MRI findings in 232 horses with lameness localized to the metacarpo(tarso)phalangeal region and without a radiographic diagnosis


King, J.N.; Zubrod, C.J.; Schneider, R.K.; Sampson, S.N.; Roberts, G.

Veterinary Radiology and Ultrasound 54(1): 36-47

2013


Two hundred and thirty-two horses with lameness localized to the metacarpo(tarso)phalangeal (MCP/MTP) region without a radiographic diagnosis were evaluated. All horses had high-field magnetic resonance (MR) imaging of the MCP/MTP region performed for the lame limb and the contralateral limb for comparison. There were 46 horses that had bilateral abnormalities in the forelimbs; 27 of these horses were not lame in the contralateral limb at the time of examination. Bilateral hind limb abnormalities were observed in 37 horses; 22 horses were not lame in the contralateral limb. Soft tissue abnormalities alone were observed in 218 limbs (162 horses). Subchondral bone and articular cartilage abnormalities alone were observed in 43 limbs (34 horses). A combination of soft tissue, subchondral bone, and cartilage abnormalities were observed in 64 limbs (36 horses). The distribution of primary abnormalities was as follows; oblique distal sesamoidean ligament desmitis (73 limbs in 56 horses), straight distal sesamoidean ligament desmitis (44 limbs in 38 horses), chronic subchondral bone injuries (15 limbs in 12 horses), suspensory ligament branch desmitis (14 limbs in 12 horses), collateral ligament desmitis (12 limbs in 12 horses), tendonitis of the superficial and deep digital flexor tendons (10 limbs in 10 horses), osteochondral defects greater than 1 cm (nine limbs in six horses), osteochondral defects less than 1 cm (eight limbs in seven horses), bone marrow lesions (six limbs in five horses), intersesamoidean ligament desmitis (five limbs in four horses). MR imaging is useful in diagnosing bone and soft tissue injuries when radiographs and ultrasound fail to yield a diagnosis.

MRI
FINDINGS
IN
232
HORSES
WITH
LAMENESS
LOCALIZED
TO
THE
METACARPO(TARSO)PHALANGEAL
REGION
AND
WITHOUT
A
RADIOGRAPHIC
DIAGNOSIS
JENNIFER
N.
KING,
CHAD
J.
ZUBROD,
ROBERT
K.
SCHNEIDER,
SARAH
N.
SAMPSON,
GREG
ROBERTS
Two
hundred
and
thirty-two
horses
with
lameness
localized
to
the
metacarpo(tarso)phalangeal
(MCP/MTP)
region
without
a
radiographic
diagnosis
were
evaluated.
All
horses
had
high-field
magnetic
resonance
(MR)
imaging
of
the
MCP/MTP
region
performed
for
the
lame
limb
and
the
contralateral
limb
for
comparison.
There
were
46
horses
that
had
bilateral
abnormalities
in
the
forelimbs;
27
of
these
horses
were
not
lame
in
the
contralateral
limb
at
the
time
of
examination.
Bilateral
hind
limb
abnormalities
were
observed
in
37
horses;
22
horses
were
not
lame
in
the
contralateral
limb.
Soft
tissue
abnormalities
alone
were
observed
in
218
limbs
(162
horses).
Subchondral
bone
and
articular
cartilage
abnormalities
alone
were
observed
in
43
limbs
(34
horses).
A
combination
of
soft
tissue,
subchondral
bone,
and
cartilage
abnormalities
were
observed
in
64
limbs
(36
horses).
The
distribution
of
primary
abnormalities
was
as
follows;
oblique
distal
sesamoidean
ligament
desmitis
(73
limbs
in
56
horses),
straight
distal
sesamoidean
ligament
desmitis
(44
limbs
in
38
horses),
chronic
subchondral
bone
injuries
(15
limbs
in
12
horses),
suspensory
ligament
branch
desmitis
(14
limbs
in
12
horses),
collateral
ligament
desmitis
(12
limbs
in
12
horses),
tendonitis
of
the
superficial
and
deep
digital
flexor
tendons
(10
limbs
in
10
horses),
osteochondral
defects
greater
than
1
cm
(nine
limbs
in
six
horses),
osteochondral
defects
less
than
1
cm
(eight
limbs
in
seven
horses),
bone
marrow
lesions
(six
limbs
in
five
horses),
intersesamoidean
ligament
desmitis
(five
limbs
in
four
horses).
MR
imaging
is
useful
in
diagnosing
bone
and
soft
tissue
injuries
when
radiographs
and
ultrasound
fail
to
yield
a
diagnosis.
©
2012
Veterinary
Radiology
&
Ultrasound
Key
words:
equine,
fetlock,
lameness,
metacarpophalangeal,
metatarsophalangeal,
MRI.
Introduction
T
HE
BONES
and
supporting
soft
tissues
in
the
metacarpo(tarso)phalangeal
(MCP/MTP)
region
are
commonly
injured
in
equine
athletes.
This
joint
has
the
greatest
range
of
motion
in
the
horse,
and
the
support-
ing
soft
tissues
absorb
most
of
the
forces
of
weight
bear-
ing
during
high-speed
exercise.
1-3
Single
traumatic
events
and
microdamage
caused
by
repetitive
cyclic
loading
are
responsible
for
bone
and
articular
cartilage
damage
in
this
joint.
Bone
injuries
like
third
metacarpal/metatarsal
condylar
fractures,
sesamoid
fractures,
and
osteochondral
fragmentation
of
the
proximal
phalanx
are
commonly
di-
agnosed
using
radiography."
The
soft
tissue
components
of
this
joint
are
injured
as
a
consequence
of
hyperextension,
medial—lateral
instability,
or
subluxation.
Ultrasonography
has
been
the
most
common
modality
used
to
image
the
ten-
dons
and
ligaments
in
this
region.
7,8
Soft
tissue
lesions
that
From
the
Department
of
Veterinary
Clinical
Sciences,
College
of
Veteri-
nary
Medicine,
Washington
State
University,
Pullman,
WA
99164
(King,
Schneider,
Sampson,
Roberts)
and
Oakridge
Equine
Hospital,
6675
East
Waterloo
Road„
Edmond
OK
73034
(Zubrod)
Address
correspondence
and
reprint
requests
to
Jennifer
N.
King,
at
the
above
address.
Email:
are
difficult
to
identify
using
ultrasonography
can
be
identi-
fied
with
magnetic
resonance
(MR)
imaging.
9-11
Magnetic
resonance
imaging
has
been
used
to
detect
subchondral
bone
damage
and
osteochondral
defects
when
there
are
no
detectable
radiographic
abnormalities.
12
Magnetic
resonance
imaging
is
useful
for
diagnosing
in-
jury
to
equine
athletes
when
conventional
imaging
fails
to
yield
a
definitive
cause
of
lameness.
9-12
Magnetic
reso-
nance
imaging
abnormalities
in
the
MCP/MTP
region
have
been
summarized
and
reported
in
a
group
of
40
horses,
in-
cluding
horses
with
radiographic
abnormalities.
13
Because
the
MCP/MTP
joint
is
a
common
location
for
lameness
problems
in
all
types
of
equine
athletes
and
radiographs
frequently
do
not
yield
a
diagnosis,
it
is
important
to
char-
acterize
abnormalities
in
a
large
group
of
horses.
Our
pur-
pose
was
to
describe
the
MR
imaging
findings
in
horses
with
lameness
localized
to
the
MCP/MTP
region
when
radiographs
were
normal.
The
objectives
were
to
identify
the
most
frequent
problems
in
a
large
population
of
per-
formance
horses
and
describe
the
clinical
features
associ-
ated
with
MR
imaging
abnormalities.
Our
hypothesis
was
that
injury
to
the
supporting
soft
tissue
structures
would
be
more
frequent
than
abnormalities
in
subchondral bone
Received
January
18,
2012;
accepted
for
publication
August
7,
2012.
doi:
10.1111/j.1740-8261.2012.01983.x
Vet
Radiol
Ultrasound,
Vol.
54,
No.
1,
2013,
pp
36-47.
36
VOL.
54,
No.
1
MRI
FINDINGS
IN
HORSES
WITH
MCP/MTP
LAMENESS
37
TABLE
1.
Magnetic
Resonance
Imaging
Sequences
Used
for
Evaluation
of
the
Metarcarpo(tarso)phalangeal
Region
Using
a
1.0
Tesla
Magnet
Image
orientation
Sequence
TR
(ms)
TE
(ms)
FA
FOV/rFOV
Matrix
size
Slice
no./width
(mm)
Gap
(mm)
Time
(min)
Transverse
TSE
T2
2143
100
90
15/12
256
x
512
30/4.5
0.5
1:57
Transverse
TSE
PD
2143
10.5
90
15/12
256
x
512
30/4.5
0.5
1:57
Transverse
STIR
1725
35
90
15/12
192
x
256
30/4.0
1.0
5:17
Sagittal
TSE
T2
1899
110
90
14/12
256
x
512
24/3.2
0.4
2:22
Sagittal
TSE
PD
1899
13.8
90
14/12
256
x
512
24/3.2
0.4
2:22
Sagittal
STIR
1500
25
90
14/12
192
x
256
24/3.0
0.6
5:12
Dorsal
3D
GE
47
8.3
25
11/10
192
x
256
40/1.5
—0.5
4:41
TSE,
turbo
spin
echo;
T2,
T2-weighted;
PD,
proton
density;
STIR,
short
r
inversion
recovery;
3D
GE,
three-dimensional
gradient
echo;
TR,
repetition
time;
TE,
echo
time;
FA,
flip
angle;
FOV,
field
of
view;
rFOV,
relative
field
of
view.
and
articular
cartilage
in
horses
that
had
lameness
localized
to
the
MCP/MTP
region,
but
did
not
have
radiographic
abnormalities.
Materials
and
Methods
Medical
records
from
all
horses
that
had
MR
imaging
performed
on
the
MCP/MTP
region
at
Oakridge
Equine
Hospital
(2004-2009)
and
Washington
State
University
(1997-2009)
were
reviewed.
All
horses
were
examined
and
imaged
because
of
lameness.
Lameness
was
localized
to
the
MCP/MTP
region
with
perineural
local
anesthesia,
intra-articular
or
digital
flexor
tendon
sheath
blocks,
or
by
observing
at
least
two
of
the
following
clinical
signs:
a
positive
response
to
distal
limb
flexion,
effusion
of
the
MCP/MTP
joint,
soft
tissue
swelling
around
the
fetlock
region,
and/or
digital
flexor
tendon
sheath
effusion.
Radio-
graphs
were
taken
following
localization
of
lameness
and
failed
to
yield
a
diagnosis
in
all
horses
included
in
this
study.
For
the
purposes
of
this
paper,
the
MCP/MTP
region
was
described
as
including
structures
from
the
distal
one-third
of
the
metacarpus/metatarsus
to
the
proximal
interpha-
langeal
joint.
Horses
with
abnormalities
in
the
proximal
interphalangeal
joint
were
excluded.
Information
obtained
from
medical
records
included
breed,
gender,
age,
use
of
the
horse,
affected
limb(s),
duration
and
severity
of
lameness,
response
to
hoof
testers,
response
to
distal
limb
flexion,
radiographic
findings,
ultrasonographic
findings,
and
MR
imaging
findings.
Lameness
was
graded
using
a
modified
American
Asso-
ciation
of
Equine
Practitioners
scale
while
trotting
over
a
smooth
hard
surface
(0—no
lameness
observed;
1—mild
lameness
while
circling;
2—mild
lameness
in
a
straight
line;
3—moderate
lameness
in
a
straight
line;
4—severe
lameness
in
a
straight
line;
5—supporting
very
little
weight
on
the
limb).
Response
to
hoof
testers
was
either
positive
or
negative.
A
positive
response
to
distal
limb
flexion
was
recorded.
Diagnostic
local
anesthesia
performed
on
horses
included
palmar
digital
nerve
blocks
with
or
without
dorsal
branches,
abaxial
sesamoid
nerve
blocks,
low
four-point,
intra-articular
anesthesia
of
the
MCP/MTP
joint,
and
intrathecal
anesthesia
of
the
digital
flexor
tendon
sheath.
Four
radiographic
projections
were
made
of
the
MCP/MTP
region
and
included
lateromedial,
dor-
sopalmar/plantar,
dorsolateral-palmar/plantaromedial
oblique,
and
dorsomedial-palmar/plantarolateral
oblique
views.
Ultrasonographic
images,
when
performed,
were
obtained
using
a
7.5
MHz
linear
probe
and
abnormalities
were
recorded
as
a
change
in
size,
shape,
or
echogenicity.
Magnetic
resonance
imaging
was
performed
in
all
horses
under
general
anesthesia
in
right
lateral
recumbency.
MR
images
at
Washington
State
University
were
obtained
using
a
1.0
Tesla
NT
Philips
Gyro
scan
Magnet
(Philips
Medical
Systems,
Best,
the
Netherlands)
imaging
system
using
a
protocol
that
has
been
described
previously
(Table
1).
14
The
MCP/MTP
joints
were
imaged
in
transverse,
sagittal,
and
dorsal
planes
using
proton
density
(PD),
T2-weighted
(T2),
short
t
inversion
recovery
(STIR),
and
3D
gradient
echo
Tl-weighted
(3D
GE)
sequences.
A
dual-echo
sequence
was
used
to
obtain
the
PD
and
T2
sequences.
MR
images
at
Oakridge
Equine
Hospital
were
obtained
using
a
1.5
Tesla
Siemens
Symphony
MR
Unit
(Siemens
Medical
Solutions
USA,
Inc.,
Malvern,
Pennsylvania)
(Table
2).
The
MCP/MTP
joint
was
imaged
in
transverse,
sagittal,
and
dorsal
planes
using
PD,
PD
with
fat
saturation
(PDFS),
T2-weighted,
Tl-weighted
(T1),
and
3D
Tl-weighted
GE
sequences
with
fat
sup-
pression
(3D
GEFS).
A
dual-echo
sequence
was
used
to
obtain
the
PD
and
T2
sequences.
All
horses
were
imaged
bilaterally;
in
horses
with
unilateral
lameness,
the
images
were
compared
to
the
contralateral
limb.
In
horses
with
bilateral
lameness,
images
were
compared
to
horses
free
of
lameness
associated
with
the
MCP/MTP
region
that
had
been
imaged
previously
at
Washington
State
University.
Abnormalities
observed
were
recorded
as
a
change
in
size,
shape,
or
signal
intensity.
All
MR
images
were
evaluated
by
at
least
two
of
the
authors.
MR
abnormalities
were
graded
as
mild,
moderate,
and
severe
and
limbs
were
subsequently
divided
into
groups
based
on
primary
abnormalities
in
either
subchondral
bone
and
cartilage
or
soft
tissue.
There
was
a
group
with
multiple
abnormalities
in
which
a
primary
diagnosis
could
not
be
made.
Results
Two
hundred
and
thirty-two
(232)
horses
with
lame-
ness
localized
to
the
MCP/MTP
region
and
without
a
radiographic
diagnosis,
met
the
inclusion
criteria
for
this
38
KING
ET
AL.
2013
TABLE
2.
Magnetic
Resonance
Imaging
Sequences
Used
for
Evaluation
of
the
Metarcarpo(tarso)phalangeal
Region
Using
a
1.5
Tesla
Magnet
Image
orientation
Sequence
TR
(ms)
TE
(ms)
FA
FOV
(cm)
Matrix
size
Slice
#/width
(mm)
Gap
(mm)
Time
(min)
Transverse
TSE
T2
5280
115
150
13.9
x
10
256
x
147
38/4.0
0.6
2:45
Transverse
TSE
PD
5280
13
150
13.9
x
10
256
x
147
38/4.0
0.6
2:45
Transverse
TSE
PDFS
3370
36
180
14.9
x
10.8
256
x
147
38/3.5
0.6
3:27
Transverse
STIR
7490
13
150
15
x
10.5
384
x
216
3.8/4.0
0.6
4:01
Sagittal
TSE
T2
2550
119
150
13.9
x
18.5
256
x
154
19/3.5
0.5
1:23
Sagittal
TSE
PD
2550
12
150
13.9
x
18.5
256
x
154
19/3.5
0.5
1:23
Sagittal
3D
GEFS
8.6
3.6
15
10.8
x
13
384
x
240
31/1.5
1.5
3:22
Sagittal
STIR
3940
13
150
13.9
x
18.5
384
x
230
19/3.5
0.5
2:15
Dorsal
TSE
T1
920
11
180
10.7
x
18.0
256
x
122
22/3.0
0.5
0:40
TSE,
turbo
spin
echo;
T2,
T2-weighted;
PD,
proton
density;
FS,
fat
saturated;
STIR,
short
r
inversion
recovery;
3D
GE,
three
dimensional
gradient
echo;
TR,
repetition
time;
TE,
echo
time;
FA,
flip
angle;
FOV,
field
of
view.
study.
Lameness
was
localized
to
the
MCP/MTP
region
by
perineural
local
anesthesia,
intra-articular,
or
digital
flexor
tendon
sheath
blocks
in
212
horses.
In
20
horses,
lame-
ness
was
localized
by
observing
at
least
two
of
the
follow-
ing
clinical
signs:
a
positive
response
to
distal
limb
flex-
ion,
effusion
of
the
MCP/MTP
joint,
soft
tissue
swelling
around
the
MCP/MTP
region,
and/or
digital
flexor
ten-
don
sheath
effusion.
Two
horses
had
lameness
localized
to
the
MCP/MTP,
but
did
not
have
visible
lesions
on
MR
imaging
and
were
excluded
from
the
study.
Follow-
ing
MR
imaging,
diagnostic
anesthesia
was
repeated
on
these
horses,
and
the
lameness
was
subsequently
localized
to
a
different
anatomic
location.
There
were
128
geldings,
83
mares,
and
21
stallions.
Breeds
of
horses
in
the
study
included
Quarter
horses
(78),
Warmbloods
(69),
Thoroughbreds
(43),
Arabians
(11),
Paints
(11),
Morgans
(3),
ponies
(3),
half-Arabians
(2),
An-
dalusians
(2),
Warmblood/Thoroughbred
crosses
(2),
Mis-
souri
Fox
Trotter
(1),
Friesian
(1),
Hackney
(1),
Lusitano
(1),
Percheron
(1),
Rocky
Mountain
Horse
(1),
grade
(1),
and
unknown
(1).
Age
ranged
from
10
months
to
26
years
(median
7
years;
mean
7.6
years).
The
age
was
unknown
in
one
horse.
Horses
were
used
for
a
variety
of
disciplines:
hunter-jumper
(37),
dressage (33),
show
(29),
racing
(27),
barrel
racing
(23),
reining
(17),
eventing
(11),
cutting
(10),
western
pleasure
(7),
pleasure
(4),
English
(3),
breeding
(3),
roping
(2),
carriage
(2),
polo
(1),
team
penning
(1),
and
steer
wrestling
(1).
The
use
was
unknown
in
21
horses.
Lameness
grades
ranged
from
0/5
to
4.5/5
(median
2/5;
mean
1.92/5).
There
were
325
limbs
(232
horses)
that
had
abnormalities
on
MR
imaging,
85
right
forelimbs,
81
right
hind
limbs,
80
left
forelimbs,
and
79
left
hind
limbs.
MR
imaging
abnor-
malities
were
seen
bilaterally
in
the
forelimbs
in
46
horses,
in
the
hind
limbs
in
37
horses,
and
in
all
four
limbs
in
one
horse.
Of
the
horses
with
bilateral
forelimb
abnormal-
ities,
27
were
not
lame
in
the
contralateral
forelimb
at
the
time
of
examination.
Of
the
horses
with
bilateral
hind
limb
abnormalities,
22
were
not
lame
in
the
contralateral
hind
limb
at
the
time
of
examination.
It
was
unknown
if
these
horses
had
been
lame
on
the
contralateral
limb
in
the
past.
TABLE
3.
Prevalence
of
Injuries
in
235
Limbs
(232
Horses)
Injuries
diagnosed
on
MR
No.
of
Injuries/%
n=
461
prevalence
of
injury
ODSL
injury
144/31%
SDSL
injury
95/21%
Chronic
SCB
injury
45/10%
SLB
injury
38/8%
CL
injury
33/7%
OC
defect
<1
cm
18/4%
OC
defect
>1
cm
16/3%
ISL
injury
15/3%
PAL
injury
13/3%
Bone
contusion
12/3%
AC
injury
10/2%
SDFT
injury
10/2%
P1
fractures
6/1%
DDFT
injury
6/1%
ODSL,
oblique
distal
sesamoidean
ligament;
SDSL,
straight
distal
sesamoidean
ligament;
SCB,
subchondral
bone;
SLB,
suspensory
liga-
ment
branch;
CL,
collateral
ligament;
OC,
osteochondral;
ISL,
inters-
esamoidean
ligament;
PAL,
palmar/plantar
annular
ligament;
AC,
artic-
ular
cartilage;
SDFT,
superficial
digital
flexor
tendon;
DDFT,
deep
digital
flexor
tendon.
All
horses
had
the
same
primary
abnormality
in
the
con-
tralateral
limb;
abnormalities
in
the
contralateral
limb
were
observed
to
be
less
severe
compared
to
the
lame
limb
in
all
horses.
The
total
prevalence
of
injuries
described
below
is
summarized
in
Table
3.
Soft
tissue
injuries
were
the
only
abnormalities
observed
in
218
limbs
(162
horses).
Oblique
distal
sesamoidean
lig-
ament
desmitis
was
diagnosed
in
144
limbs
(57
left
hind,
38
right
hind,
25
right
fore,
and
24
left
fore)
in
107
horses.
Of
these
horses,
bilateral
abnormalities
were
seen
in
32
horses
(20
horses
with
bilateral
hind
limb
oblique
distal
sesamoidean
ligament
desmitis,
11
horses
with
bilateral
forelimb
oblique
distal
sesamoidean
ligament
desmitis,
and
one
horse
with
oblique
distal
sesamoidean
ligament
desmi-
tis
in
all
four
limbs).
Oblique
distal
sesamoidean
ligament
desmitis
was
the
only
diagnosis
in
73
limbs
(56
horses).
Lameness
grades
for
this
group
of
horses
ranged
from
0/5-3/5
(median
2/5;
mean
1.64/5).
Abnormalities
in
the
oblique
distal
sesamoidean
ligaments
were
seen
as
enlarge-
ment
of
the
ligaments
and
diffuse
or
focal
increased
high
VoL.
54,
No.
1
MRI
FINDINGS
IN
HORSES
WITH
MCP/MTP
LAMENESS
39
A
B
FIG.
1.
Transverse
proton
density
(PD)
images
of
the
left
(A)
and
right
(B)
forelimbs
at
the
level
of
the
proximal
aspect
of
the
proximal
phalanx.
The
horse
had
a
left
forelimb
lameness
that
switched
to
the
right
forelimb
following
an
abaxial
sesamoid
block.
There
is
enlargement
of
both
medial
oblique
distal
sesamoidean
ligaments
with
discrete
areas
of
abnormal
high
signal
intensity
(arrows).
Lateral
is
to
the
right
in
(A)
and
to
the
left
in
(B).
signal
intensity
on
PD
and
T2
or
STIR
axial
sequences.
Due
to
the
large
variation
in
size
and
heterogeneous
ap-
pearance
of
oblique
distal
sesamoidean
ligaments
in
non-
lame
horses
15
,
enlargement
and
increased
high
signal
inten-
sity
was
determined
by
comparison
with
the
contralateral
limb.
All
horses
diagnosed
with
injury
to
the
oblique
distal
sesamoidean
ligaments
had
diffuse
or
discrete
areas
of
ab-
normal
high
signal
intensity
within
the
ligaments
(Fig.
1).
Oblique
distal
sesamoidean
ligament
insertional
injuries
were
found
in
six
horses.
Two
horses
had
enlargement
and
abnormal
high
signal
intensity
within
the
medial
oblique
distal
sesamoidean
ligament
and
increased
high
signal
in-
tensity
on
fat-suppressed
images
at
the
origin
of
the
liga-
ment
on
the
base
of
the
medial
sesamoid
bone.
Two
horses
had
similar
abnormalities
affecting
the
lateral
oblique
distal
sesamoidean
ligament
and
both
oblique
distal
sesamoidean
ligaments
at
their
origin
on
the
base
of
the
proximal
sesamoid
bones.
One
horse
had
injury
to
the
insertion
of
the
medial
oblique
distal
sesamoidean
ligament
on
the
proxi-
mal
aspect
of
the
proximal
phalanx.
This
abnormality
was
seen
as
abnormal
high
signal
intensity
at
the
insertion
on
the
proximal
phalanx
on
fat-suppressed
images.
One
horse
had
a
core
lesion
in
the
lateral
oblique
distal
sesamoidean
liga-
ment
and
insertional
injuries
on
both
the
proximal
aspect
of
the
proximal
phalanx
and
the
base
of
the
lateral
sesamoid
bone.
Nearly
all
breeds
were
diagnosed
with
an
oblique
distal
sesamoidean
ligament
injury,
yet
the
most
frequent
were
Quarter
horse
(38/35.2%),
Warmblood
(32/29.6%),
Thoroughbred
(19/17.6%),
Paint
(7/6.5%),
and
Arabian
(4/3.7%).
There
were
less
than
two
horses
of
each
of
other
breeds
(8/7.4%).
Straight
distal
sesamoidean
ligament
desmitis
was
the
second
most
commonly
diagnosed
soft
tissue
injury
in
the
MCP/MTP
region
and
was
found
to
be
abnormal
in
95
limbs
(28
right
fore,
25
right
hind,
23
left
fore,
and
19
left
hind)
in
76
horses.
Bilateral
abnormalities
in
the
straight
distal
sesamoidean
ligament
were
seen
in
19
horses
(11
horses
with
bilateral
forelimb
straight distal
sesamoidean
ligament
desmitis
and
eight
horses
with
bilateral
hind
limb
straight
distal
sesamoidean
ligament
desmitis).
Straight
distal
sesamoidean
ligament
desmitis
was
the
only
diag-
nosis
made
in
44
limbs
(38
horses).
Lameness
grades
for
the
group
ranged
from
0/5
to
3.5/5
(median
2/5;
mean
1.62/5).
Abnormalities
in
the
straight
distal
sesamoidean
ligament
were
an
increase
in
size,
diffuse
areas
of
interme-
diate
signal
intensity,
or
small
areas
of
abnormal
high
sig-
nal
when
compared
to
the
contralateral
limb
(Fig.
2).
The
most
common
breeds
with
straight
distal
sesamoidean
lig-
ament
injury
were
Warmblood
(32/42.1%),
Quarter
horse
(17
(22.4%),
Thoroughbred
(13/17.1%),
Arabian
(5/6.6%),
and
Paint
(3/3.9%).
There
was
one
of
each
of
other
breeds
affected
(6/7.9%).
Desmitis
of
the
oblique
distal
sesamoidean
ligaments
and
the
straight
distal
sesamoidean
ligament
was
seen
con-
currently
in
30
limbs
(28
horses),
and
was
the
only
diag-
nosis
made
in
21
limbs
(20
horses).
Lameness
grades
for
this
group
of
horses
ranged
from
0/5
to
3.5/5
(median
2/5;
mean
of
1.83/5).
In
those
horses
diagnosed
with
distal
sesamoidean
ligament
injuries
alone,
the
following
diagnos-
tic
anesthesia
blocks
improved
lameness
(>50%):
low
four-
point,
71/71
limbs
(100%);
digital
flexor
tendon
sheath,
22/22
limbs
(100%);
basisesamoid,
1/1
(100%);
abaxial
40
KING
ET
AL.
2013
FIG.
2.
Transverse
proton
density
(PD)
image
at
the
level
of
the
middle
of
the
proximal
phalanx
in
the
right
forelimb.
The
straight
distal
sesamoidean
ligament
is
enlarged
and
round
with
discrete
areas
of
abnormal
high
signal
intensity
(arrow).
sesamoid,
14/15
limbs
(93%);
intra-articular
MCP/MTP,
11/19
(58%);
palmar/plantar
digital
nerve,
24/70
limbs
(34%).
Suspensory
ligament
branch
desmitis
was
diagnosed
in
38
limbs
(13
right
fore,
nine
left
fore,
eight
left
hind,
and
eight
right
hind)
in
32
horses.
There
were
six
cases
of
bilat-
eral
suspensory
ligament
branch
desmitis
(five
forelimb
and
one
hind
limb).
Medial
suspensory
ligament
branch
was
di-
agnosed
in
18
limbs;
lateral
suspensory
ligament
branch
desmitis
was
present
in
15
limbs;
and
both
suspensory
branches
were
abnormal
in
five
limbs.
Suspensory
ligament
branch
desmitis
was
the
only
diagnosis
made
in
14
limbs
(12
horses).
Abnormalities
in
the
suspensory
ligament
branch
were
seen
as
enlargement
and
increased
high
signal
inten-
sity
compared
to
the
contralateral
limb.
Increased
high
sig-
nal
intensity
occurred
either
as
a
focal
area
or
diffusely
throughout
the
ligament
(Fig.
3).
Insertional
injuries
on
the
abaxial
border
of
the
proximal
sesamoid
bones
were
seen
in
11
limbs
(nine
horses).
These
horses
had
focal
areas
of
high
signal
extending
from
the
branch
of
the
suspensory
liga-
ment
into
the
proximal
sesamoid
bones
on
fat-suppressed
images
(STIR
sequences)
(Fig.
4).
Lameness
grades
ranged
from
0
to
3.5/5
(median
2.5;
mean
2.14/5).
Diagnostic
lo-
cal
anesthesia
was
performed
on
11
limbs
with
suspensory
ligament
branch
desmitis
as
the
primary
diagnosis;
10/10
limbs
improved
>80%
with
a
low-four
point
and
an
abaxial
sesamoid
block
eliminated
lameness
in
another
limb.
Collateral
ligament
desmitis
was
diagnosed
in
33
limbs
(11
right
hind,
10
left
fore,
seven
left
hind,
and
five
right
fore)
in
33
horses.
No
horse
was
observed
to
have
col-
lateral
ligament
desmitis
bilaterally.
Lateral
collateral
liga-
FIG.
3.
Transverse
proton
density
image
of
the
left
forelimb
at
the
level
of
the
junction
of
the
distal
third
of
the
proximal
metacarpus.
There
is
en-
largement
of
the
lateral
suspensory
ligament
branch
and
abnormal
increased
signal
intensity
(arrow).
Lateral
is
to
the
right
in
this
image.
ment
collateral
ligament
desmitis
was
diagnosed
in
20
limbs
and
medial
collateral
ligament
desmitis
was
diagnosed
in
13
limbs.
A
primary
diagnosis
of
collateral
ligament
desmitis
was
made
in
12
limbs
(12
horses).
Lameness
grades
ranged
from
0/5
to
4/5
(median
2.25/5;
mean
1.93/5).
Three
limbs
had
an
insertional
injury
on
the
proximal
phalanx
and
one
limb
had
injury
to
the
MCL
at
its
insertion
on
the
third
metatarsal
bone;
both
sites
had
increased
high
signal
in-
tensity
on
fat-suppressed
images,
consistent
with
injury
to
the
ligament
insertion
on
the
bone.
Collateral
ligament
ab-
normalities
were
seen
as
enlargement
of
the
ligaments
and
diffuse
increased
high
signal
intensity
when
compared
to
the
contralateral
limb
(Fig.
5).
A
low
four-point
block
was
performed
in
eight
horses
and
eliminated
lameness
in
all
horses.
An
intra-articular
block
eliminated
lameness
in
3/3
horses.
Intersesamoidean
ligament
desmitis
was
diagnosed
in
15
limbs
(seven
right
fore,
five
left
fore,
two
right
hind,
and
one
left
hind)
in
11
horses.
Four
horses
had
bilateral
in-
tersesamoidean
ligament
desmitis
in
the
forelimbs.
A
pri-
mary
diagnosis
of
intersesamoidean
ligament
desmitis
was
made
in
five
limbs
(four
horses).
Abnormalities
in
the
inter-
sesamoidean
ligament
were
seen
as
abnormal
high
signal
intensity
centrally
within
the
ligament
on
transverse
STIR
or
PD
sequences
(Fig.
6).
One
horse
had
intersesamoidean
ligament
desmitis
with
axial
osteitis
of
the
medial
proximal
sesamoid
bone.
Images
of
this
horse
revealed
a
focal
area
of
abnormal
high
signal
intensity
within
the
axial
aspect
of
the
medial
sesamoid
bone
on
all
imaging
sequences.
VoL.
54,
No.
1
MRI
FINDINGS
IN
HORSES
WITH
MCP/MTP
LAMENESS
41
4
11
10
1
/
4".
1
")
,
.10
FIG.
4.
Transverse
proton
density
(PD)
(A)
and
sagittal
STIR
(B)
images
from
a
horse
with
a
left
forelimb
lameness.
(A)
There
is
enlargement
of
the
medial
suspensory
ligament
branch
with
discrete
areas
of
abnormal
increased
signal
intensity
(arrows).
(B)
There
are
areas
of
abnormal
increased
signal
intensity
(arrows)
within
the
medial
suspensory
ligament
branch
and
medial
proximal
sesamoid
bone
at
the
site
of
ligament
insertion
to
the
bone.
Lateral
is
to
the
right
in
(A).
Abnormalities
in
the
digital
flexor
tendons
were
subtle
and
considered
to
be
the
cause
of
lameness
in
10
limbs
(10
horses).
Superficial
digital
flexor
tendonitis
was
diagnosed
in
10
limbs
(nine
horses)
and
involved
the
manica
flexoria
in
six
limbs
(five
horses).
Abnormalities
in
the
manica
flexoria
appeared
as
thickening
with
diffuse
increased
high
signal
intensity
(Fig.
7).
Abnormalities
in
the
SDFT
included
an
FIG.
5.
Transverse
proton
density
(PD)
image
of
the
right
hind
limb
at
the
level
of
the
distal
metacarpus
in
a
horse
with
bilateral
hind
limb
lameness.
There
is
periosteal
and
endosteal
irregularity
of
the
dorsomedial
cortex
of
MTIII
(arrows)
where
the
medial
collateral
ligament
inserts
on
the
bone
with
a
slight
amount
of
increased
high
signal
intensity
in
the
dorsal
portion
of
the
ligament.
Lateral
is
to
the
left
.
..-
'"
-a
te
FIG.
6.
Transverse
proton
density
(PD)
with
fat
saturation
image
at
the
level
of
the
distal
metacarpus
in
a
horse
with
a
left
forelimb
lameness
that
blocked
out
with
infra-articular
anesthesia.
There
is
a
discrete
area
of
abnor-
mal
increased
signal
intensity
within
the
intersesamoidean
ligament
(arrow).
Lateral
is
to
the
right
in
this
image.
increase
in
size,
nondiscrete
areas
of
increased
high
signal
intensity,
and
core
lesions.
Deep
digital
flexor
tendonitis
was
diagnosed
in
six
limbs
in
(six
horses).
Lesions
in
the
deep
digital
flexor
tendon
were
visualized
as
enlargement,
nondiscrete
areas
of
increased
high
signal
intensity,
and
B
42
KING
ET
AL.
2013
A
FIG.
7.
Transverse
proton
density
(PD)
image
at
the
level
of
the
junction
of
the
distal
third
of
the
proximal
metacarpus
in
a
horse
with
a
right
forelimb
lameness.
There
is
increased
signal
intensity
and
enlargement
of
the
manica
flexoria
(arrow).
There
is
effusion
in
the
digital
flexor
tendon
sheath
(large
arrowhead)
with
a
normal
synovial
fold
(small
arrowhead).
Lateral
is
to
the
left
in
this
image.
core
lesions.
Three
other
horses
were
diagnosed
with
su-
perficial
digital
flexor
and
deep
digital
flexor
tendonitis
in
the
same
limb.
Tenosynovitis
was
observed
with
flexor
ten-
donitis
in
seven
limbs
(seven
horses)
with
adhesions
present
in
three
limbs
(three
horses).
Flexor
tendon
abnormali-
ties
occurred
within
the
MCP/MTP
canal
in
16
limbs
(15
horses).
Proximal
palmar/plantar
annular
ligament
abnor-
malities
were
observed
in
13
limbs
(12
horses).
Flexor ten-
donitis
was
seen
in
only
four
limbs
(four
horses)
diagnosed
with
palmar/plantar
annular
ligament
abnormalities.
Pal-
mar/plantar
annular
ligament
abnormalities
were
seen
as
thickening
of
the
ligament
and
mildly
increased
high
signal
intensity.
There
were
insertional
injuries
to
the
proximal
sesamoid
bones
in
five
limbs
(four
horses),
with
abnormal
high
signal
intensity
visualized
on
fat-suppressed
images
(Fig.
8).
Other
soft
tissue
injuries
were
seen
infrequently
and
were
not
the
primary
diagnosis
in
any
case.
They
in-
cluded
thickening
of
the
fibrocartilage
pad
(two
horses)
and
dorsal
joint
capsule
thickening
or
tearing
(four
horses).
Bone
and
cartilage
abnormalities
were
the
only
ab-
normalities
observed
in
43
limbs
(34
horses).
The
fol-
lowing
diagnostic
anesthesia
blocks
improved
lameness
(>50%)
in
horses
with
bone
and
cartilage
abnormalities
alone:
low
four-point,
19/19
limbs
(100%);
intra-articular
MCP/MTP,
11/11
limbs
(100%);
abaxial
sesamoid,
3/3
limbs
(100%);
digital
flexor
tendon
sheath,
1/1
limb
(100%);
basisesamoid,
1/1
limb
(100%).
1
B
FIG.
8.
Transverse
short
r
inversion
recovery
(STIR)
images
of
the
left
(A)
and
right
(B)
forelimbs
at
the
level
of
the
metacarpophalangeal
joint.
The
horse
had
a
left
forelimb
lameness
that
was
localised
to
the
metacarpo(tarso)phalangeal
(MCP/MTP)
region.
A
right
forelimb
lameness
was
observed
following
this
block
and
the
horse
improved
following
intra-
articular
anesthesia
of
the
right
front
MCP/MTP
joint.
There
is
increased
signal
intensity
on
the
abaxial
aspect
of
the
medial
proximal
sesamoid
bones
bilaterally
at
the
insertion
of
the
palmar
annular
ligaments
(arrows).
Ad-
ditionally,
the
palmar
annular
ligament
is
thickened
with
increased
signal
intensity
(B)
in
the
right
forelimb
(arrowhead).
There
is
also
increased
signal
intensity
in
the
intersesamoidean
ligaments
bilaterally.
Lateral
is
to
the
right
in
(A)
and
to
the
left
in
(B).
Chronic
subchondral
bone
injuries
were
observed
in
45
limbs
(16
right
hind,
12
left
hind,
10
right
fore,
seven
left
fore)
in
30
horses.
Abnormalities
observed
were
areas
of
increased
low
signal
intensity
(>1
cm)
in
the
subchon-
dral
bone
on
PD
sequences
(Fig.
9).
These
injuries
were
VoL.
54,
No.
1
MRI
FINDINGS
IN
HORSES
WITH
MCP/MTP
LAMENESS
43
FIG.
9.
Sagittal
proton
density
(PD)
image
from
a
horse
with
a
right
forelimb
lameness.
There
is
increased
low
signal
intensity
(sclerosis)
within
the
trabecular
bone
of
the
palmar
medial
condyle
(arrows).
observed
in
the
palmar/plantar
condyles
biaxially
(17),
me-
dial
condyle
(9),
lateral
palmar/plantar
condyle
(8),
medial
palmar/plantar
condyle
(8),
proximal
P1
(5),
dorsal
cannon
bone
(5),
proximal
sesamoid
bones
(3),
and
lateral
condyle
(2).
Twelve
limbs
had
more
than
one
location
of
sclero-
sis
or
increased
low
signal
intensity.
Chronic
subchondral
bone
injuries
were
the
primary
abnormality
observed
in
15
limbs
(12
horses).
Lameness
grades
for
this
group
of
horses
ranged
from
0/5
to
4/5
(median
1.5/5;
mean
1.67/5).
Breeds
with
chronic
subchondral
bone
injuries
were
Thor-
oughbred
(12/41%),
Quarter
horse
(9/31%),
Warmblood
(6/21%),
and
Paint
(2/7%).
All
Thoroughbreds
were
used
for
racing
except
one
that
was
used
for
jumping.
Seven
of
the
nine
Quarter
horses
were
used
for
western
performance
events
(barrel
racing,
cutting,
roping).
Small
OC
defects
less
than
1
cm
were
observed
in
18
limbs
(seven
left
fore,
six
right
fore,
four
left
hind,
one
right
hind)
in
17
horses.
Small
defects
in
the
articular
cartilage
were
observed
overlying
an
area
of
increased
low
signal
intensity
in
the
subchondral
bone
on
PD
sequences
that
surrounded
a
focal
area
of
increased
high
signal
intensity
on
STIR
sequences
(Fig.
10).
Increased
high
signal
on
STIR
sequences
was
not
seen
in
all
limbs
in
this
group
(1)
and
was
occasionally
seen
on
PD
sequences
(3).
Osteochondral
defects
less
than
1
cm
were
observed
in
the
medial
condyle
(12),
sagittal
ridge
(3),
proximal
P1
(3),
lateral
condyle
(2),
and
proximal
sesamoid
bones
(2).
Four
limbs
had
more
than
one
location
with
osteochondral
defects
less
than
1
cm.
Osteochondral
defects
less
than
1
cm
were
the
primary
A
0
I L
ti
B
I
ti
FIG.
10.
Transverse
proton
density
(PD)
(A)
and
short
r
inversion
re-
covery
(STIR)
(B)
images
at
the
level
of
the
metacarpophalangeal
joint
of
a
horse
with
lameness
in
the
left
forelimb.
There
is
a
small
area
of
abnormal
high
signal
intensity
(arrows)
on
the
dorsal
medial
condyle
of
MCIII
(A,
B).
A
zone
of
increased
low
signal
intensity
(densification),
surrounds
the
focal
area
of
high
signal
intensity
on
the
proton
density
image
(A).
(B)
There
is
also
high
signal
intensity
in
the
palmar
axial
aspect
of
the
lateral
sesamoid
bone.
abnormality
in
eight
limbs
(seven
horses).
Lameness
grades
ranged
from
0/5
to
2.5/5
(median
(1.25/5;
mean
1.5/5).
Large
osteochondral
defects
measuring
greater
than
1
cm
were
observed
in
16
limbs
(seven
left
fore,
six
right
fore,
two
left
hind,
one
right
hind)
in
13
horses.
Abnormalities
observed
were
areas
of
increased
low
signal
intensity
in
\
.
1
.11111P
e7;
n.
fie
1
B
I
44
KING
ET
AL.
2013
A
A
B
FIG.
11.
Transverse
proton
density
(PD)
(A)
and
short
r
inversion
recov-
ery
(STIR)
(B)
images
from
a
horse
with
a
left
forelimb
lameness.
There
is
a
large
area
of
high
signal
intensity
(arrows)
within
the
subchondral
bone
of
the
dorsal
medial
condyle
of
MCIII.
There
is
a
larger
area
of
low
signal
intensity
(densification)
surrounding
the
area
of
high
signal
intensity
on
the
PD
image
(A).
Lateral
is
to
the
right
in
(A).
the
subchondral
bone
on
PD
sequences
that
surrounded
a
focal
area
of
increased
high
signal
intensity
on
STIR
sequences
(Fig.
11).
Defects
in
the
articular
cartilage
were
observed
overlying
the
area
of
subchondral bone
damage.
Locations
for
these
lesions
were
proximal
P1
(10),
medial
condyle
(8),
proximal
sesamoid
bones
(1),
sagittal
ridge
(1),
and
dorsal
cannon
bone
(1).
Five
limbs
had
more
than
one
osteochondral
defect
greater
than
1
cm.
Osteochondral
FIG.
12.
Transverse
(A)
and
sagittal
(B)
short
r
inversion
recovery
(STIR)
images
from
a
horse
with
a
right
forelimb
lameness.
There
is
an
ill-defined
area
of
increased
high
signal
intensity
in
the
sagittal
ridge
of
MCIII
(arrows).
(A)
There
is
also
linear
increased
signal
representing
vascular
flow
artifact.
Lateral
is
to
the
right
in
(A).
defects
greater
than
1
cm
were
the
primary
abnormality
in
nine
limbs
(six
horses).
Lameness
grades
ranged
from
0/5
to
4/5
(median
2/5;
mean
1.94/5).
Bone
marrow
lesions
were
observed
in
12
limbs
(nine
horses).
Abnormalities
observed
were
increased
high
sig-
nal
intensity
on
STIR
sequences.
Diffuse
areas
of
in-
creased
high
signal
intensity
or
focal
areas
greater
than
1
cm
were
observed
(Fig.
12).
Bone
marrow
lesions
occurred
on
the
medial
condyle
(5),
dorsal
cannon
bone
(5),
and
VOL.
54,
No.
1
MRI
FINDINGS
IN
HORSES
WITH
MCP/MTP
LAMENESS
45
lateral
condyle
(2).
Trabecular
bone
edema
was
observed
in
one
horse
in
the
third
metacarpal
bone
at
the
level
of
the
distal
physis.
Bone
marrow
lesions
were
the
primary
abnor-
mality
in
six
limbs
(five
horses).
Lameness
grades
ranged
from
0/5
to
3/5
(median
2.5/5;
mean
2.25/5).
There
was
a
group
of
10
horses
in
which
damage
to
the
articular
cartilage
was
observed,
with
no
abnormalities
ob-
served
in
the
underlying
subchondral
bone.
Abnormalities
observed
were
thinning
of
the
articular
cartilage
with
de-
creased
signal
intensity.
Partial
thickness
cartilage
damage
was
suspected
in
these
limbs.
Fractures
of
the
proximal
pha-
lanx
were
observed
in
six
horses
in
which
radiographs
were
normal;
incomplete
fractures
were
observed
in
two
and
os-
teochondral
fragments
were
observed
in
four.
There
were
two
horses
that
presented
for
severe
(>
4/5)
lameness
and
were
diagnosed
with
osteitis
of
the
proximal
first
phalanx
(1)
or
the
medial
proximal
sesamoid
bone
(1).
There
were
36
horses
in
which
a
subchondral
bone
or
cartilage
injury
and
soft
tissue
injury
were
concurrently
diagnosed
and
the
primary
cause
of
the
lameness
could
not
be
determined.
In
this
study,
the
prevalence
of
bone
and
cartilage
injury
as
a
primary
diagnosis
was
13%.
Bone
and
cartilage
in-
jury
was
less
common
in
Warmbloods
(19%)
compared
to
Thoroughbreds
(33%)
and
Quarter
horses
(23%).
Bone
and
cartilage
injury
was
more
commonly
diagnosed
in
Thor-
oughbred
racehorses
(43%)
compared
to
other
disciplines
(western
performance
27%,
hunter-jumper
19%,
dressage
12%).
Chronic
subchondral bone
injury
was
more
fre-
quently
diagnosed
in
Thoroughbreds
(22%)
compared
to
Quarter
horses
(8%)
and
Warmbloods
(8%).
Thorough-
bred
racehorses
were
diagnosed
with
chronic
subchondral
bone
injury
more
frequently
(30%)
than
other
disciplines
(western
performance
9%;
hunter-jumpers
8%;
dressage
3%).
Bone
marrow
lesions
were
more
common
in
hunter-
jumpers
(9%)
than
other
disciplines
(racing
4%;
western
performance
1%;
dressage
0%).
Fractures
were
more
com-
monly
seen
in
Thoroughbreds
(4%)
compared
to
Warm-
bloods
(1%)
and
Quarter
horses
(0%).
Thoroughbred
race-
horses
had
the
highest
prevalence
of
fractures
diagnosed
on
MRI
(6%)
compared
to
other
disciplines
(dressage
3%,
hunter-jumper
0%,
western
performance
0%).
Oblique
distal
sesamoidean
ligament
injury
was
more
common
in
Quarter
horses
(33%)
than
Thoroughbreds
(32%)
and
Warmbloods
(27%).
Oblique
distal
sesamoidean
ligament
injury
was
diagnosed
more
frequently
in
western
perfor-
mance
horses
(34%)
compared
to
hunter-jumpers
(29%),
racehorses
(27%),
and
dressage
horses
(21%).
Straight
dis-
tal
sesamoidean
ligament
injury
was
more
common
in
Warmbloods
(27%)
compared
to
Thoroughbreds
(15%)
and
Quarter
horses
(13%).
Straight
distal
sesamoidean
lig-
ament
injury
was
most
commonly
diagnosed
in
dressage
horses
(39%)
compared
to
other
disciplines
(racing
16%,
hunter-jumper
13%,
western
performance
11%).
Flexor
tendon
abnormalities
were
not
seen
in
Thoroughbred
race-
horses.
Discussion
Our
results
document
the
incidence
of
abnormalities
in
the
MCP/MTP
region
in
a
large
group
of
horses
from
a
wide
variety
of
breeds
and
disciplines.
Soft
tissue
injuries
did
occur
more
frequently
than
subchondral
bone
or
artic-
ular
cartilage
injuries
in
horses
with
radiographically
nor-
mal
fetlocks,
as
hypothesized.
This
differs
from
a
retro-
spective
where
subchondral
bone
injury
was
the
most
com-
monly
identified
lesion
in
the
MCP/MTP
region.
13
Distal
sesamoidean
ligament
desmitis
was
the
most
frequently
di-
agnosed
soft
tissue
injury
in
both
studies,
however,
oblique
distal
sesamoidean
ligament
injury
occurred
more
fre-
quently
than
injury
to
the
straight
distal
sesamoidean
liga-
ment
in
this
study.
These
results
were
similar
to
previously
reported
prevalence
of
injury
in
the
distal
sesamoidean
ligaments.
11,16
Oblique
distal
sesamoidean
ligament
in-
juries
were
observed
more
commonly
in
the
hind
limbs
here
and
in
another
study."
Oblique
distal
sesamoidean
ligament
injuries
occurred
in
all
types
of
horses,
but
were
more
commonly
seen
in
Quarter
horses
used
for
western
performance
events
such
as
reining,
cutting,
and
barrel
racing.
While
lameness
from
injury
to
the
distal
sesamoidean
lig-
aments
has
previously
been
considered
one
problem,
17,18
it
is
important
to
differentiate
injuries
to
implement
tar-
geted
treatments
(extracorporeal
shock
wave,
regenerative
therapy,
ligament
splitting,
etc.).
As
biologic
stimulation
of
ligament
healing
becomes
more
common
using
intra-
or
perilesional
injections,
accurate
diagnosis
of
soft
tissue
injuries
becomes
more
important.
Using
MR
imaging,
it
was
possible
to
detect
bone
and
cartilage
abnormalities
that
were
not
visible
on
radiographs
(Figs.
9-12).
Chronic
subchondral
bone
injury
or
sclero-
sis
was
the
most
commonly
diagnosed
bone
injury
in
this
group
of
horses,
even
though
there
was
not
a
sufficient
change
in
bone
density
to
be
apparent
on
radiographs.
The
abnormal
low
signal
intensity
on
PD
sequences
may
be
due
to
increased
bone
density
caused
by
an
adaptive
or
mal-
adaptive
response
to
repetitive
cyclic
loading
and
stress.
19-21
Subchondral
bone
damage
can
occur
alone
without
disrup-
tion
of
the
articular
cartilage
by
repetitive
cyclic
loading
or
by
one-time,
traumatic
incidents.
When
chronically
dam-
aged
subchondral
bone
is
acutely
overloaded
beyond
the
limit
of
elastic
deformation,
plastic
deformation
or
fracture
can
occur.
2
2
Although
Thoroughbred
racehorses
were
more
commonly
represented,
chronic
subchondral
bone
injuries
were
seen
in
all
types
of
horses
in
this
study.
Abnormal
low
signal
in
subchondral bone
can
be
due
to
increased
bone
density
as
a
result
of
osteoarthritis
and
loss
of
articular
46
KING
ET
AL.
2013
cartilage,
however,
none
of
these
horses
had
radiographic
evidence
of
osteoarthritis.
Osteochondral
defects
were
thought
to
be
the
result
of
osteochondrosis
or
trauma
to
localized
areas
of
cartilage
or
subchondral
bone.
Large
osteochondral
defects
(>
1
cm)
were
found
more
commonly
in
Quarter
horses
used
for
western
performance
events
in
this
study.
The
proximal
as-
pect
of
the
proximal
phalanx
and
the
medial
condyle
of
the
third
metacarpal/metatarsal
bone
were
the
most
com-
mon
locations
for
large
osteochondral
defects.
Small
osteo-
chondral
defects
occurred
most
commonly
on
the
medial
condyle
and
were
seen
in
all
types
of
horses.
Osteochondral
defects
as
a
group
were
diagnosed
more
frequently
in
the
forelimbs.
This
may
be
due
to
a
greater
percentage
of
the
weight
being
carried
on
the
forelimbs.
Bone
marrow
lesions,
greater
than
1
cm
areas
of
hyper-
intensity
on
fat-suppressed
(STIR)
images
with
indistinct
margins,
were
believed
to
be
traumatic
in
origin.
Microfrac-
tures
in
the
trabecular
bone
23
lead
to
hemorrhage
and
edema
24,
25
and
are
likely
the
source
of
the
abnormal
high
signal
intensity.
Studies
in
humans
suggest
hyperintensity
on
fat-suppressed
MR
images
was
caused
by
hemorrhage
and
edema,
24,25
however,
in
osteoarthritic
knees,
there
were
abnormalities
in
the
trabecular
bone,
as
well
as
bone
mar-
row
fibrosis
and
necrosis
without
significant
edema
in
areas
thought
to
be
edematous
based
on
MR
images.
26
Bilateral
bone
marrow
lesions
were
seen
in
three
horses;
two
horses
were
not
lame
in
the
contralateral
limb
at
the
time
of
ex-
amination.
The
time
for
resolution
of
bone
contusions
on
fat-suppressed
MR
images
of
horses
is
unknown.
Intrathecal
anesthesia
of
the
digital
flexor
tendon
sheath
was
performed
following
MR
imaging
on
22
horses
with
a
distal
sesamoidean
ligament
injury
and
lameness
im-
proved
in
every
horse.
In
horses
with
injuries
to
a
distal
sesamoidean
ligament
and
bone
or
cartilage,
intrathecal
and/or
intra-articular
anesthesia
was
performed
following
MR
imaging
to
help
determine
the
primary
cause
of
lame-
ness
and
develop
a
subsequent
treatment
plan.
In
this
study,
it
is
important
to
note
that
intra-articular
anesthesia
im-
proved
lameness
in
11
of
19
horses
with
distal
sesamoidean
ligament
desmitis
near
their
origin
on
the
base
of
the
prox-
imal
sesamoid
bones.
Lameness
due
to
collateral
ligament
injury
improved
three
of
3
horses
with
intra-articular
anes-
thesia.
Intra-articular
anesthesia
was
not
performed
on
any
horses
in
this
study
with
a
primary
diagnosis
of
a
suspen-
sory
ligament
branch
injury,
however,
lameness
can
im-
prove
with
intra-articular
anesthesia.
13
Therefore,
it
is
im-
portant
to
consider
soft
tissue
injury
within
or
in
close
proximity
to
the
MCP/MTP
joint
capsule
when
lameness
is
improved
with
intra-articular
anesthesia
of
the
MCP/MTP
joint.
Ultrasound
was
performed
in
31%
of
horses
in
this
study
(76/232).
In
horses
diagnosed
with
suspensory
ligament
branch
injuries,
11
horses
had
ultrasound
evaluation
per-
formed
prior
to
MR
imaging.
In
eight
of
these
horses,
no
significant
abnormalities
were
observed.
In
three
horses,
fiber
pattern
disruption
of
a
suspensory
ligament
branch
was
observed
with
ultrasonography
prior
to
MR
imaging.
The
diagnosis
of
suspensory
ligament
branch
desmitis
was
confirmed
using
MR
imaging
in
these
horses,
but
other
ab-
normalities
were
also
observed.
One
horse
was
diagnosed
with
an
incomplete
fracture
of
the
proximal
phalanx
and
arthroscopic
surgery
was
performed
to
further
evaluate
the
joint.
Another
horse
was
diagnosed
with
articular
cartilage
damage
and
fraying
of
the
suspensory
ligament
branch
ex-
tending
into
the
MCP
joint,
which
made
this
horse
a
can-
didate
for
arthroscopic
evaluation.
The
third
horse
was
also
diagnosed
with
deep
digital
flexor
tendonitis
that
was
not
visualized
with
ultrasound,
allowing
for
treatment
to
be
directed
at
both
problems
and
included
injection
of
the
digital
flexor
tendon
sheath.
When
ultrasound
examination
was
performed
prior
to
MR
imaging,
additional
diagnoses
were
made
in
all
horses
after
MR
imaging,
which
changed
the
treatment
regimen.
Magnetic
Resonance
imaging
evaluation
of
the
distal
sesamoidean
ligament
is
complicated
by
the
variation
in
signal
intensity
that
occurs
in
normal
ligament.
Oblique
distal
sesamoidean
ligaments
have
intermediate
signal
in-
tensity
due
to
fibrocartilage
separating
the
collagen
bundles
at
their
proximal
aspect.
15
This
intermediate
signal
pattern
is
variable
between
horses.
The
straight
distal
sesamoidean
ligament
also
contains
intermediate
signal
intensity
created
by
the
connective
tissue
that
separates
the
collagen
bundles
within
the
ligament,
creating
a
heterogeneous
appearance
to
this
structure.
15
Because
of
the
variation
between
indi-
vidual
horses,
imaging
both
limbs
is
a
necessary
step
that
can
help
identify
variations
in
signal
intensity
as
normal
or
abnormal
for
that
horse.
Accurate
assessment
of
articular
cartilage
with
MR
imaging
is
limited
in
the
equine
MCP/MTP
joint.
27
In
this
study,
there
were
few
articular
cartilage
abnormalities
that
did
not
involve
the
subchondral
bone.
The
articular
car-
tilage
in
the
MCP/MTP
is
thin,
thus
it
contains
less
total
signal
in
each
voxel,
thus
reducing
its
conspicuity.
The
volu-
metric
averaging
that
occurs
when
a
voxel
is
converted
into
a
pixel
can
make
it
difficult
to
identify
abnormalities
in
thin
articular
cartilage.
The
use
of
thin
slices
and
obtaining
slices
perpendicular
to
the
articular
surface
can
make
it
easier
to
identify
cartilage
defects.
Proton
density
or
T1-weighted
images
with
fat
suppression
will
create
differences
in
sig-
nal
intensity
between
the
articular
cartilage
and
synovial
fluid,
and
subchondral
bone,
making
identification
easier.
In
some
instances,
the
visualization
of
abnormalities
in
the
subchondral bone
can
be
used
to
identify
areas
that
must
be
closely
scrutinized
for
cartilage
damage.
Flexor
tendon
abnormalities
were
diagnosed
less
fre-
quently
than
other
injures.
This
is
likely
due
to
frequent
diagnosis
of
this
problem
with
ultrasound.
Most
horses
VoL.
54,
No.
1
MRI
FINDINGS
IN
HORSES
WITH
MCP/MTP
LAMENESS
47
in
this
study
were
imaged
because
a
diagnosis
could
not
be
made.
Flexor
tendon
injuries
were
easily
identified
by
changes
in
the
size,
shape,
and
signal
intensity
of
the
af-
fected
tendon.
High-field
MR
imaging
is
useful
in
identify-
ing
even
slight
tendon
abnormalities.
Flexor
tendon
injuries
in
the
forelimbs
are
common
and
the
low
incidence
in
this
study
was
due
to
ultrasound
imaging
of
the
tendons
and
further
imaging
was
not
pursued.
The
wide
variety
of
abnormalities
observed
herein
points
out
the
value
of
MR
imaging
for
making
an
accurate
diagnosis
in
performance
horses
with
lameness
in
the
MCP/MTP
region.
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