On the Form and Function of the Abductor Pollicis Brevis Muscle

Abstract

The abductor pollicis brevis muscle acts In conjunction with the palmaris longus and the abductor pollicis longus to abduct the first metacarpal in the sagittal plane. S e g ments of the abductor pollicis brevis which arise fiom the tendons o f the palmaris longus and/or the abductor pollicis longus and are inserted into the extensor expansion are the lumbricals o f the thumb. The lateral border of the abductor pollicis brevis presents an important muscular (in four cases 'out of ten neurovascular) hilum. The tendinous slip t o the abductor pollicis brevis from the palmaris longus presents near its origin an orifice which the palmar branch of the median nerve traverses t o become superficial.THE abductor pollicis brevis is a thin sheet of muscle, more or less triangular in shape, forming most of the surface of the muscular thenar eminence. Descriptions of the anatomy of this muscle are various, and so are the functions attributed to it.The present study is an attempt to verify the morphological data and to integrate them into a functional concept. MATERIALS AND METHODSFifty forearms and hands taken at random from embalmed cadavers were dissected by routine techniques in order to investigate : (i) the presence of the palmaris longus muscle and its relations, when present, to the abductor pollicis brevis; (ii) the presence of a separate tendon from the abductor pollicis longus muscle to the base of the abductor pollicis brevis ; and (iii) the correlation between the tendons of the palmaris brevis and the abductor pollicis longus as origins for the abductor pollicis brevis.Ten hands taken at random from nonembalmed cadavers were injected with red latex via the radial artery, fixed in 5% formalAddress for reprints : Dr M. Fahrer, DeDartment of Anatomy, University of Queensland, St Lucia, Queensland 4067.dehyde and microdissected at magnifications ranging between x 2 and x 40, in order to investigate: (i) the details of the origins and insertions of the abductor pollicis brevis; (ii) its blood and nerve supply; (iii) the relations to the muscle of the palmar branch of the median nerve. RESULTSThe abductor pollicis brevis presents two types of origin: (i) fixed origins from the flexor retinaculum and from the distal part of the fibrous sheath of the flexor carpi radialis tendon ; and (ii) mobile origins from the lateral division of the tendon of the palmaris longus, from the anterior division of the tendon of the abductor pollicis longus and from the skin of the thenar eminence. I n the first series of 50 cases, the palmaris longus was present in 4. Its tendon bifurcates shortly above the wrist crease. The medial tendon runs into the palmar aponeurosis. The lateral tendon gives origins to muscular fibres of the abductor pollicis brevis. Two patterns of origin emerge from these dissections: ( a ) A discrete, fusiform muscular belly of the abductor pollicis brevis directly continues the lateral palmaris longus tendon in 23 cases.

Effects of the adductor pollicis and abductor pollicis brevis on thumb metacarpophalangeal joint laxity before and after ulnar collateral ligament reconstruction

“…16 The results of this investigation were in agreement with the qualitative descriptions of the force vectors of the intrinsic muscles inferred from their anatomy. 3,4,15 Both the AdP and the APB reportedly are active during opposition 5-10 and the results of this study show that they both pronate the proximal phalanx, which is important in positioning the thumb for tip pinch. The 2 muscles had opposing effects on radioulnar shift and radioulnar deviation as was expected because of their opposite insertions on the proximal phalanx.…”

“…2,3 The adductor pollicis (AdP) intrinsic muscle helps to maintain ulnar stability. [2][3][4] These intrinsic muscles act together with the flexor pollicis longus (FPL), the powerful extrinsic muscle that flexes the interphalangeal and MCP joints, to produce tip pinch.…”

Human abductor pollicis brevis muscle “divisions” and the nerve hila

“…Testut and Latarget (1948) reported a possible rare innervation by the anterior branch of the radial nerve and exceptionally by the ulnar nerve. A collateral nerve from the anterior branch of the radial nerve was seen entering the muscle in four cases out of 14 dissections (Fahrer, 1977). The radial nerve branch was stimulated in 260 hands but no contraction was elicited in the thenar muscles (Fahrer and Parker, 1981).…”

“…Testut and Latarget (1948) described the abductor pollicis brevis as originating from the lateral half fibers of the flexor retinaculum, the navicular (scaphoid) and trapezium carpal bones, and, "frequently," from the abductor pollicis longus tendon. In addition, Fahrer (1977) mentioned that the flexor carpi radialis canal contributes to the origin of the APB, and so does the palmaris longus tendon according to Napier (1952). Palmar skin muscular attachments were also noted by Kaplan (1965).…”

“…Napier (1952) insisted on the stabilizing action of the APB, especially at the conclusion of opposition. Furthermore, Fahrer (1977) associated the flexor and extensor actions on the first and second phalangeal joints of the abductor pollicis brevis with those of the lumbricals. McFarlane's (1962) anatomical work lead him to insist on the contribution of various intrinsic and extrinsic "bundles" within the thumb muscles to their contribution to the extension of the second phalangeal joint.…”