Arm Bones | Bones of the Arm | Learn Bones In anatomy, the entire arm is divided into two regions, the upper portion above the elbow known as the upper arm and the lower portion below the elbow known as the forearm. Sometimes the the entire arm is referred to as the upper limb and the two portions are the arm and forearm. However, for our purposes we will use the terms upper arm and forearm. Below are detailed diagrams and information regarding the arm bones (upper arm bones and forearm bones). Learn the names of the arm bones and arm anatomy trough the arm bones diagram. List of all Arm Bones extensor primi internodii pollicis and the pronator teres muscles Furthermore, the radius is found on each arm thus contributing a total of two bones to the human body skeleton. Ulna The ulna is the third and final bone of the arm. This bone runs parallel to the radius from the elbow to the wrist. Like the other arm bones, the ulna is relatively long and slightly curved. The primary function of the ulna is allowing motion and supporting the arm. An ulna exists on each arm and thus contributes two bones to the total human body skeleton. The ulna is also the site of attachment for many muscles and ligaments.

Examples of muscles attaching to the ulna include the triceps brachii muscle Arm Bones Arm Bones Lassa Fever outbreak in Benin, West Africa - 11 Feb 2016 Arm Bones Arm bones (= bones in arm) are part of the appendicular skeleton which includes the hands, arms and shoulder girdle (clavicle and scapula ) and the feet, legs and pelvic girdle. For the whole skeleton see the human skeleton page. This diagram of an anterior view of the right arm bones includes the shoulder joint, all of the arm itself, and also the wrist and hand bones. (It is based on a photo of a model of a human skeleton, hence the metal visible at the joints.) The bones of the arm, wrist and hand labelled on the right include: the humerus (upper-arm bone and the following features on the humerus greater tubercle , head (of humerus) , lateral epicondyle , medial epicondyle ) the radius (lower-arm bone), Upper Arm: The upper-arm is the part of the arm from the shoulder to the elbow joint. The humerus bone is the largest and longest bone in the arm.

It consists of two extremities, the head of humerus at the top and a lower extremity on either side of which are the internal (medial) and external (lateral) condyles. The two extremities of the humerus bone are separated by the shaft of the humerus bone The elbow joint is formed by the articulations between three bones, the humerus, the ulna, and the radius and comprises three parts: humeroulnar joint (ulna & humerus) proximal radioulnar joint (radius & ulna) Lower Arm (= Forearm): The forearm is the part of the arm between the elbow and the wrist and comprises 2 long bones : The ulna is the larger and longer of these two bones. The upper extremity of the ulna forms part of the elbow joint. The narrowest part of the upper extremity of the ulna is the Olecranon Process . The lower extremity of the ulna is very thin and excluded from the wrist joint by fibro-cartilage tissue. The radius is located on the outer (= "lateral") side of the forearm.

The upper extremity of the radius forms only a small part of the elbow joint but its lower extremity forms the main part of the wrist joint. Wrist and Hand: Most of the bones in the upper-limbs (arms) are in the wrist and hands. The bones of the hand and wrist are sometimes studied separately from those of the main length of the arm (i.e. the humerus, ulna and radius). The hand bones may be studied in more detail due to their complexity, while study of the arm bones may include more about the muscles attached to different parts of the humerus, ulna and radius and the actions of those muscles. See also the elbow joint . Note: The information on this page used to be included on a page called "Skeletal Structures of the Feet and Hands" which consisted of simple labelled diagrams of both the leg and foot and arm and hand. That has moved to and been replaced in this section about the human skeletal system with more detailed pages (including this one about the arm bone names).

Bones of the Arm and Hand | Interactive Anatomy Guide Home > Skeletal System > Bones of the Arm and Hand Bones of the Arm and Hand The bones of the arm and hand have the important jobs of supporting the upper limb and providing attachment points for the muscles that move the upper limb. These bones form joints that provide a wide range of motion and flexibility needed to manipulate objects deftly with the arm and hand. They also provide strength to resist the extreme forces and stresses acting upon the arms and hands during sports, exercise, and heavy labor.... Move up/down/left/right: Click compass arrows Rotate image: Click and drag in any direction, anywhere in the frame Identify objects: Click on them in the image Full Bones of the Arm and Hand Description [Continued from above] . . . Consisting of the clavicle (collar bone) and scapula (shoulder blade), the pectoral girdle forms the attachment point between the arm and the chest. The clavicle, which gets its name from the Latin word for key, is a long bone that connects the scapula to the sternum (breast bone) of the chest.

It is located just under the skin in the thoracic region between the shoulder and the base of the neck. The clavicle is slightly curved like a letter S and is about five inches in length. Two joints are formed by the clavicle – the sternoclavicular joint with the sternum, and the acromioclavicular joint with the acromion of the scapula. The clavicle permits the shoulder joint to move in circles while remaining attached to the bones of the chest. Posterior to the clavicle is the scapula, a flat, triangular bone located lateral to the thoracic spine in the dorsal region of the body. The scapula forms two joints – the acromioclavicular (AC) joint with the clavicle and the shoulder (humeroscapular) joint with the humerus. The glenoid cavity is located on the lateral end of the scapula and forms the socket for the ball-and-socket shoulder joint. Many muscles attach to the scapula to move the shoulder, including the trapezius, deltoid, rhomboids, and the muscles of the rotator cuff. The humerus is the only bone of the upper arm.

It is a long, large bone that extends from the scapula of the shoulder to the ulna and radius of the lower arm. The proximal end of the humerus, known as the head, is a round structure that forms the ball of the ball-and-socket shoulder joint. On its distal end, the humerus forms a wide, cylindrical process that meets the ulna and radius to form the inner hinge of the elbow joint. The pectoral, deltoid, latissimus dorsi, and rotator cuff muscles attach to the humerus to rotate, raise, and lower the arm at the shoulder joint. Our forearm contains two long, parallel bones: the ulna and the radius. The ulna is the longer and larger of the two bones, residing on the medial (pinky finger) side of the forearm. It is widest at its proximal end and narrows considerably at its distal end. At its proximal end, the ulna forms the hinge of the elbow joint with the humerus. The end of the ulna, known as the olecranon, extends past the humerus and forms the bony tip of the elbow.

At its distal end, the ulna forms the wrist joint with the radius and the carpals. Compared to the ulna, the radius is slightly shorter, thinner, and located on the medial side of the forearm. The radius is narrowest at the elbow and widens as it extends towards the wrist. At its proximal end, the rounded head of the radius forms the pivoting part of the elbow joint that permits rotation of the lower arm and hand. At its distal end, the radius is much wider than the ulna and forms the bulk of the wrist joint with the ulna and carpals. The distal end of the radius also rotates around the ulna when the hand and forearm rotate. Despite being such a small region of the body, the hand contains twenty-seven tiny bones and many flexible joints. The carpals are a group of eight roughly cube-shaped bones in the proximal end of the hand. They form the wrist joint with the ulna and radius of the forearm and also form joints with the metacarpals of the palm of the hand. The carpals form many small gliding joints with each other to give extra flexibility to the wrist and hand.

The five long, cylindrical metacarpals form the supporting bones of the palm of the hand. Each metacarpal forms a joint with the carpals and another joint with the proximal phalanx of a finger. Metacarpals are able to abduct to spread the fingers and palm apart and can adduct to draw the fingers and palm together. The metacarpals also give flexibility to the hand when gripping an object or when touching the thumb and pinky finger together. The phalanges (singular: phalanx) are a group of fourteen bones that support and move the digits. Each digit contains three phalanges – proximal, middle, and distal – except for the thumb, which contains just a proximal phalanx and a distal phalanx. The phalanges are long bones that form hinge joints between themselves and also condyloid (oval) joints with the metacarpals. These joints permit the flexion, extension, adduction, and abduction of the digits. Our arms and hands require a balance of strength and dexterity to perform diverse tasks such as lifting heavy boxes, swimming, playing a musical instrument, and writing.

The joints of the arm and hand permit a wide range of motion while maintaining the strength of the upper limb. Many skeletal muscles attach to and pull on these bones to move them with strength, speed, and accuracy. Like all bones of the body, upper limb bones help the body to maintain homeostasis by storing minerals and fats and by producing blood cells in the red bone marrow.

Prepared by Tim Taylor, Anatomy and Physiology Instructor an "S" shaped bone located between the sternum and the scapula it articulates medially with the manubrium of the sternum and laterally with the acromion process of the scapula; it forms a strut that supports the upper limb; it is frequently fractured; it is the first bone to begin ossification during development sternal extremity the thickened proximal end of the clavicle it is triangular in cross-section; it articulates with the clavicular notch of the sternum through a synovial joint with two joint cavities separated by an articular disk; the sternoclavicular joint has the action of a ball and socket joint, but not the physical shape of one acromial extremity the flattened lateral end of the clavicle it is marked on its inferior surface at the junction of the medial 2/3 and the lateral 1/3 by a roughened area for attachment of the coracoclavicular ligament; it articulates with the coracoid process of the scapula through a syndesmosis; it articulates with the acromion process of the scapula through a synovial joint; due to

 the shape of the distal clavicle, the acromion process passes inferior to the clavicle in acromioclavicular dislocations the bone of the shoulder the scapula floats in a sea of muscles, so it is difficult to fracture; it articulates with only one bone - the clavicle at the coracoclavicular and acromioclavicular joints superior border the superior edge of the scapula the superior border of the scapula is marked by the scapular notch laterally medial border the border of the scapula that runs from the superior angle to the inferior angle it is an important site of muscle attachments for the intermediate layer of back muscles superior angle the angle of the scapula formed at the union of the superior and medial borders it is the attachment site for the levator scapulae m.

lateral border the portion of the scapula that runs inferomedially from the infraglenoid tubercle to the inferior angle it is an important site of muscle attachments for the teres major m., teres minor m. and the long head of the triceps brachii m.; it has a groove for passage of the circumflex scapular a. inferior angle the angle of the scapula formed by the union of the medial and lateral borders the inferior angle of the scapula often has a slip of origin of the latissimus dorsi attached to it glenoid cavity the articular surface located at the junction of the superior and lateral borders of the scapula it articulates with the head of the humerus; it is deepened by a fibrocartilaginous rim called the glenoid labrum supraglenoid tubercle a projection of bone located superior to the glenoid cavity it is the attachment site for the tendon of the long head of the biceps brachii m. infraglenoid tubercle a projection of bone located inferior to the glenoid cavity it is the attachment site of the tendon o of the long head of the triceps brachii m.

spine a heavy ridge that runs from the medial border of the scapula to the acromion process it supports the acromion process; it divides the posterior surface of the scapula into a supraspinatous fossa and an infraspinatous fossa scapular notch a notch on the superior border of the scapula located medial to the attachment of the coracoid process it is bridged by the superior transverse scapular ligament; the suprascapular a. passes superior to the superior transverse scapular ligament and the suprascapular n. passes inferior to it (Army goes over the bridge, Navy goes under the bridge) coracoid process a beak-like process that projects anteriorly from the lateral end of the superior border of the scapula it is the attachment site for the short head of the biceps brachii m., the coracobrachialis m., the pectoralis minor m.

and the coracoacromial and coracoclavicular ligaments acromion a broad, flat process located at the lateral end of the scapular spine it articulates with the clavicle through a synovial joint (acromioclavicular joint) supraspinatous fossa a broad depression located superior to the spine of the scapula it is the site of origin of the supraspinatus m. infraspinatous fossa a broad depression located inferior to the spine of the scapula it is the site of origin of the infraspinatus m.

humerus the bone of the arm (brachium) the humerus articulates proximally with the scapula at the glenoid fossa; it articulates distally with the radius and ulna at the elbow joint head the smooth, rounded proximal end of the ulna it articulates with the glenoid cavity of the scapula to form the shoulder joint anatomical neck the constricted region located inferolateral to the head it is located at the circumference of the smooth articular surface of the head surgical neck the proximal part of the shaft of the humerus it is located inferior to the greater and lesser tubercles; it is a site of frequent fracture; fractures of the surgical neck of the humerus endanger the axillary n. and the posterior circumflex humeral a. greater tubercle the large projection located lateral to the head of the humerus it is the attachment site of the supraspinatus, infraspinatus & teres minor mm. lesser tubercle the projection located lateral to the head of the humerus on the anterior surface it is the insertion site of the subscapularis m.

intertubercular groove the groove on the anterior surface of the humerus that is located between the crest of the greater tubercle and the crest of the lesser tubercle it is occupied by the tendon of the long head of the biceps brachii m.; the transverse humeral ligament spans the intertubercular groove and holds the biceps tendon in place; it is the attachment site for the tendon of the pectoralis major (lateral lip), teres major (medial lip), and latissimus dorsi (floor) crest of the greater tubercle the ridge of bone on the anterior surface of the humerus extending inferiorly from the greater tubercle it forms the lateral lip of the intertubercular groove; it is the attachment site for the transverse humeral ligament and the pectoralis major m. crest of the lesser tubercle the ridge of bone on the anterior surface of the humerus extending inferiorly from the lesser tubercle it forms the medial lip of the intertubercular groove; it is the attachment site for the transverse humeral ligament and the teres major m.

deltoid tuberosity the roughened process on the lateral surface of the mid-shaft of the humerus it is the insertion site of the deltoid m. radial groove the groove that spirals around the posterior surface of the shaft of the humerus it is a depression for the radial n. and the deep brachial vessels; fracture of the humerus at mid-shaft can injure the radial nerve and deep brachial vessels because they are in contact with bone at this location medial supracondylar ridge a narrow ridge running proximally from the medial epicondyle of the humerus the pronator teres m. takes origin from the common flexor tendon near the most inferior part of the medial supracondylar ridge lateral supracondylar ridge a narrow ridge running proximally from the lateral epicondyle of the humerus it is the site of origin of the brachioradialis m. and the extensor carpi radialis longus m.

lateral epicondyle a knob-like projection on the lateral side of the humerus proximal to the capitulum it is the site of attachment of the common extensor tendon which is the origin of several forearm extensor muscles (extensor carpi radialis brevis m., extensor digitorum m., extensor digiti minimi m., extensor carpi ulnaris m. and supinator m.); inflammation of the attachment of the common extensor tendon is called lateral epicondylitis which is also known as "tennis elbow" medial epicondyle a knob-like projection on the medial side of the humerus proximal to the trochlea it is the attachment site of the common flexor tendon which is the origin for the superficial group of forearm flexor muscles (pronator teres m., flexor carpi radialis m., palmaris longus m., flexor carpi ulnaris m.

and flexor digitorum superficialis m.); inflammation of the attachment of the common flexor tendon is called medial epicondylitis which is also known as "tennis elbow"; the ulnar nerve is in contact with bone as it courses posterior to the medial epicondyle where it is susceptible to injury from blunt trauma or fracture coronoid fossa the depression on the anterior surface of the humerus located proximal to the trochlea near the elbow it accommodates the coronoid process of ulna when the elbow is flexed radial fossa the depression on the anterior surface of the humerus located proximal to the capitulum near the elbow it accommodates the head of the radius when the elbow is flexed olecranon fossa the depression on the posterior surface of the humerus located just proximal to the elbow it accommodates the olecranon process of the ulna when the elbow is extended capitulum the rounded process that caps the distal end of the lateral condyle of the humerus it articulates with the head of the radius; capitulum means "little head" trochlea the grooved process that caps the distal end of the medial condyle of the humerus it articulates with the trochlear notch of the ulna

; the shape of the trochlea and the trochlear notch limits side-to-side movement and guarantees a hinge action; trochlea means "pulley" ulna the bone on the medial side of the forearm (antebrachium) the ulna articulates proximally with the trochlea of the humerus and the head of the radius; it articulates distally with the ulnar notch of the radius olecranon the proximal end of the ulna it is the insertion site of the tendon of the triceps brachii m.; when the elbow is extended, the olecranon of the ulna engages the olecranon fossa of the humerus trochlear notch the crescent shaped notch on the anterior surface of the proximal end of the ulna it is located between the olecranon and the coronoid process; it articulates with the trochlea of the humerus; a ridge within the trochlear notch fits into the groove in the trochlea of the ulna which limits side-to-side movement and guarantees a hinge action coronoid process the anterior projection of bone located distal to the trochlear notch it is the insertion site of the brachialis m.

radial notch the notch on the lateral surface of the humerus located just distal to the trochlear notch it accommodates the head of the radius; the annular ligament of the radius attaches to the anterior and posterior edges of the radial notch of the ulna to encircle the head of the radius body the long slender midportion of the ulna it is also called the shaft or diaphysis; the interosseous membrane attaches to the entire length of the interosseous border of the body of the ulna head the distal end of the ulna it is small and rounded for articulation with the radius styloid process a small projection from the distal surface of the head of the ulna it is the site of attachment of the articular disk of the distal radioulnar joint radius the bone on the lateral side of the forearm (antebrachium) the radius pivots on its long axis and crosses the ulna during pronation head the rounded proximal end of the radius it has a smooth, rounded surface for articulation with the ulna; the head of the radius is encircled by the annular ligament (4/5 of a circle) and the radial notch of the ulna (1/

5 of a circle) neck the constricted area of the radius located distal to the head the annular ligament of the radius surrounds the head of the radius, not the neck of the radius radial tuberosity a roughened area on the anteromedial surface of the radius located just distal to the neck it is the insertion site of the tendon of the biceps brachii m.

body the long, slender midportion of the radius it is also known as the shaft or diaphysis; the interosseous membrane attaches to the entire length of the body of the radius along its interosseous border; a fracture of the distal end of the body of the radius with a dorsal displacement of the distal fragment is quite common and is cal a Colles' fracture ulnar notch a shallow notch located on the medial surface of the distal end of the radius it articulates with the head of the ulna styloid process the distal-most projection from the lateral side of the radius the radial styloid process projects lateral to the proximal row of carpal bones carpal bones the bones of the wrist eight bones arranged in two rows; a pneumonic for memorizing the carpal bones is " some lovers try positions that they can't handle" - the first letters of these eight words are the first letters of the names of the eight carpal bones arranged from lateral to medial, proximal row first: scaphoid, lunate, triquitrum, pisiform/trapezium, trapezoid, capitate, hamate proximal row lateral to medial: scaphoid, lunate, triquetrum

, pisiform the scaphoid and lunate bones of the proximal row articulate with the distal end of the radius distal row lateral to medial: trapezium, trapezoid, capitate, hamate the distal row of carpal bones articulates with the metacarpal bones of the hand scaphoid the most lateral carpal bone of the proximal row the scaphoid bone is located in the floor of the anatomical snuff box; it is frequently fractured by hyperextension and abduction of the wrist; scaphoid means "boat-shaped" lunate the carpal bone located between the scaphoid and triquetrum in the proximal row the lunate is so named because it is "moon-shaped" (crescent shaped) in longitudinal section; the head of the capitate sits within the crescent of the lunate triquetrum the most medial bone in the proximal row of carpal bones it articulates with the pisiform which sits anterior to it pisiform a sesamoid bone in the tendon of the flexor carpi ulnaris m.

it articulates with the  um; the pisiform bone provides a protective function for the flexor carpi ulnaris tendon by bearing the forces generated by the tendon riding across the triquitrum, especially during wrist extension; pisiform means "pea-shaped" trapezium the most lateral carpal bone of the distal row it forms a saddle joint with the metacarpal bone of the thumb; "the thumb swings on the trapezium" trapezoid the carpal bone located between the trapezium and the capitate in the distal row the trapezoid is named for its trapezoid shape capitate the carpal bone located between the trapezoid and the hamate in the distal carpal row the capitate is the largest carpal bone; it is named for its rounded head; forces generated in the hand (as during a punching blow with the fist) are transmitted through the third metacarpal bone to the capitate and proximally through the lunate to the radius hamate the most medial carpal bone in the distal row the hamulus (hook) of the hamate is its distinguishing characteristic; it is an attachment point of the flexor

 retinaculum metacarpal bones the bones located between the carpal bones and the phalanges of the hand there are a total of five metacarpal bones in the hand; the metacarpals of the four fingers are bound together by ligaments to form a firm foundation for finger movements; the metacarpal of the thumb is more independent in its range of motion base the proximal end of the metacarpal it articulates with the distal row of carpal bones body the slender shaft of the metacarpal it is also known as the diaphysis head the rounded distal end of the metacarpal it articulates with the proximal phalanx of the corresponding digit phalanx (phalanges) the distal two or three bones in the digits of the hand there are a total of 14 phalanges in the hand; the thumb has two phalanges (proximal and distal) and each finger has three phalanges (proximal, middle and distal); phalanx means "line of soldiers" base the proximal end of the phalanx the base of the proximal phalanx articulates with the head of the corresponding metacarpal bone

; the base of the middle or distal phalanx articulates with the head of the next most proximal phalanx body Arm bones - Mayo Clinic Sign up now Arm bones Your arm is made up of three bones: the upper arm bone (humerus) and two forearm bones (the ulna and the radius).

The term "broken arm" may refer to a fracture in any of these bones. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. Advertising & Sponsorship About This Site Legal Conditions and Terms Any use of this site constitutes your agreement to the Terms and Conditions and Privacy Policy linked below. Notice of Nondiscrimination Reprint Permissions A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.org," "Mayo Clinic Healthy Living," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research. Chapter 6: The bones of the upper limb Chapter 6: The bones of the upper limb Clavicle The clavicle, or collar bone (figs. 6-1 , 6-2 , 6-3 and 6-4 ), connects the trunk to the upper limb by extending from the manubrium of the sternum to the acromion of the scapula.

It is technically a long bone with a shaft and two ends, it can be readily palpated, and it is one of the most commonly fractured bones in the body (usually at the junction of its medial two thirds and lateral one third). The medial end is rounded and is part of the sternoclavicular joint. The medial two thirds of the shaft is convex anteriorward and arches anterior to the brachial plexus and subclavian vessels. The costoclavicular ligament is attached to its inferior aspect, and a shallow groove lodges the subclavius muscle. The lateral third of the shaft is concave anteriorward and is flattened. The conoid and trapezoid parts of the coracoclavicular ligament are attached to the inferior aspect and resists upward displacement of the lateral part of the clavicle. The lateral end of the clavicle is part of the acromioclavicular joint. A vertical line through the midpoint of the clavicle is used in surface anatomy to define the midclavicular line. The clavicle is the first bone to begin ossification, which occurs in connective tissue ("membrane") during the seventh postovulatory week.

The clavicle may be defective or absent in cleidocranial dysostosis. An epiphysial center usually develops at the medial end only. Scapula The scapula, or shoulder blade (figs. 6-3 , 6-4 , 6-5 , 6-6 , 6-7 , 6-8 , 6-9 and 6-10 ), is a large, flat, triangular bone that connects the clavicle to the humerus. Its body rests on the superior part of the posterolateral thorax, and the bone includes both a spine that articulates with the acromion and a coracoid process. The scapula is highly mobile. In the anatomical position, the glenoid cavity is directed anteriorward as well as lateralward. Thus, abduction of the arm in the plane of the scapula moves the arm in an anterolateral direction. The body of the scapula is triangular and has a concave costal surface (subscapular fossa) applied to the thorax and a dorsal surface, which is divided by the spine of the bone.

The smaller superior part is the supraspinous fossa, and the inferior portion is the infraspinous fossa. The superior border of the scapula has the suprascapular notch. The medial border, usually convex, can be seen and felt. The inferior angle and the medial border usually ossify from separate epiphysial centers. The superior part of the lateral border ends in the infraglenoid tubercle. The superolateral part of the scapula is the location of the piriform glenoid cavity for articulation with the head of the humerus. The supraglenoid tubercle lies superior to the cavity. The spine of the scapula projects horizontally posteriorward from the body of the bone, and its crest can be felt subcutaneously. The trapezius and deltoid are attached to the crest. The lateral aspect of the spine is called the acromion, which articulates with the clavicle. The acromion is a subcutaneous process of the scapula, and it ossifies independently. Clinically the arm is measured from the angle of the acromion to the lateral epicondyle of the humerus.

The coracoid process projects anteriorward and can be felt indistinctly inferior to the junction of the lateral and intermediate thirds of the clavicle. It is usually ossified from two epiphysial centers. Humerus The humerus (figs. 6-3 , 6-4 , and 6-11 , 6-12 , 6-13 , 6-14 , 6-15 , 6-16 and 6-17 ) is the bone of the shoulder and arm. It articulates with the scapula at the shoulder and with the radius and ulna at the elbow. The proximal end consists of the head, anatomical neck, and greater and lesser tubercles separated from each other by an intertubercular groove. The head, almost hemispherical, faces medial, superior, and posterior. The anatomical neck is at the periphery of the head, The greater tubercle projects laterally, beyond the acromion. Unless the shoulder is dislocated, a ruler will not make contact simultaneously with the acromion and the lateral epicondyle.

The greater tubercle is covered by the deltoid muscle, which is responsible for the normal, rounded contour of the shoulder. The lesser tubercle projects anteriorward (see fig. 6-13 ). The intertubercular groove contains the tendon of the long head of the biceps. The surgical neck, a common site of fracture of the humerus, is the point at which the superior portion of the bone meets the shaft. The axillary nerve lies in contact with the surgical neck (see fig. 6-12 ). The shaft has anterolateral, anteromedial, and posterior surfaces and lateral, anterior, and medial borders. The deltoid muscle is inserted into a tuberosity on the anterolateral surface at about the middle of the shaft. The radial nerve runs inferiorward and lateral on the posterior surface in a shallow, oblique groove (see fig. 6-12 ). The distal end of the humerus includes the lateral and medial epicondyles and a condyle consisting of the capitulum and trochlea. The lateral epicondyle gives origin to the supinator and to the extensor muscles of the forearm. The capitulum articulates with the head of the radius.

The trochlea is a pulley-shaped projection that articulates with the trochlear notch of the ulna. It is set obliquely, so that a "carrying angle" exists between the arm and the extended and supinated forearm. Radial and coronoid fossae are situated anterior and superior to the capitulum and trochlea, respectively. A deeper olecranon fossa is located posteriorly, superior to the trochlea. The medial epicondyle gives origin to the flexor muscles of the forearm. The ulnar nerve lies in a groove posterior to the medial epicondyle and is palpable there ("funny bone"). The medial epicondyle gives an indication of the direction in which the head of the humerus is pointing in any given position of the arm. The distal end of the humerus is angulated anteriorward, and a decrease in the normal angulation suggests a supracondylar fracture. Because of their contact with the humerus, the axillary, radial, and ulnar nerves may be injured in fractures of the surgical neck, shaft, and medial epicondyle, respectively.

The shaft begins to ossify during the eighth postovulatory week, and a center is usually present in the head at birth. Centers for the greater and lesser tubercles appear postnatally, as do four centers for the distal end. Radius The radius (figs. 6-16 , 6-17 , 6-18 , 6-19 , 6-20 , 6-21 , 6-22 , 6-23 and 6-24 ) is shorter than and lateral to the ulna. The proximal end articulates with the humerus, the medial aspect with the ulna, and thedistal end with the carpus. The proximal end consists of a head, neck, and tuberosity. The superior, concave surface of the head articulates with the capitulum of the humerus. The circumference of the head articulates with the ulna medially but is elsewhere covered by the annular ligament (see fig. 9-6 ). The head of the radius can be felt immediately inferior to the lateral epicondyle (in the "valley" behind the brachioradialis), particularly during rotation.

The tuberosity of the radius is situated on the anteromedial aspect, immediately distal to the neck. The shaft has anterior, posterior, and lateral surfaces and anterior, posterior, and interosseous borders. The interosseous border is attached by the interosseous membrane to a corresponding border on the ulna (see fig. 6-23 ). The distal end of the radius terminates in the styloid process laterally. The process is palpable between the extensor tendons of the thumb. It gives attachment to the radial collateral ligament. The styloid process of the radius is about 1 cm distal to that of the ulna. This relationship is important in the diagnosis of fractures and in the verification of their correct reduction. On its medial side, the distal end of the radius has an ulnar notch, for articulation with the head of the ulna. At about the middle of the convex dorsal aspect of the distal end of the radius, a small prominence, the dorsal tubercle, may be felt (see fig. 6-22 ). The inferior surface of the distal end articulates with the lunate (medial) and the scaphoid (lateral).

A fall on the outstretched hand may result in a (Colles') fracture of the distal end of the radius, in which the distal fragment is displaced posteriorly and generally becomes impacted, bringing the styloid processes of the radius and ulna to approximately the same horizontal level. The shaft begins to ossify during the eighth postovulatory week, and centers appear postnatally for the lower end and the head (see fig. 6-20 ). Ulna The ulna (figs. 6-16 , 6-17 , 6-18 , 6-19 , 6-20 , 6-21 , 6-23 , 6-24 , 6-25 and 6-26 ) is longer than and medial to the radius. It articulates with the humerus proximally, the radius laterally, and the articular disc distally. The proxiaml end includes the olecranon and the coronoid process. The olecranon is the prominence of the posterior elbow, which rests on a table when a subject leans on his elbow.

The lateral epicondyle, the tip of the olecranon, and the medial epicondyle are in a straight line when the forearm is extended, but form an equilateral triangle when the forearm is flexed. The superior aspect of the olecranon receives the insertion of the triceps. The posterior aspect, covered by a bursa, is subcutaneous. The antierior part of the olecranon forms a part of the trochlear notch, which articulates with the trochlea of the humerus. The coronoid process, which completes the trochlear notch, projects anteriorward and engages the coronoid fossa of the humerus during flexion. It is prolonged inferiorward as a rough area termed the tuberosity of the ulna. The radial notch is on the lateral aspect of the coronoid process and articulates with the head of the radius. The shaft has anterior, posterior, and medial surfaces and anterior, posterior, and interosseous borders. The posterior border is completely subcutaneous and readily palpable. It separates the flexor from the extensor muscles of the forearm. The distal end includes the styloid process and the head.

The styloid process, small and conical, is situated on its posteromedial aspect and is readily palpable. The head of the ulna articulates with the ulnar notch of the radius. The inferior aspect of the head is separated from the carpus by the articular disc. The shaft begins to ossify during the eighth postovulatory week, and centers appear postnatally for the distal and proxiaml ends of the bone (see figs. 6-17 and 6-20 ). The relationships of joint capsules to epiphysial lines (see figs. 6-15 and 6-26 ) are important, because epiphysial discs tend to limit the extent of infection, but it is possible for infection to spread from the shaft to the joint when part of the diaphysis is intracapsular. Carpus The carpal bones, usually eight in number, are arranged in two rows of four (figs. 6-18 , 6-19 , 6-20 , 6-27 , 6-28 and 6-29 ).

Their names are scaphoid, lunate, triquetrum (or triquetral), pisiform, trapezium, trapezoid, capitate, and hamate. The pisiform lies anterior to the triquetrum, whereas each of the other carpals has several facets for articulation with adjacent bones. The posterior aspect of the intact carpus is convex and the anterior aspect is concave, where it is bridged by the flexor retinaculum to form the carpal canal or tunnel for the flexor tendons and the median nerve. Hence, the posterior surfaces of the carpals are generally larger than the anterior, with the exception of the lunate, where the converse holds. The flexor retinaculum extends between the scaphoid and trapezium laterally and the triquetrum and hamate medially (see fig. 11-2 ). These four bones can be distinguished by deep palpation. The scaphoid has a tubercle on its anterior side that can be felt under cover of and lateral to the tendon of the flexor carpi radialis.

A fall on the outstretched hand may result in fracture of the scaphoid, generally across its "waist." In some fractures the blood supply of the proximal fragment may be compromised, resulting in aseptic necrosis. The lunate is broader on the anterior than the posterior side. Anterior dislocation of the lunate is a fairly common injury of the wrist. In adduction of the hand, the lunate articulates with the radius only, whereas in the neutral position or in abduction, it articulates with the articular disc also (see fig. 6-19 ). The pisiform, the smallest of the carpals and the last to ossify, lies anterior to the triquetrum and can be moved passively from side to side when the flexor carpi ulnaris is relaxed. The trapezium supports the thumb by means of a saddle-shaped facet for the first metacarpal. Like the adjacent scaphoid, it has an anterior tubercle. The trapezoid is associated with the index finger. The capitate, the largest of the carpals and the first to ossify, is placed centrally and is in line with the third metacarpal.

It has a prominent head on its superior side. The hamate sends a marked hook anteriorly, which gives attachment to the flexor retinaculum. Accessory ossicles are sometimes found between the usual carpal bones, and their possible occurrence should be kept in mind in interpreting radiograms. Carpal fusions (e.g., between the lunate and triquetrum) may also occur. Each carpal bone usually ossifies from one center postnatally. Those for the capitate and hamate develop first and may appear before birth. Radiography of the carpus is frequently used for the assessment of skeletal maturation: the carpus under consideration being compared to a series of standards. Metacarpus The carpus is connected to the phalanges by five metacarpal bones, referred to collectively as the metacarpus. They are numbered from 1 to 5, from the thumb to the little finger. The first is the shortest and the second the longest. They contribute to the palm, and their posterior aspects can be felt under cover of the extensor tendons. Each metacarpal is technically a long bone, consisting of a base proximally, a shaft, and a head distally.

The base articulates with the carpus and, except for that of the first, with the adjacent metacarpal(s) also. The base of the first metacarpal has a saddle-shaped facet for the trapezium. The head of each metacarpal articulates with a proximal phalanx and forms a knuckle of the fist. The shaft of each metacarpal begins to ossify during fetal life, and centers appear postnatally in the heads of the four medial bones and in the base of the first metacarpal. Accessory centers termed "pseudoepiphyses" are sometimes seen in the head of the first and in the base of the second metacarpal. Phalanges The thumb has two phalanges, whereas each of the other fingers has three. They are designated proximal, middle, and distal. Each phalanx is technically a long bone, consisting of a base proximally, a shaft, and a head distally. The base of a proximal phalanx articulates with the head of a metacarpal, and the head of the phalanx presents two condyles for the base of a middle phalanx.

Similarly, the head of a middle phalanx presents two condyles for the base of a distal phalanx. Each distal phalanx ends in a rough expansion termed its tuberosity. Each phalanx begins to ossify during fetal life, and centers appear postnatally in their bases. Sesamoid bones are found related to the anterior aspects of some of the metacarpophalangeal and interphalangeal joints. Two located anterior to the head of the first metacarpal are almost constant. Additional reading Frazer's Anatomy of the Human Skeleton, 6th ed., rev. by A. S. Breathnach, Churchill, London, 1965. A detailed, regional synthesis of skeletal and muscular anatomy. Pyle, S. I., Waterhouse, A. M., and Greulich, W. W., (eds.), A Radiographic Standard of Reference for the Growing Hand and Wrist, Year Book Medical Publishers, Chicago, 1971. Questions 6-1 Which is the first bone to ossify? 6-1 The clavicle is the first bone to ossify, specifically during the seventh embryonic week.

It is followed closely by the mandible and maxilla. 6-2 Where is the clavicle most likely to fracture from indirect violence to the hand or shoulder? 6-2 The clavicle is likely to fracture at the junction of its medial two thirds and lateral one third, i.e., where its two curves meet. 6-3 What is the most lateral bony point of the shoulder? 6-3 The greater tubercle of the humerus is the most lateral bony point of the shoulder. 6-4 Which nerves are particularly prone to injury in fractures of the humerus? 6-4 Depending on the level, the axillary, radial, and ulnar nerves, all of which make direct contact with the humerus, are liable to injury in fractures. 6-5 What is the relationship of the epicondyles of the humerus to the tip of the olecranon? 6-5 As seen from posterior, the epicondyles and the olecranon are in a straight line when the forearm is extended, but they form an equilateral triangle when the forearm is flexed. 6-6 Why is it important to know that the styloid process of the radius ends more distally than that of the ulna?

6-6 To diagnose fractures and verify their correct reduction, it is important to appreciate that the styloid process of the radius ends more distally than that of the ulna. 6-7 What is the most famous fracture of the radius? 6-7 Fracture of the distal end of the radius was described by Abraham Colles in 1814. It is caused by a fall on the palm of the outstretched hand. The distal end of the radius is displaced dorsally ("dinner-fork deformity") and driven into the shaft so that the styloid processes of the radius and ulna are approximately at the same level. 6-8 Which carpal bone is most frequently fractured? 6-8 The scaphoid bone may be fractured across its "waist" following a fall on the outstretched hand. Tenderness is marked over the scaphoid in the anatomical snuff-box. 6-9 Which carpal bone is most frequently dislocated? 6-9 The lunate may be dislocated anteriorly. 6-10 Do any carpals show ossification at birth? >6-10 Ossification is sometimes found in the carpus at birth.

Usually the capitate and hamate do not begin to ossify until during the first postnatal year. Figure legends Figure 6-1 The right clavicle, viewed from the anterior, superior and inferior aspects. Figure 6-2 Muscular, ligamentous, and fascial attachments to the right clavicle. Figure 6-3 The shoulder of an adult. Note the acromioclavicular joint, glenoid cavity, coracoid process, and inferior angle of the scapula. Figure 6-4 The shoulder during abduction in a coronal plane. A, Resting position. B, Elevation of the arm to a right angle. C, Elevation of the limb above the head. Figure 6-5 The right scapula, costal aspect, anatomical position. Figure 6-6 The right scapula, muscular and ligamentous attachments, costal aspect. Figure 6-7 The right scapula, dorsal aspect, anatomical position. Figure 6-8 The right scapula, muscular and ligamentous attachments, dorsal aspect. The extension of the subscapularis origin to the dorsal aspect is inconstant.

Figure 6-9 The right scapula from lateral and medial aspects. The inset illustrates that the superior and inferior parts of the body form an angle, at the level of the spine, that contributes to the depth of the subscapular fossa. Figure 6-10 The right scapula, muscular and ligamentous attachments, lateral aspect. The origin of the tendon of the long head of the biceps from the supraglenoid tubercle and the glenoid lip is not shown. Figure 6-11 The right humerus. In the lowermost cross section, capital letters indicate surfaces and small letters indicate borders. Figure 6-12 Anterior and posterior views of the right humerus, showing muscular and ligamentous attachments. Note that the insertion of the deltoid muscle is fused with the pectoralis major (anterior) and with the lateral head of the triceps (posterior). The portion of the humerus related to the axillary nerve is the surgical neck and is liable to fracture.

Figure 6-13 The right humerus from above, showing the lesser tubercle (anterior), the greater tubercle (lateral), and the intertubercular groove between. The upper arrow indicates the direction in which the medial epicondyle points. The lower arrow indicates the long axis of the head. The angle between the arrows shows the amount of torsion. Figure 6-14 lateral view of the right humerus, showing muscular and ligamentous attachments. Figure 6-15 The proximal and distal ends of the right humerus, showing the usual position of the epiphysial lines and the usual line of attachment of the joint capsule. The epiphysial lines at both ends are partly extracapsular. (Modified from Mainland.) Figure 6-16 Elbows of adults. A, Anteroposterior view. Note the olecranon fossa, trochlea, and medial epicondyle of the humerus; the head and tuberosity of the radius; and the olecranon and coronoid process of the ulna. B, lateral view. Note the olecranon and coronoid process of the ulna.

(Courtesy of Sir Thomas lodge.) Figure 6-17 The elbow. A, The elbow of a child. Note the epiphysis for the capitulum and the lateral part of the trochlea of the humerus. The ulna is at left. B, The elbow of a child. Note the additional epiphyses for the medial epicondyle of the humerus and the head of the radius. C, The elbow of a child, oblique view, showing epiphyses for the capitulum, lateral part of the trochlea, and medial epicondyle. D, The epiphysis for the proximal end of the ulna. Note also the epiphysis for the head of the radius. E, A radiograph of the dried bones of a 5-year-old boy. Note the outline of the cartilage. F, The flexed elbow of an adult. Note the medial epicondyle (arrow on left) and the joint line between the olecranon and the trochlea (arrow on right). (A, B, and C, Courtesy of S. F. Thomas, M.D., Palo Alto Medical Clinic, Palo Alto, California. 0, Courtesy of G. L.

Sackett, M.D., Painesville, Ohio. F, Courtesy of V. C. Johnson, M.D., Detroit, Michigan.) Figure 6-18 Hands of adults. A, Postero-anterior view. Note the hook of the hamate and the sesamoid bones of the first, second, and fifth fingers. B, Oblique view. (A and B, Courtesy of S. F. Thomas, M.D., Palo Alto Medical Clinic, Palo Alto, California.) Figure 6-19 The hand in various positions. A, B, and C are postero-anterior views. (Note the relation to the radius of the joint line between the lunate and the triquetrum.) D, E, and F are lateral views. A, Adduction. B, Straight position. C, Abduction. D, Extension. E, Straight position. Note the lunate, capitate, scaphoid, and trapezium. F, Flexion. Figure 6-20 Various views of the hand. A and B, The forearm and hand in supination (A) and pronation (B). C, The hand of a child.

Note the epiphyses for the distal ends of the radius and ulna and for the base of the first metacarpal and an accessory epiphysis for the base of the second metacarpal. D, The hand of a child. The pisiform does not yet show. Note the epiphyses for the metacarpals and phalanges. E and F, The index finger in extension (E) and flexion (F). Note the shift in position (relative to the heads of the proximal and middle phalanges) of the bases of the middle and distal phalanges. (A, B, E, and F, Courtesy of S. F. Thomas, M.D., Palo Alto Medical Clinic, Palo Alto, California. C, Courtesy of J. Lofstrom, M.D., Detroit Memorial Hospital, Detroit, Michigan.) Figure 6-21 The right radius and ulna, anterior view. Cross-sections of the midportions of the shafts show the arrangement of surfaces and borders. Capital letters indicate surfaces, and small letters indicate borders. Figure 6-22 The right radius.

In the lateral view, note the shallow groove immediately to the right of the styloid process; this is occupied by the tendons of the abductor pollicis longus and extensor pollicis brevis. In the posterior view, note that the dorsal tubercle is grooved; the groove is occupied by the tendon of the extensor pollicis longus. The tendons of the extensor carpi radialis longus and brevis lie to the radial side of the tubercle; the tendons of the extensor indicis and extensor digitorum lie to the ulnar side. Figure 6-23 Muscular and ligamentous attachments to the right radius and ulna. About midway on the shaft of the radius is a rough area for the insertion of the pronator teres, inferior to which the shaft is covered by the tendons of the brachioradialis and the extensor carpi radialis longus and brevis. The interosseous membrane gives origin in part to the flexor pollicis longus and flexor digitorum profundus. Figure 6-24 The right radius and ulna, showing muscular and ligamentous attachments, posterior aspect.

Figure 6-25 The right ulna. Figure 6-26 The proximal and distal ends of the right radius and ulna, showing the usual position of the epiphysial lines and the usual line of attachment of the joint capsule. The epiphysial line of the head of the radius is intracapsular, that of the proximal end of the ulna partly or entirely extracapsular, and those of the distal end extracapsular. The additional views of the ulna (upper two figures) show a variation in the position of the epiphysial line. (Modified from Mainland.) Figure 6-27 Bones of the right hand, anterior and posterior aspects. The sesamoids shown are those commonly present. Figure 6-28 Bones of the right hand, showing muscular attachments, anterior view. The flexor pollicis brevis is not shown. Of the interossei, only the palmar (P) ones are shown. Figure 6-29 Bones of the right hand, showing muscular and tendinous attachments, posterior view. Each dorsal interosseous muscle (D) arises from the shafts of adjacent metacarpals. Jump to:

Question: What is the name of the longest bone in the upper arm?
Answer: HUMERUS