What are the upper extremities?

Structure and Functions

The upper extremities consist of the upper arms, forearms, and hands. Each extremity is attached to the shoulder blade (or scapula) at the shoulder joint. The upper extremity is made mostly of bones and muscles, but it also contains blood vessels, lymphatics, nerves, skin, fingernails, and other associated structures. Important directional terms associated with the upper extremity include proximal (closer to the base or attached end), distal (farther from the base or attached end), radial (on the same side as the radius and the thumb), and ulnar (on the same side as the ulna and the little finger). Along the forearm and hand, the surface bearing the palm is called palmar; the opposite surface is called dorsal.

The bones and muscles of the shoulder provide support structures for the upper extremity. Beyond the shoulder, the major parts of the upper extremity include the upper arm (or brachium), from the shoulder joint to the elbow; the forearm, from the elbow to the wrist; the carpus, or wrist; and the manus, or hand. Beginning with the thumb, the five fingers of the hand are numbered one through five. Digit two is also called the index finger, digit three the middle finger, digit four the ring finger, and digit five the little finger.

Like other parts of the body, the upper extremity is clothed in skin, or integument. The skin covering the armpit (or axilla) has more hair and also more glands (especially the apocrine sweat glands) than most other parts of the body. The palm of the hand is unusual, along with the sole of the foot, in being completely hairless and in having a very thick outermost layer, called the stratum corneum. The ridges on the palm and fingers form individually characteristic patterns called dermatoglyphics, both fingerprints and palm prints. Each finger also has on its dorsal surface a fingernail; the thin crescent of semitransparent skin covering the base of the fingernail is called the eponychium.

The bones of the upper extremity include the scapula, clavicle, humerus, radius, ulna, carpals, metacarpals, and phalanges. The scapula, or shoulder blade, develops as part of the
skeleton of the upper extremity and remains more strongly attached to the upper arm than to the trunk of the body. The outer (superficial) surface of the scapula is marked by a ridge called the spine, perpendicular to the scapular blade; the outer tip of this blade is called the acromion. The sculpted area above the spine is called the supraspinous fossa; the larger sculpted area below the spine is called the infraspinous fossa. The flat undersurface of the scapula is the subscapular fossa. The superior border of the scapula is marked by a hooklike coracoid process. At the shoulder joint itself, the scapula has a nearly spherical glenoid cavity into which the head of the humerus
fits. The clavicle, or collarbone, runs from the upper end of the sternum (the manubrium) to the edge of the glenoid cavity of the scapula. It strengthens the shoulder region and provides additional support to the upper extremity.

The humerus runs from the shoulder joint to the elbow. At the shoulder joint, it attaches to the scapula by means of a rounded head that fits into the glenoid cavity of the scapula. The head is flanked by two protruding structures, the greater and lesser tuberosities, to which various muscles attach. At the elbow joint, the humerus attaches to the ulna by means of a pulleylike structure called the trochlea. The humerus also attaches to the radius by a smaller, rounded structure called the capitulum. Areas for muscle attachment on the lower end of the humerus include the lateral epicondyle (on the outer side) and the medial epicondyle (on the inner side).

The forearm contains two bones, the radius and ulna. The ulna is the larger of the two and forms the principal attachment with the humerus by means of a semilunar notch. Part of the ulna extends proximally beyond this semilunar notch to form a projection called the olecranon process (the hard structure on which one rests the elbows). The smaller of the two forearm bones is the radius, which articulates loosely with the humerus and more strongly with the wrist and hand.

The carpus, or wrist, includes two rows of small bones. The proximal row includes (in order from the radial side to the ulnar) the scaphoid, lunate, cuneiform (triquetrum), and pisiform bones. The distal row includes the trapezium, trapezoid, capitate, and hamate bones, also in order from radial to ulnar. The trapezium supports the thumb, the trapezoid supports the index finger, the capitate supports the middle finger, and the hamate supports the two remaining digits. An important ligament called the transverse carpal ligament (or flexor retinaculum) runs across the palmar side of the wrist, forming a tunnel through which the tendons of the flexor muscles run. A similar ligament, the dorsal carpal ligament (or dorsal retinaculum) crosses the back of the wrist, forming a similar tunnel through which the tendons of the extensor muscles run. Beyond the wrist, the palm of the hand is supported by five bones called metacarpals, numbered one through five. The thumb contains two finger bones, or phalanges; each of the remaining fingers contains three phalanges.

The muscles of the upper extremity are divided into extensors (which straighten joints) and flexors (which bend joints). The shoulder muscles attaching the upper extremity to the trunk of the body include the trapezius, pectoralis major, pectoralis minor, deltoideus, coracobrachialis, subscapularis, supraspinatus, infraspinatus, teres major, teres minor, and latissimus dorsi. Of these, the trapezius, deltoideus, and supraspinatus are extensors; the coracobrachialis, latissimus dorsi, and the two pectoralis muscles are flexors; and the remaining muscles are primarily responsible for rotational movements. The trapezius originates from the cervical and thoracic vertebrae, including the adjoining ligaments and the adjacent part of the skull; its fibers converge mostly onto the spine and acromion of the scapula, but some also insert onto the clavicle. The pectoralis major is triangular; it originates from the sternum, costal cartilages, and a portion of the clavicle, from which its fibers converge toward an insertion on the greater tuberosity of the humerus. The pectoralis minor originates from the third through fifth ribs and inserts onto the coracoid process of the scapula. The deltoideus is a triangular muscle that originates from the clavicle and from the spine and acromion of the scapula; its fibers converge to insert by means of a strong tendon onto the shaft of the humerus. The coracobrachialis runs from the coracoid process to an insertion along the shaft of the humerus. The subscapularis originates from the subscapular fossa and inserts onto the lesser tuberosity of the humerus. The supraspinatus originates along the supraspinous fossa and inserts onto the greater tuberosity of the humerus. The infraspinatus originates from the infraspinous fossa and inserts onto the greater tuberosity of the humerus. The teres major and teres minor originate from the lower (inferior) border of the scapula; the teres major inserts onto the lesser tubercle of the humerus, and the teres minor inserts onto the greater tubercle. The latissimus dorsi is a broad, flat muscle that originates from the lower half of the vertebral column (and part of the ilium) by way of a tough tendinous sheet (the lumbar aponeurosis); it inserts high on the humerus.

The major flexors of the upper arm include the biceps brachii and the brachialis. The biceps brachii originates in two heads, one from the coracoid process of the scapula and one from the capsule of the shoulder joint. Both heads insert by means of a strong tendon onto a raised tuberosity of the radius. The brachialis originates from the shaft of the humerus and inserts high on the ulna.

The major extensor of the upper arm is the three-part triceps brachii, but a smaller anconeus and an epitrochlearis are sometimes present as well. The long head of the triceps originates from the scapula just below the armpit; the other two heads originate along the shaft of the humerus. All three heads insert onto the olecranon process by means of a strong tendon. The anconeus (or subanconeus) is not always present; its fibers run directly from the shaft of the humerus to that of the ulna. The epitrochlearis (or dorsoepitrochlearis), also variably present, may be viewed as a connecting band of muscle tissue from the latissimus dorsi onto the triceps brachii.

Flexors of the forearm include the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, pronator teres, flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. Many of these muscles have long, thin tendons that run in the tunnel formed beneath the transverse carpal ligament. The first five of these muscles originate from the medial epicondyle of the humerus. The pronator teres runs at an angle and inserts onto the shaft of the radius. The flexor carpi radialis inserts by a long, thin tendon onto the base of the second metacarpal. The palmaris longus ends in a broad tendon that spreads out over the palm of the hand to form the palmar aponeurosis, a sheet that sends tendinous branches into the fingers. The flexor carpi ulnaris inserts by a tendon onto the pisiform bone; the tendon then continues onto the hamate bone. The flexor digitorum superficialis originates from parts of the radius and ulna as well as the humerus; its strong tendon passes beneath the transverse carpal ligament, then divides into four branches to each of digits two through five. Each of these branches splits and then reunites to allow a tendon of the flexor digitorum to penetrate. The flexor digitorum profundus originates mostly from the shaft of the
ulna; it gives rise to four strong tendons that run beneath the transverse carpal ligament, separate from one another over the palm of the hand, run into the second through fifth fingers, penetrate through the openings in the tendons of the flexor digitorum superficialis, and insert onto the base of the terminal phalanx of each finger except the thumb. The flexor pollicis longus arises from the radius alongside the previous muscle; its tendon runs beneath the transverse carpal ligament and inserts onto the base of the distal phalanx of the thumb. The pronator quadratus consists of a muscular sheet running between the distal portions of the radius and ulna.

The more superficial (shallower) extensors of the forearm include the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum communis, and extensor digiti minimi. The brachioradialis originates from a ridge on the shaft of the humerus and inserts onto the radius at its distal end. The extensor carpi radialis longus originates from the shaft of the humerus; its tendon passes beneath the dorsal carpal ligament to insert near the base of the second metacarpal. The next four muscles originate together from the lateral epicondyle of the humerus. The extensor carpi radialis brevis gives rise to a tendon that passes beneath the dorsal carpal ligament to insert onto the base of the third metacarpal. The extensor carpi ulnaris gives rise to a tendon that passes beneath the dorsal carpal ligament and inserts onto the base of the fifth metacarpal. The extensor digitorum communis gives rise to four tendons that pass beneath the dorsal carpal ligament, then diverge to run into each finger except the thumb, where they each insert onto the base of the second phalanx, the base of the terminal phalanx, and a tendinous sheath covering the first phalanx. The extensor digiti minimi gives rise to a tendon that runs beneath the dorsal carpal ligament and unites over the first phalanx of the fifth
finger with the tendon to that digit of the extensor digitorum communis.

The deeper extensors of the forearm include the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. The supinator originates mostly from the proximal end of the ulnar shaft, but some of this muscle also originates from the capsule of the elbow joint and from the lateral epicondyle of the humerus. Its fibers spiral toward the midline of the body and insert onto the shaft of the radius. The abductor pollicis longus originates beneath the supinator from the shaft of the radius; it inserts by means of a tendon onto the base of the first metacarpal. The extensor pollicis brevis originates from the shaft of the radius and inserts by means of a tendon onto the base of the first phalanx of the thumb. The extensor pollicis longus originates from the middle portion of the shaft of the ulna; it gives rise to a tendon which runs beneath the dorsal carpal ligament to insert onto the base of the distal phalanx of the thumb. The extensor indicis arises beside the preceding muscle from the shaft of the ulna; its tendon passes beneath the dorsal carpal ligament and eventually attaches to the tendon going to the index finger from the extensor digitorum communis.

The flexor muscles that are “intrinsic” to the hand—that is, those confined to the hand—include the flexor pollicis brevis, abductor pollicis brevis, adductor pollicis, opponens pollicis, palmaris brevis, flexor digiti minimi, abductor digiti minimi, opponens digiti minimi, the lumbricales, and the interossei. There are no intrinsic extensor muscles in the hand.

The upper extremity can move in various ways. At the shoulder joint, possible movements include extension (or protraction) of the shoulder, which raises the arms; flexion (or retraction) of the shoulder, which lowers the arms; adduction of the arms, bringing them closer together; and abduction of the arms, pulling them farther apart. The two movements possible at the elbow joint are extension (straightening) and flexion (bending). Two special movements are possible within the forearm: Pronation is an inward rotation of the radius upon the ulna in such a way that the palms face downward; supination is an outward rotation of the radius upon the ulna in such a way that the palms face upward. Various movements are possible at the wrist, including flexion (bending), extension (straightening), hyperextension (bending the hand upward), radial abduction (twisting the hand toward the thumb side), and ulnar abduction (twisting the hand toward the little finger side). Movements of the phalanges include flexion (bending), extension (straightening), abduction (spreading the fingers), and adduction (bringing the fingers back together).

Blood vessels of the upper extremity include both arteries and veins. The brachial artery is the major continuation of the subclavian and axillary arteries into the upper arm; as it approaches the elbow, it divides into the radial and ulnar arteries, which supply most of the forearm. Near the wrist, each of these last two arteries divides into a branch that runs closer to the palm and another that runs closer to the back of the hand. The two palmar branches then connect with each other to form a loop called the palmar digital arch; the other two branches also connect, forming a loop called the dorsal digital arch. From these two digital arches arises a secondary digital arch running into each finger, connecting in each case to the palmar arch at one end and to the dorsal arch at the other end. This type of arrangement, called collateral circulation, uses multiple alternate routes to permit blood flow even if one of the routes is temporarily blocked.

There are several important
veins draining the upper extremity. Several of these run just beneath the skin: the cephalic vein, running along the radial margin of the forearm and upper arm; the median antebrachial vein, draining the palmar surface of the hand and forearm; and the basilic vein, continuing the median antebrachial vein along the inner side of the upper arm. The deep veins of the arm all drain into the brachial vein. As it flows into the shoulder, the brachial vein joins with the basilic vein to form the axillary vein, which then becomes the subclavian vein when it reaches the rib cage.

The major nerves to the upper extremity arise from a series of complex branchings known as the brachial plexus, originating mostly from the fifth through eighth cervical nerves and the first thoracic nerve. The major nerves of the brachial plexus are a lateral cord (formed from branches of the fifth, sixth, and seventh cervical nerves), a medial cord (formed from branches of the last cervical and first thoracic nerves), and a posterior cord (formed from branches of the sixth, seventh, and eighth cervical nerves). The major nerves of the arm include a musculocutaneous nerve arising from the lateral cord, an axillary nerve and a radial nerve arising from the posterior cord, an ulnar nerve and a medial antebrachial cutaneous nerve arising from the medial cord, and a median nerve arising from both the lateral and the medial cords. The musculocutaneous, ulnar, and median nerves constitute the main nerve supply to the flexor muscles of the arm and hand, while the axillary nerve supplies the deltoid muscle and the radial nerve supplies the remaining extensor muscles. In addition, the radial nerve supplies sensory branches to the skin of the dorsal side of the forearm and hand (except for the fifth finger and part of the fourth), while the musculocutaneous and medial antebrachial cutaneous nerves supply sensory branches to the skin over the palmar or flexor side of the arm and forearm. The median nerve sends sensory branches to the skin over most of the palmar surface of the hand from the thumb up to the middle of the fourth finger, while the ulnar nerve sends sensory branches to the skin on both the palmar and dorsal sides of the fifth finger and the ulnar half of the fourth. At the elbow, the ulnar nerve passes around the olecranon process just under the skin, where it is easily subject to accidental pressure; the tingling that results from such pressure is the source of the term “funny bone.”

Disorders and Diseases

Many types of medical conditions and disorders can affect the upper extremities. For example, many types of contact dermatitis, from poison ivy to “dishpan hands,” are first noticed on the surface of the hands and forearms. Other medical problems of the upper extremity include animal bites, injuries, and an assortment of neuromuscular disorders.

Neuromuscular disorders involving the upper extremity include nerve paralyses, uncontrolled shaking (choreic) movements, muscular atrophies, and muscular dystrophies. Nerve paralyses may arise from traumatic injury, but the most common type of
paralysis is cerebral palsy. Cerebral palsy is actually a group of paralytic disorders that begin at birth or in early childhood. The extent of the paralysis may vary, often involving large groups of muscles while sparing others. In addition to the lack of muscular control of the limbs, other symptoms may include spasms, athetoid (slow, rhythmic, and wormlike) movements, or muscular rigidity. Some types of cerebral palsy may result from injuries received at birth or in early infancy.

Uncontrolled, purposeless, and irregular shaking movements of the extremities are called choreic movements. These disorders, which involve the upper extremities more often than the lower, include both Sydenham’s chorea and Huntington’s chorea. Sydenham’s chorea (true chorea) typically begins in children and young adults, with maximum disability occurring two to three weeks after symptoms begin. Choreic symptoms typically diminish and disappear in a few months, but they may recur at a later time. The movements can be controlled with drugs. Huntington’s chorea, also called Huntington’s disease, seldom begins before the age of forty. It typically begins with uncontrolled choreic movements of the hands. The disease progressively worsens and ultimately causes death about fifteen years after onset. The disease is caused by a single dominant gene.

Muscular atrophies are a variety of diseases in which muscle tissues become progressively weaker and smaller, usually beginning between forty and sixty years of age. Spastic movements may sometimes occur. The small muscles of the hands are usually affected sooner and more severely in comparison to the large muscles of the arms and shoulders. Amyotrophic lateral sclerosis (ALS), commonly called Lou Gehrig’s disease, is a progressive muscular atrophy that usually begins with weakness and deterioration of the hand muscles. The disease proceeds to affect the rest of the extremities, then other parts of the body; it is usually fatal within three to five years after onset. A more rare type of atrophy, myelopathic muscular atrophy (or Aran-Duchenne atrophy), also begins in the small hand muscles and slowly spreads to the arms, shoulders, and trunk muscles, in that order. A degenerative lesion of the gray matter in the cervical region of the spinal cord is usually responsible. Weakness and wasting of the
muscles of the hands and forearms also characterize syringomyelia, a disorder of the glial cells in the cervical region of the spinal cord. Impairment of the cutaneous senses often occurs with this disease and frequently results in burns and other injuries to the hand when the patient, unaware of a threat, fails to withdraw or take other countermeasures.

Muscular dystrophy is an inherited disease—actually several related diseases—that usually begins in early childhood and affects males more often than females. The most common type,
Duchenne muscular dystrophy, is believed to be caused by a sex-linked recessive trait. Spastic movements do not occur, and the disease affects the large muscles of the shoulder, arm, and thigh more than the small muscles of the hand. The affected muscles become very weak but remain approximately normal in size or increase as fatty and fibrous tissue replaces muscle. Progressive weakening makes walking impossible, but patients can live for decades with proper care.

Repetitive motion injuries of the upper extremity may occur at the elbow joint (tennis elbow) or in the vicinity of the wrist. Some repetitive wrist movements are capable of producing carpal tunnel syndrome, an injury of the tendons running through the tunnel beneath the transverse carpal ligament.

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