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Structure and Function

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Fingers: Metacarpophalangeal Joints

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The metacarpophalangeal (MCP) joints of the fingers are composed of the convex distal end of each metacarpal and the concave base of each proximal phalanx (Fig. 7.1). The joints are enclosed in fibrous capsules (Fig. 7.2).

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FIGURE 7.1

An anterior (palmar) view of the hand showing metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints.

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FIGURE 7.2

An anterior (palmar) view of the hand showing joint capsules and palmar plates of the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints and the deep transverse metacarpal ligament.

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Ligamentous support of the MCP joints is provided by the palmar, collateral, and deep transverse metacarpal ligaments. The anterior portion of each capsule has a fibrocartilaginous thickening called the palmar plate or palmar ligament, which is firmly attached to the proximal phalanx and loosely attached to the metacarpals.1,2 The palmar ligaments also blend with the deep transverse metacarpal ligament that connects the MCP joints of the second through fifth digits (Fig. 7.2). The two collateral ligaments on either side of each MCP joint have a strong, cord-like part that attaches between the metacarpal and proximal phalange, running in a distal and slightly palmar direction (Fig. 7.3). A fan-shaped accessory part of the collateral ligaments connects with the palmar ligaments.1-3

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FIGURE 7.3

A lateral view of a finger showing joint capsules and collateral ligaments of the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints. The collateral ligaments have two parts: the major cord-like part that is more lateral and a fan-shaped accessory part that is more palmar.

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Osteokinematics
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The MCP joints are biaxial condyloid joints that have 2 degrees of freedom, allowing flexion–extension in the sagittal plane and abduction–adduction in the frontal plane. Abduction – adduction is possible with the MCP joints positioned in extension, but it is limited with the MCP joints in flexion because of tightening of the cord part of the collateral ligaments, and because of contact between the flatter, almost bicondylar shape of the metacarpal head and the proximal phalange.1,3 This contact between the metacarpal head and proximal phalanges occurs by about 70 degrees of MCP flexion.3 A small amount of passive axial rotation is reported at the MCP joints,2-5 but this motion is not usually measured in the clinical setting.

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Arthrokinematics
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The concave base of the phalanx slides and rolls on the convex head of the metacarpal in the same direction as movement of the shaft of the phalanx.3,6 During flexion, the ...

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