Sonographic Evaluation of the Thenar ompartment Musculature Wolfgang Grechenig, MD, Gerolf Peicha, MD, ndreas Weiglein, MD, Peter Tesch, MD, Karin Lawrence, MD, Johannes Mayr, MD, Klaus W. Preidler, MD The thenar region was studied with ultrasonography in 10 healthy volunteers. ll thenar muscles could be identified and their course followed entirely. In addition, their function could be assessed by scanning during unresisted or resisted active movements. Standard approach, normal appearance, and dynamic tests for each muscle are described. KEY WORDS: Thumb, anatomy; Thenar muscles; Muscles, thenar. Thenar muscle anatomy is complex. It includes several muscles that are responsible for the enormous range of motion of the thumb. Pathologic changes of the thumb are typically the result of either traumatic events or osteoarthritis and frequently cause severe clinical symptoms. In many cases, pathologic changes of the thenar muscles are responsible for temporary disability of the patients, since the thumb is essential for normal grip function of the hand. MR, Magnetic resonance REVITIONS Received November 9, 1999, from the Departments of Traumatology (W.G., G.P.), Pediatric Surgery (K.L., J.M.), and Radiology (K.W.P.) and the natomical Institute (.W., P.T.), Karl Franzens University of Graz, Graz, ustria. Revised manuscript accepted for publication July 24, 2000. ddress correspondence and reprint requests to Gerolf Peicha, MD, Department of Traumatology, Karl Franzens University of Graz, uenbruggerplatz 7, 8036 Graz, ustria. Diagnostic evaluation includes conventional radiography to rule out bony abnormalities and MR imaging for diagnosing pathologic soft tissue conditions. lthough MR imaging is an exquisite and elegant technique, high costs and limited availability restrict its daily clinical use. onsequently, ultrasonography has been gaining a role of growing importance in the evaluation of soft tissues of the limbs. While a number of studies deal with anatomy and various pathologic conditions in the human hand, 1 13 none has concentrated on normal sonomorphology of the thenar muscles and on a standardized examination technique, including defined scan planes that guarantee complete sonomorphologic assessment of the thenar soft tissue. Therefore, we established a standardized examination technique for sonomorphologic assessment of the thenar muscles and to describe their normal sonographic appearance. The thenar region comprises four muscles operating the carpometacarpal joint of the thumb: abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and adductor pollicis. 2000 by the merican Institute of Ultrasound in Medicine J Ultrasound Med 19:733 741, 2000 0278-4297/00/$3.50
734 THENR OMPRTMENT MUSULTURE J Ultrasound Med 19:733 741, 2000 PTIENTS ND METHODS Sonographic evaluation of the thenar muscles of 10 healthy volunteers, 16 to 50 years of age, was performed using a 12 MHz linear array transducer (HDI 5000; TL, othell, W). Patients sat with their arms resting on a table in a relaxed position during the examination. transducer with a small surface area was applied directly onto the skin using an acoustic coupling gel (Gerot, Vienna, ustria). ccess was gained from the palmar surface of the hand (supination of the forearm, with the dorsal aspect of hand and forearm in broad contact with the examination table) for all patients, except for the evaluation of the first dorsal interosseous muscle. For that purpose, the forearm and the hand were in pronation, and the transducer was applied to the dorsal aspect of the first interdigital space. Sonomorphologic evaluation was done first in a static position and then in an additional functional step, with active and passive motions of the different muscles. dditionally, 10 cadaver specimens were assessed to determine the correct angles of transducer position. RESULTS Sonographically all thenar muscles could be identified reliably. The entire course of each muscle could be outlined by placing the transducer orthograde to the specific muscle group initially and angulating the transducer in all directions. Orthograde position means that the transducer is positioned parallel to the direction of the muscle fibers without building any oblique angle. ll muscles showed typical echotexture (hypoechoic area surrounded by a hyperechoic fascia), although hyperechogenicity varied significantly depending on the position of the transducer in relation to the axial orientation of the muscle fibers to fascial planes. The thenar region comprises four muscles operating the carpometacarpal joint of the thumb: abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and adductor pollicis (Fig. 1). The flexor pollicis brevis muscle is composed of a superficial and a deep head, while the adductor muscle consists of an oblique and transverse head. The tendon of the flexor pollicis longus muscle divides these muscles into two groups. Lying to its radial side and forming the thenar eminence, the abductor pollicis brevis muscle, the opponens muscle, and the Figure 1, Schematic drawing of the the thenar anatomy from a palmar view., Schematic drawing shows muscle and vascular anatomy from palmar view after removal of the abductor pollicis brevis muscle and the flexor pollicis brevis muscle (superficial head). M. add. poll. aput transv., transverse head of adductor pollicis; M. add. poll. aput obliq., oblique head of adductor pollicis; Fs, flexor pollicis brevis, superficial head; Fp, flexor pollicis brevis, deep head; M. abd. poll. brev., abductor pollicis brevis; FR, flexor carpi radialis tendon; M. opponens poll., opponens pollicis; FPL, flexor pollicis longus tendon.
J Ultrasound Med 19:733 741, 2000 GREHENIG ET L 735 superficial head of the flexor pollicis brevis muscle can be observed; on the ulnar aspect the deep head of the flexor pollicis brevis muscle and the adductor pollicis muscle are localized. The abductor pollicis brevis muscle takes origin from the flexor retinaculum and the tubercles of the scaphoid and trapezium. This broad and flat muscle runs parallel to the lateral border of the hand, inserting on the radial aspect of the proximal phalanx of the thumb and on the tendon of the extensor pollicis longus muscle. The opponens pollicis muscle lies deep to the abductor. It also arises from the tubercles of the scaphoid and the trapezium, runs in a more oblique direction, and attaches to the lateral margin of the first metacarpal bone. The flexor pollicis brevis muscle lies medial to the abductor muscle. Its superficial head arises from the flexor retinaculum and adjacent trapezium and passes along the radial aspect of the long flexor tendon. The deep head arises from the trapezoid and capitate bones and crosses deep to the long flexor tendon to merge with the superficial head; the common distal tendon finally becomes attached to the proximal phalanx of the thumb via the radial sesamoid bone. The oblique head of the adductor pollicis arises from the bases of the second and third metacarpal bones and the trapezoid and capitate bones. The transverse head arises from the entire length of the radial aspect of the third metacarpal bone. It crosses the first dorsal interosseous muscle anteriorly and attaches via the ulnar sesamoid bone to the base of the proximal phalanx of the thumb adjacent to the flexor pollicis brevis muscle. The first dorsal interosseous muscle is bipennate, originates from the the first and second metacarpal bones, and attaches to the radial margin of the dorsal aspect of the index finger. The radial artery crosses the first interosseous space between the two heads of the first interosseous muscle. The artery then courses underneath the oblique head of the adductor pollicis and emerges between the oblique and transverse heads or passes through the latter to form the deep palmar arch. Ultrasonographic Technique In principle, longitudinal, transverse, and oblique sections can be obtained by passing the transducer across the whole thenar region in a fan shaped manner. For assessment of each muscle individually, the transducer should be placed initially orthograde to the muscle and then should be angulated in all directions to view the muscle in its entire extent. ompared to the cadaver investigation, the following transducer positions have proved to be the most efficient: Position 1: Opponens and bductor Pollicis revis Muscles Hold the ultrasonographic transducer parallel to the lateral margin of the first metacarpal bone on the palmar aspect of the hand to visualize the opponens muscle. To show the abductor pollicis brevis muscle in total extension, the transducer must be positioned upon the radial sesamoid bone and pivoted to make a range of about 20 degrees (Fig. 2). The angle between the transducer and the midline of the hand should be about 120 degrees (Fig. 2). Position 2: bductor Pollicis revis and Flexor Pollicis revis Muscles, Long Flexor Tendon Positioning the transducer on the palmar surface at a right angle to the first metacarpal bone demonstrates the abductor pollicis brevis and the flexor pollicis brevis muscles as well as the long flexor tendon in a transverse section (Fig. 3). Position 3: bductor Pollicis and Flexor Pollicis revis Muscles (Superficial and Deep Heads) Positioning the transducer from the palmar surface between the first and second metacarpal bones displays the adductor pollicis muscle and the superficial and deep heads of the flexor pollicis brevis muscle in a transverse section (Fig. 4). Position 4: dductor Pollicis Muscle (Transverse and Oblique Heads) To show both the transverse and oblique heads of the adductor pollicis in total extension, the transducer should be positioned upon the ulnar sesamoid bone and pivoted to make a range of about 60 to 70 degrees (Fig. 5). The angle between transducer and midline of the hand should be about 65 degrees for the demonstration of the transverse head and about 50 to 55 degrees for the display of the oblique head (Fig. 5, ).
736 THENR OMPRTMENT MUSULTURE J Ultrasound Med 19:733 741, 2000 Figure 2 Ultrasonographic scan approximately parallel to the first metacarpal bone (angle between transducer and midline of the hand approximately 120 degrees) from the palmar surface., Schematic drawing shows the scan plane., Photograph shows the probe position in vivo., Ultrasonographic scan shows a longitudinal section of abductor pollicis brevis and deeper opponens muscles at their sites of origin. Note fascia between abductor pollicis and opponens muscles (arrow). M. D. POLL., bductor pollicis brevis; M. OPP. POLL., opponens pollicis; OS TRP., trapezium bone; M I, first metacarpal base. Muscle Function Tests The following muscle function tests can be performed: Flexor Pollicis Longus Muscle Position 5: First Dorsal Interosseous and dductor Pollicis Muscles From the dorsum of the hand, position the transducer parallel to the second metacarpal bone to view the first interosseous space with the first dorsal interosseous muscle in longitudinal section; palmar to it, the adductor pollicis in a transverse oblique section for the transverse head and in an oblique section for the oblique head, respectively, can be visualized (Fig. 6). Position 6: First Dorsal Interosseous and dductor Muscles hanging the transducer position about 90 degrees compared to position 5, the first dorsal interosseous and the adductor muscles in the first interosseous space can be observed in a transverse section (Fig. 7). While maintaining the metacarpophalangeal joint in full extension either with a splint or with a free finger of the examiner, lead the distal phalanx of the thumb through full flexion in the plane of the hand. Test active movement without or with pressure against the volar aspect of the distal phalanx. Flexor Pollicis revis Muscle fter fixation of the first metacarpal bone, ask the patient to flex the thumb in the metacarpophalangeal joint while keeping the interphalangeal joint relaxed. This movement can be resisted by application of a force to the volar aspect of the proximal phalanx.
J Ultrasound Med 19:733 741, 2000 GREHENIG ET L 737 Figure 3 Ultrasonographic scan perpendicular to the first metacarpal bone (midshaft) from the palmar surface., Schematic drawing shows the scan plane (either dashed or solid line)., Photograph shows the probe position in vivo (dashed line in )., bductor pollicis and opponens pollicis muscles are shown in transverse sections superficial to the first metacarpal bone. Medially, the superficial and deep heads of the flexor pollicis brevis muscle can be outlined, with the tendon of the long flexor pollicis muscle between (arrows). M. D. POLL., bductor pollicis brevis; M. OPP. POLL., opponens pollicis; M I, first metacarpal bone; P. SUP., flexor pollicis brevis, superficial head; P. PROF., flexor pollicis brevis, deep head. bductor Pollicis revis Muscle While the second to fifth metacarpal bones and the wrist joint are being immobilized, ask the patient to abduct the thumb at a right angle to the plane of the hand. Resistance can be applied to the lateral border of the proximal phalanx of the thumb. First Interosseous Muscle This muscle is examined from the dorsum of the hand, with the forearm in pronation. bduction of the fingers in relation to the middle phalanx is performed after fixation of the metacarpal bones. Muscle power is tested by pressure onto the radial aspect of the index finger. Opponens Muscle The patient approaches the volar surface of the distal phalanx of the thumb with the little finger. This movement is resisted by pressing onto the palmar aspect of the head of the first metacarpal bone.
738 THENR OMPRTMENT MUSULTURE J Ultrasound Med 19:733 741, 2000 Figure 4 Transverse ultrasonographic scan between the first and second metacarpal bones from the palmar surface., Schematic drawing shows the scan plane (either dashed or solid line)., Photograph shows the probe position in vivo (dashed line in )., Ultrasonographic scan shows both heads of flexor pollicis brevis muscle in the transverse plane. More deeply, adductor pollicis and first dorsal interosseous muscles can be delineated. Note the tendons of the flexor pollicis longus muscle (right arrow) and of the flexor muscle of the index finger (left arrow), respectively. P. S., Flexor pollicis brevis, superficial head; P. P., flexor pollicis brevis, deep head; M. DD. POLL., adductor pollicis muscle; M. INTEROSS. DORS. I, first dorsal interosseous muscle; M I, first metacarpal bone; M II, second metacarpal bone. DISUSSION Evaluation of hand injuries and diseases can be a diagnostic challenge to the clinician because of the complicated anatomy of the hand with its multiple joints, muscles, tendons, fascial planes, and neurovascular pathways. In addition to the physical examination, MR imaging has been gaining an important role in the assessment of soft tissue structures. However, restricted availibility and relatively high costs of this technique limit its routine clinical use. In addition, general anesthesia is often required in pediatric patients to avoid motion artifacts. Numerous abnormalities and pathologic changes of the thenar region may require ultrasonographic imaging including atrophy of the thenar muscles in the case of carpal tunnel syndrome, foreign bodies, articular effusion of the carpometacarpal joint of the thumb, and fractures of the first metacarpal bone or tumors (e.g., ganglion cysts). Supposedly ultrasonographic evaluation of the thenar region is of limited or no value in patients who have had surgery or injuries causing a certain degree of scarring so that an orthograde positioning of the transducer is not available. With the introduction of high frequency transducers, ultrasonography has been established as an excellent diagnostic tool for superficial soft tissue assessment. s a relatively low cost and noninvasive technique, it offers the additional advantage of dynamic and functional muscle assessment. Over the past few years, numerous studies on acute and chronic affections of the hand have been published, dealing in particular with the carpal tunnel syndrome, infections, tumors, and posttraumatic entities. 1 13 However, we found no paper focused specifically on the sonoanatomy of the thenar region, including a description of the scan planes necessary for individual muscle assessment. Detailed knowl-
J Ultrasound Med 19:733 741, 2000 GREHENIG ET L 739 D Figure 5 Transverse ultrasonographic scan from the palmar surface between the second and third metacarpal bones., Schematic drawing shows the scan plane., Photograph shows the probe position in vivo., Ultrasonographic scan shows the tranverse head of adductor pollicis muscle with distinct fascial planes (arrows). Note the palmar interosseous muscle between the second and third metacarpal bones, deep to the adductor pollicis muscle. M. DD. POLL. P. TRNSV., dductor pollicis, transverse head; M II, second metacarpal bone; M III, third metacarpal bone; M. INTEROSS. PLM., palmar interosseous muscle; FD II, second finger flexor muscle; FD III, third finger flexor muscle. D, Scan shows the oblique head of adductor pollicis muscle in a longitudinal orientation (parallel to muscle fibers), including its origin. Note the lumbrical muscle in superficial position. M. DD. POLL. P. OLIQ., dductor pollicis, oblique head; M. LUMR., lumbrical muscle; P., capitate bone; M III, third metacarpal bone. edge about the normal anatomic appearance of the thenar region and particularly a standardized examination procedure, including functional assessment, are essential for recognition, interpretation, and topographic localization of pathologic entities in the thenar region. However, the only aim of this study was to show the ability of ultrasonographic evaluation of all the components of the thenar compartment and to map out the origins and insertions of the specific muscles.
740 THENR OMPRTMENT MUSULTURE J Ultrasound Med 19:733 741, 2000 Figure 6 Ultrasonographic scan of the first interossous space from dorsal position, approximately parallel to the second metatarsal bone., Schematic drawing shows the scan plane., Photograph shows the probe position in vivo., Scan shows the first dorsal interosseous muscle in a longitudinal direction and palmar adductor pollicis muscle in a more transverse oblique section. M. INTEROSS. DORS. I, First dorsal interosseous muscle; M. DD. POLL., adductor pollicis muscle. Figure 7 Ultrasonographic scan perpendicular to the scan plane used in Figure 6 from dorsal position., Schematic drawing shows the scan plane., Photograph shows the probe position in vivo., Scan shows the first dorsal interosseous muscle in a cross section between the first and second metacarpal bones and superficial to adductor pollicis muscle. Note distinct fascial planes (arrows). M. INTEROSS. DORS. I, First dorsal interosseous muscle; M. DD. POLL., adductor pollicis muscle; M I, first metacarpal bone; M II, second metacarpal bone.
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