Last updated 30 March 2006

Bones of the Upper Limb

This contains the bones of the superior appendicular skeleton:

• The clavicle and scapula (pectoral girdle)
• Humerus (arm)
• Ulna and radius (forearm)
• Carpal bones (wrist)
• Metacarpals (hand)
• Phalanges (fingers)

Bones of the Pectoral Girdle

The Clavicle (p. 501)

• This bone extends laterally and almost horizontally across the root of the neck. It extends from the manubrium of the sternum to the acromion of the scapula.
• The clavicle (L. little key) connects the upper limb to the axial skeleton and the trunk.

• The triangular-shaped medial (sternal) end of the clavicle articulates with the sternum at the sternoclavicular joint.
• The medial two-thirds of the body (shaft) of the clavicle are convex anteriorly, whereas the lateral one-third is flattened and concave anteriorly.
• Its curvature increases its resilience. The broad lateral (acromial) end of the clavicle articulates with the acromion of the scapula at the acromioclavicular joint.

The clavicle has three functions:

• To act as a strut for holding the upper limb free from the trunk so it may have maximum freedom of action;
• To provide attachments for muscles;
• To transmit forces from the upper limb to the axial skeleton.

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The Scapula (p. 501)

• This flattened, triangular bone lies on the posterolateral aspect of the thorax, covering parts of the 2^nd to 7^th ribs.
• The scapula connects the clavicle to the humerus. It is highly mobile and has a head, neck, and body.

• The body is thin and translucent.
• The scapula has a concave costal or anterior surface (subscapular fossa) and a convex posterior surface from which the spine of the scapula projects.
• The smaller part, which is superior to the spine, is called the supraspinous fossa, and the larger part, which is inferior to the spine, is called the infraspinous fossa.

• The spine continues laterally into a flattened process called the acromion. It projects anteriorly and articulates with the clavicle.

• Superolaterally, the scapula has a shallow glenoid fossa for articulation with the head of the humerus. This part of the scapula, called the head, is connected to its blade-like body by a short neck.

• The coracoid process, like a bird's beak, arises from the superior border of the head and projects superoanteriorly.

• The scapular notch is in the superior border.

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The Bone of the Arm

The Humerus (p. 539)

• The humerus is the largest bone in the upper limb.
• Its smooth, ball-like head articulates with the glenoid fossa of the scapula.

• Close to the head are the greater and lesser tubercles for the insertion of the muscles that surround and move the shoulder joint.
• The lesser tubercle is separated from the greater tubercle by the intertubercular groove (sulcus), from which lies the tendon of the long head of biceps brachii muscle.

• The anatomical neck separates the head and tubercles.
• Distal to the anatomical neck is the surgical neck. This is where the bone narrows to become the shaft. The region is called the surgical neck because it is the most frequent fracture site of the proximal end of the humerus.

• The body, or shaft, of the humerus is easy to palpate, as are its medial and lateral epicondyles. Its superior half is cylindrical.
• Anterolaterally, there is a roughness know as the deltoid tuberosity for the insertion of the deltoid muscle.
• There is a shallow, oblique radial groove for the radial nerve that extends inferolaterally on the posterior aspect of the body.

• The distal end of the humerus is expanded from side to side. The trochlea (L. pulley) fits into the trochlear notch of the ulna, which swings on this pulley when the elbow is flexed.
• Just proximal to the trochlea are the coronoid fossa and the olecranon fossa, which accommodate corresponding parts of the ulna.
• Adjoining the lateral part of the trochlea is a rounded ball of bone called the capitulum (L. little head).
• A prominent process, the medial epicondyle, projects from the trochlea, and the lateral epicondyle projects from the capitulum. The epicondyles being subcutaneous are easily felt. The medial epicondyle is more prominent.
• From each epicondyle, a bony ridge runs proximally; these are know as the medial and lateral supracondylar ridges, respectively.

Fractures to the Humerus

• Fractures of the surgical neck are common in elderly persons and usually from falls on the elbows when the arm is abducted.
• The fracture line occurs superior to the insertion of the pectoralis major, teres major and latissimus dorsi muscles.
• Because nerves are in contact with the humerus, the axillary, radial, and ulnar nerves may be injured in fractures of the humerus.
• Traumatic separation of the proximal epiphysis of the humerus can occur in young persons because this epiphysis does not fuse with the body of the humerus until about 18 years of age in females and 20 years of age in males.
• Fracture-separation of the proximal epiphysis occurs in children because the articular capsule of the shoulder joint is stronger than the epiphyseal cartilaginous plate.

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Bones of the Forearm

The Radius (p. 555)

• This is the shorter of the two forearm bones.
• It was given its name because it resembles the spoke of a wheel (in Latin).
• The proximal end of the radius has a disc-shaped head, a smooth cylindrical neck, and an oval prominence or tuberosity, distal to the neck.

• The body (shaft) of the radius increases in size from its proximal to its distal end; it has a slight lateral convexity or bowing.
• The body is concave anteriorly in its proximal three-fourths and flattened in its distal one-fourth.
• The anterior oblique line of the radius runs obliquely across the body from the region of the radial tuberosity to the area of greatest bowing.
• The medial aspect of the body has a sharp interosseous border for attachment of the interosseous membrane. Its lateral border is rounded.

• The distal end of the radius has a medial ulnar notch into which the head of the ulna fits, forming the distal radioulnar joint.
• Laterally the distal end of the radius tapers abruptly into a prominent pyramidal styloid process.
• The inferior surface of the distal end of the radius is smooth and concave where it articulates with the wrist or carpal bones.
• Posteriorly there is a prominent dorsal tubercle on the distal end of the radius.

Fractures of the Radius

• A fall on the outstretched hand may result in a fracture of the distal end of the radius.
• Sometimes there is also a fracture of the styloid process of the ulna.
• In the common Colle's fracture, the distal fragment of the radius is displaced posterior. The result is the radial and ulna styloid processes being at approximately the same horizontal level which is an abnormal condition (dinner fork deformity).

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The Ulna (pp. 555, 558)

• The ulna (L. elbow) is the longer bone of the forearm.
• This prismatic bone looks somewhat like a pipe wrench, with the olecranon resembling the upper jaw, the coronoid process the lower jaw, and the trochlear notch the mouth.

• The olecranon and coronoid processes clasp the trochlea of the humerus; somewhat like a pipe wrench clasps a pipe.
• The proximal "wrench-like" end of the ulna is larger that the small, rounded distal end called the head.
• The lateral side of the coronoid process has a small, shallow radial notch for the disc-shaped head of the radius.
• Inferior to the radial notch is the triangular supinator fossa, which provides an attachment for the supinator muscle. This fossa is bounded posteriorly by a distinct supinator crest.
• The irregular anterior surface of the coronoid process is rough and ends distally in a tuberosity onto which the brachialis, the chief flexor muscle of the forearm, inserts.

• The body (shaft) of the ulna is thick proximally. Its prominent lateral edge, the interosseous border, is where the interosseous membrane attaches.
• The small, slender distal end of the ulna has a rounded head and a conical styloid process. The styloid process projects distally, about 1 cm proximal to the styloid process of the radius.
• The distal end of the ulna has a convex articular surface on its lateral side for articulation with the ulnar notch of the radius.

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Bones of the Wrist and Hand

The Carpus (pp. 560-1)

• The eight small bones of the wrist, called carpal bones are referred to collectively as the carpus (L. wrist).
• They are arranged in proximal and distal rows, each containing four bones.

• The proximal row of carpal bones (lateral to medial) consists of the scaphoid (navicular), lunate, triquetrum, and pisiform.

• The boat-shaped scaphoid is the largest bone of the proximal row and was given its name because of its resemblance to a rowboat (G. scaphe).
• The lunate is moon-shaped.
• The pea-shaped pisiform (L. pisum, pea) is included in the proximal row, even though it is a sesamoid bone in the tendon of flexor carpi ulnaris muscle. The pisiform bone is a clinically important landmark that is easily palpable.

• The distal row of carpal bones (lateral to medial) consists of the trapezium, trapezoid, capitate, and hamate.

• The hamate can be identified by its prominent process, the hook of the hamate, which projects anteriorly.
• The capitate has a rounded head (L. caput).

• The carpal bones articulate with each other at synovial intercarpal joints and are bound together with ligaments to form a compact mass.

• The carpus has an anterior concavity known as the carpal groove (sulcus). The groove is converted into an osseofibrous carpal tunnel (canal) by the flexor retinaculum), which is attached to the scaphoid and trapezium laterally and to the pisiform and the hook of the hamate bone medially.
• The carpal tunnel is filled with tendons and the median nerve.
• Compression of the median nerve in the carpal tunnel produces the carpal tunnel syndrome.

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The Metacarpus (pp. 561, 565)

• The five metacarpal bones are miniature long bones.
• They extend from the carpus (wrist) to the digits (thumb and fingers) and are numbered from the lateral side.
• The first metacarpal is much shorter than the others.

• Although covered with tendons, the metacarpals can easily be palpated throughout their whole length on the dorsum of the hand.
• The heads of the metacarpals are at their distal ends, where they articulate with the phalanges (bones of the digits).
• They form knuckles of the hand that become visible when the fist is clenched.
• On the dorsal surface of each head is a small tubercle on each side for attachment of collateral ligaments and joint capsules.

• The bodies (shafts) of the metacarpal are slightly concave on their medial and lateral sides, where the dorsal interosseous muscles attach.

• The bases of the metacarpals are arranged in a fan-shaped manner from the distal row of carpal bones.

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The Phalanges (p. 565)

• Each phalanx (bone of a digit) is a miniature long bone, which consists of a body (shaft), a larger proximal end or base, and a smaller distal end or head.

• The thumb (first digit) has two phalanges (proximal and distal) and each finger (second to fifth digits) has three phalanges (proximal, middle and distal). The phalanges in the first digit are shorter and broader than those in the other digits.
• The proximal phalanges are the longest and the distal ones are the shortest.

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