Chapter 6. The Upper Extremity: The Elbow, Forearm, Wrist, and Hand

At the conclusion of this chapter, the student should be able to:

• 1. Name, locate, and describe the structure and ligamentous reinforcements of the articulations of the elbow, forearm, wrist, and hand.
• 2. Name and demonstrate the movements possible in the joints of the elbow, forearm, wrist, and hand regardless of the starting position.
• 3. Name and locate the muscles and muscle groups of the elbow, forearm, wrist, and hand, and name their primary actions as agonists, stabilizers, neutralizers, or antagonists.
• 4. Analyze the fundamental movements of the forearm, hand, and fingers with respect to joint and muscle actions.
• 5. Describe the common athletic injuries of the forearm, elbow, wrist, and fingers.
• 6. Perform an anatomical analysis of the elbow, forearm, wrist, and hand in a motor skill.

In much the same way that the shoulder girdle’s cooperation with the shoulder joint contributes to the wide range of motion available to the hand, the cooperative movements of the elbow, radioulnar, and wrist joints contribute to the versatility and precision of its movements. Although the hand is intrinsically skillful, its usefulness is greatly impaired when anything interferes with the motions of the forearm or wrist. Injury to any one of the joints involved makes this painfully obvious to the sufferer.

Structure

The elbow is far more complex than the simple hinge joint that it appears to be. The two bones of the forearm attach to the humerus in totally different ways. The humeroulnar joint is indeed a true hinge joint, but the humeroradial joint is far from it. It has been classified as an arthrodial or gliding type of joint, but it is more accurately described as a restricted ball-and-socket joint. Inspection of the articulating surfaces as depicted in Figure 6.1 or of the skeleton itself will help make this clear. The distal end of the humerus presents a spool-like process (trochlea) on the medial side and a spherical knob (capitulum) on the lateral side. The ulna articulates with the humerus by means of a semicircular structure that is cupped around the back and underside of the trochlea. The inner surface of this is known as the semilunar notch. It terminates below and in front in the small coronoid process, and above and in back in the broad olecranon process.

The radius articulates with the humerus by means of a slightly concave, saucerlike disc, which is directly beneath the capitulum when the arm is hanging straight down. In spite of the joint’s ball-and-socket structure, the radius is unable to abduct or adduct because of the annular ligament that encircles the radial head and binds it to the radial notch of the ulna. Furthermore, because of this and other ligamentous connections with the ulna, the radius is unable to rotate independently (Figures 6.2 and 6.3). Hence, the only movements it is free to engage in at the elbow are flexion and extension. For this reason, one is justified in classifying the elbow joint as a hinge joint.

The two articulations of the elbow joint, as well as the proximal radioulnar articulation, are completely enveloped in a single, extensive capsule. This is lined by the synovial membrane, which extends into the proximal radioulnar articulation, covers the olecranon, coronoid, and radial fossae, and lines the annular ligament. The capsule is strengthened by five ligaments: the anterior, posterior, lateral collateral, lateral ulnar collateral (not pictured), and ulnar collateral. The last named is the strongest. It is a thick triangular band attached above by its apex to the medial epicondyle of the humerus and below by its base to the medial margins of the coronoid and olecranon processes of the ulna and the intervening ridge.

In the anatomical position, the forearm is abducted in relation to the humerus, an alignment caused by the angle of articulation of the humerus and ulna at the elbow joint. Normally this angle, called the carrying angle, is larger in women than in men. If the forearm were to hang straight down in women as it does in men, it would not clear the female pelvis. Not only is the female’s pelvis broader than the male’s, her shoulders also are narrower. This exaggerated carrying angle, referred to as cubitus valgus, disappears during elbow flexion or forearm pronation.

Movements

Flexion

From the anatomical position this is a forward-upward movement of the forearm in the sagittal plane (Figure 6.4a).

Extension

Return movement from flexion. A few individuals are able to hyperextend the elbow joint. This is probably because of a short olecranon process rather than loose ligaments (Figure 6.4a).

Structure of Proximal Radioulnar Joint

The disc-shaped head of the radius fits against the radial notch of the ulna and is encircled by the annular ligament (see Figures 6.1, 6.2, and 6.3). The notch and annular ligament between them form a complete ring within which the radial head rotates. Inasmuch as the superior surface of the radial head articulates with the capitulum of the humerus, rotation must occur here, too, although strictly speaking, this is not part of the radioulnar joint. The three joints in this region, the humeroulnar, humeroradial, and proximal radioulnar, all share a common capsule.

Structure of Distal Radioulnar Joint

At the distal end of the forearm the radius articulates with the head of the ulna by means of a small notch (see Figure 6.1). A triangular fibrocartilaginous disc lies between the head of the ulna and the proximal row of wrist bones (see Figure 6.12) and serves to reinforce the joint, as well as to separate it from the wrist. The joint is also strengthened by the volar radioulnar and dorsal radioulnar ligaments. Both the proximal and distal radioulnar joints are classified as pivot joints.

Movements

Pronation

This is a rotation of the forearm around its longitudinal axis in such a way that the palm turns medially. It corresponds to medial or inward rotation of the humerus.

Supination

This is a rotation of the forearm around its longitudinal axis in such a way that the palm turns laterally. It corresponds to lateral or outward rotation of the humerus. During pronation and supination, the distal end of the radius moves about the ulna, whereas the proximal end of the radius rotates or pivots about its long axis.

Note: When the elbow is in an extended position, pronation of the forearm tends to accompany inward rotation of the upper arm, and supination tends to accompany outward rotation. In the anatomical position of the arm, the humerus is rotated outward and the forearm is supinated. The full range of forearm pronation and supination is best seen when the elbow is maintained at a 90-degree angle (see Figure 6.4). When the upper arms are at the sides of the body and the forearms are extended forward in the horizontal position, the mid or neutral position relative to pronation and supination is with the thumbs up and the palms facing each other. An excellent way to study what happens to the two forearm bones in these movements is suggested in Laboratory Experience 4.

Location

The muscles of the elbow and radioulnar joints are listed here according to their positions relative to the joints involved:

Anterior (Elbow Region)

• Biceps brachii
• Brachialis
• Brachioradialis
• Pronator teres

Anterior (Wrist Region)

• Pronator quadratus

Posterior

• Triceps brachii
• Anconeus
• Supinator

Characteristics and Functions of Individual Muscles

Biceps Brachii

This is primarily a muscle of the elbow and radioulnar joints (Figure 6.5), but, as noted in the last chapter, it also acts at the shoulder joint. Unless prevented from doing so (by the action of neutralizers or by fixation of the hand when the subject is hanging from a bar), it simultaneously flexes and supinates the forearm. Studies by Basmajian and others (Basmajian and DeLuca 1985) have shown that the biceps is active during flexion of the supine forearm under all conditions of static and dynamic contraction. In most instances in which the forearm is pronated, however, the biceps shows little activity unless external resistance is applied (Figure 6.6). This is because its tendon wraps around the radius and therefore has a poor line of pull. External resistance is also necessary for the biceps to be active in supination of the extended arm. It may be palpated on the anterior surface of the upper arm when the forearm is flexed, especially in the supinated position.

Brachialis

The sole function of this muscle (Figure 6.7) is flexion of the elbow joint, and it is said to be the unexcelled flexor under all conditions (Basmajian and DeLuca 1985). Because it attaches on the proximal end of the ulna, its line of pull remains the same regardless of whether the forearm is pronated or supinated. It is partially covered by the biceps but can be palpated just lateral to this muscle if the contraction is sufficiently strong, and especially if the forearm is maintained in the pronated position as it is being flexed (see Figure 6.6b).

Brachioradialis

In addition to its role as a contributor to elbow flexion when the movement is resisted, it has been suggested that this muscle (Figure 6.8) may tend to “derotate” the forearm as it flexes. This has not been confirmed by electromyographic research. It has been found, however, that the brachioradialis neither supinates nor pronates the fully extended forearm unless the movement is strongly resisted. It has also been noted that this muscle is most active in quick movements. It is more active in a semipronated than a supinated forearm position (Basmajian and DeLuca 1985). It may be palpated on the anteroradial aspect of the upper half of the forearm.

Pronator Teres

This is primarily a pronator of the forearm (Figure 6.8), but it assists in elbow flexion against resistance. The angle of the elbow joint does not influence the pronation activity of this muscle (Basmajian and DeLuca 1985). It is difficult to palpate.

Pronator Quadratus

This muscle’s (Figure 6.9) sole action is pronation of the forearm. EMG experiments have shown that the electrical activity of the pronator quadratus is definitely greater than that of the pronator teres, irrespective of the speed of the movement or the degree of elbow flexion. It is too deep to palpate successfully.

Triceps Brachii

Virtually three muscles in one (Figures 6.10 and 6.11), the triceps covers the entire posterior surface of the upper arm. Its long head is the only one of the three to cross the shoulder joint. It is a powerful extensor of the elbow joint and has two factors in its favor: the number and size of its fibers (see Structural Classification of Muscles on the Basis of Fiber Arrangement), and a favorable angle of pull (see Angle of Attachment). In a comparison of the three heads, it was noted that the medial head appeared to be the principal extensor of the elbow joint, usually accompanied by the lateral head. All three heads participate when there is resistance (Basmajian and DeLuca 1985). The muscle is an easy one to see as well as to palpate.

Anconeus

This muscle, working with the triceps, extends the forearm (Figure 6.11). This muscle is moderately active during pronation and supination of the forearm, and therefore it is suggested that the anconeus acts as a stabilizer of the elbow joint (Basmajian and DeLuca 1985). The muscle may be palpated on the back of the elbow at the lateral margin of the olecranon process.

Supinator

Although assisted by others, this muscle (see Figures 6.7 and 6.10) is the primary one for supination under all conditions. Palpation with any degree of success is extremely difficult.

Flexion

There are three important flexors of the forearm: the brachialis, the brachioradialis, and the biceps—the three Bs. Their relative participation in and contribution to flexion of the forearm have been the subjects of much study. Because elbow flexion may be performed with the forearm pronated, semipronated, or supinated, with or without resistance, slowly or rapidly, with or against gravity, there have been many variables to study.

Investigators agree that the brachialis serves as a flexor under all conditions, and there is general agreement that the biceps is more active in flexion when the arm is supinated than when it is pronated.

It is now generally accepted that during maximal isometric contractions (1) the biceps is most active when the forearm is supinated and least active when it is pronated; (2) the brachioradialis is most active when the forearm is either in the midposition or in supination and least active when the forearm is in extreme pronation or supination; (3) the pronator teres, as a moderate flexor, is most active in a position of pronation; and (4) the isometric force exerted by the elbow flexors during maximal voluntary contractions is greatest when the forearm is supinated or in midposition and least when the forearm is pronated.

Extension

When not produced by the force of gravity, the forearm is extended at the elbow joint by the triceps and anconeus.

Pronation

Movement of the forearm at the two radioulnar joints. Produced by the combined action of the pronator teres and pronator quadratus.

Supination

Movement of the forearm at the two radioulnar joints. Produced by the supinator and biceps brachii. The two heads of the biceps are not equally active in all supination motions. Functional capacity in each of the heads is related to initial muscle length. The long head of the biceps was found to be more active with a greater muscle length (elbow extension), whereas the short head was more active with a shortened initial muscle length (elbow flexion) (Murray et al. 2000).

The hand and wrist owe their mobility to their generous supply of joints (Figure 6.12). The most proximal of these is the radiocarpal, or wrist, joint. Just beyond this are the two rows of carpal bones, each row consisting of four bones. The carpal joints include the articulations within each of these rows, as well as the articulations between the two rows. The carpometacarpal joints (Figure 6.13a) are located at the base of the hand. Closely associated with them are the intermetacarpal joints, those points of contact between the bases of the metacarpal bones of the four fingers. The fingers unite with the hand at the metacarpophalangeal joints. Within the fingers themselves are two sets of interphalangeal joints, the first between the proximal and middle rows of phalanges and the second between the middle and distal rows. The thumb differs from the four fingers in having a more freely movable metacarpal bone and in having only two phalanges instead of three. The metacarpal bone of the thumb is so similar to a phalanx that it might well be described as a cross between a phalanx and a metacarpal (Figure 6.13b).

Structure of the Wrist (Radiocarpal) Joint

The wrist joint is a condyloid (ovoid) joint formed by the union of the slightly concave, oval-shaped surface of the proximal row of carpal bones (i.e., the scaphoid, lunate, and triquetral bones, but not the pisiform). The distal radioulnar joint is in close proximity to the wrist joint and shares with it the articular disc that lies between the head of the ulna and the triquetral bone of the wrist. However, it is not a part of the wrist joint because each joint has its own capsule. The capsule of the wrist consists of four ligaments that merge to form a continuous cover for the joint. These are the volar radiocarpal, dorsal radiocarpal, ulnar collateral, and radial collateral (Figures 6.14 and 6.15).

Movements of the Hand at the Wrist Joint

Flexion

From the anatomical position (Figure 6.16a), this is a forward-upward movement in the sagittal plane, whereby the palmar surface of the hand approaches the anterior surface of the forearm.

Extension

Return movement from flexion.

Hyperextension

A movement in which the dorsal surface of the hand approaches the posterior surface of the forearm—the exact opposite of flexion.

Radial Flexion (Abduction)

From the anatomical position this is a sideward movement in the frontal plane, whereby the hand moves away from the body with the thumb side leading (Figure 6.16b). The movement corresponds to abduction of the humerus. This motion is also referred to as radial deviation.

Ulnar Flexion (Adduction)

From the anatomical position this is a sideward movement in the frontal plane, whereby the hand moves toward the body with the little finger side leading. The movement corresponds to adduction of the humerus. This motion is also referred to as ulnar deviation.

Circumduction

A movement of the hand at the wrist whereby the fingertips describe a circle, and the hand as a whole describes a cone. It consists of flexion, radial flexion, hyperextension, and ulnar flexion occurring in sequence in either this order or the reverse. If there appears to be rotation when one performs this movement, it is taking place in the radioulnar joints, not the wrist joint.

Structure and Movements of the Midcarpal and Intercarpal Joints

These are the joints within the wrist itself. The articulation between the four carpal bones in the proximal row with the four in the distal row is known as the midcarpal articulation. The joints between the adjacent bones within either row are known as the intercarpal joints of the proximal and distal rows, respectively. These joints are all diarthrodial in structure. Within this classification they belong to the nonaxial group and thus permit only a slight gliding motion between the bones. These slight movements, however, add up to a modified hinge type of movement for the midcarpal joint as a whole.

A further characteristic of the carpal region is that the bones are shaped and arranged in such a way that the anterior surface is slightly concave from side to side. This provides a protected passageway for the tendons, nerves, and blood vessels supplying the hand. Referred to as the carpal tunnel, this is the site of many pathologies of the hand and wrist. Among the many carpal ligaments, the volar radiocarpal ligament is the strongest. Its fibers radiate from the capitate to the scaphoid, lunate, and triquetral bones on the anterior surface of the wrist.

Structure of the Carpometacarpal and Intermetacarpal Joints (Figures 6.13, 6.17, and 6.18)

The carpometacarpal joint of the thumb is a prime example of a saddle joint (see Figure 6.13a). It is enclosed in an articular capsule that is stronger in back than in front. The capsule is thick but loose and serves to restrict motion rather than to prevent it. There are no additional ligaments.

The carpometacarpal joints of the four fingers not only are encased in capsules but also are protected by the dorsal, volar, and interosseous carpometacarpal ligaments (Figures 6.17 and 6.18). Closely associated with these joints are the intermetacarpal articulations, the joints between the bases of the metacarpal bones of the four fingers. These are irregular joints. They share the capsules of the carpometacarpal joints and are further reinforced by the dorsal, volar, and interosseous basal ligaments and also by the transverse metacarpal ligament, a narrow fibrous band that connects the heads of the four outer metacarpal bones.

Movements of the Carpometacarpal Joint of the Thumb

The names of the movements of the thumb may seem illogical until they are viewed in the context of the resting thumb position; that is, turned on its axis so that it faces in a plane perpendicular to the other fingers.

Abduction (Figure 6.19a)

A forward movement of the thumb at right angles to the palm.

Adduction

Return movement from abduction.

Hyperadduction (Figure 6.19b)

A backward movement of the thumb at right angles to the hand.

Extension (Figure 6.19c)

A lateral movement of the thumb away from the index finger, on a level with the palm.

Flexion (Figure 6.19d)

Return movement from extension.

Hyperflexion (Figure 6.19e)

A medially directed movement of the thumb from a position of slight abduction. The thumb slides across the front of the palm.

Circumduction

A movement in which the thumb as a whole describes a cone and the tip of the thumb describes a circle. It consists of all the movements just described, performed in sequence in either direction.

Opposition (Figure 6.19f)

This movement, which makes it possible to touch the tip of the thumb to the tip of any of the four fingers, is essentially a combination of abduction and hyperflexion and, according to some investigators, slight inward rotation. Others, including the authors, claim that what appears to be inward rotation of the metacarpal is actually a slight medial movement of the trapezium with which the metacarpal articulates. The movements of the metacarpal are accompanied by flexion of the two phalanges, especially the distal. The apparent rotary movement is explained in part by the oblique axis of motion about which abduction and adduction of the thumb occur, and in part by the movement of the trapezium that accompanies flexion of the thumb. The total movement of the thumb in opposition might well be described as a movement of partial circumduction.

Movements of the Carpometacarpal and Intermetacarpal Joints of the Fingers

Largely because of the short ligaments in this region, especially in the case of the second, third, and fourth digits, the motion in both the carpometacarpal and intermetacarpal joints is almost nonexistent, being limited to slight gliding. The fifth carpometacarpal joint is slightly more mobile and permits a limited motion of the fifth metacarpal bone, resembling in small degree the motion of the thumb.

Structure of the Metacarpophalangeal Joints (Figures 6.13, 6.17, and 6.18)

The joint at the base of the four fingers, uniting the proximal phalanx with the corresponding metacarpal bone, is a condyloid (ovoid) joint. The oval, convex head of the metacarpal fits into the shallow oval fossa at the base of the phalanx. The fossa is deepened slightly by the fibrocartilaginous volar accessory ligament. The joint is encased in a capsule and is protected on each side by strong collateral ligaments.

The metacarpophalangeal joint of the thumb has flatter joint surfaces than do the corresponding joints of the four fingers and has more of the characteristics of a hinge joint. In addition to the articular capsule, it is protected by a collateral ligament on each side and by a dorsal ligament.

Movements of the Metacarpophalangeal Joints of the Four Fingers (Figure 6.20)

Flexion

The anterior surface of the finger approaches the palmar surface of the hand.

Extension

Return movement from flexion. Most individuals are able to achieve slight hyperextension in these joints.

Abduction

For the fourth, fifth, and index fingers this is a lateral movement away from the middle finger. This movement is limited and cannot be performed when the fingers are fully flexed.

Adduction

Return movement from abduction.

Note: In abduction and adduction of the fingers, a different point of reference is used than in abduction and adduction of the hand as a whole. The centerline of the hand—that is, the line passing through the middle finger when the latter is in its normal, extended position—is the reference line for the second, fourth, and fifth digits. Comparable movements of the middle finger are called radial and ulnar flexion.

These lateral finger movements are actually movements of the proximal phalanx, with the action occurring at the metacarpophalangeal joint, but the entire finger moves as a unit because no lateral action is possible at the interphalangeal joints.

Circumduction

The combination of flexion, abduction, extension, and adduction performed in sequence in either direction.

Movements of the Metacarpophalangeal Joints of the Thumb

Flexion

The volar surface of the thumb approaches that of the thenar eminence (base of thumb).

Extension

Return movement from flexion. Individuals vary greatly in their ability to hyperextend the thumb at this joint.

The Interphalangeal Joints

These are the joints between the adjacent phalanges of any of the five digits. They are all hinge joints; hence, their only movements are flexion and extension. These correspond to flexion and extension of the first phalanx at the metacarpophalangeal joints. Hyperextension is slight, if present at all. Each joint is enclosed within an articular capsule, which is strengthened in front by an accessory volar ligament and on each side by a strong collateral ligament.

Location

The muscles of the wrist, fingers, and thumb are classified according to their location on the forearm or the hand and within each group are listed alphabetically (Table 6.1). Of the nineteen muscles of the fingers and thumb, ten are located entirely within the hand and are called intrinsic muscles. Those located outside the hand on the forearm but with tendon attachments on the thumb or fingers are extrinsic muscles.

The wrist flexor muscles originate (proximal attachments) on the medial epicondyle of the humerus or ulna; the wrist extensors have their proximal attachments on the lateral epicondyle of the humerus. These attachments allow these muscles to remain effective across the wrist joint regardless of the position of the forearm. They also contribute to stabilization of the elbow joint, which contributes further to enhancing effective action of these muscles at the wrist joint. The major disadvantage, as with most multijoint arrangements, is the limiting of the range of motion when there is simultaneous movement across all joints.

Characteristics and Functions of Muscles

Wrist Muscles (Figures 6.21, 6.22, and 6.23a)

As one would expect from their location, the flexor carpi radialis and flexor carpi ulnaris are important flexors of the wrist. The palmaris longus, however, is a weak contributor to wrist flexion and is absent in a small part (6–25 percent) of the population. The flexor carpi radialis is also active in radial flexion (abduction) and the flexor carpi ulnaris in ulnar flexion. The tendons of these muscles may be readily palpated on the anterior surface of the wrist (see Figure 6.21). The palmaris longus tendon, if present, is clearly visible if the hand is flexed against slight resistance (see Figure 6.21). The ulnaris tendon (see Figure 6.21) is best identified by its relation to the pisiform bone. It should not be confused with the tendon lying close on the ulnar side of the palmaris tendon. This is a tendon of the flexor digitorum superficialis, probably the one for the fourth finger (Figure 6.24a).

Both radial extensor muscles of the wrist are active in extension and radial flexion (abduction), with the extensor carpi radialis brevis more active in extension than the extensor carpi radialis longus. The extensor carpi ulnaris works cooperatively with the extensor carpi radialis muscles in wrist extension and participates in ulnar flexion (adduction) (see Figure 6.23).

The three wrist extensor muscles may be palpated on the dorsal surface of the forearm when the forearm and hand are resting palm down on a table, the carpi radialis longus on the radial side at elbow level and slightly below, the brevis slightly below the longus, and the carpi ulnaris on the ulnar margin of the dorsal surface about midway between the elbow and wrist. The tendon of the carpi radialis longus may be palpated on the dorsal surface of the wrist in line with the index finger.

The flexor carpi radialis and extensor carpi radialis longus, together with the abductor pollicis longus of the thumb, team up to produce radial flexion(abduction) of the wrist. The extensor and flexor carpi ulnaris muscles team up similarly to produce ulnar flexion (adduction).

Muscles of the Fingers and Thumb (Figures 6.22, 6.23, 6.24, 6.25, 6.26, 6.27, 6.28, and 6.29)

In most instances, the names of the muscles of the fingers and thumb indicate their chief function. These muscles will therefore not be discussed individually. Some of these muscles, however, have important additional roles, and these should be identified. In addition to being an extensor of the interphalangeal joints, the extensor digitorum is an important wrist extensor. Similarly, the flexor digitorum superficialis is active in wrist flexion as well as in flexion at the proximal phalangeal joints. The abductor pollicis longus both abducts and flexes the metacarpophalangeal joint of the thumb, and the abductor pollicis brevis, together with the opponens pollicis, is active in extension and abduction of the thumb. Both the flexor and extensor pollicis longus are active in adduction and opposition of the thumb, and the adductor pollicis participates in opposition and flexion.

The Wrist

Fundamental movements of the wrist are movements of the hand as a unit. They occur chiefly at the radiocarpal joint but involve the midcarpal and intercarpal joints when flexion or hyperextension is carried to the limit of motion.

Flexion

Performed by the flexors carpi radialis, carpi ulnaris, and digitorum superficialis, with possible help from the palmaris longus, flexor pollicis longus, and flexor digitorum profundus.

Extension and Hyperextension

Performed synchronously by the extensors carpi radialis longus, carpi radialis brevis, carpi ulnaris, and extensor digitorum, with possible help from the pollicis longus and extensors indicis and digiti minimi.

Radial Flexion (Abduction)

Performed by the extensors carpi radialis longus and brevis and flexor carpi radialis, with possible help from the abductor pollicis longus and the extensors pollicis longus and brevis.

Ulnar Flexion (Adduction)

Performed by the extensor carpi ulnaris and the flexor carpi ulnaris.

The Fingers

For a better understanding of all the actions of the finger and thumb muscles, they should be studied both on the skeleton (using elastic bands to represent muscles) and on another person. Particular attention should be paid to the relation of each muscle to every joint it crosses, to the muscle’s line of pull, and to the leverage involved.

As an aid to recognizing the secondary actions of the muscles, a record of all the joints crossed by all the finger and thumb muscles is included here.

Forearm Muscles of the Fingers

All five of these muscles cross four sets of joints: wrist, carpometacarpal, metacarpophalangeal, and proximal interphalangeal. The extensor digitorum and extensor digiti minimi also cross both the elbow and the distal interphalangeal joint, making a total of six joints crossed. The flexor digitorum superficialis crosses the elbow but not the distal interphalangeal joint, and both the extensor indicis and flexor digitorum profundus cross the distal interphalangeal joint but not the elbow.

Intrinsic Muscles of the Fingers

Of these six muscles, only the abductor digiti minimi and flexor digiti minimi brevis cross both the carpometacarpal and the metacarpophalangeal joints. The two interossei muscles, dorsales and palmaris, and the lumbricales cross only the metacarpophalangeal joint. The opponens digiti minimi, like the opponens pollicis, crosses only the carpometacarpal joint. The two work together in the cupping action of the palm as well as independently in other opposition movements.

Forearm Muscles of the Thumb

All four of these muscles cross both the wrist and carpometacarpal joints, and all but the abductor pollicis longus also cross the metacarpophalangeal joint. The extensor and flexor pollicis longus muscles cross the interphalangeal joint as well. The thumb, of course, has no second interphalangeal joint.

Intrinsic Muscles of the Thumb

All four of these muscles cross the carpometacarpal joint, and all but the opponens pollicis cross the metacarpophalangeal joint.

The muscular action of the fingers is given in terms of the movement of each phalanx. Movement of the proximal phalanx occurs at the metacarpophalangeal joint, of the middle phalanx at the proximal interphalangeal joint, and of the distal phalanx at the distal interphalangeal joint. For convenience in referring to individual fingers, numbers are assigned as follows: 2 for the index finger, 3 for the middle finger, 4 for the ring finger, and 5 for the little finger.

Flexion

Proximal Phalanx

Flexed by the lumbricales manus (all fingers), interossei palmaris (palmar interossei) (2,4,5), interossei dorsales manus (2,3,4), flexor digiti minimi brevis (5), and opponens digiti minimi (5), with possible help from the flexors digitorum superficialis and profundus.

Middle Phalanx

Flexed by the flexor digitorum superficialis, which acts on all four fingers and at the same time contributes to flexion of the metacarpal bones.

Distal Phalanx

Flexed by the flexor digitorum profundus, which also acts on all four fingers and at the same time contributes to flexion of the proximal and middle phalanges.

Extension

Proximal Phalanx

Extended by the extensor digitorum (all fingers), extensor indicis (2), and extensor digiti minimi (5). The extensor digitorum is also able to help extend the middle and distal phalanges.

Middle and Distal Phalanges

Extended by the lumbricales manus (all fingers) and interossei dorsales manus (dorsal interossei) (2,3,4). The abductor digiti minimi (5) and the extensor digitorum (all fingers) are also able to help extend the middle and distal phalanges at the same time that they are extending the proximal phalanx.

Note: When all the fingers flex or extend, the antagonists relax in reciprocal innervation. However, if a single finger moves, the antagonists will contract in an attempt to keep the other fingers still.

Abduction and Adduction

Abduction is brought about by the interossei dorsales manus (2,4) and abductor digiti minimi (5), and adduction by the interossei palmaris (2,4,5).

Radial and ulnar flexion of the middle finger is performed by the interossei dorsales manus (3).

Opposition

The fifth digit, or little finger, being at the outer margin of the hand, has greater freedom of movement than do the other fingers. Through the action of the opponens digiti minimi, the metacarpal bone of this finger can engage in a slight degree of opposition at the carpi metacarpal joint. Together with the thumb, it participates in this movement when the hand is “cupped,” as when scooping up water, and also when the tip of the little finger is brought forcibly against the tip of the thumb.

The Thumb

The muscular action of the thumb is given in terms of the movements of the metacarpal bone and the two phalanges, proximal and distal.

The Thumb Metacarpal

Flexion

The metacarpal is flexed and hyperflexed after being slightly abducted by the flexor pollicis brevis and the adductor pollicis. The flexor pollicis longus also participates and becomes more dominant when the action is full flexion (Basmajian and DeLuca 1985).

Extension

Performed chiefly by the abductor pollicis longus, with help from the opponens pollicis, the abductor pollicis brevis, and the extensors pollicis longus and brevis.

Abduction

Four muscles are responsible for this movement, two from the forearm, the abductor pollicis longus and the extensor pollicis brevis, and two from the thenar eminence, the abductor pollicis brevis and the opponens pollicis. Under some conditions these may be helped by the flexor pollicis brevis.

Adduction

This movement is performed mainly by the adductor pollicis, with some help from the flexor pollicis brevis and, in certain positions, from the extensor pollicis longus.

Opposition

This action is performed mainly by the opponens, but with appreciable help from the flexor pollicis brevis. As opposition is not a single, well-defined movement but varies according to the finger that is being opposed and to the exact position of that finger, the muscles controlling the thumb must adapt to the demands of the situation. This includes the action of the phalanges as well as that of the metacarpal.

The Thumb Phalanges

Flexion

The flexor pollicis longus flexes both of the phalanges. Additional flexors of the proximal phalanx include the flexor pollicis brevis and the adductor pollicis, with help from the abductor pollicis brevis when necessary.

Extension

The extensor pollicis longus extends both of the phalanges. This is joined by the brevis in the extension of the proximal phalanx.

The plane in which flexion and extension of the thumb phalanges occurs is determined by the position of the metacarpal bone of the thumb.

Length of Long Finger Muscles Relative to Range of Motion in Wrist and Fingers

An interesting characteristic of the long finger muscles is that they do not have sufficient length to permit the full range of motion in the joints of the fingers and wrist at the same time. For instance, one cannot achieve complete flexion of the fingers and wrist simultaneously because the extensor digitorum will not elongate enough to permit it. If maximum finger flexion is maintained, the wrist is able to flex only slightly. Similarly, if maximum wrist flexion is maintained, it will be impossible to achieve a real grip with the fingers. They flex incompletely and without appreciable force. Or, if one makes a tight fist and then determines to flex the wrist completely, the individual will soon discover that the fingers loosen their grip and tend to open up in spite of efforts to prevent it. This is not caused by contraction of the finger extensors but by their inability to elongate sufficiently, due to the countercurrent nature of the muscle action of the multiarticular muscles, as discussed in Chapter 3.

The same type of reaction occurs if one attempts to achieve maximum extension of the fingers when the wrist is fully hyperextended. This involuntary movement due to the tension of opposing muscles is known as the tendon or pulley action of multijoint muscles. Because of this arrangement of the muscles, the strongest finger flexion can be obtained when the wrist is held rigid in either a straight or slightly hyperextended position, and the strongest finger extension when the wrist is rigid in either a straight or slightly flexed position. The most powerful wrist action—either flexion or hyperextension—can occur only when the fingers are relaxed. In other words, strong finger action requires a rigid wrist; strong wrist action requires relaxed fingers.

Using the Hands for Grasping

Grasping, or prehension, is a fairly complex act that is used more frequently than almost any other human motion. Reaching for a thrown ball, grasping a badminton racquet, moving a computer mouse, or gripping a door key all combine action of the hand, wrist, and forearm, often with involvement of the shoulder as well. To produce a grasping motion, one must first position the hand in space, often through arm motion. The hand must then be shaped for the task by moving the thumb and fingers. The hand and fingers are then moved into position around the object. Finally, the fingers close and grasp the object.

The nature of the grasp (or grip) pattern is determined by both the object to be handled and by the objective of the handling. Grasps are often divided into the major categories of power grip and precision grip. A power grip involves flexion of all the fingers. The thumb may participate in the grip, or it may simply stabilize the hand or the object. There are three basic classifications of the power grip: (1) cylindrical (Figure 6.30d), (2) spherical (Figure 6.30e and g), and (3) hook (Figure 6.30h). Ulnar deviation of the wrist enhances the force of the cylindrical grip. The spherical grip is similar to the cylindrical grip but with a greater spread of the fingers. The hook grip excludes use of the thumb but sometimes includes use of the palm. Therefore, the hook grip is sometimes categorized as precision handling.

Precision handling involves the use of the thumb and one or two fingers in various positions in order to accommodate a multiplicity of grasping functions. It entails great variability in pressure and fine motor control to manipulate efficiently the various objects (Figure 6.30a–c).

The muscular involvement also depends on the nature of the grasp. A complex interplay occurs between the extrinsic and intrinsic muscular involvement, which varies with the force and spread of the grasp. Generally speaking, the extrinsic rather than the intrinsic muscles appear to be the major force for compression actions, power gripping, and the gross movements associated with precision gripping. The intrinsic muscles are of greater significance in the refinements of precision movements and the adduction actions that are part of these movements. The wrist extensors are also active during grasping motions, because they stabilize the wrist against the flexion tendencies of those finger flexors that cross the front of the wrist joint (Basmajian and DeLuca 1985).

In sports and gymnastics there is probably less concern with the fine, precise movements of the fingers and thumb than with the grosser movements such as the grasping of balls, striking implements, and suspension apparatus. In general, grasping activities involve flexion of the fingers (usually all three joints), opposition of the thumb metacarpal, and flexion of the phalanges. The degrees of these movements, together with the degree of abduction that may be present in the fingers, depend on the shape and size of the object being grasped, as well as on the purpose of the movement (Figure 6.30).

In sport, whether pitching, throwing for distance, or tossing a ball straight upward, the movements of the forearm and hand are of prime importance. The greater the force desired for moving the ball, the greater the contribution of the upper arm, but because this discussion applies only to the forearm and hand, the upper arm is not considered here. Ignoring the finer movements, the essential action of the forearm in both overhand pitching and in throwing for distance is extension; of the wrist, “flexion” from the hyperextended to the extended position (with an abrupt check of the motion when the wrist is straight); and of the fingers, extension.

In a vertical toss, starting with the forearm forward at a slight downward slant—that is, with the elbow at a slightly obtuse angle—the movements are elbow flexion followed by finger extension and wrist flexion from the hyperextended position. The active muscles are mainly the elbow flexors, the wrist flexors in static contraction, and the finger extensors. The reader may find it of interest to analyze the joint and muscle actions in other kinds of throws.

Fractures of the Forearm

These are common among children, teenagers, and the elderly and are usually caused either by a direct blow or by falling on a rigidly outstretched arm. It is more usual for both the radius and ulna to break than for either one to break alone, and in the younger age group the fracture of either or both bones is likely to be of the greenstick type.

It is important to immobilize the elbow joint in the treatment of a fractured radius, even though the fracture is close to the wrist. This is because in pronation and supination, as the radial head rotates against both the capitulum of the humerus and the radial notch of the ulna, the broad distal end swings halfway around the ulna. The need for immobilizing the elbow joint in the event of a radial fracture should be apparent to anyone who is conversant with kinesiology.

Elbow Dislocation and Fracture

The majority of these dislocations consist of the backward displacement of the ulna and radius in relation to the humerus. The most common cause is catching oneself from a fall by taking the weight on the outstretched hand with the elbow in rigid extension or hyperextension. This can be a very serious injury because it is likely to involve blood vessels and nerves.

Elbow dislocations are frequently accompanied by fractures, the most common being a fracture of the medial epicondyle, especially in the middle- to late-adolescent age group in those whose epicondylar epiphyses have not yet closed. These dislocations often occur because of repeated forceful acts such as pitching or serving in tennis.

Sprained or Strained Wrist

This type of wrist injury is very common and, like so many of the other upper extremity injuries, is caused by catching oneself from a fall by thrusting the arm downward and taking the weight on the palm with the hand hyperextended at the wrist and the elbow rigidly extended. Although the injury is usually called a sprain, it is often a strain, because the site of the trouble may be at the tendon attachments rather than at the attachments of the anterior ligaments (Arnheim and Prentice 1998). It may also involve fracture of a carpal bone.

Carpal Tunnel Syndrome

In the wrist, the carpal arch and transverse carpal ligament form the carpal tunnel through which the finger flexors and median nerve pass (Figure 6.26). Overuse may result in pain caused by nerve compression and numbing of the fingers caused by blood vessel involvement. Carpal tunnel syndrome is a classic example of a repetitive stress injury (RSI). Such injuries are becoming more common as more people spend longer hours working with small hand tools and keyboards. This condition is often treated with rest followed by support and intermittent use. Extreme or very painful conditions may require surgery.

Avulsion Fracture

An avulsion fracture occurs when an external force applied to a tendon pulls off the bit of bone to which it is attached. It occurs at the weakest link in the structure. Avulsion fractures of the forearm and hand are often the result of high stress on the tendon, frequently from very rapid pronation or supination actions in the radioulnar joints or high-energyflexion of the fingers. The probability of occurrence is greatest in youth at the epiphyseal plates, and in the elderly because of osteoporosis.

Epicondylitis

Lateral epicondylitis (“tennis elbow”) and medial epicondylitis (“golfers elbow”) are further examples of repetitive stress injuries. Although the term epicondylitis implies an inflammatory condition, most such injuries are actually microtraumas or tears in the muscle and soft tissue in the region of the proximal attachment sites of the flexor (medial) or extensor (lateral) muscles of the wrist. The valgus load on the elbow during the overhand throwing motion in pitching puts high-energy stress on the medial side of the elbow and is a leading cause of medial epicondylitis in throwing athletes. In extreme cases medial epicondylitis may be accompanied by an avulsion fracture (Grana 2001). Rest, ice, anti-inflammatory drugs, and cortizone injections are often prescribed for these conditions. In some cases, pain can be reduced through surgery or counterforce bracing (Field and Savoie 1998; Whiting and Zernicke 1998).

Elbow and Forearm: Joint Structure and Function

• 1. Record the essential information regarding the structure, ligaments, and cartilages of the two articulations of the elbow joint and, likewise, the two radioulnar articulations. Study the movements of these joints both on the skeleton and on the living body, and explain how their structure facilitates or inhibits movement.
• 2. Using a protractor or goniometer, measure the range of motion on five subjects for the following movements: flexion, pronation, and supination of the forearm.
• 3. Repeat Experience 22 from Chapter 5, this time writing the joint analysis of (a) the starting position of the forearm at the elbow and radioulnar joints, and (b) the movement from the starting position to the final pull-up position. Discuss with partner.
• 4. Assume a handshaking grasp with a skeleton with the elbow flexed and the forearm approximately horizontal. Slowly pronate your forearm and note the movement of the skeleton’s forearm. Observe carefully each end of the radius and ulna and describe what happens. Now supinate your forearm as far as possible and carefully observe the radioulnar movements of the skeleton. Note the way the edge of the radial head rotates against the notch of the ulna and the way the superior surface of the radial head revolves against the capitulum of the humerus. At the distal end, note the way the broad articular process of the radius swings around the head of the ulna and the radial shaft crosses over that of the ulna. Note that the ulna itself does not rotate, although it may appear to do so when the elbow is fixed in extension and pronation of the forearm occurs in conjunction with inward rotation of the humerus.

Elbow and Forearm: Muscular Action

Record the results using a format similar to that found in Table 1.2.

• 5. Flexion
  • Subject: Sit with the entire arm resting on a table. Flex the forearm (a) with palm up (forearm supinated), (b) with thumb up (forearm in neutral position), and (c) with palm down (forearm pronated).
  • Assistant: Resist the movement by holding the wrist. Steady the upper arm if necessary.
  • Observer: Palpate as many of the forearm flexors as possible. Do you notice any difference in the muscular action in a, b, and c?
• 6. Extension
  • a. Subject: Lie face down on a table with one arm raised to shoulder level with the upper arm resting on the table, the forearm hanging down. Extend the forearm without moving the upper arm.
    • Assistant: Steady the upper arm and resist the forearm at the wrist.
    • Observer: Palpate the triceps and anconeus.
  • b. Subject: On hands and knees, flex and extend the arms at the elbows in a push-up exercise.
    • Observer: Palpate the triceps and anconeus.
• 7. Supination
  • Subject: Assume a handshaking position with the assistant and supinate the forearm.
  • Assistant: Assume the same position with the subject and resist the movement.
  • Observer: Palpate and identify the muscles that contract.
• 8. Pronation
  • Subject: Assume a handshaking position with the assistant and pronate the forearm.
  • Assistant: Assume the same position with the subject and resist the movement.
  • Observer: Palpate and identify the muscles that contract. What is their function? Can you palpate the principal movers?

Action of Muscles Other Than Movers

• 9. Supination without Flexion
  • Subject: Sit with the arm supported, elbow in a slightly flexed position and relaxed. Supinate the forearm without increasing or decreasing flexion at the elbow.
  • Observer: Palpate the triceps. Explain.
• 10. Vigorous Flexion of Forearm
  • Subject: Flex forearm vigorously, then check the movement suddenly before completing the full range of motion.
  • Observer: Palpate the triceps. Does it contract during any part of the movement? Explain.
• 11. Perform a movement in which the supinator acts as a neutralizer.

Elbow and Forearm: Applications

• 12. Working with a partner, execute a knee push-up; that is, a push-up from the front lying position, onto the knees instead of the toes, until the elbows are fully extended. Keep the body straight from the knees to the top of the head. Return to the starting position slowly and in good form.
  • a. Analyze the joint and muscular action of the elbows in the push-up.
  • b. Do the same for the return movement.
  • c. What force is responsible for the movement in a? In b?
  • d. What is the chief difference in the type of muscular action used in the push-up and in the letdown (return movement)? (See Types of Contraction.)
• 13. In reading the section on common injuries it may have been noted that several injuries to the forearm, elbow, and wrist are caused by taking the weight on the outstretched hand with the elbow rigidly extended when catching oneself from a fall. The following exercise is designed to accustom one to the practice of giving at the elbow and other upper extremity joints at the moment the hand strikes the ground. If practiced frequently, this technique should become a habit.
  • Kneel on a gymnasium mat with the knees slightly separated, hips in extension, and body erect. Shift your weight to the side until you lose your balance and fall to a side sitting position with your arm outstretched and your hand reaching to catch your weight. At the moment of contact let your elbow give (i.e., flex) and, if the force is sufficient, roll onto your shoulder and back with knees drawn up. Practice this many times, both to right and left. Experiment with variations.

Wrist and Hand: Joint Structure and Function

• 14. Record the essential information regarding the structure, ligaments, and cartilages of the radiocarpal, carpometacarpal, metacarpophalangeal, and interphalangeal articulations. Study the movements both on the skeleton and on the living body and explain how the joint structure affects functions. Pay particular attention to the carpometacarpal joint of the thumb.
• 15. With a protractor or goniometer measure the amount of hyperextension possible at the wrist (a) with the fingers flexed, (b) with fingers extended. Likewise measure the amount of flexion possible at the wrist (a) with fingers flexed, (b) with fingers extended. Explain.

Wrist and Hand: Muscular Action

(See procedures for anatomical analysis of movements in Chapter 1.) If possible, get someone who plays the piano to serve as a subject.

• 16. Flexion at Wrist
  • Subject: Sit with forearm resting on a table with palm up. Flex hand at wrist.
  • Assistant: Resist movement by holding palm.
  • Observer: Palpate, identify, and explain the action of as many muscles as possible.
• 17. Extension and Hyperextension at Wrist
  • Subject: Sit with forearm resting on a table with palm down. Extend hand at wrist.
  • Assistant: Resist movement by holding back of hand.
  • Observer: Palpate, identify, and explain the action of as many muscles as possible.
• 18. Radial Flexion at Wrist
  • Subject: Sit with forearm resting on a table, ulnar side (little finger side of hand) down. Keeping thumb against hand, raise hand from table without moving forearm.
  • Assistant: May give slight resistance to hand.
  • Observer: Palpate and identify the muscles responsible for radial flexion.
• 19. Ulnar Flexion at Wrist
  • Subject: Lie face down or bend forward in such a way that radial side of hand (thumb side) is on supporting surface, with forearm supported and wrist neither flexed nor hyperextended. Keeping little finger against hand, raise hand without moving forearm.
  • Assistant: May give slight resistance to hand.
  • Observer: Palpate and identify the muscles responsible for ulnar flexion.
• 20. Finger Flexion
  • Subject: Sit with forearm resting on a table with palm up. Flex fingers without flexing wrist.
  • Assistant: Resist movement by hooking own fingers over those of subject.
  • Observer: Palpate, identify, and explain the action of as many muscles as possible.
• 21. Finger Extension
  • Subject: Sit with forearm resting on a table with palm down, fingers curled over edge of table. Extend fingers.
  • Assistant: Resist movement by holding hand over subject’s fingers.
  • Observer: Palpate, identify, and explain the action of as many muscles as possible.
• 22. Abduction of Thumb
  • Subject: Place the hand on a table with the palm up and the thumb slightly separated from the index finger. Abduct the thumb at the carpometacarpal joint by raising it vertically upward.
  • Assistant: Give slight resistance to the thumb at the proximal phalanx.
  • Observer: Palpate the abductor pollicis brevis in the thenar eminence.
• 23. Hyperflexion of Thumb in Position of Slight Abduction
  • Subject: Place the hand on a table with the palm up and the thumb slightly raised from the table. Hyperflex the thumb at the carpometacarpal joint.
  • Assistant: Give slight resistance to the proximal phalanx of the thumb.
  • Observer: Palpate the flexor pollicis brevis in the thenar eminence.
• 24. Extension of Thumb
  • Subject: Rest the fully extended hand on its ulnar border with the thumb uppermost. Extend the thumb as far as possible.
  • Observer: Identify the tendons of the abductor pollicis longus, extensor pollicis longus, and extensor pollicis brevis.
• 25. Opposition of Thumb
  • Subject: Press the thumb hard against the tip of the middle finger.
  • Observer: Palpate and identify the opponens pollicis and adductor pollicis.

Action of Muscles Other Than Movers

• 26. Perform a movement in which the extensor carpi ulnaris and extensor carpi radialis longus and brevis act as neutralizers to prevent flexion at the wrist.
• 27. Perform a movement in which the extensor carpi ulnaris and flexor carpi ulnaris act as mutual neutralizers.

Hands: Application

• 28. Inspect the various styles of grasping sport objects in Figure 6.30 and analyze a few of these. First identify the joint position of the wrist, fingers, and thumb, and then determine the chief muscular involvement.

Kinesiological Analysis

• 29. Choose a simple motor skill from Appendix G. Do a complete anatomical analysis of the elbow, forearm, wrist, and hand, following the analysis outline in Tables 1.1 and 1.2.