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STRUCTURE AND FUNCTION

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Radiocarpal and Midcarpal Joints

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Anatomy
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The wrist is comprised of two joints, the radiocarpal and midcarpal joints, both of which are important to function. The radiocarpal joint lies closer to the forearm, whereas the midcarpal joint is closer to the hand. The proximal joint surface of the radiocarpal joint consists of the distal radius and radioulnar articular disc (Fig. 6.1; see also Fig. 5.7).1 The disc connects the medial aspect of the distal radius to the distal ulna. The distal radius and the disc form a continuous concave surface.2,3 The distal joint surface includes three bones from the proximal carpal row—the scaphoid, lunate, and triquetrum—which are connected by interosseous ligaments to form a convex surface (Fig. 6.1). The radius articulates with the scaphoid and lunate, whereas the radioulnar disc articulates with the triquetrum and, to a lesser extent, the lunate. The pisiform, although found in the proximal row of carpal bones, does not participate in the radiocarpal joint. The joint is enclosed by a strong capsule and is reinforced by the palmar radiocarpal, ulnocarpal, dorsal radiocarpal, ulnar collateral, and radial collateral ligaments and numerous intercarpal ligaments (Figs. 6.2 and 6.3).

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FIGURE 6.1

An anterior (palmar) view of the right wrist showing the radiocarpal and midcarpal joints.

Graphic Jump Location
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FIGURE 6.2

An anterior (palmar) view of the right wrist showing the palmar radiocarpal, ulnocarpal, and collateral ligaments.

Graphic Jump Location
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FIGURE 6.3

A posterior view of the right wrist showing the dorsal radiocarpal and collateral ligaments.

Graphic Jump Location
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The midcarpal joint is distal to the radiocarpal joint. The predominant central and ulnar portions of the midcarpal joint consist of the concave surfaces of the scaphoid, lunate, and triquetrum proximally and the convex surfaces of the capitate and hamate distally (Fig. 6.1). On the radial side of the midcarpal joint, a smaller convex surface of the scaphoid contacts the concave surfaces of the trapezium and trapezoid. The midcarpal joint has a joint capsule that is continuous with each intercarpal joint and some carpometacarpal and intermetacarpal joints. Many of the ligaments that reinforce the radiocarpal joint also support the midcarpal joint (Figs. 6.2 and 6.3).

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Osteokinematics
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The radiocarpal and midcarpal joints are of the condyloid type, with 2 degrees of freedom.2 The wrist complex (radiocarpal and midcarpal joints) permits flexion–extension in the sagittal plane around a medial–lateral axis and radial–ulnar deviation in the frontal plane around an anterior–posterior axis. Both joints contribute to these motions.4,5,6 Some sources also report that a small amount of supination–pronation occurs ...

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