Introduction
The physical examination of the hand and wrist can be very rewarding because the majority of the anatomy is readily available to the examiner’s fingertips. One may palpate, stretch, or stress most of the underlying structures. Therefore, armed with a broad knowledge of the anatomy of the distal upper extremity, one may develop a quick differential for the patient’s pathology without the use of expensive imaging or tests.
Anatomy
Bones, Ligament, and Joints
The bones of the upper extremity increase in number from proximal to distal. The single humerus forms the upper arm and the two bones of the forearm are the radius and ulna. If one considers the pisiform a mere sesamoid bone, then the proximal carpal row has three bones (the scaphoid, lunate, and triquetrum), while the distal carpal row contains four (the trapezium, trapezoid, capitate, and hamate). Finally there are five sets of metacarpals and digits ( Fig. 6.1 ).
Distal Radioulnar Joint
In conjunction with the proximal radial-ulnar joint and the interosseous membrane, the distal radioulnar joint (DRUJ) provides for pronation and supination of the forearm. The DRUJ is a synovial pivot joint. The ulnar head articulates with the sigmoid notch of the much larger distal radius. The DRUJ has dorsal and palmar radioulnar ligaments. These ligaments attach the distal radius and ulna offering stability. Nestled between and blended with these two ligaments is the cartilaginous disc of the triangular fibrocartilage forming the triangular fibrocartilage complex (TFCC) ( Fig. 6.2 ).
Radiocarpal Joint
As the name suggests, the radiocarpal joint is the articulation between the distal radial bone and the proximal row of carpal bones. There are eight carpal bones in the wrist joint, arranged in a proximal and a distal row (see Fig. 6.1 ). The proximal-row carpal bones (radial to ulnar) are the scaphoid, lunate, triquetrum, and pisiform. The pisiform bone lies on the palmer aspect of the triquetrum, so essentially, there are functionally only three carpal bones in the proximal row. The distal-row carpal bones (radial to ulnar) are the trapezium, trapezoid, capitate, and hamate. It follows that the distal radius articulates with the proximal row of carpal bones, the proximal row of carpal bones articulates with the distal row of carpal bones, and the distal row of carpal bones articulates with the metacarpal heads. Each “row” of articulation has a separate compartment and is physically distinct from the next. Therefore, each synovial cavity has its own synovial fluid production and can have its own “effusion.”
Ligaments
The wrist has a tremendous number of ligaments. The intrinsic ligaments include the palmar, dorsal, and interosseous ligaments, which connect the carpal bones together ( Fig. 6.3 ). The remaining ligaments are the extrinsic ligaments. The ulnar collateral ligament connects the ulnar head with the (proximal carpal row) triquetrum and pisiform. Then the ulnar collateral ligament sends fibers to the (distal carpal row) hamate, and finally fibers extend to the base of the fifth metacarpal. The ulnar head is separated from the trapezium by the TFCC and forms one of the synovial compartments of the wrist (see Fig. 6.2 ). On the lateral side of the hand, the radial collateral ligament sends fibers from the distal radius to the (proximal carpal row) scaphoid and fibers continue to the (distal carpal row) trapezium.
The radiocarpal joint or the proximal row of articulation is a condyloid joint. The joints between adjacent carpal bones are arthrodial joints. The distal radius articulates with the scaphoid, lunate, and triquetrum. There are interosseous ligaments between the scaphoid and lunate, as well as between the lunate and triquetrum. Therefore, the second synovial cavity of the “wrist” is bounded medially by the ulnar collateral ligament, laterally by the radial collateral, proximally by the radius, distally by the first row of carpal bones and their interosseous ligaments. This constitutes the radiocarpal joint. The third and largest synovial cavity of the wrist joint is distal to the proximal row of carpal bones and their interosseous ligaments. This synovial cavity includes the distal row of carpal bones and ends at the metacarpal heads and their interosseous ligaments and constitutes the midcarpal joint. The fourth synovial cavity in the wrist region, bounded by carpometacarpal (CMC) ligaments, is between the trapezium and the first metacarpal head (base of the thumb) forming the thumb CMC joint. The fifth and final synovial cavity in the wrist region is between pisiform and the triquetrum bones forming the pisotriquetral joint.
There are multiple ligaments, both palmar and dorsal, interconnecting the carpal bones (see Fig. 6.3 ).
Carpal Tunnel
The carpal tunnel is a semirigid bony and ligamentous structure that is clinically important as the site of pathology in carpal tunnel syndrome and is the most common area of compression of the median nerve. The transverse carpal ligament connects the most volar bony structures of the wrist, which are called the pillars. These are the scaphoid tubercle on the radial side of the wrist and the pisiform and hook of the hamate on the ulnar side of the wrist ( Fig. 6.4 ). This ligament and the carpal bones beneath form the carpal tunnel. Nine tendons (flexor pollicis longus [FPL] and four each from the flexor digitorum superficialis [FDP] and flexor digitorum profundus [FDP]) and one nerve (median) pass beneath the transverse carpal ligament.
Guyon Canal
Guyon canal is clinically important as the second most common site of ulnar nerve compression. Unlike the carpal tunnel, the borders of Guyon canal are less rigid and more heterogeneous. Guyon canal lies volar to the carpal tunnel on the ulnar side of the wrist, and the transverse carpal ligament, along with the hypothenar muscles, form the floor of Guyon canal. The roof consists of the volar carpal ligament. The radial border is the hook of the hamate, and the ulnar border is the pisotriquetral joint, the pisiform, and abductor digiti minimi muscle belly. Smaller ligaments that are clinically important include the pisohamate and pisometacarpal. As their names suggest, these ligaments run from the pisiform bone to the hamate and fifth metacarpal, respectively. The ligament from the pisiform to the hook of the hamate also forms the roof of Guyon canal. Both branches of the ulnar nerve enter this canal already divided into the deep and superficial palmar branches (see Ulnar Nerve ).
Muscles
Forearm Based (Extrinsics)
Our discussion of the extrinsic and intrinsic muscles of the hands focuses on the major action and innervation. A full discussion of each and every muscle, including origins and insertions of the muscles, should be sought in an anatomy text.
Flexor Group
The pronator teres (PT) arises from the medial epicondyle of the humerus and the medial coronoid process of the ulna ( Fig. 6.5 ). It inserts onto the lateral edge of the middle third of the radius. The median nerve innervates the PT, and the root levels are C6 and C7. The major action is forearm pronation with the elbow slightly flexed.
The pronator quadratus (PQ), as the name indicates, is a quadrangular shaped muscle with origin and insertion on the distal ulna and radius, respectively. The PQ assists pronation of the forearm and is the last muscle innervated by the anterior interosseous nerve (AIN), the root level most commonly sited at C7 and C8 (perhaps some T1).
The palmaris longus (PL) is absent in a certain percentage of the population and does not travel beneath the flexor retinaculum at the wrist. The PL origin is at the medial epicondyle of the humerus from the common flexor tendon, and the insertion is at the palmar aponeurosis of the hand. The major action is assisting wrist flexion. The median nerve innervates the PL and the root levels are C7, C8, and some T1.
The flexor carpi radialis (FCR) is medial to the PT and lateral to the PL and flexor carpi ulnaris. The FCR muscle’s origin is at the medial humeral epicondyle from the common flexor tendon, and the insertion is at the second and third metacarpal bones in the hand (see Fig. 6.5 ). The FCR does not go deep to the flexor retinaculum at the wrist and, therefore, similar to the PL, is not within the carpal tunnel. The major action of the FCR is wrist flexion with a slight pronation component. The major innervation is from the median nerve from the root levels C6 and C7.
The flexor carpi ulnaris (FCU) has two heads of origin: from the medial humeral epicondyle and common flexor tendon and from the proximal posterior surface of the ulna just medial to the origin of the extensor carpi ulnaris. The major action of the FCU is wrist flexion with ulnar deviation. The major innervation is from the ulnar nerve from the root levels C8 and T1.
The FDS has two heads of origin: from the medial to the humeral epicondyle at the common flexor tendon and coronoid process of the ulna and from the lateral radius just distal to the insertion of the supinator. The median nerve and the ulnar artery lie deep to this muscle and pass between the two heads of the FDS. The FDS muscle gives rise to four tendons in the distal forearm. These four tendons pass deep to the flexor retinaculum at the wrist and therefore the FDS lies within the carpal tunnel at the wrist. The four tendons then continue on to each of digits two, three, four, and five. The final insertion of the tendons of the FDS is the middle phalanx of digits two to five. Interestingly, each tendon splits just proximal to the final insertion to allow the tendon of the FDP to pass through. Therefore, the tendons of the FDS insert on both the medial and lateral aspects of the middle phalanx of digits two to five. The major action of the muscle is flexion of the middle phalanx of digits two to five. In addition, this muscle can aid in flexion at the metacarpal phalanges (MCP) and wrist joints. The median nerve innervates the FDS from the root levels C7, C8, and T1.
The FDP has extensive origin from the anterior and medial ulna and adjacent interosseous membrane. The FDP muscle then gives rise to four tendons that pass deep to the flexor retinaculum at the wrist. Therefore, similar to the FDS, the FDP tendons lie within the carpal tunnel. The four tendons of this muscle then divide, and one tendon goes to each of digits two to five. The final insertion is the proximal distal phalanx, after passing through the split tendons of the FDS muscle. The major action of the FDP is flexion of the distal phalanx. The FDP can also secondarily aid more proximal phalangeal flexion and wrist flexion. The lateral portion of the FDP to digits two and three is innervated by the AIN, whereas the medial portion to the fourth and fifth digits is innervated by the ulnar nerve. The root levels innervating the FDP are C7 and C8.
The FPL originates just lateral to the FDP on the interosseous membrane and the adjacent radial bone. In fact, the AIN runs between the two muscles and innervates them both. The insertion of the FPL is at the base of the distal phalanx of the thumb. The FPL tendon passes within the carpal tunnel and is the most laterally situated tendon. The major action of the FPL is flexion of the distal phalanx of the thumb. The FPL can secondarily flex the more proximal phalanx and the wrist with radial deviation. It is innervated by the AIN from root levels C7 and C8.
Extensor Group
The extensor carpi radialis longus (ECRL) originates at the lateral supracondylar ridge of the humerus, the adjacent intermuscular septum, and the lateral humeral epicondyle ( Fig. 6.6 ). It inserts at the base of the second metacarpal bone. The major action of the ECRL is extension of the wrist with a lateral or radial deviation. The innervation of the ECRL is from the radial nerve, root levels C7 and C8.
The extensor carpi radialis brevis (ECRB) originates at the lateral humeral epicondyle at the common extensor tendon (see Fig. 6.6 ). The ECRB and the ECRL share a common tendon sheath and extensor compartment at the wrist. The ECRB inserts at the base of the third metacarpal. The major action of the ECRB is wrist extension. The radial nerve innervates the ECRB from the root levels C7 and C8.
The extensor digitorum communis (EDC) originates from the common extensor tendon at the lateral humeral epicondyle and inserts into the middle and distal phalanges of digits two, three, four, and five. The major action is extension of these digits. The radial nerve innervates the EDC from the root levels C7 and C8.
The extensor digiti minimi (EDM) is a small muscle originating at the common extensor tendon of the lateral humeral epicondyle and runs immediately adjacent to the EDC. The EDM has a separate extensor compartment at the wrist from the EDC and is considered a separate muscle from the EDC. It inserts at the middle and distal phalanx of the fifth digit ( Fig. 6.7 ). The major action is to extend the fifth digit. The radial nerve innervates the EDM from the root levels C7 and C8.
The extensor carpi ulnaris (ECU) originates from the lateral humeral epicondyle at the common extensor tendon and from the posterior surface of the proximal ulna. The ECU is the most medial muscle in the extensor group. It inserts at the base of the fifth metacarpal bone (see Fig. 6.7 ). The major action is extension of the wrist with ulnar deviation. The radial nerve innervates the ECU from the root levels C7 and C8.
The abductor pollicis longus (APL) originates on the proximal ulna, adjacent intermuscular septum, and the radius, just distal and posterior to the insertion of the supinator. The insertion of the APL is at the base of the first metacarpal bone. The major action of the APL is abduction of the thumb. The radial nerve innervates the APL from the root levels C7 and C8.
The extensor pollicis longus (EPL) originates distal to the APL on the intermuscular septum and the ulna just lateral to the origin of the extensor carpi ulnaris. The insertion of the EPL is the proximal end of the first distal phalanx (see Fig. 6.7 ). The major action is extension of the distal phalanx of the thumb. A secondary action of the EPL is wrist extension with radial deviation. The radial nerve innervates the EPL from root levels C7 and C8.
The extensor pollicis brevis (EPB) originates on the posterior surface of the radius and the adjacent intermuscular septum. The insertion is at the base of the proximal phalanx of the thumb. The major action is extension of the proximal phalanx of the thumb. The radial nerve innervates the EPB from root levels C7 and C8.
The extensor indicis (EI) originates on the distal posterior radius and inserts on the extensor surface of the index finger at the middle and distal phalanx (see Fig. 6.7 ). The major action is extension of the index finger. The EI is the last muscle innervated by the radial nerve from root levels C7 and C8.
Hand Based (Intrinsics)
This section discusses the muscles that have their origin and insertion entirely within the hand, distal to the wrist. These are also called the intrinsic muscles.
The abductor pollicis brevis (APB) originates from the flexor retinaculum, trapezium, and scaphoid. The APB muscle inserts at the base of the proximal phalanx of the pollicis (thumb), with some fibers inserting on the adjacent extensor expansion ( Fig. 6.8 ). The major action of the APB muscle is abduction of the thumb. In addition, the fibers inserting on the extensor expansion can extend the thumb’s interphalangeal joint. The median nerve innervates the APB muscle from root levels C8 and T1.
The flexor pollicis brevis (FPB) has superficial and deep heads. The superficial head originates from the flexor retinaculum and trapezium. The deep head originates from the trapezoid and the capitate. The two heads converge and insert on the base of the proximal phalanx just palmar to the insertion of the APB muscle (see Fig. 6.8 ). The major action of the FPB is flexion of the first MCP and CMC joints. The FPB can also help in adduction and opposition of the thumb. The FPB has dual innervation with the median nerve innervating the superficial head from root levels C8 and T1. The ulnar nerve innervates the deep head from root levels C8 and T1.
The opponens pollicis (OP) originates from the flexor retinaculum and the adjacent trapezium. The OP inserts along the entire shaft of the first metacarpal on the radial side (see Fig. 6.8 ). The major action is opposition of the first metacarpal bone toward the other digits. The median nerve innervates the OP from root levels C8 and T1.
The adductor pollicis (AP) has an oblique head and a transverse head. The transverse head originates from the third metacarpal bone, and the oblique head originates from the adjacent carpal bones: capitate, trapezoid, trapezium, and probably a small slip from the base of the second metacarpal. The two heads converge and insert on the base of the first digit’s proximal phalanx. The major action of the AP is adduction and flexion of the thumb. The ulnar nerve innervates the AP from root levels C8 and T1.
The lumbrical muscles originate from the four tendons of the FDP and insert on the extensor tendon hood of digits two, three, four, and five (see Fig. 6.8 ). The major action of lumbricals is extension of the distal interphalangeal joints and flexion of the MCP joints. Lumbricals have dual innervation with the median nerve innervating the lateral two lumbricals (digits 2 and 3), whereas the ulnar nerve innervates the medial two lumbricals (digits 4 and 5).
Three palmar interosseous muscles are numbered 1, 2, and 3. They originate on the volar aspect of the shaft of the second, fourth, and fifth metacarpals. The palmar interosseous muscles insert on the lateral aspect of the base of the corresponding second, fourth, and fifth proximal phalanges and extensor expansion. The first palmar interosseous muscle inserts on the medial (ulnar) side of the second proximal phalanx and extensor expansion (index finger). The second and third insert on the lateral (radial) side of the proximal fourth and fifth phalanx and extensor expansions. It follows that the major action of the palmar interosseous muscles are adduction (bringing the fingers toward midline) of the phalanges. A secondary action is flexion of the metacarpal joints and extension of the interphalangeal joints. The ulnar nerve innervates all interossei muscles from root levels C8 and T1.
Four dorsal interosseous (DI) muscles are numbered 1, 2, 3, and 4. The DI muscles are larger than the palmar interosseous, have two head origins (bipennate), and lie between adjacent metacarpals. The first dorsal interosseous muscle (FDI) originates from both the first (thumb) and second metacarpals (index finger). At the base of the two heads of origin, the FDI has an opening through which the radial artery passes from dorsal to volar. The second DI muscle originates between the second (index) and third (middle) metacarpals. The third DI muscle originates from between the third (middle) and fourth (ring) metacarpals. The fourth DI muscle originates from between the fourth (ring) and fifth metacarpals. The second, third, and fourth DI muscles all have openings between their two heads through which pass bridging arteries from the dorsal to palmar blood supplies. All the DI muscles insert at the base of the corresponding proximal phalanx and extensor hood, opposite the palmar interosseous insertions. Phalangeal adduction, or movement of the fingers away from the middle finger, is the major action of these muscles. The ulnar nerve innervates the interosseous muscles from root levels C8 and T1.
The abductor digiti minimi (ADM) originates on the pisiform and the tendon of the FCU. The ADM inserts on the medial (ulnar) side of the base of the fifth proximal phalanx and the extensor expansion. The major action is abduction of the fifth digit. Secondarily, the ADM is responsible for flexion of the fifth MCP joint and extension of the fifth interphalangeal joints. The ulnar nerve innervates the ADM from root levels C8 and T1.
The flexor digiti minimi (FDM) originates from the hook of the hamate and the adjacent flexor retinaculum and inserts on the base of the proximal phalanx of the fifth digit. The major action is flexion of the MCP joint of the fifth digit. The ulnar nerve innervates the FDM muscle from root levels C8 and T1.
The opponens digiti minimi (ODM) muscle originates on the flexor retinaculum and the hook of the hamate and inserts along the medial (ulnar) shaft of the fifth metacarpal. The major action is flexion and rotation of the fifth metacarpal bone with respect to the plane of the other metacarpal bones. The ulnar nerve innervates the ODM muscle from root levels C8 and T1.
The palmaris brevis (PB) is a small muscle originating at the medial palmar aponeurosis that runs transversely across the palm and inserts into skin, as well as the pisiform. The palmaris brevis tightens the skin on the palm and may also protect the ulnar nerve and artery. The ulnar nerve innervates this muscle from root levels C8 and T1.
Nerves
Median Nerve
The median nerve is formed by nerve fibers from the lateral and medial cords of the brachial plexus containing nerve fibers from the cervical root levels C6 to T1 ( Fig. 6.9 ). This nerve enters the arm running with the ulnar nerve and the brachial artery and travels within the forearm just medial to the biceps tendon insertion and anterior to the elbow joint. The median nerve dives deep to the PT, between its two heads, and runs between the FDS and FDP muscles. The median nerve innervates the PT, PL, FDS, and FCR in the forearm. The median nerve gives off the AIN just after crossing the elbow joint. The AIN runs deep to the FDP and innervates the FDP to digits 1 and 2, the FPL, and the PQ. The median nerve continues between the tendons of the FDS and FDP at the wrist, just radial (lateral) to the superficialis tendon, ulnar (medial) to the FCR, and just deep (and lateral) to the PL tendon. The median nerve gives off the palmar cutaneous branch just proximal to the flexor retinaculum. It then passes deep to the flexor retinaculum and supplies the (superficial head) FPB, APB, OP, and lumbricals 1 and 2.
Ulnar Nerve
The ulnar nerve enters the arm as the extension of the medial cord of the brachial plexus with nerve fibers from the cervical root levels C8 and T1 ( Fig. 6.10 ). The nerve enters the arm slightly posterior to the brachial artery, innervating no muscles in the arm, and passes posterior to the medial humeral condyle in the ulnar groove. In the forearm, the ulnar nerve lies between the FCU and FDP and innervates the FDP to digits 3 and 4 and the FCU. Next, the ulnar nerve crosses the wrist joint medial to the FCU tendon and lateral to the ulnar artery. Once in the hand, the ulnar nerve passes medial to the pisiform bone, splitting into the superficial and deep palmar branches. These two branches enter the canal of Guyon together but exit to different endpoints. The space between the pisiform and the hook of the hamate forms the walls of Guyon canal. The roof of Guyon canal is the distal extension of the FCU tendon, and the floor is the pisohamate ligament. The superficial palmar branch supplies skin sensation to the medial half of the fourth and all of the fifth digits. The deep palmar branch travels (medial side) around the hook of the hamate and travels laterally to innervate the lumbricals 4 and 5, all interosseous muscles, all hypothenar muscles, the deep head of the FPB, and the AP.
Radial Nerve
The radial nerve is the extension of the posterior cord of the brachial plexus with nerve fibers from the root levels C5 to C8 ( Fig. 6.11 ). It enters the upper arm through the quadrangular space (borders teres major, minor, long head of the triceps and the humerus). In general, the radial nerve innervates all extensor muscles of the elbow, wrist, and fingers. The radial nerve has cutaneous innervation to the back of the arm, forearm, and hand. Once in the arm, the radial nerve lies against the humerus traveling distally and laterally in the spiral groove of the humerus, between the lateral and medial heads of the triceps. In the distal arm, the radial nerve lies between the anterior brachialis muscle and the posterior brachioradialis and ECRL muscles. At the elbow, the radial nerve courses anterior to the lateral condyle of the humerus and splits into superficial and deep branches before entering the belly of the supinator. The superficial branch travels under the brachioradialis muscle becoming subcutaneous lateral to the tendon in the distal forearm. The superficial branch provides cutaneous innervation to the dorsum of the lateral hand and base of the thumb. The deep branch travels distally between the superficial and the deep extensor muscle groups. After innervating the supinator muscle, the radial nerve is called the posterior interosseous nerve (PIN). The deep branch (PIN) provides sensory input to the posterior of the wrist and carpal bones. The radial innervated muscles include the triceps (all heads), brachioradialis, ECRL, ECRB, supinator, EDC, EDM, APL, EPL, EPB, and EI. The last radial innervated muscle is the EI.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
