Chapter 7: Wrist and Hand Anatomy and Biomechanics

Comprehensive vocabulary flashcards covering the osteology, arthrology, musculature, deformities, and vascular supply of the wrist and hand for occupational therapy and functional anatomy.

Biomechanical Frame of Reference

An occupational therapy frame of reference that applies anatomical and physiological concepts to restore strength, range of motion (ROM), and endurance in clients with an intact central nervous system.

Lister's Tubercle

A small, rounded bony prominence situated on the dorsal aspect of the distal radius that acts as a pulley for the extensor pollicis longus tendon.

Proximal Carpal Row

The row of carpal bones nearest the forearm, consisting of the scaphoid, lunate, triquetrum, and pisiform.

Distal Carpal Row

The row of carpal bones articulating with the metacarpals, consisting of the trapezium, trapezoid, capitate, and hamate.

Palmar Arches

The three structural curvatures of the hand—the proximal transverse arch, distal transverse arch, and longitudinal arch—that provide functional cupping and grasp dexterity.

Open-Packed Position

The joint position characterized by minimal surface contact between articulating bones and slack ligaments, making it optimal for joint mobilizations.

Close-Packed Position

The joint position characterized by maximum articular surface congruency and taut ligaments, providing the greatest mechanical stability.

Distal Radioulnar Joint (DRUJ)

A uniaxial pivot joint between the distal radius and ulna supported by volar and dorsal radioulnar ligaments that produces forearm pronation and supination.

Radiocarpal Joint

A biaxial ellipsoid joint between the distal radius and proximal carpal bones that permits flexion, extension, radial deviation, and ulnar deviation; its close-packed position is full extension with slight ulnar deviation.

Triangular Fibrocartilage Complex (TFCC)

A fibrocartilaginous structure that cushions the articulation between the distal ulna and carpal bones, providing stability to the ulnar side of the wrist.

Carpometacarpal (CMC) Joints of the Fingers

Non-axial gliding joints between the distal carpal row and the bases of the second through fifth metacarpals that allow volar and dorsal gliding movements.

Metacarpophalangeal (MCP) Joints (Fingers)

Biaxial ellipsoid joints connecting the metacarpal heads to the proximal phalanges, permitting flexion, extension, abduction, and adduction; their close-packed position is $70^\text{o}\text{--}90^\text{o}$ of flexion.

Interphalangeal (IP) Joints

Uniaxial hinge joints (PIP and DIP) that permit flexion and extension; their close-packed position is full extension ($0^\text{o}$).

Carpometacarpal (CMC) Joint of the Thumb

A biaxial saddle joint between the trapezium and the first metacarpal that permits radial abduction, palmar abduction, adduction, and opposition; its close-packed position is full opposition.

Extrinsic Muscles of the Hand

Muscles that originate proximal to the wrist joint on the forearm or humerus and insert in the hand to provide gross power and forceful movement.

Intrinsic Muscles of the Hand

Muscles that have both their origin and insertion located entirely within the hand, responsible for precision control and fine motor coordination.

Palmaris Longus

A superficial extrinsic wrist flexor that inserts into the palmar aponeurosis and assists with object grasp.

Flexor Digitorum Superficialis (FDS)

An extrinsic flexor muscle that splits to insert into the sides of the middle phalanges, primarily flexing the MCP and PIP joints of digits $2$ through $5$.

Camper's Chiasm

The structural bifurcation of each flexor digitorum superficialis (FDS) tendon that allows the flexor digitorum profundus (FDP) tendon to pass through toward the distal phalanx.

Flexor Digitorum Profundus (FDP)

A deep extrinsic flexor muscle passing through Camper's chiasm to insert on the base of the distal phalanges, serving as the sole flexor of the DIP joints.

Digital Pulley System

A retinacular system comprising $5$ annular pulleys ($A_1\text{--}A_5$) and $3$ cruciate pulleys per finger that keeps the flexor tendons close to the phalanges and prevents bowstringing.

Flexor Pollicis Longus (FPL)

A deep extrinsic flexor muscle that flexes all joints of the thumb, enabling tip pinch, texting, and fine manipulation.

Extensor Retinaculum

A thickened fibrous dorsal band that partitions the extrinsic extensor tendons into $6$ distinct fibro-osseous compartments across the wrist.

Anatomical Snuffbox

A triangular dorsal depression at the base of the thumb bounded laterally by the abductor pollicis longus and extensor pollicis brevis tendons and medially by the extensor pollicis longus tendon.

Thenar Muscles

The intrinsic muscle group at the base of the thumb comprised of the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.

Hypothenar Muscles

The intrinsic muscle group controlling the small finger (fifth digit) comprised of the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi.

Palmar Interossei

Three intrinsic hand muscles that adduct the second, fourth, and fifth digits toward the middle finger and contribute to MCP flexion with PIP/DIP extension.

Dorsal Interossei

Four intrinsic hand muscles that abduct digits $2$ through $4$ away from the midline of the third digit and assist in MCP flexion with IP extension.

Adductor Pollicis

A fan-shaped intrinsic muscle with oblique and transverse heads that adducts the first metacarpal toward the palm for lateral pinch activities such as turning a key.

Lumbricals

Four intrinsic muscles originating from FDP tendons and inserting into the extensor expansions that flex the MCP joints while extending the PIP and DIP joints.

Intrinsic Plus Position

A functional hand posture characterized by simultaneous MCP joint flexion and PIP/DIP joint extension, sustained by active contraction of the lumbricals and interossei.

Intrinsic Minus Position

A hand deformity characterized by clawing of the fingers with hyperextension at the MCP joints and flexion at the PIP and DIP joints due to intrinsic muscle paralysis.

Active Insufficiency

A state occurring when a multi-joint muscle is shortened across all its joints simultaneously and cannot produce adequate active tension to complete the movement.

Passive Insufficiency

A state occurring when a multi-joint muscle is fully stretched over all its articulated joints, preventing full passive range of motion at the opposing joints.

Tenodesis

The biomechanical passive finger flexion resulting from active wrist extension (and finger extension during wrist flexion), commonly used to achieve functional grasp after a C6 spinal cord injury.

Boutonniere Deformity

A finger deformity characterized by PIP flexion and DIP hyperextension, caused by rupture or laxity of the central slip of the extensor hood mechanism.

Swan-Neck Deformity

A finger deformity marked by PIP hyperextension and DIP flexion, caused by rupture or laxity of the volar plate along with terminal tendon compromise.

Ulnar Artery

The primary vascular contributor to the hand providing approximately $60\%$ of total blood flow and predominately feeding the superficial palmar arch.

Allen's Test

A vascular assessment evaluating arterial patency of the radial and ulnar arteries in which arterial refill in $6\text{ s}$ or less indicates normal vascular replenishment.