Ultrasound of the palmar aspect of the hand: normal anatomy and clinical applications of intrinsic muscles imaging

Abstract

Intrinsic hand muscles play a fundamental role in tuning the fine motricity of the hand and may be affected by several pathologic conditions, including traumatic injuries, atrophic changes induced by denervation, and space-occupying masses. Modern hand surgery techniques allow to target several hand muscle pathologies and, as a direct consequence, requests for hand imaging now carry increasingly complex diagnostic questions. The progressive refinement of ultrasound technology and the current availability of high and ultra-high frequency linear transducers that allow the investigation of intrinsic hand muscles and tendons with incomparable resolution have made this modality an essential tool for the evaluation of pathological processes involving these tiny structures. Indeed, intrinsic hand muscles lie in a superficial position and are amenable to investigation by means of transducers with frequency bands superior to 20 MHz, offering clear advantages in terms of resolution and costs compared to magnetic resonance imaging. In addition, ultrasound allows to perform dynamic maneuvers that can critically enhance its diagnostic power, by examining the questioned structure during stress tests that simulate the conditions eliciting clinical symptoms. The present article aims to review the anatomy, the ultrasound scanning technique, and the clinical application of thenar, hypothenar, lumbricals and interossei muscles imaging, also showing some examples of pathology involving these structures.

Keywords: hand imaging; hypothenar; lumbricals; thenar; ultrasound.

Fig. 1.

Thenar eminence anatomy. Anatomic dissection, schematic drawing, and oblique 18–5 MHz US image demonstrate the normal anatomy of the thenar eminence muscles. APB – abductor pollicis brevis; FPB₁ – the superficial belly of the flexor pollicis brevis; FPB₂ – the deep belly of the flexor pollicis brevis; AddP – adductor pollicis; OppP – opponens pollicis; Int – I dorsal interosseous; I Met – I metacarpal; II Met – II metacarpal; I lum – I lumbrical muscle; arrow – flexor pollicis longus tendon. The bar in A indicates the position of the probe in C

Fig. 2.

Strain injury of the thenar muscles in a patient with distraction trauma of the first metacarpophalangeal joint. A. Short-axis 22–8 MHz US image obtained at the level of the first metacarpal neck demonstrates edematous changes with muscle hyperechogenicity (arrowheads) affecting the abductor pollicis brevis (APB), the opponens pollicis (OppP), and the most radial fibers of the flexor pollicis brevis (FPB), corresponding to a grade I distraction injury. B. Correlative transverse oblique tSE T2-weighted MRI with fat saturation shows high signal intensity corresponding to edema at the distal myotendinous junction of the abductor pollicis brevis (arrowhead) and opponens pollicis (outlined arrowhead). Note mild edema of the flexor pollicis brevis (asterisk) and minor strain of the intramuscular aponeurosis of the adductor pollicis (arrow). Outlined arrow, flexor pollicis longus tendon; Int, first dorsal interosseous muscle. C. Long-axis 22–8 MHz US image shows a full thickness tear (arrowhead) of the ulnar collateral ligament of the first metacarpophalangeal joint (UCL). The torn ligament maintains its regular position underneath the adductor aponeurosis (arrows), so the patient was managed conservatively. I Pha – first phalanx; I Met – first metacarpala

Fig. 3.

Intramuscular lipoma in a patient with a progressively enlarging lump at the thenar eminence. A. Transverse and B. Longitudinal 22–8 MHz US images demonstrate a large hyperechoic lesion (arrow) located inside the muscle belly of the adductor pollicis (AddP). The mass lies over the bony cortex of the II metacarpal and dislocates superficially the flexor tendons for the index (FT) and the first lumbrical muscle (I Lum). Note the striated echotexture characteristic of lipomatous tumor. Histologic analysis confirmed a well-differentiated lipoma and the patient was managed conservatively

Fig. 4.

Hypothenar eminence anatomy. Anatomic dissection, schematic drawing, and oblique 18-5MHz US image demonstrate the normal anatomy of the hypothenar muscles. ADM – abductor digiti minimi; FDM – flexor digiti minimi; ODM – opponens digiti minimi; V int – third ventral interosseous; D Int – fourth dorsal interosseous; FR – flexor retinaculum; Pis – pisiform; outlined arrowhead – pisohamate hiatus; IV Met – fourth metacarpal; V Met – fifth metacarpal. The bar in A indicates the position of the probe in C

Fig. 5.

Hypothenar muscle wasting in a patient with right ulnar nerve neurotmesis repaired through epineurial suture. A. Transverse and B. Longitudinal 22-8 MHz US image obtained at the level of the proximal Guyon tunnel demonstrates a hypertrophic intraneural scar (arrows) located inside the ulnar nerve (white arrowhead), with loss of the fascicular echotexture and derangement of the axons. Note the suture (outlined arrowhead) inside the nerve. These findings should be interpreted as a failure in nerve healing with the development of a neuroma-in-continuity. Pis – pisiform; black arrowhead – ulnar artery. C. Transverse 18-5MHz US image demonstrated atrophy of the Abductor (ADM) Opponens (ODM) and Flexor (FDM) digiti minimi. VM, fifth metacarpal

Fig. 6.

Intramuscular arteriovenous malformation in a patient with a soft lump at the level of the hypothenar eminence. A, B. Short-axis 24–8 MHz US images obtained at the level of the hypothenar eminence, A with and B without exerting compression of the soft tissue with the probe, respectively, demonstrate a compressible mass (arrows) with a mixed echotexture consisting of ectasic and convoluted vascular structures (outlined arrowheads) surrounded by a hyperechoic matrix. The mass is located inside the muscle bellies of the abductor (ADM) and flexor (FDM) digiti minimi, whereas the opponens (ODM) is spared. C. Short-axis 24–8 MHz doppler image shows flow signals inside the convoluted vessels. These findings are consistent with an arteriovenous malformation

Fig. 7.

Lumbrical muscles, normal anatomy. A. Schematic drawing demonstrates the relationship of the lumbricals with the deep transverse intermetacarpal ligaments (star) and their distal insertions on the lateral band (outlined arrow), Landsmeer ligament (black arrowhead) and transverse fibers of the extensor hood (asterisk). Black arrow, central band. B, C. Short axis 22–8 MHz US images obtained at the level of the distal third of the metacarpals show the position of the second (II Lum), third (III Lum), and fourth (IV Lum) lumbricals in between the tendon slips for the index, middle, and ring finger of the flexor digitorum superficialis (IIS, IIIS, and IVS) and flexor digitorum profundus (IIP, IIIP, and IVP). Note in (B) the unipennate origin of the second lumbrical from the radial side of the tendon slip for the middle of the flexor digitorum profundus and in (C) the bipennate origin of the third lumbrical from the ulnar side of the tendon slip for the middle and from the radial side of the tendon slip for the ring. Arrowheads, common digital nerves; outlined arrowheads, common digital arteries

Fig. 8.

Selective atrophy of the second lumbrical in a patient with traumatic injury of the first common digital nerve. A. Long-axis 22–8 MHz US demonstrates the transected first common digital nerve (arrowheads) ending with a stump neuroma (arrow). Short-axis axis 22–8 MHz US shows severe atrophic changes affecting the second lumbrical (II Lum). Note the normal aspect of the third lumbrical muscle (III Lum) which in this patient presents a bipennate origin from the slips of the flexor digitorum profundus for the middle (IIIP) and ring (IVP) fingers. IIIS, flexor digitorum superficialis of the middle finger; IVS flexor digitorum superficialis of the ring finger

Fig. 9.

Dorsal and Ventral Interossei, normal anatomy. A, B. Schematic drawings show the proximal and distal insertions of the dorsal and ventral Interossei from the metacarpal shafts and the phalanges, respectively. C, D. Short-axis 22–8 MHz US images respectively obtained placing the probe on the dorsal and palmar aspect of the hand at the level of the metacarpal shafts demonstrate the normal appearance of the second (II DI) and third (III DI) dorsal and the first (I VI) and second (II VI) ventral interossei. Met – metacarpal shafts; II L and III L – second and third lumbricals; FT – flexor tendons

Fig. 10.

First dorsal interosseous strain injury in a patient with traumatic full thickness tear of the radial collateral ligament of the second metacarpophalangeal joint. A, B. Longitudinal 22-8 MHz US images respectively obtained A. at the level and B. proximal to the radial aspect of the second metacarpophalangeal joint show severe swelling and inhomogeneous appearance of the preinsertional part (arrowheads) of the distal tendon of the first dorsal interosseous (I DI), in relation to a strain injury. A partial tear (outlined arrowhead) of the deep fibers of the interosseous tendon is demonstrated extending in depth and involving the full thickness of the radial collateral ligament (arrows). C, D. Short-axis 22-8 MHz US images of the first dorsal interosseous of the C affected and D. contralateral hand demonstrate edematous changes with significant hyperechogenicity of the muscle belly associated with mild thickening of the intramuscular aponeurosis (arrowhead). E. Coronal STIR MRI confirms the full thickness tear of the ligament (arrow), which shows a hyperintense cleft (outlined arrowhead) in its proximal part. Note moderate edematous changes of the distal tendon of the first dorsal interosseous (arrowhead), which appears thickened and hyperintense