DOI:10.2214/AJR.07.2281
AJR 2007; 189:1190-1197
© American Roentgen Ray Society
Communicating Foramen Between the Tendon Sheaths of the Extensor Carpi Radialis Brevis and Extensor Pollicis Longus Muscles: Imaging of Cadavers and Patients
Oliver A. Cvitanic1,
Gregory M. Henzie1 and
Medhi Adham2
1 Southwest Oklahoma MRI, 230 SW 80th St., Oklahoma City, OK 73139.
2 Section of Plastic Surgery, Department of Surgery, University of Oklahoma
Health Sciences Center, Oklahoma City, OK.
Received September 20, 2006;
accepted after revision May 19, 2007.
Address correspondence to O. A. Cvitanic
(ocvitanic{at}aol.com).
Abstract
OBJECTIVE. The purpose of this study was to examine the anatomic
features and imaging appearance of the intersection of the extensor pollicis
longus (EPL) tendon with the extensor carpi radialis brevis (ECRB) and longus
(ECRL) tendons in cadavers and patients.
MATERIALS AND METHODS. MR and CT tenography were performed on 10
cadaveric wrists, and tenosynovial endoscopy and dissection of the EPL tendon
sheath were performed on five additional cadaveric wrists. A computer-assisted
search of dictated MRI reports identified 12 wrists of patients with
simultaneous EPL tenosynovitis and ECRB and ECRL tenosynovitis. The relation
between EPL tenosynovitis and ECRB and ECRL tenosynovitis was studied with
chi-square testing. Interobserver agreement was calculated with kappa
statistics.
RESULTS. MR and CT tenography revealed a communicating foramen
between the sheaths of the ECRB and EPL tendons in all 10 cadavers studied.
Endoscopic evaluation and dissection of five additional cadaveric wrists
further confirmed the presence of foramina. In the patients, the presence of
EPL tenosynovitis and that of ECRB and ECRL tenosynovitis had strong
correlation (p < 0.001). The incidence of simultaneous EPL
tenosynovitis and ECRB and ECRL tenosynovitis in our referral population of
wrist MRI examinations was 0.8% (12/1,540).
CONCLUSION. A normal foramen exists between the sheaths of the EPL
and ECRB tendons where they intersect in the wrist. Such foramina allow
synovial fluid to communicate between the tendon sheaths and probably account
for the high prevalence of tenosynovitis in more than one tendon on clinical
MRI studies.
Keywords: anatomy • intersection syndrome • tendon sheath • tenography • tenosynovitis
Introduction
Extensor tendinopathy is a common cause of dorsal wrist pain
[1–4].
Most of the injuries are overuse syndromes among non-athletic persons who
perform repetitive manual tasks, which can give rise to a variety of overuse
syndromes. Certain extensor tendons can be involved in more than one overuse
syndrome and in inflammatory arthritides and fractures. For these reasons, the
types of extensor tendinopathy can be difficult to differentiate clinically,
and MRI is frequently used to assist in diagnosis
(Table 1).
The extensor pollicis longus (EPL) muscle originates on the dorsal aspect
of the middle third of the ulna, traverses Lister's tubercle, obliquely
crosses over the extensor carpi radialis brevis (ECRB) and extensor carpi
radialis longus (ECRL) tendons, and inserts on the dorsal aspect of the distal
phalanx of the thumb. EPL tenosynovitis most often occurs after fractures of
the distal portion of the radius and is probably next most commonly found in
association with rheumatoid arthritis, which also involves other tendons. EPL
tenosynovitis due to overuse is rare, and no consensus exists regarding the
pathophysiologic mechanism [3].
The pain of EPL tenosynovitis characteristically initially involves the entire
dorsum of the wrist and later radiates to the thumb. EPL tenosynovitis is
often misdiagnosed clinically as de Quervain's disease. The effectiveness of
MRI in the diagnosis of EPL tendinopathy has been questioned
[5]. Specifically, it has been
claimed [5,
6] that the combination of
magic angle artifact (a localized increase in signal intensity on short-TE
pulse sequences in tendons in which the constituent collagen fibers are
oriented at 55° to the B field) and the small, flat configuration of the
EPL tendon impede visualization of the tendon.
The ECRB and ECRL muscles originate on the humerus and insert on the dorsum
of the bases of the second and third metacarpals. Functionally, the EPL tendon
extends the distal phalanx of the thumb, and the ECRB and ECRL tendons abduct
and extend the whole hand. When the thumb is abducted, the EPL tendon elevates
the skin to form the dorsomedial boundary of the anatomic snuffbox.
Tenosynovitis involving the extensor carpi tendons distal to Lister's tubercle
(wrist level) is frequently misinterpreted as intersection syndrome. True
intersection syndrome, however, is confined to the forearm and does not extend
into the wrist [2].
We have been unable to find satisfactory anatomic illustrations or clinical
images of the intersection of the EPL with the ECRB and ECRL tendons in the
wrist. Most standard anatomy references and dissection manuals show the
tendons completely separate at the point of intersection. In one dissection
study [7], however, the
anatomist found that the EPL tendon directly enters the common sheath of the
extensor carpi tendons at the intersection. Findings in another anatomic study
[8] suggested the existence of
a foramen between the sheaths of the EPL and the ECRB tendons. In a clinical
study [9], investigators
described communication of contrast material in the second, third, and fourth
dorsal extensor compartments after tendon sheath injections but did not
identify the precise location or nature of the communication.
The main purpose of this investigation was to use advanced medical imaging
techniques to assess the anatomic features of the intersection between the EPL
and the ECRB and ECRL tendons. We report the findings from high-resolution MRI
and CT of 10 cadaveric wrists after injection of contrast medium into the
tendon sheaths and from endoscopy and follow-up dissection of the EPL tendon
sheaths of an additional five cadaveric wrists. We also describe and discuss
the cases of 12 patients with the MRI appearance of simultaneous EPL
tenosynovitis and ECRB and ECRL tenosynovitis.
Materials and Methods
Technique of Tenography of Cadaveric Forearms
To help establish a baseline for normal tendon sheath anatomy, we studied
10 forearms from five fresh-frozen cadavers (four men, one woman; mean age at
death, 79 years; range, 71–84 years). One forearm was imaged before
tenography to establish an optimum protocol for MRI and CT. Dissection of the
dorsal aspect of each of the cadaveric forearms was performed to localize the
common sheath of the ECRB and ECRL tendons in five forearms and the sheath of
the EPL tendon in the five contralateral forearms. Dissections were performed
in concert by a plastic surgeon specializing in the upper extremity and a
musculoskeletal radiologist. A 22-gauge angiocatheter was threaded into each
of the exposed tendon sheaths. The catheter tips were positioned 1–2 cm
proximal to Lister's tubercle in each of the forearms. Catheter position was
confirmed with injection of 2–4 mL of iodinated contrast material
(iopromide, Ultravist, Bayer HealthCare) under fluoroscopic guidance. In
preparation for MRI, a maximum of 8 mL of gadopentetate dimeglumine
(Magnevist, Bayer HealthCare) diluted in saline solution (1 mL of
gadopentetate dimeglumine per 200 mL of normal saline solution) was injected
into each of the 10 forearms.
MR Tenography in Cadaveric Forearms
MRI was performed on a 3-T unit (Signa, GE Healthcare) with an
eight-channel phased-array dedicated wrist coil according to the following
parameters: axial T1-weighted fast spin-echo images with fat saturation
(TR/TEeff, 850/15); echo-train length, 2; matrix size, 512 x
256; number of signals averaged, 4; field of view, 8 cm; slice thickness, 2
mm; interslice gap, 0.5 mm. The axial images were obtained from the level of
the first carpometacarpal articulation proximal to Lister's tubercle for an
average length of 6 cm. A 3-T unit was used for the higher spatial resolution
it affords.
CT Tenography in Cadaveric Forearms
To exploit the high spatial resolution of helical CT, thin-slice CT was
performed within 5 minutes after MR tenography. No additional contrast
material was administered. The CT images were obtained with a 4-MDCT scanner
(LightSpeed Plus 4, GE Healthcare). The scanning parameters were as follows:
0.625-mm slice collimation width, 120 kVp, 100 mAs, 512 x 512 matrix,
detail reconstruction kernel. We compared the CT images with the corresponding
MR images to establish a consensus on the anatomy of the synovial sheath,
including the outline of the foramen.
Endoscopy and Dissection of Tendon Sheaths in Cadaveric Forearms
Five fresh-frozen forearms (three left, two right) from five cadavers
(three men, two women; mean age at death, 78 years; range, 70–89 years)
not used for tenography were obtained for anatomic study of the tendon sheath.
The surgeon and the radiologist performed endoscopy and dissection in concert.
In each forearm, the EPL tendon was transected at a level immediately proximal
to Lister's tubercle. After the sheath was flushed with saline solution, a
2.3-mm-diameter rigid endoscope was introduced into the proximal EPL tendon
sheath and advanced slowly beneath the tendon in the distal direction to
assess the sheath floor. After endoscopy, localized dissection of the EPL
tendon sheath was performed at the point of its intersection with the
ECRB.
Patients
A computer-assisted search of MRI reports dictated from July 2000 through
December 2006 was undertaken to find patients with an imaging diagnosis of
tenosynovitis of the wrist. The study was compliant with the HIPAA.
Institutional review board approval had been obtained, and retrospective
review of the images and telephone interviews with patients were allowed
without informed consent. The MRI studies and clinical records of patients
thus identified were reviewed. A total of 62 cases of tenosynovitis in 62
patients were identified (Fig.
1). Six of the 62 patients had distal radial fractures, and one
had rheumatoid arthritis. Twelve of the 62 patients had tenosynovitis
involving both the EPL and the ECRB and ECRL tendons
(Table 2). All 12 of these
patients (six women, six men; age range, 29–59 years) had dorsal wrist
pain, and eight had thumb pain. Seven of the 12 described use of the wrist in
heavy and repetitive gripping and twisting before the onset of symptoms.
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Fig. 1 —Histogram shows prevalence of tenosynovitis of wrist of all
causes by compartment. Values are numbers of patients among 62 with MRI
finding that given compartment was involved with tenosynovitis. ECU = extensor
carpi ulnaris, APL = abductor pollicis longus, EPB = extensor pollicis brevis,
ECRB = extensor carpi radialis brevis, ECRL = extensor carpi radialis longus,
EPL = extensor pollicis longus.
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TABLE 2: Clinical Findings Among Patients with Simultaneous Extensor Carpi
Radialis Brevis and Longus and Extensor Pollicis Longus Tenosynovitis in the
Absence of a Distal Radial Fracture or Rheumatoid Arthritis
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MRI in Clinical Subjects
The MR images were obtained with a 1.5-T unit (Signa, GE Healthcare) and a
commercially available quadrature wrist coil with the wrist in neutral
position. The axial, sagittal, and T1-weighted coronal pulse sequences were
performed with a 14-cm field of view, 3-mm slice thickness, 1-mm gap, 256
x 160 matrix, and 2 signals averaged. The fat-saturated T2-weighted
coronal sequences were obtained with a 14-cm field of view, 3-mm slice
thickness with 1-mm gap, 320 x 160 matrix, and 2 signals averaged. The
following five unenhanced MRI pulse sequences were performed: coronal
T1-weighted conventional spin-echo images (TR/TE, 550/22), coronal T2-weighted
fast spin-echo images with fat saturation (TR/TEeff, 1,850/60),
sagittal T1-weighted fast spin-echo images (TR/TEeff, 416/14),
axial proton density–weighted fast spin-echo images with fat saturation
(TR/TEeff, 2,300/30), and axial gradient-echo images (TR/TE,
600/15; 30° flip angle).
Prospective MR Image Interpretation
The computer search identified the prospective MRI interpretations in this
study. These interpretations were performed as part of the routine workload by
one of two radiologists over a 5-year period. Each of the radiologists had
more than 10 years of experience in musculoskeletal MRI. The integrity of the
triangular fibrocartilage, intrinsic ligaments, carpal bones, and tendons was
assessed. At interpretation, the radiologists were aware only of the clinical
data provided on the intake paperwork.
Retrospective MR Image Interpretation
The retrospective interpretations represented the second time the
radiologists evaluated the MR images of the 62 patients in the study group.
These interpretations were made independently solely for this study by the
same two radiologists who performed the prospective interpretations. The
retrospective interpretations specifically targeted peritendinous edema and
thickening or abnormal signal intensity in the tendons. Tenosynovitis was
diagnosed when edema completely surrounded a tendon over a length of at least
1.5 cm. This criterion was based on the authors' cumulative experience. It
also was decided that for the condition to be considered communicating
tenosynovitis, edema had to completely surround both the EPL and the ECRB
tendons at the point of intersection. Tendon thickening and intrinsic
T2-weighted hyperintensity were subjectively assessed by comparison with
tendons in the first, fourth, fifth, and sixth dorsal extensor compartments.
To avoid false-positive findings due to magic angle artifact, the T1-weighted
images were not assessed for abnormal tendon signal intensity.
Statistical Analysis
With data from the retrospective reinterpretations of all 62 cases gleaned
from the initial computer-assisted search, sensitivity and specificity were
calculated, and the chi-square test for paired data was performed to determine
whether an association existed between EPL tenosynovitis and ECRB and ECRL
tenosynovitis [10]. The null
hypothesis that no association exists between EPL tenosynovitis and ECRB and
ECRL tenosynovitis was rejected if p 
0.05, and 95% CIs were
calculated for sensitivity and specificity. Interobserver agreement regarding
the presence of EPL tenosynovitis and ECRB and ECRL tenosynovitis was
calculated with kappa statistics
[11].
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Fig. 2A —Cadaver of 80-year-old man with communicating foramen.
Sequential axial T1-weighted fat-suppressed MR images show contrast material
surrounding intersecting extensor pollicis longus (arrowhead),
extensor carpi radialis brevis (short arrow, A), and
extensor carpi radialis longus (long arrow, A)
tendons and outline of small shelf (dashed arrow, B
and C), which is part of foramen, in medial aspect of sheath separating
crossing tendons.
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Fig. 2B —Cadaver of 80-year-old man with communicating foramen.
Sequential axial T1-weighted fat-suppressed MR images show contrast material
surrounding intersecting extensor pollicis longus (arrowhead),
extensor carpi radialis brevis (short arrow, A), and
extensor carpi radialis longus (long arrow, A)
tendons and outline of small shelf (dashed arrow, B
and C), which is part of foramen, in medial aspect of sheath separating
crossing tendons.
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Fig. 2C —Cadaver of 80-year-old man with communicating foramen.
Sequential axial T1-weighted fat-suppressed MR images show contrast material
surrounding intersecting extensor pollicis longus (arrowhead),
extensor carpi radialis brevis (short arrow, A), and
extensor carpi radialis longus (long arrow, A)
tendons and outline of small shelf (dashed arrow, B
and C), which is part of foramen, in medial aspect of sheath separating
crossing tendons.
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Fig. 2D —Cadaver of 80-year-old man with communicating foramen.
Sequential axial T1-weighted fat-suppressed MR images show contrast material
surrounding intersecting extensor pollicis longus (arrowhead),
extensor carpi radialis brevis (short arrow, A), and
extensor carpi radialis longus (long arrow, A)
tendons and outline of small shelf (dashed arrow, B
and C), which is part of foramen, in medial aspect of sheath separating
crossing tendons.
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Results
MR and CT Tenography in Cadaveric Forearms
Both MR and CT tenography were effective in revealing communication between
the sheaths of the ECRB and EPL tendons in all 10 cadaveric forearms studied
(Figs. 2A,
2B,
2C,
2D and
3A,
3B,
3C,
3D). In every case, contrast
material appeared in the sheaths of the intersecting tendons into which
injections had not been made. Both MRI and CT findings confirmed a common
sheath of the ECRB and ECRL tendons before their divergence, which was
immediately distal to their intersection with the EPL tendon. The tendon
sheaths were outlined by contrast material from the point of injection in the
distal part of the forearm to the points of termination at the bone insertions
of the tendons. There was no obstruction to the flow of contrast material in
any of the tendon sheaths.
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Fig. 3A —Cadaver of 84-year-old man with communicating foramen.
Sequential axial CT images show contrast material in sheaths of extensor
pollicis longus (arrowhead), extensor carpi radialis brevis
(short arrow, A), and extensor carpi radialis longus
(long arrow, A) tendons. Small shelf (arrow,
C and D) inferior in relation to extensor pollicis longus tendon
is evident.
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Fig. 3B —Cadaver of 84-year-old man with communicating foramen.
Sequential axial CT images show contrast material in sheaths of extensor
pollicis longus (arrowhead), extensor carpi radialis brevis
(short arrow, A), and extensor carpi radialis longus
(long arrow, A) tendons. Small shelf (arrow,
C and D) inferior in relation to extensor pollicis longus tendon
is evident.
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Fig. 3C —Cadaver of 84-year-old man with communicating foramen.
Sequential axial CT images show contrast material in sheaths of extensor
pollicis longus (arrowhead), extensor carpi radialis brevis
(short arrow, A), and extensor carpi radialis longus
(long arrow, A) tendons. Small shelf (arrow,
C and D) inferior in relation to extensor pollicis longus tendon
is evident.
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Fig. 3D —Cadaver of 84-year-old man with communicating foramen.
Sequential axial CT images show contrast material in sheaths of extensor
pollicis longus (arrowhead), extensor carpi radialis brevis
(short arrow, A), and extensor carpi radialis longus
(long arrow, A) tendons. Small shelf (arrow,
C and D) inferior in relation to extensor pollicis longus tendon
is evident.
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Endoscopy and Dissection in Cadaveric Forearms
In all five specimens studied, findings at endoscopy and dissection of the
EPL tendon sheaths at the tendon intersection confirmed the presence of a
well-defined foramen between the sheaths of the EPL and ECRB tendons
(Fig. 4). These foramina
measured approximately 4–7 mm in width and 5–10 mm in length and
had semielastic margins.
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Fig. 4 —Cadaver of 78-year-old woman with communicating foramen.
Endoscopic image obtained from inside of extensor pollicis longus (EPL) tendon
sheath shows EPL tendon as it crosses over extensor carpi tendons. Edge of
foramen (arrows) is in foreground. ECRB = extensor carpi radialis
brevis tendon, ECRL = extensor carpi radialis longus tendon.
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Tenosynovitis in Clinical MRI
The probability of finding tenosynovitis in the EPL if tenosynovitis was
also present in the ECRB and ECRL was 86% with a 95% CI of 68–100%. The
probability of not finding tenosynovitis in the EPL if tenosynovitis was not
also present in the ECRB and ECRL was 96% with a 95% CI of 84–100%.
Strong association between EPL tenosynovitis and ECRB and ECRL tenosynovitis
was confirmed (p < 0.001). In effect, the ratio of cases of
simultaneous EPL, ECRB, and ECRL tenosynovitis to cases of isolated ECRB and
ECRL tenosynovitis or EPL tenosynovitis was 6:1. Interobserver agreement
regarding the detection of EPL tenosynovitis and ECRB and ECRL tenosynovitis
was excellent (
= 0.92). The ECRB and ECRL tendons had identical
thicknesses of peritendinous edema in all cases of tenosynovitis. None of the
involved tendons was abnormally thick, and no intrinsic abnormal signal
intensity was appreciated. In no case did the peritendinous edema extend
proximally into the forearm.
The finding in three of the six patients with distal radial fractures was
focal nonvisualization of the EPL tendon at the level of Lister's tubercle,
interpreted as tendon rupture. Two of these patients had evidence of both ECRB
and ECRL tenosynovitis and EPL tenosynovitis, and one of the patients had EPL
tenosynovitis alone. All of the patients with simultaneous ECRB and ECRL
tenosynovitis and EPL tenosynovitis listed in
Table 2 had the clinical
presentation of dorsoradial wrist pain. There also was a high frequency of
thumb pain, but no association between wrist pain and thumb pain was
confirmed.
Comparison of Prospective and Retrospective Interpretations
At the prospective screening interpretations, seven cases of simultaneous
EPL tenosynovitis and ECRB and ECRL tenosynovitis and seven cases of isolated
ECRB and ECRL tenosynovitis were diagnosed. In the retrospective
reinterpretations, however, five of the seven patients originally found to
have isolated ECRB and ECRL tenosynovitis were also found to have abnormal
peritendinous edema (tenosynovitis) in the EPL
(Fig. 1). Therefore, the total
number of cases of simultaneous ECRB and ECRL tenosynovitis and EPL
tenosynovitis increased from seven at prospective interpretation to 12 at
retrospective interpretation.
Surgical Findings and Clinical Follow-Up
One of the two patients who received surgical treatment underwent
synovectomy of the EPL and ECRB and ECRL tendon sheaths at the level of the
tendon intersection. The other underwent release of the second dorsal extensor
compartment at the level of the extensor retinaculum. In both cases, the
surgical notes described clear yellow serous fluid oozing from the incised
tendon sheaths, and the pathologic findings confirmed the presence of
synovitis. Symptoms resolved within 3 weeks after surgery in both cases. All
of the subjects who did not undergo surgical treatment took one or more
courses of oral nonsteroidal anti-inflammatory medications, and two also
received steroid injections. After this treatment, all but two patients,
including the two who had received steroid injections, described persistent
dorsal wrist pain (Table
2).
Discussion
In their dissection study of 40 wrists from adult cadavers, Zbrodowski et
al. [8] characterized the
communication between the EPL and ECRB tendons as an oval orifice 5–12
mm long and 2–4 mm wide. We found the orifice appeared to be somewhat
wider than Zbrodowski and colleagues indicated. In some cadaveric forearms,
the communication essentially equaled the width of the EPL tendon sheath
itself, raising questions about whether this area should be called a foramen
or merely a shared tendon sheath as suggested by Landsmeer
[7]. We chose to accept the
term "foramen" because we found small ingrowths of sheath between
the crossing tendons at the point of intersection
(Fig. 5). However, although
the existence of the foramen has been described, the implications of the
intersynovial communication for MRI interpretation have not.
Intersection syndrome in the forearm involves tenosynovitis of the ECRB and
ECRL tendons where the extensor tendons of the first dorsal compartment cross
over them. The mechanism of injury to the ECRB and ECRL tendons in forearm
intersections (intersection syndrome) has been postulated to involve either
stenosing tenosynovitis in the second compartment or direct impingement of the
tendons of the first dorsal extensor compartment on the underlying ECRB and
ECRL tendons. Concerning the intersection of the ECRB and ECRL tendons and EPL
tendon in the wrist, however, it is unlikely that either of these pathogenic
conditions exists. The important difference lies in the anatomy. Although the
ECRB and ECRL tendons are encased in a tight compartment in the forearm, no
such confinement exists in the distal aspect of the wrist, where tendons are
surrounded only by loose connective tissue. This configuration reduces the
likelihood of stenosing tenosynovitis in the ECRB and ECRL at the level of the
wrist. In addition, the absence of bone marrow edema in Lister's tubercle in
any of the clinical subjects in this study reduces the likelihood of
tendon-on-bone impingement. Regarding the potential for direct tendonon-tendon
impingement, the fact that the crossing EPL tendon has a significantly smaller
cross-sectional area than the underlying ECRB and ECRL tendons militates
against this possibility. As a result, we consider the potential for
tenosynovitis secondary to stenosis or impingement to be low.
The EPL, ECRB, and ECRL tendons were intrinsically normal in all of our
clinical MRI cases. Thus, we consider communicating tenosynovitis to be an
entirely peritendinous phenomenon (Fig.
6A,
6B,
6C). Although it is
theoretically possible that overuse can affect both tendon compartments
simultaneously, we found no evidence of this condition in the literature.
Because the ECRB and ECRL tendons are larger and more prone to tenosynovitis
than is the EPL tendon, we speculate that tenosynovitis probably begins in the
ECRB and ECRL tendon sheath and secondarily involves the EPL tendon sheath
[12,
13].
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Fig. 6A —47-year-old female ice cream shop worker with dorsal wrist
and thumb pain and surgically confirmed communicating tenosynovitis.
Sequential axial proton density–weighted fat-suppressed MR images
(TR/TEeff, 2,300/30) show thick peritendinous edema in extensor
carpi radialis brevis (short arrow, A) and longus
(long arrow, A) tendons and in crossing extensor
pollicis longus (arrowhead) tendon. Foramen is not evident.
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Fig. 6B —47-year-old female ice cream shop worker with dorsal wrist
and thumb pain and surgically confirmed communicating tenosynovitis.
Sequential axial proton density–weighted fat-suppressed MR images
(TR/TEeff, 2,300/30) show thick peritendinous edema in extensor
carpi radialis brevis (short arrow, A) and longus
(long arrow, A) tendons and in crossing extensor
pollicis longus (arrowhead) tendon. Foramen is not evident.
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Fig. 6C —47-year-old female ice cream shop worker with dorsal wrist
and thumb pain and surgically confirmed communicating tenosynovitis.
Sequential axial proton density–weighted fat-suppressed MR images
(TR/TEeff, 2,300/30) show thick peritendinous edema in extensor
carpi radialis brevis (short arrow, A) and longus
(long arrow, A) tendons and in crossing extensor
pollicis longus (arrowhead) tendon. Foramen is not evident.
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Regarding the treatment of patients with conventional EPL tenosynovitis,
steroid injections are discouraged because they are associated with an
increased risk of rupture of the EPL tendon
[14]. By contrast, surgical
release of the third dorsal extensor compartment has had documented success in
two case reports [3,
14]. Current guidelines favor
an initial trial of conservative care before surgery
[3]. In this study, favorable
clinical outcome was achieved in the cases of two patients who underwent
synovectomy; results were mixed after conservative measures.
Lack of recognition of EPL tenosynovitis at prospective interpretation in
five of the 12 cases seems to support the concerns expressed by other authors
[5] regarding the limitations
of MRI in assessment of the EPL tendon. We believe, however, that the increase
in sensitivity for EPL tenosynovitis in the targeted retrospective
interpretations compared with the prospective interpretations in this study
highlighted observer performance more than the efficacy of MRI. Failure to
thoroughly evaluate all extensor tendons was probably responsible for the
relatively poor observer performance at prospective interpretation.
Several limitations of this study were identified. First, the advanced age
of the cadavers in this study means that it is at least theoretically possible
that the foramina we evaluated were actually degenerative perforations of the
tendon sheath. Second, the small number of patients in this study limited our
ability to assess whether passive intersynovial transfer of fluid and any
accompanying cells from an inflamed tendon sheath might have been sufficient
to cause secondary inflammatory tenosynovitis in the crossing tendon. A larger
number of patients are needed to answer this question and to determine whether
MRI has value in differentiating primary inflammatory tenosynovitis and
passive intersynovial decompression of fluid through a foramen. Third,
selection bias was present because only patients who had undergone MRI were
included. In effect, MRI might not have been performed if the clinical index
of suspicion for tendinopathy had been either very high or very low.
To our knowledge, the appearance of the communicating foramen between the
ECRB and EPL tendons has not been previously studied with MRI or CT. We used
3.0-T MRI and helical CT to confirm the presence of foramina in cadavers. In
the clinical component of the study we identified a high (0.8%) incidence of
simultaneous ECRB and ECRL tenosynovitis and EPL tenosynovitis, an association
that has not, to our knowledge, been previously reported. We suggest this
association stems directly from the communicating foramen. However, the
question whether the communicating synovial fluid and cells can induce active
inflammation in the sheath of the crossing tendon was not answered.
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Abstract
Introduction
