REIDER PART 1
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Chapter 4

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Hand and Wrist

Figurę 4-63. Assessing First dorsal interosseous strength in isolation.

radial nerve. Because thc cxtcnsor pollicis brevis inserts at the base of thc proximal phalanx of the thumb, the extensor pollicis longus is the main extensor of the inter-phalangcal joint. The intrinsic muscles of the thumb, particularly the abductor pollicis brevis and the adduc-tor pollicis, insert into the extensor hood distal to the MCP joint and can provide weak extension of the thumb at the interphalangeal joint. The strength of the two muscles can be evaluated together by asking the patient to extend the thumb as if hitchhiking. The cxaminer then presses on the dorsum of the proximal phalanx of the thumb, attempting to force the MCP joint into flexion (Fig. 4—65A). The examiner should sense moderate resistance before overcoming thc strength of the thumb extensors.

To test the strength of the extensor pollicis longus alone, the cxamincr should isolate the interphalangeal joint. Again, the patient is asked to extend the thumb as if hitchhiking. This time, the examiner stabilizes thc proxi-mal phalanx of the patients thumb between the thumb and the index finger of one hand and attempts to force the interphalangeal joint into flexion by pressing on the patienfs thumbnail with the index finger of the other hand (Fig. 4-65B). The examincr should sense strong resistance before ovcrcoming the strength of the patient s extensor pollicis longus. Extensor pollicis longus tendon rupture, a common event in rheumatoid arthritis and sometimes following fractures of thc distal radius, is asso-ciated with a complctc loss of strength of extcnsion at the interphalangeal joint of the thumb.

Thumb flexion is powered by the JJexor pollicis longus and the flexor pollicis brevis. The flcxor pollicis longus is innervated by the anterior interosseous branek of the median nerve, whereas thc flexor pollicis brevis is innervated on thc radial side of the FPL by the motor median nerve after the nerve passes through the carpal tunnel and on the ulnar side of the FPL by the ulnar nerve. Because the brevis inserts at the base of the proxi-mal phalanx of the thumb and the longus inserts on the distal phalanx, the flexor pollicis longus is uniqucly responsible for flcxion of the interphalangeal joint of the thumb. The strength of thumb flexion can be tested by having thc patient flex the thumb across the palm. The patient is then instructed to maintain the thumb in flex-ion while thc examiner attempts to force it back into cxtcnsion (Fig. 4-66). The examiner should feel moder-ately strong resistance before being ablc to overcome the strength of the thumb flexors. Rupture or laceration of the jlexor pollicis longus rcsults in complete loss of flexion strength at the interphalangeal joint of the thumb.

Radial abduction of the thumb is powered by the abductor pollicis longus and innervatcd by the radial nerve, whereas palmar abduction is powered by thc abductor pollicis brevis, which is innervated by thc motor median nerve after the nerve passes through the carpal tunnel. To test thumb palmar abduction, the examiner stabilizes the patients hand in a supinated position and instructs the

Figurę 4-64. Assessing Finger adduction strength.