RADIOLOGICAL DIFFERENCES IN TISSUE CHARACTERISTICS BETWEEN
UNEVEN FEET IN FOOT LAME HORSES
R.P.A. Nicolai, A.J.M. Van den Belt, J. Bakker, F. ter Braake, P. Meeus, L.J. Hofland, and
W. Back
Summary
Reasons to perform study: An important feature of foot conformation is unevenness, as this
has been reported to lead to early retirement of elite horses from a warmblood population.
The aim of this study was to compare radiological differences between uneven feet to
improve our understanding of the mechanism behind this asymmetrical development.
Material and methods: A complete set of good quality radiographs of both distal forelimbs
was objectively compared for a group of 121 ‘foot lame’ horses that had been admitted to a
privately owned and a university equine hospital for MRI of one or both front feet (20032010). Statistical software was used to test for a significant radiological difference between
the upright and the weak foot (p<0.05).
Results: It appeared that 60% of the horses were lame at the upright and 40% at the weak
foot. In 84% of the horses the navicular bone had a significantly more radiolucent,
osteoporotic structure and in 80% a more pronounced dorsal border of the navicular bone
(NB) in the upright compared to the weak foot (p<0.05). Moreover, in 88% of the horses a
significantly more radiodense, pronounced deep flexor tendon (DDFT) was found in the
upright foot (p<0.05).
Conclusions: It appeared that the navicular bone showed a more osteoporotic structure in the
upright foot, while the DDFT appeared more compact, both indicating a chronically too low
loading period. In contrast, the advanced enthesophyte formation on the dorsal navicular
border in the upright foot points towards a chronically too high proximal navicular ligament
loading compared to the weak foot.
Practical relevance: There obviously is a need to adopt horse management systems that
prevent uneven feet to develop certainly at the growing, young age, thus to expose distal limb
tissues to a balanced biomechanical loading towards their performing, adult age.
Introduction
For many years the foot-conformation of the horse is a point of discussion for equine
clinicians, farriers and owners. Farriers and equine clinicians always tried to achieve a
dorsopalmar foot balance, while the lateromedial foot-pastern axis should be straight.. The
dorsal hoof wall is ideally parallel to the dorsal surface of the pastern region and the horn
tubules at the heels are at a similar angle to those at the dorsal hoof wall3,6. An important
feature of foot-conformation is unevenness, i.e. left-right asymmetry7. When a horse has
uneven feet, then one foot is the upright foot and one foot is the weak foot. Uneven feet will
be characterised by a difference in shape and a difference in heelheight. The weak foot has a
broken backward foot axis and a long-toe/low heels conformation. Then the dorsal hoof angle
is smaller than that of the pastern. The heels are weakened and the horn tubules in the heel
region bend and their angle relative to the ground is decreased, resulting in the heels sinking
and becoming under-run. This change in conformation increases the load on the palmar
aspect of the foot during weightbearing, producing biomechanical changes including
permanent extension of the distal interphalangeal (DIP) joint and decreased angle of
deviation of the deep digital flexor tendon (“DDFT”) around the navicular bone8. The upright
foot has a broken forward foot axis and a short toe/high heels conformation. The dorsal hoof
angle is higher than that of the pastern. The heels are high and the angle of the heels relative
to the ground is increased. This change in conformation reduces the load on the palmar aspect
of the foot during weightbearing, producing biomechanical changes including increased angle
of deviation of the DDFT around the navicular bone6. It’s commonly accepted and suspected
that the upright foot is the bad foot, the pathological and lame foot. Lameness is the most
common cause of early retirement in performance horses, especially in jumping horses. Hoof
imbalance has been implicated in the development of lameness3. The angle between the
dorsal hoof wall and the ground, is an important factor involved in hoof balance in the
saggital plane6,8. Hoof growth between two shoeing sessions leads to a substantial increase of
the moment about the distal, but not proximal, interphalangeal joint. Unevenness seems to
lead to early retirement of elite horses from a warmblood population, especially showjumpers
seem to leave the population within three years of competing at international level4,5.
Unevenness should be recognized by the examination of horses. Navicular lame horses easily
develop an upright foot because of unloading the heels1. When the heels becomes unloaded,
then the foot becomes upright. In the past much research has done to the commencement of
uneven foot by foals. There are anatomical, physiological and also pathological causes for the
development of uneven feet. In the nowadays breeding of horses people went a step too far,
because of the many characteristics a horse must have, like long forelimbs and a small head.
In this way it’s inseparable that farmers will create problems like uneven feet. Foals with long
forelimbs and small heads have to put their front legs further apart to graze and are thus
predisposed to develop laterality and that causes uneven feet7. Physiological causes include
congenital rigidity or flexibility. Trauma of the neck and weak parts around the neck that
affects bending of the neck is a pathological cause for the development of uneven feet. Hoof
pain is assumed to be one of the most likely causing factors for retraction of and thus
unloading this foot. This will be followed by protraction of the other foot. The protracted foot
becomes the weak foot and the retracted foot to become the upright foot.
The aim of this study was to evaluate the radiological consequences of uneven feet and its
biomechanical loading effects for distal limb tissue development.
Material and methods
A total group of n=442 foot lame horses had been admitted for MRI (of one or both frontfeet)
to two veterinary hospitals in the period from 2003 to 2010, including a privately owned
(Emmeloord) and a university (Utrecht) equine hospital. The total group of n=442 horses is
the foot lame population of the study. Because of low quality of some radiographs and some
incomplete radiographs, a complete, good quality set of radiographs (both LM (left)/ML
(right) and DPa upright pedal view directions) of both forelimbs was available for n=121
horses (n=55/173: 34% radiographs in Utrecht and n=66/278: 24% radiographs in
Emmeloord). In this examination the radiological settings and distances are standardized. By
all the radiographs a standard focus-film distance of 1 meter was applied. Using the
radiographs will indicate the (possible) extent of inequality. Because this examination is
retrograde it’s not possible to register the film-focal and the object-film distance to
standardize, but in Utrecht and Emmeloord there’s always used about the same distances. The
measurements on the radiographs were done manually for the printed radiographs and with
the help of free available software (ImageJ) for the digital radiographs. This is neccesary
because not all radiographs are in digital available. These printed radiographs will therefore
be critisized for the light cabinet. The digital radiographs will be critisized with the help of
the program ImageJ. With this programme you can measure the distances and angles between
different structures, so it’s very useful for the hoof. The distances between the different
structures in the hoof will be given in centimeters and the angles between different structures
in the hoof will be given in degrees. Furthermore, Graphpad, Win Episcope and SPSS were
used to test for a statistical significance difference between the upright and the weak foot
(p<0.05, Chi2-test) and to set up the diagrams about the amount of horses with or without the
score of the judge. In particular, for the digital radiographs from the privately owned clinic
(Emmeloord) custom-made software ‘Rogan Delft View Pro-X’ was specifically available to
measure distances, angles and ratio’s between distal limb structures. You can also change the
radiological settings to make the differences clear. The distances between the different
structures in the hoof will be given in millimeters and the angles between the different
structures in the hoof will be given in degrees.
At first the length of the heels in centimeters is used to differentiate between the upright and
the weak foot. All radiographs will be judged on the position of the navicular bone compared
to phalanx II in degrees (the angle between the flexor side of the navicular bone and phalanx
II), the length of the flexor side of the navicular bone in centimeters, the density and structure
of the navicular bone on LM/ML and DPa radiographs, the quality of the navicular bone, the
position (angle) of the dorsal side of the coffin bone compared to the sole in degrees, the
angle of the flexor side of the navicular bone compared to the sole in degrees, the angle
between the flexor side of the navicular bone and the sole in degrees, the distance between
the proximal border of the navicular bone and the palmar condyl of the second phalanx in
centimeters on LM/ML and DPa radiographs, the angle between the bottom side of the coffin
bone and the flexor side of the navicular bone in degrees, the angle between the line
'proximal point coffin bone to ventral point navicular bone' with the bottom side of the coffin
bone in degrees, the shape of the navicular bone on the DPa upright pedal view-recordings.
There are four different shapes of the navicular bone possible. Shape 1 is the convex shape.
This is the worst shape because of the lots of traction on the ligaments. Shape 2 is the wavesshape. Shape 3 is the straight one and shape 4 is the concave shape. By shape 4 there’s less
traction on the ligaments than by shape 1 navicular bones. Also the proximal border of the
navicular bone on LM/ML and DPa radiographs and the density of the DDFT were evaluated
between the contralateral limbs.
These data will be written down and thereafter the differences can be administered. In this
way I can evaluate these radiological data to make clear the differences between the upright
foot and the weak foot and thereby the lame foot of the horses and accessory percentages.
Results
Of all values the association between the upright and the weak foot is evaluated with the use
of the Chi-square with Yates correction, to see the association is statistically significant or not
(p<0.05). The programme Graphad was used for the Chi-square test. The diagrams include
the number of horses, not the percentage of horses. The “U” in the diagrams is the university
equine hospital and the “P” is the privately owned equine hospital.
The lameness score is the ratio lame at the upright foot versus lame at the weak foot. This
ratio is 60% (29 horses):40% (20 horses) in the university equine hospital, so there’s a higher
lameness score in the upright foot. It’s not statistically significant, but it’s important for the
study. In the privately owned equine hospital this ratio is 50% (29 horses):50% (30 horses)
and also not statistically significant (see figure 1).
Figure 1
It appeared that in 84% (42 horses of the total 50 horses) of the foot lame horses in the
university equine hospital the navicular bone had a more radiolucent texture, so the fibers are
more coarse in structure (osteoporotic) in the upright foot on the DPa upright pedal view (see
figure 2ab), while on the LM/ML view that was 74% (32 horses of the total 43 horses) of the
foot lame horses in the university equine hospital (p<0.05, see figure 3ab). In the privately
owned equine hospital it appeared that in 77% (47 horses of total 61 horses) of the foot lame
horses the navicular bone had a more radiolucent texture in the upright foot on the DPa
upright pedal view (see figure 2ab), while on the LM/ML view that was 90% (45 horses of
the total 50 horses) of the foot lame horses (p<0.05, see figure 3ab).
Figure 2a
Figure 2b
Figure 3a
In 80% (28 horses of the total 35 horses) of the horses in the university equine hospital the
navicular bone in the upright foot on LM/ML view had a more pronounced dorsal flexor side,
in the privately owned equine hospital 93% (41 horses of the total 43 horses) of the foot lame
horses had a more pronounced dorsal flexor side of the navicular bone (see figure 4ab). More
than 88% of the horses (48 horses of the total 55 horses in the university equine hospital, 41
horses of the total 43 horses in the privately owned equine hospital) showed a more radiodens
DDFT in the upright foot (p<0.05, see figure 5a and the yellow arrows in figure 5b).
Also the MRI images were used to compare with the radiographs of the upright and weak
feet2. Figure 5c shows an MRI image of a normal DDFT without a lesion. If there’s a lesion
of the DDFT then the radiograph and the MRI image show a difference. In the MRI image
the lesion is obviously clear (see figure 5d). In the radiograph it appeared there’s a difference
in the size and density of the DDFT. If there is an (old) lesion in the DDFT, you can see a
denser and wider DDFT (see figure 5e for a DDFT without a lesion and figure f for a DDFT
with a lesion in this tendon).
Figure 4a
Figure 5b
Figure 5a
Figure 5c
Figure 5e
Figure 5d
Figure 5f
When there was a difference in shape between the uneven feet in the university equine
hospital, then shape 1 (worst) was in the upright foot, while in the weak foot always a shape 2
or 3 (regular) was found (p<0.05, see figure 6a for the diagram and figure 6b for an
illustration of the different shapes). But there was only a number of 5 horses in total.
Figure 6a
Figure 6b
In the university equine hospital the mean distance between the proximal border of the
navicular bone and the palmar condyl of phalanx II in the upright foot was found smaller in
36 horses of the total 54 horses, but not statistically significant (p=0.1060). In the privately
owned equine hospital this value was found smaller in 46 of the total 66 horses (p<0.05, see
figure 7ab). In the university equine hospital the mean angle between the bottom side of the
coffin bone and the sole was larger in 28 of 45 horses in the upright foot (p<0.05), in the
privately owned equine hospital this value was found larger in 43 of 63 horses (p<0.05, see
figure 8ab). In the university equine hospital the mean angle between the flexor side of the
navicular bone and the sole was also found larger in the upright foot in 34 of the total 50
horses (p<0.05, see figure 9ab). In the privately owned equine hospital this value was found
larger in 35 of 64 horses in total, but this value isn’t statiscally significant (p=0.781, see
figure 9ab). In the university equine hospital the mean angle between the bottom side of the
pedal bone and the flexor side of the navicular bone was found larger in the upright foot in 31
of total 50 horses (p<0.05, see figure 10ab). In the privately owned equine hospital this value
was found larger in 30 of 65 horses in total and wasn’t statistically significant (p=0.758, see
figure 10ab).
Figure 7a
Figure 7b
Figure 8a
Figure 8
Figure 9a
Figure 9b
Figure 10a
Figure 10b
In the university equine hospital the mean angle between the ‘line proximal point pedal bone
to ventral point navicular bone’ and the bottom side of the pedal bone was also found larger
in the upright foot in 27 of total 50 horses, but not statistically significant (p=0.360, see figure
11ab). In the privately owned equine hospital this value was found larger in 42 of the total 64
horses (p<0.05, see figure 11ab).
Figure 11a
Figure 11b
In the university equine hospital 67% of all abnormalities of the navicular bone and the
ligaments (seen on MRI) take place in the upright foot. The referred abnormalities include a
more than grade 2 classified navicular bone and injuries of the ligaments of the navicular
bone. 80% of all injuries to the proximal ligament of the navicular bone (p<0.05) take place
in the upright foot, 56% of all collateral ligament injuries (coffin joint) take place in the
upright foot, 58% of all injuries to the DDFT take place in the upright foot. Otherwise 83% of
the overfilled coffin joint and takes place in the weak foot.
Discussion and conclusion
The radiolucent navicular bone indicates an osteoporotic structure, which would be related to
chronic unloading of the navicular bone within the upright foot. In the characteristic grazing
posture of foals, the retracted foot becomes less loaded indeed, while the protracted foot
becomes more loaded and thus is used as a pivot point to grazing around. Vice versa, when
experiencing chronic limb pain, the foal would tend to unload the foot and would adopt a
retracted placing of that particular limb. That position would induce traction on the proximal
ligament presumably causing a more pronounced dorsal flexor side of the navicular bone and
more pressure and less fluid in the DDFT, thus appearing more radiodense. On the
radiographs of the upright foot was observed that there was a more radiodense DDFT. Also
when there is less traction of the tendon, the fibers will stay together and the tendon will
appear more radiodense too. It could also be that there has been a tendinitis of the DDFT, so
that the DDFT will be thicker, but this has not been verified yet by MRI2 and the animals
were lame also on the weak foot in 40% of the cases, while in more than 80% the DDFT
appeared more radiodense.
Thus, the biomechanical consequences of uneven feet from detailed radiological description
of uneven feet in a hoof lame horse population could be evaluated. The navicular bone was
more radiolucent and the fibers are coarser in structure in the upright foot and showed a more
radiodense DDFT in the upright foot, while possibly due to the retracted position the
navicular bone also had a more pronounced dorsal border. There obviously is a need to adopt
horse management systems that prevent uneven feet to develop certainly at the growing,
young age, thus to expose distal limb tissues to a balanced biomechanical loading towards
their performing, adult age.
Acknowledgements
The authors would like to acknowledge the technical, statistical support of Jan van den Broek
and the critically, radiologically reading of the manuscript by George Voorhout.
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