Bones of the shoulder girdle
- The clavicle is an s-shaped bone that connects the sternum to the shoulder blade
- It has two ends:
- The shaft
- Impressions on the clavicle
- Subclavian groove: groove on the inferior surface of the medial half of the clavicle into which the subclavius muscle is inserted
- Impression for costoclavicular ligament (medial): insertion point for the costoclavicular ligament
- Tuberosity for coracoclavicular ligament (lateral): insertion point for the coracoclavicular ligament
- Conoid tubercle: insertion point for the conoid ligament
- Trapezoid line: insertion point for the trapezoid ligament
- The scapula is a flat and triangular bone
- It has three borders (medial, lateral/axillary, and superior), three angles (superior, inferior, and lateral), and two surfaces
- Posterior (dorsal) scapular surface landmarks
- Spine of scapula: A bony horizontal ridge on the dorsal aspect of the scapula that ends as the acromion.
- Acromion: The continuation of the spine of scapula that projects above the glenoid cavity.
- Supraspinatous fossa: A concave depression above the spine on the dorsal aspect of the scapula.
- Infraspinatus fossa: A concave depression below the spine on the dorsal aspect of the scapula.
- Costal (ventral) scapular surface landmarks:
- Subscapular fossa: A concave depression on the ventral aspect of the body of the scapula.
- Coracoid process: A bony hook that arises from the superior border of the scapula and lies below the lateral end of the clavicle
- Suprascapular notch
- The glenoid cavity is located on the lateral scapular border and is the socket of the glenohumeral joint!
- Suprascapular nerve entrapment
Scapular anastomosis: An anastomosis between the branches of the first part of the subclavian artery and third part of the axillary artery that provides collateral circulation in case of occlusion of one of the involved branches.
- Subscapular fossa: subscapular artery
- Infraspinatus fossa: circumflex scapular artery, branch of the subscapular artery
- Supraspinous fossa: suprascapular artery, branch of the thyrocervical trunk
- Inferior angle: anastomosis between dorsal scapular artery and the subscapular artery
- Lateral border of scapula: subscapular artery (branch of axillary artery)
- Medial border of scapula: Dorsal scapular artery
Joints of the shoulder girdle
Type of joint: synovial saddle joint between the medial end of the clavicle and the manubrium sternum
- The only true anatomical joint connecting the pectoral girdle to the torso.
- Anterior sternoclavicular ligament and posterior sternoclavicular ligament: between the manubrium and the sternal end of the clavicle; strengthens the joint capsule
- Interclavicular ligament: unites the sternal ends of both clavicles
- Costoclavicular ligament: unites the first rib to the sternal end of the clavicle
- Type of joint: synovial between the lateral end of the clavicle and the acromion of the scapula
- Strengthens the superior aspect of the joint capsule
- Resists anteroposterior displacement of the AC joint
- Coracoclavicular ligament
- Acromioclavicular ligament
Movements of the shoulder girdle
- Elevation (shrugging) of shoulder: trapezius (upper fibers), levator scapulae, and the rhomboids
- Depression of shoulder: trapezius (lower fibers), latissimus dorsi, pectoralis minor, and subclavius
- Protraction (forward thrusting; scapular abduction): serratus anterior, pectoralis major and pectoralis minor
- Retraction (scapular adduction): the rhomboids, trapezius
- Lateral (upward) rotation of the scapula: serratus anterior, trapezius (upper fibers)
- Medial (downward) rotation of the scapula: rhomboids, levator scapulae, pectoralis minor
- Type of joint: synovial ball-and-socket joint between the head of the humerus and the glenoid cavity of the scapula
- Capsule: a fibrous capsule envelops the entire joint
- Glenoid labrum: a soft tissue rim surrounding the glenoid fossa of the scapula
- Coracoacromial ligament
- Extends from the coracoid process to the greater and lesser tubercles of the humerus
- Strengthens the anterior part of the joint capsule
- Glenohumeral ligament: strengthens the joint capsule between the supraglenoid tubercle of the scapula and the anatomical neck of the humerus
- Transverse humeral ligament
- Rotator cuff muscles (see below)
- Tendon of the long head of biceps brachii: supports the superior aspect of the joint
- Synovial fluid-filled sac that lies between the deltoid muscle (superiorly) and the head of the humerus (inferiorly)
- Extends medially under the acromion
- Does not communicate with the shoulder joint cavity
- Facilitates smooth gliding movement of the head of the humerus under the acromion
- Clinical significance: abduction caused by repetitive overhead shoulder
- Flexion and extension
- Medial and lateral rotation
- Abduction and adduction
- See for further details.
- Blood supply
- The medial part of the shoulder drains mainly into the subclavian lymph trunk from the:
- The remaining shoulder drains mainly into the subclavian lymph trunk from the:
- Clinical significance : see
Bone structures associated with the glenohumeral joint differ in size. The head of the humerus is approximately four times larger than the joint socket of the scapula. The result is a greater range of motion but also joint instability!
- The contour of the shoulder is formed mainly by the deltoid muscle.
- Rotator cuff muscles are responsible for providing the glenohumeral joint with stability and mobility.
- Several fascial slings of muscles move the scapula.
- The movement of the scapula and glenohumeral joint are also supported by the muscles of the arm, such as the and .
- The tendons of the rotator cuff muscles surround the head of the humerus from all sides and pull the humeral head to the articular surface of the scapula.
- The rotator cuff tendons extend into the shoulder joint capsule and strengthen the stability of the joint.
- The deltoid muscle rests on the rotator cuff, acting as a protective cap; however, it is not considered part of the rotator cuff.
- Clinical significance: and
All originate from the scapula
All insert into the humerus
All movements occur at the shoulder joint
|Supraspinatus|| || |
|Teres minor muscle|| || || |
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- Fascial slings are made up of several functionally antagonistic muscles.
- There are four fascial slings in the shoulder region, which move the scapula in different directions (oblique sling, horizontal sling, anterior vertical sling, and posterior vertical sling).
- The trapezius muscle is divided into three parts (anterior, transverse, and descending) that have different functions
- Components: rhomboid muscles and serratus anterior muscles
- Function: protraction and retraction; cranial and caudal rotation
- Components: serratus anterior muscle and transverse part of the trapezius
- Function: medial/lateral motion and rotation of the scapula
|Transverse part of the trapezius|
The serratus anterior muscle is part of both the oblique and horizontal slings!
Anterior vertical sling
- Components: pectoralis minor muscle and descending part of the trapezius
- Function: craniocaudal movement and rotation of the scapula
|Descending part of trapezius|| |
Posterior vertical sling
- Components: levator scapulae muscle and ascending part of the trapezius
- Function: craniocaudal movement and rotation of the scapula
|Levator scapulae|| |
Muscles of the shoulder that insert into the arm
- In addition to the antagonistic fascial slings, the shoulder is brought to motion by other muscles that insert into the arm.
- The deltoid muscle primarily forms the contour of the shoulder.
|Ventral muscles|| |
(forms the anterior axillary fold)
| || |
|Lateral muscle||Deltoid|| || |
|Dorsal muscles|| |
(forms the posterior axillary fold)
| || |
|Teres major muscle|| || |
Other muscles involved in shoulder motion
| || |
|Biceps brachii|| || |
|Triceps brachii|| || || || |
- Definition: A pyramid-shaped area at the junction of the arm and thorax, inferior to the shoulder joint, through which important vessels and nerves pass from the trunk to the arm
- Apex (axillary inlet): lateral border of the 1st rib, superior border of scapula, and the clavicle
- Anteriorly: pectoralis major and minor muscles
- Posteriorly: latissimus dorsi muscle, teres major muscle, subscapularis muscle
- Laterally: humerus, coracobrachialis muscle
- Medially: serratus anterior and the 1st–4th ribs and intercostal muscles
- The continuation of the subclavian artery at the outer border of the 1st rib
- Lies lateral to the axillary vein in the axillary fossa
- Continues as the brachial artery at the outer border of the teres major
- Divided into 3 parts by the overlying pectoralis minor muscle
- Branches from:
- 1st part (proximal to the pectoralis minor muscle): superior thoracic artery
2nd part (lies under the pectoralis minor muscle):
- Thoracoacromial artery
- Lateral thoracic artery
- 3rd part (distal to the pectoralis minor muscle):
- Formed at the outer border of the teres major by the union of the basilic vein and the accompanying veins of the brachial artery
- Continues as the subclavian vein at the outer border of the 1st rib
- Receives two major tributaries: the cephalic and basilic veins
- Drains the upper limb, axilla, and lateral chest wall
- Anterior group (pectoral): drain mammary and pectoral regions
- Posterior group (subscapular): drain the upper back and posterior neck
- Lateral group (humeral): drain the upper limb
- Central group (lies in axillary fat): receives lymphatics from the anterior, posterior, and lateral groups
- Apical group (lies behind the pectoralis minor): receives lymphatics from the central group and upper outer quadrant of the breast
- Description: : A network of nerves that are derived from C5–T1 spinal nerves spinal nerves and give rise to the peripheral nerves of the upper limb and shoulder.
Roots: anterior rami of C5–T1 spinal nerves
- arises directly from C5
- arises from roots C5, C6, and C7
- First intercostal nerve arises from T1
Trunks: the roots form 3 trunks that are located in the neck
C5 and C6 → upper trunk
- The subclavius arise from the upper trunk (C5, C6) and nerve to
- C7 → middle trunk
- C8 and T1 → lower trunk
- C5 and C6 → upper trunk
Divisions: all 3 trunks divide into anterior and posterior divisions that enter into the axillary fossa
- All anterior divisions: innervate the flexor compartment of the arm and forearm (i.e., the anterior compartment)
- All posterior divisions: innervate the extensor compartment of the arm and forearm (i.e., the posterior compartment)
- Only the cords and proximal portions of their branches lie in the axillary fossa.
- There are 3 cords, which are named according to their position in relation to the axillary artery.
- Anterior divisions of upper and middle trunks → lateral cord
- Anterior division of the middle trunk → medial cord
- Posterior divisions of all trunks → posterior cord
- Provides the motor innervation of all upper limb and shoulder muscles except for the trapezius, which is supplied by the .
- Provides the sensory innervation of the axilla and the upper limb except for medial portion of the arm, which is supplied by the intercostobrachial nerve.
- Clinical significance: see
The main branch of the lateral cord is the musculocutaneous nerve
The main branch of the medial cord is the ulnar nerve
The main branches of the posterior cord are the radial nerve and axillary nerves
Branches from the medial and lateral cords form the median nerve
- Anatomical spaces (2 triangular; 1 quadrilateral) bound by the teres minor muscle (cranially) and the teres major muscle (caudally) through which axillary contents leave the axilla.
A triangular space and with a cranial, caudal, and lateral border and apex facing medially (no medial border)
- Structures within: circumflex scapular artery and veins Run into the infraspinatus fossa
A quadrangular space
- Posterior humeral circumflex vessels
- Axillary nerve
A triangular space with a cranial, lateral, and medial border and apex facing caudally (no caudal border)
- Deep brachial artery
- Radial nerve
A simple trick for remembering the structures at the borders of the axillary spaces is to simulate them with the middle and index fingers of both hands. Form a victory sign with both hands and superimpose them at ∼ 90°. Three spaces are created that simulate the axillary spaces.