The Shoulder girdle

 

• The shoulder girdle is joined to the axial skeleton by the sternoclavicular joint.
• The shoulder girdle is a term often used to discuss the activities of the scapula and clavicle and, to a lesser degree, the sternum
•  The shoulder is a triaxial ball-and-socket joint.
• There is a coupling between the motions of the clavicle and the scapula.

The shoulder complex consists of the scapula, clavicle, sternum, humerus, and rib cage,

and includes the sternoclavicular joint, acromioclavicular joint, glenohumeral joint, and “scapulothoracic articulation” In other words, it includes the shoulder girdle (scapula and clavicle) and the shoulder joint (scapula and humerus).

 The close-packed position is abduction and lateral rotation.

 Concave joint surfaces move in the same direction as the joint motion. Sliding joint is in the opposite direction of angular movement of the bone

 Convex joint surfaces move in the opposite direction as the joint motion. Sliding joint is in the same direction as the angular movement of the bone.

The shoulder joint is convex on concave.

BONES

Two bones are involved scapula and clavicle which move as a unit

JOINTS

*Sternoclavicular joint 

( 15 degree anterior and posterior)

*Acromioclavicular

(20-30 degree gliding and rotation)

*Scapulothoracic

( 25 degree abduction/adduction , 60 degree up/down rotation , 55 degree elevation/depression)

*Coracoclavicular joint

Permit little or no movement

*Glenohumeral joint (shoulder joint)

Ball and socket , freely moveable joint enabling flexion/extension, hyperextension, abduction/adduction, horizontal adduction/abduction ,medial/lateral rotation.

MOVEMENTS

Wherever scapula goes, the clavicle follows

The shoulder girdle has both linear and angular motions

Abduction (protraction):

 Movement of the scapula laterally away from the spinal column, as in reaching for an object in front of the body 25°

The lateral end of the clavicle and the scapula move anteriorly around the rib cage, with the medial border of the scapula moving away from the midline 5 to 6 inches (13 to 15 cm)

Adduction (retraction):

Movement of the scapula medially toward the spinal column, as in pinching the shoulder blades together 25°

Elevation:

 Upward or superior movement of the scapula, as in shrugging the shoulders, the distal end of the clavicle and the acromion process move superiorly (toward the ear) approximately 60°.

Depression:

 Downward or inferior movement of the scapula, as in returning to a normal position from a shoulder shrug  5° to 10°

Upward rotation:

Turning the glenoid fossa upward and moving the inferior angle superiorly and laterally away from the spinal column to assist in raising the arm out to the side  60°

Downward rotation:

 Returning the inferior angle medially and inferiorly toward the spinal column and the glenoid fossa to its normal position, as in bringing the arm down to the side.  60°

Lateral tilt (outward tilt):

 Consequential movement during abduction in which the scapula rotates about its vertical axis, resulting in posterior movement of the medial border and anterior movement of the lateral border

Medial tilt (inward tilt):

 Return from lateral tilt consequential movement during extreme adduction in which the scapula rotates about its vertical axis, resulting in anterior movement of the medial border and posterior movement of the lateral border 90°

Anterior tilt (upward tilt):

Consequential rotational movement of the scapula about the frontal axis occurring during hyperextension of the glenohumeral joint, resulting in the superior border moving anteroinferior and the inferior angle moving posterosuperior

Posterior tilt (downward tilt):

 Consequential rotational movement of the scapula about the frontal axis occurring during hyperflexion of the glenohumeral joint, resulting in the superior border moving posteroinferiorly and the inferior angle moving anterosuperiorly

Scapulohumeral rhythm

A regular pattern of scapular rotation that accompanies and facilitates humeral abduction

 The first 30 degrees of shoulder joint motion is pure shoulder joint motion.

However, after that, for every 2 degrees of shoulder flexion or abduction that occurs, the scapula must upwardly rotate 1 degree. This 2:1 ratio is known as the scapulohumeral rhythm.

Scapulohumeral rhythm is an example of the combined motions of these joints.

Bursae

sacs secreting synovial fluid internally that lessen friction between soft tissues around joints

NERVE INNERVATION

The shoulder girdle is primarily innervated by cervical plexus

 Shoulder girdle muscles—location and action

*Anterior

Pectoralis minor—abduction, downward rotation,

and depression

Subclavius—depression and abduction

*Posterior and laterally

Serratus anterior—abduction and upward rotation

*Posterior

Trapezius

Upper fibres—elevation and extension and

rotation of the head at the neck

Middle fibres—elevation, adduction, and

upward rotation

Lower fibres—adduction, depression, and

upward rotation

Rhomboid—adduction, downward rotation, and

elevation

Levator scapulae—elevation

It is important to understand that muscles may not necessarily be active throughout the absolute full range of motion for which they are noted as being agonists.

*Rotator cuff muscles

band of tendons of the subscapularis, supraspinatus, infraspinatus, and trees minor, which attach to the humeral head

Reverse Action Of Muscles

The actions of the shoulder girdle muscles have been described as moving insertion toward the origin. However, if the insertion is stabilized, the origin will move, this is called the reversal of muscle action.

Example

 Stabilizing the shoulder girdle upper trapezius fibres assist in extending head and neck with ipsilateral bending whereas the lower trapezius fibres act in reverse action elevating the trunk.

Force Couple on the Shoulder girdle

A force couple is defined as muscles pulling in different directions to accomplish the same motion.

Upward rotation

In the case of the shoulder girdle, the upper trapezius muscle pulls up, the lower trapezius muscle pulls down, and the lower fibres of the serratus anterior muscle pull outward in a horizontal direction. The net effect is that the

Scapula rotates upward.

Downward rotation

This is another example of a force couple. The combined effect of the pectoralis minor muscle pulling down, the rhomboid muscles pulling in, and the levator scapular muscle pulling up is the downward rotation of the scapula. This motion is accomplished when the shoulder joint is forcefully extended scapula rotates upward

STRENGTHENING OF MUSCLES

TRAPEZIUS

Innervated by

The spinal accessory nerve (cranial nerve XI) and

branches of C3, C4

Fibres

*Upper fibres

weak fibres, assist in the elevation of clavicle and extension of the head

*Middle fibres

Strong fibres, strong elevation, upward rotation, adduction/retraction of scapula. It positions shoulder for posture. Tenderness occurs in these fibres.

*Lower fibres

Weak fibres depress/retract/rotate the scapula

STRENGTHENING

* Strengthening of the upper and middle fibres can be accomplished through shoulder-shrugging exercises.

* The middle and lower fibres can be strengthened through bent-over rowing and shoulder joint horizontal abduction exercises from a prone position.

* The lower fibres can be emphasized with a chest proud shoulder retraction exercise attempting to place the elbows in the back pants pockets with depression. Parallel dips or body dips are also helpful for emphasizing the lower trapezius.

STRETCHING OF TRAPEZIUS

To stretch the trapezius, each portion needs to be specifically addressed.

* The upper fibres may be stretched by using one hand to pull the head and neck forward into flexion or slight lateral flexion to the opposite side while the ipsilateral hand is hooked under a table edge to maintain the scapula in depression.

* The middle fibres are stretched to some extent with the procedure used for the upper fibers, but they may be stretched further by using a partner to passively pull the scapula into full protraction.

*The lower fibres are perhaps best stretched with the subject in a side-lying position while a partner grasps the lateral border and inferior angle of the scapula and moves it passively into maximal elevation and protraction.

Subclavius muscle 

Innervation

Nerve fibres from C5 and C6

Action

Stabilization and protection of the sternoclavicular joint

Depression

Abduction (protraction)

Application

The subclavius pulls the clavicle anteriorly and inferiorly toward the sternum. In addition to assisting in abducting and depressing the clavicle and the shoulder girdle, it has a significant role in protecting and stabilizing the sternoclavicular joint during upper-extremity movements.

Strengthening

It may be strengthened during activities in which there is active depression, such as dips, or active abduction, such as push-ups.

Stretching

Extreme elevation and retraction of the shoulder girdle provide a stretch to the subclavius.

LEVATOR SCAPULAE MUSCLE

Innervated by

Dorsal scapular nerve C5 and branches of C3 and C4

Action

Elevates the medial margin of the scapula

Weak downward rotation

Weak adduction

Application

The levator scapulae is a very common site for tightness, tenderness, and discomfort secondary to chronic tension and from carrying items with straps over the shoulder.

STRENGTHENING

Shrugging the shoulders calls the levator scapulae muscle into play, along with the upper trapezius muscle. Fixation of the scapula by the pectoralis minor muscle allows the levator scapulae muscles on both sides to extend the neck or to flex laterally if used on one side only

STRETCHING

The levator scapulae is perhaps best stretched by rotating the head approximately 45 degrees contralaterally and flexing the cervical spine actively while maintaining the scapula in a relaxed, depressed position

Serratus anterior muscle

Innervation

Long thoracic nerve (C5–C7)

Action

Abduction (protraction):

draws the medial border of the scapula away from the vertebrae

Upward rotation:

longer, lower fibres tend to draw the inferior angle of the scapula farther away from the vertebrae, thus rotating the scapula upward slightly

Application

The serratus anterior muscle is used commonly in movements drawing the scapula forward with slight upward rotation, such as throwing a baseball, punching in boxing, shooting and guarding in basketball, and tackling in football. It works along with the pectoralis major muscle in typical action, such as throwing a baseball.

Strengthening

The serratus anterior muscle is used strongly in doing push-ups, especially in the last 5 to 10 degrees of motion. The bench press and overhead press are good exercises for this muscle. A winged scapula condition usually results from weakness of the rhomboid and/or the serratus anterior.

Stretching

The serratus anterior can be stretched by standing, facing a corner and placing each hand at shoulder level on the two walls. As you lean in and attempt to place your nose in the corner, both scapulae are pushed into an adducted position, which stretches the serratus anterior.

Injury

Serratus anterior weakness may result from an injury to the long thoracic nerve

Pectoralis minor muscle 

Innervation

Medial pectoral nerve (C8–T1)

Action

Abduction (protraction):

 draws the scapula forward and tends to tilt the lower border away from the ribs

Downward rotation:

 as it abducts, it draws the scapula downward

Depression:

 when the scapula is rotated upward, it assists in depression

Application

The pectoralis minor muscle is used, along with the serratus anterior muscle, in true abduction (protraction) without rotation.

The serratus anterior draws the scapula forward with a tendency toward upward rotation, the pectoralis minor pulls forward with a tendency toward downward rotation, and the two pulling together give true abduction.

Strengthening

The pectoralis minor is most used in depressing and rotating the scapula downward from an upwardly rotated position, as in pushing the body upward on dip bars or in body dips.

Stretching

The pectoralis minor is often tight due to being overused in activities involving abduction, which may lead to forward and rounded shoulders. As a result, stretching may be indicated, which can be accomplished with a wall push-up in the corner as used for stretching the serratus anterior. Additionally, lying supine with a rolled towel directly under the thoracic spine while a partner pushes each scapula into retraction places this muscle on stretch.

Rhomboid muscles—major and Minor

Innervation

Dorsal scapular nerve (C5)

Action

The rhomboid major and minor muscles work together.

Adduction (retraction):

draw the scapula toward the spinal column

Downward rotation:

 from the upward rotated position; draw the scapula into the downward rotation

Elevation:

 slight upward movement accompanying adduction

Application

The rhomboid muscles fix the scapula in adduction (retraction) when the muscles of the shoulder joint adduct or extend the arm

Strengthening

Chin-ups, dips, and bent-over rowing are excellent exercises for developing strength in this muscle.

Stretching

 The rhomboids may be stretched by passively moving the scapula into full protraction while maintaining depression. Upward rotation may assist in this stretch as well.

LOAD ON SHOULDER

 The weight of each body segment acts at the segmental centre of mass. The moment arm for the entire arm segment with respect to the shoulder is, therefore, the perpendicular distance between the weight vector (acting at the arm’s centre of gravity) and the shoulder The torque created at the shoulder by the weight of the arm is the product of arm weight and the perpendicular distance between the arm’s centre of gravity and the shoulder

references

• Brunnstrom's clinical kinesiology
• Clinical kinesiology and Anatomy(Lynn S. Lippert)
• Manual of structural Kinesiology (R.T.Floyd)
• Basic biomechanics (Susan J. Ha