Pectoral Girdle, Clavicle & Scapula Anatomy

• The pectoral girdle connects the upper limbs to the axial skeleton/bony thorax
• It is composed of the clavicle and scapula
• The clavicle connects to the sternum at the sternoclavicular joint
• This joint is the only articulation of the upper limbs with the axis

Clavicle

• The sternal end is opposite the acromial end
• The diaphysis separates these ends
• Rough areas on the undersurface serve as points for ligament attachment

Scapula

• The scapula, or shoulder blade, is a flat bone
• The posterior aspect features a spinous process that terminates at the acromion
• The acromion is where the clavicle articulates
• The coracoid process sticks out on the anterior view of the scapula
• The scapula has 3 angles: superior, inferior & lateral
• The posterior aspect has the supraspinous fossa and infraspinous fossa
• The anterior face has a subscapular fossa and a glenoid cavity to fit the humerus

Humerus

• The humerus is the single long bone of the arm
• Proximally, it articulates with the scapula at the glenohumeral joint
• Distally, it articulates with the radius and ulna at the elbow joint
• The humerus has an anatomical neck, just distal to the head
• It also has a surgical neck, which is thin and prone to breaking
• The greater tubercle is located laterally
• The lesser tubercle is on the anterior face
• These two are separated by the intertubercular sulcus
• The deltoid tuberosity is on the lateral edge, next to the radial groove where the radial nerve runs
• The distal end has two condyles: the capitulum (lateral) and the trochlea (medial)
• These are adjacent to the lateral and medial epicondyles, respectively
• Small fossae accompany these condyles on the lateral face: radial (lateral) and coronoid (medial)
• The olecranon fossa is located on the posterior aspect and accommodates the olecranon process of the ulna during elbow flexion

Radius and Ulna

• They articulate with each other at the distal and proximal radio-ulnar joints
• They articulate with the humerus and carpal bones
• The antebrachial interosseous membrane covers the gap between the bones

Ulna Features

• Olecranon process - at the summit of the bone
• Trochlear notch - between the processes
• Coronoid process - sticks up anteriorly
• Radial notch - under the coronoid process, above the ulnar tuberosity
• Head of the ulna - at the distal end
• Ulnar styloid process

Radius Features

• Head - horizontal, lies next to the coronoid process and articulates with the capitulum condyle of the humerus
• Neck
• Radial tuberosity - adjacent to the ulnar tuberosity
• Radial styloid process and the carpal articular surface distally
• The trochlear notch of the ulna articulates with the trochlea of the humerus

Carpal Bones

• The carpal bones are arranged in two rows of four short bones each
• Proximal row (lateral to medial): scaphoid, lunate, triquetrum, pisiform
• Distal row (lateral to medial): trapezium, trapezoid, capitate, hamate

Other hand bone information

• The hand contains 8 carpals, 5 metacarpals, and 14 phalanges
• Metacarpals and phalanges are long bones
• The thumb is also called the pollex
• Most upper limb joints are diarthroses/synovial joints
• The scapulothoracic joint has no bone-to-bone articulation
• The antebrachial interosseous membrane is an amphiarthrosis of DICT

Joints and Classifications

• The sternoclavicular joint is a uniaxial plane joint
• The radius rotates around the ulna in a pivot joint
• The shoulder joint is a ball and socket joint
• Carpometacarpal of digit 1 is a saddle joint
• Metacarpophalangeal (MCP) joint is a condyloid joint
• Proximal interphalangeal joint is a hinge joint

Sternoclavicular Joint

• It is the only articulation between the upper limb and axial skeleton.
• The shape resembles a saddle joint
• Functions like a ball and socket joint.
• A disc between the sternal end of the clavicle and the clavicular notch of the manubrium acts as a shock absorber.
• The joint has 3 ligaments: anterior and posterior sternoclavicular, interclavicular, and costoclavicular ligaments

Acromioclavicular Joint

• It is a plane synovial joint for gliding between the acromial end of the clavicle and the acromion of the scapula
• Intrinsic ligaments includes the acromioclavicular ligament
• Extrinsic ligaments includes coracoclavicular ligaments
• Coracoclavicular ligaments attach the clavicle to the coracoid process
• Muscle fibres of the trapezius support the joint

Glenohumeral Joint

• Ball and socket joint for allowing rotation
• The head of the humerus is bigger than the glenoid cavity which allows for greater ROM
• The glenoid labrum, a fibrocartilaginous rim, deepens the cavity to stabilize movement
• The joint is supported superiorly by the inferior aspect of the acromion and the coracoid process (coracohumeral ligament)
• Absence of rotator cuff muscles inferiorly leaves the joint vulnerable to dislocation
• A tendon runs through the joint capsule, connecting the biceps muscle to the shoulder; this stabilizes the head of the humerus and is covered by a tendinous sheath
• Subdeltoid and subacromial bursae help to reduce friction
• Shoulder separation occurs with a gap in the acromioclavicular joint
• Shoulder dislocation occurs when the head of humerus leaves the glenoid cavity

Scapulothoracic Joint

• The scapulothoracic joint is not a true joint as it has no ligaments or capsule
• Muscles are intercalated between the bones
• This allows the scapula to move in relation to the thoracic cage
• Upward rotation describes when the glenoid cavity points up
• Movement occurs with movement at the glenohumeral joint

Elbow Joint

• Compound joint that involves several bones and 2 articulations
• Humeroulnar articulation: trochlea of humerus and trochlear notch of ulna
• Humeroradial articulation: capitulum of humerus and head of radius
• Allows for flexion and extension (hinge joint)
• The annular ligament stabilizes the radial head within the radial notch of the ulna
• The radial collateral ligament stabilizes the lateral aspect with the radius and the humerus
• The ulnar collateral ligament stabilizes the medial aspect with the ulna and humerus

Olecranon Bursitis

• Olecranon bursitis describes the inflammation of the bursa around the olecranon

Radio-Ulnar Joints

• Multiple radio-ulnar joints
• Radius rotates around the stationary ulna
• Bones connected by an antebrachial interosseous membrane
• Supination describes when palms are up
• Pronation describes when palms are down

Radiocarpal Joint

• Wrist joint or radiocarpal joint is a condyloid joint between the radius and three carpal bones (all except pisiform)
• The ulna does not participate as it is segregated by an articular disc
• The fibrous capsule is strengthened by ant and post ligaments and ulnar and radial collateral ligaments
• Intercarpal joints are present within the capsule
• Allows for flexion/extension, abduction/adduction

Muscle Terminology

• Agonist: muscle responsible for the majority of the force producing a movement
• Antagonist: muscle that opposes the movement, located on the opposite side of the joint
• When both contract simultaneously, they act as fixators
• Synergists: help the agonist by adding extra force to the same movement
• Origin: point of the muscle that stays fixed during concentric contraction
• Insertion: attachment point that moves closer to the origin during muscle contraction, usually distal
• Brachialis: flexion of elbow joint
• Levator scapulae: elevate the scapulae
• Nuchal ligament: from the occipital protuberance to the spinous process of C7
• Pectoral girdle: scapula + clavicle

Pectoral Girdle Muscles

• Trapezius: located in the back and neck, inserts at the spine of scapula & lateral clavicle (horseshoe)
• Different fibres are involved in different movements (upper fibres elevate, middle fibres retract, lower fibres depress the scapula)
• Upper and lower fibres work together for upper rotation
• Originates at the occipital bone, nuchal ligament, spinous processes of C7 to T12; CN XI
• Levator scapulae: originates from the transverse processes C₁ to C₄ to the medial border of the scapula
• It elevates the scapula and assists with downward rotation with the dorsal scapular nerve
• Rhomboid minor: originates at spinous processes of C₇ and T₁
• It retracts and rotates downwards; insert at the medial border and has the dorsal scapular nerve
• Rhomboid major: originates at spinous processes of T2 to T5. Inserts at the medial border of the scapula. Retracts and rotates downwards with the dorsal scapular nerve
• Subclavius: inserts at the posterior of the clavicle and depress, originates at rib 1
• Pectoralis minor: originates at ribs 3-5 and inserts on the coracoid process; it draws the scapula inferiorly and anteriorly by the medial pectoral nerve
• Serratus anterior: originates at ribs 1-8 and attaches to the medial border of scapula
• It separates it from the thoracic bones with the long thoracic nerve and abducts/protracts the scapulae

Glenohumeral Joint Muscles

• Pectoralis major: originates on clavicular head and a sternocostal head at ribs 1-6
• The clavicular head flexes the shoulder joint, while the sternocostal head adducts and medially rotates as well as extend from the flexed position
• Inserts at the intertubercular sulcus of the humerus with the medial and lateral pectoral nerves
• Deltoid: originates at the lateral clavicle, acromion, and spine of scapula
• Inserts at the deltoid tuberosity of the lateral humerus
• Anterior part of the GH flexes and medially rotates, posterior part extends and laterally rotates with the axillary nerve
• Teres major: On the posterior side of the body
• It adducts and medially rotates the GH joint
• Originates at the scapula and inserts at the intertubercular sulcus with the latissiumus dorsi synergists
• Latissiumus dorsi: Also inserts at the intertubercular sulcus with a broad origin
• It adducts, powerfully extends & medially rotates the GH joint

Rotator Cuff Muscles

• Rotator cuff muscles form a musculotendinous cuff around the glenohumeral joint
• Involved with rotation and stabilization
• There are no muscles on the inferior side, making it the most common site for joint dislocation
• These muscles include the supraspinatus, infraspinatus & teres minor

Forearm Rotator Cuff Muscles

• Supraspinatus: fills out the supraspinous fossa and the space under the acromion
• Originates at the medial edge of the scapula and inserts at the greater tubercle; responsible for abduction of the humerus
• Infraspinatus: fills out the infraspinous fossa
• Originates at the medial edge of the scapula and inserts at the greater tubercle; laterally rotates
• Teres minor: originates at the lateral border of the scapula
• Inserts at the greater tubercle and laterally rotates
• Subscapularis: On the anterior face of the scapula (subscapular fossa), between it and the ribs
• Originates at the medial border of the scapula and inserts at the lesser tubercle; medially rotates

Axilla

• The axilla is an armpit/pyramidal space under the glenohumeral joint. It is a Protective passageway for neurovascular structures
• It's anterior wall is covered by the serratus anterior, medial wall by pectoralis minor and major, lateral wall by the scapula and subscapularis & the posterior wall by the teres major

Axillary Artery

• The axillary artery is one of the vessels found in the axilla, which comes off the subclavian and continues to teres major
• Part 1: from rib 1 to pectoralis minor, the superior thoracic artery is included
• Part 2: under pectoralis minor
• Thoraco-acromial, Lateral thoracic
• Part 3: from pectoralis minor to teres major
• Posterior circumflex, Anterior circumflex, and Subscapular

Brachial Plexus

• Formed by the union of anterior rami from C5 to T1
• It is formed by overlapping fibres and compound nerves with fibres from at least 2 spinal segments
• Superior trunk: C5 + C6
• Middle trunk: C7
• Inferior trunk: C8 + T1
• Each trunk forms anterior and posterior divisions, which join to form 3 cords named in relation to their position relative to the axillary artery: lateral, posterior and medial
• These end as 5 terminal branches: axillary, radial, musculocutaneous, ulnar and median

Arm Muscles

• It is covered by the arm muscles
• Anterior and posterior compartments are divided by an extension of fascia which attaches to the humerus, which are called the medial and lateral intermuscular septa
• Anterior compartment contains: biceps brachii, coracobrachialis, brachialis are all innervated by the musculocutaneous nerve
• Posterior compartment contains: triceps brachii, anconeus, that are all innervated by the radial nerve

Other muscle characteristics

• Biceps brachii: originates at: the lateral long head on the supraglenoid tubercle and at the medial short head on the coracoid process
• Both heads insert at the radial tuberosity and the fascia of the forearm via the bicipital aponeurosis and functions to flex the elbow joint and supinates the radio-ulnar joint
• Coracobrachialis: originates at the coracoid process and inserts at the middle ½ of the humerus
• Brachialis: deep to biceps brachii: originates on the humerus and inserts at the ulna and flexes the elbow joint

rupture of the tendon

• Musculocutaneous nerve pierces the coracobrachialis and continues distally between the biceps brachii and brachialis
• Rupture of the tendon at the proximal end of biceps brachii causes Popeye's sign
• Triceps brachii: three headed muscle.
• Originates at: long head on the infraglenoid tubercle, lateral head on the posterior surface of the humerus above the radial groove and the medial head on the posterior surface of the humerus below the radial groove, most distal
• All of these insert at the olecranon process
• The long head assists in extension of the GH joint, and all assist in the extension of the elbow

Blood Supply Info

• The radial nerve runs in the radial groove, piercing the lateral intermuscular septum
• The brachial artery is the continuation of the axillary artery after teres major.
• The deep brachial artery runs alongside the radial nerve and anastomoses with the brachial artery at the elbow
• Collateral circulation exists to preserve blood supply when one artery is compressed during a muscular movement

Cubital Fossa

• The cubital fossa is the transition area over the elbow between the upper and forearm
• The lateral border is formed by the brachioradialis and the medial border is formed by the pronator teres
• These are associated with the epicondyles
• Structures, lateral to medial: biceps brachii tendon, brachial artery and median nerve

Forearm Muscles

• Produce movement in the hand, wrist, and fingers and are surrounded by antebrachial fascia
• Divided into 2 compartments separated by the interosseous membrane: anterior and posterior
• Anterior compartment, muscles of flexion and pronation, supplied by the medial and ulnar nerves
• Posterior compartment, muscles of extension and supination, supplied by the radial nerve
• Tendons are anchored to the wrist by a thickened band of connective tissue called flexor and extensor retinaculum
• The superficial and intermediate muscles share a common origin of a tendon at the medial epicondyle
• Flexor digitalis profundus: medial half innervated by ulnar nerve, lateral half innervated by median nerve
• Compression of the median nerve causes carpal tunnel syndrome, the flexor retinaculum and the carpal bones form the anterior and posterior sides of the carpal tunnel respectively
• This tunnel contains the median nerve as well as the tendons of the FDS, FDP, and the FPL
• The posterior forearm consists of two layers and are involved in extension and supination and attach at the extensor retinaculum
• The tendons of the extensor digitorum pass under the extensor retinaculum and flatten out past the MCP joints
• Intertendinous connections are bits of connective tissue that can restrict the independent extension of digits