Relationships of age and shape of the navicular bone to the development of navicular disease: a radiological study


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

Equine Veterinary Journal 33(2): 172-175

2001


Estimating the shape of the proximal articular border of the navicular bone and grading the radiological navicular bone condition (grades 3 and 4 representing the most severe changes), the aim of this study was to assess potential age-related implications of the previously reported shape predisposition to navicular disease in 746 normal and 174 clinically affected Dutch Warmbloods age 3-19 years. A significant, age-independent, shape-grade association found in normal and affected horses emphasises the fundamental character of the shape predisposition to navicular disease. A significant age-related increase of the least susceptible shape prevalence was found in elderly normal horses. A shape-independent low grades 3 and 4 prevalence (mean 15%) was found in normal horses, vs. a high grades 3 and 4 prevalence (mean 85%) in the affected horses. Therefore, the clinical manifestation of the disease is grade-rather than shape-dependent. A significant age-related appearance of inverted flask-shaped channels and enthesophytes was found in the clinically affected horses. However, considering the significant shape-radiological features association previously reported in 3-year-old normal horses, this association may be shape- rather than age-dependent.

172
EQUINE
VETERINARY
JOURNAL
Equine
vet.
J.
(2001)
33
(2)
172-175
Relationships
of
age
and
shape
of
the
navicular
bone
to
the
development
of
navicular
disease:
a
radiological
study
K.
J.
DIK*,
A.
J.
M.
VAN
DEN
BELT
and
J.
VAN
DEN
BROEKt
Department
of
Radiology
and
tCentre
of
Biostatistics,
Faculty
of
Veterinary
Medicine,
University
of
Utrecht,
Yalelaan
10,
3584
CM
Utrecht,
The
Netherlands.
Keywords:
horse;
navicular
disease;
navicular
bone
shape;
predisposition;
radiography
Summary
Estimating
the
shape
of
the
proximal
articular
border
of
the
navicular
bone
and
grading
the
radiological
navicular
bone
condition
(grades
3
and
4
representing
the
most
severe
changes),
the
aim
of
this
study
was
to
assess
potential
age-
related
implications
of
the
previously
reported
shape
predisposition
to
navicular
disease
in
746
normal
and
174
clinically
affected
Dutch
Warmbloods
age
3-19
years.
A
significant,
age-independent,
shape-grade
association
found
in
normal
and
affected
horses
emphasises
the
fundamental
character
of
the
shape
predisposition
to
navicular
disease.
A
significant
age-related
increase
of
the
least
susceptible
shape
prevalence
was
found
in
elderly
normal
horses.
A
shape-independent
low
grades
3
and
4
prevalence
(mean
15%)
was
found
in
normal
horses,
vs.
a
high
grades
3
and
4
prevalence
(mean
85%)
in
the
affected
horses.
Therefore,
the
clinical
manifestation
of
the
disease
is
grade-
rather
than
shape-dependent.
A
significant
age-related
appearance
of
inverted
flask-
shaped
channels
and
enthesophytes
was
found
in
the
clinically
affected
horses.
However,
considering
the
significant
shape-radiological
features
association
previously
reported
in
3-year-old
normal
horses,
this
association
may
be
shape-
rather
than
age-dependent.
Introduction
Navicular
disease
is
a
degenerative,
osteoarthritis-like
syndrome
(Wright
et
al.
1998)
involving
the
navicular
bone
and
associated
soft
tissues,
such
as
the
navicular
bursa,
the
distal
aspect
of
the
deep
digital
flexor
tendon
and
the
collateral
and
distal
impar
sesamoidean
ligaments.
Bony
pathological
changes
of
the
navicular
bone
can
be
detected
by
radiography
and
may
include
widened,
pointed,
conical
or
inverted
flask-shaped
radiolucent
channels,
cystic
lucencies,
enthesophytes
at
the
extremities
or
along
the
proximal
border,
chip
fragments
of
the
distal
border,
and
medullary
sclerosis
or
osteoporosis.
The
association
between
the
radiological
and
clinical
features
of
this
syndrome
is
controversial.
However,
the
use
of
a
standardised
classification
*Author
to
whom
correspondence
should
be
addressed.
system
of
the
radiographic
findings,
which
includes
all
these
features
(Dik
1992;
Dik
and
van
den
Broek
1995),
enables
the
quantitative
comparison
of
the
navicular
bone
pathology
of
different
horses.
In
this
system,
grades
0
and
1
reflect
the
normal
navicular
bone,
grade
2
stands
for
a
fair
radiological
condition,
and
grades
3
and
4
for
the
more
severe
radiological
conditions.
Apart
from
pathological
alterations,
radiography
also
shows
the
shape
of
the
navicular
bone.
On
dorsoproximal-palmarodistal
oblique
(upright
pedal)
radiographs
the
proximal
contour
of
the
flexor
cortex
of
the
navicular
bone
is
usually
convex,
but
the
proximal
articular
border
may
be
concave
(shape
1),
undulating
(shape
2),
straight
(shape
3)
or
convex
(shape
4).
In
the
Dutch
Warmblood
this
variation
in
shape
has
been
found
to
be
genetically
determined
and
appears
to
be
one
of
the
conformational
determinants
of
the
susceptibility
for
the
development
of
navicular
disease,
probably
due
to
a
shape
dependent
distribution
of
the
biomechanical
forces
exerted
on
the
bone
(Dik
and
van
den
Broek
1995).
Shape
1
shows
the
highest
prevalence
of
grades
3
and
4,
therefore
representing
the
poorest
shape
conformation,
and
shape
4
reflects
the
least
susceptible
shape.
There
are
clear
differences
between
breeds
in
the
prevalence
of
radiographic
changes
that
fit
within
the
syndrome
of
navicular
disease.
In
a
study
on
586
normal
3-year-old
Dutch
Warmbloods
(Dik
and
van
den
Broek
1995)
the
average
grades
3
and
4
prevalence
was
16%,
shape
1
prevalence
36%
and
shape
4
prevalence
9%.
In
121
normal,
3-year-old
Friesian
horses
the
average
grades
3
and
4
prevalence
was
2%,
shape
1
was
not
observed
and
shape
4
prevalence
was
80%
(K.J.
Dik,
unpublished
data).
In
100
cadaver
forefeet
of
Finnhorses,
a
breed
where
navicular
disease
is
also
a
rare
diagnosis,
shape
1
prevalence
was
11%
and
shape
4
prevalence
38%
(Ruohoniemi
et
al.
1998).
There
is
increasing
evidence
that
the
syndrome
of
navicular
disease
results
from
biomechanical
overloading
of
the
navicular
structures
(Wright
and
Douglas
1993).
The
ultimate
loading
of
this
region
is
determined
by
workload
and
conformation.
Workload
is
usually
age
related.
However,
it
is
not
known
whether
the
shape
predisposition
to
radiological
changes
associated
with
navicular
disease
also
has
a
relation
with
age.
The
aim
of
this
study
was
to
investigate
a
possible
relationship
by
analysing
various
age/shape/grade
associations
in
normal
and
clinically
affected
Dutch
Warmbloods
of
different
ages
and
by
determining
the
association
between
navicular
bone
shape,
age
and
the
specific
radiological
features
of
cases
with
grades
3
and
4
in
the
affected
horses.
K.
J.
Dik
et
al.
173
TABLE
1:
Navicular
bone
shape
prevalence
in
normal
horses
TABLE
3:
Navicular
bone
shape/grades
3
and
4
and
association
in
normal
horses
Age
(years)
Shape
3
10-14
15-19
1
212
(36%)
26
(25%)
10
(19%)
2
137
(24%)
29
(27%)
19
(35%)
3
182
(31%)
37
(35%)
14
(26%)
4
55
(9%)
14
(13%)
11
(20%)
TABLE
2:
Navicular
bone
shape
prevalence
in
clinically
affected
horses
Age
(years)
Shape
3-4
5-9
10-14
15-19
1
7
(44%)
20
(31%)
28
(36%)
4
(24%)
2
8
(50%)
26
(41%)
25
(33%)
9
(53%)
3
0
(0%)
13
(24%)
18
(23%)
3
(18%)
4
1
(6%)
5
(8%)
6
(8%)
1
(5%)
Materials
and
methods
Animals
The
normal
material
consisted
of
the
586
Dutch
Warmbloods
age
3
years
also
used
for
the
initial
study
on
the
predisposing
role
of
the
shape
of
the
navicular
bone
(Dik
and
van
den
Broek
1995),
106
age
10-14
years
and
54
age
15-19
years
with
no
history
of
forelimb
lameness.
The
clinically
affected
material
consisted
of
16
Dutch
Warmbloods
age
3
or
4
years,
64
age
5-9
years,
77
age
10-14
years
and
17
age
15-19
years.
The
minimum
criteria
for
inclusion
as
a
case
of
clinical
navicular
disease
were
bilateral
lameness
of
more
than
2
months
duration,
an
obvious
response
to
a
palmar
digital
nerve
block
and
the
absence
of
evidence
of
other
forelimb
problems.
Age
(years)
3
10-14
15-19
Grades
Grades
Grades
Shape
No.
3
and
4
No.
3
and
4
No.
3
and
4
1
212
48
(23%)
26
8
(30%)
10
2
(20%)
2
137
20
(15%)
29
3
(10%)
19
3
(16%)
3
182
18
(10%)
37
7
18%)
14
3
22%)
4
55
1
(2%)
14
0
(0%)
11
0
(0%)
TABLE
4:
Navicular
bone
shape
-
grades
3
and
4
association
in
clinically
affected
horses
Age
(years)
3-4
5-9
10-14
15-19
Grades
Grades
Grades
Grades
Shape
No.
3
and
4
No.
3
and
4
No.
3
and
4
No.
3
and
4
1
7
5
(71%)
20
19
(95%)
28
26
93%)
4
4
(100%)
2
8
5
(63%)
26
23
(88%)
25
24
(96%)
9
9
(100%)
3
0 0
(0%)
13
9
(69%)
18
15
(83%)
3
3
(100%)
4
1
0
(0%)
5
1
(20%)
6
5
(83%)
1 1
(100%)
Data
processing
The
statistical
significance
of
the
age/shape/grade
associations
in
the
normal
and
clinically
affected
horses
and
the
age/shape/radiological
features
associations
in
the
clinically
affected
horses
was
determined
by
use
of
a
log-linear
model,
in
combination
with
the likelihood
test
(Lindsey
1995).
A
significance
level
of
0.05
was
chosen.
Results
Radiography
The
radiographic
examination
of
all
horses
was
performed
at
the
Department
of
Radiology,
Faculty
of
Veterinary
Medicine,
University
of
Utrecht.
The
examination
always
included
lateromedial
and
dorsoproximal-palmarodistal
oblique
(upright
pedal)
projections
of
both
forefeet,
using
the
same
technique
as
described
for
the
initial
study
on
the
role
of
the
shape
of
the
navicular
bone
(Dik
and
van
den
Broek
1995).
Classification
The
character
of
the
radiological
features
was
recorded
for
each
horse
and
classified
using
the
standardised
0-4
scale
as
outlined
earlier
(Dik
1992;
Dik
and
van
den
Broek
1995).
Each
horse
was
classified
according
to
the
navicular
bone
with
the
highest
grade.
From
each
horse
the
shape
of
the
proximal
articular
border
of
the
navicular
bone
outlined
on
the
dorsopalmar
radiograph
was
classified
on
the
1-4
scale
as
proposed
by
Dik
and
van
den
Broek
(1995).
Here
also,
the
horse
was
classified
according
to
the
highest
scale.
The
radiological
evaluation
was
performed
independently
and
blind
by
2
equine
radiologists
(KJD.
and
AJ.M.v.).
In
case
of
differing
opinions,
consensus
was
reached
by
collective
re-evaluation.
Prevalence
of
the
various
shapes
The
shape
1-4
prevalences
in
the
normal
and
clinically
affected
horses
are
summarised
in
Tables
1
and
2.
A
significant
shape/age
association
(P
=
0.007)
was
found
in
both
the
normal
and
the
affected
population.
When
combining
both
groups,
i.e.
normal
and
clinically
affected
horses,
shapes
1
and
2
had
the
highest
prevalence
in
the
horses
age
3
or
4
years.
In
the
normal
horses,
the
shape
1
prevalence,
i.e.
the
poorest
shape
conformation,
relatively
decreased
and
the
shape
4
prevalence,
i.e.
the
least
vulnerable
shape,
relatively
increased
in
the
older
age
classes.
Compared
with
normal
animals,
there
was
a
tendency
towards
an
over-representation
of
shapes
1
and
2
at
all
ages
in
the
affected
horses
(P
=
0.083).
Association
of
shape
with
grades
3
and
4
The
shape/grades
3
and
4
associations
in
the
normal
and
the
clinically
affected
horses
are
summarised
in
Tables
3
and
4.
In
the
normal
horses
the
mean
overall
percentage
of
grades
3
and
4
was
15%.
In
the
affected
animals
this
figure
was
much
higher
(85%).
A
significant,
age-independent,
shape/grade
174
The
development
of
navicular
disease
association
(P
=
0.000)
was
found
in
the
normal
population,
with
the
risk
for
grades
3
and
4
reducing
towards
shape
4.
Contrary
to
the
normal
horses,
in
the
clinically
affected
animals
the
prevalence
of
grades
3
and
4
within
all
4
shape
classes
was
age
related
with
a
significant
increase
in
grade
3/4
prevalence
in
older
animals
(P
=
0.007).
In
the
affected
animals
the
percentage
of
grades
3
and
4
in
the
shape
1/2
classes
was
already
high
in
the
horses
age
3
or
4
years.
This
percentage
increased
further
in
the
older
age
groups.
The
percentage
of
animals
with
grades
3/4
in
shape
class
3
increased
abruptly
in
animals
age
5-9
years
and
remained
high.
For
shape
4
this
percentage
increased
in
affected
horses
age
10-14
years.
The
increase
of
this
percentage
at
different
ages,
i.e.
for
the
shape
1/2
classes
already
high
in
age
3
or
4
years,
in
the
shape
3
class
increased
in
the
age
5-9
years
and
in
the
shape
4
class
increased
in
age
10-14
years,
was
statistically
insignificant
(P
=
0.47).
Association
of
shape
and
age
with
radiological
findings
The
relation
of
the
shape
with
the
radiological
features
as
seen
in
grades
3
and
4
in
the
clinically
affected
horses
is
summarised
in
Table
5.
The
radiological
changes
in
affected
animals
with
shape
1/2
navicular
bones
consisted
mainly
of
inverted
flask-shaped
channels
and,
to
a
lesser
extent,
of
enthesophytes.
In
horses
with
shape
3/4
navicular
bones,
enthesophytes
and
cystic
lesions
were
more
prevalent.
However,
these
associations
were
not
statistically
significant.
A
significant
association
was
found
between
age
and
radiological
features.
Inverted
flask-shaped
channels
were
more
prevalent
in
horses
age
5-9
years,
whereas
enthesophytes
were
mainly
encountered
in
age
10-14
years
cases
(P
=
0.020).
Discussion
The
clinical
criteria
used
in
this
study
for
the
diagnosis
of
navicular
disease,
i.e.
a
bilateral
forelimb
lameness
of
more
than
2
months
duration,
an
obvious
response
to
a
palmar
digital
nerve
block
and
the
absence
of
evidence
of
other
forelimb
lameness,
do
not
exclude
other
causes
of
palmar
heel
pain.
Therefore,
the
study
may
have
included
a
limited
number
of
false
positives.
The
diagnosis
can
be
made
more
specific
by
blocking
the
distal
interphalangeal
joint
and
the
navicular
bursa
(Dyson
and
Kidd
1993),
but
these
procedures
are
not
entirely
without
risk.
For
this
reason
they
were
not
included
in
the
routine
clinical
protocol.
In
this
study,
the
radiological
evaluation
was
based
on
dorsoproximal-palmarodistal
oblique
(upright
pedal)
and
lateromedial
radiographs.
The
noncooperative
behaviour
of
many
normal
horses
age
3
or
4
years,
and
the
lack
of
consent
by
the
owners
with
respect
to
the
use
of
sedatives,
precluded
the
use
of
the
palmaroproximal-palmarodistal
oblique
view
which
would
have
led
to
a
better
visualisation
of
roughening
or
erosion
of
the
flexor
surface
of
the
navicular
bone
or
medullary
sclerosis
(O'Brien
et
al.
1975).
These
conditions
are
classified
as
grade
3
(medullary
sclerosis)
or
grade
4
(roughening
or
erosion
of
the
flexor
surface)
(Dik
and
van
den
Broek
1995)
and
are
mainly
seen
in
severely
lame
horses
(Wright
1993a).
Therefore,
in
the
clinically
affected
animals,
the
grades
3
and
4
prevalence
may
have
been
slightly
underestimated.
No
normal
horses
were
available
in
the
age
5-9
year
class.
However,
considering
the
gradual
decrease
of
the
shape
1
prevalence
and
the
general
increase
of
the
shape
4
prevalence
in
elderly
normal
horses,
as
well
as
the
age-independent
shape-
grade
association
in
the
normal
population,
it
was
thought
that
this
age
group
was
not
indispensable
for
evaluation
of
the
age/shape/grade
associations.
It
has
been
stated
that
the
association
between
the
radiological
and
clinical
features
of
navicular
disease
is
questionable
and
controversial,
as
clinical
navicular
disease
may
be
present
in
the
absence
of
radiological
changes
(Wright
et
al.
1998).
However,
although
in
individual
cases
clinical
and
radiological
signs
may
not
always
correspond,
the
low
grades
3
and
4
percentage
in
the
normal
horses
(mean
15%)
vs.
the
high
grades
3
and
4
percentage
(mean
85%)
in
the
clinically
diseased
horses
demonstrates
the
diagnostic
value
of
the
standardised
radiological
classification
of
Dik
and
van
den
Broek
(1995)
for
at
least
the
majority
of
the
Dutch
Warmblood
population.
In
the
Dutch
Warmbloods
available
for
this
study,
navicular
disease
was
diagnosed clinically
in
horses
age
3-19
years,
the
age
groups
with
the
highest
number
of
cases
being
ages
5-9
years
(36%)
and
10-14
years
(44%).
Mean
age
was
9.1
years,
which
is
comparable
with
the
peak
incidence
at
9
years
reported
by
MacGregor
(1984)
and
Wright
(1993b).
In
less
recent
studies,
Wintzer
(1964)
and
van
de
Watering
and
Morgan
(1975)
recorded
a
peak
age
of
7
years
in
the
Netherlands.
Since
1987,
Dutch
Warmblood
stallions
with
grade
4
lesions
have
not
been
certified
for
breeding.
It
is
possible
that
this
selection
in
the
past
decade
has
resulted
in
a
shift
of
the
mean
age
at
which
the
disease
becomes
clinically
manifest
in
the
Dutch
Warmblood
population,
but
this
cannot
be
verified.
TABLE
5:
Association
navicular
bone
shape
-
character
of
simple
grades
3
and
4
features
in
clinically
affected
horses
Inverted
flask-shaped
channels
Enthesophytes
Cystic
lesions
Age
(years)
Age
(years)
Age
(years)
Shape
No.
No.
3-4
5-9
10-14
15-19
No.
3-4
5-9
10-14
15-19
No.
3-4
5-9
10-14
15-19
1
27
14
0
8
4
2
11
0
2
8
1
2
0
0
2
0
(52%)
(41%)
(7%)
2
42
23
2
12
7
2
16
2
3
10
1
3
0
2
1
0
(55%)
(38%)
(7%)
3
16
4
0
0
3
1
9
0
2
6
1
3
0
2
1
0
(25%)
(56%)
(19%)
4
4
1
0
0
1
0
2
0 0
2
0
1
0
0
1
0
(25%)
(50%)
(25%)
42
2
20
15
5
38
2
7
26
3
9
0
4
5
0
Total
(5%)
(49%) (35%)
(11%)
(5%)
(19%)
(68%)
(8%)
(0%)
(44%)
56%)
(0%)
K.
J.
Dik
et
al.
175
The
very
significant
(P
=
0.0001),
age-independent,
shape-
grade
association,
in
both
normal
and
clinically
affected
horses,
further
emphasises
the
fundamental
character
of
the
previously
reported
predisposing
role
of
the
shape
of
the
navicular
bone
in
the
pathogenesis
of
navicular
disease
in
Dutch
Warmbloods
(Dik
and
van
den
Broek
1995).
This
is
supported
by
reports
from
other
breeds
where
a
high
shape
4
frequency
coincides
with
a
low
grade
3/4
prevalence
(and
a
low
prevalence
of
clinical
navicular
disease),
such
as
the
Friesian
and
Finnhorse
breeds
(Ruohoniemi
et
al.
1998).
The
high
prevalence
of
shapes
1
and
2
at
early
age
in
both
normal
and
clinically
affected
horses,
the
relative
increase
in
prevalence
of
the
least
vulnerable
shape
4
in
elderly
normal
horses,
and
the
tendency
towards
an
over-representation
of
shapes
1
and
2
at
all
ages
in
clinically
affected
animals,
are
all
factors
that
indicate
the
survival
of
individuals
with
shapes
of
the
navicular
bone
that
are
least
prone
to
the
development
of
navicular
disease.
Therefore,
studies
into
the
relationship
of
navicular
bone
shape
and
(radiological)
signs
of
navicular
disease
can
be
undertaken
only
in
young
populations
where
selection
has
not
yet
taken
its
toll.
The
fact
that
the
difference
in
grade
3
and
4
prevalence
between
normal
and
affected
animals
was
shape-independent
indicates
that
the
clinical
manifestation
of
the
disease
is
grade-
dependent
rather
than
shape-dependent,
despite
the
fundamental
pathogenetic
role
of
the
navicular
bone
shape.
The
significant,
shape-independent,
increase
of
the
grades
3
and
4
prevalence
in
older
affected
horses
suggests
that
biomechanical
overload
may
result
from
age
related
accumulation
of
workload.
In
other
words,
the
accumulated
workload
over
the
years
will
increase
the
grade
3/4
prevalence
also
in
the
less
vulnerable
shape
classes.
The
majority
of
the
most
vulnerable
shapes
will
have
been
eliminated
in
these
older
horses,
so
this
phenomenon
also
reflects
the
survival
of
the
less
susceptible
shapes.
In
the
clinically
affected
horses,
the
association
of
the
shape
with
the
radiological
features
of
grades
3
and
4
was
statistically
insignificant
(P
=
0.29).
However,
in
the
586
normal
3-year-old
horses
this
association
was
significant
(P
=
0.035).
Therefore,
the
significant
association
with
age
of
the
prevalence
of
inverted
flask-shaped
channels
and
enthesophytes,
found
in
this
study
and
also
reported
by
Doige
and
Hoffner
(1983)
and
Hertsch
et
al.
(1997),
may
be
more
shape-
than
age-dependent
and
hence
may
also
reflect
the
survival
of
horses
with
less
vulnerable
navicular
bone
shapes.
This
study
relates
to
the
Dutch
Warmblood
horse,
but
considering
the
shape-grades
3
and
4
association
found
in
normal
3-year-old
Friesian
horses
and
in
cadaver
forefeet
of
Finnhorses,
the
findings
may
also
apply
to
other
breeds.
It
may
be
concluded
that
there
is
now
further
evidence
that
navicular
bone
shape
plays
a
role
in
the
pathogenesis
of
navicular
disease.
This
is
reflected
by
a
significant,
age-
independent,
shape-grades
3
and
4
association
in
both
normal
and
clinically
affected
horses,
the
risk
for
grades
3
and
4
reducing
from
shape
1
to
shape
4.
The
fact
that
also
the
less
vulnerable
shapes
appear
to
have
a
higher
incidence
of
grades
3
and
4
at
older
ages,
indicates
that
(accumulated)
biomechanical
(over)load
is
harmful
to
all
shapes
and
is
a
reflection
of
the
survival
of
individuals
with
less
susceptible
shapes.
This
applies
also
to
the
age-related
appearance
of
specific
radiological
features
which
is
a
more
shape-
dependent
than
age-dependent
phenomenon.
Acknowledgement
The
authors
are
very
grateful
to
Dr
P.
R.
van
Weeren
for
his
critical
review
of
the
manuscript.
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Accepted:
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