Received: 29 January 2018
Revised: 25 April 2018
Accepted: 28 April 2018
DOI: 10.1111/vru.12667
O R I G I N A L I N V E S T I G AT I O N
High field magnetic resonance imaging anatomy of feline carpal ligaments is comparable to plastinated specimen anatomy Rachel M. Basa
Juan M. Podadera
Sydney School of Veterinary Science, Faculty of Science, University of Sydney, New South Wales, 2006, Australia Correspondence Rachel Maria Basa, Sydney School of Veterinary Science, Faculty of Science, University of Sydney, NSW, 2006, Australia. Email:
[email protected]
Gavin Burland
Kenneth A. Johnson
Abstract Feline carpal ligament injuries are often diagnosed indirectly using palpation and stress radiography to detect whether there is instability and widening of joint spaces. There are currently no reports describing normal feline carpal ligament anatomy and the magnetic resonance imaging (MRI) appearance of the carpal ligaments. The objective of this prospective, anatomic study was to describe normal feline carpal ligament anatomy using gross plastinated specimens and MRI. We hypothesized that MRI could be used to identify the carpal ligaments as previously described in the dog, and to identify species specific variations in the cat. The study was conducted using feline cadaver antebrachii that were radiographed prior to study inclusion. Three limbs were selected for MRI to confirm repeatability of anatomy between cats. The proton density weighted pulse sequence was used and images were acquired in transverse, dorsal, and sagittal planes. Following MRI, the limbs were plastinated and a collagen stain was used to aid in identification of carpal ligament anatomy. These limbs were sliced in sagittal section, and a further six paired limbs were included in the study and sliced in transverse and dorsal planes. Anatomic structures were initially described using MRI and then subjectively compared with gross plastinated specimens. Readers considered the transverse MRI plane to be most useful for visualizing the majority of the carpal ligaments. Findings indicated that MRI anatomy of the carpal ligaments was comparable to plastinated anatomy; therefore MRI appears to be a beneficial imaging modality for exploration of feline carpal pathology.
KEYWORDS
antebrachiocarpal joint, carpal injuries, cat, hyperextension
1
INTRODUCTION
The reported incidence of feline carpal injuries in one epidemiological study is 0.29%.3 The antebrachiocarpal joint is most commonly
Feline carpal ligament injuries are often diagnosed indirectly by stress
injured, followed by the carpometacarpal and middle carpal joints. This
radiography and palpation.1 However, there is variability between indi-
is often manifested as hyperextension injury at the level of the car-
vidual cats with the normal degree of carpal extension ranging from
pometacarpal joint, and medial collateral ligament sprain.1 Reports in
10–25 degrees and therefore the contralateral carpus should be used
the literature on the diagnosis and treatment of feline carpal ligament
as a point of reference.1 In people, magnetic resonance imaging (MRI)
injuries are limited to case reports and a few case series focusing on
has become an important imaging modality to assess injuries, such
epidemiology and outcomes following treatment with pan-carpal or
as carpal instability, disorders of the triangular fibrocartilage, ulnar
partial carpal arthrodesis.3–7
impaction syndrome, distal radioulnar joint instability, fracture, avas-
Studies describing the appearance of the canine and equine car-
cular necrosis, tendinopathy, nerve entrapment, synovial abnormali-
pus with MRI have been published.8–10 The objectives of this study
ties, and soft tissue masses.2
are to describe normal feline carpal ligament anatomy and to compare
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. c 2018 The Authors. Veterinary Radiology & Ultrasound published by Wiley Periodicals, Inc. on behalf of American College of Veterinary Radiology Vet Radiol Ultrasound. 2018;1–10.
wileyonlinelibrary.com/journal/vru
1
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BASA ET AL .
appearance of the ligaments in magnetic resonance images with the
and 0.8 mm thick band saw blade. Slices were cut at a thickness of
appearance in gross plastinated specimens.
1.5 ± 0.1 mm before cleaning and then transferred in to –25◦ C technical grade acetone for freeze substitution dehydration for a period of 7 days. They were transferred to room temperature to undergo
2
MATERIALS AND METHODS
2.1
degreasing of the tissue. After 5 days the slices were stained before being transferred in to a clean bath of technical grade acetone. The degreasing process was continued until the acetone stabilized above
Subject selection
99% purity. Slices were then impregnated and surrounded with an
The study was a prospective, anatomic design. Overall 13 feline
ice bath inside a vacuum chamber at room temperature for 24 h
cadaveric forelimbs were harvested from mature cats after they had
before being cast via the sandwich method and subsequently cured for
been euthanized for reasons unrelated to the study in accordance
three days at 40◦ C.
with guideline GL001 from the University of Sydney animal ethics
The first series of plastinated specimens were unstained, however,
committee. Sample size was based on the methodology of a previous
it was difficult to distinguish the off-white ligaments from the sur-
similar study.8 These were Domestic Short Hair cats ranging in size
rounding carpal bones. The staining process entailed 30 s in eosin stain
from 3.5 to 5.0 kilograms. Three limbs were selected for the pilot study
and 3 min in technical grade acetone. A different staining protocol was
so that each could be sectioned in standard transverse, sagittal, and
attempted with 30 s in eosin stain, 3 min in technical grade acetone,
dorsal sections, allowing the authors to assess the suitability of the
30 s in quick green stain, and 3 min in technical grade acetone, however,
plastination process in identifying small anatomical structures. The
the eosin stain alone was the most useful for highlighting the carpal
authors selected nine limbs for inclusion in the final study to account
ligaments.
for anatomical differences between cats, and three limbs had MRI performed. Inclusion criteria were the absence of preexisting articular diseases based on lack of radiographic findings of the carpus and manus. Exclusion criterion was the presence of suspected soft tissue
2.3 Pilot study of the magnetic resonance imaging protocol
abnormality during the MRI. The inclusion criteria were agreed upon
A pilot study was performed on a single, cadaveric feline forelimb using
by a veterinary surgery resident, a board certified veterinary surgeon,
a three Tesla MRI (GE Healthcare Milwaukee, USA, Model Discov-
and a board certified veterinary radiologist (J.M.P.).
ery MR750) in order to subjectively evaluate the anatomy with multiple sequences including T2, short tau inversion recovery and proton
2.2
Pilot study of the epoxy plastination process
Three feline cadaver limbs were used in a pilot study to evaluate the
density weighted (specifications noted in Table 1). The proton density weighted sequence was selected for the final scans given the higher signal-to-noise ratio.
epoxy plastination process. A scientific officer (G.B.) with experience in the plastination process prepared sections for study inclusion. The forelimb serial sections were produced following a previously published process of freeze substitution, dehydration, degreasing, impregnation, and curing (Biodur standard E12).11,12
2.4 Comparison between magnetic resonance imaging and plastinated specimen anatomy Three feline cadaver limbs were transected at the level of the mid-
The limbs were set in 20% gelatin blocks to facilitate handling and
antebrachium and fixed for 24 h in 20% gelatin prior to MRI. A 3 Tesla
correct orientation of the limbs during the slicing process. The limbs
MRI (GE Healthcare Milwaukee, USA, Model Discovery MR750) was
were then frozen to –80◦ C before slicing using a band saw (Thomson
used to scan three gelatin embedded limbs with the carpus in exten-
400 band saw, Thompson Meat Machinery, Crestmead, Qld, Australia)
sion using a human wrist coil (specifications noted in Table 1). The scan
TA B L E 1
MRI sequences used to image the feline carpus
Sequence
T2 weighted (pilot)
T2 fractional shortening (pilot)
Protein density weighted
Flip angle (degrees)
111
111
111
Repetition time (ms)
2700
2698
2000
Echo time (ms)
80
50
39
Acquisition time (min)
20
20
20
Field of view (mm)
50
50
60
Matrix (number of pixels)
352 × 192
352 × 192
320 × 320
Slick thickness (mm)
2
2
2
Fat saturation
No
Yes
No
Inter-slice gap
0.2
0.2
0.2
Number of excitations
12
12
4
3
BASA ET AL .
TA B L E
2
Definitions
for
feline
carpal
ligament
anatomy
abbreviations
to the articular surface of the radius and planned on dorsal and sagittal planes. The sagittal plane was aligned parallel to the lateral surface of
Abbreviation
Definition
the accessory carpal bone and was planned using transverse and dor-
ABCJ
antebrachiocarpal joint
sal planes. The dorsal plane was parallel to the dorsal surfaces of the
RUL
radioulnar ligament
carpal bones and was planned using transverse and sagittal planes. The
DRL
dorsal radiocarpal ligament
PF
palmar carpal fibrocartilage
AUL
accessorioulnocarpal ligament
images were saved as Digital Imaging and Communications in Medicine (DICOM). The limbs were processed using the same plastination protocol that was described in the pilot study above. Each of the limbs was sliced
AQL
accessorioquartile ligament
AML
accessoriometacarpal ligament
FR
flexor retinaculum
ture dependent changes in the gelatin, these were unable to be sec-
SUCL
short ulnar collateral ligament
tioned in transverse and dorsal planes. Six further limbs were selected
SRCL
short radial collateral ligament
for study inclusion and, following plastination, three were sectioned in
ICL
intercarpal ligament
the transverse and three were sectioned in the dorsal plane. An eosin
in sagittal section with a 1.5 mm slice thickness. The contralateral limbs were initially included in the study, however, due to tempera-
RCB
radial carpal bone
stain was used which stained the collagen, muscle, and cytoplasm as
UCB
ulnar carpal bone
varying shades of orange and pink.
ACB
accessory carpal bone
A board certified veterinary radiologist viewed all of the magnetic
PUL
palmar ulnocarpal ligament
PRCL
palmar radiocarpal ligament
PRML
palmar radiocarpal-metacarpal ligament
resonance images using medical imaging software (OsiriX, Pixmeo SARL, Bernex, Switzerland) on a desktop (Mac Pro 3.5 GHz 6-core Intel Xeon), viewed with a medical monitor (Eizo, RX340, North Sydney, Australia), and identified ligaments in each scan using previously reported canine ligament anatomy as a guideline.8,13,14 This was
time for each limb was approximately 20 min with transverse, sagittal,
completed using a dissection microscope (Olympus S261 dissection
and dorsal planes included. The transverse plane was aligned parallel
microscope, Olympus, Dandenong, Victoria, Australia) at two times
TA B L E 3 Ligament
Descriptions of ligament origins, insertions, orientation and optimal imaging plane Origin
Insertion
Orientation
Optimal imaging Plane
RUL
Distal aspect of the radius
Distal aspect of the ulna
Transverse
Transverse
PRML
Palmar aspect of the RCB
Proximopalmar aspect metacarpal II and III
Proximo-distal
Sagittal
DRL
Mid portion of the distal radial articular surface
Dorsolateral border of the UCB
Proximomedial-distolateral oblique
Sagittal
ICL
Mid portion of the RCB
Mid portion of the UCB
Transverse
Transverse
SUCL
Lateral aspect of the styloid process of the ulna
UCB
Proximo-distal
Dorsal
SRCL
Medial aspect of the styloid process of the radius
Palmarolateral aspect of the RCB
Proximomedial-distolateral oblique
Transverse
PUL
Axial surface of the distal ulna
Proximolateral aspect of the RCB
Proximolateral-distomedial oblique
Dorsal
PRCL
Palmar aspect of the radius
RCB
Proximo-distal
Sagittal
AUL
Dorsodistal portion of the ACB
Palmar aspect of the UCB
Transverse
Transverse and Sagittal
AQL
Distal aspect of the ACB
Palmar aspect of the fourth carpal bone
Proximo-distal
Sagittal
AML
Free end of the ACB
Palmar surface of the fourth and fifth metacarpal bones
Proximo-distal
Transverse and Sagittal
PF
Attaches to the proximal part of the metacarpals and to all of the carpal bones except the ACB
Transverse
Transverse
FR
Modification of the caudal carpal fascia with a superficial and deep band
Transverse
Transverse
Notes. RUL, radioulnar ligament; PRML,palmar radiocarpal-metacarpal ligament; DRL,dorsal radiocarpal ligament; ICL, intercarpal ligament; SUCL,short ulnar collateral ligament; SRCL, short radial collateral ligament; PUL, palmar ulnocarpal ligament; PRCL, palmar radiocarpal ligament; AUL, accessorioulnocarpal ligament; AQL, accessorioquartile ligament; AML, accessoriometacarpal ligament; PF, palmar carpal fibrocartilage; FR, flexor retinaculum.
4
BASA ET AL .
F I G U R E 1 Mid- dorsal section at the level of the antebrachiocarpal joint. The lateral aspect of the antebrachiocarpal joint is to the left of the images, and proximal is at the top of the images. The radioulnar ligament can be seen as a transverse band at the level of the distal radioulnar joint. The short ulnar collateral ligament runs diagonally from the lateral aspect of the styloid process of the ulna to the ulnar carpal bone. A, Plastinated anatomic section; B, corresponding proton-density weighted magnetic resonance image [Color figure can be viewed at wileyonlinelibrary.com]
magnification to compare the plastinated specimens to the MRI
and the plastinated specimens as described in Table 3. Selected
sequences; this step was undertaken by a board certified veterinary
anatomical features detected on MRI and corresponding plastinated
surgeon and a veterinary surgery resident (R.M.B.). The veterinary
specimens are labeled in the figures. Where there was discrepancy
surgery resident was involved in the ligament identification using both
between anatomies of individual cats or suspected volume averag-
MRI and plastinated specimens. Images were documented using a digi-
ing, this was carefully scrutinized and compared to the plastinated
tal camera (Olympus PEN EPS camera, Olympus, Dandenong, Victoria,
specimens.
Australia).
The radioulnar ligament (Figure 1 and 2) attached to the distal aspects of the radius and ulna and was best visualized as multiple hypo-intense striations on the dorsal and transverse views. This
3
RESULTS
was unable to be identified on the sagittal view. In the second study, there was a hyper-intensity associated with the mid portion of the radioulnar ligament. The articular disc could not be distin-
3.1 Magnetic resonance imaging anatomy of feline carpal ligaments
guished from the radioulnar ligament on either MRI or in the gross specimens.
Abbreviations for feline carpal ligaments are defined in Table 2.
The dorsal radio-carpal ligament (Figure 3) provides reinforcement
Ligaments were identified as hypointense bands and their origin and
of the dorsal joint capsule and extensor tendons. It was best seen
insertions were described using multiple magnetic resonance planes
on the sagittal view as a triangular hypo-intense band from the mid
5
BASA ET AL .
portion of the distal radial articular surface and extending laterally to insert on the dorsolateral border of the ulnar carpal bone. It could also be visualized on dorsal and transverse views. The intercarpal ligament joints the mid portion of the ulnar carpal bone and radial carpal bone. It is best visualized on the transverse plane as linear, fibrillar, hypo-intense bands. It was poorly defined on the dorsal plane images. Palmar carpal fibrocartilage (Figure 4) attaches to the proximal part of the metacarpals and to all of the carpal bones except the accessory carpal bone. This was best identified on the sagittal and transverse planes. The distal portion of the palmar carpal fibrocartilage is adjacent to the proximal aspect of metacarpals III and IV. Both of these structures are characterized by low signal in the proton density weighted sequence. This resulted in border effacement of the structures, making it difficult to demarcate the distal portion of the palmar carpal fibrocartilage. FIGURE 2
Magnetic resonance image; transverse plane sectioned proximal to the antebrachiocarpal joint. The radioulnar ligament can be seen as a horizontal band between the distal aspect of the radius and ulna [Color figure can be viewed at wileyonlinelibrary.com]
The short ulnar collateral ligament consists of hypo-intense striations extending from the lateral aspect of the styloid process of the ulna to the ulnar carpal bone best seen on the dorsal view. It was unable to be seen on the transverse and sagittal views.
F I G U R E 3 Sagittal section at the level of the antebrachiocarpal joint. The dorsal aspect of the antebrachiocarpal joint is to the left of the images, and proximal is at the top of the images. The origin of the dorsal radio-carpal ligament can be seen at the mid portion of the distal radial articular surface, and it inserts on the dorsolateral border of the ulnar carpal bone (not seen in this image). A, Plastinated anatomic section; B, corresponding proton-density weighted magnetic resonance image [Color figure can be viewed at wileyonlinelibrary.com]
6
BASA ET AL .
F I G U R E 4 Transverse section at the level of the proximal metacarpus. The lateral aspect of the metacarpus is to the left of the image, and the top of the image is dorsal. The palmar carpal fibrocartilage is seen palmar to metacarpals II, III, IV, and V. A, Plastinated anatomic section; B, corresponding proton-density weighted magnetic resonance image [Color figure can be viewed at wileyonlinelibrary.com]
The short radial collateral ligament was seen on the transverse view
of the fourth and fifth metacarpal bones. These ligaments can be identi-
as a grey to black hypo-intense band extending from the medial aspect
fied on sagittal and transverse views, and were more hypo-intense than
of the styloid process of the radius and fanned distally to insert on the
the intercarpal ligament.
palmarolateral aspect of the radial carpal bone, deep to the abductor
The flexor retinaculum is also identified as the transverse palmar
pollicus longus. The ligament was identified on the dorsal but not the
carpal ligament and extends as a black hypo-intense band most eas-
sagittal plane images.
ily identified on the transverse view. It is a modification of the caudal
The palmar ulnocarpal ligament was best seen on the dorsal view as
part of the carpal fascia with two bands. One lies superficial to, and
a hypo-attenuating band extending from the axial surface of the distal
the other between the superficial and deep digital flexor tendons. The
ulna and diagonally to insert on the proximolateral aspect of the radial
superficial layer was easier to identify. The smaller intercarpal ligaments between the individual carpal
carpal bone (Figure 5). The borders of the ligament were poorly demarcated on the transverse and sagittal views. The sagittal view was the best for identifying the palmar radiocarpal ligament, which originates from the palmar aspect of the radius to
bones and from the carpal bones to the metacarpals were difficult to identify. The intercarpal ligament between the radius and ulna, and between the second and third carpal bones were seen.
attach distally to the radial carpal bone (Figure 6). This structure corresponded to poorly demarcated hypo-attenuating bands on the transverse and dorsal views and appeared as a thickening of the antebrachial fascia.
3.2 Comparison between magnetic resonance anatomy and plastinated specimen anatomy
The palmar radiocarpal metacarpal ligament was similarly seen
The ligaments appeared as dark red striated bands in the plastinated
best on the sagittal view extending from the palmar aspect of the
specimens. Locations and characteristics of carpal ligaments visual-
radial carpal bone and diverges distally to attach to the proximopalmar
ized in the plastinated specimens were comparable to those visualized
aspects of metacarpals II and III. It was deep to the tendon of the flexor
using MRI.
carpi radialis and small in size. The accessorioulnocarpal ligament (Figure 7) originates from the dorsodistal portion of the accessory carpal bone to insert on the pal-
4
DISCUSSION
mar aspect of the ulnar carpal bone. This was seen on transverse and sagittal views, but not easy to identify on the dorsal view. The accessorioquartile ligament (Figure 7) was seen as a hypointense band on the sagittal view extending from the distal aspect of the accessory carpal bone to the palmar aspect of the fourth carpal bone. In the transverse plane, it was poorly demarcated and irregular. The accessoriometacarpal ligaments (Figure 7) originate from the free end of the accessory carpal bone to insert on to the palmar surface
To the authors’ knowledge, this is the first published report describing normal feline carpal ligament anatomy using high field MRI, plastinated anatomic specimens, and previously published references for ligament origins and insertions in the dog.14 The current standard diagnostic tests for suspected carpal instability in feline patients include stress radiography (varus/ valgus stress tests for suspected short radial and ulna collateral ligament injuries, extension/ flexion stress for suspected carpal hyperextension injuries with damage to the
7
BASA ET AL .
F I G U R E 5 Magnetic resonance image; dorsal plane sectioned at the mid antebrachium. The palmar ulnocarpal ligament can be seen extending from the medial aspect of the distal ulna to the proximolateral aspect of the radial carpal bone [Color figure can be viewed at wileyonlinelibrary.com]
palmar carpal fibrocartilage) and computed tomography.3 One previous report described the use of arthroscopy in the feline elbow with a 1.9 mm 30 degree fore oblique arthroscope, however no published studies describing arthroscopic evaluation of the feline carpus were found.15 Stress MRI could possibly be used to directly assess articular stability in addition to carpal ligament morphology, however it was
F I G U R E 6 Magnetic resonance image; sagittal section at the mid antebrachium. The origin and insertion of the palmar radiocarpal ligament can be seen extending from the palmar aspect of the radius to the radial carpal bone [Color figure can be viewed at wileyonlinelibrary.com]
not considered feasible in the current study due to the difficulty in selectively transecting the small feline carpal ligaments and prolonged
assessing the carpal ligaments in a clinical context is that it may assist
general anesthesia in a live patient.
in the management of feline carpal injuries.
In the cat, the short radial collateral ligament is important for
The recommendation in veterinary musculoskeletal imaging is to
resisting palmar dislocation of the radial carpal bone and rupture
use a 1.5 Tesla MRI or higher, and to use quadrature surface coils.16
of the short radial collateral ligament and dorsomedial joint capsule
The authors have access to both low and high field MRI, however
alone can result in complete antebrachiocarpal luxation.6,7 The medial
high field was preferentially chosen because the feline carpus is a
collateral ligament counteracts valgus stress and prevents dislocation
small anatomical area that benefits from the improved signal-to-
of the carpal bones in a palmar direction.1 The value of directly
noise ratio, resulting in increased image resolution and decreased
8
BASA ET AL .
F I G U R E 7 Mid sagittal section at the level of the accessory carpal bone. The dorsal aspect of the carpus is at the left hand side of the image and the proximal aspect is at the top of the image. The accessorioulnocarpal ligament is seen as a transverse band extending between the accessory carpal bone and ulnar carpal bone. The accessorioquartile ligament extends from the distal aspect of the accessory carpal bone to the palmar aspect of the fourth carpal bone, and the accessoriometacarpal ligaments originate from the free end of the accessory carpal bone to insert on metacarpals IV and V. A, Plastinated anatomic section; B, corresponding proton-density weighted magnetic resonance image [Color figure can be viewed at wileyonlinelibrary.com]
exam time.17 In a previous study of the equine carpus, high field
difficult to identify without special stains.20 The plastination process
MRI was preferred because it allowed for identification of some
allows for staining of tissue slices and the specimens were preserved
structures not seen with low field MRI, such as layers of the carpal
and sliced to 1.5 mm thickness.21 This technique has been previously
fascia.10
utilized for correlation of anatomy and magnetic resonance tomogra-
Previous studies have used plastinated sections for comparison
phy imaging in descriptive anatomical studies in people.22
with different imaging modalities.10,18,19 There have been reports
Proton density images display tissue contrast based on the density
whereby gross frozen specimens were cut at different slice thick-
of protons within each tissue.27 The proton density sequence was
nesses, however the concern in this study is that although this would
selected for use in this study because the high signal-to-noise ratio
provide an appropriate image of muscle and bone, the ligaments are
allowed for maximal spatial resolution and anatomic detail.23,28 These
9
BASA ET AL .
sequences have a long relaxation time with a short echo time that
radius and ulna, and to allow for load transmission from the carpus to
allows for high signal-to-noise ratio consequently permitting the
the antebrachial bones.26 A potential limitation of this study is that
acquisition of thinner slices. Normal ligaments are generally homoge-
although plastination is useful for descriptive anatomy, histopathology
nous with low signal (hypo-intense); however this varies with the
and the use of a dedicated cartilage stain would have provided more
sequence and density of collagen bundles within the ligament.23 The
information regarding the presence of this disc.
ligaments varied in signal intensity with the AMLs being more hypo-
Cadaveric limbs were used in the study and underwent a freeze–
intense than the intercarpal ligaments, and the short radial collateral
thaw cycle, which means that there is hydrogen atom loss in the form
ligament varying in signal intensity from a grey to black hypo-intense
of water and the potential for imaging artifact.29 The distal aspect
band. In this study, the intermediate signal intensity of the intercarpal
of the palmar carpal fibrocartilage was indistinct from the proximal
ligaments was suspected to be due to their small size and volume
aspect of metacarpals III and IV. This could be due to the presence of
averaging with high signal intensity synovial fluid.23
In a clinical setting
hypo-intense cortical bone of metacarpal III and IV, and hypo-intensity
where there is pathology, multiple imaging sequences and planes
of the adjacent portion of the palmar fibrocartilage leading to border
would be recommended. Further studies are required in order to
effacement of the structures. Despite the use of cadaveric limbs, all
verify the sensitivity of sequences in the diagnosis of carpal ligament
of the ligaments were hypo-intense. Advantage of using cadavers is
injury.
that this allowed for the placement of limbs in a physiological position
The carpi were imaged using dorsal, transverse, and sagittal planes
without general anesthesia, reducing the risk of motion and pulse arti-
with the limb in a neutral position and in the center of wrist coil.
fact during image acquisition. However, the use of live animals would
This is similar to recommendations in people, in which the dorsum
be important for the detection of pathology seen as changes in signal
of the hand must be parallel to the coronal plane of the magnet
intensity, or the size and shape of the ligament.23
(prone ‘superman’
position).2
The carpal ligaments have different
In conclusion, findings of this study indicated that high field MRI
orientations and in order to display those ligaments in a representative
characteristics of feline carpal ligament anatomy are comparable to
way, the transverse plane to the direction of the ligament reduces the
plastinated specimen anatomy. This supports the use of high field MRI
impact of volume averaging therefore displaying the anatomy more
as an adjunctive diagnostic test to evaluate the feline carpus when
objectively. The transverse plane has been noted as the most useful
concerns about ligament injury exist. Future studies are needed to
plane for identification of soft tissue structures by previous authors
whether MRI findings are comparable with clinical findings and stress
that described the anatomy of the canine tarsus.20 The obliquity of
radiography findings in patients with joint instability. Further studies
some ligaments also means that they are unable to be seen in their
are needed in order to assess the most appropriate MRI protocols in
entirety.18
the clinical context.
In this study, the transverse plane allowed for identification and demarcation of the majority of the feline carpal ligaments. The sagittal plane is aligned with the longitudinal axis of the majority of the carpal ligaments. In addition, the feline ligaments are very thin structures.
LIST OF AUTHOR CONTRIBUTIONS Category 1
These two variables increase the chances of volume averaging leading to poor demarcation of the ligaments and reduced visualization of
(a) Conception and Design: Johnson KA, Basa RM
anatomical structures.23 Although the sagittal plane proves beneficial
(b) Acquisition of Data: Burland G, Basa RM
for following the dorsal radio-carpal ligament, palmar radiocarpal lig-
(c) Analysis and Interpretation of Data: Basa Rm, Podadera JM
ament, palmar radiocarpal metacarpal ligament, and accessorioquartile ligament, it appears to be less beneficial when trying to identify and demarcate the intercarpal ligament and radioulnar ligament. Planning cross sectional imaging with planes perpendicular to the axis of the ligament may be important in order to minimize volume averaging artefact and increase the chance to sample a representative part of the anatomy leading to better evaluation of the ligament and reduction of
Category 2 (a) Drafting the Article: Basa RM, Podadera JM, Burland G, Johnson KA (b) Revising Article for Intellectual Content: Basa RM, Podadera JM, Burland G, Johnson KA
possible false positive abnormalities. The radioulnar ligament was easily identified however we were unable to verify the presence of a fibrocartilage articular disc in the gross specimens.8,24 To the author's knowledge, the presence of a
Category 3 (a) Final Approval of the Completed Article: Basa RM, Podadera JM, Burland G, Johnson KA
fibrocartilage disc has not been described in domestic cats but has been identified in one study of the cheetah antebrachiocarpal joint.25 Previous histological studies in dogs have found that the articular
ACKNOWLEDGMENTS
disc is synonymous with the triangular cartilage complex in people.
The authors would like to thank Jane Bursill for her contribution in
Macroscopically it has the appearance of cartilage and microscopically
the use of dissection microscopes, and Domenic Soligo at Southern
it is composed of fibrocartilagenous
tissue.26
The role of this disc is
speculated to be improved congruency between the distal end of the
Radiology, the Brain Mind Research Institute for his assistance with magnetic resonance image acquisition.
10
BASA ET AL .
ORCID Rachel M. Basa
http://orcid.org/0000-0002-9599-3054
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How to cite this article: Basa RM, Podadera JM, Burland G, Johnson KA. High field magnetic resonance imaging
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anatomy of feline carpal ligaments is comparable to plasti-
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https://doi.org/10.1111/vru.12667
nated specimen anatomy. Vet Radiol Ultrasound. 2018;1–10.
