Basic Anatomy. of the hand superimposed on the skeletal structures.

Transcription

1 Basic Anatomy The arm and hand are divided into volar or palmar, and also dorsal, aspects. Distal to the elbow, structures are termed radial or ulnar to the middle finger axis rather than lateral and medial, respectively, because with forearm pronation and supination, the latter terms become confusing. The nomenclature of digits has become standardized. The hand has five digits, namely the thumb and four fingers (the thumb is not called a finger). The four fingers are respectively termed the index, long (middle), ring, and small (little) fingers. The use of numbers to designate digits is no longer accepted (Fig. 70-1). Within the hand, those structures close to the fingertips are termed distal, whereas those further up toward the wrist are termed proximal. Motion in a palmar direction is flexion, whereas dorsal motion is termed extension. Finger motion away from the long finger axis is termedabduction, whereas motion toward the axis of the long finger is termed adduction. The description of the motion of the thumb is sometimes confusing. Extension of the thumb is in the plane of the palm of the hand, whereas palmar abduction of the thumb is the motion that occurs at 90 degrees away from the plane of the palm. Finally, side to side motion of the wrist is termed radial and ulnar deviation. FIGURE 70-1 Surface anatomy of the hand. A, Hand surfaces and nomenclature. B, Skin creases of the hand superimposed on the skeletal structures.

2 Intrinsic muscles of the hand are those that have their origins and insertions in the hand, whereas the extrinsic muscles have their muscle bellies in the forearm and their tendon insertions in the hand. The intrinsic muscles that make up the thenar eminence are the abductor pollicis brevis (APB), flexor pollicis brevis (FPB), opponens pollicis (OP), and adductor pollicis (AP). There are four dorsal interossei that arise from adjacent sides of each metacarpal and provide abduction of the metacarpophalangeal (MP) joints of the index, middle, and ring fingers. There are three palmar interossei that adduct the index, ring, and little fingers toward the middle finger. Four lumbricals originate on the flexor digitorum profundus (FDP) tendons in the palm and insert on the radial sides of the extensor mechanisms of the four fingers. Together with the interossei, these bring about flexion of the MP joints and extension of the interphalangeal (IP) joints of the fingers (Fig. 70-2). The FPB flexes the thumb at the MP joint, in contrast with the extrinsic flexor pollicis longus (FPL), which flexes the thumb IP joint. FIGURE 70-2 Outline of first dorsal interosseous muscle on the index finger shows how it passes volar to the fulcrum of flexion of the metacarpophalangeal joint (MP) and dorsal to the IP joints. Interossei flex MP joints and extend proximal and distal IP joints. The long extrinsic extensor tendon passes dorsal to all joints. The hypothenar muscles consist of the flexor digiti minimi (FDM), which flexes the little finger at the MP joint, as well as the abductor digiti minimi (ADM) and opponens digiti minimi (ODM). A small muscle called the palmaris brevis is located transversally in the subcutaneous tissue at the base of the hypothenar imminence. It is innervated by the ulnar nerve, puckers the skin, and helps in cupping the skin of the palm during grip (Table 70-1). Table Intrinsic Muscles of the Hand MUSCLE Abductor pollicis brevis (APB) Median Abducts the thumb

3 MUSCLE Flexor pollicis brevis (FPB) Median Flexes the thumb Opponens pollicis (OP) Median Opposes the thumb Lumbricals Median and ulnar Flexes metacarpal phalangeal (MCP) joints and extends interphalangeal (IP) joints Palmaris brevis Wrinkles the skin on the medial (ulnar) side of the palm Adductor pollicis (AdP) Adducts the thumb Abductor digiti minimi (ADM) Abducts the small finger Flexor digiti minimi (FDM) Flexes the small digit Opponens digiti minimi (ODM) Opposes the small finger Dorsal interossei Abducts the fingers; flexes MCP joints and extends the IP joints Palmar interossei Adducts the fingers; flexes MCP joints and extends the IP joints * All the thenar intrinsic muscles are supplied by the median nerve except the AdP; all the remaining intrinsic muscles are supplied by the ulnar nerve except the two radial lumbricals. The extrinsic muscles originate proximal to the wrist and comprise the long flexors and extensors of the wrist and digits. The extensors are located dorsally and are divided into three subgroups. The radialmost

4 subgroup is termed the mobile wad and comprises the brachioradialis (BR), extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB). The ECRL and ECRB extend the wrist and deviate it radially. The second group is located in a more superficial layer and comprises three muscles namely, the extensor carpi ulnaris (ECU), extensor digiti minimi-quinti (EDM-Q), and extensor digitorum communis (EDC). The ECU deviates the wrist in an ulnar direction and extends the wrist, whereas the EDM and EDC extend the MP joints of the fingers. The third and deeper subgroup comprises four muscles, three of which act on the thumb; the remaining muscle influences the index finger. The abductor pollicis longus (APL), extensor pollicis longus (EPL), and extensor pollicis brevis (EPB) provide function to the thumb, and the extensor indicis proprius (EIP) extends the MP joint to the index finger. Last of the deep muscles is the supinator, which is located proximally in the forearm (Table 70-2). Table Extrinsic Muscles of the Dorsal Forearm MUSCLE Extensor pollicis brevis (EPB) Abducts the hand and extends the thumb at the proximal phalanx Abductor pollicis longus (APL) Abducts the hand and thumb Extensor carpi radialis longus (ECRL) Extends and radially deviates the hand Extensor carpi radialis brevis (ECRB) Extends and radially deviates the hand Extensor pollicis longus (EPL) Extends the distal phalanx of the thumb Extensor digitorum communis (EDC) Extends the fingers and the hand Extensor indicis proprius (EIP) Extends the index finger Extensor digiti minimi/quinti (EDM/Q) Extends the small finger Extensor carpi ulnaris Extends and ulnarly deviates the wrist

5 MUSCLE (ECU) Supinator Supination Brachioradialis Flexes the forearm * All muscles of the dorsal forearm are innervated by the radial nerve and its respective branches. The extensor tendons pass through six compartments deep to the extensor retinaculum at the dorsum of the wrist. From radial to ulnar side, these tendons and compartments are arranged as follows. The first compartment contains the APL and EPB, which also forms the radial boundary of the so-called anatomic snuffbox. The second compartment consists of the ECRL and ECRB, and the third compartment (which also forms the ulnar boundary of the anatomic snuffbox) contains the EPL. The EIP and EDC pass through the fourth compartment and the EDM through the fifth compartment, where they overlie the distal radioulnar joint. The sixth compartment contains the ECU (Fig. 70-3). FIGURE 70-3 A, B, Surface anatomy of the six dorsal extensor compartments at the wrist. Note that the first (APL and EPB) and third (EPL) compartments form the radial and ulnar boundaries, respectively, of the anatomic snuffbox. At the level of the MP joints, the long extrinsic extensor tendons broaden out to form the extensor hood. The proximal part of the hood at this level is called the sagittal band. It loops around the MP joint and blends into the volar plate, thus forming a lasso around the base of the proximal phalanx, through which it extends the MP joint. The insertions of the interossei and lumbricals enter into the extensor hood as the lateral bands. These lateral bands insert distally and dorsally to the axis of the PIP joint, and it is through this distal insertion that the intrinsic muscles (the interossei and lumbricals) are flexors of the MP joints and yet extensors of the IP joints. The extensor hood inserts to the base of the middle phalanx, which is

6 termed the central slip, and finally proceeds on to the base of the distal phalanx, where it inserts through the terminal slip, thus extending the distal interphalangeal (DIP) joint (Fig. 70-4). FIGURE 70-4 Extensor mechanism of the fingers. A, Lateral view. B, Dorsal view. The extrinsic flexor muscles are located on the volar aspect of the forearm and are arranged in three layers. The superficial layer comprises four muscles pronator teres (PT), flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), and palmaris longus (PL). The PL muscle may be absent in as many as 10% to 12% of individuals. These muscles originate from the medial humeral epicondyle in the proximal forearm and function to flex the wrist and pronate the forearm. The intermediate layer consists of the flexor digitorum superficialis (FDS), which allows independent flexion of the proximal interphalangeal (PIP) joints of the fingers. In the deep layer, there are three muscles: the FPL, which flexes the IP joint to the thumb; the FDP, which flexes the DIP joints of the fingers; and a distal quadrangular muscle that spans between the radius and ulna termed the pronator quadratus, which helps in pronation of the forearm (Table 70-3). Table Extrinsic Muscles of the Volar Forearm MUSCLE Pronator teres (PT) Median Pronation Flexor carpi radialis (FCR) Median Flexion and radial deviation of the wrist Palmaris longus (PL) Median Flexion of the wrist

7 MUSCLE Flexor carpi ulnaris (FCU) Flexion and ulnar deviation of the wrist Flexor digitorum superficialis (FDS) Median Flexion of the proximal interphalangeal (PIP) joint Flexor digitorum profundus (FDP) Median and ulnar Flexion of the distal interphalangeal (DIP) joint Pronator quadratus Median Pronation Flexor pollicis longus (FPL) Median Flexion of the thumb * All muscles of the volar forearm are innervated by the median nerve and its branches except the two ulnar digits of the FDP and FCU, which are innervated by the ulnar nerve. Nerve supply to the hand is by three nerves, the median, ulnar, and radial nerves. A knowledge of the surface anatomy of nerves helps when evaluating specific lacerating injuries (Fig. 70-5). The ulnar attachment to the flexor retinaculum is to the pisiform and hook of the hamate, and the radial attachment is to the scaphoid and ridge of the trapezium. The median nerve passes through the carpal tunnel between these landmarks. It gives sensation to the thumb, index finger, middle finger, and radial half of the ring finger. The palmar cutaneous branch of the median nerve originates from its radial side 5 to 6 cm proximal to the wrist, providing sensation to the palmar triangle. The ulnar nerve travels to the radial side of the pisiform and passes to the ulnar side of the hook of the hamate in its passage through Guyon's canal. It gives sensation to the little finger and ulnar half of the ring finger; the dorsal branch of the ulnar nerve (arising proximal to the wrist and curving dorsally around the head of the ulna) supplies the same digits on their dorsal aspects. The superficial radial sensory nerve emerges from under the brachioradialis in the distal forearm, dividing into two or three branches proximal to the radial styloid, which then proceed in a subcutaneous course across the anatomic snuffbox, innervating the skin of the dorsum of the first web space. The number of fingers served by each nerve is variable. However, as an absolute rule, the palmar surfaces of the index and little fingers are always served by the median and ulnar nerves, respectively.

8 FIGURE 70-5 Surface anatomy of median (red) and ulnar (black) nerves. H, Hook of hamate; P, pisiform; S, scaphoid; T, trapezium. With regard to the motor supply of these nerves, the ulnar nerve supplies the hypothenar muscles, interossei, ulnar two lumbricals, adductor pollicis, and deep head of the flexor pollicis brevis. The median nerve supplies the abductor pollicis brevis, opponens pollicis, radial two lumbricals, and superficial head of the flexor pollicis brevis. In summary, the median nerve thus supplies all the extrinsic digit flexors and wrist flexors (except the FDP to the ring and little fingers and the FCU, which are supplied by the ulnar nerve) and all the thumb intrinsic muscles (except the AP, innervated by the ulnar nerve). The ulnar nerve supplies all the interossei, all the lumbricals (except the radial two, supplied by the median nerve), and the adductor of the thumb. The radial nerve innervates all of the wrist, finger, and thumb extrinsic long extensors. Copyright 2013 Elsevier Inc. All rights reserved. Read our Terms and Conditions of Use and our Privacy Policy. For problems or suggestions concerning this service, please contact: