Brief Summary
Alright students, let's quickly revise the upper limb, focusing on important exam points. We'll cover muscle origins, insertions, actions, nerve supplies, and related clinical aspects. Key areas include the pectoral region, scapula, deltoid, rotator cuff muscles, brachial plexus, arm, forearm, wrist, and hand. We'll also touch upon common nerve injuries like Erb's palsy and Klumpke's paralysis, and conditions like carpal tunnel syndrome.
- Pectoralis Major: Origin, insertion, action, and nerve supply (medial and lateral pectoral nerves).
- Rotator Cuff Muscles: Supraspinatus, infraspinatus, teres minor, and subscapularis – actions and nerve supply.
- Brachial Plexus: Formation, branches, and related nerve injuries (Erb's palsy, Klumpke's paralysis).
- Carpal Tunnel Syndrome: Compression of the median nerve and its consequences.
Pectoralis Major and Clavipectoral Fascia
Pectoralis major originates from the medial two-thirds of the clavicle, sternum, second to sixth costal cartilages, and external oblique aponeurosis. It inserts on the lateral lip of the bicipital groove of the humerus. Its actions include adduction, flexion, and medial rotation of the arm at the shoulder joint. It's a composite muscle supplied by both medial and lateral pectoral nerves. The clavipectoral fascia, lying deep to pectoralis major, originates from the clavicle and inserts into the axilla, enclosing the subclavius and pectoralis minor muscles.
Rotator Cuff and Deltopectoral Groove
The lesser tubercle of the humerus is the attachment site for subscapularis, which medially rotates the arm. The greater tubercle has attachments for supraspinatus (abduction from 0-15 degrees), infraspinatus, and teres minor (lateral rotation). These four muscles form the rotator cuff. The clavipectoral fascia is pierced by the cephalic vein, thoracoacromial artery, lateral pectoral nerve, and lymphatics from the breast. The deltopectoral groove, located between the deltoid and pectoralis major, contains the cephalic vein, which pierces the clavipectoral fascia and drains into the axillary vein.
Clavicle and Scapula
The clavicle's medial two-thirds are convex anteriorly, while the lateral one-third is concave. Muscle attachments include pectoralis major (anterior medial), deltoid (lateral), trapezius (posterior lateral), and sternocleidomastoid. The inferior surface has a groove for the subclavius muscle. On the dorsal aspect of the scapula, the supraspinous fossa contains supraspinatus, and the infraspinous fossa contains infraspinatus. The inferior part of the spine and lateral acromion attach the deltoid, while the superior part of the spine and medial acromion attach the trapezius.
Scapula Muscle Attachments
The lateral border of the scapula has attachments for teres minor and teres major. Muscles attaching to the medial border include levator scapulae (superior angle to spine), rhomboid minor (opposite the spine), and rhomboid major (below the spine). The costal surface of the scapula features the subscapularis muscle. The infraglenoid tubercle attaches the long head of triceps, while the supraglenoid tubercle attaches the long head of biceps brachii. The coracoid process serves as the origin for coracobrachialis and the short head of biceps. Serratus anterior attaches to the costal surface and medial border.
Deltoid and Serratus Anterior
The deltoid has clavicular (anterior), spinal (posterior), and acromial fibers. Anterior fibers flex and medially rotate, posterior fibers extend and laterally rotate, and acromial fibers abduct from 15-90 degrees. The axillary nerve supplies the deltoid and teres minor, also giving off the upper lateral cutaneous nerve of the arm. Injury to the axillary nerve results in loss of sensation on the upper lateral arm, known as the "regimental badge sign." Serratus anterior originates from the upper eight ribs and inserts on the costal surface and medial border of the scapula, protracting the scapula.
Serratus Anterior Action and Axilla Boundaries
Serratus anterior protracts the scapula, assists in overhead abduction (above 90 degrees), and laterally rotates the scapula. It is supplied by the long thoracic nerve (C5-C7), and injury leads to winging of the scapula. Winging on attempted movement indicates serratus anterior paralysis, while winging at rest suggests trapezius paralysis. The anterior wall of the axilla is formed by pectoralis major, pectoralis minor, and subclavius. The posterior wall is formed by subscapularis, teres major, and latissimus dorsi.
Axilla Boundaries and Axillary Artery
The medial boundary of the axilla is formed by the ribs and serratus anterior, while the lateral boundary is formed by the humerus. The apex of the axilla, also known as the cervicoaxillary canal, is bounded by the clavicle (anteriorly), scapula (posteriorly), and the outer border of the first rib (medially). The subclavian artery becomes the axillary artery at the outer border of the first rib. The axillary artery continues as the brachial artery below the lower border of teres major. Pectoralis minor divides the axillary artery into three parts.
Axillary Artery Branches and Brachial Plexus
The first part of the axillary artery gives off the superior thoracic artery. The second part gives off the lateral thoracic and thoracoacromial arteries. The third part gives off the anterior circumflex humeral, posterior circumflex humeral, and subscapular arteries. The subscapular artery gives off the circumflex scapular artery, which participates in anastomosis on the dorsal aspect of the scapula. The brachial plexus is formed by the ventral rami of C5 to T1.
Brachial Plexus Formation and Branches
The brachial plexus consists of roots, trunks, divisions, cords, and branches. C5 and C6 join to form the upper trunk, C7 forms the middle trunk, and C8 and T1 form the lower trunk. Each trunk divides into anterior and posterior divisions. The anterior divisions of the upper and middle trunks form the lateral cord. The anterior division of the lower trunk continues as the medial cord. The posterior divisions of all three trunks form the posterior cord.
Brachial Plexus Cords and Nerves
The lateral cord gives off the lateral pectoral nerve, lateral root of the median nerve, and musculocutaneous nerve. The medial cord gives off the medial pectoral nerve, medial root of the median nerve, medial cutaneous nerve of the arm, medial cutaneous nerve of the forearm, and ulnar nerve. The posterior cord gives off the upper subscapular, lower subscapular, thoracodorsal (nerve to latissimus dorsi), axillary, and radial nerves. Branches from the roots include the dorsal scapular nerve (C5) and the long thoracic nerve (C5-C7).
Brachial Plexus Location and Axillary Artery Relations
The roots, trunks, and divisions of the brachial plexus lie in the neck, while the cords and nerves lie in the axilla. The cords are present in the first and second parts of the axillary artery, while the nerves are present in the third part. The cords are named according to their position relative to the second part of the axillary artery (lateral, medial, and posterior).
Arm Muscles: Biceps Brachii and Coracobrachialis
Biceps brachii has a long head (originating from the supraglenoid tubercle) and a short head (originating from the coracoid process). It inserts on the radial tuberosity and is supplied by the musculocutaneous nerve. Its actions include supination (especially in a mid-flexed elbow), flexion of the elbow, and flexion of the shoulder. The long head prevents upward dislocation of the humerus. Coracobrachialis originates from the tip of the coracoid process and inserts on the medial aspect of the middle half of the shaft of the humerus. It is a weak flexor of the shoulder joint.
Arm Muscles: Brachialis and Musculocutaneous Nerve
Brachialis originates from the anterior aspect of the shaft of the humerus below the insertion of coracobrachialis and inserts on the ulnar tuberosity. It is the chief flexor of the elbow joint and is supplied by the musculocutaneous nerve. The musculocutaneous nerve, a branch of the lateral cord (C5-C7), pierces coracobrachialis and lies between biceps and brachialis. It continues as the lateral cutaneous nerve of the forearm, supplying the skin on the lateral aspect of the forearm.
Erb's Palsy
Erb's palsy involves injury to the upper trunk of the brachial plexus (C5-C6), mainly affecting the axillary and musculocutaneous nerves. The arm is adducted and medially rotated due to paralysis of the deltoid and teres minor. There is loss of sensation on the upper lateral aspect of the arm (regimental badge sign). The forearm is extended and pronated due to paralysis of brachialis and biceps, resulting in a "waiter's tip hand" or "policeman's tip hand" deformity.
Klumpke's Paralysis and Forearm Muscles
Klumpke's paralysis involves injury to the lower trunk of the brachial plexus (C8-T1), mainly affecting the median and ulnar nerves. This results in a claw hand deformity due to paralysis of the intrinsic muscles of the hand. Additionally, T1 involvement can lead to Horner's syndrome. The superficial muscles of the anterior forearm include pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, and flexor carpi ulnaris.
Cubital Fossa and Deep Forearm Muscles
The cubital fossa is bounded by brachioradialis (laterally), pronator teres (medially), and an imaginary line joining the epicondyles (superiorly). Its floor is formed by brachialis and supinator. Contents include the median nerve, brachial artery, tendon of biceps, and radial nerve. Deep muscles of the anterior forearm include pronator quadratus, flexor pollicis longus, and flexor digitorum profundus.
Forearm Nerve Supply
The ulnar nerve supplies flexor carpi ulnaris and the medial half of flexor digitorum profundus. The median nerve supplies the remaining superficial muscles. The anterior interosseous nerve (a branch of the median nerve) supplies flexor pollicis longus, pronator quadratus, and the lateral half of flexor digitorum profundus. Flexor digitorum profundus is a composite muscle, supplied by both ulnar and median nerves.
Arm and Forearm Review
In a cross-sectional view of the arm and forearm, key structures include biceps brachii, brachialis, musculocutaneous nerve, median nerve, ulnar nerve, flexor digitorum profundus, radial nerve, and supinator. The musculocutaneous nerve is found by lifting the biceps. The median and ulnar nerves lie on flexor digitorum profundus. The radial nerve divides into superficial and deep branches in the cubital fossa.
Carpal Tunnel Anatomy
The carpal tunnel is formed by the carpal bones and the flexor retinaculum. Structures passing through the carpal tunnel include the tendons of flexor carpi radialis, flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus (enclosed in the radial bursa), and the median nerve. The ulnar bursa encloses the tendons of flexor digitorum superficialis and profundus.
Structures Above Flexor Retinaculum
Structures passing above the flexor retinaculum include the ulnar nerve and artery (through Guyon's canal), the palmar cutaneous branch of the ulnar nerve (supplying the skin over the hypothenar eminence), the tendon of palmaris longus, the palmar cutaneous branch of the median nerve (supplying the skin over the thenar eminence), and the superficial palmar branch of the radial artery. Carpal tunnel syndrome involves compression of the median nerve in the carpal tunnel.
Hand Muscles: Lumbricals and Interossei
Lumbricals arise from the tendons of flexor digitorum profundus and insert on the lateral aspect of the base of the proximal phalanges and the base of the distal phalanges. They cause flexion at the metacarpophalangeal joints and extension at the interphalangeal joints. The first and second lumbricals are supplied by the median nerve, while the third and fourth are supplied by the ulnar nerve. Palmar interossei adduct the fingers, while dorsal interossei abduct the fingers. All interossei are supplied by the ulnar nerve.
Hand: Thenar and Hypothenar Eminence
The thenar eminence is supplied by the palmar cutaneous branch of the median nerve, while the hypothenar eminence is supplied by the palmar cutaneous branch of the ulnar nerve. Movements of the thumb occur at right angles to the fingers. Muscles of the thenar eminence include abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis, all supplied by the median nerve.
Hand: Ulnar Nerve Supply and Carpal Tunnel Syndrome
In carpal tunnel syndrome, the thumb comes in line with the other fingers (ape thumb deformity). Muscles supplied by the ulnar nerve in the hand include the hypothenar muscles (abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi), the third and fourth lumbricals, all interossei, the deep head of flexor pollicis brevis, and adductor pollicis. The adductor pollicis is known as the "graveyard of the ulnar nerve."
Median and Ulnar Nerve Formation
The median nerve is formed by the lateral and medial roots from the lateral and medial cords, respectively. The medial root is longer and crosses the axillary artery. The median nerve crosses the brachial artery from the lateral to the medial side in the cubital fossa. The ulnar nerve is a branch of the medial cord and lies between the axillary artery and vein, with the medial cutaneous nerve of the forearm above it.
Ulnar Nerve Course and Triceps
The ulnar nerve pierces the medial intermuscular septum along with the superior ulnar collateral artery and goes behind the medial epicondyle. In the forearm, it lies on flexor digitorum profundus and below flexor carpi ulnaris. The ulnar nerve supplies flexor carpi ulnaris and the medial half of flexor digitorum profundus. The triceps brachii has a long head (originating from the infraglenoid tubercle), a lateral head (arising above the spiral groove), and a medial head (arising below the spiral groove). All three heads insert on the olecranon process of the ulna, causing extension at the elbow joint.
Radial Nerve Course and Branches
The radial nerve is a continuation of the posterior cord (C5-T1). It passes through the axilla, spiral groove, lateral aspect of the arm, and cubital fossa. In the axilla, it gives off two muscular branches (to the long and medial heads of triceps) and one cutaneous branch (posterior cutaneous nerve of the arm). In the spiral groove, it gives off three muscular branches (to the lateral and medial heads of triceps and anconeus) and two cutaneous branches (posterior cutaneous nerve of the forearm and lower lateral cutaneous nerve of the arm).
Radial Nerve in the Forearm and Anatomical Snuffbox
On the lateral aspect of the arm, the radial nerve supplies brachioradialis, extensor carpi radialis longus, and brachialis (lateral half). In the cubital fossa, it divides into superficial (sensory) and deep (posterior interosseous) branches. The posterior interosseous nerve supplies the deep muscles in the back of the forearm. The anatomical snuffbox is bounded by abductor pollicis longus and extensor pollicis brevis (laterally) and extensor pollicis longus (medially). The floor is formed by the scaphoid and trapezium, and the content is the radial artery.
Triangular and Quadrangular Spaces
The upper triangular space is bounded by teres minor, teres major, and the long head of triceps, containing the circumflex scapular artery. The lower triangular space is bounded by teres major, the long head of triceps, and the shaft of the humerus, containing the radial nerve and profunda brachii artery. The quadrangular space is bounded by teres minor, teres major, the long head of triceps, and the neck of the humerus, containing the axillary nerve and posterior circumflex humeral artery.
Spaces of the Hand and Shoulder Joint
A septum drawn from the palmar aponeurosis to the third metacarpal bone divides the spaces in the hand into the thenar space and the midpalmar space. The thenar space contains the first tendons of flexor digitorum superficialis and profundus with the first lumbrical. The midpalmar space contains the second, third, and fourth tendons with the rest of the lumbricals. The shoulder joint is a ball-and-socket synovial joint. Stability is maintained by the glenoid labrum, transverse humeral ligament, coracohumeral ligament, and capsular ligament.
