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Joints and ligaments of the wrist and hand

This is an excerpt from Kinetic Anatomy 5th Edition by Rachel M. Koldenhoven,Robert S. Behnke.

With the large number of bones composing the wrist (ulna, radius, eight carpals, and five metacarpals), it makes sense that several joints make up the structure known as the wrist (figure 5.4). There are joints between the forearm bones and the proximal row of the carpals (radiocarpals), joints between the proximal and distal rows of carpals (midcarpals), and joints between the distal row of carpals and the five metacarpal bones of the hand (carpometacarpals). In addition to these wrist joints, there are joints between the carpal bones within each row (intercarpals).

What is commonly referred to as the wrist joint is the articulation between the distal end of the radius and primarily two bones of the proximal row of carpal bones: the scaphoid (navicular) and the lunate. The movement between these bones produces a gliding type of action as they roll or slide over each other. The radiocarpal joints are classified as condyloid joints because of their movements.

There are five main ligaments of the wrist (figure 5.5). A capsular ligament runs between the distal ends of the ulna and radius to the proximal row of carpal bones. There is a volar (palmar) radiocarpal ligament and a dorsal radiocarpal ligament. The volar radiocarpal ligament is found between the anterior surface of the radius and its styloid process and the proximal row of carpal bones (figure 5.5). The dorsal radiocarpal ligament is found between the distal end of the radius and the proximal row of carpal bones (figure 5.5). The two additional ligaments of the wrist are collateral ligaments: the radial (lateral) and ulnar (medial) collateral ligaments (figure 5.5). The radial collateral ligament of the wrist runs between the styloid process of the radius and the scaphoid carpal bone. The ulnar collateral ligament runs between the styloid pro-cess of the ulna and the medial portions of the pisiform and triquetrum bones.

The intercarpal joints between the carpal bones of the wrist are connected by three forms of intercarpal ligaments: those that connect the four carpal bones in the proximal row, those that connect the four carpal bones in the distal row, and those that connect the carpals of the proximal row to those of the distal row. The intercarpal ligaments can be further divided into volar, dorsal (see figure 5.5), interosseous, radial and ulnar collateral, pisohamate, and pisometacarpal ligaments. All of these ligaments are referred to in this text as simply the intercarpal ligaments. The intercarpal joints move in a gliding motion.

The last group of joints considered to be part of the wrist are the carpometacarpal joints, of which there are five: four between the four carpal bones in the distal carpal row and the bases of the four metacarpal bones of the hand, and one between the trapezium and the base of the first (thumb) metacarpal bone. The motion of these joints is gliding. The ligaments of the four carpometacarpal joints of the hand are the dorsal, volar, interosseous, and capsular carpometacarpal ligaments. The dorsal and volar (palmar) carpometacarpal ligaments (see figure 5.5) are found between the dorsal and volar surfaces of the distal row of carpal bones and the bases of the metacarpal bones. The interosseous ligaments are found between the hamate and capitate bones and the bases of the third and fourth metacarpal bones. The capsular ligaments are located between the distal row of carpals and the bases of the four metacarpals of the hand. The first (thumb) carpometacarpal joint is unique compared with the other four carpometacarpal joints; its ligamentous structure consists of a loose capsular carpometacarpal ligament that is found between the trapezium and the base of the first (thumb) metacarpal bone. The carpometacarpal joint of the thumb is referred to as a saddle joint because of its shape.

Two additional ligamentous structures of the wrist are the flexor (volar) and extensor (dorsal) retinacula (figure 5.6), which are bands of connective tissue over the volar surface (flexor retinaculum) and the dorsal surface (extensor retinaculum) of the wrist. The flexor retinaculum forms a bridge over the carpal bones to form the carpal tunnel through which the flexor muscle tendons of the wrist and hand pass. There is a much smaller space between the extensor retinaculum and the carpal bones through which pass the extensor tendons of the wrist and hand.

The joints of the hand and fingers include five metacarpophalangeal (MCP) joints, which are articulations between the five long metacarpal bones of the hand and the five proximal phalanges of the fingers. Also, the four fingers, each having three phalanges, have proximal interphalangeal (PIP) joints and distal interphalangeal (DIP) joints. The thumb, having only two phalanges, has only one interphalangeal (IP) joint. All five MCP, four PIP, and four DIP joints of the fingers and the IP joint of the thumb have capsular ligaments and ulnar and radial collateral ligaments (see figure 5.5).

POP QUIZ

In the photo, the gymnast has the wrists taped to reinforce what structures?

a. flexor retinaculum

b. carpal tunnel

c. extensor retinaculum

d. proximal carpal row

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FOCUS ON
Carpal Tunnel Syndrome

In addition to the various tendons, blood vessels and nerves pass through the carpal tunnel. Anything causing inflammation of these tissues in the tunnel, such as direct trauma or overuse of muscles that have tendons pass-ing through the tunnel, can cause swelling within the tunnel. Pressure on the tendons, blood vessels, or nerves can result in pain and diminished functioning of any of these tissues. This condition is often referred to as carpal tunnel syndrome.

Repetitive motions that stress the wrist may lead to carpal tunnel syndrome. A common cause of carpal tunnel syndrome is typing at a computer keyboard. In an effort to alleviate this stress, design engineers and biomechanists use an understanding of anatomy to produce new and safer keyboards. The field of study that attempts to improve biomechanical working conditions is known as ergonomics.

More Excerpts From Kinetic Anatomy 5th Edition

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