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New Zealand Veterinary Journal
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Pathophysiology and diagnosis of third carpal bone
disease in horses: A review
CJ Secombe a b , EC Firth a , NR Perkins a & BH Anderson a c
a Institute of Veterinary, Animal and Biomedical Sciences , Massey University ,
Palmerston North, New Zealand
b Division of Veterinary and Biomedical Sciences , Murdoch University , Murdoch,
Western Australia E-mail:
c Ballarat Veterinary Practice , 1410 Sturt St, Ballarat, VIC 3350, Australia
Published online: 22 Feb 2011.
To cite this article: CJ Secombe , EC Firth , NR Perkins & BH Anderson (2002) Pathophysiology and diagnosis of third
carpal bone disease in horses: A review, New Zealand Veterinary Journal, 50:1, 2-8, DOI: 10.1080/00480169.2002.36241
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2
New Zealand Veterinary Journal 50(1), 2-8, 2002
Review
Pathophysiology and diagnosis of third carpal bone disease in horses:
a review
†
CJ Secombe §, EC Firth , NR Perkins and BH Anderson
Abstract
al 1992). The carpus is a common location of disease causing
lameness. Fractures of the carpal bones during training or racing
may account for 1–8% of all injuries in some populations
(Mohammed et al 1991; Wilson et al 1992; Mizuno 1996). C3
is one of the more commonly injured carpal bones, (Schneider
et al 1988), the frequency of injury being higher in Standardbred
horses than in Thoroughbreds (Park et al 1970; Palmer 1986;
McIlwraith 1996; Mizuno 1996; Lucas et al 1999).
Third carpal bone (C3) disease is a significant cause of lameness
in Standardbred and Thoroughbred horses. The bone density
of C3 increases as a result of exercise, reducing the compliance
of the bone and predisposing it to injury. Currently, the most
widely used method of diagnosis is subjective radiography using
the tangential view. Radiographically, increases in bone mineral
density (BMD) appear as sclerosis but it is not known at what
point increases in sclerosis indicate the onset of disease or
increased risk of C3 fracture. A quantitative assessment of the
BMD of C3 in horses would improve understanding of the
changes that occur within this bone and guide athletic
management, as it is thought that BMD changes precede
articular cartilage damage.
Increased bone density or sclerosis of C3 may be the earliest
indicator of disease within this bone and slab fractures are likely
to be the end result of disease (Pool 1996). Subchondral lucency
and cartilage lesions of the radial and intermediate facet of C3
have recently been described as a separate clinical entity and may
involve the same pathophysiological process, and perhaps precede
slab fractures (Ross et al 1989; Moore and Schneider, 1995).
Methods of non-invasive bone-mineral analysis used for the
detection of osteoporosis in humans include single photon
absorptiometry (SPA), dual x-ray absorptiometry (DXA),
computed tomography (CT), radioabsorptiometry (RA),
quantitative ultrasonography (QU) and magnetic resonance
imaging (MRI). To date, DXA and RA are the most commonly
used methods of quantitative non-invasive bone-mineral analysis
in horses. The cost of equipment and difficulties in performing
DXA in live animals preclude the routine use of this technique
for diagnostic purposes. RA may become clinically applicable
to C3 analysis in horses, but small variations in x-ray beam
angle when taking the tangential view significantly affect results,
making this technique clinically inapplicable at this time.
Currently, methods of quantitative non-invasive bone-mineral
analysis of C3 in horses are not suited to clinical application.
Scientific knowledge regarding the diagnosis, treatment and
prognosis of osseous disease has increased greatly over the last 30
years. Research aimed at preventing osseous disease has received
less attention, the exception being the development of a variety
of non-invasive methods of bone-mineral analysis used in the
prevention of osteoporosis in humans. Such methods may be
useful for the detection of changes in the skeleton of horses trained
for athletic pursuits. However, all of these techniques have been
developed to detect a decrease in bone mass, rather than an
increase in bone mass such as occurs with C3 disease in racing
horses. This paper reviews the pathogenesis and diagnosis of C3
disease, the current methods of non-invasive bone-mineral
analysis and their application to the horse.
KEY WORDS: Horse, lameness, carpal bone, bone-mineral
analysis, absorptiometry, computed tomography, quantitative
ultrasonography, magnetic resonance imaging.
Pathophysiology of C3 Disease
In most horses, the carpus consists of 7 carpal bones arranged in
2 rows between the radius and the metacarpal bones. C3 is the
largest bone of the distal row, contributing to two-thirds of the
Introduction
Retrospective studies performed in several countries have
demonstrated that lameness appears to be the most common
resaon for disruption of training schedules of performance horses,
resulting in lost days in work, a prolonged spell, or retirement
from racing (Jeffcott et al 1982; Rossdale et al 1985; Lindner et
BMC
BMD
C2
Bone mineral content
Bone mineral density
Second carpal bone
Third carpal bone
C3
C4
Fourth carpal bone
Institute of Veterinary, Animal and Biomedical Sciences, Massey University,
Palmerston North New Zealand.
† Current address: Ballarat Veterinary Practice, 1410 Sturt St, Ballarat VIC 3350,
Australia.
§ Author for correspondence. Current address: Division of Veterinary and
Biomedical Sciences, Murdoch University, Murdoch, Western Australia. Email:
csecombe@central.murdoch.edu.au
CT
Computed tomography
Dual x-ray absorptiometry
Magnetic resonance imaging
Quantitative ultrasonography
Radiographic absorptiometry
Single photon absorptiometry
DXA
MRI
QU
RA
SPA

Secombe et al
New Zealand Veterinary Journal 50(1), 2002
3
medial to lateral dimension. The 2 facets of the proximal surface
are separated by a dorsopalmar ridge. The medial facet (concave),
known as the radial facet, articulates with the distal surface of
the radial carpal bone. The lateral facet (concave dorsally and
convex palmarly) is known as the intermediate facet and
articulates with the distal surface of intermediate carpal bone.
The distal surface of C3 articulates almost entirely with the third
metacarpal bone, and the lateral and medial aspects of the bone
articulate with the fourth metacarpal bone and second metacarpal
bone, respectively (Getty 1975).
on the dorsal aspect of both facets. When moving at slow gaits
such as walking and trotting, the load is distributed evenly over
the radial and intermediate facets, excluding the most dorsal
aspect. Under load conditions that mimic those of galloping, the
load is transferred to include the dorsal rim of the intermediate
and radial facets shifting towards the dorsomedial aspect of the
radial facet (Firth and Hartman 1983; Palmer et al 1994).
Microradiographic examination of C3’s from horses that have
undergone different levels of exercise show evidence of modelling,
which is particularly apparent in racing horses. When horses are
actively training and racing, modelling can result in increased
trabecular thickening to the point that the intra-trabecular spaces
are completely replaced with bone (Young et al 1989; Young et
al 1991). In a transverse section of C3, 3mm from the dorsal
margin, modelling is seen as an increase in photodensity and
change in bony architecture. Increased radiographic photodensity
is due to increased BMD (Uhlhorn et al 1998; Cantley et al
1999; Firth et al 1999a; Firth et al 1999b). In one of these studies,
Firth et al (1999a) took sagittal sections in a dorsopalmar direction
of the intermediate and radial facets of C3, and radiographs were
taken of the sagittal sections and compared with BMD
measurements performed using DXA. In another study, Uhlhorn
et al (1998) radiographed isolated C3’s in a proximal–distal view
and compared them with bone volume measurements obtained
using morphometry. In both studies it was found that bone
density in the dorsal proximal, dorsal central and dorsal distal
regions of C3 was significantly greater in trained compared with
untrained horses, the dorsal central regions of interest having the
greatest increase in density. Similar findings have been observed
in Thoroughbred horses trained on a treadmill. BMD increases
in the distal dorsal region of C3, then the proximal dorsal region
and finally the central dorsal region (EC Firth, unpublished data).
When axially loaded during maximal exercise, most of the carpal
articulations allow an interlocking wedge arrangement to be
formed. Some of the load is transferred to the intercarpal ligaments
(Bramlage et al 1988). It is thought that through this mechanism,
sudden stress is converted into a longer elastic loading stress and
thus the strain rate is decreased (Deane and Davies 1995). It
appears that the carpus requires such a mechanism for energy
absorption as its elastic ability to over-extend is limited by the
palmar soft tissues when supra-physiologic loads are applied. This
dispersal of energy may not occur on the medial aspect of the
intercarpal joint, as loads from the radius may pass on to the
radial carpal bone and directly on to the radial facet of C3 without
being dissipated to the intercarpal ligaments. This predisposes
the 3 major weight bearing bones to injury, in particular the
radial facet of C3 (Bramlage et al 1988).
When the major weight-bearing carpal bones are loaded, the fluid
component of the articular cartilage exits causing instant
deformation. As the load is shifted to the solid component of the
articular cartilage there is slower ‘creep’ deformation, which
continues until equilibrium is reached between the cartilage and
the external force applied; this is typical of all viscoelastic materials
(Palmer and Bertone 1996). Collagen is concentrated in the
superficial zones of articular cartilage, providing tensile strength.
Consequently, small pathological alterations within this area may
weaken the articular surface and its resistance to shear, tensile
and compressive forces (Setton et al 1993). Compliant
subchondral bone acts as a shock absorber between articular
cartilage and epiphyseal bone, thereby helping to minimise
pathology at the articular surface. Calcified cartilage, with its
intermediate mechanical properties, acts as an interface between
articular cartilage and subchondral bone to reduce shear stresses
(Palmer and Bertone 1996). Calcified cartilage undergoes
remodelling throughout life and the processes of physiological
aging and injury produce reduplication of the ‘tidemark’ (the
junction between calcified and non-calcified cartilage), resulting
in cartilage thinning (Bullough 1981; Burr and Schaflet 1997).
Bony adaptation to exercise is a physiological process. However,
continued modelling in response to high loads leads to
pathological changes as seen in microradiographs (Young et al
1989). Continued modelling causes sharp gradients in bony
stiffness 5–10mm from the dorsal edge of C3 which may result
in incomplete dissipation of forces within articular cartilage during
loading, predisposing it to injury (Young et al 1991). Repetitive
micro-trauma to the articular cartilage leads to chondrocyte injury,
which in turn responds by producing enzymes that destroy the
extracellular cartilage matrix.The gross articular cartilage changes
that may be seen include yellowish discolouration, dullness and
fibrillation, as well as eburnation of subchondral bone.
Microscopic changes include disruption of the various zones of
articular cartilage, changed chondrocyte morphology, exposure
of the calcified cartilage and polishing of the exposed subchondral
bone (Pool 1996). Uhlhorn et al (1998) found that bones with
cartilage lesions of the radial facet of C3 had a significantly higher
bone volume density than those that did not. Pool (1996) found
that, although there did not appear to be a good correlation
between the extent of deterioration of the articular cartilage and
subchondral bone, sclerosis appeared in varying amounts in
affected bones.
Bone is a constantly adapting tissue and it is widely accepted
that relative density increases with exercise (Young et al 1989;
Young et al 1991; Palmer et al, 1994). During exercise the
subchondral bone deforms when placed under a mechanical load.
Repetitive loading stimulates the osteoblasts lining the spongiosa
to up-regulate, leading to thickening of the trabeculae at the
expense of the intra-trabecular spaces; this is termed modelling
(Pool 1996). As subchondral bone density increases the shock-
absorptive capacity decreases.
Remodelling occurs concurrently with modelling. True
remodelling occurs when there is no net increase in BMD; repair
and damage occur at the same rate. When the rate of damage
(presumably from the sharp change in stiffness gradient within
the subchondral bone as a result of modelling) exceeds that of
repair it is presumed that microfractures disrupt the canalicular
system and possibly the capillary bed.The result is a wedge-shaped
In order to explain the exercise induced distribution of changes
that occur within C3, it is important to study loading patterns at
rest and at varying gaits. At rest the palmar aspect of both the
radial and intermediate facets bear the most weight. Application
of high loads in this position result in intermittent weight bearing

4
New Zealand Veterinary Journal 50(1), 2002
Secombe et al
portion of ischaemic sclerotic subchondral bone within C3.This
secondary lesion usually measures 8–10mm in length, 3–5mm
in width and 1–2mm in depth. It is located 2–4mm from the
dorsal proximal margin of the radial facet and is composed of
acellular fragments of sclerotic bone, the deep surface being
separated from viable compacted bone by a line of resorption. A
vascular response arises adjacent to the bone to fill the trough
with osteogenic granulation tissue that replaces the necrotic
subchondral bone (Pool 1996).
when damage to the bone exceeds repair. In vivo and in vitro
studies have demonstrated that traumatic loading induces
subchondral bone sclerosis and damage to calcified cartilage before
inducing damage to articular cartilage (Silyn-Roberts et al 1990;
Verner et al 1992). Therefore, it has been proposed that early
detection of increased BMD may be helpful in predicting
degenerative joint disease and fractures (DeHaan et al 1987).
Currently the most commonly used method to detect increased
BMD in C3 is subjective radiography.
It is suggested these lesions predispose to partial or complete slab
fractures. Small areas of diseased bone appear to undergo repair
without destabilisation of overlying cartilage. Unsupported
articular cartilage either collapses into the underlying cavity or
becomes detached. Studies of slab fractures by Pool suggest these
fractures occur in pathological bone (Pool 1996). All lesions began
at the dorsoproximal surface of C3 in an area of chronic injury
and repair. The fracture line extends distally where it either turns
obliquely to create a partial slab fracture or continues to create a
compete slab fracture. Usually the proximal quarter of the fracture
line appears irregular and contains fibrous tissue, the distal three-
quarters appears as an acute fracture (Pool 1996).
Current Method of Diagnosis of
C3 Disease
Radiography is the main diagnostic tool used in the assessment
of carpal injuries in horses. As with all radiographic evaluations,
several views are taken to ensure adequate assessment, as
superimposition is a problem in the radiographic evaluation of
joints. The tangential or skyline view of the distal row of carpal
bones is essential to diagnose changes in C3.There are 2 tangential
views used to assess the distal carpal row. One view involves
placing the plate distal to the flexed carpus and angling it towards
the beam as close to 90° as possible (Figure 1). This view results
in little distortion of C3, although some magnification does occur
(Figure 2).The second view involves flexing the carpus and placing
the plate on the dorsal aspect of the third metacarpal bone; this
view causes little magnification but a significant amount of
distortion, as the beam angle is not perpendicular to the plate
(Figure 3 and 4). The x-ray beam angle, leg angle and C3 beam
angle are similar between both views, however, the plate angle
differs.
In an attempt to adapt to the mechanical stresses of exercise, C3
subchondral bone increases in density and modifies its
architecture. This physiological process becomes pathological
The occurrence of C3 sclerosis (an increase in radio-opacity and
loss of trabecular structure) in the absence of other radiographic
changes has led to the development of 2 similar grading scales
used to assess this (O’Brien et al 1986; Uhlhorn and Carlsten
1999). The radiographic view used to assess sclerosis has
historically been the view in which the x-ray beam angle is not at
90° to the x-ray plate (Figure 3). The radiographic quality must
be such that the trabecular pattern can be recognised, not only
in C3 but also in C2 and C4, as the latter is used as a control in
one grading system. In the first grade, trabeculation in clearly
evident, there are no areas of focal thickening and no loss of
trabeculation between the cortex or medulla. In the second grade,
trabeculation remains clearly evident but focal thickening is
Figure 1. Tangential view of C3. The plate is angled so that the X-ray
beam contacts the plate at as close to 90° as possible.
C4
C3
fracture
Figure 2. A radiograph of C3 and C4 using the method illustrated in Figure 1. A fracture is present within the radial facet of C3.

Secombe et al
New Zealand Veterinary Journal 50(1), 2002
5
present. The first and second grades are believed to represent
physiological adaptation (O’Brien et al 1986). In the third grade,
focal loss of trabeculation and loss of definition between the cortex
and the medulla occurs. In the fourth grade, the majority of the
radial or intermediate facets have lost trabecular structure and
definition between cortex and medulla.
1999a), and it is currently unknown at what stage an increase in
BMD and change in architecture of the subchondral bone
becomes a pathological as opposed to a physiological response.
Thus, subjective radiographic analysis of changes in BMD is not
without problems. It has been generally believed that changes in
BMD of less than 30% cannot be detected subjectively. Although
this was based on experiments performed 60 years ago (Lachmann
and Whelan 1936), a more recent study agrees with this
hypothesis for bones of the peripheral skeleton (Finsen and Andra
1988). Other studies have shown that, although this was true for
cortical bone sites, a change of only 8–14% can be detected for
bones with high trabecular content (Garton et al 1994). All of
the studies reporting subjective assessments of BMD have been
done in humans, in the context of detecting decreased BMD.
This differs from the usual case in the young working horse in
which disease is usually associated with increased BMD. As
subjective analysis of radiographs may not differentiate between
physiological and pathological sclerosis in C3, a quantitative
method of detection of sclerosis would be useful.
C4 sclerosis is rarely seen and, if apparent, is likely to be due to
radiographic artefact (O’Brien et al 1986). Investigation of
subchondral bone changes within C4 have not been reported to
date. There are a few reports on slab fractures of C4; these are
usually sagittal fractures and are often accompanied by a slab
fracture of the intermediate carpal bone. It is speculated that the
cause of these fractures is abnormal force acting on normal bones,
although this has not been proven (Auer et al 1986; Field and
Zaruby 1994).
The subjective grading of sclerosis of C3 has been examined
(Uhlhorn et al 1998). In that study, only radiographs of the
tangential view in which C2 and C4 could be examined were
included. Radiographs were graded, horses were euthanased and
the distal row of carpal bones were disarticulated and radiographed
again in a proximodistal direction. C3 was then assessed for bone
volume density using bone morphometry. The authors found
that subjective assessment of the tangential radiographic view
allowed differentiation between sclerotic and non-sclerotic C3’s,
however, the grade of sclerosis could not be accurately determined.
Although this is a significant finding, some degree of sclerosis is
believed to be a physiological response to exercise (Firth et al
Quantitative Non-Invasive Bone-
Mineral Analysis – Potential Methods of
Diagnosis of C3 Disease
The high prevalence of osteoporosis in humans has resulted in
the development of many methods of non-invasive bone-mineral
analysis in order to detect early disease and monitor its progression
and response to therapy. The most commonly used methods at
this time are discussed below. Non-invasive bone-mineral analysis
has been used in animals, including horses, to study bone density
in a number of bones.
Absorptiometry
Absorptiometry methods use the transmission of x-rays or gamma
rays through the bone of interest. The degree of attenuation of
the rays by the bone is measured by a scintillation detector system
and there is a direct relationship between the number of photons
absorbed and bone mineral content (BMC) (Mazess and Wahner
1988). As these methods do not take into account bone volume,
only BMC can be measured. To assess BMD, the cross-sectional
Figure 3. Tangential view of C3. The plate is parallel to the third
metacarpal bone and the X-ray beam contacts the plate at 30°.
C4
C3
fracture
Figure 2. A radiograph of the same distal row of carpal bones as shown in Figure 2 using the method illustrated in Figure 3. A fracture is present
within the radial facet of C3.

6
New Zealand Veterinary Journal 50(1), 2002
Secombe et al
area of the bone must also be measured, for example, using
ultrasonic transmission velocity; dividing BMC by cross-sectional
area yields BMD (Greenfield et al 1981).
studies, the technique involves taking a conventional radiograph
of a subject’s hand together with a reference standard, both of
which are placed in a predetermined position on the plate. Image
analysis of the resulting radiograph is used to determine the result.
The reference standard is included in the radiographic image to
correct between-film differences due to film quality, exposure
and processing. The ideal reference standard has the same
absorption coefficient as the material being measured and the
most common metallic standard used is aluminium or an
aluminium alloy (Clobert and Bachtell 1981). This technique is
highly accurate and reproducible (Yang et al 1994).
SPA, a single source of low-energy photons in the form of a
radionuclide, has been used in horses to assess BMC in
combination with ultrasonic transmission velocity to determine
cross-sectional area, hence BMD, of the third metacarpal bone
and changes that occur to BMD in response to immobilisation
(Jeffcott et al 1986; Buckingham and Jeffcott 1991). Although
this is a relatively precise method, it has several disadvantages,
including a requirement that the horse stand still for at least 90
seconds (Jeffcott 1986). Results are expressed in terms of BMC
per unit length of bone and do not take account of differences in
bone size. This technique was found to only be useful for
comparing changes in horses that have negligible variation in
bone cross-sectional area (Jeffcott et al 1986). Although once a
useful research tool, this technique is now rarely used.
The consistency with which RA measures bone mass is high,
even between populations and skeletal sites. RA is thought to be
as good as, or in some cases better than, other bone-mass
measurement techniques and its predictive association of fracture
risk is high (Baran et al 1997). The technique has several
advantages: it is readily available and no large capital expenditure
is required.The radiographs are taken and submitted to an image
analysis laboratory for interpretation, so the technique is useful
in remote areas where access to other bone-mass analysis methods
is limited.
DXA, developed using the principles of SPA, was introduced for
commercial use in the late 1980’s. The source is an x-ray tube
generating x-rays of 2 distinct energy levels. These are attenuated
by tissues to different degrees, eliminating the need for a constant
soft-tissue covering (Mazess 1981). Numerous additional
advantages over other forms of absorptiometry have made DXA
the most widely used method for assessing BMD in clinical and
population medicine, as well as the primary research tool for
BMD assessment. In horses, DXA has only been used on excised
bones (including C3), as the time taken to scan is prohibitively
long for use on live subjects (Firth et al 1999a). As such, it is
unlikely to have clinical application in horses for assessing BMD
changes in C3.
RA has been used on excised dog and horse bones with limited
success (Delaquerriere-Richardson et al 1982; Scotti and Jeffcott
1988). More recently, RA has been used to assess changes in BMD
of the third metacarpus in live horses and found to be a useful
diagnostic tool (Hoekstra et al 1999; Hoffman et al 1999). As
RA has a number of advantages over other methods of BMD
assessment, it may be useful in the assessment of C3 disease using
a tangential radiographic view but, unfortunately, small variations
in x-ray beam angle significantly affect the measured radiographic
density, thereby giving false results (Secombe 2000).
Computed tomography
CT involves the obtainment of multiple cross-sectional images
using narrow-beam x-rays and computer processing, integration
and analysis of these. This method offers high levels of soft-tissue
differentiation and no superimposition of overlying structures,
as the third dimension is known.This results in major advantages
over conventional radiography and allows the quantification of
tissue densities (Hathcock and Stickle 1993). CT has recently
become a popular method for assessing the BMD of trabecular
bone, which has a high turnover rate compared with cortical
bone, reflected by rapid subtle changes in BMD. Osseous
architecture as well as BMD can be studied using this technology,
resulting in a better indication of bone strength than other
methods. The disadvantages of CT include exposure of patients
to high doses of radiation, long scan times and, although this
technique is precise and accurate, reproducibility is a problem
due to inaccuracies in patient positioning (Andre and Resnick
1995; Wong and Sartoris 1996).
Quantitative ultrasound
QU uses measurement of the speed of sound through a bone of
known diameter to assess BMD. Quantitative ultrasound provides
information on bone quantity and quality, as the speed of sound
may be influenced by bone mass, quantities of cortical and
trabecular bone and bone architecture (Grampp et al 1996; Baran
et al 1997). Ultrasound beam attenuation is thought to depend
on bone structure and relates to trabecular orientation and size.
The more complex the structure, the more the ultrasound beam
is attenuated or blocked (Baran et al 1997). There are relatively
few studies assessing bone mass in women using QU, but this
method has been useful for predicting fracture risk in both
retrospective and prospective studies (Baran et al 1997).
Ultrasound velocity measurements have been used in horses in
combination with SPA to monitor the effects of treadmill exercise
on the third metacarpal bone (McCarthy and Jeffcott 1988).That
study found that ultrasound velocity altered with training, but
BMC and BMD did not change. This may be due to a change in
the apparent architecture of the bone that was not associated
with a change in BMD.To the authors’ knowledge this technique
has not been used to measure the BMD of C3 in horses.
CT has been used in both small and large animals for the diagnosis
of a variety of disorders, but little work has been done on the
assessment of BMD. Detecting changes in BMD of C3 is possible
using this method, but general anaesthesia is likely to be required
and the high cost of equipment will limit availability.
Magnetic resonance imaging
Radioabsorptiometry
MRI is commonly used clinically to assess occult traumatic or
atraumatic insufficiency fractures that often occur in osteoporotic
patients. MRI can detect very subtle structural changes at a
fracture site and distinguish between acute and chronic defects,
resulting in a high level of sensitivity and specificity when used
for fracture diagnosis. Recent research suggests that MRI can be
RA measures BMD objectively by measuring the radiographic
photodensity of bones in comparison with that of a material of
known density. The technique has been available for over 50 years
but prior to the use of computers, was inaccurate, imprecise and
time consuming (Yang et al 1994; Yates et al 1995). In human

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New Zealand Veterinary Journal 50(1), 2002
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used to determine the relationship between BMD, bone structure
and strength, which is an advantage over most of the above-
mentioned techniques for non-invasive bone-mineral analysis,
and allows more accurate determination of fracture risk in
osteoporotic patients. As the signal measured by MRI is generated
by hydrogen atoms there is no radiation and therefore it can be
safely used in pregnant women and children (Majumdar and
Genant 1995). MRI has been used in horses, mostly on cadavers
and, to the authors’ knowledge, BMD and bone architecture has
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C3 disease is a significant problem in the equine industries, more
so in Standardbred horses than in Thoroughbreds. The end stage
of C3 disease is thought to be slab fractures, for which the
prognosis for return to athletic function is guarded. The current
understanding of the pathophysiology of this disease is that the
bone adapts to exercise by increasing BMD and altering its
architecture. The benefits of increased strength are to the
detriment of compliance within the bone. Increased stiffness
results in vulnerability to mechanical damage that cannot be
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consuming and are usually used on excised bones. DXA and RA
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invasive bone-mineral analysis in horses. The cost of equipment
and difficulties in performing DXA in live animals preclude the
routine use of this technique as a diagnostic modality. RA may
become clinically applicable to C3 analysis in horses, but small
variations in x-ray beam angle when taking the tangential view
significantly affected results (Secombe 2000), making this
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Accepted for publication 1 August 2001