The bones of the upper limb

The bones of the upper limb

Upper Extremity
Humerus (2)
Radius (2)
Ulna (2)
Carpals (16)
Metacarpals (10)
Phalanges (28)

Clavicle

The clavicle, or collar bone , 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 , 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  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 . 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 .
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 .
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 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 . 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 .
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 . 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.

Ulna

The ulna 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 .
The relationships of joint capsules to epiphysial lines 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. 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 . 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. 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.