Thenar Muscles

The intrinsic muscles of the hand lie on the palm and can be divided into three main groups the thenar muscles for the thumb the hypothenar muscles for the little finger the lumbrical muscles and the interosseous muscles located in the central palm and in between the metacarpals respectively (Fig. 11.6). 

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-... 

A corresponding enzyme is also absent from the blood plasma of patients with this disease (Mapes et al., 1970). Schibanoff et al. (1969) studied the distribution of the glycosphingolipids in Fabry s disease patients they found the trihexosyl ceramide to be the predominant neutral glycolipid in all tissues, including liver, spleen, kidney, lymph node, pancreas, prostate gland, heart muscle, thenar muscle, gastrointestinal smooth muscle, cerebral cortex, anterior thalamus, brain stem, peripheral autonomic ganglion, and renal artery. 

Physical examination found him to be moderately built and nourished. Both hands showed diminished power of the flexors and the extensors to 2/5 on the right and 3/5 on the left.Wasting of the small muscles of the thenar eminence was also noted in both hands. Reflexes of the bra-chioradialis, biceps, and triceps were diminished to 1/4 in the right and 2/4 in the left arm. There was loss of pain and temperature sensation over the distribution of median and radial nerves. All other muscle groups and sensations were normal. Cranial nerves were normal. Abdominal palpation revealed hepatosplenomegaly, which was subsequently confirmed by ultrasound. Oral examination found yellowish plaques on the posterior pharyngeal wall. Eyes, ears, and nose were normal. 

Govindu, N.K. Babski-Reeves, K.L. (2012) Thermographic assessment of the thenar thumb muscles during pipetting. International Journal of Human Factors and Ergonomics, 1, 268-281. 

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 flexor pollicis longus tendon traverses the thenar eminence between the superficial and deep bellies of the flexor pollicis brevis muscle. It then enters the osteofibrous canal of the thumb to insert at the volar aspect of the base of the distal phalanx. At the metacarpal head level, this tendon courses between two sesamoid bones, one (lateral) included in the combined tendon of the flexor pollicis brevis and abductor pollicis longus, the other (medial) in the adductor pollicis tendon. 

Hand lipomas are often large and lobulated. They frequently develop over the palmar aspect of the hand and the thenar eminence, extending with elongated processes among muscles and flexor tendons. The blending of the fat into surrounding subcutaneous or muscular tissue usually results in ill-defined margins. US can easily characterize these lesions based on their echotexture and compressibility. 

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