194


PART III THE UPPER EXTREMITY


10.4 List the major ligaments and connective tissue structures of the wrist and hand, and discuss their function in terms of stability and the movements they limit.


10.5 Describe the structures that form the carpal tunnel and the structures that traverse through the tunnel. 10.6 Compare the structure and function of the three arches of the hand. 10.7 Discuss the function of the individual muscles of the wrist and hand and their synergistic action during finger and thumb activities and during functional use of the hand.


10.8 Demonstrate the tenodesis action of the hand, and describe its mechanism of action and how it can be used to assist with grasp.


10.9 Explain the flexor tendon pulley system and the extensor mechanism of the hand. 10.10 Discuss the use and purpose of the types of power grasps and prehension.


WRIST COMPLEX STRUCTURES


Note to Students: It is recommended that you review the pretest questions before reading the chapter to better understand the critical elements of the text. As you complete each section, stop and answer the corresponding questions to test your comprehension. The pretest does not cover all the material in each chapter and should not be used as a sole means of self-assessment of knowledge.


The wrist complex is made up of the articulations between the distal radius and the carpal bones. The distal ulna, which is considered more of a primary bone for the elbow, does not articulate directly with the carpals because a fi brocartilaginous disc separates it from the carpals. The function of the wrist, whether acting as a stabilizer or as a mover, affects the position and function of the hand. Because many of the muscle tendons that move the hand and fi ngers cross the wrist, their ability to generate power, lengthen when additional range of motion is needed, or produce fi ne intrinsic motion is infl uenced by the position of the wrist. In addition to the small articulations between each of the carpal bones, the wrist complex is composed of the radiocarpal and mid- carpal joints (Fig. 10.1). The bony structures and con- nective tissues related to these joints are examined fi rst before studying the kinematics and muscles that control the wrist complex.


BONY STRUCTURES


The distal end of the lateral radius forms the radial styloid process, and the ulna forms the ulna styloid process. The distal articular surface of the radius is concave in both the sagittal and the frontal planes and is tilted medially toward the ulna approximately 25° (Fig. 10.2A). This tilt allows the wrist to move through a larger range of ulnar deviation compared with radial deviation. The radial surface is also angled about 10° toward the palm. This palmar orientation allows more fl exion than extension at the wrist (Fig. 10.2B). On the dorsal surface of the radius is the dorsal (Lister’s) tubercle. This bony area separates


Radiocarpal joint


the tendons of the extensor carpi radialis brevis from the extensor pollicis longus (Fig. 10.3).


The eight small carpal bones are arranged in two horizontal rows: The scaphoid, lunate, triquetrum, and pisiform make up the proximal row of the carpals, and the trapezium, trapezoid, capitate, and hamate make up the distal row (Fig. 10.3). The pisiform is classifi ed as a sesamoid bone because it is located within the fl exor carpi ulnaris tendon. The scaphoid, lunate, and trique- trum articulate with the radius. The scaphoid and tra- pezium are located in what is referred to as the fl oor of the “anatomical snuff box.” The anatomical snuff box is located between the tendon of the extensor pollicis longus and the tendons of the extensor pollicis brevis (EPB) and abductor pollicis longus (APL); the depression between the tendons is the “fl oor,” where the scaph- oid and trapezium are located (Fig. 10.4). The scaphoid, lunate, and triquetrum are often involved with injuries of the distal radius; the scaphoid is the most frequently fractured carpal, followed by the lunate and then the triquetrum. In a scaphoid fracture, the snuff box fl oor


Midcarpal joint


Ulna


Radius


Figure 10.1 Anterior view of the radiocarpal and midcarpal joints of the wrist. (From Starkey C, Brown D. Examination of Orthopedic & Athletic Injuries, 4th ed. Philadelphia, PA: F. A. Davis Company, 2015, p. 732, with permission.)


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