Abductor Pollicis Brevis

Median Nerve, Medial Cord, Anterior Division, Lower Trunk, C8, Tl. 

From the palmar retinaculum, the tubercle of the scaphoid and that of the trapezium. 

Lateral side of the base of the proximal phalanx of the thumb. 

Midpoint of a line drawn between the volar aspect of the first metacarpophalangeal joint (MP-1) and the carpometacarpal joint (C-MC). Insert to depth of one-fourth to one-half inch. 

If the electrode is inserted too deeply it will be in the flexor pollicis brevis. 

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The causative oiganophosphate was identified in nine patients four fenthion, two dimethoate. two monocrotophos, and one mclhamidophos. Standard biochemistry and cerebrospinal fluid examination were normal. Cholinesterase (ChE) assays were not available. Electromyography (EMG) showed normal motor and sensory nerve conduction velocities and normal needle myography. Tetanic stimulafion of the abductor pollicis brevis muscle 24-48 hr after the onset of IMS showed a marked fade at 20 and 50 Hz. A train of four stimuli applied at 2 Hz produced no changes in the amplitude of the compound muscle action potential (CMAP). CMAPs are the motor responses recorded with surface electrodes over a muscle after stimulation of its motor nerve. 

RNS (at 3 Hz with square-wave pulses 0.3 ms in duration) of the facial nerve to the orbicularis oculi and orbicularis nasalis, accessory nerve to the trapezius, and median nerve to the abductor pollicis brevis muscles can be studied. Hand-held bipolar electrodes and adhesive surface electrodes are used for stimulation and recording, respectively. Routine nerve conduction studies (NCS) of all four limbs, including the VII nerve, can also be performed. 

Studies Blood chemistries including thyroid and parathyroid tests are normal. Nerve conductions showed severe bilateral dyssdiwannian neuropathy of the median nerves, with prominent conduction block across both wrists. Nerve conductions across the elbow and elsewhere were normal. BMG showed, in both hands, slight-moderate recent denervation in the opponens pollicis and abductor pollicis brevis. Nerve conductions and BMG in the lower limbs were normal. 

FIGURE 37.11 Sketch of the H-coil version used in this study placed on a human head. The coil orientation shown in the figure is designated for optimal stimulation ofthe left abductor pollicis brevis (APB) (indicated by a black spot). 

Scatterplot of the evoked EMG amplitudes and latencies of the abductor pollicis brevis (APB) muscle following monkey median nerve transection and repair by either large pore conduit (Tube 85A) or nerve autograft to bridge a 4 mm deficit (A) evoked EMG amplitudes (B) EMG latencies. 

Fig. 10.47a-c. Ape hand deformity in the right hand of a patient with severe median neuropathy at the carpal tunnel level, a Photograph of the palmar aspect of the hand reveals a skin depression (arrows) due to loss in bulk of the intrinsic muscles at the thenar eminence, b Transverse 12-5 MHz US image at the dorsal aspect of the hand demonstrates a hyperechoic appearance of the abductor pollicis brevis (asterisk) and opponens poUicis (star) related to neurogenic fatty atrophy, d Contralateral healthy side. The insert at the upper right side of the figure indicates probe positioning... 

The thenar muscles are innervated by the recurrent branch of the median nerve and are basically responsible for the complex movement of the thumb. They include the superficial abductor pollicis brevis, the flexor pollicis brevis and the deep opponens pollicis muscles. The abductor pollicis brevis is a broad flat muscle located on the more lateral side of the thenar eminence. It arises from the radial side of the transverse carpal ligament and the tubercle of the trapezium and inserts into the base of the proximal phalanx. The flexor pollicis brevis is located medial to the abductor pollicis and has two muscular bellies the superficial head arises from the transverse carpal ligament and the tubercle of the trapezium, the deep head (first palmar interosseous muscle) from the trapezoid and the capitate. Both heads insert through the radial sesamoid over the metacar-... 

This muscle inserts into the lateral half of the palmar surface of the 1st Metacarpal. It lies deep to the Abductor Pollicis Brevis and lateral to the Flexor Pollicis Brevis. 

The electrode is placed between the abductor pollicis brevis and the... 

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