Bones of the Arm, Elbow, Shoulder

A normal human arm and elbow is made up of 3 bones on each side.  The shoulder pictured below shows the scapula and clavicle.  A human skeleton has 2 scapula and 2 clavicle.  The arms, shoulders and elbows comprise a total of 10 bones (roughly 4.9%) out of the total 206 bones in the human adult skeleton.  The bones of the arm, elbow and shoulder are made up of the ulna, radius, humerous, scapula and clavicle - one on each side of the body.

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Additional Information

Clavicle

General information
The clavicle acts as a strut to suspend the upper extremity from the chest wall. It is short, but quite thick and is not a straight bone. On its sternal end, the clavicle has a convex shape (bowing away from the body) while nearer the acromial end the clavicle becomes concave (bowing toward the body). The curved shape of the bone is an important feature in understanding the movements of the scapula and humerus. A direct blow or even a fall on the outstretched arm can fracture the clavicle.

Articulations
The clavicle attaches to the sternum at the sternoclavicular joint (SC joint). There is a small meniscus interposed between the head of the clavicle and the facet of the manubrium of the sternum. The head of the clavicle does not touch the first rib, but it is held down to that rib by strong costoclavicular ligaments. On the distal end of the clavicle, the acromioclavicular joint (AC joint) can be located. The distal end of the clavicle is secured to the coracoid process below by strong coracoclavicular ligaments.

Muscle attachments
Muscles attaching to the clavicle become very important when a patient fractures the clavicle. Activation of a muscle attaching on the clavicle could potentially disrupt healing of the fracture. Those muscles attaching on the clavicle include pectoralis major, upper part of trapezius, anterior portion of deltoid, sternocleidomastoid, and the small muscle underlying the clavicle, the subclavius.
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Coracoid Process

This finger like bony spur projects upwards from the upper aspect of the head and neck of the scapula, and then bends sharply forwards and laterally.

Attachments
It gives attachment to: coracobrachialis, pectoralis minor, the short head of biceps and the coracoclavicular ligaments.
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Scapula

General information
The scapula is a large flat bone that serves as an attachment point for the muscles of the trunk as well as those of the upper limb. It virtually 'floats' in its location on the posterior aspect of the rib cage, being suspended from the thorax by the clavicle. The scapula has a superior angle, an inferior angle, a vertebral border, an axillary border, and several prominences and projections including the acromion process, the coracoid process, and the scapular spine. Fossas, or shallow depressions, in the surface of the bone are found on the volar surface (the subscapular fossa) and on both sides of the scapular spine on the posterior aspect of the scapula (the supraspinous fossa and infraspinous fossa).

Articulations
The clavicle articulates with the scapula at the acromion process, forming the acromioclavicular joint. The volar surface of the scapula rests against the posterior aspect of the rib cage but does not form a true joint. The humerus articulates with the scapula at the glenoid fossa, the joint being the glenohumeral joint.

Muscle attachments
Muscles of the shoulder area, such as the rotator cuff muscles, abductors, adductors, and flexors attach to the scapula. Muscles of the chest wall (serratus anterior and pectoralis minor) and superficial back muscles (trapezius and latissimus dorsi), as well as intermediate layers of the back (rhomboids and levator scapulae) also attach to the scapula.

Muscles that attach to the scapula include trapezius, latissimus dorsi (occasionally), deltoid (middle and posterior parts), levator scapulae, rhomboideus major, rhomboideus minor, serratus anterior, triceps brachii (long head), teres minor, teres major, subscapularis, supraspinatus, infraspinatus, pectoralis minor, coracobrachialis, and biceps brachii.
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Radius

General information
The radius is the lateral bone of the forearm when the body is in anatomical position. During pronation of the forearm, the distal end of the radius moves medially, thus making the alignment of the two forearm bones somewhat confusing. The radius is always on the thumb side of the forearm regardless of position. The proximal end of the radius is a round shape, allowing the pronation/supination movement of the forearm. This rounded end of the bone is called the radial head. The distal end of the bone is quite broad in comparison to the proximal end and includes the most lateral projection of the distal radius, the styloid process. On the dorsum of the bone, at its distal end, one will find indentations or grooves created by the presence of tendons crossing the extensor aspect of the wrist.

Articulations
At its proximal end, the radius articulates with the radial notch of the ulna. At the distal end of the bone, the radius articulates with the scaphoid, the lunate and in part with the triangular fibrocartilage from the ulnar side of the radiocarpal joint.

Muscle attachments
Muscles attaching to the radius include biceps brachii, pronator teres, flexor digitorum superficialis, flexor pollicis longus, pronator quadratus, abductor pollicis longus, extensor pollicis brevis, brachioradialis, extensor carpi radialis longus, and supinator.
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Ulna

General information
The ulna is quite large proximally and quite small distally. It is the more medial bone of the forearm when the forearm is in the anatomical position. During pronation, the radius rotates around the ulna making the ulna (distal end) appear to lie lateral to the radius. The general arrangement will always place the ulna on the little finger side of the forearm regardless of position. The proximal end of the ulna finds a large articular surface for the humerus, this area of the ulna is the hollowed area called the trochlear notch. The trochlear notch is bordered posteriorly by the olecranon and anteriorly by the coronoid process. On the lateral side of the proximal end of the ulna one will locate the radial notch, an indentation for the radial head. Many ridges can be found along the shaft of the ulna, created by muscle and membrane attachments. At the distal end of the ulna is the ulnar head. A distal projection on the ulnar head is the ulnar styloid.

Articulations
The trochlea of the ulna articulates with the trochlea of the humerus. Slightly more distally, the radial head articulates with the ulna at the radial notch, and distally, the ulna articulates with the radius lying laterally. More distally, the ulnar head articulates with the triangular fibrocartilage. The ulna has no direct articulation with carpal bones of the wrist.

Muscle attachments
The proximal end of the ulna serves as a point of attachment for elbow extensors (triceps brachii and anconeus) and brachialis on the flexor surface. Pronators and supinators of the forearm also attach on the ulna with the exception of biceps brachii, which serves as a supinator of the forearm but attaches to the radius. Muscles of the flexor forearm that attach on the ulna include flexor carpi ulnaris, flexor digitorum superficialis, and flexor digitorum profundus. On the extensor surface, the ulna serves as a point of attachment for abductor pollicis longus, extensor indicis, extensor pollicis longus, and extensor carpi ulnaris.
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Lesser Tubercle

The lesser tubercle is a bony prominence on the anterior side of the upper end of the humerus. It merges with the shaft below, and is separated from the greater tubercle by the intertubercular groove and from the head by the anatomical neck.

Attachments
It gives attachment to the tendon of subscapularis.
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Greater Tubercle

The greater tubercle is a bony prominence on the lateral side of the upper end of the humerus. It merges with the shaft below, and is separated from the head medially by the anatomical neck and from the greater tubercle by the intertubercular groove.

Attachments
It gives attachment to: supraspinatus, infraspinatus and teres minor.
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Humerous

General information
The humerus is the longest bone of the upper limb. It serves to provide great mobility of the limb through its articulation at the shoulder joint. The humerus is vulnerable to injury due to its length and location, and may often fracture. One anatomical concern with such a fracture is the presence of the radial nerve on the bone. On the posterior side of the humerus there is a groove called the 'spiral groove'. This long groove is where the radial nerve lies on its path through the arm. A fracture in the mid-shaft of the humerus could disrupt the spiral groove and injure the radial nerve.

Articulations
At its proximal end, the head of the humerus articulates with the scapula at the glenoid fossa, thus forming the glenohumeral joint. At the distal end of the bone, the trochlea of the humerus articulates with the trochlear notch of the ulna, forming part of the elbow joint.

Muscle attachments
Muscles that attach at the proximal end of the bone include shoulder movers such as the deltoid, the rotator cuff muscles, latissimus dorsi, and pectoralis major to name a few. Coracobrachialis and brachialis attach along the shaft of the bone anteriorly, while the posterior side of the bone is occupied by the medial and lateral heads of triceps brachii. The distal end of the bone serves as an attachment point to the volar forearm muscles via the medial epicondyle, whereas the lateral epicondyle serves as an attachment point to the dorsal forearm muscles.

Muscles attaching to the humerus include the deltoids, pectoralis major, triceps brachii (lateral and medial heads), teres minor, teres major, subscapularis, supraspinatus, infraspinatus, coracobrachialis, anconeus, pronator teres (humeral head), flexor carpi radialis and palmaris longus (both via the common flexor tendon), flexor carpi ulnaris (humeral head), flexor digitorum superficialis, flexor pollicis longus, extensor digitorum (communis), extensor digiti minimi, extensor carpi ulnaris, brachioradialis, extensor carpi radialis brevis, and supinator.
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Lateral Epicondyle

Distally the humerus becomes an undulating condyle that has articular and non-articular parts.

The prominent lateral epicondyle is the non-articular part on the lateral side and is readily palpable.

Attachments
It gives attachment to the common extensor tendon.
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Capitulum

Distally the humerus becomes an undulating condyle with two continuous articular surfaces: the capitulum and the trochlea.

The convex capitulum lies laterally and covers the inferior and anterior surfaces of the humeral condyle. It articulates with the head of the radius.
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Trochlea

Distally the humerus becomes an undulating condyle with two continuous articular surfaces, the capitulum, and the trochlea.

The trochlea is situated medially on the humeral condyle, is pulley-shaped, and covers the anterior, inferior, and posterior surfaces of the humeral condyle. It articulates with the concave trochlear notch of the ulna.
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