Keywords
wrist - tendons - MR-imaging - ultrasound - intersection syndrome - De Quervain tenosynovitis
Abbreviations
ACP:
acute calcific periarthritis
APL:
abductor pollicis longus
DECT:
dual-energy computed tomography
ECRB:
extensor carpi radialis brevis
ECRL:
extensor carpi radialis longus
ECU:
extensor carpi ulnaris
EDC:
extensor digitorum communis
EDM:
extensor digiti minimi
EI:
extensor indicis
EPB:
extensor pollicis brevis
EPL:
extensor pollicis longus
FCR:
flexor carpi radialis
FCRB:
flexor carpi radialis brevis
FCU:
flexor carpi ulnaris
FPL:
flexor pollicis longus
MCP:
metacarpophalangeal joint
MRI:
magnetic resonance imaging
PL:
palmaris longus
RA:
rheumatoid arthritis
STT:
scapho-trapezium-trapezoid
UTE:
ultrashort echo time
Introduction
The anatomy of the wrist tendons can be divided into the flexor and extensor tendons
based on their function and location. Furthermore, the extensor tendons can be assigned
to different compartments defined by the extensor retinaculum. Anatomic variants of
the tendons and muscles are common and must be distinguished from pathological findings.
Pathologies of the wrist tendons are common and are especially reported among individuals
involved in activities with repetitive stress on their wrists, e.g., de Quervain tenosynovitis,
which is more common in mothers. Imaging techniques such as ultrasound and magnetic
resonance are suitable for depicting the different pathologic conditions. However,
advanced imaging techniques like dual-energy computed tomography will also be briefly
discussed. In this article, we will review the normal anatomy and anatomical variants
of the wrist tendons and provide an overview of common pathologies and their presentation
on imaging. This will be done by discussing common pathologies and imaging modalities
especially in context with the current literature. However, this article does not
represent a meta-analysis but rather an overview on these topics, and thus might be
considered an unstructured literature review with a focus on clinical relevance. Additionally,
postoperative findings will be not discussed in this article. Nevertheless, we believe
that we are providing a structured review of a clinically relevant topic that might
be of value for interested readers.
Imaging techniques
Ultrasound has gained popularity in the daily clinical practice of hand surgeons and
has become a routine diagnostic tool. The lack of ionizing radiation and the low cost,
portability, dynamic real-time assessment, and comparison with the unaffected hand
are some of the advantages [1]. An additional benefit of ultrasound is that it can be more readily available than
other cross-sectional imaging. The ancillary use of duplex Doppler and power Doppler
can further reveal blood flow on the synovial membranes and is recommended for the
detection of tenosynovitis [2]
[3]. The superficial location of the wrist tendons allows the use of high-frequency
ultrasound probes with high spatial resolution. Tendons at the level of the wrist
can be examined with a linear ultrasound transducer (10–18 MHz) or even a high-frequency
ultrasound probe (14–33 MHz) such as a “hockey stick” transducer with a smaller field-of-view
[2]. In the setting of distal radius fractures, diagnostic ultrasound is an accurate
tool with a sensitivity and specificity of 88% and 99%, respectively, for identifying
a specific tendon as ruptured and 88% and 87%, respectively, for tendon abnormalities
in general [4]. While ultrasound is dependent on the experience of the examiner, MRI is a noninvasive
imaging technique that can produce cross-sectional images on any plane, allowing simultaneous
examination of soft tissues, synovium, tendons, articular cartilage, and bone. It
delivers the information obtained by ultrasound more objectively and with higher contrast
resolution and is considered as the reference standard [5]. In the setting of early inflammatory arthritis, MRI appears to be more sensitive
than ultrasound for detecting tenosynovitis [6]
[7] and its use may be helpful for detecting ongoing disease in rheumatoid arthritis
[8]. Bone marrow edema that cannot be depicted on ultrasound can be visualized via MRI,
which is especially of interest in the setting of rheumatoid arthritis, where it is
thought to be a strong predictor for erosive progression [9]
[10]. When comparing 1.5T systems with 3T systems, the latter should be favored, because
it provides a nearly twofold increase in signal-to-noise ratio, that can be used to
increase the speed of imaging, achieve a better contrast-to-noise ratio, and improve
spatial resolution [11]. The use of 7.0T to image the musculoskeletal system is still in the early, primarily
research stages. In tendon imaging there is a special focus on ultrashort echo time
(UTE) magnetic resonance imaging, which makes it possible to image short T2 tissues,
such as tendons, with a high signal. However, most of the UTE-MRI techniques are still
in the validation phase [12].
Computed tomography is in general not used for tendon imaging. However, dual-energy
computed tomography is used in the diagnosis of gout arthropathy, which can involve
the wrist tendons as well, with a reported sensitivity and specificity of 89% and
91%, respectively [13].
Specific tendon pathologies are going to be addressed in this article while providing
an overview of parameters on different imaging modalities.
Anatomy of the extensor tendons of the wrist
Anatomy of the extensor tendons of the wrist
At the level of the distal forearm, the extensor tendons are guided through six dorsal
extensor sheets ([Fig. 1]), formed by the extensor retinaculum, a strong, fibrous, oblique running band, consisting
of a strengthened part of the distal forearm fascia. The extensor retinaculum runs
from the anterior border of the radius to the triquetral and pisiform bones. Beginning
at the radius and moving toward the ulna, the first dorsal compartment contains the
abductor pollicis longus (APL) and the extensor pollicis brevis (EPB) tendons [14]
[15]. In 40% of cases, there may be a complete or partial septation between the two tendons,
which splits the compartment into two sub-compartments [16]. The APL tendon frequently consists of multiple bundles, with even up to nine bundles
described in the literature [17]
[18]. Thus, the diagnosis of splitting of the APL tendon should be handled with caution.
Fig. 1 Normal anatomy of the wrist at the level of the extensor retinaculum on an axial T2-weighted
MR image. The colored arrows point to the extensor tendons, with the color-matched
roman numerals indicating their equivalent extensor compartment. I (blue arrows) =
first extensor compartment containing the abductor pollicis longus (APL) and the extensor
pollicis brevis (EPB) tendons. II (orange arrows) = second extensor compartment containing
the extensor carpi radialis longus (ECRL) and the extensor carpi radialis brevis (ECRB)
tendons. III (green arrow) = third extensor compartment containing the extensor pollicis
longus tendon (EPL). IV (red arrows) = fourth extensor compartment containing the
extensor digitorum (ED) and extensor indicis (EI) tendons. V (grey arrow) = fifth
extensor compartment containing the extensor digiti minimi tendon (EDM). VI (yellow
arrow) = sixth extensor compartment containing the extensor carpi ulnaris tendon (ECU).
The white arrow points to Lister’s tubercle (LT), separating the II from the III compartment.
The mnemonic at the bottom of the image makes it easier to remember the sequence of
-longus and -brevis in the first three extensor compartments.
Approximately four to eight centimeters proximal to the dorsal tubercle of the radius
(Lister’s tubercle) lies the “proximal intersection” (proximal crossing), where the
tendons from the first compartment run across over tendons of the second extensor
compartment [14]. The latter is located between the first compartment and Lister’s tubercle and contains
the extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB)
tendons with communicating tendon sheets. They also communicate through a normal foramen
with the extensor pollicis longus (EPL) tendon at the distal intersection point [19]. Thus, if fluid is present in the tendon sheath at this distal location it tends
to surround all three tendons (ECRL, ECRB, EPL). The ECRL inserts at the dorsum of
the second metacarpal bone. The ECRB runs on the ulnar side of the ECRL and inserts
at the base of the third metacarpal bone and the adjacent parts of the second, and
sometimes forth metacarpal bone [15]. Additional muscle and tendon segments are common in the second extensor compartment
[14]. The EPL tendon is located in the third dorsal extensor compartment. The EPL tendon
passes on the ulnar side of the Lister’s tubercle, crosses obliquely above the radial
wrist extensor tendons, and forms the “anatomical snuffbox” at the base of the thumb
with the EPB tendon. The EPL lies immediately adjacent to the EPB tendon at the dorsolateral
aspect of the first metacarpophalangeal joint (MCP) and inserts at the base of the
distal phalanx of the thumb [15]. Of note: To make it easier to remember the names of the tendons of the first three
extensor compartments, it is helpful to know that they end alternating: “Longus, Brevis, Longus, Brevis, Longus” (APL, EPB, ECRL, ECRB, EPL) ([Fig. 1]) [20].
The fourth dorsal compartment of the wrist contains the extensor indicis (EI) and
the extensor digitorum communis (EDC) tendons. The fifth dorsal compartment of the
wrist contains the extensor digiti minimi (EDM) tendon, which commonly has two slips.
The sixth dorsal compartment contains the extensor carpi ulnaris (ECU) tendon [14]
[15]
[21]. The tendon is formed by spiral fibers originating from two muscle bellies with
fibrovascular tissue at the center of the tendons at the level of the distal radioulnar
joint, explaining a frequently found centrally increased signal within the tendon
[22]. At the level of the distal ulna, the ECU tendon is covered by a subsheath. The
tendon’s position in the wrist changes with forearm pronation and supination undergoing
a physiologic movement and can be seen outside the ulnar groove on axial MR imaging
and ultrasound in asymptomatic subjects in supination [23]
[24]
[25]. The ECU tendon inserts at the base of the 5th metacarpal on the dorsal surface [15].
Common pathologies of the extensor tendons of the wrist
Common pathologies of the extensor tendons of the wrist
De Quervain tenosynovitis
De Quervain tendinopathy is defined as tenosynovitis of the first dorsal extensor
compartment tendons (APL and EPB), as they pass through the fibro-osseous sheath at
the wrist joint. Commonly seen as an overuse injury in activities involving repeated
movements of the hand such as radioulnar deviation or repetitive gripping with the
thumb, it has been described during pregnancy and in the immediate postpartum period
(thought to be a result of endocrine influences and fluid retention) in new mothers
(prolonged carrying of babies with the wrist held in flexion and ulnar deviation and
with the thumb in extension) and in athletes participating in golf or racquet sports.
Risk factors include female gender and increased age, repeated or sustained wrist
bending activities, and twisting motions [26]
[27]
[28]
[29]
[30]
[31]. The diagnosis is usually made by physical examination, termed the Finkelstein test
[32]. The patient presents with wrist pain localized to the dorsoradial side of the wrist,
with gradual onset of pain not associated with trauma, with limitation of thumb motion,
and with swelling [26]
[33]. MRI and ultrasound might be able to identify various changes associated with de
Quervain tenosynovitis, such as sheath or retinaculum thickening, increase in tendon
thickness, and presence of sheath effusion often with surrounding reactive soft tissue
([Fig. 2]) [34]. The appearance of tendinopathy can range from mild tendon swelling to longitudinal
splitting of the tendon in severe cases [35]. Based on ultrasound-guided studies, the retinacular sheath is nearly three times
thicker in patients with de Quervain tenosynovitis [36].
Fig. 2 (A and B) De Quervain’s tenosynovitis in a 59-year-old man. Longitudinal (A) and transverse (B) ultrasound images showing the first extensor compartment. The white arrows show
thickening of the overlying retinaculum and the synovial sheath. (C) Ultrasound image of De Quervain’s tenosynovitis in a 64-year-old woman shows that
the pathology is additionally accompanied by peritendinous subcutaneous (arrowhead)
and synovial hyperemia (arrow) on Doppler imaging at the first extensor compartment.
Rad = Radius; Scaph = Scaphoid; Trap = Trapezium; EPB = extensor pollicis longus;
APL = abductor pollicis longus.
Nonsurgical treatment includes rest and splinting and can be combined later on with
corticosteroid injections into the first extensor compartment. If conservative treatment
fails, surgical release may be necessary [26]
[37].
Patients with de Quervain disease are more likely to have a septum dividing the compartment
(62.2%) in comparison to normal cadaver wrists (43.7%), which has implications for
both conservative and surgical treatment, because the presence of a septum may limit
the reach of the injected steroid to only a portion of the compartment and surgical
treatment may result in inadequate decompression of all compartments [38]
[39]. Ultrasound is a useful tool to depict such types of anatomic variations in the
first extensor compartment [39].
Proximal intersection syndrome
Proximal intersection syndrome refers to noninfectious peritendinous inflammation
due to overuse at the site where the tendons of the first dorsal extensor compartment
(APL and EPB) cross the tendons of the second dorsal compartment (ECRL and ECRB),
approximately 4 to 8 cm proximal to Lister’s tubercle. The most commonly proposed
etiology is due to friction [26]
[40], while others have postulated stenosis of the second extensor compartment [41]. Reported activities involve repetitive flexion and extension of the wrist, frequently
seen in association with athletic activities, including rowing [42], skiing [43], and tennis [44]. The syndrome is also seen in patients working with agricultural or digging tools
as well as in carpenters, office workers [45], and supermarket checkout clerks [46]. Patients present with pain proximal to the wrist, located dorsally, often with
localized swelling at the intersection of the first and second dorsal compartments,
and there is often audible crepitus or “squeaking” with wrist motion [47]
[48]. The proximal location should be taken into account when planning the MR examination,
as most standard wrist MRI protocols will not include this area [49]. On ultrasound, edematous changes in the APL and EPB (typically at the myotendinous
junctions), the loss of a hyperechoic plane dividing the two different compartments,
sheath effusion and swelling, typically of the tendons in the second extensor compartment
can be noted [2]. MRI findings include peritendinous edema and fluid around all four tendons at the
point of the intersection, commonly adjacent subcutaneous edema, and proximal and
distal extension of the peritendinous edema and fluid ([Fig. 3]) [50]
[51].
Fig. 3 T2-weighted fat-saturated axial MR image in an 18-year-old female at the level of
the proximal intersection in the distal forearm. Shown is the crossing of the first
extensor compartment tendons (blue arrows; APL= abductor pollicis longus, EPB = extensor
pollicis brevis), over the second extensor compartment tendons (orange arrows; ECRL
= extensor carpi radialis longus, ECRB = extensor carpi radialis brevis). Fluid around
all four tendons can be noted in this patient with proximal intersection syndrome
(white arrow).
Distal intersection syndrome
Distal intersection syndrome is located distal to Lister’s tubercle, where the third
extensor compartment tendon (EPL) crosses over the second extensor compartment tendons
(ECRL and ECRB). It is less common than the classic forearm intersection syndrome.
Patients sometimes present after a traumatic event and symptoms can mimic those of
osteoarthritis or a ganglion cyst. Due to mechanical friction, Lister’s tubercle can
irritate the EPL, particularly if there has been a previous fracture [52]
[53]
[54]. The inflammation can spread to the communicating second and third extensor compartments
at the crossing point [19]. Imaging shows peritendinous edema, fluid, and distention of the second and third
extensor compartment at their crossing point, and additional findings like tendinosis
with thickening and/or increased signal on fluid-sensitive sequences on MRI in the
EPL, ECRB, and ECRL ([Fig. 4]), partial tendon tears, and reactive marrow edema of Lister’s tubercle [52]
[54]. Most patients respond to conservative treatment, but some patients may progress
to a complete tear of the extensor pollicis longus needing synovectomy and tendon
repair [52]
[54].
Fig. 4 T2-weighted fat-saturated MR image of a 33-year-old female with distal intersection
syndrome. The extensor pollicis longus tendon (EPL; green arrow) crosses over the
second extensor compartment tendons (orange arrows; ECRL = extensor carpi radialis
longus tendon, ECRB = extensor carpi radialis brevis tendon). Fluid around all three
tendons can be noted (white arrows).
Extensor pollicis longus tendon rupture at the level of Lister’s tubercle
Rupture of the EPL tendon is a well described complication of distal radius fractures,
with a reported incidence of 0.2–5%, occurring on average 6–8 weeks after fracture
[55]. On imaging, a tendon tear is seen as discontinuity of the tendon, stump retraction,
and fluid in the tendon gap, which appears hypoechoic on ultrasound ([Fig. 5]) and hyperintense on fluid-sensitive MR sequences [56]. The mechanical theory hypothesizes that there are dorsal cortical irregularities
from fractures that can injure the tendon. The vascular theory outlines a watershed
area of the EPL tendon at the level of Lister’s tubercle in which the tendon sheath
is poorly vascularized, whereby almost all nutrition is provided by the synovial fluid.
Swelling, edema, and hematomas narrow the space and result in increased pressure on
the EPL tendon in the watershed area, thereby decreasing vascularity and nutrition
and eventually causing ischemia and rupture [55]. The incidence is higher in nondisplaced fractures versus displaced fractures, suggesting
that an intact extensor retinaculum, which most likely is the case in nondisplaced
distal radius fractures, creates a rigid space in which the EPL tendon becomes compressed
by the aforementioned swelling, edema, hematoma and eventually in a later stage by
fracture callus [55]. Extensor tendon ruptures were also noted after volar plating, including damage
secondary to screw penetration of the dorsal cortex, with the EPL tendon being the
most ruptured extensor tendon [57]. Spontaneous EPL tendon ruptures can occur with underlying chronic inflammation
such as rheumatoid arthritis or use of local or systemic steroids [58].
Fig. 5 (A and B) 46-year-old man after a fall on ice. Lateral radiograph of the wrist (A) shows a slightly dislocated distal radius fracture with a dorsal cortical step off
(arrow). The combined longitudinal ultrasound images (B) depict the full thickness tear of the extensor pollicis longus tendon (EPL) with
retraction of the EPL stumps (arrows). The dehiscence of the tendon stumps is visualized
by the green markers. The radius fracture is located between the retracted stumps
(arrowhead). Rad = Radius.
Extensor carpi ulnaris subsheath injury
The ECU tendon in the sixth dorsal extensor compartment is additionally held in place
at the level of the ulnar head by the ECU subsheath to prevent subluxation with wrist
rotation [14]
[26]. A rupture of this subsheath can result in a luxation of the ECU tendon especially
in supination ([Fig. 6]). Most patients recall a traumatic episode, and many of these episodes involve a
sporting activity like tennis or golf, where supination, ulnar deviation, and wrist
flexion increase the angulation of the ECU tendon relative to the ulna, resulting
in maximal force upon the ECU subsheath [59]
[60]. Three types of disruption of the fibro-osseous sheath are reported ([Fig. 7]) [61]. The fibro-osseous sheath can rupture ulnar, and the torn sheath will then lay superficial
to the tendon. When the fibro-osseous sheath ruptures radially, the torn sheath lies
in the ulnar groove beneath the tendon. And lastly, a detachment of the periosteum
from the ulnar side of the ulna in continuity with the fibro-osseous sheath can occur,
forming a false pouch into which the tendon can dislocate [61]. Ultrasound is the modality of choice to check for ECU subsheath injury, due to
the possibility of dynamic evaluation of instability ([Fig. 8]). In supination, the unstable ECU tendon subluxates/luxates volarly while relocating
into the groove with pronation. Additionally, it gives the opportunity to examine
the contralateral side to make sure the subluxation is not physiologic [24]
[62]. However, this diagnosis might be harder on MRI if the exam is only performed in
pronation. Other MRI signs of subsheath injuries include tendinopathy, tenosynovitis,
and marrow edema in the ulnar head, while acute injuries of the subsheath will be
associated with edema and hemorrhage surrounding the tendon [60]
[63]. The clinical significance of the tendon subluxation or dislocation is questionable,
as it can be found in asymptomatic volunteers [23]
[24].
Fig. 6 Axial T2-weighted MR image of a 33-year-old man. Posttraumatic rupture of the extensor
carpi ulnaris subsheath (arrow) with luxation of the extensor carpi ulnaris tendon
(arrowhead).
Fig. 7 The three patterns of disruption of the extensor carpi ulnaris subsheath (green) are
shown in this schematic illustration. The disruption of the subsheath results in transient
dislocation of the extensor carpi ulnaris tendon (orange) in supination (left side),
followed by relocation in pronation (right side). In A the fibro-osseous sheath is ruptured on the ulnar side, resulting in transient dislocation
of the tendon in supination, followed by relocation in pronation, with the tendon
returning to a position beneath the subsheath. When the fibro-osseous sheath ruptures
radially (B), the tendon will lie on top of the torn subsheath after relocation in pronation.
In C, a detachment of the periosteum occurred on the ulnar side of the ulna in continuity
with the fibro-osseous sheath, forming a false pouch into which the extensor carpi
ulnaris tendon can dislocate in supination.
Fig. 8 A dynamic ultrasound examination of a 20-year-old female with ulnar-sided wrist pain
reveals luxation (arrow) of the extensor carpi ulnaris tendon (asterisk) over the
styloid process of the ulna (S) in supination, compared to neutral position which
shows the tendon more centered in the ulnar groove (G). Of note: R marks the distal
radius.
Anatomy of the flexor tendons of the wrist
Anatomy of the flexor tendons of the wrist
Most flexor tendons of the wrist are located deep with respect to the flexor retinaculum
(transverse carpal ligament) ([Fig. 9]). The flexor retinaculum is a fascial band located at the volar aspect of the hand,
near the wrist, forming the carpal tunnel [15]. It attaches radial to the scaphoid tubercle and the trapezium and ulnar to the
pisiform and hook of the hamate [14]. From superficial to deep, the tunnel contains the flexor digitorum superficialis
tendons and the flexor digitorum profundus tendons on the ulnar side, and the median
nerve and flexor pollicis longus tendon (FPL) on the radial side. Three flexor tendons
run outside the carpal tunnel: the flexor carpi ulnaris tendon (FCU), which attaches
to the pisiform bone, the flexor carpi radialis tendon (FCR), and the palmaris longus
tendon (PL) [15]
[26]. The FCR runs radial to the carpal tunnel in its own fibro-osseous tunnel separated
from the carpal tunnel by a vertical retinacular septum [64]. The palmaris longus lies subcutaneous above the flexor retinaculum and is present
in at least 75–85% of the population [15]
[26].
Fig. 9 Axial T2-weighted MR images of the wrist showing the flexor tendons: (A) at the level of the distal radius, (B) at the level of the proximal carpal row showing the insertion of the flexor carpi
ulnaris tendon (FCU; yellow arrow) to the pisiform bone (asterisk), (C) at the level of the flexor retinaculum. The tendons of the flexor pollicis longus
(FPL; orange arrow), flexor digitorum superficialis (FDS, grey arrows) and flexor
digitorum profundus (FDP; red arrows) course inside the carpal tunnel, while the tendon
of the flexor carpi radialis (FCR; blue arrow) courses in its own fibro-osseous sheath.
PL (green arrow) = palmaris longus tendon.
Common pathologies of the flexor tendons of the wrist
Common pathologies of the flexor tendons of the wrist
Flexor tendon ruptures
Flexor tendon ruptures can occur accidentally, e.g., due to an injury with a knife.
Additionally, flexor tendon ruptures can occur after distal radius volar plating.
Approximately 33% of surgeons reported in a time period over one year after plating
at least one flexor tendon injury, with the flexor pollicis longus being the most
commonly reported tendon injury [57]. On imaging, the tendon tear is seen – as described earlier in the setting of EPL
tendon ruptures – as a discontinuity of the tendon, stump retraction, and fluid in
the tendon gap that is hypoechoic on ultrasound and hyperintense on fluid-sensitive
MR sequences.
Flexor carpi radialis tendinopathy
At the level of the wrist, the FCR tendon runs in a close anatomical relation to the
subjacent volar surfaces of the scaphoid and trapezium, in contact with the volar
aspect of the capsule of the scapho–trapezium–trapezoid (STT) articulation or triscaphe
joint. This close relationship to the STT bones can make the tendon vulnerable to
injury by cortical bone irregularities as have been described in case reports in scaphoid
fracture [65], fracture malunion [66], and joint degeneration [67]. The coexistence of FCR tendinopathy and STT arthritis can be demonstrated by MR
imaging. It can lead to a partial-thickness tear or complete discontinuity of the
FCR tendon ([Fig. 10]) [67].
Fig. 10 (A) sagittal T2-weighted fat-saturated MR image of a normal flexor carpi radialis tendon
(arrowhead) inserting at the base of the second metacarpal bone (arrow). (B) sagittal image of the wrist of a 69-year-old female. The patient reported radiopalmar
pain without history of trauma. The open arrowheads delineate the retracted stumps
of the torn flexor carpi radialis tendon. II = Second metacarpal bone; Td = Trapezoid;
S = Scaphoid; R = Radius.
Anatomical variants
In most cases the lumbrical muscles arise from the flexor digitorum profundus tendons
just distal to the carpal tunnel [15]
[68]. In about 22% of individuals, the most proximal portions of the lumbrical muscles
can be found between the deep flexor tendons within the carpal tunnel ([Fig. 11]) [68] and can be a cause of carpal tunnel syndrome [69].
Fig. 11 T2-weighted axial MR image of a 16-year-old male. As an anatomical variant, a lumbrical
muscle (arrowhead) can be found between the deep flexor tendons within the carpal
tunnel. This finding was asymptomatic. Normal signal intensity of the median nerve
(arrow). The study was conducted for suspected TFCC lesion.
A rare accessory muscle, the flexor carpi radialis brevis (FCRB), was described to
be associated with pain by causing an atypical intersection syndrome of the wrist.
This intersection occurs between the tendon of the FCRB muscle and the tendon of the
FCR muscle, and was reported with an associated longitudinal split tear of the FCR
tendon [70].
Inflammatory diseases
In general, tendons can be damaged by inflammatory processes, such as chronic inflammatory
underlying conditions, in particular rheumatoid arthritis (RA) [71]. The most common tendon pathology due to inflammatory disease is tenosynovitis.
However, in severe cases, a tendon rupture can also occur [71].
In RA, tenosynovitis occurs frequently, as it targets synovial tissue, with reported
prevalence of about 50% to 80% [72], as an early inflammatory feature [73]
[74]. Tenosynovitis may manifest before development of clinical arthritis [75] and be associated with subsequent bone erosion [76]. An important complication of RA in the wrist is tendon rupture, which seems to
be related to synovial invasion of the tendon [77]
[78] and mechanical attrition. In particular, these tendon ruptures were commonly reported
at predilection sites of bone erosions, which can lead to sharp spurs. Especially
the extensor tendons of the ulnar-sided wrist, the EDM, and the EDC of the fifth digit
are at risk. This is because the eroded ulnar head or ulnar styloid process, in combination
with a volar subluxation of the radius, causes the dorsal riding ulna to rub against
the overlying tendons [26]
[79]. Rupture of the EPL tendon is common [80], while on the flexor side, rupture of the FPL at the palmar scaphoid referred to
as a Mannerfelt lesion, and rupture of the FDP of the index finger have been reported
[79]. MRI and ultrasound play an important role in the initial diagnosis, staging, treatment
monitoring, and assessment of remission in patients with RA [81].
Tenosynovitis is included in the RA MRI scoring system and is defined as peritendinous
effusion and/or tenosynovial postcontrast enhancement, seen on axial sequences over
≥ 3 consecutive slices [82]. A small amount of fluid can be seen in a normal tendon sheath, but a fluid thickness
of more than 1 mm is suggested as abnormal. The tenosynovium may be thickened and
revealed as a bright signal surrounding a tendon on T1-weighted postcontrast and T2-weighted
sequences ([Fig. 12]). The tendon itself may show morphological and signal changes, best identified on
axial images as an increased signal on T1 with a low signal on T2 or an increased
signal on both T1 and T2 sequences, and may show postcontrast enhancement [83]
[84].
Fig. 12 44-year-old female with diagnosed seropositive rheumatoid arthritis. In the T1-weighted
image (A), a thickened tendon sheath (white arrowhead) of the sixth dorsal extensor compartment
can be appreciated with the extensor carpi ulnaris tendon marked with an asterisk.
After gadolinium administration (B), contrast enhancement of the tenosynovium (white arrowhead) signaling tenosynovitis
of the sixth dorsal extensor compartment is seen.
On ultrasound, tenosynovitis may appear as hypoechoic or anechoic thickened tissue,
and may or may not be accompanied by fluid within the tendon sheath. This can be assessed
on two perpendicular planes and may be associated with a Doppler signal [85].
As for gout, deposition of uric acid crystals may involve tendons in the wrist, most
commonly enveloping the tendons (45%) [86], leading to tenosynovitis and tendon ruptures [87]
[88].
On ultrasound, tophaceous deposits are hyperechoic with an anechoic rim. Additionally,
they have a nodular or infiltrative appearance and may exhibit posterior acoustic
shadowing due to sound-beam attenuation and possible calcification [89]. MRI cannot specifically identify uric acid crystals, while features of gout may
vary. Gouty tophi have an intermediate or low signal intensity on T1-weighted images
and heterogeneous signal intensity on T2-weighted sequences, possibly due to varying
amounts of calcium, and can express uniform enhancement or a non-enhancing center
[89].
Dual-energy computed tomography (DECT) has the advantage of diagnosing urate crystals
by exploiting the photon energy–dependent attenuation of different materials, displaying
them in 2D or 3D color-coded maps ([Fig. 13]) [90].
Fig. 13 54-year-old male with gout crystal arthropathy. T1-weighted axial MR image at the
level of the ulnar head (A) shows peritendinous soft-tissue inflammation around the extensor carpi ulnaris tendon
(white arrowhead) with strong contrast enhancement in the post gadolinium, T1-weighted
fat-saturated image (B) and contrast enhancement of the little erosion in the ulnar head (white arrow).
Urate crystals could be confirmed with dual-energy computed tomography, where crystals
are marked in green in the color-coded 3D image (white open arrowhead) (C). The erosion can be depicted by computed tomography, as shown in the coronal plane
(D) at the base of the ulnar styloid process (white arrow). Small tophi calcifications
are depicted as well (white open arrowhead).
In psoriatic arthritis, the tendons are commonly affected by inflammatory changes
as well, with no difference in frequency compared to RA. However, in RA, extensor
tendons might be more commonly affected than flexor tendons, whereas in psoriatic
arthritis the opposite can be observed [91]. Inflammatory changes in flexor tendons of the digits are most frequently observed,
followed by the extensor carpi ulnaris and flexor carpi radialis tendons of the wrist
[91]
[92].
In general, soft-tissue calcifications can lead to inflammatory reactions in the surrounding
soft tissue, which can affect tendons [93]
[94]. This mechanism is particularly known in the shoulder as calcific tendinitis. In
rare cases, such calcifications can also affect the wrist tendons, notably the flexor
carpi ulnaris at the pisiform ([Fig. 14]). Rupture of the calcium deposits is thought to result in an acute inflammatory
response, where clinical symptoms can be easily misdiagnosed as acute infection [93]. In these cases, imaging is crucial to depict the calcifications, in order to avoid
unnecessary invasive interventions. On ultrasound, calcium hydroxyapatite depositions
can be seen as echogenic areas with shadowing within the tendon or around the tendon
sheath [95]. On radiographs, they demonstrate a characteristic amorphous, “cloud-like” appearance,
with no cortex or internal trabecular pattern [93]. On MR imaging, calcium deposits are hypointense on T1- and T2-weighted images and
can be surrounded by an inflammatory, edema-like reaction [96].
Fig. 14 (A, B, C) 38-year-old male with peritendinitis calcarea and partial tear of the flexor carpi
ulnaris (FCU) tendon. AP radiograph of the wrist (A) shows a cloud-like calcification (arrow) distal to the ulnar styloid process. Coronal
T2-weighted fat-saturated MR image (B) shows the calcification as a hypointense structure (arrow) with surrounding edema
along the FCU tendon (arrowhead). On the axial T2-weighted fat-saturated image (C), the hypointense calcification (arrow) and the partial tear of the FCU (arrowhead)
can be seen as hyperintense signal with fiber disruption within the tendon.
Conclusion
This article gives an overview over the anatomy and the pathologies of the wrist tendons.
Knowledge of this anatomy and its anatomical variants is key to avoid misdiagnosis,
and to understand certain pathologies. Anatomical crossings of tendons, for example,
facilitates intersection syndromes. The tendons of the thumb, i.e. extensor and flexor
pollicis longus, are most commonly torn after distal radial fracture (EPL) and osseous
hardware fixation (FPL). Both ultrasound and MR imaging are appropriate modalities
to assess the tendons of the wrist.
