• Identify the bones and primary bony features relevant to the wrist complex. • Describe the supporting structures of the wrist. • Cite the normal ranges of motion for wrist flexion and extension and radial and ulnar deviation. • Describe the planes of motion and axes of rotation for the joints of the wrist. • Cite the proximal and distal attachments and innervation of the primary muscles of the wrist. • Justify the primary actions of the muscles of the wrist. • Describe how compressive forces are transferred from the hand through the wrist. • Explain the function of the wrist extensor muscles when grasping. • List the structures that travel within the carpal tunnel. • Explain the synergistic action between the muscles of the wrist when flexion-extension and radial and ulnar deviation are performed. From a radial (lateral) to ulnar direction, the proximal row of carpal bones includes the scaphoid, lunate, triquetrum, and pisiform. The distal row includes the trapezium, trapezoid, capitate, and hamate (see Figures 6-2 and 6-3). The bones within the proximal row are loosely joined. In contrast, strong ligaments tightly bind the bones of the distal row. The natural stability of the distal row provides an important rigid base for articulations with the metacarpal bones. The joints of the wrist are enclosed within a fibrous capsule. The capsule is thickened by extrinsic and intrinsic ligaments. Extrinsic ligaments have their proximal attachments outside the carpal bones but attach distally within the carpal bones. Intrinsic ligaments, in contrast, have both their proximal and distal attachments located within the carpal bones. Table 6-1 lists the main attachments and primary functions of the four primary extrinsic ligaments: radial collateral, ulnar collateral, dorsal radiocarpal, and palmar radiocarpal. Three of the four primary extrinsic ligaments are indicated by red dots in Figure 6-6, A and B, and are summarized along with their individual functions in Table 6-1. The detailed anatomy of the intrinsic ligaments is beyond the scope of the text. As a group, however, the intrinsic ligaments (1) interconnect various carpal bones; (2) help transfer forces between the hand and the forearm; and (3) maintain the natural shapes of radiocarpal and midcarpal joints, thereby minimizing joint stress during movement. On average, from a neutral (0-degree) position, the wrist flexes approximately 70 to 80 degrees and extends approximately 60 to 65 degrees, for a total of approximately 130 to 145 degrees (Figure 6-9, A). Total flexion normally exceeds extension by approximately 15 degrees. Extension is normally limited by tension in the thicker palmar radiocarpal ligaments, as well as by contact of the carpal bones with the slightly elongated dorsal side of the distal radius. On average, from a neutral (0-degree) position, the wrist allows approximately 30 to 35 degrees of ulnar deviation and approximately 15 to 20 degrees of radial deviation, for a total of about 45 to 55 degrees of motion (Figure 6-9, B). Maximum ulnar deviation is normally twice that of radial deviation, mostly because of the void created by the ulnocarpal space. Radial deviation is blocked by contact between the styloid process of the radius and the radial side of the carpal bones.
Structure and Function of the Wrist
Osteology
Distal Radius and Ulna
Carpal Bones
Carpal Tunnel
Arthrology
Joint Structure
Radiocarpal Joint
Ligaments of the Wrist
Table 6-1
Ligament
Function
Comments
Dorsal radiocarpal ligament
Resists extremes of flexion
Attaches between the radius and the dorsal side of the carpal bones
Radial collateral ligament
Resists extremes of ulnar deviation
Strengthened by muscles such as the abductor pollicis longus and the extensor pollicis brevis
Palmar radiocarpal ligament
Resists extremes of wrist extension
Thickest ligament of the wrist; consists of three parts
Ulnar collateral ligament
Resists extremes of radial deviation
Part of the ulnocarpal complex; helps stabilize the distal radioulnar joint
Wrist Instability
Kinematics
Osteokinematics
Sagittal Plane: Flexion and Extension
Frontal Plane: Radial and Ulnar Deviation
You may also need
Structure and Function of the Wrist
Only gold members can continue reading. Log In or Register to continue
WordPress theme by UFO themes