The shoulder girdle, also called the pectoral girdle, is an incomplete bony ring formed by the clavicle and scapula on each side of the body, joined anteriorly by the manubrium of the sternum. The bones of the shoulder girdle articulate with each other and partake in the formation of 4 joints that include:
- The sternoclavicular joint - formed between the sternum and clavicle.
The acromioclavicular (AC) joint - formed between the scapula and the clavicle.
- The glenohumeral (shoulder) joint - formed between the scapula and humerus.
- The scapulothoracic joint - formed between the scapula and the posterior thoracic cage.
The shoulder girdle functions as the anchor that attaches the upper limbs to the axial skeleton. Additionally, the shoulder girdle allows for a large range of motion, mainly in the highly mobile scapulothoracic joint.
This article will discuss the anatomy and functions of the shoulder girdle.
|Definition||Incomplete bony ring that connects the upper limbs to the bones to the axial skeleton.|
|Bones||Scapula and clavicle on each side, joined anteriorly by the manubrium of the sternum|
Acromioclavicular joint: Between the acromion of the scapula and the acromial (distal) end of the clavicle.
Sternoclavicular joint: Between the manubrium of the sternum and the first costal cartilage with the sternal (proximal) end of the clavicle.
Glenohumeral joint: Between the head of the humerus and the glenoid fossa of the scapula
Scapulothoracic joint: Between the anterior surface of the scapula and the posterior thoracic cage.
|Vascularization||Suprascapular and thoracoacromial arteries (acromioclavicular joint)
Internal thoracic and suprascapular arteries (sternoclavicular joint)
Anterior and posterior circumflex humeral arteries (glenohumeral joint)
|Innervation||Subscapular, lateral pectoral, axillary nerves (acromioclavicular joint)
Medial suprascapular nerve (sternoclavicular joint)
Axillary, suprascapular, lateral pectoral nerves (glenohumeral joint)
|Functions||Forms a connection between upper libms and thoracic cage;
Faciliates movements of the upper limb in the glenohumeral (shoulder) joint.
- Definition and structure
- Clinical notes
Definition and structure
The shoulder girdle is a bony ring formed by the clavicle and scapula. This bony ring is incomplete posteriorly while being closed off anteriorly by the manubrium of the sternum. The shoulder girdle connects the upper limb to the axial skeleton on the left and right sides of the body.
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Note that the clavicle and scapula make up the shoulder girdle, while the left and right pelvic bones (hip bones) together with the sacrum and coccyx form the pelvic girdle. The shoulder girdle and bones of the free part of the upper limb form the superior appendicular skeleton, while the pelvic girdle and bones of the free part of the lower limb form the inferior appendicular skeleton.
The shoulder girdle is formed by two pairs of bones, the scapulae and the clavicles.
The clavicle, or collarbone, is an S-shaped long bone lying superficial to the skin and is palpable along its entire length. In conjunction with the scapula, it serves as a connection between the axial and appendicular skeleton.
The clavicle is composed of a sternal (proximal) end, a shaft (body) and a acromial (distal) end. The medial end of the clavicle articulates with the manubrium of sternum (sternoclavicular joint), while the acromial end articulates with the acromion of the scapula (acromioclavicular joint).
The acromial and sternal ends of the clavicle contain several bony landmarks that serve as attachment points for ligaments of their respective joints. Likewise, the shaft of the clavicle acts as an attachment site for several muscles, such as the trapezius, deltoid, pectoralis major, and sternocleidomastoid muscles.
The surface markings of the clavicle include:
- The trapezoid line, which provides an attachment point for the trapezoid ligament.
- The subclavian groove in the medial third of the shaft, which is a site of attachment of the subclavius muscle.
- The conoid tubercle, onto which the conoid ligament attaches.
The scapula, or shoulder blade, is a triangular flat bone that lies on the posterolateral aspect of the thorax, overlying the 2nd – 6th or 7th ribs.
The convex posterior surface of the scapula is unevenly divided by a thick projecting ridge of bone (spine of the scapula) into a small supraspinous fossa and a much larger infraspinous fossa. The spine continues laterally as the flat expanded acromion, which forms the subcutaneous point of the shoulder and articulates with the acromial end of the clavicle (acromioclavicular joint).
The concave anterior surface of the scapula forms a large subscapular fossa, which forms a muscular connection with the posterior thoracic cage (scapulothoracic joint).
Superolaterally, the lateral surface of the scapula contains the glenoid fossa (Greek word meaning “Socket”), which articulates with the head of the humerus to form the glenohumeral (shoulder) joint. The glenoid fossa is a shallow, concave, oval cavity directed anterolaterally and slightly superiorly, that is considerably smaller than the ball (head of the humerus) for which it serves as socket. The beak-like coracoid process is superior to the glenoid fossa and projects anterolaterally.
The broad bony surfaces of the three fossae provide attachments for several muscles. The spine and acromion serve as levers for the attached muscles, particularly the trapezius muscle. The glenohumeral (shoulder) joint is almost directly inferior to the acromioclavicular joint, thus the scapula mass is balanced with that of the free limb, and the suspending structure (coracoclavicular ligament) lies between the two masses.
The bones of the shoulder girdle establish connections between each other and other structures, forming 3 anatomical (true) joints, and one physiological joint:
- The sternoclavicular (SC) joint, formed between the manubrium of the sternum and the sternal end of the clavicle.
- The acromioclavicular (AC) joint, formed by the acromion of scapula and the acromial end of the clavicle.
- The glenohumeral (shoulder) joint, formed between the glenoid fossa of the scapula and the head of the humerus.
- The scapulothoracic joint, formed between the anterior surface of the scapula and the posterior thoracic cage. This joint is not a true joint but rather a physiological joint established by the several muscles, including the trapezius, rhomboids and serratus anterior.
Sternoclavicular (SC) joint
The sternoclavicular (SC) joint is a synovial saddle joint but functions as a “ball and socket” synovial joint. This joint is formed by the manubrium of the sternum and the sternal (proximal) end of the clavicle. Additionally, the superior surface of first costal cartilage partakes in the formation of this joint by connecting with the clavicle.
The SC joint is the only articulation between the upper limb and the axial skeleton, and it can be readily palpated because the sternal end of the clavicle lies superior to the manubrium of the sternum. The SC joint is strengthened by several ligaments, such as the anterior and posterior sternoclavicular ligaments, interclavicular ligament and the costoclavicular ligament.
The SC joint is vascularized by the internal thoracic and the suprascapular arteries; and innervated by the branches of the medial suprascapular nerve and the nerve to subclavius muscle.
Although the SC joint is extremely strong, it is significantly mobile allowing anterior and posterior movements of the shoulder girdle, elevation and depression as well as a special form of circumduction which is performed by moving the acromial end along a circular path.
Acromioclavicular (AC) joint
The acromioclavicular (AC) joint is a plane synovial joint formed by the acromion of scapula and the acromial (distal) end of the clavicle.
The AC joint is strengthened by several ligaments that span between the acromion and clavicle, as well as the coracoid process of the scapula and the clavicle or acromion. Some of these ligaments include the acromioclavicular, trapezoid, conoid and the coracoclavicular ligament.
Glenohumeral (shoulder) joint
The glenohumeral (shoulder) joint is a ball and socket type of synovial joint formed between the glenoid fossa of the scapula and the head of the humerus.
The glenohumeral joint is supported by its loose fibrous joint capsule and several ligaments that include:
- The transverse humeral ligament
- The coracoacromial ligament
- The glenohumeral ligament
In addition, the glenohumeral joint is supported by the rotator cuff, a musculotendinous sleeve formed around the joint. The muscles that form the rotator cuff are the supraspinatus, infraspinatus, teres minor and subscapularis muscles.
The rotator cuff always pops up in exam questions! Make sure you're prepared for questions on its attachments, innervations and functions with our upper extremity muscle anatomy revision chart.
The internal surface of the joint capsule is well lined by synovial membrane and the joint is also rich in bursae (sac-like cavities) which contain capillary films of synovial fluid secreted by the synovial membrane. Those bursae include the subscapular bursa and the subacromial bursa.
The glenohumeral joint is vascularized by the anterior and posterior circumflex humeral arteries as well as branches of the suprascapular artery. Its nervous supply stems from the axillary, suprascapular, and the lateral pectoral nerves.
The glenohumeral joint does not allow movements of the shoulder girdle itself, but it does allow movements of the upper limb. In fact, it is one of the most mobile joints of the human body, permitting a wide range of movements of the arm, including flexion, extension, abduction, adduction, rotation (medial and lateral rotation), and circumduction.
The scapulothoracic joint is a physiological joint formed by the anterior surface of the scapula and the posterior thoracic cage. It is musculotendinous in nature, formed mainly by the trapezius, rhomboids and serratus anterior muscles, while the pectoralis minor muscle also plays a role in its movements.
The scapulothoracic joint permits gliding movements of the scapula around the fulcrum of the acromioclavicular joint. The scapula moves by gliding against the chest wall. The movements in this joint include elevation, depression, retraction, protraction and superior and inferior rotation of the scapula.
The shoulder girdle is very mobile. However, movements of the shoulder girdle are mainly permitted by the scapulothoracic joint. Scapular mobility is important for the proper positioning of the shoulder girdle in space. The movements of the scapula are translated to the shoulder girdle as follows:
- Protraction of the scapula: By moving the scapula laterally away from the spine, the shoulders are moved anteriorly and inwards.
- Retraction of scapula: This movement pulls the scapula medially towards the spine and moves the shoulders backwards and inwards.
- Elevation of scapula: Movement that allows the shoulder girdle to move upwards as in shrugging the shoulders.
- Depression of scapula: In contrast to the latter, this movement allows for the scapula and shoulder girdle to move downwards.
- Upward rotation of scapula: By rotating the lower scapula laterally and upwards the shoulder girdle moves upwards and inwards.
- Downward rotation of scapula: Movement that rotates the lower scapula towards the spinal column that moves the shoulder girdle downwards.
Want to learn more about the types of body movements? Check out our articles, video tutorials, quizzes, and labeled diagrams.
Fracture of the clavicle
The clavicle is a long bone and fractures usually occur in its middle portion. Occasionally, the bone will break where it attaches at the ribcage (SC joint) or shoulder blade (AC joint). Clavicle fractures are often caused by a direct blow to the shoulder. This can happen during a fall onto the shoulder or a car collision. A fall onto an outstretched arm can also cause a clavicle fracture. In babies, these fractures can occur during the passage through the birth canal.
Clavicle fractures can be very painful and may cause difficulty in moving the arm. Additional symptoms include:
- Sagging shoulder (down and forward)
- Inability to lift the arm because of pain
- A grinding sensation if an attempt is made to raise the arm
- A deformity or "bump" over the fracture
- Bruising, swelling, and/or tenderness over the collarbone
Fracture of the scapula
Fracture of the scapula is usually the result of severe trauma, as occurs in pedestrian – vehicle accidents. Usually there are also fractured ribs. Most fractures require little treatment because the scapula is covered on both sides by muscles. Most fractures involve the protruding subcutaneous acromion.
Other clinical conditions
Other clinical conditions of the pectoral girdle include:
- Dislocation of the acromioclavicular joint
- Glenoid labrum tears
- Adhesive capsulitis of the glenohumeral joint
- Dislocation of the glenohumeral joint
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