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Toe length and plantar angle in the hind feet are associated with gluteal pain in adult horses

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PURPOSE: In an earlier study, we documented an association between long toes in the hind feet and pain on palpation of the gluteal region. In the present study, we retrospectively examined associations between gluteal pain and the breakover distance (BD, a measure of toe length) and plantar angle (PA) of the third phalanx in the hind feet of 144 adult horses. MAIN FINDINGS: The presence of gluteal pain was significantly associated with BD (P < 0.001) and with PA (P < 0.05). For every 1-mm increase in BD, the likelihood of having gluteal pain increased by about 14% (OR: 1.14; 95% CI: 1.06-1.24). For every 1° decrease in PA, the likelihood of having gluteal pain increased by about 23% (OR: 0.77; 95% CI: 0.59-0.98). In addition, BD was significantly associated with gluteal pain score, graded from absent to severe (P < 0.05). In a follow-up survey completed by 57 owners, soundness and performance were improved in 86% of horses, and behavior was also improved in 42% of horses, following trimming or shoeing to optimize the BD (to a range of 5-15 mm). CONCLUSIONS: The 'long-toe, low-heel' hoof shape may be just as problematic in the hind feet as in the front feet. Trimming or shoeing to optimize breakover distance can improve the comfort and performance of riding horses.
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Toe length and plantar angle in the hind feet
are associated with gluteal pain in adult horses
Richard A. Mansmann, VMD, PhD, hon. DACVIM-LA;a Megan Radkin, DVM;b Kurt vom
Orde;a and Christine King, BVSc, MANZCVS (equine), MVetClinStudc
a Equine Podiatry & Rehabilitation Mobile Practice, Chapel Hill, North Carolina, USA.
b 3H Equine Hospital and Mobile Veterinary Services, New Hill, North Carolina, USA.
c Anima Vet, Park Ridge, Queensland, Australia.
Corresponding author:
Richard A. Mansmann, VMD, PhD, hon. DACVIM-LA. Equine Podiatry & Rehabilitation
Mobile Practice, Chapel Hill, North Carolina, USA. email: dickmansmann@gmail.com.
Competing Interests
None.
Funding Sources
None.
Author Contributions
RAM and MR were responsible for study design, data acquisition, and editorial input. KvO
provided technical assistance (farriery). CK performed statistical analysis and manuscript
preparation (principal medical writer).
Mansmann et al. Hoof shape and gluteal pain in horses
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Abstract
Purpose: In an earlier study, we documented an association between long toes in the hind
feet and pain on palpation of the gluteal region. In the present study, we retrospectively
examined associations between gluteal pain and the breakover distance (BD, a measure
of toe length) and plantar angle (PA) of the third phalanx in the hind feet of 144 adult horses.
Main findings: The presence of gluteal pain was significantly associated with BD (P < 0.001)
and with PA (P < 0.05). For every 1-mm increase in BD, the likelihood of having gluteal pain
increased by about 14% (OR: 1.14; 95% CI: 1.06–1.24). For every 1° decrease in PA, the
likelihood of having gluteal pain increased by about 23% (OR: 0.77; 95% CI: 0.59–0.98).
In addition, BD was significantly associated with gluteal pain score, graded from absent
to severe (P < 0.05). In a follow-up survey completed by 57 owners, soundness and
performance were improved in 86% of horses, and behavior was also improved in 42%
of horses, following trimming or shoeing to optimize the BD (to a range of 5–15 mm).
Conclusions: The ‘long-toe, low-heel’ hoof shape may be just as problematic in the hind feet
as in the front feet. Trimming or shoeing to optimize breakover distance can improve the
comfort and performance of riding horses.
Key words: horse, equine, hoof, hindlimb, plantar angle, breakover
Mansmann et al. Hoof shape and gluteal pain in horses
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Introduction
In an earlier observational study,1 we reported that horses with long toes in the hind feet
often show a pain response on palpation of the gluteal region adjacent to the sacrum, and
that shortening the toe to decrease the breakover distance (BD) — i.e., move the point of
breakover back, closer to the third phalanx (P3) — relieves or resolves the gluteal pain in
days or weeks. In passing, we mentioned that riders and trainers had reported that their horses
were moving better or otherwise showed an improvement in performance following this
change in shoeing.
Although not investigated in that study, we noted that the hind feet in horses with long
toes usually have low heels as well. Typical of the ‘long-toe, low-heel’ (LTLH) hoof shape,
these hind feet lack adequate mass in the heel region, in some cases having ‘crushed’,
‘underslung’, or ‘collapsed’ heels, as described for negative palmar angle syndrome (heel
collapse) in the front feet.2,3
Lateral radiographs of these hind feet usually show that the solar or plantar angle (PA)
of P3 relative to the ground is zero or negative — i.e., the plantar processes or ‘wings’ of P3
are level with (zero PA) or lower than (negative PA) the dorsodistal margin or ‘tip’ of P3.
In a recent North American study,4 the median PA in the hind feet of 80 sound horses was 3°;
and although it ranged from 0° to 9°, the interquartile range was 1° to 4°. Furthermore, the
likelihood of a horse having a ‘neutral/negative’ PA (defined in that study as < 2°) was
almost 4 times greater in horses with hindlimb lameness than in sound horses.
These radiographic observations may provide a clue as to why a structural abnormality
at the distal extremity of the limb might cause a functional abnormality or pain response at
the proximal extremity: the loss of heel mass and consequent low PA associated with the
LTLH hoof shape may increase passive tension in the deep digital flexor tendon which is
transmitted proximally through the various myofascial and skeletal connections in the
hindlimb. Alternatively, or additionally, the long toe may independently increase the work
of breakover to an extent not comfortably tolerated by the myofascial structures involved.5
Functional myofascial connections in the equine forelimb have recently been described
in detail.6 According to those authors, similar connections are also present in the hindlimb.7
Of particular relevance, movements of the distal hindlimb are probably directed past the
mobile coxofemoral joint into the lumbosacral fascia dorsally and laterally via the gluteal
fascia and fascia latae. The authors go on to add that coordinated movements afforded by
such myofascial connections are a foundational component of locomotion in the horse.
In order to advance our theory, we must further examine the association between hoof
shape (defined by BD and PA) in the hind feet and the presence and severity of pain in
the gluteal region. We must also show that there is an observable, functional result of this
association. To these ends, we examined the medical records of a group of adult horses
presented to our Equine Podiatry and Rehabilitation Service for which lateral radiographs
of the hind feet and gluteal pain score at the same visit were available. Variables examined
included the BD and PA in each hind foot and the presence and severity of gluteal pain.
We also conducted a brief follow-up survey of the horses’ owners to determine whether
or not shortening the BD affected the horse’s gait or performance, and if so, in what way.
Mansmann et al. Hoof shape and gluteal pain in horses
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Methods
This retrospective observational study used data collected from horses presented to our
Equine Podiatry and Rehabilitation Service between 2009 and 2018. We began by searching
our medical records for all horses with lateral radiographs of the hind feet, regardless of the
reason for presentation.
Study group
Horses were included in the study if they had numerical data recorded for (1) BD in the hind
feet as measured on lateral radiographs, and (2) gluteal pain (GP) score at the same visit.
Lack of corresponding PA data did not exclude the horse. These variables are described
below.
The full dataset included horses currently in work (intermittent/occasional or full work)
and horses not in work. At each visit, the horse was evaluated and then trimmed and shod
(unless kept barefoot) to optimize BD, as previously described.1 Briefly, each hind foot was
trimmed, and in shod horses the shoe selected and positioned, to create a BD in the range
of 5–15 mm. In 2016, a brief follow-up survey was sent by email to the owners of horses
in work at the time of their evaluation. A copy of the survey is provided as Supplementary
Figure S1.
Breakover Distance (BD)
Lateral radiographs of each hind foot were obtained as previously described.1 Briefly, the
horizontal x-ray beam is centered approximately 1 cm proximal to the loading surface of the
hoof wall, midway between heel and toe, so that both plantar processes of P3 are precisely
superimposed on the radiograph. In this study, the BD (in millimeters) was defined as the
horizontal distance between two vertical lines drawn on the radiograph: one at the tip of P3
and the other at the dorsalmost point at which the hoof (bare foot) or shoe (shod foot) is in
contact with the ground (Fig. 1).
Figure 1. Lateral radiograph of a left hind foot and photograph of the same foot, showing the classic ‘long-toe,
low-heel’ hoof shape. Breakover distance (BD) — the horizontal distance between the two vertical lines drawn
(in pink) on this radiograph — was 34 mm. Plantar angle (PA) the degree of divergence at the tip of the third
phalanx (P3) between a line drawn parallel to the solar or plantar margin of P3 (yellow line) and a line drawn
parallel to the positioning block on which the horse is standing (green line)was -1°.
Mansmann et al. Hoof shape and gluteal pain in horses
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In our 2010 study, a BD of 20 mm was the proposed upper limit for the average-size
horse.1 Subsequent clinical experience suggests that 20 mm may be too long, and we
currently aim for a BD in the range of 5–15 mm in the average horse. When BD differed
between left and right hindlimb pairs, we used the higher value (longer toe) for analysis,
as explained below.
Plantar Angle (PA)
On the same lateral radiographs, the PA (in degrees) was measured for each hind foot,
defined as the divergence of two straight lines drawn on the radiograph: one representing
the solar or plantar margin of P3 and the other drawn parallel to the ground surface such that
the point of divergence is at the tip of P3 (Fig. 1). When PA differed between left and right
hindlimb pairs, we used the lower value (lower heel) for analysis, as explained below.
Gluteal Pain (GP) Score
The presence and severity of gluteal pain was assessed as previously described and by the
same experienced person (RAM) in each case.1 Briefly, the person stands on one side of the
horse’s hindquarter, facing the horse; reaching over the croup, the person applies uniform
digital pressure to the soft tissues adjacent to the sacrum (gluteal fascia and middle gluteal
muscle) on the opposite side of the horse. The process is then repeated on the other side of
the horse.
The horse’s response to palpation was graded as follows: 0 (absent), no response; 1
(mild), modest dipping of the pelvis; 2 (moderate), dropping of the hindquarters, with evasive
action or other moderate behavioral response; 3 (severe), exaggerated response such as
buckling of the hindlimbs and/or threatening to kick.
Other Variables
The horse’s age (years), breed (categorized), and gender (female/male) were also extracted.
Breed was categorized from smallest/lightest to largest/heaviest as pony, Arabian, other
lighthorse breed (American Saddlebred, Tennessee Walking Horse, etc.), American Quarter
Horse, Thoroughbred, Warmblood, and draft. Each crossbred horse was identified by the
larger or heavier of its component breeds. For example, a Warmblood–Thoroughbred cross
was categorized as a Warmblood, as that horse would more likely have a Warmblood- than
a Thoroughbred-type physique, including hoof conformation. Similarly, Appaloosas and
American Paint Horses were categorized as Quarter Horses. In this way, we endeavored
to use breed as a rough proxy for height, weight, build, and hoof conformation.
Statistical Analysis
Data were analyzed using GraphPad Prism 9, version 9.1.0.a As the data were not normally
distributed for any variable, nonparametric tests were used. Descriptive statistics for the
continuous variables are presented with their medians and interquartile ranges (IQR; 25th
to 75th percentiles). Statistical significance was set at P < 0.05 and trends toward significance
as P = 0.05–0.09.
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Comparison of left and right limbs
The raw data for BD and PA suggested potentially significant disparities between left
and right limb pairs in several horses, so Wilcoxon matched-pairs signed-rank tests were
conducted to compare the left and right limbs for both variables. There were no significant
differences between left and right limbs for either variable. However, mismatching of the
hind feet — defined in this instance as a difference in BD of > 5 mm and/or a difference in
PA of > 2° between left and right limbs — occurred in 11% (BD) to 17% (PA) of horses,
so in each horse the highest BD and lowest PA value was used for subsequent analysis.
Correlations and comparisons
A Spearman’s rank correlation matrix was generated to examine relationships among
the 6 variables of interest and to identify correlations that could cause collinearity problems
in a multivariable analysis. Data for BD and PA were then categorized by GP score and
comparisons made among GP categories using the Kruskal-Wallis test as a nonparametric
alternative to the one-way ANOVA. The Mann-Whitney U test was then used as a
nonparametric alternative to the t test for pairwise comparisons among GP categories.
Multivariable logistic regression
Multivariable logistic regression was performed, including age, breed, BD, and PA as
independent variables and gluteal pain as the dependent variable, categorized as present
(GP score of 1, 2, or 3) or absent (GP score of 0). Odds ratios (OR) are reported with their
95% confidence intervals (CI).
Results
A total of 144 horses were included in the study group; 4 of these horses lacked PA data
but otherwise had complete demographic and clinical data. Table 1 summarizes the key
characteristics of the study group…
Table 1. Summary of demographic and clinical data for all 144 horses
n
median (IQR)
range
category
Age (yrs)
144
11 (8 – 14)
2 – 29
Breed
pony
Arabian
PA (degrees)
140
0 (-3 – 0)
-8 – 6
other lighthorse
BD (mm)
144
26 (22 – 30)
-2 – 48
Quarter Horse*
GP score
144
2 (1 2)
0 – 3
Thoroughbred**
%
Warmblood**
0
14
9.7%
draft**
1
41
28.5%
2
84
58.3%
Gender
female
3
5
3.5%
male (geldings)
Mansmann et al. Hoof shape and gluteal pain in horses
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BD, breakover distance; GP, gluteal pain; IQR, interquartile range (25th75th percentiles); PA, plantar angle.
Gluteal pain score was categorized as 0 (absent), 1 (mild), 2 (moderate), or 3 (severe). * Includes related breeds
such as Appaloosa and American Paint Horse. ** Includes crossbred horses in which the listed breed is the
larger/heavier of the component breeds.
The median age was 11 years; two-thirds were Warmbloods or Quarter Horses; and there
were twice as many geldings as mares. These demographics reflect our practice population
and that of adult performance horses in this region.
As illustrated in Figure 2, all but 12 horses (92%) had a BD > 15 mm, and 115 horses
(80%) had a BD > 20 mm, the proposed upper limit in our earlier study. Only 33 horses
(23%) had a positive PA. All but 15 horses (90%) had some degree of gluteal pain; 88 horses
(61%) had moderate or severe gluteal pain (GP score of 2 or 3).
Figure 2. Scatter plot of breakover distance, plantar angle, and gluteal pain score (color coded) in the 140 horses
with data for all 3 variables. Gluteal pain score key: green, 0 (absent); blue, 1 (mild); red, 2 (moderate); purple, 3
(severe). The axes cross at BD 15 mm and PA 1°.
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Six horses (4%) had BD and PA values consistent with the “bullnose” hoof shape:
compact hoof with a low heel (low PA) and a tall toe (short BD but hoof wall vertical height
much greater at the toe than at the heel), and with a somewhat convex dorsal hoof wall
profile.8 Of those with a BD < 15 mm and a PA 0°, 3 horses had a GP score of 0 and the
other 3 horses had a GP score of 2.
Figures 3 and 4 plot BD and PA, categorized by GP score. These data are summarized
numerically in Supplementary Table S1.
Figure 3. Breakover distance for the full dataset (n=144), categorized by gluteal pain score.!Individual horses
are represented by dots (dot size reflects the number of horses with that value). Medians and interquartile ranges
(25th to 75th percentiles) are represented by horizontal lines and gray boxes, respectively. Significant differences
between GP categories are shown with square brackets and P values (Mann-Whitney U test).
Figure 4. Plantar angle for the full dataset (n=140), categorized by gluteal pain score. Individual horses are
represented by dots (dot size reflects the number of horses with that value). Medians and interquartile ranges
(25th to 75th percentiles) are represented by horizontal lines and gray boxes, respectively. Significant differences
between GP categories are shown with square brackets and P values (Mann-Whitney U test).
Mansmann et al. Hoof shape and gluteal pain in horses
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Correlations and Comparisons
There was a small but statistically significant, positive correlation between age and gender
(P = 0.032; r = 0.179). In effect, mares were likely to be younger than geldings, or older
horses were more likely to be geldings than mares. Although this association was considered
clinically irrelevant, gender was left out of the multivariable model lest it pose a collinearity
problem with age. In addition, there were trends for a negative correlation between age and
breed (P = 0.089; r = -0.142), and between PA and GP score (P = 0.075; r = -0.151). Except
for PA and GP score, these correlations were considered unimportant and were not examined
further. In this study group, BD and PA were not correlated.
When BD and PA were each categorized by GP score, BD was significantly
associated with GP score (P = 0.035). Pairwise comparisons among GP categories revealed
significant differences in BD between GP scores 0 and 1 (P = 0.004) and 0 and 2 (P = 0.010;
Fig. 3). Plantar angle was not significantly associated with GP score, and the only trend in
pairwise comparisons for PA was between GP scores 0 and 2 (P = 0.082; Fig. 4).
Multivariable Logistic Regression
In the multivariable model, the presence of gluteal pain was significantly associated with BD
(P < 0.001) and with PA (P = 0.047; Fig. 5). For every 1-mm increase in BD, the likelihood
of having gluteal pain increased by about 14% (OR: 1.14; 95% CI: 1.06–1.24). For every 1°
decrease in PA, the likelihood of having gluteal pain increased by about 23% (OR: 0.77;
95% CI: 0.59–0.98). Age and breed were not significantly associated with the presence
of gluteal pain.
Figure 5. Summary of multivariable logistic regression, in which gluteal pain was categorized as present
or absent. Results are plotted as odds ratios with their 95% confidence intervals (95% CI). Scale: log2.
Mansmann et al. Hoof shape and gluteal pain in horses
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Owner Survey
Of the 74 surveys emailed to owners, 57 responses were received. The most common
equestrian discipline represented was dressage (42%); next most common were pleasure/trail
riding and show hunter (10.5% each). Others included eventing, show jumping, endurance,
and barrel racing. The primary concern reported by the owner at initial examination was a
history of lameness (44%). Others included poor hoof conformation (23%), back soreness
or hind end weakness (14%), poor performance (12%), and prevention (5%). No reason was
given by one owner.
The responses were divided into three categories: soundness (as perceived by the owner),
performance, and behavior. The owner reported an improvement in soundness and
performance in 49 horses (86%). In 24 horses (42%) the owner also reported an improvement
in the horse’s behavior, although none had cited behavioral issues as a concern at initial
presentation. One owner discontinued this shoeing strategy because it had made the horse
worse, but the rest continued having their horses shod in this manner until the horse was
retired, sold, or deceased.
Discussion
Our main goal was to further examine the association between hoof shape (defined by BD
and PA) in the hind feet and the presence, severity, and functional effect of pain in the gluteal
region. In our study group, long toes (long BD) and low heels (low PA) were significantly
associated with the presence of gluteal pain, and BD was significantly associated with the
severity of gluteal pain (GP score). Furthermore, our brief follow-up survey indicated that
shortening the BD in horses with long toes in the hind feet improved owner-reported
soundness and performance in the majority of horses. The main findings and limitations
of our study are discussed in more depth below.
Study Group
It must be acknowledged that relatively few of the horses in our study group had normally
shaped hind feet, as reflected by BD and PA values (Fig. 2). The primary inclusion criterion
was a record of lateral radiographs of the hind feet, but in our practice we don’t routinely
obtain radiographs of the hind feet if there are no clinical indications for doing so. Thus,
we had few radiographs of normal hind feet in horses with corresponding GP scores.
The owner survey provides a good overview of the various reasons why horses are
presented to our Equine Podiatry and Rehabilitation Service and radiographs obtained of their
hind feet: most of the horses (70%) represented by the survey had a history of lameness
(forelimb or hindlimb), back soreness, ‘hind end weakness’, or poor performance. Poor hoof
conformation was a less common reason for concern (~ 25%), and prevention represented a
paltry 5%. Owing to the nature of our specialty practice and our study design, there was no
‘control’ group of well-performing horses with normally shaped hind feet in which to
evaluate BD, PA, and GP score. It would be worthwhile examining these variables in such
horses.
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It is also important to note that not all of the horses in our study group were in work at the
time of their evaluation. Most were adult riding horses, but in order to include as many horses
as possible, we decided against using age, breed, equestrian discipline, work history, current
activity, or medical history in our inclusion/exclusion criteria. Thus, another study limitation
is that we made no attempt to investigate other possible causes of gluteal pain in these horses,
such as exercise-induced myopathy (notably, equine polysaccharide storage myopathy and
recurrent exertional rhabdomyolysis), injury, or simply overwork.9
The two predominant breeds in our study group — Quarter Horses and Warmbloods —
are both predisposed to equine polysaccharide storage myopathy.10 However, the breeds
represented in our study and their relative frequency are consistent with our practice
population and with the popular horse breeds in this region of the US, so our study design
is unlikely to have inadvertently selected for horses with this condition. Furthermore, breed
was not associated with gluteal pain in our study. Even so, we cannot discount exercise-
induced myopathy as a cause of gluteal pain in at least some of the horses in this study.
As a counterpoint, we showed in our earlier study that simply shortening the toe to
decrease the BD improved or resolved gluteal reactivity in a group of 10 Thoroughbred
and Warmblood broodmares kept barefoot.1 No other changes were made to the feet nor to
the herd’s environment or management. Those findings are discussed in more detail below.
Similarly, the brief follow-up survey in the present study indicated a general improvement in
comfort and function after trimming/shoeing to optimize the BD, in a variety of riding horses.
Admittedly, the design of our owner survey is a further limitation of our study. Our goal
was to maximize the response rate by keeping the survey short and easy to understand and
complete. However, use of such a survey to determine the functional result of the change
in trimming/shoeing precluded any meaningful statistical analysis.
Nonetheless, we contend that our study group is a reasonably good representation of adult
horses presented for hindlimb gait or performance issues in equine veterinary and farriery
practices. In our experience, the LTLH hoof shape is very common in the hind feet and is
often associated with performance problems and gait abnormalities, if not overt lameness.
We further suggest that evaluating hoof shape in the hind feet, with lateral radiographs when
indicated, should become a standard part of the diagnostic evaluation in such horses.
Toe Length and Plantar Angle
In this heterogeneous group of adult horses, toe length and heel height (represented by BD
and PA, respectively) in the hind feet were significantly associated with pain on palpation of
the gluteal region. Interestingly, these two hoof variables were not associated with each other.
The lack of correlation between these aspects of the same hoof shape (long-toe, low-heel)
might be explained by our broad inclusion criteria. While most of the horses in the study had
the typical LTLH hoof shape (upper-left quadrant in Fig. 2), several did not. A handful of
horses had BD and PA values consistent with the bullnose hoof shape (lower-left quadrant),
and even more had long toes with adequate heel height (upper-right quadrant), illustrating
that PA can be independent of BD.
This study confirms and expands upon our earlier findings of a significant association
between BD and the presence and severity of pain on palpation of the gluteal region.1 Here
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we showed that BD was significantly associated with GP score, the median BD being
significantly greater in the horses with a GP score of 1 or 2 than in those with a GP score
of 0 (Fig. 3). In the multivariable model, the likelihood of a horse having gluteal pain
significantly increased with increasing BD. Although the odds ratio was quite small, the
effect would be cumulative with every 1-mm increase in BD. For example, a 6-mm increase
in BD, such as from 15 mm to 21 mm, increased the likelihood of having gluteal pain more
than 2-fold (odds ratio 1.146). By the same token, an improvement in gluteal pain may be
expected simply by shortening the BD, as we documented in our earlier study.1
In that study, the gluteal pain response was recorded as negative (absent), positive, or
mildly positive. All 10 horses (broodmares living on the same farm) were ‘positive’ on initial
examination, at which time the mean BD was 24 mm (range, 18–31 mm). After examination,
the toe was trimmed with hoof nippers to shorten the BD to a mean of 11 mm (range, 6–17
mm); no other changes were made to the hoof. The mares were re-evaluated 1 week later, at
which time all 10 mares showed an improvement in gluteal reactivity: 8 mares were now
‘negative’ and the other 2 mares were ‘mildly positive’.
Along the same lines, Page et al.5 reported that shortening breakover resulted in an
improvement in lameness grade in horses with fore- or hindlimb lameness localized by
palmar/plantar digital nerve blocks to the heel region of the affected limb(s). In 50% of the
study group (15 of 30 horses), lameness was improved by 1 grade (on a 5-point scale) within
1 hour after trimming/shoeing to shorten breakover. This figure increased to 73% (22 of 30
horses) within 6 weeks after shortening breakover. Interestingly, radiographs repeated 1 hour
after trimming/shoeing to shorten breakover showed improvement in the hoof-pastern axis:
there was a mean change in angle between the first phalanx (P1) and P3 of -5.5°. According
to that report, no particular trimming or shoeing methods were used to alter the hoof-pastern
axis; merely shortening breakover effected this improvement.
In the present study, the likelihood of a horse having gluteal pain significantly increased
with decreasing PA. As with BD, the odds ratio was quite small, but the effect would be
cumulative with every 1° decrease in PA. For example, a 3° decrease in PA, such as from
2° to -1°, increased the likelihood of having gluteal pain by 54% (1 – 0.773).
Our findings thus support the concept of a functional link between hoof shape
(specifically, toe length and plantar angle) in the hind feet and pain in the gluteal region.
Two recent studies showed a significant association between a PA < 2º in the hind feet
and the presence of hindlimb lameness.4,11 The results of our brief follow-up survey further
indicate that there is a functional cost to the LTLH hoof shape in the hind feet, and that
simply shortening the BD improves the horse’s gait and/or performance in the majority
of cases (86% in our survey). The fact that more than 40% of the horses also showed an
improvement in behavior is perhaps an indication of the more insidious cost of the LTLH
hoof shape in comfort and function, as none of those owners had reported a behavioral issue
at initial presentation.
Taken together, these hindlimb studies suggest that recognizing and correcting the LTLH
and the bullnose (short-toe, low-heel) hoof shape early may prevent some cases of hindlimb
lameness; it may also improve the horse’s gait and/or performance in the absence of overt
lameness. In addition, shortening the BD when needed may resolve some behavioral issues,
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including those related to farriery on the hind feet. However, these outcomes remain
speculative at this time.
Shortening the toe is much easier to accomplish than increasing heel mass and thus PA
in horses with the LTLH hoof shape. Two recent papers describe some fairly complicated
methods for increasing the PA in horses with low heels in the hind feet.3,8 In contrast, BD
can immediately be reduced simply by trimming the toe in a barefoot horse and by the
selection and placement of an appropriate shoe in a shod horse.1,5 Page et al.5 used a target
BD in the hind feet of 56 mm for horses weighing 400–600 kg. We have found in our
practice that aiming for a BD in the range of 5–15 mm is appropriate for most horses.
Concluding Remarks
Much is still to be learned about the biomechanics of the equine hindlimbs, individually
and as a functional pair. Unlike the human body, the extensive fascial connections and
interconnections in the equine body enable the horse to use a variety of myofascial pathways
in its efforts to optimize locomotion and adapt to structural or functional abnormalities, such
as the LTLH hoof shape.12 Clinical lameness need not be present for the horse’s comfort
and function to suffer the consequences of such biomechanical ‘work-arounds’ or strains
on a system not designed for such loads.
Our main goal with this work is to encourage equine veterinarians and farriers to look
more closely at the hind feet and consider the LTLH hoof shape to be just as problematic
in the hind feet as it is in the front feet. It is also to show that simply by shortening the toe,
gluteal pain may be relieved and the horse’s gait, performance, and even behavior may
be improved.
Manufacturers
a GraphPad Software LLC, San Diego, California, 92108, USA.
References
1. Mansmann RA, James S, Blikslager AT, vom Ord K. Long toes in the hind feet and pain
in the gluteal region: an observational study of 77 horses. J Eq Vet Sci 2010;30:720–6.
2. Floyd AE. Use of a grading system to facilitate treatment and prognosis in horses with
negative palmar angle syndrome (heel collapse): 107 cases. J Eq Vet Sci 2010;30:666–75.
3. Clements P. Therapeutic farriery of the hind feet for horses with hindlimb orthopaedic
injuries. UK-Vet Equine 2021;5:6–11.
4. Pezzanite L, Bass L, Kawcak C, Goodrich L, Moorman V. The relationship between
sagittal hoof conformation and hindlimb lameness in the horse. Equine Vet J
2019;51:464–9.
5. Page BT, Bowker RM, Ovnicek G, Hagen TL. How to mark the foot for radiography.
Proc Am Assoc Equine Practit 1999;45:148–150.
Mansmann et al. Hoof shape and gluteal pain in horses
Copyright © 2021 Richard A. Mansmann & Megan Radkin
14
6. Lusi CM and Davies HMS. Fascial Anatomy of the Equine Forelimb. CRC Press, Bosa
Roca, USA; 2018.
7. Davies HMS, Lusi CM, Ismail SM. Synchronization of head and limb movements in the
horse. Proceedings, 4th International Fascia Research Congress, Reston, Virginia, USA;
2015. https://www.fasciacongress.org/2015/Abstracts/39_Davies.pdf.
8. O’Grady SE, Turner TA, Ridley JT. How to apply the appropriate farriery principles to the
horse with low heels in the hind feet. Proc Am Assoc Equine Practit 2018;64:419–426.
9. Valberg SJ. Muscle conditions affecting sport horses. Vet Clin North Am Equine Pract
2018;34(2): 253–76.
10. McCue ME, Anderson SM, Valberg SJ, Piercy RJ, Barakzai SZ, Binns MM, et al.
Estimated prevalence of the type 1 polysaccharide storage myopathy mutation in selected
North American and European breeds. Anim Genet 2010 Dec;41 Suppl 2:145–9.
11. Clements PE, Handel I, McKane SA, Coomer RP. An investigation into the association
between plantar distal phalanx angle and hindlimb lameness in a UK population of horses.
Equine Vet Educ 2020;32:52–9.
12. Davies HMS, personal communication.
Mansmann et al. Hoof shape and gluteal pain in horses
Copyright © 2021 Richard A. Mansmann & Megan Radkin
15
Supplementary Materials
Figure S1. Follow-up survey sent to owners of horses in work at the time of their first evaluation.
Client name: ___________________ Date: _________________
Horse name: ___________________
What is your horse’s job (pasture pet, hunter, eventer, etc)?
Have there been any recent events that have affected your horse’s soundness?
If so, please explain.
Have you noticed improvement in your horse’s general movement around the barn, stall, and/or
pasture?
Have you noticed any change in your horse’s behavior?
How many shoeings has your horse had since seeing Dr. Mansmann?
Have you ridden your horse regularly since your appointment?
Have you noticed improvement in your horse’s walk?
Have you noticed improvement in your horse’s trot?
Have you noticed improvement in your horse’s canter?
Yes No
Yes No Haven’t noticed
Yes – improved Yes – worse No
Yes No
Yes No
Yes No
Yes No
Mansmann et al. Hoof shape and gluteal pain in horses
Copyright © 2021 Richard A. Mansmann & Megan Radkin
16
Table S1. Clinical data for all 144 horses, categorized by gluteal pain (GP) score.
GP 0
GP 1
GP 2
GP 3
BD (mm), n
n
14
41
84
5
median (IQR)
19 (11 – 27)
26 (22.5 32)
26 (22 30)
24 (21.529)
range
0 34
12 41
-2 48
1930
PA (degrees)
n*
14
41
80
5
median (IQR)
0 (-1 2)
0 (-2 0)
-0.5 (-3 0)
-1 (-6 – 2)
range
-5 – 5
-5 – 6
-8 – 6
-8 – 3
BD, breakover distance (see main text); GP, gluteal pain (see main text); IQR, interquartile range (25th75th
percentiles); PA, plantar angle (see main text).
* Four horses lacked PA data, so total n=140 for this variable.
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
Radio-opaque markers placed on the hoof capsule when radiographs of the equine digit are taken show the location of the third phalanx (PIII) with respect to the hoof capsule. This information can be used to position the breakover of the shoe or hoof capsule relative to PIII. Breakover of the shoe relative to the bony column can potentially decrease lameness in the digit and improve a low hoof–pastern axis. Authors' addresses: Colorado Equine Clinic, 9616 Titan Rd, Littleton, CO 80125; (Page and Hagen); Dept. of Anatomy, Michigan State University College of Veterinary Medicine, East Lansing, MI 48824 (Bowker); and 525 Half Moon Rd., Columbia Falls, MT 59912 (Ovnicek). 1999 AAEP.
Article
Low heels and negative plantar angles in the hind feet are the most common hind foot conformational abnormality. A causal relationship has been demonstrated between these conditions and hindlimb lameness. It is important these abnormalities are recognised during thorough orthopaedic examinations, so they can be quantified with radiography and appropriately treated with therapeutic farriery to restore optimal hoof conformation, balance and function. This is an essential part of a holistic approach to treating horses with hindlimb lameness. Farriery intervention for these abnormalities involves returning the plantar half of the foot to a load-sharing plane between the frog and heels, restoring phalangeal alignment and providing increased ground surface plantar to the centre of rotation of the distal interphalangeal joint.
Article
Low heels are the most common hoof conformational abnormality seen in both the front and hind feet of horses. A low/negative distal phalanx angle in the front feet has been associated with palmar heel injuries but only recently has the significance of low/negative angles in the hind feet received attention. A study including a greater number of horses more representative of the UK horse population would be useful to UK equine practitioners. Our null hypothesis was that the plantar distal phalanx angle does not differ between horses with and without hindlimb lameness. For this prospective case‐controlled study, horses presenting for orthopaedic complaints underwent a complete lameness assessment. The plantar distal phalanx angulation (PDPA), the angle between a line parallel to solar surface contacting the ground and the solar margin of the distal phalanx, was calculated from lateromedial radiographs. Horses were included in the study if hindlimb lameness was definitively localised by diagnostic anaesthesia. Student's t‐tests and multivariable linear regression models were used for statistical analysis. One hundred and eighty‐two horses met the inclusion criteria, 132 with hindlimb lameness and 50 controls. The mean left PDPA for HLL group was −1.0° vs. +1.8° for the controls. The mean right PDPA for HLL group was −1.1° vs. +1.4° in controls (both P<0.001). Lameness was most frequently localised to the stifle (59% of horses), followed by the distal tarsal joints and the proximal suspensory region. A limitation of the study was that the control group included some forelimb lame horses. It was concluded that horses with hindlimb lameness, including lameness localised to the stifle, were more likely to have negative PDPAs. While Pezzanite et al. (2019) previously reported a relationship between negative/neutral PDPA and tarsal/metatarsal lameness, this study is the first to find a relationship to stifle lameness, which may reflect differences in the populations of horses examined. Further kinematic studies are required to determine whether it is a cause or effect relationship.
Article
Background Lameness can be multifactorial and may result from the accumulation of multiple seemingly unrelated causes. The identification of factors associated with lameness could be one method to decrease incidence of lameness and prolong the equine athlete's competitive life. Objectives To determine if there is an association between hoof balance in the sagittal plane and hindlimb lameness. Study design Case‐control study. Methods Eighty client‐owned horses with hindlimb lameness (cases) and 80 horses with no detectable hindlimb lameness (controls) were prospectively enrolled following lameness evaluation as either cases (lameness localised with regional anaesthesia) or controls (no hindlimb lameness). Lameness cases were divided based on location (stifle, tarsus, proximal metatarsus, and other sites). Lateromedial radiographs were performed of hind hooves and plantar angle of the distal phalanx (PADP) was determined. The prevalence of negative/neutral PADP and median PADPs were calculated. Conditional logistic regression and Wilcoxon signed rank tests were used to analyse PADPs, and odds ratios were calculated. Significance was set at P<0.05. Results The mean PADP was significantly smaller in cases compared to controls. The mean PADP was significantly smaller in horses with lameness localised to tarsus and proximal suspensory, but not the stifle. Lameness in horses was associated with a negative/neutral PADP (Odds ratio [OR] 3.87, 95% confidence interval [95%CI] 1.97–7.61, p<0.01), with lameness localised to the tarsus (OR 4.98, 95%CI 1.34–18.54, p = 0.01) and proximal suspensory (OR 5.16, 95%CI 1.11–23.89, p = 0.03) being associated with a negative/neutral PADP. Main limitations It is unknown whether the negative/neutral PADP contributed to lameness or lameness resulted in lower PADP. Conclusions Horses with hindlimb lameness localised to the distal tarsus and proximal metatarsus, but not the stifle, were more likely to have negative/neutral PADPs. Corrective farriery to improve PADP may be investigated further as one component in the treatment of hindlimb lameness localised to regions proximal to the foot. This article is protected by copyright. All rights reserved.
Article
Optimal function of skeletal muscle is essential for successful athletic performance. Even minor derangements in locomotor muscle function will impact power output, coordination, stamina, and desire to work during exercise. In this review, the presenting clinical signs, differential diagnoses, approach to diagnostic testing and treatment of muscle atrophy and weakness, focal muscle strain, and exertional myopathies are discussed. Exertional myopathies include polysaccharide storage myopathies, recurrent exertional rhabdomyolysis, malignant hyperthermia, and myofibrillar myopathy.
Article
This study deals with the relationship between long toes in the hind feet and pain in the gluteal region in horses, and the remedial value of trimming/shoeing that moves the breakover point back at the toe. Seventy seven client-owned horses were studied, 67 shod riding horses retrospectively and 10 barefoot broodmares prospectively. The 10 mares were evaluated twice, and 24 of the 67 riding horses were re-evaluated at the next shoeing, for a total of 111 observations. Each horse underwent gluteal palpation and lateral radiographs of both hind feet. Toe length was quantified as breakover distance (BD), the horizontal distance between the tip of the third phalanx and the dorsalmost point at which the wall/shoe was in contact with the ground. The BD was then shortened with trimming +/− shoeing to a length of ≤15mm (shod horses) or ≤20 mm (barefoot horses). The 24 riding horses were re-evaluated 4-6 weeks later and the 10 broodmares 1 week after trimming.The results showed that of the 67 riding horses, 75% were positive for gluteal pain at initial evaluation. The mean BD for the positive and negative horses was 24.2 ± 1.3 mm and 18.8 ± 2.0 mm, respectively (p = 0.04). At the next shoeing, the mean BD was 10.9 ± 2.3 mm and gluteal pain was improved in all 24 horses; 20 horses (83%) were negative and 4 horses (17%) were now only mildly positive. The 10 broodmares were all positive for gluteal pain initially. The mean BD before and after trimming was 23.7 ± 1.2 mm and 10.9 ± 1.1 mm, respectively. One week later, gluteal pain was improved in all 10 mares; 8 mares (80%) were negative, and the other 2 mares (20%) were only mildly positive.The conclusion is that excessive toe length in the hind feet may be accompanied by pain in the gluteal region and, in our experience, may be associated with gait or performance problems. Shortening the toe can alleviate this pain within days or weeks. Aiming for a BD of between 0 and 20 mm probably is appropriate for the average-size horse.
Article
Negative palmar angle syndrome refers to the condition of progressive heel collapse and its consequences on gait and performance. Treatment and prognosis are facilitated by grading the severity of biomechanical disorder according to physical and radiographic features. Although negative palmar angle syndrome in grades I (mild) and II (moderate) can be corrected with trimming and routine shoeing, grades III (severe) and IV (complicated by flexor contracture) require more intensive mechanical intervention and patience—however, comfort and function can be improved immediately.
Article
The GYS1 gene mutation that is causative of Type 1 Polysaccharide Storage Myopathy (PSSM) has been identified in more than 20 breeds of horses. However, the GYS1 mutation frequency or Type 1 PSSM prevalence within any given breed is unknown. The purpose of this study was to determine the frequency of the GYS1 mutation and prevalence of genetic susceptibility to Type 1 PSSM in selected breeds from Europe and North America. The GYS1 mutation was detected in 11 breeds, including, in order of increasing allele frequency, Shires, Morgans, Appaloosas, Quarter Horses, Paints, Exmoor Ponies, Saxon-Thuringian Coldbloods, South German Coldbloods, Belgians, Rhenish German Coldbloods and Percherons. The prevalence of genetic susceptibility to Type 1 PSSM in these breeds varied from 0.5% to 62.4%. The GYS1 mutation was not found in the sampled Thoroughbreds, Akhal-Tekes, Connemaras, Clydesdales, Norwegian Fjords, Welsh Ponies, Icelandics, Schleswig Coldbloods or Hanoverians, but failure to detect the mutation does not guarantee its absence. This knowledge will help breed associations determine whether they should screen for the GYS1 mutation and will alert veterinarians to a possible differential diagnosis for muscle pain, rhabdomyolysis or gait abnormalities.
Synchronization of head and limb movements in the horse
  • Hms Davies
  • C M Lusi
  • S M Ismail
Davies HMS, Lusi CM, Ismail SM. Synchronization of head and limb movements in the horse. Proceedings, 4 th International Fascia Research Congress, Reston, Virginia, USA; 2015. https://www.fasciacongress.org/2015/Abstracts/39_Davies.pdf.