Key words
arthrography - hand - radiography - MR imaging
What is “carpal instability”?
What is “carpal instability”?
Joints are considered stable if they can maintain their articular relationship for
a physiological range of motion and load transfer. To achieve this, any external force
affecting the wrist from any direction is counteracted by internal stabilizers that
re-establish the status quo. If a joint loses the ability to react adequately to external
force vectors, it becomes unstable, resulting in the loss of anatomical congruency
in motion or at rest [1]
[2]. From a pathophysiological perspective, carpal instabilities can be the result of
intrinsic and/or extrinsic factors. “Intrinsic” refers to insufficiency of the primary
and secondary wrist stabilizers such as carpal ligaments, joint capsules, flexor,
and extensor tendons. Scapholunate or lunotriquetral ligament tears are common examples
for this group [3]
[4]. “Extrinsic” mostly refers to an abnormal joint surface geometry of the distal forearm
section. Incorrectly healed distal radius fractures with pathological joint surface
inclination are representatives of this group [5]
[6].
Clinically, carpal instability causes pain and varying degrees of dysfunction, secondarily
leading to progressive osteoarthritis. Complementing trauma and inflammatory anamnesis,
the physical examination should include inspection (swelling, deformity, skin injury),
checking the active and passive mobility of the wrist, test of grip strength and examination
of the neurovascular status [7].
Imaging techniques
Radiography
X-ray scans are usually the first kind of imaging a patient receives when reporting
with wrist pain or reduced hand mobility. They serve as primary means of fracture
detection after trauma and provide valuable information on the stability of the carpus.
Several image findings hint at the presence of structural carpal disorder. In dorsopalmar
projection, interruption of the carpal arches is suspicious for instability and should
be succeeded by further investigation [7]. Instability of the central carpal column is indicated by a triangular (in dorsal
extension) or crescent shape (in palmar flexion) of the lunate [7]
[8]. In the lateral view, any angulation that exceeds the standard values of [Table 1] must be considered pathological, pointing to intercalated segment instability. [Fig. 1] depicts the most frequent carpal instability forms with corresponding pathological
angle measurements. It is important to know that severe ligament injuries can be present
without evident signs of instability in radiography at rest. To detect these dynamic
instabilities, additional stress imaging is recommended [9]
[10].
Table 1
Reference values for carpal angulations in lateral radiographs.
Tab. 1 Referenzwerte für karpale Winkelbestimmungen im seitlichen Röntgenbild.
|
angle
|
reference (range)
|
|
radiolunate angle
|
0° (–15° to 15°)
|
|
radioscaphoid angle
|
45° (30° to 60°)
|
|
capitolunate angle
|
0° (–15° to 15°)
|
|
scapholunate angle
|
45° (30° to 60°)
|
Fig. 1 For angle measurements in lateral radiographs, the longitudinal axes of the radius
(R) and lunate (L) as well as the palmar tangent of the scaphoid (S) are required.
a Scapholunate dissociation. Palmar flexion of the scaphoid and dorsal extension of the lunate result in pathologic
widening of the scapholunate angle (above 60–70°). b
Lunotriquetral dissociation. Simultaneous flexion of the scaphoid and lunate results in widening of the radiolunate
(above 15°) and radioscaphoid (above 60°) angles, while the scapholunate angle remains
within the normal range or decreases (below 30°). c
Unstable scaphoid nonunion. The proximal scaphoid fragment and lunate bone extend dorsally, while the distal
scaphoid fragment rotates to palmar. The scapholunate angle is subsequently increased
(above 60–70°). d
Radiocarpal structural disorder. Pathological inclination of the radial articular surface after fracture leads to
combined dorsal extension of the scaphoid and lunate. Therefore, the radiolunate angle
decreases (below –15°), while the radioscaphoid angle remains normal or decreases
(below 30°).
Abb. 1 Für Winkelmessungen im seitlichen Projektionsradiogramm werden die Längsachsen von
Radius (R) und Lunatum (L) sowie die palmare Tangente am Skaphoid (S) benötigt. a
Skapholunäre Dissoziation. Palmare Flexion von Skaphoid und dorsale Extension von Lunatum führen zu einer pathologischen
Erweiterung des skapholunären Winkels (über 60–70°). b
Lunotriquetrale Dissoziation. Gleichzeitige Flexion von Skaphoid und Lunatum resultiert in einer Zunahme des radiolunären
(über 15°) und radioskaphoidalen (über 60°) Winkels, während der skapholunäre Winkel
im Referenzbereich bleibt oder abnimmt (unter 30°). c
Instabile Kahnbeinpseudarthrose. Dorsalextension von proximalem Kahnbeinfragment und Lunatum bei simultaner Palmarflexion
des distalen Skaphoidfragments führen zu einer Aufweitung des skapholunären Winkels
(über 60–70°). d
Radiokarpale Gefügestörung. Aufgrund der pathologischen Inklination der distalen Radiuskonsole kommt es zu einer
Dorsalextension von Skaphoid und Lunatum. Dadurch verkleinert sich der radiolunäre
Winkel (unter –15°), der radioskaphoidale Winkel bleibt normal oder nimmt ebenfalls
ab (unter 30°).
Cinematography
Fluoroscopy may be helpful if suspected instability cannot be explained by rest and
stress images. Recordings of wrist motion can be customized depending on the causative
pathology. In suspected scapholunate dissociation, dorsopalmar recordings of radio-ulnar
deviation usually suffice to secure the diagnosis. In contrast, lateral projections
are preferable to visualize midcarpal instability, as the characteristic “clicking”
or “snapping” can be provoked in radio-ulnar deviation or flexion and extension of
the wrist. An additional series of movements in which patients provoke the click or
snap effect themselves might also be helpful [11]
[12].
MRI
Due to the complex structure of the wrist, MRI requirements include high spatial resolution
as well as optimized signal-to-noise (SNR) and contrast-to-noise ratio (CNR). Technically,
multi-channel phased-array coils and 3.0 Tesla scanners are considered the state of
the art. While promising results can be achieved with stronger magnets up to 7.0 Tesla,
these ultra-high field systems are not established in the clinical routine thus far.
Volume coverage is preferably performed with interleaved acquisition. The slice thickness
for 2 D and partitions for 3 D imaging should not exceed 2 mm and 0.5 mm, respectively.
Narrowing the field of view to 60–80 mm provides superior resolution, which is particularly
important for the depiction of microstructural alterations [5].
[Fig. 2] displays different MRI techniques for the detection of interosseous carpal ligament
injury. Without application of contrast agent, ligament injuries can only be visualized
in T2-weighted sequences if joint effusion surrounds the rupture site ([Fig. 2a, b]). The detection rate of scapholunate and lunotriquetral ligament tears is 55 % to
60 % for plain MRI compared to arthroscopy as the reference standard. In contrast-enhanced
MRI, focal gadolinium enhancement in fat-saturated T1-weighted sequences occurs at
the rupture site because of hyperemia of the synovial and fibrovascular repair tissue
([Fig. 2c, d]). The contrast agent accumulation can be observed for about six months after trauma.
By intravenous gadolinium administration, the detection rate of intrinsic carpal ligament
injuries can be increased to 80–95 %.
Fig. 2 Imaging of scapholunate ligament injury using fat-saturated (fs) fast spin echo (FSE)
sequences and MR/CT arthrography. a T1 FSE fs b PD-weighted FSE fs c T1 FSE d T1 FSE fs after intravenous application of gadolinium e T1 FSE fs after multicompartment wrist arthrography f Multidetector CT after multicompartment wrist arthrography
Abb. 2 Bildgebende Diagnostik skapholunärer Bandläsionen mittels fettgesättigter (fs) Fast-Spin-Echo
(FSE) -Sequenzen sowie MR-/CT-Arthrografie. a T1-FSE fs. b PD-FSE fs. c T1-FSE. d T1-FSE fs nach intravenöser Kontrastmittelapplikation. e T1-FSE fs nach Mehrkompartment-Arthrografie. f Multidetektor-CT nach Mehrkompartment-Arthrografie.
Direct MR arthrography is a minimally invasive procedure with articular injection
of diluted gadolinium under fluoroscopy. Arthrography has major advantages for the
examiner who is able to observe the distribution of the contrast medium in different
compartments in real time if ligament ruptures are present. Application of contrast
agent further leads to distension of carpal joints, improving discernibility of the
intrinsic ligaments from the surrounding articular cartilage. Moreover, the injected
gadolinium increases the contrast around the ligaments by T1 shortening ([Fig. 2e]). Compared to arthroscopy, direct MR arthrography has a sensitivity and specificity
of more than 90 % each [13]
[14]
[15]
[16]
[17]. Despite being relatively easy to conduct, MR arthrography of the wrist remains
a specialized procedure that is not performed at many centers.
CT
The benefit of CT scans in early stages of carpal instability is mostly insignificant.
In late stages, however, CT is the method of choice to depict arthrosis in the radioscaphoid
and midcarpal joints due to superior visualization of articular surface incongruities,
cartilage defects, and subchondral sclerosis [15]
[17]. While ligamentous causes of instability are not directly visible in plain computed
tomography, CT imaging after multi-compartment arthrography of the wrist has high
diagnostic value for interosseous ligament lesions, achieving comparable results to
MR arthrography in the detection of scapholunate and lunotriquetral ligament injuries
([Fig. 2f]) [16]
[18]
[19]. Furthermore, high-resolution CT in thin slice technique is considered the diagnostic
reference standard in primary imaging of scaphoid fractures. With scaphoid displacement
being a common reason for dissociative instability, early CT examinations can prevent
delayed diagnosis and immobilization with increased risk for nonunion.
Novel imaging techniques
Cone-beam computed tomography (CBCT) portrays an alternative approach to CT imaging
that was first established for dental and maxillofacial applications in the 1980 s.
Combining pyramid-shaped beam geometry with large-scale flat-panel detectors, CBCT
can provide superior spatial resolution compared to conventional multidetector CT
at a low radiation dose [20]. Due to the emergence of dedicated extremity scanners in the last decade, CBCT has
gained increasing attention for appendicular skeletal imaging. With the current generation
of multi-use systems that are also capable of radiography and fluoroscopy, CBCT possesses
potential for “one-stop-shop” imaging, possibly superseding multidetector CT in the
near future for trauma imaging tasks, such as the diagnosis of carpal instability.
Combining the benefits of motion recording with 3 D imaging, dynamic MRI and “four-dimensional
CT” (three spatial dimensions + time) present another promising concept for the visualization
of wrist kinematics. While fluoroscopic cinematography remains limited to the detection
of structural misalignments, these imaging approaches can simultaneously provide additional
information about bone microarchitecture, adjacent cartilage and even depict the interosseous
carpal ligaments (in case of dynamic MRI). Clinical applicability has been shown for
either technique in recent years. However, both dynamic CT and MRI are still considered
specialized procedures not regularly performed in the clinical routine [21]
[22].
Forms of carpal instability
Forms of carpal instability
Four main groups of carpal instability can be discerned: dissociative, non-dissociative,
complex and adaptive instabilities [8]. Differentiation between these forms is essential for choosing the right treatment.
Imaging of the wrist is particularly challenging as multiple anatomical components
collaborate to ensure stability and different microstructural alterations can lead
to similar clinical symptoms. Therefore, diagnosis depends on thorough anamnesis and
examination, understanding of the biomechanical concepts of mobility and load distribution
as well as correct application and interpretation of diagnostic imaging [5]
[23].
Dissociative carpal instabilities (CID)
In dissociative disorders, the components of the proximal carpal row are displaced
with respect to each other: If an intrinsic ligament is ruptured, either the scaphoid
is shifted in the opposite direction of the lunate or the lunate is shifted in the
opposite direction of the triquetrum [24]
[25]. In the presence of a scaphoid fracture/nonunion, the two scaphoid bone fragments
can be displaced with respect to each other [26]. CID is by far the most common form of carpal instability with scapholunate dissociation
being the most frequent pathoanatomical correlate [13]
[27]. The lunate as an intercalated and potentially unstable member of the carpus can
present different forms of misalignment. Dorsiflexed intercalated segment instability
(DISI) is described when the lunate rotates into extension, widening the radiolunate
angle. This constellation is most frequently encountered in scapholunate dissociation.
In contrast, palmar-flexed intercalated segment instability (PISI) is present with
flexion of the lunate to palmar. This rather rare finding can be seen in midcarpal
instability and lunotriquetral dissociation [17]
[28]. The acronyms “DISI” and “PISI” are descriptions for the pathological arrangement
of the lunate in the central carpal column, but do not describe independent clinical
conditions.
Scapholunate dissociation (SLD)
Scapholunate dissociation (SLD)
Pathoanatomy
Ruptures of the scapholunate ligament (SLL) are mostly trauma-associated, often occurring
after a fall on the dorsally extended hand. About 10 % of radius fractures that involve
the radiocarpal joint are associated with SLL tears [6]
[14]. If SLD is observed without adequate trauma in the patient history, particularly
calcium pyrophosphate dihydrate (CPPD) arthropathy has to be evaluated. Discontinuities
are mostly located off-center in the scaphoid portion of the ligament [5]. Isolated injury of the SLL results in the scaphoid and lunate rotating in different
directions, resulting in a dissociative structural disorder (CID-DISI) [8]
[24]
[29].
Clinical presentation
Acute SLD is characterized by radial-sided swelling, dorsal pressure pain, and limited
wrist mobility [30]. Watson’s scaphoid displacement test is important for diagnosis. The examiner tries
to induce a dorsal subluxation of the proximal scaphoid pole by applying volar pressure
to the scaphoid tubercle, while the wrist is simultaneously moved from ulnar to radial
deviation with the other hand. If the SLL is disrupted, the scaphoid will subluxate
over the dorsal edge of the distal radius and the patient will experience significant
pain during the maneuver [31].
Staging
In stages I and II, radiography under resting conditions is inconspicuous despite
a partial or complete rupture of the SLL. Dynamic instability only becomes evident
in stress imaging or fluoroscopy and is not visible without load or movement [29]
[32]. It manifests if the extrinsic carpal ligaments, i. e., the scaphotrapeziotrapezoid
(STTL), radioscaphocapitate (RSCL), palmar (pRLTL), and dorsal radiolunotriquetral
ligaments (dRLTL), that function as the secondary stabilizers of the wrist remain
intact ([Fig. 3]) [33]. In contrast, combined injury of the SLL and secondary stabilizers results in static
instability that can be diagnosed at rest [8]
[25]. Stage III is characterized by simultaneous rotary subluxation of the scaphoid (RSS),
as well as DISI configuration of the central carpal column ([Fig. 4]). In the lateral radiograph, widening of the scapholunate angle is present. Dorsopalmar
images might show additional widening of the scapholunate gap to more than 3 mm (“Terry
Thomas sign”). However, this is not mandatory ([Fig. 5]) [34]. Finally, osteoarthritis and loss of carpal height indicate stage IV of SLD, the
so-called SLAC wrist (Scapholunate Dissociation Advanced Collapse). Depending on the
extent of arthrosis, SLAC I (only radioscaphoid joint), II (entire radiocarpal joint)
and III (additional midcarpal joint osteoarthritis) can be differentiated [18]
[35]
[36]
[37]. Ligament conditions in different stages of SLD are summarized in [Table 2].
Fig. 3 Schematic display of intracapsular carpal ligaments. a
Palmar “V” ligaments. The proximal palmar “V” consists of the palmar radiolunotriquetral ligament (pRLTL)
on the radial side and the ulnolunate (ULL) and ulnotriquetral ligaments (UTL) on
the ulnar side. The radial leg of the distal palmar “V” is formed by the radioscaphocapitate
(RSCL) and scaphocapitate ligament (SCL), while the triquetrocapitoscaphoid ligament
(TCSL = arcuate ligament) constitutes its ulnar leg. b
Dorsal “V” ligaments. In contrast to the palmar side, the ligamentous anatomy of the dorsal carpus resembles
a horizontal “V” with the dorsal radiolunotriquetral ligament (dRLTL) as the proximal
leg and the intercarpal dorsal ligament (ICDL) as the distal leg.
Abb. 3 Schematische Darstellung der intrakapsulären karpalen Ligamente. a
Palmare V-Bänder. Das proximale palmare „V“ besteht aus dem Lig. radiolunotriquetrum palmare (pRLTL)
auf der radialen Seite und den ulnolunären (ULL) und ulnotriquetralen Ligamenten (UTL)
auf der ulnaren Seite. Der radiale Schenkel des distalen palmaren „V“ wird durch das
Lig. radioscaphocapitatum (RSCL) und das Lig. scaphocapitatum (SCL) gebildet, während
das Lig. triquetrocapitoscaphoideum (TCSL = Lig. arcuatum) als ulnarer Schenkel fungiert.
b
Dorsale V-Bänder. Im Gegensatz zu den palmaren Bändern ähnelt die Bandanatomie der dorsalen Seite
einem horizontalen „V“, bei dem das Lig. radiolunotriquetrum dorsale (dRLTL) den proximalen
Schenkel und das Lig. intercarpale dorsale (ICDL) den distalen Schenkel darstellt.
Fig. 4 Rotational deformities in scapholunate dissociation a Dorsal extension of the lunate (DISI configuration) in sagittal T1 FSE fs after wrist
arthrography b Schematic display of opposite rotational tendencies of the scaphoid and lunate in
scapholunate dissociation c Palmar flexion of the scaphoid in sagittal T1 FSE after wrist arthrography
Abb. 4 Rotationsfehlstellungen bei skapholunärer Dissoziation. a Dorsalextension des Os lunatum (DISI-Konfiguration) in sagittaler T1-FSE fs nach
karpaler Arthrografie. b Schematische Darstellung der entgegengesetzten Rotationstendenzen von Skaphoid und
Lunatum bei skapholunärer Dissoziation. c Palmarflexion des Os scaphoideum in sagittaler T1-FSE fs nach karpaler Arthrografie.
Fig. 5 Static form of scapholunate dissociation a Despite static instability, scapholunate distance can appear normal in dorsopalmar
projection. b Lateral view, however, shows the characteristic combination of dorsally extended
lunate and rotatory subluxation of the scaphoid, resulting in pathologic widening
of the scapholunate angle (above 70°).
Abb. 5 Statische Form der skapholunären Dissoziation. a Im dorsopalmaren Röntgenbild kann die Distanz zwischen Skaphoid und Lunatum auch
bei statischen Dissoziationen normwertig erscheinen. b Die seitliche Aufnahme zeigt jedoch die typische Kombination aus Dorsalextension
des Mondbeins und Rotationssubluxation des Kahnbeins mit folglich pathologischer Erweiterung
des skapholunären Winkels (über 70°).
Table 2
Watson and Black’s classification of scapholunate dissociation, modified by Schmitt
[2]
[37].
Tab. 2 Klassifikation skapholunärer Dissoziationen nach Watson und Black, modifiziert durch
Schmitt [2]
[37].
|
stage
|
severity
|
scapholunate ligament
|
secondary stabilizers
|
|
I
|
pre-dynamic
|
partial tear
|
intact
|
|
II
|
dynamic
|
complete tear
|
intact
|
|
III
|
static
|
complete tear
|
ruptured
|
|
IV
|
arthritis
|
complete tear
|
ruptured
|
Therapy
Depending on the severity and acuteness of the instability, treatment options include
immobilization, scapholunate transfixation, ligament suture, plasty of the extrinsic
ligaments (dorsal capsulodesis), stabilization of the scaphoid with a tendon strip
or partial arthrodesis, implantation of bone-ligament-bone grafts, as well as salvage
procedures in late stages with advanced osteoarthritis [27]
[35]
[38]
[39].
Lunotriquetral dissociation (LTD)
Lunotriquetral dissociation (LTD)
Pathoanatomy
Compared to SLD, LTD is a rare condition [4]
[13]
[14]. Injuries of the lunotriquetral ligament (LTL) occur through axial trauma to the
pronated wrist, often associated with perilunate dislocation injuries. For LTL injuries
to become clinically apparent, additional insufficiency of the secondary stabilizers
is necessary, mostly of the pRLTL and dRLTL [5]
[40]. In LTD, the triquetrum extends dorsally, while the lunate rotates in the palmar
direction. Due to maintained connection through the SLL, the scaphoid follows the
lunate’s rotation to a lesser extent, thus reducing the scapholunate angle to less
than 30° ([Fig. 6]) [4]
[8]. The resulting PISI deformity of the central carpal column displays pathological
widening of the radiolunate and capitolunate angles. Similar to SLD, carpal height
is reduced in advanced LTD [25]
[41]. The dissociative structural disorder (CID-PISI) caused by instability of the lunotriquetral
compartment must be distinguished from midcarpal instability, a non-dissociative disorder
that is also characterized by palmar flexion of the lunate (CIND-PISI). LTL injuries
are frequently associated with lesions of the triangular fibrocartilage complex (TFCC)
[13]
[42].
Fig. 6 Static form of lunotriquetral dissociation a After healing of a distal radius fracture and removal of the osteosynthesis plate,
incongruence of the lunotriquetral articulation and interruption of the proximal carpal
arch is present in the dorsopalmar view. b The lunate has adopted a palmar rotary subluxation in the lateral view (PISI). The
scapholunate angle has decreased below 30°.
Abb. 6 Statische Form der lunotriquetralen Dissoziation. a Nach Heilung einer distalen Radiusfraktur und Entfernung der Osteosyntheseplatte
liegt in der dorsopalmaren Aufnahme eine Inkongruenz der lunotriquetralen Artikulation
mit Unterbrechung des proximalen Karpalbogens vor. b Das seitliche Röntgenbild zeigt, dass sich das Lunatum in einer palmar gerichteten
Rotationssubluxation befindet (PISI). Der skapholunäre Winkel beträgt weniger als
30°.
Clinical presentation
Patients report ulnar-sided wrist pain and click effects during dorsal extension and
ulnar deviation. Pressure pain can be induced over the lunotriquetral joint and Reagan’s
ballottement test is positive (painful displacement of the triquetrum in relation
to the lunate under pressure) [2].
Staging
A classification similar to the one used in SLD is recommended. In stages I and II
of LTD, due to the stabilizing effect of the pRLTL, dRLTL and ulnocarpal ligaments,
structural arrangement of the carpus remains normal at rest. When the secondary stabilizers
are also injured, static disorders become evident in stages III and IV. Slightly differing
from the SLD classification, asymptomatic stage I of LTD can include a complete tear
of the LTL. In stage II, characterized by pain in motion and dynamic instability detectable
in fluoroscopy or stress imaging, additional discontinuity of the pRLTL is present.
Stage III relates to static structural disorders without accompanying degeneration.
In stage IV of LTD, carpal osteoarthritis has manifested [5]
[13]
[41].
Therapy
Treatment of LTD remains controversial. In acute injury, repositioning and lunotriquetral
transfixation is performed. In the case of TFCC and LTL lesions associated with increased
ulna length and subsequent carpal osteoarthritis, ulna shortening through osteotomy
is recommended. In the case of static PISI disorders and a normal ulna length, lunotriquetral
arthrodesis or ligament replacement surgery may be appropriate [41]
[43].
Scaphoid nonunion
Pathoanatomy
In displaced scaphoid nonunion, an osseous form of dissociative instability is present.
While the proximal scaphoid fragment is detached from the carpal alignment and subsequently
follows its natural tendency into an extension position, the distal fragment moves
into a flexion position due to the axial load. Interconnected to the proximal scaphoid
fragment by the SLL and LTL, the lunate and triquetrum also rotate into extension,
resulting in a DISI configuration of the central carpal column [26]. [Fig. 7] depicts the combination of scaphoid nonunion, osteoarthritis and carpal collapse
named SNAC wrist (Scaphoid Nonunion Advanced Collapse) [18]
[35].
Fig. 7 Scaphoid nonunion advanced collapse (SNAC wrist) a Dorsopalmar view depicts nonunion of the scaphoid and advanced osteoarthritis in
the radiocarpal and (less pronounced) midcarpal joints. Carpal height is reduced.
b Lateral view shows dorsal extension of the lunate alongside the proximal scaphoid
fragment with resulting DISI configuration. The distal scaphoid fragment adopts a compensatory
flexion position.
Abb. 7 Karpaler Kollaps bei Skaphoidpseudarthrose (SNAC wrist). a Die dorsopalmare Röntgenaufnahme zeigt eine Pseudarthrose des Kahnbeins mit fortgeschrittenen
arthrotischen Veränderungen im radiokarpalen und (weniger ausgeprägt) im mediokarpalen
Gelenk. Die Höhe des Karpus ist reduziert. b In der seitlichen Ansicht kommt die Dorsalextension von Lunatum und proximalem Skaphoidfragment
mit resultierender DISI-Fehlstellung zur Darstellung. Das distale Kahnbeinfragment
nimmt eine kompensatorische Flexionsposition ein.
Clinical presentation
The healing of a scaphoid fracture should be completed after about three months. If
fracture consolidation has not taken place at this time, healing is delayed. After
six months, nonunion can be described [5]. The symptoms of scaphoid nonunion are manifold. Early stages can cause moderate
pain during radial wrist deviation or thumb flexion. In the case of carpal instability,
stress-related symptoms increase and swelling of the radial wrist occurs. In the stage
of osteoarthritis, the wrist can also be limited in strength [18]
[35].
Staging
In delayed union, decreasing mineralization around the fracture gap becomes evident.
If no bony consolidation occurs, pseudocystic resorption areas in both scaphoid fragments
indicate the irreversible onset of nonunion [5]
[36]. The ensuing sclerosis of the fragment edges can either be smooth (atrophic form)
or bulgy through formation of osteophytes (hypertrophic form). Depending on the filling
tissue in the gap, unstable and stable nonunion can be distinguished. Unstable nonunion
leads to secondary osteoarthritis, beginning between the radial styloid and distal
scaphoid fragment (SNAC I). In later stages, the midcarpal joint is also affected,
starting between the proximal scaphoid fragment and the capitate head (SNAC II) and
before reaching the articular surfaces between the capitate head and the lunate (SNAC
III) [35].
Therapy
Depending on the stage of scaphoid nonunion, different surgical approaches can be
used. In the case of mere nonunion, spongiosaplasty and transfixation are commonly
performed. If the proximal scaphoid fragment is also necrotic, corticocancellous bone
grafts from the radius, iliac crest, or femoral condyle can be inserted into the defect
and connected with the palmar or dorsal blood vessels of the wrist to revascularize
the surrounding tissue [35]
[44].
Non-dissociative carpal instabilities (CIND)
Non-dissociative carpal instabilities (CIND)
In CIND, the proximal carpal row is intact. However, it is either incorrectly aligned
with the distal carpal row or dislocated from the forearm. Pathoanatomically, lesions
of the extrinsic intracapsular ligaments or a displaced radius joint surface is causative
for development of CIND [45]
[46].
Radiocarpal instability (RCI)
Radiocarpal instability (RCI)
Ulnar translocation
The slingshot ligaments, namely the radioscaphocapitate ligament (RSCL), pRLTL, and
dRLTL, antagonize the natural tendency of the carpalia for ulnar deviation that is
based on the inclination of the distal radius joint surface. If the slingshot ligaments
become insufficient, the entire carpus drifts to the ulnar side, subsequently effecting
the physiological load distribution from the wrist to the distal forearm [9]
[23]. Apart from traumatic injuries, later stages of rheumatoid arthritis or CPPD arthropathy
can also cause ulnar (and palmar) deviation of the wrist through inflammatory ligament
destruction. Translocation may further be induced by extensive surgical resection
of the radial styloid or the ulnar head. In Madelung deformity, a congenital disorder
characterized by exaggerated palmar and ulnar tilt of the radiocarpal articulation,
excessive ligament loading leads to insufficiency and carpal translocation over time.
Two forms of ulnar translocation can be differentiated according to Taleisnik [47]: In the first form, the entire carpus deviates towards the ulnar side, resulting
in a gap of more than 2 mm between the radial styloid and scaphoid, while the lunate
loses its contact with the radius. In the second form, the scaphoid stays in place,
while the remaining carpus drifts to the ulnar side, consecutively widening the scapholunate
gap. Differentiation of the latter condition and isolated SLD is important for treatment
[2]
[30].
Radial translocation
Decreased inclination of the radial articular surface may cause radial (or dorsal)
dislocation of the proximal carpal row ([Fig. 8]). Radial translocation of the carpus mainly occurs in displaced Chauffeur’s fractures
(fractures of the radial styloid process) [26]. Loss of bone substance due to friction between the distal radius and scaphoid in
SLAC or SNAC wrist can also lead to radial shifting of the wrist [37]. In all forms of carpal translocation, incongruence of the radiocarpal joint surfaces
results in early-onset osteoarthritis [36].
Fig. 8 Radiocarpal instability a Schematic display of the carpalia as an interconnected ring. Red arrows indicate
that the cause of instability is located proximal to the carpus. b The dorsopalmar view shows a healed distal radius fracture. c The lateral X-ray reveals the pathological inclination of the radial joint surface
and zigzag alignment of the carpus.
Abb. 8 Radiokarpale Instabilität. a Schematische Darstellung der Carpalia als zusammenhängender Ring. Rote Pfeile zeigen
an, dass die Ursache der Instabilität proximal des Karpus liegt. b Die dorsopalmare Ansicht zeigt eine verheilte distale Radiusfraktur. c In der seitlichen Röntgenaufnahme werden die pathologische Neigung der Radiusgelenkfläche
und die Zick-Zack-Deformität des Karpus deutlich.
Midcarpal instability (MCI)
Midcarpal instability (MCI)
Instability of the entire midcarpal joint
The characteristic feature of MCI is the abnormal mobility of the proximal carpal
row in motion or at rest. In radial deviation of the wrist, the proximal carpal row
adopts a flexion position (CIND-PISI), while ulnar deviation of the wrist triggers
the proximal carpalia to extend dorsally (CIND-DISI). With both tiers behaving like
separate entities instead of one unit, the distal row of the carpus rotates in the
opposite direction of the proximal row [24].
Insufficiency of the dRLTL on the dorsal side and the triquetrocapitoscaphoid ligament
(TCSL = arcuate ligament) on the palmar side are suspected to induce midcarpal joint
disorders. During radial deviation of the wrist, insufficient ligament stability causes
the triquetrum to jump from its natural palmar (proximal) to a dorsal (distal) position.
Because the SLL and LTL are intact, the scaphoid and lunate follow the rotation of
the triquetrum, with the capitate head dislocating in front of the anterior horn of
the lunate ([Fig. 9]) [26]
[46]. MRI has limited applicability for diagnosis of midcarpal instability as all interosseous
carpal ligaments present intact. Thus, fluoroscopy imaging in motion is key for differentiating
between midcarpal instability and lunotriquetral dissociation.
Fig. 9 Midcarpal instability a Schematic display of the carpalia as an interconnected ring. Red arrows indicate
that the cause of instability is located between both carpal rows. b After midcarpal “clicking” during ulnar deviation of the wrist, fluoroscopy shows
palmar flexion of the scaphoid and incongruence between the capitate and lunate bones.
c In the lateral projection, flexion of the proximal and extension of the distal carpalia
is clearly visible under stress load from the patient’s opposite hand. Both the radiolunate
and capitolunate angles are pathologically extended (both above 15°).
Abb. 9 Mediokarpale Instabilität. a Schematische Darstellung der Carpalia als zusammenhängender Ring. Rote Pfeile zeigen
an, dass die Ursache der Instabilität zwischen den beiden karpalen Reihen liegt. b Nach einem durch ulnare Abduktion provozierten mediokarpalen Klick-Effekt zeigt sich
in der Kinematografie eine Palmarflexion des Skaphoids sowie eine Inkongruenz zwischen
Kapitatum und Lunatum. c In der lateralen Projektion ist unter Belastung durch die gegenseitige Patientenhand
die Flexion der proximalen und Extension der distalen Carpalia gut erkennbar. Sowohl
der radiolunäre als auch der kapitolunäre Winkel sind pathologisch aufgeweitet (beide
über 15°).
The “jumping” of the carpal rows causes a moderately painful click effect on the ulnar
side of the wrist. Patients can usually trigger the effect themselves during closure
of the fist in ulnar deviation. If the clicking can be antagonized through pressure
on the pisiform bone, MCI should be suspected. In late stages, patients might experience
severe pain and a weakness of grip [48].
Depending on the underlying cause, therapy can consist of radial osteotomy, capitolunate
partial arthrodesis or “four corner fusion” of lunate, triquetrum, capitate and hamate.
Ligament reconstructions of the extrinsic carpal ligaments are rarely successful.
Capitolunate instability
Referring to a structural disorder limited to the articulation between the capitate
head and lunate, this special form of MCI is only visible in motion and cannot be
detected at rest. The capitolunate instability pattern (CLIP) is present if subluxation
of at least half the width of the capitate head can be documented in stress imaging.
In most cases, the capitate head can only be dislocated dorsally from the lunate [24]
[45].
Unstable necrosis of the lunate (Kienböck’s disease)
In advanced lunate necrosis (stages IIIb and IV), the decreasing height of the lunate
bone has destabilizing effects on the entire wrist. Increased axial load and loss
of lunate height cause the scaphoid to move into a flexed position. The loss of carpal
height can be quantified using the indices of Youm (reference: 0.54 ± 0.03) [49] and Nattrass (reference: 1.57 ± 0.05) [50].
Complex carpal instabilities (CIC)
Complex instability can refer to different combinations of ligament tears, cartilage
injuries and/or luxation fractures. The instability patterns are manifold and mostly
contain combinations of dissociative and non-dissociative elements. CIC is mostly
seen in high impact accidents, resulting in different perilunate dislocation patterns
that are characterized by injuries of the greater and/or lesser arcs of the wrist
[8]
[24].
Adaptive carpal instabilities (CIA)
Adaptive instabilities are characterized by an extra-carpal cause of instability,
i. e. the causative injury is located proximal to the carpal bones. They can lead
to gross deformation and functional incapacity of the hand. The most frequent extrinsic
causes of instability are incorrectly healed distal radius fractures with or without
concomitant ligament injuries [8]
[47]. Pathological angulation of the radial joint surface leads to structural disorder
of the carpus with the wrist adopting a zigzag-shaped compensatory position relative
to the radius. Externally, a fork-like or bayonet-like deformation of the wrist may
be noticeable. Unphysiological loading causes pain and swelling as well as early-onset
of osteoarthritis [5]
[36].
Conclusion
Wrist function is associated with high individual and socioeconomic relevance. Impairing
motion range and grip strength of the hand, carpal instability needs adequate treatment.
In order to choose the correct approach from a variety of therapeutic options, surgeons
require proper imaging beforehand. As the term “carpal instability” refers to a large
number of conditions with different stages and patterns, diagnosis and categorization
oftentimes pose intricate challenges ([Table 3]). The early stages of each entity of carpal instability are particularly difficult
to differentiate because radiographic signs might be subtle or even completely missing
[2]
[9]. With many osseous, ligamentous and cartilaginous structures working together to
ensure stability of the wrist, isolated injuries can be compensated by secondary stabilizers
and therefore remain inapparent in X-ray scans at rest [40]. The addition of fluoroscopy and stress imaging may help to diagnose these dynamic
forms of instability, although the extent of ligament damage cannot be quantified
[29]
[32]. While radiography is limited to the depiction of structural disorders caused by
instability, MR and CT arthrography as well as (dynamic) MRI can directly visualize
the actual ligament injury responsible for the instability – in most cases SLL and
LTL tears. As osteoarthritis and subsequent disability of the wrist are common results
of instability, any radiologist should be aware of this challenging topic and the
importance of early and precise diagnosis. Moreover, close collaboration of radiologists
and wrist surgeons is necessary to ensure optimal and timely treatment of patients.
Table 3
Characteristics of carpal instability according to Schmitt and Lanz [5].
Tab. 3 Charakteristiken karpaler Instabilitäten nach Schmitt und Lanz [5].
|
category
|
subcategory
|
characteristic
|
|
time
|
acute
|
1st week
|
|
subacute
|
2nd to 6th week
|
|
chronic
|
after 6th week
|
|
severity
|
pre-dynamic
|
no instability despite predisposition
|
|
dynamic
|
instability in motion
|
|
static
|
instability at rest
|
|
etiology
|
traumatic
|
e. g. Fall on the outstretched hand
|
|
inflammatory
|
e. g. CPPD arthropathy, rheumatoid arthritis
|
|
congenital
|
e. g. Madelung deformity
|
|
direction
|
PISI
|
palmar misalignment of the lunate
|
|
DISI
|
dorsal misalignment of the lunate
|
|
translocation
|
carpal dislocation opposite forearm
|
|
pattern
|
CID
|
instability in the proximal carpal row
|
|
CIND
|
instability between carpal rows
|
|
CIC
|
combination of CID and CIND
|
|
CIA
|
extra-carpal cause of instability
|
CPPD – calcium pyrophosphate dihydrate; PISI – palmar intercalated segment instability;
DISI – dorsal intercalated segment instability; CID – carpal instability dissociative;
CIND – carpal instability non-dissociative; CIC – carpal instability complex; CIA
– carpal instability adaptive.
Funding
Interdisciplinary Center of Clinical Research Würzburg, Germany: Z-2/CSP-06 (recipient:
Jan-Peter Grunz)
