Shoulder girdle

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Shoulder girdle
Human shoulder girdle or pectoral girdle
Details
Identifiers
Latincingulum pectorale
TA98A01.1.00.020
TA2361
FMA23217
Anatomical terms of bone

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

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

The shoulder girdle is the anatomical mechanism that allows for all upper arm and shoulder movement in humans. [1]

Muscles

The shoulder girdle consists of five muscles that attach to the

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

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.

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

The

extension
of the arm.

Acromioclavicular joint

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

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

The scapulocostal joint (also known as the scapulothoracic joint) is a

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

The suprahumeral joint (also known as the subacromial joint) is a physiological joint formed by an articulation of the

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

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

Shoulders are a common place for tissue injuries, especially if the person plays overhead sports such as tennis,

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

ligaments, and cartilage can all cause pain. Also, past injury compensation, and stress can result in complicated shoulder pain.[7]

Disorders

In humans, winged scapula is a condition in which the shoulder blade protrudes from a person's back in an abnormal position.

Other animals

Leptopelis brevirostris
.

The pectoral girdle demonstrates an enormous variation in

ribs
.

In dinosaurs

In

glenoid
. The scapula served as the attachment site for a dinosaur's back and forelimb muscles.

In primates

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

Notes

  1. ^ 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

  1. ^ 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
  2. ^ Saladin, K. (2011). Human Anatomy (3rd ed.). New York, NY: McGraw-Hill Companies
  3. ^ Lippert, L. (2011). Clinical Kinesiology and Anatomy (5th ed.). Philadelphia, PA: F. A. Davis Company
  4. ^ 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.
  5. ^ Arend CF. Ultrasound of the Shoulder. Master Medical Books, 2013. Free section on snapping scapula available at ShoulderUS.com
  6. ^ 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
  7. PMID 16282408
    .
  8. PMID 16533312. Fig. 1
  9. S2CID 2470602
    .

Further reading
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