CHAPTER 10 Structure and Function of the Wrist and Hand Complex Medial View Radius Ulna Radius


Styloid process


A 10° 25° Medial tilt B


Styloid process Palmar tilt


Figure 10.2 Medial (A) and palmar (B) tilt of the radial styloid process. (From Roy S, Wolf SL, Scalzitti DA. The Rehabilitation Specialist’s Handbook, 4th ed. Philadelphia, PA: F. A. Davis Company, 2013: p. 53, with permission.)


JOINT AND LIGAMENT STRUCTURES


Metacarpal: Head


Shaft Base


Hamate Capitate


Trapezoid Trapezium Scaphoid


Groove for extensor carpi radialis brevis


Groove for extensor pollicis longus


Radius Pisiform


Lunate Triquetrum


Dorsal tubercle


Ulna


Figure 10.3 Anterior view of the distal radius and ulna and the carpal bones.


is often painful and tender to palpation. Clinically, it is important to check someone who has sustained radius and ulna fractures similar to those in the x-ray in Figure 10.5 for signs and symptoms of a scaphoid fracture. The capitate, the largest and most central bone of the wrist, is located between the hamate and the trapezoid. Its distal surface articulates with the base of the third metacarpal bone, providing rigid longitudinal stability to the wrist and hand. Ulnar and radial deviation of the wrist occurs around an axis through the capitate in a dorsopalmar direction. The trapezium forms a saddle- shaped articulation with the base of the fi rst metacarpal of the thumb. The trapezoid, located between the capitate and the trapezium, articulates with the base of the second metacarpal. The hamate articulates with the fourth and fi fth metacarpals and contributes to mobility of the ulnar side of the hand (see Fig. 10.3).


The radiocarpal joint is made up of the distal biconcave surface of the radius, the articular disc, and the biconvex surfaces of the scaphoid and the lunate. The disc binds the radius and ulna at the distal radioulnar joint and sepa- rates this joint from the radiocarpal joint. The triquetrum functions as a component of the joint when the wrist is in full ulnar deviation as it comes in contact with the disc. Although there are several small intercarpal joints between the carpals, the midcarpal joint is considered the second main joint of the wrist. The joint consists of the articulation between the proximal and distal rows of carpals.


The extrinsic ligaments in the wrist attach the distal forearm to the wrist. The dorsal radiocarpal ligament supports the posterior aspect of the radiocarpal joint. It blends with the joint capsule and attaches to the lunate and triquetrum. The radial collateral ligament is a thickening of the lateral capsule of the wrist. The palmar radiocarpal ligaments are three ligaments between the radius and the carpals: the radioscaphocapitate, the radiolunate, and the radioscapholunate. These ligaments become taut as the wrist moves into terminal extension. The ulnar collateral ligament is located on the ulnar side of the wrist and is a thickening of the medial wrist joint capsule. The intrin- sic ligaments of the wrist run between the carpal bones. These strong ligaments bind the distal row of the carpals to the base of the metacarpals (Fig. 10.6).


CARPAL TUNNEL


The fl exor retinaculum and the extensor retinaculum are components of the ligamentous structures of the wrist. These connective tissue bands confi ne the tendons of the fi nger fl exors and extensors, maintaining them close to the bony structures, and prevent “bowstringing” away from the carpals as they cross the wrist. The muscles


Radial notch for ulna


195


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