Chapter 7: The Hand

STRUCTURE AND FUNCTION

Fingers: Metacarpophalangeal Joints

Anatomy

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 (Figs. 7.2 and 7.3). The anterior portion of each capsule has a fibrocartilaginous thickening called the palmar plate (palmar ligament), which is loosely attached to the metacarpals and firmly attached to the proximal phalanx.^1,2 Ligamentous support is provided by palmar, collateral, and deep transverse metacarpal ligaments.

Osteokinematics

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 collateral ligaments.² A small amount of passive axial rotation has been reported at the MCP joints,^2,3,4 but this motion is not usually measured in the clinical setting.

Arthrokinematics

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.⁵ During flexion the base of the phalanx slides and rolls anteriorly toward the palm, whereas during extension the base of the phalanx slides and rolls dorsally. In abduction, the base of the phalanx slides and rolls in the same direction as the movement of the finger.

Capsular Pattern

Cyriax and Cyriax⁶ report that the capsular pattern is an equal restriction of flexion and extension. Kaltenborn⁷ notes that all motions are restricted with more limitation in flexion.

Fingers: Proximal Interphalangeal and Distal Interphalangeal Joints

Anatomy

The structure of both the proximal interphalangeal (PIP) and the distal interphalangeal (DIP) joints is very similar (see Fig. 7.1). Each phalanx has a concave base and a convex head. The joint surfaces comprise the head of the more proximal phalanx ...