Set of bones which connects the arm to the axial skeleton on each side
The
shoulder girdle
or
pectoral girdle
is the set of
bones
in the
appendicular skeleton
which connects to the
arm
on each side. In humans it consists of the
clavicle
and
scapula
; in those
species
with three bones in the shoulder, it consists of the clavicle, scapula, and
coracoid
. Some
mammalian
species (such as the
dog
and the
horse
) have only the scapula.
The pectoral girdles are to the upper limbs as the
pelvic girdle
is to the lower limbs; the girdles are the parts of the
appendicular skeleton
that anchor the
appendages
to the axial skeleton.
In humans, the only true anatomical
joints
between the shoulder girdle and the axial skeleton are the
sternoclavicular joints
on each side. No anatomical joint exists between each scapula and the
rib cage
; instead the
muscular
connection or physiological joint between the two permits great mobility of the shoulder girdle compared to the compact
pelvic girdle
; because the
upper limb
is not usually involved in weight bearing, its stability has been sacrificed in exchange for greater mobility. In those species having only the scapula, no joint exists between the
forelimb
and the
thorax
, the only attachment being muscular.
In humans
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The shoulder girdle is the anatomical mechanism that allows for all upper arm and shoulder movement in humans.
[1]
Muscles
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The shoulder girdle consists of five muscles that attach to the
clavicle
and
scapula
and allow for the motion of the
sternoclavicular joint
(connection between sternum and clavicle) and
acromioclavicular joint
(connection between clavicle and scapula).
[2]
The five muscles that comprise the function of the shoulder girdle are the
trapezius muscle
(upper, middle, and lower),
levator scapulae muscle
,
rhomboid muscles
(major and minor),
serratus anterior muscle
, and
pectoralis minor muscle
.
[3]
The shoulder girdle consists of the clavicle and the scapula, which serve to attach the upper limb to the sternum of the axial skeleton.
Joints
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The shoulder girdle is a complex of 5 joints that can be divided into two groups. 3 of these joints are true
anatomical
joints, while 2 are
physiological
("false") joints.
[explain 1]
Within each group, the joints are mechanically linked so that both groups simultaneously contribute to the different movements of the shoulder to variable degrees.
[4]
: 20
In the first group, the scapulohumeral or
glenohumeral joint
is the anatomical joint mechanically linked to the physiological subdeltoid or
suprahumeral joint
(the "second shoulder joint") so that movements in the suprahumeral joint results in movements in the
glenohumeral
joint.
In the second group, the scapulocostal or
scapulothoracic joint
is the important physiological joint that can not function without the two anatomical joints in the group, the
acromioclavicular
and
sternoclavicular joints
, i.e. they join both ends of the
clavicle
.
[4]
: 20
Glenohumeral joint
[
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The
glenohumeral joint
is the articulation between the
head of the humerus
and the
glenoid cavity
of the
scapula
. It is a
ball and socket
type of
synovial
joint with three rotatory and three translatory degrees of freedom. The glenohumeral joint allows for
adduction
,
abduction
,
medial
and
lateral rotation
,
flexion
and
extension
of the arm.
Acromioclavicular joint
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The
acromioclavicular joint
is the articulation between the
acromion process
of the scapula and the
lateral
end of the
clavicle
. It is a
plane
type of synovial joint. The acromion of the scapula rotates on the acromial end of the clavicle.
Sternoclavicular joint
[
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The
sternoclavicular joint
is the articulation of the
manubrium
of the
sternum
and the first
costal cartilage
with the
medial
end of the
clavicle
. It is a
saddle
type of synovial joint but functions as a plane joint. The sternoclavicular joint accommodates a wide range of scapula movements and can be raised to a 60° angle.
Scapulocostal joint
[
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The scapulocostal joint (also known as the scapulothoracic joint) is a
physiological
joint formed by an articulation of the
anterior
scapula
and the
posterior
thoracic rib cage
. It is musculotendinous in nature and is formed predominantly by the
trapezius
,
rhomboids
and
serratus anterior
muscles. The
pectoralis minor
also plays a role in its movements. The gliding movements at the scapulocostal joint are
elevation
,
depression
,
retraction
,
protraction
and superior and inferior rotation of the scapula. Disorders of the scapulocostal joint are not very common and usually restricted to
snapping scapula
.
[5]
Suprahumeral joint
[
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The suprahumeral joint (also known as the subacromial joint) is a physiological joint formed by an articulation of the
coracoacromial ligament
and the
head of the humerus
. It is formed by the gap between the humerus and the acromion process of the scapula. This space is filled mostly by the
subacromial bursa
and the
tendon
of
supraspinatus
. This joint plays a role during complex movements while the arm is fully flexed at the glenohumeral joint, such as changing a lightbulb, or painting a ceiling.
Movements
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From its neutral position, the shoulder girdle can be rotated about an imaginary vertical axis at the medial end of the clavicle (the sternoclavicular joint). Throughout this movement the scapula is rotated around the chest wall so that it moves 15 centimetres (5.9 in) laterally and the glenoid cavity is rotated 40?45° in the horizontal plane. When the scapula is moved medially it lies in a frontal plane with the glenoid cavity facing directly laterally. At this position, the lateral end of the clavicle is rotated posteriorly so that the angle at the acromioclavicular joint opens up slightly. When the scapula is moved laterally it lies in a sagittal plane with the glenoid cavity facing anteriorly. At this position, the lateral end of the clavicle is rotated anteriorly so that the clavicle lies in a frontal plane. While this slightly closes the angle between the clavicle and the scapula, it also widens the shoulder.
[4]
: 40
The scapula can be elevated and depressed from the neutral position to a total range of 10 to 12 centimetres (3.9 to 4.7 in); at its most elevated position the scapula is always tilted so that the glenoid cavity is facing superiorly. During this tilting, the scapula rotates to a maximum angle of 60° about an axis passing perpendicularly through the bone slightly below the spine; this causes the inferior angle to move 10 to 12 centimetres (3.9 to 4.7 in) and the lateral angle 5 to 6 centimetres (2.0 to 2.4 in).
[4]
: 40
Injury
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Shoulders are a common place for tissue injuries, especially if the person plays overhead sports such as tennis,
volleyball
, baseball, swimming, etc. According to Bahr's major injury related statistics, shoulder dislocations or subluxations account for 4% of injuries in adults ages 20?30 and 20% of shoulder injuries are fractures.
[6]
Damage to the shoulder and adjacent features can fluctuate in severity depending on the person's age, sport, position, recurring shoulder dysfunction, and many other factors. Some other common shoulder injuries are fractures to any shoulder girdle bones i.e.
clavicle
, ligamentous sprains such as
AC joint
or GH ligaments, rotator cuff injuries, different labral tears, and other acute or chronic conditions related to shoulder anatomy.
Shoulder girdle pain can be
acute
or
chronic
and be due to a number of causes.
Inflammation
or injury of associated
tendons
,
bone
,
muscles
,
nerves
,
ligaments
, and
cartilage
can all cause pain. Also, past injury compensation, and stress can result in complicated shoulder pain.
[7]
Disorders
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In humans,
winged scapula
is a condition in which the shoulder blade protrudes from a person's back in an abnormal position.
Other animals
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The shoulder girdle of various
hyperoliid
frogs
:
Phlyctimantis verrucosus
,
Cryptothylax greshoffii
,
Leptopelis calcaratus
,
Leptopelis anchietae
,
Leptopelis aubryi
and
Leptopelis brevirostris
.
The pectoral girdle demonstrates an enormous variation in
amniotes
(vertebrates adapted to a full terrestrial life), both among extant species and along evolutionary lines, and determining
homologies
for individual pectoral elements is difficult. Except for the sternum, these elements (along with the
pelvic girdle
) were, however, present in early
bony fishes
before there were even limbs, arising from their ancestral external armor plates. In digitless
choanates
, the
cleithrum
, clavicle, and
interclavicle
are
dermal
and linked to the caudal part of the head while the humerus articulates with a small
scapulocoracoid
bone. As the first digits appeared, the pectoral structure lost its direct connection to the head skeleton while the scapulocoracoid grew more prominent and started to face laterally. In true tetrapods, the dermal part of the girdle was gradually reduced and the scapulocoracoid split into a dorsal scapula and a ventral coracoid.
[8]
As for the sternum, it also came from the fusion of the inner ends of the pectoral girdles in
tetrapods
, subsequently growing between the
ribs
.
In dinosaurs
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In
dinosaurs
, the main bones of the pectoral girdle were the
scapula
(shoulder blade) and the
coracoid
, both of which directly articulated with the
clavicle
. The clavicle was present in
saurischian
dinosaurs but largely absent in
ornithischian
dinosaurs. The place on the scapula where it articulated with the
humerus
(upper bone of the forelimb) is the called the
glenoid
. The scapula served as the attachment site for a dinosaur's back and forelimb muscles.
In primates
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Chimpanzees
are far better at
brachiation
than humans. Their clavicles possess a cranially oriented twist on the acromial end, conducive to better force transfer through it - a very important function in arboreal locomotion. Chimpanzee scapulas also possess a considerably larger supraspinous fossa, allowing for a larger supraspinatus muscle. Through the process of evolution, humans have lost the atlantoclavicularis muscle, originating on the atlas of the vertebral column, and inserting onto the acromial clavicle. This muscle acts to elevate the clavicle.
[9]
See also
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Notes
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- ^
Physiological joints are called "false" joints because they lack the characteristics of "true" anatomical joints, such as tendons and a capsule, but they are still joints because the gliding movements they provide play an important biomechanical role. (
Roy 2009
, Focused anatomy)
References
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- ^
Moezy, A., Sepehrifar, S., Dodaran, M. S. (2014). The effects of scapular stabilization based exercise therapy on pain, posture, flexibility and shoulder mobility in patients with shoulder impingement syndrome: a controlled randomized clinical trial. Medical Journal of the Islamic Republic of Iran (MJIRI) Iran University of Medical Sciences, (Vol 28.87), 1-15
- ^
Saladin, K. (2011). Human Anatomy (3rd ed.). New York, NY: McGraw-Hill Companies
- ^
Lippert, L. (2011). Clinical Kinesiology and Anatomy (5th ed.). Philadelphia, PA: F. A. Davis Company
- ^
a
b
c
d
Kapandji, Ibrahim Adalbert (1982).
The Physiology of the Joints, Volume One: Upper Limb
(5th ed.). New York, N.Y.: Churchill Livingstone.
- ^
Arend CF. Ultrasound of the Shoulder. Master Medical Books, 2013. Free section on snapping scapula available at
ShoulderUS.com
- ^
Bahr, R. (2012). IOC Manual of Sports Injuries : An Illustrated Guide to the Management of Injuries in Physical Activity. Somerset, NJ, USA: John Wiley & Sons
- ^
Mitchell, Caroline; et al. (2005).
"Shoulder Pain: Diagnosis and Management in Primary Care"
.
BMJ
.
331
(7525): 1124?1128.
doi
:
10.1136/bmj.331.7525.1124
.
PMC
1283277
.
PMID
16282408
.
- ^
Vickaryous, Matthew K.; Hall, Brian K. (March 2006).
"Homology of the reptilian coracoid and a reappraisal of the evolution and development of the amniote pectoral apparatus"
.
Journal of Anatomy
.
208
(3): 263?285.
doi
:
10.1111/j.1469-7580.2006.00542.x
.
PMC
2100248
.
PMID
16533312
.
Fig. 1
- ^
Bramble, Dennis; Lieberman, Daniel (23 September 2004).
"Endurance running and the evolution of Homo"
(PDF)
.
Nature
.
432
(7015): 345?352.
Bibcode
:
2004Natur.432..345B
.
doi
:
10.1038/nature03052
.
PMID
15549097
.
S2CID
2470602
.
Further reading
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