UPPER LIMB - BONES OF THE UPPER LIMB CLAVICLE The clavicle extends laterally and almost horizontally across the neck, from manubrium to acromion, being wholly subcutaneous. The acromial end (lateral, flat) articulates with the acromion The sternal end (medial, enlarged) articulates with the manubrial clavicular facet The shaft has two surfaces : The superior surface is smooth and palpable The inferior surface has a roughening near the lateral end: the conoid tubercle and the trapezoid line The anterior border (concave in its lateral 1/3 and convex in its medial 2/3) Posterior border SCAPULA The scapula, a flat, triangular bone, overlaps in part the second to seventh ribs on the posterolateral thoracic aspect. It has : costal and dorsal surfaces superior, lateral and medial borders lateral, superior and inferior angles three processes - spinous, acromial and coracoid The costal (anterior) surface is slightly hollow. The posterior surface is divided by the scapular spine into a smaller supraspinous fossa and larger infraspinous fossa The lateral border is sharp. Superiorly it widens into a infraglenoid tubercle. The superior border, sharp and shortest, is separated laterally from the coracoid process by a suprascapular notch. The medial border (from the inferior to the superior angle) The superior angle (at the junction of superior and medial borders) The inferior angle (palpable through the skin, it is also visible when the arm is raised) The lateral angle is expanded to form the glenoid cavity (for articulation with humerus) The scapular spine is triangular process and continues laterally as the acromion. The acromion articulates with the clavicle. The coracoid process springs from the summit of the scapular head (lateral angle) HUMERUS Humerus has a proximal end, body and distal end. The proximal end The head is hemispherical and articulates with the scapula. The anatomical neck adjoins the articular heads margin The lesser tubercle lies on its medial side and the greater tubercle lies on its lateral side. The intertubercular sulcus lies between the tubercles. The surgical neck is the junction between the proximal end and the shaft, and a common site of the fracture. The humeral shaft The anterolateral surface (deltoid tuberosity is proximal to surfaces midpoint) The anteromedial surface The posterior surface (the middle 1/3 is crossed by the radial sulcus) The anterior, lateral and medial border The distal end Capitulum is an anterolateral hemispherical articular surface that coapts the head of radius. The trochlea is a medial pulley-shaped articular surface that coapts the trochlear notch of the ulna. The radial fossa is located above the capitulum on the anterior aspect. The coronoid fossa is located above the trochlea on the anterior aspect. Medial epicondyle and lateral epicondyle The olecranon fossa is located on the posterior aspect of the humerus (receives the olecranon upun the full extension of forearm) RADIUS The radius, lateral in the forearm, has a proximal end, body and distal end. The proximal end The head articulates with the capitulum of the humerus; its articular periphery contacts with the ulnar radial notch. The neck is the constriction distal to the head. The tuberosity is distal to the medial part of the neck. The shaft The anterior, posterior and lateral SURFACE and the anterior, posterior and interosseous BORDER The distal end The distal end, the widest part, has the lateral, medial, anterior, posterior and inferior surfaces. The lateral surface projecting distally as a styloid process. The medial surface is the ulnar notch (articulating with the ulnas head) The anterior surface is smooth and the posterior surface is grooved by the tendons. The inferior (carpal articular) surface has facets for the scaphoid and lunate bone ULNA The ulna, medial in the forearm, has a proximal end, body and distal end. The proximal end The olecranon is the curved projection on the back of the elbow. The coronoid process is located below the trochlear notch. The trochlear notch receives the trochlea of the humerus. The radial notch accommodates the head of the radius. The shaft The anterior, posterior and medial surface The anterior, posterior and interosseous border The distal end The head The styloid process BONES OF HAND The hands skeleton has 3 regions: the carpus, the metacarpus and the phalanges. The carpus The carpus contains 8 bones in proximal and distal rows of four. Proximal row (lateral to medial): scaphoid bone, lunate bone, triquetral bone and the pisiform bone Distal row (lateral to medial): trapezium bone, trapezoid bone, capitate bone and hamate bone (a hook-like process called hamulus) The metacarpus Five metacarpal bones are miniature long bones consisting of bases (proximal ends), shafts (bodies) and heads (distal ends) The phalanges Three rows of phalanges comprise the skeletons of the second through fifth digits; the thumb has only two phalanges. JOINTS OF THE UPPER LIMB GLENOHUMERAL (SHOULDER ) JOINT This is a synovial joint of the ball and socket variety, between the shallow glenoid cavity of the scapula and the hemispherical head of the humerus. The glenoid cavity is deepened by the glenoidal labrum, a ring of fibrocartilage attached to its boundaries. Ligamentous support. Its lax fibrous capsule is reinforced by tough articular ligaments: a. Superior, middle, and inferior glenohumeral ligaments run from the glenoid lip to the anatomic neck of the humerus. b. The coracohumeral ligament between the coracoid process and the humerus supports the dead weight of the free portion of the upper extremity. Movement. As a ball-and-socket joint, it has three degrees of freedom. a. Flexion/extension b. Abduction/adduction c. Medial/lateral rotation d. Circumduction ELBOW JOINT The elbow joint consists of three articulations between the humerus, radius and ulna. 1. The humeroulnar joint is formed by the trochlea of the humerus and the trochlear notch of the ulna. This joint has one degree of freedom, permitting flexion/extension about a transverse axis through the trochlea. It is reinforced by the ulnar (medial) collateral ligament. 2. The humeroradial joint is formed by the capitulum of the humerus and the head of the radius. It has two degrees of feedom; flexion/extension occurs about an axis through the trochlea; pronation/supination occurs about an axis that passes through both centers of curvature of the proximal and distal radioulnar joints. It is reinforced by the radial (lateral) collateral ligament. 3. The proximal radioulnar joint is formed by the side of the head of the radius and the radial notch of the ulna. It has one degree of freedom, permitting pronation/supination. It is reinforced by the annular ligament. WRIST JOINT This is a synovial joint of the ellipsoid variety. The faceted lower end of the radius and fibrocartilaginous disc overlying the head of the ulna articulate with the proximal row of carpal bones, the scaphoid, lunate and triquetral. Movement: a. Abduction (radial deviation)/adduction (ulnar deviation) b. Flexion/extension c. Circumduction Ligamentous support: a. The ulnar collateral ligament b. The radial collateral ligament c. The dorsal radiocarpal ligament d. The palmar radiocarpal ligament e. The dorsal ulnocarpal ligament f. The palmar ulnocarpal ligament MIDCARPAL JOINT This is synovial joint between the proximal and distal rows of carpal bones. CARPOMETACARPAL JOINTS There are five carpometacarpal joints between the metacarpals and related distal row of carpal bones. The carpometacarpal joint of the thumb possessing considerable mobility by virtue of its saddleshaped articulation. Flexion, extension, abduction, adduction, circumduction and rotation are all possible. The combined movement brings the thumb into contact with the other finger tips and is known as opposition. METACARPOPHALANGEAL JOINTS The rounded heads of the metacarpals articulate with bases of the proximal phalanges. INTERPHALANGEAL JOINTS OF HAND The interphalangeal joints are hinge joints. They have a strong palmar ligament and two collateral ligaments. MUSCLES OF THE UPPER LIMB MUSCLES CONNECTING THE UPPER LIMB AND THORACIC WALL THE SCAPULOHUMERAL MUSCLE MUSCLES OF THE UPPER ARM MUSCLES OF THE UPPER LIMB Muscles of the upper limb may be grouped as follows: 1. MUSCLES CONNECTING THE UPPER LIMB AND THORACIC WALL 2. SCAPULOHUMERAL MUSCLES 3. MUSCLES OF THE UPPER ARM 4. MUSCLES OF THE FOREARM 5. MUSCLES OF THE HAND Muscles Connecting the Upper Limb and Thoracic Wall Muscle Pectoralis major Clavicular head Origin Medial 2/3 of clavicle Sternum&costal cartilages1-6 Insertion Lateral lip of intertubercular groove of humerus Action Innervation -Adducts and medially rotates arm; Lateral pectoral nerve Medial pectoral nerve Sternocostal head - Accessory muscle of respiration Vagina m. recti abdominis Abdominal part - Depression the scapula - Accessory muscle of respiration Medial pectoral nerve Clavicle (groove on inferior surface) Depresses and protracts clavicle Nerve to subclavius Medial border of scapula Protracts and rotates scapula Long thoracic nerve Pectoral minor Outer surface of ribs 3-5 Coracoid process Subclavius First rib Serratus anterior Outer surface of ribs 1-9 The Scapulohumeral Muscles Muscle Deltoid Origin Anterior border of lateral third of clavicle Acromion of scapula Spine of scapula (lower edge of its crest) Insertion Action Innervation Deltoid tuberosity of Humerus Major abduct the arm Axillary nerve Subscapularis Subscapular fossa Lesser tubercle of Humerus Medially rotates arm and stabilizes shoulder joint Subscapular nerve Supraspinatus Supraspinous fossa of scapula Greater tubercle of Humerus Abduction of arm Suprascapular nerve Infraspinous fossa of Infraspinatus scapula Gretater tubercle of humerus Laterally rotates arm Suprascapular nerve Teres minor Lateral border of scapula Laterally rotates arm Axillary nerve Teres major Inferior angle of scapula Greater tubercle of humerus Medial lip of intertubercular groove of humerus Extends, adducts and medially rotates arm Subscapular nerve Muscles of the Upper Arm Muscle Origin Insertion Action Innervation Anterior compartment Biceps brachii Long head Supraglenoid tubercle of scapula Tuberosity of radius Short head Coracoid process Coracobrachialis Coracoid process of scapula Brachialis Distal half of anterolateral and anteromedial Flexes forearm at the elbow joint, and supinates the forearm Musculocutaneous nerve Middle 1/3 of anteromedial surface of humerus Flexes the arm Musculocutaneous Tuberosity of ulna Flexes forearm Musculocutaneous nerve nerve surface of humerus Posterior compartment Muscle Origin Triceps brachii Long head Lateral head Medial head Insertion Infraglenoid tubercle of scapula Posterior surface of humerus superior to the radial groove Posterior surface of humerus inferior to the radial groove Olecranon of ulna Action Extends forearm at the elbow joint Extends, and adducts arm (long head) Innervation Radial nerve MUSCLES OF THE UPPER LIMB MUSCLES OF THE FOREARM MUSCLES OF THE HAND MUSCLES OF THE ANTERIOR COMPARTMENT OF FOREARM Muscle Origin Insertion Action Innervation Pronation Median nerve Bases of second metacarpal Flexes and abducts wrist Median nerve Palmar aponeurosis Tenses skin of palm Median nerve Superficial group Pronator teres Humeral head Ulnar head Flexor carpi radialis Palmaris longus Medial epycondyle of humerus Ulnar coronoid process Medial epicondyle of humerus Medial epicondyle of humerus Lateral aspect of midradius Flexor carpi ulnaris Humeral head Ulnar head Medial epicondyle of humerus Upper 2/3 of posterior border of the ulna Flexor digitorum superficialis Humero-ulnar head Radial head Medial epicondyle of humerus Anterior radial border Flexes and adducts wrist Pisiform bone Sides of the middle phalanx of II through V digits (over the proximal phalanx each tendon SPLITS and encircles the corresponding tendon of flexor digitorum profundus) Flexes proximal interphalangeal joint, metacarpophalangeal joint and wrist Ulnar nerve Median nerve Deep group Flexor digitorum profundus Anterior and medial surfaces of ulna and interosseous membrane Flexor pollicis longus Anterior surface of radius and interosseous membrane Pronator quadratus Distal ¼ of anterior surface of the ulna Palmar surface of the base of distal phalanx of second through fifth digits Second phalanx of thumb Distal quarter of anterior surface of the radius Flexes distal and proximal interphalangeal joint, metacarpophalangeal joint and wrist Flexes thumb, metacarpophalangeal joint and wrist The principal pronator of forearm Lateral part: median nerve Medial part: ulnar nerve Median nerve Median nerve MUSCLES OF THE LATERAL and POSTERIOR COMPARTMENT OF FOREARM Muscle Origin Insertion Action Innervation Flexion of the elbow Radial nerve Lateral group Brachioradialis Uper 2/3 of the lateral ridge of the humerus Styloid process of radius Extensor carpi radialis longus Extensor carpi radialis brevis Lower 1/3 of the lateral ridge of the humerus Dorsal surface of base of second metacarpal bone Lateral epicondyle of humerus Dorsal surface of base of third metacarpal bone Extends and abducts wrist Radial nerve Extends and abducts wrist Radial nerve Posterior (superficial) group Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris Lateral epicondyle of humerus Lateral epicondyle of humerus Lateral epicondyle of humerus Humeral head Ulnar head Anconeus Posterior border of ulna Lateral epicondyle of humerus Dorsal aspect of palanges second to fifth digits Extends MP joint, extends hand at wrist joint All phalanges of fifth digit Extends fifth digit Radial nerve Base of fifth metacarpal bone Extends and adducts wrist Radial nerve Postreior surface of ulna Extends forearm at elbow joint Radial nerve Radial nerve Posterior (deep) group Lateral epicondyle of humerus Posterior surface of radius and ulna and interosseous membrane Lateral aspect of midradius Supinates forearm Radial nerve Base of first metacarpal bone Abducts thumb and wrist Radial nerve Extensor pollicis brevis Posterior midshaft of radius and interosseous membrane Base of proximal phalanx of thumb Extends thumb Radial nerve Extensor pollicis longus Posterior surface of ulna and interosseous membrane Posterior surface of ulna and interosseous membrane Base of distal phalanx of thumb Phalanges of index finger Extends thumb and abduct wrist Radial nerve Extends index and wrist Radial nerve Action Innervation Supinator Abductor pollicis longus Extensor indicis MUSCLES OF THE HAND Muscle Origin Insertion THE THENAR MUSCLES Abductor pollicis brevis Opponens pollicis Flexor pollicis brevis Superficial head Deep Head Adductor pollicis Oblique head Scaphoid Flexor retinaculum, Trapezium Flexor retinaculum, Trapezoid, capitate First phalanx of thumb First metacarpal bone Lateral side of base of first phalanx Abducts phalanx Median nerve Opposes thumb Median nerve Flex thumb Median nerve Ulnar nerve Capitate and II and III metacarpals III metacarpal First phalanx of thumb Adduct thumb Ulnar nerve Corrugates palmar skin Ulnar nerve Base of fifth proximal phalanx Abduct the fifth digit Ulnar nerve Base of fifth proximal phalanx Flexes fifth MP joint Ulnar nerve Opposition Ulnar nerve Transverse head THE HYPOTHENAR MUSCLES Palmaris brevis Palmar aponeurosis Skin over hypothenar region Abductor digiti minimi Pisiform bone, flexor retinaculum Flexor digiti minimi brevis Flexor retinaculum and hamate Opponens digiti minimi Flexor retinaculum and hamate Fifth metacarpal CENTRAL PALM SPACE MUSCLES Muscle Origin Insertion Lumbricals 1 and 2 Tendons of the flexor digitorum profundus Lateral side of dorsal expansion of second and third digits Action Innervation Flexing the metacarpophalangeal joints and extending the interphalangeal joints Median nerve Lumbricals 3 and 4 Dorsal interossei (4) Palmar interossei (3) Tendons of the flexor digitorum profundus Medial side of first metacarpal; both sides of second, third and fourth metacarpal and lateral side of fifth metacarpal Medial side of second and lateral side of fourth and fifth metacarpals Lateral side of dorsal expansion of fourth and fifth digits Proximal phalanx of second third and fourth digits Tubercle of proximal phalanx and dorsal aponeurosis: medially on second digit, laterally on fourth and fifth digits Flexing the metacarpophalangeal joints and extending the interphalangeal joints Ulnar nerve Abduct second, third and fourth digits from the midline of hand. Flex proximal and extend middle and distal phalanx Ulnar nerve Adduct the second, fourth and fifth digits to the midline of hand. Flex proximal and extend middle and distal phalanx Ulnar nerve BLOOD VESSELS OF THE UPPER LIMB ARTERIES OF UPPER LIMB The Axillary artery is the continuation of the subclavian artery beyond the outer border of the 1 rib. It arches downwards and laterally through the axilla and becomes the brachial artery at the lower border of teres major. As the artery passes through the axilla it is surrounded by the cords and branches of the brachial plexus. The axillary vein lies medial to this neurovascular bundle. Branches: the superior thoracic artery the thoracoacromial artery the lateral thoracic artery the subscapular artery the anterior and posterior circumflex humeral artery st The Brachial artery a continuation of the axillary artery, begins at the distal edge of the teres major muscle. It descends rather superficially along medial border of the arm. In the cubital fossa it lies deeply to the bicipital aponeurosis, superficially to the brachialis muscle, medially the biceps brachii tendon, and lateral to the median nerve. Brachial artery ends in cubital fossa by dividing into radial and ulnar artery. Branches : 1. The arteria profunda brachii (deep artery of arm) - accompanies the radial nerve in the radial groove and supplies the posterior muscles of the upper arm and elbow joint. It divides into middle collateral artery and radial collateral artery. 2. The superior ulnar collateral artery 3. The inferior ulnar collateral artery The Radial artery arises as a lateral branch of the brachial artery in the cubital fossa and descends laterally under cover of the brachioradialis muscle. It curves over the radial side of the carpal bones, runs through the anatomical snuff-box, enters the palm and divides into its terminal branches: the princeps pollicis artery and the deep palmar arch. The radial pulse may be palpated at the wrist between the tendons of the brachioradialis and the flexor carpi radialis muscle. Branches: The radial recurrent artery The palmar and dorsal carpal branch The superficial palmar branch The Ulnar artery is the larger medial branch of the brachial artery. It descends between the flexor digitorum superficialis and profundus muscles; it enters the hand anterior to the flexor retinaculum, lateral to the pisiform bone. The ulnar artery divides into terminal branches: the superficial palmar arch and the the deep plamar branch. Branches : The ulnar recurrent artery The common interosseous artery The palmar and dorsal carpal branch VEINS OF UPPER LIMB Superficial veins Cephalic and Basilic veins are two main superficial veins of the upper limb. The cephalic vein originates from the lateral side of the dorsal venous network. It ascends on the radial side of the forearm, crosses anterior to the cubital fossa and lies lateral to biceps in the upper arm. It turns medially in the deltoido-pectoral groove, pierces the clavipectoral fascia and joins the axillary vein. The basilic vein originates from the medial side of the dorsal venous network. It ascends on the ulnar side of the forearm, crosses anterior to the cubital fossa and lies medial to biceps. In the middle of the upper arm it pierces the deep fascia to join the brachial veins. The median cubital vein is communication between the basilic and cephalic veins in the cubital fossa; it lies anterior to the bicipital aponeurosis. Considerable variation occurs in the connection of the basilic and cephalic veins in the cubital fossa. The median vein of the forearm drains the superficial palmar venous network. It ascedens anterior in the forearm to join the basilic or median cubital vein; it may divide distal to the elbow to join both. Deep veins Deep veins (venae comitantes) accompany arteries, usually in pairs. The radial and ulnar veins join to form the brachial veins, which continue as the axillary vein at the lower border of teres major. NERVES OF THE UPPER LIMB BRACHIAL PLEXUS This plexus supplies the upper limb. It is formed from ventral rami of the lower four cervical and the first thoracic nerves (C5-C8 and T1). These ventral rami are the five roots of the plexus and emerge between the anterior and middle scalene muscles in the neck. The unite to form three trunks: the upper trunk is formed by joining the upper two roots ( C5 & C6) the middle trunk is continuation of root C7 the lower trunk forms the lower two roots (C8 & T1) Each trunk divides into anterior and posterior division: the lateral cord form the anterior divisions of the upper and middle trunk the medial cord is continuation of the anterior division of the lower trunk the posterior cord form the three posterior divisions The three cords pass into the axilla; they are named according to their arrangement around the axillary artery. The posterior cords ends by dividing into: axillary nerve radial nerve The lateral cords ends by dividing into: musculocutaneous nerve lateral head of the median nerve The medial cords ends by dividing into: ulnar nerve medial head of the median nerve medial brachial cutaneous nerve medial antebrachial cutaneous nerve Branches of the brachial plexus : From roots : dorsal scapular nerve, long thoracic nerve From trunks : subclavius nerve, suprascapular nerve From cord : lateral pectoral nerve (lateral cord), medial pectoral nerve (medial cord), subscapular nerves (posterior cord), thoracodorsal nerve (posterior cord) THE MUSCULOCUTANEOUS NERVE This is a terminal branch of the lateral cord of the brachial plexus and descends deeply placed in the upper arm, to end anterior to the elbow joint, as the lateral antebrachial cutaneous nerve. In the axilla it lies lateral to the axillary artery and pierces coracobrachialis muscle. The musculocutaneous nerve innervates all the muscles in the anterior compartment of the arm. The lateral antebrachial cutaneous nerve supplies the radial side of the forearm. THE MEDIAN NERVE The median nerve arises by the union of its medial and lateral heads, these being terminal branches of the corresponding cords of the brachial plexus. It descends through the anterior compartment of the upper arm and reaches the cubital fossa.The nerve first lies lateral to the axillary and brachial artery but halfway down the upper arm it passes in front of the latter and reaches its medial side. In the cubital fossa the nerve is medial to the brachial and ulnar arteries. In the forearm it passes between the flexor digitorum superficialis and the flexor digitorum profundus muscles. The median nerve enters the hand through the carpal tunnel, deep to the flexor retinaculum. The median nerve innervates: - all of the muscles of the forearm except the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus - in the hand: the abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and the 1 and 2 lumbrical muscles - the skin of the lateral 3 / digits on the palmar surface, and dorsal surface of the distal phalanges (nailbeds) of the same digits. st nd 1 2 THE ULNAR NERVE This is a terminal branch of the medial cord of the brachial plexus and descends on the medial side of upper arm, initially in the anterior compartment but pierces the medial intermuscular septum and continues in the posterior compartment. It passes behind the medial epicondyle and enters the forearm. From behind the medial epicondyle the nerve descends deep to the flexor carpi ulnaris on the medial side of the forearm. It enters the hand lateral to the pisiform bone, passes anterior to the flexor retinaculum. The ulnar artery lies on its lateral side in the lower forearm and hand. The ulnar nerve innervates: - the flexor carpi ulnaris and the ulnar half of flexor digitorum profundus - in the hand: the hypothenar muscles, all the interossei, 3 and 4 lumbrical muscles and adductor pollicis - the skin of the medial 1 / digits on the palmar and dorsal surface of the hand rd 1 th 2 THE RADIAL NERVE The radial nerve arises as a terminal branch of the posterior cord of the brachial plexus behind the axillary artery. It leaves the axilla and takes an oblique course through the posterior compartment of the arm. It runs with the profunda brachii artery in the radial groove of the humerus. It pierces the lateral intermuscular septum, passes anterior to the elbow and enters the forearm. It divides into the superficial and deep branches before entering the forearm. The radial nerve innervates: - all the muscle of the posterior compartment of the arm and forearm - skin of posterior aspect of upper arm (the posterior cutaneous nerve of the arm) and the skin of the posterior aspect of the forearm (the posterior cutaneous nerve of the forearm) - in the hand the skin of the lateral 2 / digits on the dorsal surface, as far as the distal interphalangeal joints 1 2 THE AXILLARY NERVE It arises from the posterior cord of the brachial plexus; passes posteriorly through the quadrangular space accompanied by the posterior circumflex humeral artery. The axillary nerv winds around the surgical neck of the humerus. It gives rise to the lateral brachial cutaneous nerve. The axillary nerve innervates: - the teres minor and the deltoid muscles - skin over the deltoid muscle REGIONAL ANATOMY OF THE UPPER LIMB THE AXILLA This is a fat filled space between the lateral thoracic wall and the upper limb. Its shape is pyramidal with apex, base and 4 wall. Walls Anterior wall contains 3 muscles in two layer: superficially: pectoralis major, deep: pectoralis minor and subclavius Posterior wall is composed of 3 muscles: subscapularis, teres major and latissimus dorsi Medial wall comprise the upper 5 ribs and intercostal spaces, these structures being covered by serratus anterior Lateral wall the narrow intertubercular groove on the humerus Contents - axillary artery and vein - brachial plexus - axillary lymph nodes and lymph vessels, and fat CUBITAL FOSSA This triangular fossa is situated in front of the elbow joint. Lateral border - brachioradialis Medial border - pronator teres Base - a line between humeral epicondyles Floor - brachialis Content (from medial to lateral side): - The median nerve - The brachial artery and its terminal branches (the radial and ulnar arteries) - The tendon of the biceps brachii muscle CARPAL TUNNEL The carpal tunnel is a space, through which pass most of the structures of the flexor aspect of the forearm. The tunnel is formed as a result of the concavity of the carpal bones: the pisiform and the hamate on the ulnar side, with the scaphoid and crest of the trapezium on the radial side. The tunnel is roofed in by a thick flexor retinaculum. Crowded together in the tunnel are nine tendons: 4 flexor digitorum superficialis and 4 flexor digitorum profundus, and the flexor pollicis longus. Crunched in with these tendons, and lying most superficially, is the median nerve.
