
Glenohumeral Joint

SUPRASPINATUS
+ Drives the superior roll of the humeral head
+ Compresses the humeral head firmly against the glenoid fossa
+ Creates a semi-rigid spacer above the humeral head, restricting
excessive superior translation of the humerus
INFRASPINATUS, TERES MINOR, AND SUBSCAPULARIS
+ Exert a depression force on the humeral head

INFRASPINATUS AND TERES MINOR

+ Externally rotate the humerus

80. Supra-

the humeral head su spinatus
abduction while also compressing the joint
for added stability.
exert a downward translational force
on the humeral head to counteract excessive
superior translation, especially that c Subscapularis
eltoid contraction. Infraspinatus
Teres minor

81. Teres minor

Coracoacromial /Short head of biceps (cut)
ligament / Coracobrachialis (cut)
Supraspinatus

R Sub-
Long head of S scapularis
biceps tendon (cut)

Coracobrachialis (cut)

Note that the distal attachments of these muscles blend into and reinforce

the superior and posterior and posterior aspects of the

"

82. MUSCLES THAT ADDUCT AND EXTEND THE SHOULDER

* primary adductor and extensor ms of
shoulder are the post deltoid, LD, teres A
major, long head of the triceps, and \

sternocostal head of the pectoralis major

Clavicular

head
* extensor and adductor muscles are capable

of generating the largest torques of any
muscle group of shoulder. Pectorals
major

Stemo-
costal

Their high torque potential can be appreciated jaa

in tasks such as pulling the arm against
resistance when climbing a rope or propelling
through water.

83. MUSCLES THAT INTERNALLY AND EXTERNALLY ROTATE THE SHOULDER

OMS. that IR GH joint are the subscapularis, pectoralis major, LD, teres major, and
anterior deltoid.

OMany of the internal rotators are also powerful extensors and adductors, such as
those used during the propulsive phase of swimming.

Ototal muscle mass of the shoulder’s internal rotators exceeds that of the external
rotators. This fact is reflected by the larger maximal-effort torque produced by the
internal rotators, during Both eccentric and concentric activations.

Q On average the IR produce about 40-70% greater torque than the ER ; however,
this difference varies considerably based on test positon, type and speed of muscle
activation, and individual physical characteristics.

84. Superior view

+ Superior view of the right shoulder showing
the group action of IRaround the

glenohumeral joint’s vertical axis of rotation.

+ In this case the scapula is fixed and the
humerus is free to rotate. The line of force of
the pectoralis major is shown with its internal
moment arm.

* Note the roll-and-slide arthrokinematics
of the convex-on-concave motion. For
clarity, the anterior deltoid is not shown.

85. FIG 538 Posterior view ofa shoulder showing the muscular interaction
berween the scapulothoracic downward totaors and the glenohumeral
adductor (and extensors) of the right shoulder. For clarity, the long head
of the triceps is not shown, The teres major is shown with its internal
moment arm (dark line) extending from the glenohumeral joint. The
thomboids are shown with the internal moment arm extending from the
scapulas axis (ee text for further detal). IF infrspinatus and teres
minor; LD, ltssimus dors PD, posterior deltoid RB, homboids, IM,

teres major.