Chapter 33. Hand

Big Picture

The fascia of the hand is continuous with the fascia of the forearm (antebrachium). In the hand, the fascia varies in thickness and divides the hand into five separate compartments that correspond with the five digits and have similar blood supply, innervation, and actions.

Fascial Layers of the Palmar Side of the Hand (Figure 33-1A)

• Palmar aponeurosis. Located over the palm of the hand and covers the flexor tendons and deeper structures of the hand. The palmar aponeurosis extends distally and becomes continuous with the fibrous digital sheaths.
• Fibrous digital sheaths. Form a tunnel that encloses the flexor tendons of digits 2 to 5 and the tendon of the flexor pollicis longus muscle and their associated synovial sheaths.
• Flexor retinaculum (transverse carpal ligament). Forms a roof over the concavity created by the carpal bones, forming a tunnel (i.e., the carpal tunnel). The median nerve and the tendons of the flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus muscles, and their associated synovial sheaths, pass through this tunnel. The flexor retinaculum anchors medially to the pisiform and the hook of the hamate. Laterally, the flexor retinaculum is anchored to the scaphoid and trapezium.
• Transverse palmar ligament. Continuous with the extensor retinaculum from the dorsal side of the wrist and wraps around, anteriorly, to form a fascial band around the flexor tendons. This ligament should not be confused with the flexor retinaculum, which is located deeper to the transverse palmar ligament.

Fascial Compartments of the Palmar Side of the Hand

The fascial layers divide the palmar side of the hand into the following five compartments (Figure 33-1A):

• Thenar compartment. Contains three muscles that act on digit 1 (thumb).
• Hypothenar compartment. Contains three muscles that act on digit 5.
• Central compartment. Located between the thenar and hypothenar compartments and contains the flexor tendons and the lumbrical muscles.
• Adductor compartment. Contains the adductor pollicis muscle.
• Interosseous compartment. Located between the metacarpals and contains the dorsal and palmar interossei muscles.

Fascial Layers of the Dorsal Side of the Hand

• Extensor retinaculum. Continuous with the fascia of the forearm and attached laterally to the radius and medially to the triquetrum and pisiform bones. The extensor retinaculum works to retain the tendons that are near the bone while allowing proximal and distal gliding of the tendons (Figure 33-1B).
• Dorsal digital expansions. An aponeurosis covering the dorsum of the digits and attaches distal to the distal phalanx. Proximally and centrally, the extensor digitorum, extensor digiti minimi, extensor indicis, and extensor pollicis brevis muscles attach to the dorsal digital expansion. Laterally, the lumbricals and the dorsal and palmar interossei muscles attach. The small intrinsic muscles that attach laterally are responsible for delicate finger movements that would not be possible with the extensor digitorum, flexor digitorum superficialis, and profundus muscles alone. Because of the attachment of the muscles and the location of the hood, the small intrinsic muscles will produce flexion at the metacarpophalangeal joint while extending the interphalangeal joints.

Fascial Compartments of the Dorsal Side of the Wrist

The extensor retinaculum of the hand divides the dorsum of the wrist into the following six compartments:

• Compartment 1. Contains the abductor pollicis longus and extensor pollicis brevis muscles.
• Compartment 2. Contains the extensor carpi radialis longus and brevis muscles.
• Compartment 3. Contains the extensor pollicis longus muscles.
• Compartment 4. Contains the extensor digitorum and extensor indicis muscles.
• Compartment 5. Contains the extensor digiti minimi muscles.
• Compartment 6. Contains the extensor carpi ulnaris muscles.

Big Picture

The hand consists of five digits (four fingers and a thumb). The thumb is considered digit 1; index finger is digit 2; middle finger is digit 3, ring finger is digit 4, and the little finger is digit 5. There are 19 bones and 19 joints in the hand distal to the carpal bones. Each digit has carpometacarpal, metacarpophalangeal, and interphalangeal joints.

Actions of the Fingers

The finger joints and associated movements are as follows (Figure 33-1C):

• Carpometacarpal joints. Sliding joints that allow for gliding and rotation.
• Metacarpophalangeal joints. Condylar joints that allow for flexion and extension as well as abduction and adduction. Movements of abduction and adduction are described in relation to digit 3 (the middle finger). All movements away from digit 3 are considered abduction, and movements toward digit 3 are considered adduction. Rotation is limited because of the collateral ligaments.
• Interphalangeal joints. Hinge joints that allow for flexion and extension. There is a proximal interphalangeal joint and a distal interphalangeal joint for digits 2 to 5. They are often referred to as PIP and DIP, respectively.

Actions of the Thumb

The thumb joints and associated movements are as follows (Figure 33-1D):

• Carpometacarpal joint. Saddle joint that allows for opposition and reposition.
• Metacarpophalangeal joint. Hinge joint that allows for flexion and extension.
• Interphalangeal joint. Hinge joint that allows for flexion and extension. There is only one interphalangeal joint for digit 1 (the thumb).

The thumb is rotated 90 degrees to digits 2 to 5. Therefore, abduction and adduction occur in the sagittal plane, and flexion and extension occur in the coronal plane.

Big Picture

Muscles that act on the joints of the hand can be either extrinsic (originating outside the hand) or intrinsic (originating within the hand), and they may act on a single joint or on multiple joints. The result is movement of multiple joints for activities such as functional grasping or writing (Table 33-1).

Muscles in the Thenar Compartment

Thenar muscles have a common innervation from the recurrent branch (motor branch) of the median nerve (C8–T1), except for the deep head of the flexor pollicis brevis muscle. The thenar muscles consist of the following (Figure 33-2A):

• Abductor pollicis brevis muscle. Attaches to the flexor retinaculum, scaphoid, and trapezium, proximal phalanx and dorsal digital expansion of the thumb. The abductor pollicis brevis muscle produces abduction of the thumb at the metacarpophalangeal joint.
• Flexor pollicis brevis muscle. Attaches to the carpals, flexor retinaculum and proximal phalanx of digit 1. Produces flexion of digit 1 and is innervated by the deep branch of the ulnar nerve (C8–T1).
• Opponens pollicis muscle. Attaches to the trapezium, flexor retinaculum, and metacarpal 1. The opponens pollicis muscle opposes and flexes the thumb.

Muscles in the Hypothenar Compartment

Hypothenar muscles have a common innervation from the deep branch of the ulnar nerve (C8–T1) (Figure 33-2A).

• Abductor digiti minimi muscle. Attaches to the pisiform, pisohamate ligament, and proximal phalanx of digit 5. Produces abduction of digit 5 at the metacarpophalangeal joint.
• Flexor digiti minimi brevis muscle. Attaches to the hamate, flexor retinaculum, and the proximal phalanx of digit 5. Produces flexion of digit 5 at the metacarpophalangeal joint.
• Opponens digiti minimi muscle. Attaches to the hamate, flexor retinaculum, and metacarpal 5. The opponens digiti minimi muscle produces lateral rotation of metacarpal 5.

Muscles in the Central Compartment

Consists of the tendons of flexor digitorum superficialis and profundus and lumbrical muscles (Figure 33-2A and B).

• Lumbrical muscles. Attach to the tendons of the flexor digitorum profundus and to the lateral sides of the dorsal digital expansions of digits 2 to 5. The medial two lumbricals are innervated by the deep branch of the ulnar nerve (C8–T1), and the lateral two lumbricals are innervated by the digital branches of the median nerve (C8–T1). As a result of the insertion on the dorsal digital expansion, the lumbricals flex the metacarpophalangeal joints and extend the proximal and distal interphalangeal joints of digits 2 to 5.

Muscles in the Adductor Compartment

• Abductor pollicis muscle. Consists of a transverse and oblique head, both innervated by the deep branch of the ulnar nerve (C8–T1) (Figure 33-2A). As its name implies, this muscle adducts the thumb.
  • Transverse head. Attaches to metacarpal 3 and the proximal phalanx and the dorsal digital expansion of the thumb.
  • Oblique head. Attaches to the capitate bone, metacarpals 2 and 3 and the proximal phalanx and dorsal digital expansion of the thumb.

Muscles in the Interossei Compartment

All the interossei muscles share a common innervation from the deep branch of the ulnar nerve (C8–T1).

• Dorsal interossei muscle. Attaches to the sides of the metacarpals and base of the proximal phalanx and dorsal digital expansions (Figure 33-2C). The dorsal interossei muscle abducts at the metacarpophalangeal joint. However, because the dorsal interossei muscle attaches to the dorsal digital expansion, it can also produce flexion of the metacarpophalangeal joint and extension at the proximal and distal interphalangeal joints. A helpful acronym to remember the dorsal interossei muscle is “DAB,” where “D” represents dorsal and “AB” represents abduction.
• Palmar interossei muscle. Attaches to the sides of the metacarpals they act on and to the base of the proximal phalanx and the dorsal digital expansions (Figure 33-2D). The palmar interossei muscle adducts the metacarpophalangeal joint. However, because the muscle attaches to the dorsal digital expansion, it can also produce flexion of the metacarpophalangeal joint and extension at the proximal and distal interphalangeal joints. A helpful acronym to remember the palmar interossei muscle is “PAD,” where “P” represents palmar and “AD” represents adduct.

Big Picture

The median nerve innervates lumbricals 1 and 2 and the thenar muscles (excluding the deep head of the flexor pollicis brevis). The ulnar nerve provides the remaining motor innervation to the hand. The superficial radial nerve, median nerve, and ulnar nerve provide sensory innervation to the hand.

Ulnar Nerve

In the forearm, the ulnar nerve gives rise to a dorsal branch and a palmar branch (Figure 33-3A).

• Dorsal branch of ulnar nerve. Provides cutaneous innervation to the medial side of the dorsum of the hand, digit 5, and the ulnar half of digit 4.
• Palmar branch of ulnar nerve. Provides cutaneous innervation to the medial palmar surface of the hand.

The ulnar nerve enters the hand superficial to the carpal tunnel, laterally to the pisiform with the ulnar artery, and then bifurcates into a deep and a superficial branch.

• Deep branch of ulnar nerve. Crosses the palm in a fibro-osseous tunnel (Guyon's tunnel) and supplies the hypothenar compartment, adductor pollicis, dorsal interossei, palmar interossei, and two medial lumbricals.
• Superficial branch of ulnar nerve. Supplies the palmaris brevis and then bifurcates into the common and the proper palmar digital branches to travel along digit 5 and the medial side of digit 4 to supply the surrounding skin.

Median Nerve

Proximal to the carpal tunnel, the median nerve gives rise to a palmar branch (Figure 33-3B).

• Palmar branch of the median nerve. Provides cutaneous innervation to the lateral palmar surface of the hand.

After passing through the carpal tunnel, the median nerve branches into the recurrent branch and the palmar digital branches.

• Recurrent branch of the median nerve. Innervates the thenar muscles of the hand.
• Palmar digital nerves. Travels along the first three digits and the lateral side of the fourth, supplying the lateral two lumbricals, the palmar skin of the first three digits, and the lateral side of the fourth digit.

Radial Nerve

The superficial branch of the radial nerve enters the hand by passing superficially to the anatomical snuffbox, and supplies the skin on the dorsal side of the first three digits (Figure 33-3C). The radial nerve has no motor innervation to intrinsic muscles of the hand and only innervates the extrinsic muscles that send tendons from muscles that originate in the posterior forearm to the thumb and digits.

Big Picture

The blood supply to the hand is provided by the radial and ulnar arteries, which give rise to a superficial and a deep palmar arch and to smaller tributaries as they travel distally to the tips of the fingers. The blood is returned to the axillary and subclavian veins via a deep and superficial venous system. The deep venous system follows the arteries.

Ulnar Artery

The ulnar artery, with the ulnar nerve, enters the hand lateral to the pisiform, where it gives rise to the deep palmar branch and becomes the principal contributor to the superficial palmar arch (Figure 33-4A).

• Deep palmar branch. Curves medially around the hook of the hamate to the deep layer of the palm, where it anastomoses with the deep palmar arch of the radial artery. It also gives rise to the palmar metacarpal arteries, which in turn anastomose with the common palmar digital arteries and bifurcate into the proper palmar digital arteries.
• Superficial palmar arch. Anastomoses with the palmar branch of the radial artery just deep to the palmar aponeurosis, where it gives rise to the common palmar digital arteries. These arteries then bifurcate to become the proper palmar digital arteries that supply the digits.

Radial Artery

The radial artery courses through the anatomical snuff box, contributes to the dorsal carpal arch, and then travels deep into the hand, becoming the principal contributor to the deep palmar arch (Figure 33-4B).

• Deep palmar arch. Travels deep to the adductor pollicis and anastomoses with the deep palmar branch of the ulnar artery, giving rise to the palmar metacarpal arteries.
• Dorsal carpal arterial arch. Courses along the dorsal side of the wrist, giving rise to the dorsal metacarpal and dorsal digital arteries.

Veins of the Hand

The hand contains a deep and a superficial venous system. The deep veins are named according to the arteries they follow (Figure 33-4C). The superficial venous system drains into the dorsal venous arch. From the dorsal venous arch, the radial side of the hand drains to the cephalic vein and the ulnar side of the hand drains to the basilic vein.

Big Picture

Each digit has a carpometacarpal, metacarpophalangeal, and one (digit 1) or two interphalangeal joints (digits 2–5).

Joints of Digits 2 to 4

• Carpometacarpal joints. Articulate between the distal row of carpal bones and the metacarpals of digits 2 to 4. The carpometacarpal joints are classified most often as plane synovial joints (gliding) (Figure 33-5C).
• Metacarpophalangeal joints. Articulate between the metacarpal head and the base of the proximal phalanx. The metacarpophalangeal joints are classified as a synovial condyloid joint that produces flexion and extension and abduction and adduction.
• Interphalangeal joints. Digits 2 to 4 each have two interphalangeal joints (proximal and distal). Articulation of the interphalangeal joints occurs between the head of the proximal phalanx and the base of the phalanx distal to the proximal phalanx. The interphalangeal joints are classified as a synovial hinge that produces flexion and extension.

Joints of Digit 1 (Thumb)

• Carpometacarpal joints. A saddle joint that produces flexion and extension and abduction and adduction. The carpometacarpal joints also produce some rotation when combined with other motions of the thumb (Figure 33-5C).
• Metacarpophalangeal joints. Articulate between the head of the first metacarpal and the base of the first proximal phalanx. The metacarpophalangeal joints are classified as synovial condyloid joints that produce flexion and extension and abduction and adduction.
• Interphalangeal joints. Articulates between the head of the proximal phalanx and the base of the distal phalanx. The interphalangeal joints are classified as synovial hinge joints that produce flexion and extension.

Ligamentous and Capsular Support

• Carpometacarpal joints. Supported by articular capsules and dorsal, palmar, and interosseous ligaments (Figure 33-5C).
• Metacarpophalangeal. Supported by a capsule as well as a palmar and two collateral ligaments, a volar plate, and the deep transverse metacarpal ligament.
  • Palmar ligaments. Located between the collateral ligaments on the palmar side and support the palmar side of the joint.
  • Collateral ligaments. Attached proximally to the sides of the metacarpal and run distally in an anterior direction to attach to the phalanges. These ligaments are important for stability of the medial and lateral joint capsules.
  • Volar plate. Structure that increases joint congruence. It is composed of fibrocartilage and is connected to the proximal phalanx and the joint capsule.
  • Deep transverse metacarpal ligaments. Connect the metacarpal heads of digits 2 to 4 as well as connect laterally to the volar plate.
• Interphalangeal joints. A joint capsule, a volar plate, and two collateral ligaments support both the proximal and distal interphalangeal joints.
  • Volar plate. Supports and reinforces the joint capsule of the interphalangeal joints.
  • Collateral ligaments. Located on the medial and lateral sides of the capsule and provide medial and lateral support throughout the proximal and distal interphalangeal movement.

Muscular Support

• Interphalangeal joints (Figure 33-5A and B)
  • Palmar side. The flexor digitorum superficialis and the flexor digitorum profundus muscles will cross anteriorly at the proximal interphalangeal joint, whereas only the flexor digitorum profundus will cross anteriorly at the distal interphalangeal joint.
  • Dorsal side. At the proximal and distal interphalangeal joint, the extensor digitorum, extensor digiti minimi, extensor pollicis longus, extensor pollicis brevis, lumbricals, and interossei muscles will support the dorsal aspect of the joint primarily through their attachment to the dorsal digital expansion.
• Metacarpophalangeal joints
  • Palmar side. Support to the metacarpophalangeal joints is provided by the flexor digitorum superficialis, flexor digitorum profundus, lumbricals, interossei, flexor digiti minimi brevis, flexor pollicis longus, and flexor pollicis brevis muscles.
  • Dorsal side. Support is provided by the extensor digitorum, extensor indicis, extensor digiti minimi, extensor pollicis longus, and extensor pollicis brevis muscles.