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Chapter 16

Chapter 16. Forearm, Wrist and Hand. Overview. The carpus, or wrist, represents a highly complex anatomic structure, comprising: A core structure of eight bones More than twenty radiocarpal, intercarpal, and carpometacarpal joints Twenty-six named intercarpal ligaments

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Chapter 16

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  1. Chapter 16 Forearm, Wrist and Hand

  2. Overview • The carpus, or wrist, represents a highly complex anatomic structure, comprising: • A core structure of eight bones • More than twenty radiocarpal, intercarpal, and carpometacarpal joints • Twenty-six named intercarpal ligaments • The six or more parts of the triangular fibrocartilage complex (TFCC)

  3. Overview • The hand accounts for about 90% of upper limb function • The thumb is involved in 40-50% of hand function • The index finger is involved in about 20% of hand function • The middle finger, which accounts for about 20% of all hand function, is the strongest finger, and is important for both precision and power functions

  4. Anatomy • Distal radio-ulnar joint • A double pivot joint that unites the distal radius and ulna and an articular disc (TFCC) • The rounded head of the ulnar head contacts both the ulnar notch of the radius laterally, and the TFCC distally • The ulnar styloid process is approximately one-half inch shorter than the radial styloid process, resulting in more ulnar deviation than radial deviation

  5. Anatomy • Triangular fibrocartilage complex (TFCC) • The TFCC is essentially comprised of the fibrocartilage disc interposed between the medial proximal row and the distal ulna within the medial aspect of the wrist • The primary function of the TFCC is to improve joint congruency and to cushion against compressive forces • The TFCC transmits about 20% of the axial load from the hand to the forearm

  6. Anatomy • The Wrist • Comprised of the distal radius and ulna, eight carpal bones, and the bases of five metacarpals • The carpal bones lie in two transverse rows • The proximal row contains (lateral to medial) the scaphoid (navicular), lunate, triquetrum, and pisiform • The distal row holds the trapezium, trapezoid, capitate, and hamate

  7. Anatomy • Mid Carpal Joints • The midcarpal joint lies between the two rows of carpals • A ‘compound’ articulation because each row has both a concave and convex segment • The proximal row of the carpals is convex laterally and concave medially. • The scaphoid, lunate, trapezium trapezoid, and triquetrum present with a concave surface to the distal row of carpals • The scaphoid, capitate and hamate present a convex surface to a reciprocally arranged distal row

  8. Anatomy • Carpal Ligaments • The major ligaments of the wrist include the palmar intrinsic ligaments, the volar extrinsic and the dorsal extrinsic and intrinsic ligaments • The extrinsic palmar ligaments provide the majority of the wrist stability • The intrinsic ligaments serve as rotational restraints, binding the proximal row into a unit of rotational stability

  9. Anatomy • Radiocarpal Joint • Formed by the large articular concave surface of the distal end of the radius, the scaphoid and lunate of the proximal carpal row, and the TFCC

  10. Anatomy • Antebrachial Fascia • A dense connective tissue ‘bracelet’ that encases the forearm and maintains the relationships of the tendons that cross the wrist

  11. Anatomy • The Extensor Retinaculum • This retinaculum serves to prevent the tendons from ‘bow-stringing’ when the tendons turn a corner at the wrist • The tunnel-like structures formed by the retinaculum and the underlying bones are called fibro-osseous compartments

  12. Anatomy • The extensor retinaculum compartments, from lateral to medial, contain the tendons of: • Abductor pollicis longus and extensor pollicis brevis • Extensor carpi radialis longus and brevis • Extensor pollicis longus • Extensor digitorum and indicis • Extensor digiti minimi • Extensor carpi ulnaris

  13. Anatomy • The Flexor Retinaculum • Transforms the carpal arch into a tunnel, through which pass the median nerve and some of the tendons of the hand • Proximally, the retinaculum attaches to the tubercle of the scaphoid and the pisiform • Distally it attaches to the hook of the hamate, and the tubercle of the trapezium • In the condition known as ‘carpal tunnel syndrome’ the median nerve is compressed in this relatively unyielding space

  14. Anatomy • Carpal Tunnel • Serves as a conduit for the median nerve and nine flexor tendons • The palmar radiocarpal ligament and the palmar ligament complex form the floor of the canal • The roof of the tunnel is formed by the flexor retinaculum (transverse carpal ligament) • The ulnar and radial borders are formed by carpal bones (trapezium and hook of hamate respectively) • Within the tunnel, the median nerve divides into a motor branch and distal sensory branches

  15. Anatomy • Tunnel of Guyon • A depression superficial to the flexor retinaculum, located between the hook of the hamate and the pisiform bones • The palmar (volar) carpal ligament, palmaris brevis muscle, and the palmar aponeurosis form its roof • Its floor is formed by the flexor retinaculum (transverse carpal ligament), pisohamate ligament, and pisometacarpal ligament • The tunnel serves as a passage way for the ulnar nerve and artery into the hand

  16. Anatomy • Phalanges • Fourteen in number • Each consist of a base, shaft, and head • Two shallow depressions, which correspond to the pulley-shaped heads of the adjacent phalanges, mark the concave proximal bases • Two distinct convex condyles produce the pulley-shaped configuration of the phalangeal heads

  17. Anatomy • Metacarpophalangeal (MCP) Joints of the 2nd-5th Fingers • The 2nd-5th metacarpals articulate with the respective proximal phalanges in biaxial joints • The MCP joints allow flexion-extension and medial-lateral deviation associated with a slight degree of axial rotation

  18. Anatomy • Carpometacarpal Joints • Articulation between the distal borders of the distal carpal row bones and the bases of the metacarpals • Stability of the CMC joints is provided by the palmar and dorsal carpometacarpal and intermetacarpal ligaments

  19. Anatomy • First Carpometacarpal Joint • Functionally the sellar (saddle-shaped) carpometacarpal (CMC) joint is the most important joint of the thumb • Consists of the articulation between the base of the first metacarpal and the distal aspect of the trapezium

  20. Anatomy • First Carpometacarpal Joint • Motions that can occur at this joint include flexion/extension, adduction/abduction and opposition (which includes varying amounts of flexion, internal rotation, and palmar adduction)

  21. Anatomy • Metacarpophalangeal Joint of the Thumb • A hinge joint • Consists of a convex surface on the head of the metacarpal, and a concave surface on the base of the phalanx

  22. Anatomy • Interphalangeal (IP) Joints • Adjacent phalanges articulate in hinge joints that allow motion in only one plane • The congruency of the IP joint surfaces contributes greatly to finger joint stability • The proximal IP joint is a hinged joint capable of flexion and extension • The distal IP joint has similar structures but less stability and allows some hyperextension.

  23. Anatomy • Palmar Aponeurosis • A dense fibrous structure continuous with the palmaris longus tendon and fascia covering the thenar and hypothenar muscles • Dupuytren’s contracture is a fibrotic condition of the palmar aponeurosis that results in nodule formation or scarring of the aponeurosis, and which may ultimately cause finger flexion contractures

  24. Anatomy • Extensor Hood • A complex tendon, which covers the dorsal aspect of the digits is formed from a combination of the tendons of insertion from extensor digitorum, extensor indicis, and extensor digiti minimi • Creates a ‘cable’ system that provides a mechanism for extending the MCP and IP joints, and allows the lumbrical, and possibly interosseous muscles, to assist in the flexion of the MCP joints

  25. Anatomy • Synovial Sheaths • Long narrow balloons filled with synovial fluid, which wrap around a tendon so that one part of the balloon wall (visceral layer) is directly on the tendon, while the other part of the balloon wall (parietal layer) is separate

  26. Anatomy • Flexor Pulleys • Annular (A) and cruciate (C) pulleys restrain the flexor tendons to the metacarpals and phalanges and contribute to fibro-osseous tunnels through which the tendons travel • A1 from the MP joint and volar plate • A2 from the proximal phalanx • A3 from the PIP joint volar plate • A4 from the middle phalanx • A5 from the DIP joint volar plate

  27. Anatomy • Muscles of the Wrist and Forearm • Can be subdivided into the 19 intrinsic muscles that arise and insert within the hand, and the 24 extrinsic muscles that originate in the forearm and insert within the hand • The flexors, located in the anterior compartment flex the wrist and digits • The extensors, located in the posterior compartment, extend the wrist and the digits

  28. Anatomy • Anterior Compartment • Superficial muscles • Pronator teres • Flexor carpi radialis (FCR) • Palmaris longus • Flexor carpi ulnaris (FCU)

  29. Anatomy • Anterior Compartment • Intermediate Muscle • Flexor Digitorum superficialis (FDS) • Deep Muscles • Flexor pollicis longus (FPL) • Flexor digitorum profundus (FDP) • Pronator quadratus

  30. Anatomy • Posterior Compartment • Superficial muscles • Extensor carpi radialis longus (ECRL) • Extensor carpi radialis brevis (ECRB) • Extensor digitorum and Extensor digiti minimi • Extensor carpi ulnaris (ECU)

  31. Anatomy • Posterior Compartment • Deep muscles • Abductor pollicis longus (APL) • Extensor pollicis brevis (EPB) • Extensor pollicis longus (EPL) • Extensor indicis (EI)

  32. Anatomy • Muscles of the Hand • Short muscles of the thumb • Abductor pollicis brevis (APB) • Flexor pollicis brevis (FPB) • Opponens pollicis (OP) • Adductor pollicis (AP)

  33. Anatomy • Muscles of the Hand • Short muscles of the 5th digit • Abductor digiti minimi (ADM) • Flexor digiti minimi (FDM) • Opponens digit minimi (ODM)

  34. Anatomy • Muscles of the hand • Interosseous muscles of the hand • Three palmar interossei. Each functions to adduct the digit, to which it is attached, toward the middle digit • Four dorsal interossei. Each functions to abduct the index, middle and ring fingers from the mid-line of the hand

  35. Anatomy • Muscles of the hand • Lumbricales • Function to perform the motion of IP joint extension with the MCP joint held in extension • Can assist in MCP flexion

  36. Anatomy • Anatomic Snuff Box • A depression on the dorsal surface of the hand at the base of the thumb, just distal to the radius • Formed by the tendons of the APL and EPB, while the ulnar border is formed by the tendon of the EPL • Along the floor of the snuffbox is the deep branch of the radial artery and the tendinous insertion of the ECRL. Underneath these structures, the scaphoid and trapezium bones are found

  37. Anatomy • Functional arches of the hand • The transverse arch • The metacarpal arch • The longitudinal arch • The oblique arches

  38. Anatomy • Neurology • The three peripheral nerves that supply the skin and muscles of the wrist and hand include the median, ulnar, and radial nerve

  39. Anatomy • Vasculature of the wrist and hand • The brachial artery bifurcates at the elbow into radial and ulnar branches, which are the main arterial branches to the hand • Vascular arches of the hand • Dorsal arches • Palmar arches

  40. Biomechanics • The wrist contains several segments whose combined movements create a total range of motion that is greater than the sum of its individual parts

  41. Biomechanics • Pronation • Approximately 90° of forearm pronation is available • During pronation, the concave ulnar notch of the radius glides around the peripheral surface of the relatively fixed convex ulnar head • Pronation is limited by the bony impaction between the radius and the ulna

  42. Biomechanics • Supination • Approximately 85-90° of forearm supination is available • Supination is limited by the interosseous membrane, and the bony impaction between the ulnar notch of the radius, and the ulnar styloid process

  43. Biomechanics • Wrist flexion and extension • The movements of flexion and extension of the wrist are shared among the radiocarpal articulation, and the intercarpal articulation, in varying proportions

  44. Biomechanics • Wrist flexion and extension • During wrist flexion, most of the motion occurs in the midcarpal joint (60% or 40° versus 40% or 30° at the radiocarpal joint), and is associated with slight ulnar deviation and supination of the forearm • During wrist extension, most of the motion occurs at the radiocarpal joint (66.5% or 40° versus 33.5% or 20° at the midcarpal joint), and is associated with slight radial deviation and pronation of the forearm

  45. Biomechanics • Radial Deviation • Radial deviation occurs primarily between the proximal and distal rows of the carpal bones • The motion of radial deviation is limited by impact of the scaphoid onto the radial styloid, and ulnar collateral ligament

  46. Biomechanics • Ulnar deviation • Ulnar deviation occurs primarily at the radiocarpal joint • Ulnar deviation is limited by the radial collateral ligament

  47. Biomechanics • Thumb motions • Within the first CMC joint, the longitudinal diameter of the articular surface of the trapezium is generally concave from a palmar to dorsal direction • The transverse diameter is generally convex along a medial to lateral direction • The proximal articular surface of the first metacarpal is reciprocally shaped to that of the trapezium

  48. Biomechanics • Thumb flexion and extension • Thumb flexion and extension occur around an anterior-posterior axis in the frontal plane that is perpendicular to the sagittal plane of finger flexion and extension • In this plane, the metacarpal surface is concave, and the trapezium surface is convex

  49. Biomechanics • Thumb abduction and adduction • Thumb abduction and adduction occur around a medial-lateral axis in the sagittal plane, that is perpendicular to the frontal plane of finger abduction and adduction • During thumb abduction and adduction, the convex metacarpal surface moves on the concave trapezium

  50. Biomechanics • A number of grips have been recognized: • Fist grip • Cylindrical grip • Ball grip • Hook grip • Ring grip • Pincer grip • Pliers grip

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