Role of navicular bone shape in the pathogenesis of navicular disease: a radiological study


Dik, K.J.; van den Broek, J.

Equine Veterinary Journal 27(5): 390-393

1995


From progeny lists of 30 Dutch Warmblood sires, 586 3-year-old females by these stallions were randomly selected, each progeny group aimed at 20 animals for statistical reasons. The front feet of the sires and female progeny were examined radiographically using lateromedial and dorsopalmar upright pedal projections. The radiological features associated with navicular disease were classified 0-4 using a standardized classification, grades 3 and 4 representing the more severe changes. The shape of the proximal articular border of the navicular bone outlined on the dorsopalmar view was classified 1-4: 1=concave; 2=undulating; 3=straight; 4=convex. A significant shape-grade association was found, the highest grades 3 and 4 incidence associated with shape 1 and the lowest grades 3 and 4 incidence demonstrated by shape 4. In shapes 1 and 2, navicular bones grades 3 and 4 features were mainly characterized by inverted flask-shaped channels. In shape 3, navicular bones grades 3 and 4 were dominated by enthesiophytes. These findings indicate an apparent shape predisposition to radiological changes associated with navicular disease. The shape of the navicular bone in the offspring was on average the same as the sire, indicating an hereditary element in navicular bone shape.

390
EQUINE
VETERINARY
JOURNAL
Equine
vet.
J.
(1995)
27
(5)
390-393
Role
of
navicular
bone
shape
in
the
pathogenesis
of
navicular
disease:
a
radiological
study
K.
J.
DIK
and
J.
van
den
BROEK*
Departments
of
Radiology
and
*Centre
for
Biostatistics,
Faculty
of
Veterinary
Medicine,
University
of
Utrecht,
Yalelaan
10,
3584
CM
Utrecht,
The
Netherlands.
Keywords:
horse;
navicular
disease;
navicular
bone
shape;
radiography;
heredity
Summary
From
progeny
lists
of
30
Dutch
Warmblood
sires,
586
3-year-
old
females
by
these
stallions
were
randomly
selected,
each
progeny
group
aimed
at
20
animals
for
statistical
reasons.
The
front
feet
of
the
sires
and
female
progeny
were
examined
radiographically
using
lateromedial
and
dorsopalmar
upright
pedal
projections.
The
radiological
features
associated
with
navicular
disease
were
classified
0-4
using
a
standardised
classification,
grades
3
and
4
representing
the
more
severe
changes.
The
shape
of
the
proximal
articular
border
of
the
navicular
bone
outlined
on
the
dorsopalmar
view
was
classified
1-4:
1=concave;
2=undulating;
3=straight;
4=convex.
A
significant
shape-grade
association
was
found,
the
highest
grades
3
and
4
incidence
associated
with
shape
1
and
the
lowest
grades
3
and
4
incidence
demonstrated
by
shape
4.
In
shapes
1
and
2,
navicular
bones
grades
3
and
4
features
were
mainly
characterised
by
inverted
flask-shaped
channels.
In
shape
3,
navicular
bones
grades
3
and
4
were
dominated
by
enthesiophytes.
These
findings
indicate
an
apparent
shape
predisposition
to
radiological
changes
associated
with
navicular
disease.
The
shape
of
the
navicular
bone
in
the
offspring
was
on
average
the
same
as
the
sire,
indicating
an
hereditary
element
in
navicular
bone
shape.
Introduction
Navicular
disease
is
a
degenerative
syndrome
involving
the
navicular
bone,
the
palmar
aspect
of
the
distal
interphalangeal
joint,
the
navicular
bursa,
distal
aspect
of
the
deep
digital
flexor
tendon,
collateral
and
impar
sesamoidean
ligaments
(Wright
and
Douglas
1993).
Radiography
outlines
the
navicular
bone
pathology
associated
with
this
syndrome,
the
involvement
of
1
or
more
of
these
structures
reflected
by
the
character
of
the
radiological
features.
Widened,
pointed
or
conical
vascular
channels
reflect
the
tendency
for
compensation
of
a
disturbed
arterial
supply
of
the
navicular
bone
(Rijkenhuizen
et
al.
1989).
Rounded
and
inverted
flask-shaped
channels
may
be
a
consequence
of
a
reduced
arterial
blood
supply
(Colles
1979),
but
these
channels
are
also
associated
with
the
load
on
the
distal
interphalangeal
joint,
arthrosis
and
increased
intra-articular
pressure
(Hertsch
et
al.
1982).
Cystic
lucencies
frequently
represent
flexor
cortical
defects
and
flexor
cortical
abnormalities
are
usually
associated
with
lesions
of
the
bursa
and
the
deep
digital
flexor
tendon
(Poulos
1983).
Cystic
lesions
limited
to
the
medullary
spongiosa
may
result
from
ischaemic
necrosis
(Colles
1979).
Enthesiophytes
(spurs)
at
the
extremities,
or
along
the
Fig
1:
Dorsopalmar
upright
pedal
radiograph
of
navicular
bone
specimen
showing
the
variable
shape
of
the
proximal
articular
border
1=concave;
2=undulating;
3=straight;
4=convex.
Contrary
to
the
variable
outline
of
the
proximal
articular
border
the
proximal
flexor
cortex
is
convex
in
all
4
bones.
proximal
border,
result
from
strain
of
the
collateral
ligaments
(Pool
et
al.
1989).
Chip
fragments
within
the
impar
ligament
may
represent
fractures
of
the
distal
margin
of
the
navicular
bone,
ossification
secondary
to
ligamentous
damage,
separate
centres
of
ossification
within
the
impar
ligament
or
ossification
of
cartilage
particles
in
adjacent
synovial
tissue
(Poulos
et
al.
1989).
Medullary
sclerosis
is
associated
with
increased
forces
exerted
by
the
deep
digital
flexor
tendon
on
the
flexor
cortex
of
the
navicular
bone
(Pool
et
al.
1989),
consequently
medullary
osteoporosis
may
K.
J.
Dik
and
J.
van
den
Broek
391
TABLE
1:
Radiographic
classification
-
navicular
bone
(Dik
1992)
Radiographic
findings
Grade
Condition
Bone
texture
Vascular
channels
Shape
and
border
not
visible
or
several
narrow
(0.1-0.3
mm)
conical
channels
some
short
widened
(1-3
mm)
pointed
or
conical
channels
many
short,
or
some
moderately
penetrating
widened
(1-3
mm)
pointed
or
conical
channels
many
moderately,
or
some
deeply
penetrating
widened
(1-3
mm)
pointed
conical,
or
rounded
channels
many
deeply
penetrating
widened
(1-3
mm)
pointed
conical
or
rounded
channels,
or
inverted
flask-shaped
channels
variable
shape
-
bilateral
symmetric
roughening
distal
border
'chip
fragment(s)'
less
extensive
smooth
walled
new
bone
formation
along
the
proximal
border,
or
a
small
spur
on
medial
and/or
lateral
extremity
extensive
irregular
new
bone
formation
along
proximal
border,
large
spur(s),
roughening
or
erosion
of
the
flexor
surface,
fracture
0
excellent
fine
trabecular
pattern,
sharp
interface
spongiosa
-
compacta
flexor
surface
1
good
fine
trabecular
pattern,
sharp
interface
spongiosa
-
compacta
flexor
surface
2
fair
minimal
diffuse
osteoporosis
or
sclerosis,
blurring
of
the
interface
spongiosa
-
compacta
flexor
surface
3
poor
extensive
diffuse
osteoporosis
or
sclerosis,
loss
of
the
interface
spongiosa
-
compacta
flexor
surface
4
bad
cystic
radiolucency
result
from
decreased
loading.
The
association
between
the
radiological
features
and
degree
of
lameness
may
be
questionable
and
controversial,
but
standardised
classification
of
the
radiographic
findings
enables
quantified
comparison
of
the
navicular
bone
pathology
of
different
horses.
Quantifying
radiographic
navicular
scoring
systems
have
been
reported
(Rose
et
al.
1978;
Huskamp
and
Becker
1980;
MacGregor
1986),
but
these
methods
are
based
only
upon
the
distal
vascular
channels.
Only
the
radiographic
classification
reported
by
Dik
(1992)
includes
all
the
features
generally
associated
with
navicular
disease.
Radiography
also
shows
the
shape
of
the
navicular
bone.
Particularly
on
dorsopalmar
upright
pedal
radiographs
the
navicular
bone
shape
varies
considerably
between
horses,
but
is
normally
a
mirror
image
of
that
of
the
contralateral
limb
(Butler
et
al.
1993).
The
proximal
navicular
border
is
commonly
made
up
of
2
separate
lines:
one
being
the
proximal
articular
border
and
the
second
representing
the
flexor
cortex
(Kaser-Hotz
and
Ueltschi
1992).
On
dorsopalmar
upright
pedal
radiographs
the
proximal
border
of
the
flexor
cortex
usually
is
convex
and
a
straight
proximal
articular
border
is
considered
normal
(Park
1989).
In
the
Warmbloods
we
examined,
a
striking
shape
variation
concerns
the
proximal
articular
border:
instead
of
a
straight
contour,
this
border
may
also
be
concave,
undulating
or
convex
(K.
J.
Dik,
unpublished
observations).
There
is
mounting
evidence
that
mechanical
factors
associated
with
the
size,
shape
and
balance of
the
foot
and
distal
limb
conformation,
have
an
aetiological
role
in
the
syndrome
(Wright
and
Douglas
1993).
Also
the
shape
of
the
navicular
bone
may
influence
the
distribution
and
deflexion
of
the
forces
exerted
on
the
navicular
structures,
but
studies
quantifying
the
forces
exerted
on
these
structures
are
not
available.
A
familial
and
hereditary
disposition
of
navicular
disease
has
also
been
demonstrated
(van
der
Meij
et
al.
1967;
Bos
et
al.
1986)
but
an
hereditary
predisposition
of
the
navicular
bone
shape
has
not
been
reported.
The
objectives
of
this
study
were
to
assess
the
navicular
bone
shape
predisposition
to
radiological
features
of
navicular
disease
and
to
determine
the
association
between
the
navicular
bone
shapes
of
sire
and
offspring.
Materials
and
methods
Animals
The
radiographic
study
was
performed
on
30
Dutch
Warmblood
stallions
and
586
3-year-old
female
progeny.
The
stallions
were
born
in
1982-1984
and
examined
radiographically
in
1985-1987.
The
selection
criteria
used
for
these
stallions
were
variable
radiographic
navicular
bone
shapes
and
pathology,
as
well
as
at
least
30
female
3-year-old
registered
offspring
in
order
to
reach
statistically
sufficient
offspring
group
of
20
randomly
chosen
mares.
Using
these
criteria,
30
out
of
the
39
breeding
stallions
examined
in
1985-1987
qualified
for
the
study.
From
2
stallions
21
female
progeny
randomly
chosen
from
the
registered
3-year-
old
female
offspring
were
used,
20
stallions
had
20,3
stallions
19,
2
stallions
18
and
3
stallions
had
17
offspring
in
the
study.
Reasons
for
not
reaching
the
desired
number
of
20
were
mainly
unwillingness
of
the
owner,
the
current
owner
not
being
traceable
or
death
of
the
mare.
All
mares
were
examined
between
November
1992
and
October
1993.
Radiography
The
radiographic
examination
of
sires
and
progeny
was
performed
at
the
Department
of
Radiology,
Faculty
of
Veterinary
Medicine, University
of
Utrecht.
The
examination
always
included
lateromedial
and
dorsopalmar
upright
pedal
projections
of
both
front
feet,
after
removal
of
the
shoe,
cleaning
and
trimming
of
the
sole
and
the
frog
positioned
in
a
wooden
block
which
lifted
the
foot
16
cm
from
the
floor
and
tilted
the
heel
55°
upwards.
For
both
projections
the
x-ray
beam
was
directed
392
Navicular
bone
shape
TABLE
2:
Grade-shape
association
in
progeny
TABLE
3:
Association
navicular
bone
shape
-
character
of
grades
3
and
4
features
in
progeny
Shape
No
Radiographic
classification
Grade
0
and
2
Grade
3
and
4
1
212
164
48
(22.6%)
2
137
117
20
(14.6%)
3
182
164
18
(9.9%)
4
55
54
1
(1.8%)
P<0.001.
horizontally
and
centred
approximately
1
cm
above
the
coronary
band
in
the
midline.
Each
examination
began
with
the
lateromedial
projections
made
without
a
grid,
the
cassette
holder
placed
vertically
against
the
medial
aspect
of
the
foot,
the
beam
aligned
parallel
to
a
line
drawn
across
the
bulbs
of
the
heel.
After
packing
the
frog
and
sole
with
soft
soap
the
dorsopalmar
radiographs
were
obtained
using
a
grid
(10:1
ratio,
36
lines/cm)
incorporated
in
the
frontside
of
the
cassette
holder,
which
was
placed
vertically
to
the
bulbs
of
the
heel.
Radiological
evaluation
was
made
by
a
team
consisting
of
1
radiologist
and
2
equine
practitioners,
responsible
since
1985
for
the
radiographic
classification
of
the
stallions
prior
to
their
breeding
certification.
Classification
From
each
horse
the
character
of
the
radiological
features
was
recorded
and
the
changes
were
classified
0-4
using
the
standardised
classification
reported
by
Dik
(1992)
and
summarised
in
Table
1.
Grades
0
and
1
reflect
the
normal
navicular
bone,
grade
2
represents
a
fair
radiological
condition
and
grades
3
and
4
the
more
severe
radiological
features.
At
least
one
of
the
changes
listed
in
Table
1
had
to
be
present
for
grade
classification.
From
each
horse
the
navicular
bone
with
the
higher
grade
was
used.
The
shape
of
the
proximal
articular
border
of
the
navicular
bone
outlined
on
the
dorsopalmar
upright
pedal
radiographs
was
classified
I
—4:
1=concave;
2=undulating;
3=straight
and
4=convex
(Fig
1).
From
each
horse
the
shape
of
the
navicular
bone
showing
the
higher
grade
was
used.
Data
processing
The
quantified
data
of
the
progeny
were
used
to
determine
the
shape-grade
association
and
to
assess
the
association
between
the
navicular
bone
shape
and
the
character
of
grades
3
and
4
feature.
The
statistical
significance
was
determined
by
use
of
log-linear
models
(Agresti
1990),
using
a
significance
level
of
0.05.
In
order
to
describe
the
association
between
the
navicular
bone
shapes
of
the
sires
and
offspring,
several
log-linear
models
were
fitted:
the
independence
model,
symmetry
model,
quasi-symmetry
model
and
the
symmetric
random
walk
with
reflecting
boundaries
(Lindsey
1992).
A
model
was
rejected
at
a
significance
level
of
0.05.
Results
The
incidence
of
shapes
1-4
and
the
shape-grade
association
in
the
586
female
progeny
available
for
this
study
are
summarised
in
Table
2.
The
independence
model
of
this
association
was
rejected
(deviance
23.12
on
of
freedom,
P<0.001).
Modelling
the
log-
odds
linear
in
the
shape
fitted
the
data
well
(deviance
1.99
on
of
freedom).
This
indicates
a
significant
shape-grade
association
Character
Inverted
flask-
Shape
No
shaped
channels
Enthesiophytes
Complex
1
48
23
(47.9%)
12
(25%)
13
(27.1%)
2
20
11
(55%)
8
(40%)
1
(5%)
3
18
4
(22.2%)
11
(62.2%)
3
(16.7%)
4
1
1
(100%)
P=0.035.
(P<0.001)
shape
1
showing
the
highest
grades
3
and
4
incidence
(22.6%),
shape
4
associated
with
a
very
low
grades
3
and
4
incidence
(1.8%).
The
odds
ratio
is
0.57
showing
that
the
odds
of
grades
3
and
4
vs.
grades
0
and
2
are
reduced
by
a
factor
0.57
for
a
unit
change
in
shape
towards
shape
4.
Therefore,
roughly
the
relatively
risk
for
grades
3-4
is
reduced
by
a
factor
0.5
for
each
shape
towards
shape
4.
The
association
between
the
navicular
bone
shape
and
the
character
of
grades
3
and
4
features
in
the
offspring
are
summarised
in
Table
3.
This
association
was
statistically
significant
(P=0.035),
In
shapes
1
and
2,
navicular
bones
grades
3
and
4
were
mainly
characterised
by
inverted
flask-shaped
channels
(47.9%
and
55%
respectively).
Grades
3
and
4
predominantly
resulting
from
the
presence
of
enthesiophytes
or
based
upon
a
complex
character
of
the
radiological
features,
i.e.
the
presence
of
several
of
the
features
listed
in
Table
1,
were
encountered less
frequently.
In
shape
3,
navicular
bones
grades
3
and
4
were
dominated
by
enthesiophytes
(61.1%).
The
association
between
the
navicular
bone
shapes
of
the
sires
and
offspring
is
summarised
in
Table
4.
If
there
is
dependence
one
can
model
the
transition
probabilities,
i.e.
the
probability
that
the
progeny
has
another
bone
shape
than
the
sire.
If
theses
probabilities
are
the
same
in
each
direction,
the
model
is
known
as
a
quasi-symmetry
model.
If,
besides
quasi-symmetry,
the
marginal
totals
of
the
Table
are
the
same,
then
there
is
symmetry.
In
random
walk
models
the
transition
probability
of
2
classes
depends
on
the
distance
between
these
2
classes.
If
the
probability
that
a
sire
has
progeny
one
class
higher
than
its
own,
is
the
same
as
the
probability
of
having
progeny
one
class
lower,
then
the
random
walk
is
symmetric.
If
one
incorporates
the
fact
that
there
cannot
be
a
bone
shape
higher
than
4
and
not
lower
than
1,
the
model
is
called
a
symmetric
random
walk
with
reflecting
boundaries.
Of
the
4
models,
only
the
quasi-symmetry
and
the
symmetric
random
walk
fitted
the
data
well.
Because
the
latter
need
less
parameters
to
be
estimated,
it
is
to
be
preferred.
Consequently,
the
shape
of
the
navicular
bone
in
the
progeny
is
on
average
the
same
as
the
sire,
indicating
an
hereditary
element
in
navicular
bone
shape.
Discussion
A
combination
of
good
quality
lateromedial
and
dorsopalmar
upright
pedal
radiographs
visualises
clearly
most
of
the
radiological
features
associated
with
navicular
disease.
The
advantages
of
a
palmaroproximal-palmarodistal
oblique
projection
over
these
standard
projections
are
better
recognition
of
roughening
or
erosion
of
the
flexor
surface
and
medullary
sclerosis
(O'Brien
et
al.
1975).
However,
this
projection
was
difficult,
if
not
impossible
to
obtain
in
the
young
nonco-operative
K.
J.
Dik
and
J.
van
den
Broek
393
TABLE
4:
Association
navicular
bone
shape
of
sires
and
progeny
Progeny
Shapes
1
2
3
4
1
47
17
11
6
Sire
2
70
64
45
14
3
68
41
85
19
4
27
15
41
16
kinematic
gait
analysis
combined
with
assessment
of
the
shape,
size
and
balance
of
the
foot
and
distal
limb
conformation,
navicular
bone
shape
determination
and
classification
of
the
radiological
features
may
further
substantiate
the
proposed
theory.
An
hereditary
disposition
of
navicular
disease
has
been
reported
(Bos
et
a/.
1986).
The
additional
hereditary
predisposition
of
the
navicular
bone
shape
and
the
shape
disposition
to
radiological
changes
complicate
the
heredity
of
this
syndrome.
Attempts
to
clarify
the
hereditary
shape-disease
interaction
by
comparing
the
shape-grade
combinations
of
the
sires
and
progeny
were
not
successful.
This
may
be
a
consequence
of
the
unknown
complexity
of
the
genetic
bases
and
the
unknown
influence
of
other
pathogenic
factors
such
as
the
workload,
size,
shape
and
balance
of
the
feet
and
the
distal
limb
conformation
of
these
horses.
Log-linear
models
Deviance
°F
References
Independence
52.23
9
<0.00
Symmetry
122.52
6
<0.00
Quasi-symmetry
3.90
2
0.14
Symm.
random
walk
6.72
6
0.35
horses
used
for
this
study,
because
the
use
of
sedatives
was
not
allowed
by
many
of
the
horse
owners.
Therefore,
this
projection
was
not
included.
Consequently,
roughening
or
erosions
of
the
flexor
cortex
and
medullary
sclerosis
were
not
assessable.
However,
comparing
lame
and
nonlame
or
lesser
lame
limbs
flexor
cortical
defects
and
medullary
sclerosis
are
particularly
over-represented
in
the
more
severely
lame
horses
(Wright
1993).
Therefore,
the
palmaroproximal-palmarodistal
oblique
projection
was
not
considered
indispensable
for
evaluation
of
these
nonlame
horses.
In
all
horses
the
shape
of
the
proximal
articular
border
of
the
navicular
bone
is
a
mirror
image
of
that
of
the
contralateral
limb
(Butler
et
al.
1993).
The
ultimate
association
between
navicular
bone
shape
and
the
radiological
features
of
navicular
disease
are
best
demonstrated
by
the
poorest
radiological
findings.
Differences
of
more
than
1
grade
between
the
2
limbs
were
only
encountered
in
13
(2.2%)
of
the
616
horses.
This
justifies
the
use
of
the
navicular
bone
with
the
higher
grade
from
each
horse.
Based
on
our
study,
the
role
of
the
navicular
bone
shape
in
the
pathogenesis
of
navicular
disease
is
an
apparent
shape
predisposition
to
radiological
changes.
Shape
1
shows
the
highest
grade
3
and
4
incidence,
therefore
representing
the
poorest
shape
conformation
and
shape
4,
associated
with
a
very
low
grade
3
and
4
incidence,
reflects
the
least
susceptible
shape.
Considering
the
aetiological
role
of
mechanical
factors
in
the
syndrome
in
shapes
1
and
2
navicular
bones,
grades
3
and
4
were
mainly
characterised
by
inverted
flask-shaped
channels.
These
channels
are
associated
with
overloading
of
the
distal
interphalangeal
joint
(Hertsch
et
al.
1982).
In
shape
3,
navicular
bones
grades
3
and
4
were
dominated
by
enthesiophytes.
These
changes
indicate
strain
of
the
collateral
ligaments
(Pool
et
al.
1989).
Consequently,
the
association
between
the
navicular
bone
shape
and
the
character
of
grades
3
and
4
features
suggest
a
shape
dependent
distribution
of
the
forces
exerted
on
the
navicular
bone.
Quantified
kinematic
gait
analysis
enables
assessment
of
the
loading
exerted
on
specific
limb
regions
(Back
1994).
Therefore,
Agresti,
A.
(1982)
Categorial
Data
Analysis.
J.
Wiley,
New
York.
pp
130-260.
Back,
W.
(1994)
Development
of
Equine
Locomotion
from
Foal
to
Adult.
PhD
Thesis,
Utrecht.
Bos,
H.,
van
der
Meij,
G.J.W.
and
Dik,
K.J.
(1986)
Heredity
of
navicular
disease.
Vet.
Quarterly.
8,
68-72.
Butler,
J.A.,
Colles,
C.M.,
Dyson,
Si.,
Kold,
S.E.
and
Poulos,
P.W.
(1993)
Clinical
Radiology
of
the
Horse.
Blackwell
Scientific
Publications,
London.
p
58.
Colles,
C.M.
(1979)
Ischaemic
necrosis
of
the
navicular
bone
and
its
treatment.
Vet.
Rec.
104,
133-137.
Dik,
K.J.
(1992)
Radiographic
examination.
In:
The
Pre-Purchase
Examination
of
the
Horse,
2nd
edn.
Ed: G.
Wagenaar.
Bunge,
Utrecht.
pp
54-78.
Hertsch,
B.,
Wissdorff,
H.
and
Zeller,
R.
(1982)
Die
sogenannten
"Gefasslocher"
des
Strahlbeins
and
ihre
Beziehung
zum
Hufgelenk.
Tierdrtzl.
Prax.
10,
365-379.
Huskamp,
B.
and
Becker,
M.
(1980)
Diagnosis
and
prognosis
of
changes
in
the
navicular
bone
of
the
forelimb
of
horses
as
seen
by
radiography
during
examination
before
sale.
An
attempt
to
classify
the
findings.
Praktische
Tierarzt.
61,
858-863.
Kaser-Hotz,
B.
and
Ueltschi,
G.
(1992)
Radiographic
appearance
of
the
navicular
bone
in
sound
horses.
Vet.
Radio!.
Ultrasound
33,
9-17.
Lindsey,
J.K.
(1992)
The
Analysis
of
Stochastic
Processes
using
GLIM.
Springer
Verlage,
Berlin.
pp
33-39.
MacGregor,
C.M.
(1986)
Radiographic
assessment
of
navicular
bones,
based
on
changes
in
the
distal
nutrient
foramina.
Equine
vet.
J.
18,
203-206.
van
der
Meij,
G.J.W.,
Kleyn,
E.F.
and
van
de
Watering,
C.C.
(1967)
Een
onderzoek
naar
de
erfelijke
aanleg
voor
podotrochleitis.
Tijdschr.
Diergeneesk.
92,
1261-
1271.
O'Brien,
T.R.,
Millman,
T.M.,
Pool,
R.R.
and
Suter,
P.F.
(1975)
Navicular
disease
in
the
Thoroughbred
horse:
a
morphologic
investigation
relative
to
a
new
radiographic
projection.
J.
Am.
vet.
Rad.
Soc.
16,
39-51.
Park,
R.D.
(1989)
Radiographic
examination
of
the
equine
foot.
Vet.
Clin.
N.
Am.:
Equine
Pract.
5,
47-66.
Pool,
R.N.,
Meagher,
D.M.
and
Stover,
S.M.
(1989)
Pathophysiology
of
navicular
syndrome.
Vet.
Clin.
N.
Am.:
Equine
Pract.
5,
109-129.
Poulos,
P.W.
(1983)
Correlation
of
the
radiographic
signs
and
histologic
changes
in
navicular
disease.
Proc.
Am.
Ass.
equine
Practnrs.
29,
241-255.
Poulos,
P.W.,
Brown,
A.
and
Gamboa,
L.
(1989)
On
navicular
disease
in
the
horse.
A
roentgenological
and
pathoanatomic
study
Part
2.
Osseous
bodies
associated
with
the
impar
ligament.
Vet.
Radiol.
30,
54-58.
Rose,
R.J.,
Taylor,
B.J.
and
Steel,
J.D.
(1978)
Navicular
disease
in
the
horse:
an
analysis
of
seventy
cases
and
assessment
of
a
special
radiographic
view.
J.
equine
Med.
Surg.
2,
492-497.
Rijkenhuizen,
A.B.M.,
Nemeth,
F.,
Dik,
K.J.
and
Goedegebuure,
S.A.
(1989)
The
arterial
supply
of
the
navicular
bone
in
adult
horses
with
navicular
disease.
Equine
vet.
J.
21,
418-424.
Wright,
I.M.
(1993)
A
study
of
118
cases
of
navicular
disease:
radiological
features.
Equine
vet,
J.
25,
493-503.
Wright,
I.M.
and
Douglas,
J.
(1993)
Biomechanical
considerations
in
the
treatment
of
navicular
disease.
Vet.
Rec.
133,
109-114.
Received
for
publication:
11.7.94
Accepted:
30.3.95