AJR 2002; 178:1451-1457
© American Roentgen Ray Society
Sonography of the Finger
Girolamo Moschilla1 and
William Breidahl
1 Both authors: Department of Diagnostic and Interventional Radiology, Royal
Perth Hospital, Wellington St., GPO Box X2213, Perth, Western Australia, 6847
Australia.
Received November 1, 2000;
accepted after revision December 6, 2001.
Address correspondence to G. Moschilla.
Introduction
The development of high-frequency sonography probes has allowed the imaging
of small superficial structures at resolutions of 300 µm. Small
"footprint" probes have improved the ability of radiologists to
scan small curved surfaces such as a finger. Our purpose is to show the value
of sonography in the evaluation of finger pathology. Sonography was performed
with a broadband 7.5- to 10-MHz linear array scan head with the transducer
placed directly on the skin using abundant coupling gel. A 3-mm-thick standoff
gel pad may be useful for assessment of superficial (e.g., cutaneous) lesions.
We describe the main sonographic findings in a variety of lesions.
Traumatic Lesions
Foreign bodies that may be radiolucent on radiography, such as nonopaque
glass fragments, wood splinters, and palm spikes, are accurately detected on
sonography [1]. Wooden foreign
bodies as small as 2.5 mm in length can be effectively localized
[2]. They appear as hyperechoic
structures with variable acoustic shadowing. If they have been present for
more than a week, they develop a hypoechoic rim of variable thickness that
represents a foreign body reaction or abscess formation
(Fig. 1).
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Fig. 1. —Longitudinal sonogram of 38-year-old man who presented after
injury while gardening shows fragment of palm spike (arrow) posterior
to third metacarpal (M) and proximal phalanx (P). Note surrounding hypoechoic
reaction to foreign body.
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Injuries to the ulnar collateral ligament (UCL) of the first
metacarpophalangeal joint are common. The injury is often referred to as
gamekeeper's thumb or skier's thumb. Sonography can identify a tear of the UCL
and differentiate displaced and nondisplaced tears. Injuries in which the UCL
is displaced superficially to the adductor aponeurosis (Stener lesion) may
require surgical intervention, whereas nondisplaced tears can be treated
conservatively [3]. With
complete tears, the displaced UCL is seen as a linear echogenic structure that
is redundant and retracted with a hypoechoic hematoma surrounding the
redundant margin (Fig.
2A,2B,2C,2D,2E).
An avulsed fragment, if present, is seen as a small hyperechoic structure.
With incomplete tears, the UCL may be markedly thickened but in a normal
position. Previous studies have found that sonographic findings correspond to
surgical findings in up to 90% of cases of proven UCL tears
[3]. Collateral ligament
injuries may also be shown at the second to fifth metacarpophalangeal joints
(Fig.
3A,3B).
The index and little fingers are most commonly involved, and the radial
collateral ligament is most commonly affected.
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Fig. 2A. —Ulnar collateral ligament (UCL) injury of right thumb.
Drawing shows position of probe used to evaluate UCL. Sonography probe is
applied to ulnar side of first metacarpophalangeal joint in longitudinal
orientation following anatomic course of UCL.
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Fig. 2C. —Ulnar collateral ligament (UCL) injury of right thumb.
Sonogram obtained in same patient as in B shows complete tear of UCL of
right thumb, with hypoechoic mass adjacent to metacarpal head (m) and loss of
continuity of ligament. p = base of proximal phalanx, small arrow = proximal
margin of torn UCL, large arrow = distal end of UCL tear.
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Fig. 2D. —Ulnar collateral ligament (UCL) injury of right thumb.
Drawing shows Stener lesion. Torn UCL is displaced and trapped superficially
to adductor aponeurosis. Torn ligament cannot return to its normal position
beneath adductor aponeurosis; therefore, surgical repair is required.
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Fig. 2E. —Ulnar collateral ligament (UCL) injury of right thumb.
Transverse sonogram of 33-year-old man shows Stener lesion with hypoechoic UCL
(open arrow) superficial to echogenic adductor aponeurosis (AD APON,
solid arrow).
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Fig. 3A. —Ulnar collateral ligament (UCL) injury of left ring finger in
22-year-old man. Cursors indicate metacarpal head. Comparative transverse
sonograms show dorsal—ulnar aspect of metacarpal head of ring finger.
UCL on left (X) is much thicker than that on right (Y).
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Fig. 3B. —Ulnar collateral ligament (UCL) injury of left ring finger in
22-year-old man. Cursors indicate metacarpal head. Axial proton density
fat-saturated MR image of left hand shows that UCL (arrows) of ring
finger is thickened and edematous, consistent with previous tear.
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Sonography can depict all the tendons of the hand and fingers from their
myotendinous origin to their osseous insertion. Partial tendon tears are seen
as tendon swelling, focal tendon hypoechogenicity, and signs of incomplete
tendon discontinuity. With complete tears, the tendon is not visualized at the
site of injury, and its retracted ends can be seen proximally and distally
(Fig. 4).
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Fig. 4. —Tendon laceration in 31-year-old woman. Longitudinal
composite sonogram obtained in dual mode of left index finger just proximal to
meta carpophalangeal joint shows laceration with complete tear of flexor
digitorum superficialis with loss of continuity and thickened retracted
proximal end (thick solid arrow). LT = left, thin solid arrow =
distal flexor digitorum superficialis, open arrow = intact flexor digitorum
profundus, curved arrow = retained glass fragment.
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An echogenic focus in the retracted tendon may represent an avulsed bone
fragment (Fig.
5A,5B,5C).
Acutely, effusion in the tendon sheath is usually seen. Sonography is also
useful in assessing surgically repaired tendons and in distinguishing
tenodesis (adhesions) from retears (Fig.
6).
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Fig. 5A. —Flexor digitorum profundus avulsion in 28-year-old man.
Lateral radiograph of left ring finger shows radiolucency at volar aspect of
base of distal phalanx. Small avulsed bone fragment lies anterior to head of
proximal phalanx (arrow).
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Fig. 5B. —Flexor digitorum profundus avulsion in 28-year-old man.
Comparative longitudinal sonogram of left and right ring fingers shows distal
interphalangeal joints. Normal fibrillar echogenic flexor digitorum profundus
tendon inserts into base of distal phalanx (right image, arrows) of
right ring finger. Left flexor digitorum profundus tendon is absent (left
image, arrow).
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Fig. 5C. —Flexor digitorum profundus avulsion in 28-year-old man.
Longitudinal sonogram obtained volar to metacarpal of left ring finger shows
echogenic focus deep in relation to normal flexor digitorum superficialis
tendon, representing avulsed bone fragment (open arrow). Retracted
flexor digitorum profundus tendon appears as hypoechoic mass (solid
arrows). SUP = superior.
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Fig. 6. —Dehiscence of tendon repair in 40-year-old man. Longitudinal
sonogram obtained at level of carpometacarpal joint of thumb shows that
redundant suture material (between calipers) is present between
proximal and distal retracted extensor pollicis brevis (EPB) tendon margins
(arrows). With intact repair, there is no tendon defect.
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Dynamic imaging of the finger tendons can be helpful in distinguishing a
normal finger tendon from one that has adhesions. Disruption of the finger
flexor (annular) pulley system is a recognized injury in elite rock climbers.
The injury involves disruption of the A2 pulley of the fibrous retinacular
sheath that arises from the distal end of the base of the proximal phalanx and
extends 20 mm toward the proximal interphalangeal joint
[4]. A tear of the A2 pulley
results in volar subluxation of the flexor tendons. Sonography shows an
increased distance between the volar cortex of the proximal phalanx and the
flexor tendons, which becomes more pronounced on active finger flexion
(bowstringing) [5] (Fig.
7A,7B,7C).
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Fig. 7A. —Acute A2 pulley injury of left index finger in 23-year-old
man. Schematic diagram of flexor pulley system in en face projection
shows that fibrous retinacular sheath for fingers is divided into five annular
(A) bands and three cruciform (C) ligaments and extends from neck of
metacarpal and ends at distal phalanx.
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Fig. 7B. —Acute A2 pulley injury of left index finger in 23-year-old
man. Comparative side-by-side longitudinal sonograms of abnormal left and
normal flexor tendons of right index finger obtained in extension volar to
proximal shaft of proximal phalanx show that effusion surrounds flexor tendons
on left, which are displaced anteriorly relative to bony cortex
(arrows).
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Fig. 7C. —Acute A2 pulley injury of left index finger in 23-year-old
man. Comparative sonograms of abnormal left index finger obtained in extension
(left) and with resisted flexion (right) show that deep aspect of flexor
tendon (curved arrow) becomes further displaced anteriorly from bony
cortex (straight arrow) in flexion.
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Extensor hood injuries of the finger occur rarely in patients without
rheumatoid arthritis. The injury involves disruption of the sagittal bands of
the hood with subluxation or dislocation of the extensor tendon to the side of
the metacarpophalangeal joint. Tears usually involve the radial sagittal band
with ulnar subluxation of the extensor tendons
[6,
7] (Figs.
8A,8B
and
9A,9B).
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Fig. 9A. —Extensor hood injury in 42-year-old woman. Transverse
sonogram obtained through dorsal aspect of left middle finger shows
subluxation of extensor tendon (arrow) to side of proximal phalanx.
Note hypoechoic soft-tissue swelling in expected location of extensor
tendon.
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Inflammatory and Metaplastic Conditions
Sonography can be used in the diagnosis of tenosynovitis, which can be
inflammatory or infective in origin. In tenosynovitis, the synovial thickening
and fluid appear as hypoechoic regions surrounding the echogenic tendon
(Fig. 10). Power Doppler
sonography may help to distinguish thickened synovium from fluid by depicting
flow in the vascularized synovium. Sonographically guided aspiration of fluid
and injection with steroids can be performed. Hypertrophic synovitis, if
present in cases of rheumatoid or psoriatic arthropathy, will be evident as
hyperechoic villous projections in the synovial fluid
[1]. Metaplastic conditions
such as synovial chondromatosis can also be evaluated on sonography
(Fig. 11).
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Fig. 10. —Tenosynovitis in 36-year-old man. Transverse sonogram of
right thenar eminence shows normal echogenic flexor pollicis longus tendon (F)
surrounded by increased amount of hypoechoic synovial fluid
(arrow).
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Localized Masses
Localized masses of the finger may be further characterized on sonography.
Ganglia appear as well-defined anechoic structures with posterior enhancement
(Fig. 12). Digital ganglia
occur at the base of the fingers, the third and fourth being most commonly
involved [1]. Sonography is
useful in evaluating a ganglion's size, location, and relation to adjacent
structures, as well as for needle aspiration or steroid injection.
Giant cell tumor of the tendon sheath is the second most common cause of a
finger mass. The tumor is a benign lesion that has a high risk for local
recurrence. Histologically, the tumor cells resemble synoviocytes that
proliferate into solid nodular aggregates
[8]. On sonography, giant cell
tumors appear as hypoechoic solid masses with well-defined margins, usually
close to the flexor tendons. Unlike ganglia, these tumors have internal echoes
and lack posterior acoustic enhancement. Doppler sonography can show internal
vascularity (Fig.
13A,13B).
Local excision is the treatment of choice.
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Fig. 13A. —Giant cell tumor of tendon sheath in 38-year-old man.
Transverse (A) and longitudinal (B) sonograms show giant cell
tumor (arrows) of extensor tendon (EXT TN, cursors) sheath.
M = middle phalanx.
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Fig. 13B. —Giant cell tumor of tendon sheath in 38-year-old man.
Transverse (A) and longitudinal (B) sonograms show giant cell
tumor (arrows) of extensor tendon (EXT TN, cursors) sheath.
M = middle phalanx.
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The morphologic appearances of a giant cell tumor of the tendon sheath are
not specific, and a fibroma of tendon sheath may have an identical appearance
(Fig. 14).
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Fig. 14. —Fibroma of tendon sheath in 32-year-old woman. Longitudinal
sonogram obtained at volar aspect of interphalangeal joint of thumb shows
well-circumscribed hypoechoic mass (solid arrows) in contact with
palmar surface of flexor pollicis longus tendon (FPL, open arrow)
just proximal to its insertion.
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Glomus tumors are seen as solid homogenous hypoechoic masses in the
subungual or palmar aspects of the finger. No one finger or site is most
commonly involved. Phalangeal erosions may be seen, and Doppler sonography
shows marked hypervascularity
[1] (Fig.
15A,15B).
A lesion that occurs in the subungual aspect of the finger is a mucous cyst.
This benign lesion predominately occurs in elderly women in the index and long
fingers. Osteoarthritis of the distal interphalangeal joint is a frequent
associated finding. Like a ganglion, this lesion tends to be anechoic and
shows enhanced transmission (Fig.
16). A synovia-lined pedicle connects the mucous cyst and the
adjacent distal interphalangeal joint. Failure to resect the pedicle and the
adjacent osteophyte at surgery will predispose to recurrence.
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Fig. 16. —Mucous cyst in 62-year-old woman. Longitudinal sonogram shows
mucous cyst (thin arrow) of right middle finger at dorsal aspect of
distal phalanx (D). Open arrow = nail, PHLX = phalanx.
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In conclusion, sonography is useful for evaluating a variety of lesions of
the finger. Its wide spread availability, relatively low cost, and high
spatial resolution make it an excellent tool for investigating finger
disorders.
Acknowledgments
We thank Barbara Taylor and the department of medical illustrations of
Royal Perth Hospital and the imaging services of Royal Perth Hospital and
Perth Radiological Clinic for their assistance in completing this
manuscript.
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Introduction
Traumatic Lesions
