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Pectoral Girdle
The pectoral girdle, or shoulder girdle, consists of the clavicle and scapula on each side. It connects the upper limb to the axial skeleton, provides extensive sites for muscular attachment, and combines mobility with sufficient stability for positioning and movement of the upper limb.
RegionUpper Limb
SystemMusculoskeletal System
The pectoral girdle, also called the shoulder girdle, forms the skeletal connection between the upper limb and the trunk. It consists of the clavicle and scapula on each side of the body.
The pectoral girdle is designed primarily for mobility. Unlike the pelvic girdle, which forms a strong weight-bearing ring, the pectoral girdle permits extensive movement of the upper limb while relying heavily on muscles for stability and positioning.
The clavicle is the only bone of the pectoral girdle that forms a direct synovial articulation with the axial skeleton. Medially, it articulates with the manubrium of the sternum at the sternoclavicular joint. Laterally, it articulates with the acromion of the scapula at the acromioclavicular joint. The scapula itself is suspended against the posterior thoracic wall primarily by muscles.
Components of the Pectoral Girdle
| Bone | Number | Main Role |
|---|---|---|
| Clavicle | One on each side | Connects upper limb to axial skeleton and acts as a strut |
| Scapula | One on each side | Provides glenoid cavity and extensive muscle attachment |
Relationship to the Axial Skeleton
The pectoral girdle is attached to the axial skeleton through the sternoclavicular joint. There is no direct bony articulation between the scapula and the ribs or vertebral column.
This limited skeletal attachment contributes substantially to the mobility of the shoulder complex.
Clavicle
The clavicle is an elongated, S-shaped bone positioned horizontally at the root of the neck. It extends between the manubrium of the sternum medially and the acromion of the scapula laterally.
It can be palpated along almost its entire length because of its superficial position.
Functions of the Clavicle
The clavicle acts as a rigid strut that holds the scapula and upper limb away from the thorax. This positioning allows the arm to move through a wide range without being restricted by the chest wall.
It also transmits forces from the upper limb toward the axial skeleton and protects underlying neurovascular structures passing between the neck and upper limb.
Ends of the Clavicle
The clavicle has a large medial sternal end and a flatter lateral acromial end.
Sternal End
The sternal end articulates with the clavicular notch of the manubrium and participates in the sternoclavicular joint. It is relatively large and robust.
Acromial End
The acromial end is flattened and articulates with the medial border of the acromion at the acromioclavicular joint.
Shaft of the Clavicle
The shaft of the clavicle has a characteristic double curvature. The medial portion is convex anteriorly, while the lateral portion is concave anteriorly.
This shape contributes to its mechanical properties and provides attachment surfaces for several muscles.
Inferior Surface of the Clavicle
The inferior surface contains several important landmarks associated with ligament and muscle attachments.
Conoid Tubercle
The conoid tubercle lies near the lateral end of the clavicle and provides attachment for the conoid part of the coracoclavicular ligament.
Trapezoid Line
The trapezoid line extends from the region of the conoid tubercle and provides attachment for the trapezoid part of the coracoclavicular ligament.
Subclavian Groove
The subclavian groove lies along the inferior surface of the middle portion of the clavicle and provides attachment for the subclavius muscle.
Impression for the Costoclavicular Ligament
Near the medial end is a roughened area for attachment of the costoclavicular ligament, which helps stabilize the sternoclavicular joint.
Major Clavicular Landmarks
| Landmark | Importance |
|---|---|
| Sternal end | Articulates with manubrium |
| Acromial end | Articulates with acromion |
| Conoid tubercle | Attachment of conoid ligament |
| Trapezoid line | Attachment of trapezoid ligament |
| Subclavian groove | Attachment of subclavius |
| Costoclavicular impression | Attachment of costoclavicular ligament |
Scapula
The scapula is a flat, triangular bone positioned on the posterolateral thoracic wall. It provides a mobile base for the upper limb and serves as an attachment site for numerous muscles that move and stabilize the shoulder.
The scapula contains three borders, three angles, two major surfaces, and several prominent processes.
Surfaces of the Scapula
The scapula has a costal surface facing the thoracic wall and a posterior surface facing posteriorly.
Costal Surface
The costal surface is dominated by the broad subscapular fossa, which provides origin for the subscapularis muscle.
Posterior Surface
The posterior surface is divided by the scapular spine into the supraspinous fossa superiorly and the infraspinous fossa inferiorly.
Spine of the Scapula
The spine of the scapula is a prominent ridge on the posterior surface. It provides attachment for the trapezius and deltoid muscles and expands laterally to form the acromion.
Acromion
The acromion is the broad lateral continuation of the scapular spine. It forms the highest bony point of the shoulder and articulates with the clavicle.
Together with associated soft tissues, it forms part of the superior boundary over the humeral head.
Coracoid Process
The coracoid process projects anteriorly from the superior part of the scapula. It serves as an attachment site for muscles and ligaments, including pectoralis minor, coracobrachialis, the short head of biceps brachii, and components of the coracoclavicular and coracoacromial ligaments.
Glenoid Cavity
The glenoid cavity, or glenoid fossa, is a shallow articular depression on the lateral aspect of the scapula. It articulates with the head of the humerus to form the glenohumeral joint.
Its relatively shallow geometry permits extensive mobility but provides less inherent bony stability than a deeper socket would provide.
Supraglenoid Tubercle
The supraglenoid tubercle lies immediately superior to the glenoid cavity and provides attachment for the tendon of the long head of biceps brachii.
Infraglenoid Tubercle
The infraglenoid tubercle lies inferior to the glenoid cavity and provides attachment for the long head of triceps brachii.
Scapular Borders
| Border | Location |
|---|---|
| Superior border | Shortest border, extending toward the superior angle |
| Medial border | Runs approximately parallel to vertebral column |
| Lateral border | Thick border extending toward glenoid region |
Superior Border and Scapular Notch
The superior border contains the suprascapular notch near the base of the coracoid process. The superior transverse scapular ligament bridges this notch.
The suprascapular nerve typically passes beneath the ligament, while the suprascapular artery usually passes above it.
Angles of the Scapula
The scapula has superior, inferior, and lateral angles.
Superior Angle
The superior angle is formed by the junction of the superior and medial borders.
Inferior Angle
The inferior angle is formed where the medial and lateral borders converge. It is readily palpable and moves substantially during rotation of the scapula.
Lateral Angle
The lateral angle is thickened and contains the glenoid cavity and associated supraglenoid and infraglenoid tubercles.
Scapular Fossae
| Fossa | Associated Muscle |
|---|---|
| Subscapular fossa | Subscapularis |
| Supraspinous fossa | Supraspinatus |
| Infraspinous fossa | Infraspinatus |
Major Scapular Landmarks
| Landmark | Importance |
|---|---|
| Spine | Divides posterior surface into supraspinous and infraspinous fossae |
| Acromion | Articulates with clavicle |
| Coracoid process | Major muscle and ligament attachment site |
| Glenoid cavity | Articulates with humeral head |
| Supraglenoid tubercle | Long head of biceps attachment |
| Infraglenoid tubercle | Long head of triceps attachment |
| Suprascapular notch | Related to suprascapular neurovascular structures |
Sternoclavicular Joint
The sternoclavicular joint is the articulation between the sternal end of the clavicle, the manubrium, and the adjacent first costal cartilage. It is the only direct synovial articulation connecting the upper limb skeleton to the axial skeleton.
Articular Disc
An articular disc divides the sternoclavicular joint into two synovial compartments. It improves congruity and contributes to stability while allowing movement of the clavicle.
Ligaments of the Sternoclavicular Joint
The joint is reinforced by anterior and posterior sternoclavicular ligaments, the interclavicular ligament, and the costoclavicular ligament.
Movements at the Sternoclavicular Joint
The clavicle can elevate, depress, protract, retract, and rotate around its longitudinal axis. These movements are essential components of normal scapular motion.
Acromioclavicular Joint
The acromioclavicular joint is a plane synovial joint between the acromial end of the clavicle and the acromion of the scapula.
Small gliding and rotational movements at this joint allow the scapula to adjust its position relative to the clavicle during movements of the upper limb.
Acromioclavicular Ligament
The acromioclavicular ligament reinforces the superior aspect of the joint capsule and contributes to horizontal stability.
Coracoclavicular Ligament
The coracoclavicular ligament is a strong ligament connecting the coracoid process to the clavicle. It is composed of the conoid and trapezoid parts.
It is a major stabilizer of the relationship between the scapula and clavicle.
Conoid and Trapezoid Ligaments
| Part | Clavicular Attachment | General Role |
|---|---|---|
| Conoid ligament | Conoid tubercle | Resists excessive displacement and contributes to vertical stability |
| Trapezoid ligament | Trapezoid line | Stabilizes clavicle and scapula against displacement |
Scapulothoracic Articulation
The scapulothoracic articulation is a functional articulation rather than a true synovial joint. It describes movement of the scapula over the posterior thoracic wall.
Muscles and fascial planes separate the scapula from the ribs and permit smooth movement during positioning of the upper limb.
Scapular Movements
The scapula can elevate, depress, protract, retract, rotate upward, and rotate downward. These movements change the position and orientation of the glenoid cavity.
Major Scapular Movements
| Movement | Description |
|---|---|
| Elevation | Scapula moves superiorly |
| Depression | Scapula moves inferiorly |
| Protraction | Scapula moves anterolaterally around thoracic wall |
| Retraction | Scapula moves posteromedially toward vertebral column |
| Upward rotation | Glenoid cavity rotates superiorly |
| Downward rotation | Glenoid cavity rotates inferiorly |
Muscles Moving the Scapula
Scapular position is controlled by several muscles connecting the pectoral girdle to the axial skeleton. These include trapezius, serratus anterior, levator scapulae, rhomboid major, rhomboid minor, and pectoralis minor.
Scapular Stabilization
Stable positioning of the scapula is essential for efficient movement of the humerus. The scapula provides the base from which many muscles of the shoulder act.
If the scapula is poorly stabilized, the mechanical effectiveness of muscles moving the humerus can be reduced.
Scapulohumeral Rhythm
Elevation of the upper limb involves coordinated movement at the glenohumeral joint and rotation of the scapula. This coordinated relationship is commonly described as scapulohumeral rhythm.
Movement is distributed across the glenohumeral, sternoclavicular, acromioclavicular, and functional scapulothoracic articulations.
Muscle Attachments to the Clavicle
| Muscle | General Clavicular Attachment |
|---|---|
| Sternocleidomastoid | Medial clavicle |
| Pectoralis major | Anterior medial clavicle |
| Deltoid | Anterior lateral clavicle |
| Trapezius | Posterior lateral clavicle |
| Subclavius | Inferior middle clavicle |
Muscle Attachments to the Scapula
The scapula provides attachment for a large number of muscles. These muscles connect it to the axial skeleton, humerus, and forearm and are essential for shoulder stability and movement.
Selected Scapular Muscle Attachments
| Muscle | Scapular Attachment |
|---|---|
| Supraspinatus | Supraspinous fossa |
| Infraspinatus | Infraspinous fossa |
| Subscapularis | Subscapular fossa |
| Teres minor | Lateral border |
| Teres major | Region near inferior angle and lateral border |
| Trapezius | Spine and acromion |
| Deltoid | Spine and acromion |
| Serratus anterior | Anterior surface of medial border |
| Rhomboids | Medial border |
| Levator scapulae | Superior medial border |
Rotator Cuff Relationship
Four rotator cuff muscles originate from the scapula: supraspinatus, infraspinatus, teres minor, and subscapularis. Their tendons blend with the glenohumeral joint capsule and contribute importantly to stabilization of the humeral head.
Mechanical Role of the Pectoral Girdle
The pectoral girdle positions the glenoid cavity so that the humerus can move through a large three-dimensional range. At the same time, the clavicle maintains the shoulder laterally away from the trunk.
Mobility Versus Stability
The pectoral girdle favors mobility more than the pelvic girdle. Stability is achieved not through deep bony sockets or a rigid ring, but through coordinated action of muscles, ligaments, joint capsules, and the clavicular connection to the sternum.
Pectoral Versus Pelvic Girdle
| Feature | Pectoral Girdle | Pelvic Girdle |
|---|---|---|
| Primary function | Mobility and positioning of upper limb | Weight transmission and stability |
| Axial attachment | Relatively limited | Strong attachment through sacroiliac joints |
| Socket | Shallow glenoid cavity | Deep acetabulum |
| Bone structure | Clavicle and scapula | Right and left hip bones |
| Mobility | High | More restricted |
Surface Anatomy
Several components of the pectoral girdle are readily palpable. The clavicle is subcutaneous along nearly its entire length. The acromion forms the bony summit of the shoulder, while the scapular spine and inferior angle can be palpated posteriorly.
Palpable Landmarks
| Landmark | Surface Location |
|---|---|
| Clavicle | Anterior root of neck and superior chest |
| Acromion | Superior-lateral shoulder |
| Coracoid process | Deeply palpable anterior shoulder |
| Scapular spine | Posterior shoulder |
| Medial scapular border | Posterior thoracic wall |
| Inferior angle | Inferior tip of scapula |
Clavicle Fracture
The clavicle is one of the most frequently fractured bones. Fractures commonly occur in the middle region, where the curvature and cross-sectional geometry change.
After fracture, the weight of the upper limb and muscular forces can produce characteristic displacement of the fragments.
Neurovascular Structures Beneath the Clavicle
The brachial plexus and subclavian vessels pass deep to the clavicle. Severe displacement from trauma can therefore threaten important neurovascular structures, although such complications are less common than uncomplicated fractures.
Acromioclavicular Joint Injury
Trauma to the shoulder can disrupt the acromioclavicular joint. More severe injuries may also tear the coracoclavicular ligament, allowing substantial displacement between the clavicle and scapula.
Shoulder Separation
An injury involving disruption of the acromioclavicular and supporting coracoclavicular structures is commonly referred to as a shoulder separation. It is anatomically distinct from dislocation of the glenohumeral joint.
Scapular Fractures
The scapula is protected by surrounding muscles and its position against the thoracic wall. Fracture generally requires substantial trauma and may occur with associated injuries to the thorax or shoulder girdle.
Winging of the Scapula
Scapular winging occurs when the medial border of the scapula becomes abnormally prominent away from the thoracic wall. One important cause is weakness or paralysis of serratus anterior following injury to the long thoracic nerve.
Effect of Serratus Anterior Weakness
Serratus anterior normally helps hold the scapula against the thoracic wall and contributes to upward rotation. Loss of its function can impair elevation of the upper limb and produce visible medial winging.
Suprascapular Notch and Nerve Entrapment
The suprascapular nerve passes through the region of the suprascapular notch and can be affected by compression or traction. Because the nerve supplies supraspinatus and infraspinatus, injury can impair shoulder abduction initiation and external rotation.
Development of the Clavicle
The clavicle has a distinctive developmental pattern. Much of its shaft begins ossification through intramembranous mechanisms, although cartilage contributes to development at its ends.
It begins ossifying early in embryonic development and completes maturation relatively late.
Development of the Scapula
The scapula develops through multiple ossification centers, with substantial portions forming through endochondral ossification. Secondary centers contribute to structures such as the acromion and other peripheral regions.
Functions of the Pectoral Girdle
| Function | Role |
|---|---|
| Upper limb attachment | Connects the free upper limb to the trunk |
| Positioning | Orients the glenoid cavity and shoulder |
| Mobility | Allows extensive movement of the upper limb |
| Muscle attachment | Provides origins and insertions for numerous muscles |
| Force transmission | Transfers forces from upper limb toward axial skeleton |
| Neurovascular protection | Clavicle overlies major structures entering upper limb |
| Shoulder stability | Provides skeletal framework for dynamic muscular stabilization |
Key Features of the Pectoral Girdle
| Feature | Key Point |
|---|---|
| Bones | Clavicle and scapula |
| Direct axial articulation | Sternoclavicular joint |
| Clavicle-scapula articulation | Acromioclavicular joint |
| Functional thoracic articulation | Scapulothoracic articulation |
| Socket for humerus | Glenoid cavity |
| Superior shoulder projection | Acromion |
| Anterior scapular projection | Coracoid process |
| Major clavicle-scapula stabilizer | Coracoclavicular ligament |
| Principal design emphasis | Mobility |
| Important dynamic stabilizers | Muscles surrounding and positioning the scapula |
Anatomical and Functional Importance
The pectoral girdle creates a highly mobile skeletal platform from which the upper limb operates. The clavicle maintains the shoulder at a distance from the trunk and provides the only direct synovial skeletal connection between the upper limb and axial skeleton.
The scapula provides the glenoid cavity for articulation with the humeral head and broad surfaces for muscular attachment. Its ability to glide and rotate across the thoracic wall substantially expands the range through which the upper limb can be positioned.
Movement of the pectoral girdle depends on coordinated motion at the sternoclavicular and acromioclavicular joints together with functional scapulothoracic movement. Muscles such as trapezius and serratus anterior control scapular rotation and stabilization, while the clavicle transmits forces toward the sternum.
The pectoral girdle therefore integrates upper limb attachment, shoulder mobility, scapular positioning, muscle leverage, force transmission, joint stability, and coordinated movement of the entire shoulder complex.
Published on October 15, 2026
Last updated on October 15, 2026
Last updated on October 15, 2026