Shoulder Girdle

Overview

Movements

Bone Landmarks

Joints

Overview

Upper extremity = shoulder girdle, shoulder, arm, elbow, forearm, wrist, & hand
Shoulder girdle (shoulder complex): interacts with the shoulder and arm to provide mobility of the upper extremity
- consists of the scapula, clavicle, and sternum & sternoclavicular (SC), acromioclavicular (AC), and scapulothoracic joints
- Joints the upper extremity of the appendicular skeleton to the axial skeleton

Movements

Sternoclavicular (SC) = movement of scapula on the thoracic cage

Plane of the scapula: ~30 degrees forward of the frontal plane (between flexion/abduction
Scaption: describe the movements of the shoulder joint that occur in the scapular plane
Scapular elevation: linear movement when the scapula moves in a superior direction
Scapular depression: linear movement when the scapula moves inferiorly
Scapular protraction: scapular abduction when the scapula moves away from the vertebral column
Scapular retraction: scapular adduction when the scapula moves toward the vertebral column
Scapular upward rotation: rotation of the inferior angle of the scapula laterally and superiorly, away from the vertebral column
- Occur within the frontal plane about the horizontal axis
Scapular downward rotation: rotation of the inferior angle medially and inferiorly, toward the vertebral column
- Occur within the frontal plane about the horizontal axis
- Does not move past anatomical position
Scapular tilt: rotation of the inferior angle posteriorly with respect to the superior angle
- Occurs within the sagittal plane about a horizontal axis
Scapular winging: movement of the medial border of the scapula posteriorly, away from the thoracic cage
Scapulohumeral Rhythm: describes the relationship of movement between the shoulder girdle and the shoulder joint; 2:1 ratio of shoulder abduction to scapular upward rotation
- First 30 degrees of shoulder abduction occur only at the glenohumeral joint
- Helps maintain the functional length-tension relationships of muscles

Bone Landmarks

Scapula: broad, triangular-shaped, irregular bone located superficially on the posterior aspect of the thoracic cage between the 2nd & 7th ribs

1. Superior angle: superior medial aspect, attachment for levator scapula
2. Inferior angle: most inferior point where vertebral and axillary borders meet; point of reference for determining scapular rotation
3. Vertebral border: medial border between superior/inferior angles; attachment for rhomboid, levator scapula, & serratus anterior muscles
4. Axillar border: lateral border between glenoid fossa & inferior angle; attachment for teres major, teres minor, and triceps brachii
5. Spine: projection on posterior surface from vertebral border to acromion process; attachment for middle/lower trapezius and posterior deltoid muscles
6. Coracoid process: hook-shaped projection on anterior-superior surface; attachment for pectoralis minor, coracobrachialis, & bicep brachii (short head)
7. Acromion process: lateral, broad, flat end of spine of scapula; attachment for upper trapezius & middle deltoid
8. Glenoid fossa: slightly concave surface at superior end of axillary board; faces slightly anteriorly, laterally and superiorly; third angle of triangular shape of scapula; articulates with humerus

Clavicle: s-shaped bone connecting the upper extremity appendicular skeleton to axial skeleton at the SC joint; serving as a "crank" to assist the scapular upward rotation

1. Sternal end: medial end, articulating with the sternum; attachment for sternocleidomastoid
2. Acromial end: lateral end, articulating with acromion process of scapula; attachment for upper trapezius, pectoralis major & anterior deltoid
3. Body: area between the sternal & acromial ends

Sternum

Joints

Sternoclavicular (SC) Joint: synovial joint articulation of the manubrium of the sternum and medial (sternal) end of the clavicle
- Only direct attachment for app. Skeleton & axial skeleton
- Three degrees of freedom- moving within all three planes/axes
- Movements of the SC joint is in respect to the clavicle movement
- Clavicle moves on the stationary manubrium - only one joint side is moveable
- Articular disc of the upper SC joint attaches to the posterior-superior clavicle and the disc of the lower part attaches to the manubrium and first costal cartilage
- Follows the concave/convex rule
Acromioclavicular (AC) Joint: plane synovial joint at the articulation of the acromion process of the scapula and lateral (acromial) end of the clavicle
- Movements accompany SC to increase ROM of scapular upward rotation
- Minimal AC joint movement occurs during scapular tilt and scapular winging
Scapulothoracic Joint: not a true joint; the scapula (concave) moves on the thoracic cage (convex)
- Do not follow the concave/convex rule
- Movement in this relationship is a result from movement of the SC/AC joints

Ligaments

SC Joint

1. Joint capsule: surrounds articular borders of joint
2. Sternoclavicular ligament: connects clavicle to manubrium of sternum; divided into two to reinforce the joint capsule
3. Posterior sternoclavicular ligament: posterior portion of the SC ligament connecting posterior manubrium to posterior clavicle
  - Limits posterior movement of medial clavicle on manubrium during scapula protraction
4. Anterior sternoclavicular ligament: anterior portion of SC ligament connecting anterior manubrium to anterior clavicle
  - Limits anterior movement of medial clavicle on manubrium during scapular retraction
5. Costoclavicular ligament: short, flat rhomboid-shaped connecting inferior surface of medial clavicle to superior surface of costal cartilage of first rib; limiting clavicular elevation
6. Interclavicular ligament: located superiorly on manubrium, connecting the superior & medial clavicles to limit clavicular depression

AC Joint

1. Acromioclavicular ligament: two ligament portions connecting the lateral clavicle to the scapula acromion to reinforce the joint capsule
2. Superior acromioclavicular ligament: superior portion of AC ligament connecting superior clavicle to superior acromion, reinforcing the superior capsule
3. Inferior acromioclavicular ligament: inferior AC ligament, connecting the inferior clavicle to inferior acromion, reinforcing the inferior capsule
4. Coracoclavicular ligament: two portion: lateral trapezoid and medial conoid; connecting the superior surface of coracoid process of scapula to inferior clavicle
  - Limits posterior movement of clavicle and rotation of scapula
5. Coracoacromial ligament: forms roof over head of humerus to connecter lateral superior surface of coracoid process and inferior surface of acromion
  - Protects the head of the humerus and limits superior movement of humeral head with upward force is transmitted on humerus

Muscles

Trapezius muscle: large, triangular, sheet-like superficial muscle of the middle/upper back

- Three parts - have different functions based on attachments to create different lines of pull
- Origin is broad - insertion is narrow
- All are synergist for scapular retraction
- Upper/lower = antagonist during scapular elevation/depression & agonist for scapular upward rotation

Upper trapezius muscle:

1. origin = occipital protuberance, superior nuchal line, spinous processes of cervical vertebrae via nuchal ligament
2. Insertion = lateral third of clavicle, acromion process
3. Action: scapular elevation, upward rotation, retraction
  1. Bilateral - capital/cervical extension (scapula stable)
  2. Unilateral - capital/cervical extension & lateral flexion (scapula stable)
4. Line of pull is more superior (upward) than horizontal (inward)

Middle trapezius muscle:

1. origin = spinous process of C7-T3 via supraspinal ligament
2. Insertion = medial acromion & spine of scapula
3. Action: scapular retraction & minimal upward rotation
4. Line of pull is horizontal

Lower trapezius muscle:

1. origin = spinous process of T4-T14 via supraspinal ligament
2. Insertion = base of spine of scapula
3. Action: scapular depression, upward rotation, retraction
4. Line of pull is more inferior (down) than inward (horizontal)

Levator scapula muscle:

1. origin = transverse processes C1-C4
2. Insertion = vertebral border of scapula between superior angle & spine of scapula
3. Action: scapular elevation, downward rotation, lateral flexion of cervical spine
4. Diagonal line of pull - mostly vertical

Rhomboid muscle: two part (major/minor), rhomboidal shaped muscles deep to the trapezius

1. origin = spinous processes C7-T5 via nuchal & supraspinal ligaments
2. Insertion = vertebral border of scapula between inferior angle & spine of scapula
3. Action: scapular retraction, downward rotation, elevation
4. Line of pull is oblique

Serratus anterior muscle: large, serrated-shaped, powerful muscle deep to the scapula

1. origin = superficial, lateral surface of 1st-8th ribs
2. Insertion = vertebral border of scapula, anterior surface
3. Action: scapular protraction, upward rotation, elevation of thoracic cage; accessory muscle for ventilation (inhalation)
4. Line of pull is horizontal

Pectoralis Muscles

1. Pectoralis major not active in scapular movement
2. Pectoralis minor: lies deep to the pectoralis major
3. origin = anterior surface, third through fifth ribs
4. Insertion = coracoid process of scapula
5. Action: scapular depression, protraction, downward rotation, tilt
6. Line of pull is vertical

Muscle Groups

Elevators

Upper trapezius
Levator scapulae

Depressors

Pectoralis minor
Lower trapezius

Retractors

Middle trapezius
Rhomboids

Protractors

Pectoralis minor
Serratus anterior

Upward Rotation

Upper trapezius
Lower trapezius
Serratus anterior

Downward Rotation

Levator scapulae
Rhomboids
Pectoralis minor

Common Pathologies

Acromioclavicular (AC) separation: separation of the articulation of the acromion process & clavicle
- AC joint capsule is fragile and susceptible to injury
- First degree sprain - AC ligament is stretched
- Second degree sprain - AC ligament is ruptured/coracoclavicular ligament is stretched
- Third degree sprain - AC & coracoclavicular ligament is ruptured
Clavicular fractures: occurring in the body of the clavicle as a result of imposition of upward forces through the upper extremity or imposition medially directed forces on the acromial end of the clavicle
Winging: occurs when the serratus anterior is weak and the scapula moves posterior away from the thoracic cage

Back to Main Menu

Page updated

Google Sites

Report abuse