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Chapter 4_Hand and Wrist 127

c

the metacarpophalangeal joints are flexed to 90°, the col-lateral ligaments are fully taut and abduction-adduction is not possible. At positions of flexion between 0° and 90\ abduction-adduction of the metacarpophalangeal joints is proportionally limited according to the amount of flex-ion present. Because the collateral ligaments of the inter-phalangeal joints are taut in all positions of flexion, abduction-adduction at these joints is not possible.

Abduction-adduction of the MCP joints is usually tested with the elbow flexed to 90°, the forearm pronated, and the fingers fully extended. The neutral position is that in which the fingers are held side by side. To measure abduction at the MCP joints, the patient is asked to spread the fingers as wide as possible (Fig. 4-40). A linę drawn through the long finger and the third metacarpal is considered the neutral axis for measurement of abduction. Abduction can be quantitated by measuring the angle that each fully abducted finger makes with this neutral axis. The overall amount of abduction can also be ąuantitated by measuring the span between the tips of the index and the little fingers. Finger abduction is often assessed simply on a qualitative basis. Abnormalities of the ulnar nerve, which innervates the intrinsic muscles, weaken or prevent active abduction. To assess adduction, the patient is asked to return the fingers to the neutral position (Fig. 4-41).

When abduction is measured in this fashion, the long finger remains in the neutral position. Abduction of the long finger can be measured, if desired, by asking the patient to abduct the other fingers and then abduct the long finger to each side in turn until it touches the index and the ring fingers, respectively (Fig. 4-42).

Thumb Motion

The thumb is capable of complex combinations of motion. Many believe that it is the versatility of the thumb that has permitted the advancement of human technology. The complexity of these motions has also madę for some confusion in descriptive nomenclature.

Flexion and Extension. The motions of the interpha-langeal and MCP joints of the thumb are fairly straight-forward. Movement at these two joints is limited primarily to flexion and extension and is usually assessed simultane-ously. The neutral position is considered to be that point at which the dorsum of the distal phalanx, proximal pha-lanx, and first metacarpal all form a straight linę. To assess flexion of the interphalangeal and MCP joints of the thumb, the patient is asked to bend the thumb across the palm as far as possible (Fig. 4-43). Flexion of the interphalangeal joint is normally possible to 80° or 90° degrees. Flexion at the MCP joint varies morę widely; it may be as little as 20° degrees or as great as 90° degrees. Comparison with the opposite side is important to establish the normal amount for each particular patient. To measure extension of the interphalangeal and MCP joints of the thumb, the patient is asked to extend the thumb as fully as possible, as if hitchhiking (Fig. 4-44). Hypercxtcnsion of about 10° degrees is usual in the interphalangeal joint, and hyperex-tension of 10° degrees in the MCP joint is not unusual. Reduced motion in these two joints is most commonly the result of stiffness following a soft tissue injury or post-traumatic arthritis.

Abduction and Adduction. The greater freedom of movement at the trapeziometacarpal or basilar joint of

the thumb makes assessment much morę complex. Abduction and adduction are most commonly assessed in the piane perpendicular to the palm, and this is described as palmar abduction and adduction.

To assess palmar abduction, the elbow is positioned in 90° of flexion with the forearm fully supinated. With the interphalangeal and MCP joints in extension, the patient is asked to move the thumb as far away from the palm and the rest of the hand as possible in a piane perpendicular to the palm (Fig. 4-45). Although this move-ment occurs primarily at the basilar joint, some concomitant motion at the MCP joint also takes place. The angle between the axis of the thumb and the piane of the hand is considered the amount of palmar abduction present. In the normal patient, this motion averages about 60°. To assess palmar adduction, the patient is asked to return the side of the thumb to the palm and index finger (Fig. 4-46). Fuli approximation to this neutral position should be possible.

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