Anatomy: Pectoral Girdle

Introduction to Pectoral Girdle

• The pectoral girdle, also known as the shoulder girdle, includes the clavicle (collarbone) and the scapula (shoulder blade)
• It functions to connect the upper limbs to the axial skeleton
• It provides attachment sites for muscles that facilitate movement of the upper limbs
• The pectoral girdle enhances upper limb mobility because the scapula can move freely across the thorax.
• The scapula is not directly attached to the axial skeleton, allowing for greater range of motion.

Clavicle (Collar Bone)

• The clavicle, derived from the Latin word for "small key", is a long bone; it has a cylindrical shaft and two ends, referred to as lateral and medial.
• It provides support to the shoulder, allowing the arm to swing freely from the trunk.
• This bone transmits the weight of the limb to the sternum.
• It is the only long bone that lies horizontally
• It is subcutaneous throughout

Side Determination of Clavicle

• The lateral end is flat, while the medial end is large and quadrilateral in shape.
• The shaft is slightly curved, convex forwards in its medial two-thirds, and concave forwards in its lateral one-third.
• The inferior surface features a longitudinal groove in its middle one-third.

Features of the Clavicle Shaft

• The shaft is divided into lateral one-third and medial two-thirds.
• The lateral one-third of the shaft is flattened from above downwards, featuring anterior and posterior borders
• The anterior border is concave forwards and posterior border is convex backwards
• This part of the bone has two surfaces, superior and inferior
• The superior surface is subcutaneous, and the inferior surface presents the conoid tubercle and the trapezoid ridge
• The medial two-thirds of the shaft is rounded and is said to have four surfaces
• The anterior surface is convex forwards and the posterior surface is smooth
• The superior surface is rough in its medial part
• The inferior surface has a rough oval impression (costal tuberosity) at the medial end
• The lateral half of this surface has a longitudinal subclavian groove, and the nutrient foramen lies at the lateral end of the groove.

Ends of the Clavicle

• The Lateral (Acromial) End is flattened from above downwards
• Bears a facet to articulate with the acromion process of the scapula, forming the acromioclavicular joint
• The Medial (Sternal) End is quadrangular in shape
• It articulates with the clavicular notch of the manubrium sterni, forming the sternoclavicular joint.

Muscular Attachments of the Clavicle

• Sternocleidomastoid muscle originates from the half of the superior surface of the medial two thirds of the clavicle, manubrium of sternum and inserts on the mastoid process of temporal bone, superior nuchal line of occipital bone
• Pectoralis Major muscle originates from the most of the anterior surface of the medial two thirds of clavicle, sternum, upper costal cartilages and inserts on the lateral lip of intertubercular groove of humerus
• Deltoid muscle originates from the anterior border of the lateral third of clavicle, acromion, spine of scapula and inserts on the deltoid tuberosity of humerus
• Trapezius muscle originates from the occipital bone, nuchal ligament, spinous processes of C7-T12 vertebrae and inserts on the posterior border of the lateral third of clavicle, acromion, spine of scapula
• Subclavius muscle originates from the first rib and its costal cartilage and its insertion is on the subclavian groove on inferior surface of middle third of clavicle

Ligament Attachments of the Clavicle

• Costoclavicular Ligament forms at the oval impression on the inferior surface at the medial end which gives attachment to costoclavicular ligament
• It attaches the clavicle to the first rib, preventing excessive elevation
• Coracoclavicular Ligament have conoid tubercle and trapezoid ridge giving attachment to the conoid and trapezoid parts of coracoclavicular ligaments
• It attaches the clavicle to the coracoid process of the scapula, preventing dislocation

Joints of the Clavicle

• Sternoclavicular Joint articulates with the manubrium of the sternum & first costal cartilage and is a saddle synovial joint
• The movements are elevation, depression, protraction, retraction, rotation
• Acromioclavicular Joint articulates with the acromion process of scapula and is a plane synovial joint
• There are slight gliding movements during shoulder motion.

Movements of the Clavicle

• Elevation & Depression results in shrugging shoulders
• Protraction & Retraction leads to moving shoulders forward and backward
• Axial Rotation happens during shoulder abduction

Clinical Conditions of the Clavicle

• The clavicle is commonly fractured by falling on the outstretched hand (indirect violence).
• The most common site of fracture is the junction between the two curvatures of the bone, which is the weakest point.
• The lateral fragment is displaced downwards by the weight of the limb as the trapezius muscle alone is unable to support the weight of the upper limb.

Scapula (Shoulder Blade)

• The scapula is a large, flat, triangular bone located on the posteriolateral aspect of the thoracic cage
• It has two surfaces, 3 borders, 3 angles, and 3 processes.

Side determination of the Scapula

• The lateral or glenoid (Greek shallow form) side is large and bears the glenoid cavity.
• The dorsal surface is convex and is divided by the triangular spine into the supraspinous and infraspinous fossae
• The costal surface is occupied by the concave subscapular fossa to fit on the convex chest wall.
• The thickest lateral border runs from the glenoid cavity above to the inferior angle below.

Surfaces of Scapula

• Costal Surface (Anterior) faces the ribs and has a concave subscapular fossa, where the subscapularis muscle attaches.
• Dorsal Surface (Posterior) gives attachment to the spine of the scapula which divides the surface into a smaller supraspinous fossa and a larger infraspinous fossa.

Borders of Scapula

• The superior border is thin and shorter:
• Near the root of the coracoid process it presents the suprascapular notch
• The lateral border is thick:
• At the upper end it presents the infra-glenoid tubercle.
• The medial border is thin:
• It extends from the superior angle to the inferior angle

Angles of the Scapula

• The Superior Angle, is located at the junction of the superior and medial borders.
• The Inferior Angle is formed by the convergence of the medial and lateral borders, it moves during scapular motion.
• The Lateral Angle contains the glenoid cavity, which articulates with the humerus to form the shoulder joint.

Processes of The Scapula

• Spine or the spinous process is a triangular plate of bone
• It divides the dorsal surface of the scapula into supra-spinous and infraspinous fossae
• Acromion Process is a lateral extension of the spine
• It has a facet that articulates with the clavicle at the acromioclavicular joint
• Coracoid Process is a beak-like projection that serves as an attachment for muscles, including the pectoralis minor, coracobrachialis, and short head of the biceps brachii

Muscular Attachments to the Anterior (Costal) Surface of the Scapula

• Subscapularis muscle originates from the subscapular fossa and inserts on the lesser tubercle of humerus
• Serratus Anterior muscle originates from the ribs 1-8 (lateral surface) and inserts on the medial border of scapula

Muscles Attached to the Posterior (Dorsal) Surface of the Scapula

• Supraspinatus muscle originates from supraspinous fossa and inserts on the greater tubercle of humerus
• Infraspinatus muscle originates from infraspinous fossa and inserts on the greater tubercle of humerus

Muscles Attached to the Borders of the Scapula

• Omohyoid (Inferior Belly) muscle originates from the near the Suprascapular notch and inserts on the Hyoid bone
• Levator Scapulae muscle originates from the transverse processes of C1-C4 and inserts on the Dorsal aspect of the medial border, from the superior angle up to the root of the spine
• Rhomboid Minor muscle originates from the spinous processes of C7-T1 and inserts at the Medial border (dorsal aspect opposite the root of the spine) of scapula
• Rhomboid Major muscle originates from the spinous processes of T2-T5 and inserts at the Medial border (dorsal aspect between the root of the spine and inferior angle) of scapula
• Teres Minor muscle originates at the upper lateral border of scapula (dorsal aspect) and inserts at the Greater tubercle of humerus
• Teres Major muscle originates from the lower lateral border of scapula (dorsal aspect and inferior angle) and Inserts at the Intertubercular sulcus of humerus

Muscles Attached to the Angles of the Scapula

• Levator Scapulae originates at the Transverse processes of C1-C4 and inserts on the Superior angle of scapula
• Teres Major originates from the Lower lateral border of scapula (dorsal aspect and inferior angle) and inserts on the Intertubercular sulcus of humerus
• Frequently few fibers of latissimus dorsi also act on the Inferior Angle

Muscles Attached to the tubercles of the Scapula

• Long Head of Biceps Brachii originates from the Supraglenoid Tubercal and inserts on the Radial Tuberosity
• Long Head of Triceps Brichii originates from the Infraglenoid Tubercal and inserts on the Olecranon process

Muscles Attached to the Processes of the Scapula

• Trapezius originates from the Occipital bone and spinous processes of C7-T12 and inserts to the Spine of scapula
• Deltoid originates from the Spine of scapula and inserts to the Deltoid tuberosity of humerus
• Trapezius orginates from the Occipital bone and spinous processes of C7-T12 and inserts to the Acromion of scapula
• Deltoid originates from the Acromion of scapula and inserts to the Deltoid tuberosity of humerus
• Pectoralis Minor originates from the Ribs 3-5 and inserts to the Medial border of Coracoid process of scapula

Ligaments of the Scapula

• The coracoacromial ligament attaches to the lateral border of the coracoid process, and the medial side of the tip of the acromion process.
• The coracohumeral ligament is attached to the root of the coracoid process.
• The coracoclavicular ligament is attached to the coracoid process: The trapezoid part on the superior aspect, and the conoid part near the root.
• The transverse ligament bridges across the suprascapular notch and converts it into a foramen which transmits the suprascapular nerve. The suprascapular vessels lie above the ligament.
• The spinoglenoid ligament may bridge the spinoglenoid notch and the suprascapular vessels and nerve pass deep to it.

Joint Articulation

• The Glenohumeral Joint, or Shoulder Joint, is a ball-and-socket synovial joint composed of the humeral head with the glenoid cavity of the scapula
• The Acromioclavicular Joint is a plane synovial joint that articulates with the lateral (acromial) end of the clavicle
• It allows for slight gliding movements during shoulder motion

Movements of the Scapula

• Elevation is when the scapula moves upward, like when you shrug your shoulders
• Depression is when the scapula moves downward, as seen when you lower your shoulders after shrugging.
• Protraction (Abduction) is when the scapula moves away from the spine, often seen when you reach forward.
• Retraction (Adduction) is when the scapula moves toward the spine, like when you squeeze your shoulder blades together.
• Upward Rotation is when the scapula rotates such that the glenoid (socket part of the shoulder) moves upward, and is essential for raising the arm overhead.
• Downward Rotation is when the scapula rotates in the opposite direction, bringing the glenoid downward, as when the arm is lowered from an overhead position.

Clinical Condition

• Winging of the scapula is caused due to paralysis of the serratus anterior, and is when the medial border of the bone becomes unduly prominent and the arm cannot be abducted beyond 90 degrees.