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\begin{document}

\title{Should radiographs of the thoracolumbar spine remain part of the
pre-purchase examination?}



\author[1]{Maty Looijen}%
\author[1]{Rhiannon Morgan}%
\affil[1]{The Royal Veterinary College}%


\vspace{-1em}



  
  \date{June 13, 2024}


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\selectlanguage{english}
\begin{abstract}
The inclusion of thoracolumbar radiographs in a pre-purchase examination
(PPE) is a topic of current and intense debate, subsequent to a
statement from the Federation of European Equine Veterinary Associations
(FEEVA) advocating the exclusion of spinous process radiography from the
PPE. This review will consider the reasons behind the addition of such
radiographs into PPEs, the limitations of radiography in ambulatory
practice and therefore the diagnostic limitations to the practitioner,
the diagnostic benefit of a complete radiographic examination, and
discussion of common and less-frequent thoracolumbar pathologies. We
will focus on laterolateral radiographs of the spinous processes as
these are most commonly acquired during the PPE. The lack of consistent
and repeatable grading systems highlights the subjective nature and
variability in assessing this region radiographically. Coupled with the
sparse evidence of correlation between clinical symptoms and
radiographic abnormalities of the thoracolumbar spine leads us to
conclude that taking radiographs of the back during PPEs should not be
performed unless the clinical examination indicates otherwise.%
\end{abstract}%



\sloppy


\textbf{Should radiographs of the thoracolumbar spine remain part of the
pre-purchase examination?}

Keywords\textbf{:} equine, back, thoracolumbar spine, spinous processes,
pre-purchase examination, radiographs.

\textbf{Summary}

The inclusion of thoracolumbar radiographs in a pre-purchase examination
(PPE) is a topic of current and intense debate, subsequent to a
statement from the Federation of European Equine Veterinary Associations
(FEEVA) advocating the exclusion of spinous process radiography from the
PPE. This review will consider the reasons behind the addition of such
radiographs into PPEs, the limitations of radiography in ambulatory
practice and therefore the diagnostic limitations to the practitioner,
the diagnostic benefit of a complete radiographic examination, and
discussion of common and less-frequent thoracolumbar pathologies. We
will focus on laterolateral radiographs of the spinous processes as
these are most commonly acquired during the PPE. The lack of consistent
and repeatable grading systems highlights the subjective nature and
variability in assessing this region radiographically. Coupled with the
sparse evidence of correlation between clinical symptoms and
radiographic abnormalities of the thoracolumbar spine leads us to
conclude that taking radiographs of the back during PPEs should not be
performed unless the clinical examination indicates otherwise.

\textbf{Main text}

Introduction

Ongoing discussion exists on the necessity of a radiographic examination
of the equine thoracolumbar spine during the pre-purchase examination
(PPE). In 2018, the Federation of European Equine Veterinary
Associations (FEEVA) stated that they do not recommend radiography of
spinous processes (SP) of the thoracolumbar spine as part of the PPE
(\emph{FEEVA Position Statement of Pre-Purchase Radiography on Dorsal
Spinous Processes} , 2018). However, other federations such as the
British Equine Veterinary Association (BEVA), American Association of
Equine Practitioners (AAEP) and others have not followed up on this
statement. The German Equine Veterinary Association (DVG) decided not to
include the thoracolumbar spine in their 2018 PPE guidelines, and this
will likely remain in 2023 (R\selectlanguage{ngerman}öntgen-Leitfaden (2018) - Leitfaden Fu\selectlanguage{english}r Die
R\selectlanguage{ngerman}öntgenologische Beurteilung Bei Der Kaufuntersuchung Des Pferdes,
2018). Still, the fact remains that radiography of the thoracolumbar
spine is a common occurrence during PPEs.

Radiographs of the SP are often included in the PPE due to a request by
the client, the purchasing party. Reasons for purchasers to request
these radiographs are numerous and may involve ridden or clinical
queries, the ``just to exclude'' reason or for re-sale purposes. Often,
decision making is done upon exclusion; if the horse does not show any
radiographic abnormalities of the thoracolumbar spine, this is a
positive outcome, if the horse does show abnormalities then many factors
are involved in the final decision. Another facet of the process are the
insurance companies. Most companies do not request radiographs for their
policies; however, some require radiographs for horses worth over
£10,001.

Clinical examination

Abnormalities on clinical examination involving the thoracolumbar spine
may be another reason for performing radiographs during the PPE. There
are a considerable number of clinically significant osseous and soft
tissue related primary back problems but one cannot always distinguish
those with back pain as a secondary consequence from orthopaedic
conditions (Henson, F. M.D.Kidd, 2009). A systematic protocol for the
clinical part of the PPE is therefore an important feature. Guidance
notes on the 5 stage vetting of a horse are written by the BEVA, in
association with the RCVS, preluding a structured approach to this (RCVS
\& BEVA, 2018). Unfortunately, clinical symptoms are often vague and
encompass a multitude of variable combinations. Symptoms are; back pain,
abnormal spinal conformation, muscle wastage, abnormal reaction on
palpation and manipulation, back stiffness, unwillingness to go
forwards, poor performance, lameness, bucking, pain or resentment on
saddling and/or girth tightening and other gait abnormalities such as an
abnormal canter, disunited gait, poor hindlimb impulsion,
`'bunny-hopping'' and difficulty to transfer from one gait to another
(Henson, F. M.D.Kidd, 2009). The cause of back pain can be very
challenging to discover and often requires a combination of clinical
examination and diagnostic aids such as regional blocks and diagnostic
imaging. The former diagnostic aid not being a regular part in the PPE.
In the majority of cases, a diagnosis can only be made by elimination of
other conditions which may cause back pain and a thorough work-up is
needed before the final diagnosis can be made.

Radiography

Radiography of the equine thoracolumbar spine in horses is a common
diagnostic procedure. Portable machines are likely sufficient for the
thoracic spinous processes; however, a high-output stationary generator
is often required for the vertebral bodies, articular process joints and
the lumbar spine (Manso-Diaz et al., 2018). These anatomical regions
often require higher exposure settings; the subsequent effect of
increased scatter radiation must be controlled by use of an appropriate
grid (Butler, Janet A. et al., 2017). A lead sheet may be placed behind
the detector plate to prevent backscatter (Butler, Janet A. et al.,
2017). A standard radiographic examination of the thoracolumbar spine of
an adult horse involves a series of multiple overlapping laterolateral
(LL) views (Figure 1) of the SP and, if possible, the vertebral bodies
(Manso-Diaz et al., 2018). The latter sometimes needs to be performed
separately due to differences in laterolateral thickness of the horse
more dorsally compared to ventrally, and additionally this allows
tighter collimation. If taken in one view, this may result in exposure
failures on either anatomical structure; quite often seen as
overexposure of the spinous processes. Additional oblique projections
(L20V-RDO and R20V-LDO, respectively left 20 degrees ventral to right
dorsal oblique and right 20 degrees ventral to left dorsal oblique)
(Figure 2) can be acquired to separate the left and right articular
process joints (Manso-Diaz et al., 2018). When acquiring radiographs of
the thoracolumbar spine it is helpful to add dorsal radiopaque markers
(Figure 3), which will enable the identification of specific vertebrae
and SP in relation to the horse, ensuring each view overlaps slightly
and therefore all SP are included (Manso-Diaz et al., 2018).

Radiographic quality is an important feature when obtaining radiographs
of the thoracolumbar spine. Successful interpretation will result from a
radiograph that shows exactly what is necessary for diagnosis and this
depends on multiple factors (Cervantes, 2016). Accessing the quality of
radiographs is subjective, however, the main important physical features
are judgement of contrast, sharpness and quantum noise (Dhiego Donizethe
Ferreira \& Israel de Souza, 2021; Kjelle \& Chilanga, 2022). There is a
distinguishable difference between radiographs taken with a high-output
stationary system in comparison to those taken with a low-output
portable machine of which the image examiner should be aware of during
interpretation. The main difference between these are the limitations in
radiographic technique based on exposure limits. The large mass of the
thoracolumbar spine requires a generator output of 75-120kV and
100-250mAs (Butler, Janet A. et al., 2017). However, more recently other
resources describe less exposure is needed, varying from 65-90kV and
20-40mAs (Manso-Diaz et al., 2018). This is likely due the advent to
digital radiography and the improvement in flat panel detector
technology being able to register signal difference over a very wide
range of exposures, having a `wide dynamic range'. In addition,
exposures may differ due to the major differences in the horse's size
and conformation and may be hard to predict. As previously stated, when
taking radiographs in ambulatory practice, diagnostic radiographs of
anatomical locations other than the SP are difficult to obtain, and
conditions such as spondylosis of the vertebral bodies or severe
osteoarthritis of the articular process joints cannot be easily
diagnosed.

Regardless of the system and machine used, there are several other
elements described which may also contribute to the difficulty of image
interpretation of the SP (Looijen et al., 2022a). The impossibility for
orthogonal views, scatter radiation and magnification due to increased
film-patient distance may result in variable quality of radiographs
(Looijen et al., 2022a). Measuring the interspinous spaces of the equine
thoracolumbar spine on computed tomographic images in comparison to
radiographs resulted in inconsistencies in those measurements, most
likely due to geometric distortion because of x-ray beam angulation
(Djernæs et al., 2017). Moreover, differences in head and neck
positioning resulted in inconsistent measurements of the interspinous
space with lower positions leading to increasing interspinous distances
(Berner et al., 2012). A consistent and neutral head position is
imperative when taking radiographs of the thoracolumbar spine. We
recommend using a head stand, or something to act as a head stand, set
at the height of the horses' shoulders to provide a neutral head and
neck position.

Image interpretation

For optimal interpretation of radiographs of the equine thoracolumbar
spine, good anatomical knowledge is required (Figure 1). We do need to
be aware of anatomical variations seen in SP but also, we should be
aware of other possible radiographic abnormalities associated with
abnormal clinical findings within the remainder of the spine. Other
anatomical structures to be aware of are the articular processes, the
vertebral bodies, the ribs, the transverse processes and/or surrounding
soft tissues. In addition, we need to consider overlying structures such
as the epaxial and hypaxial musculature, the scapula and ileum which are
superimposed over important structures of the thoracolumbar spine and
may contribute to image distortion. The nuchal ligament and its
continuation as the supraspinous ligament, as well as the interspinous
ligaments are also important to assess. These ligaments, in combination
with the spinal musculature, offer core stability and contribute to a
clinically healthy back (Townsend et al., 1986).

When assessing radiographs of the thoracolumbar spine it is important,
as with any image interpretation, to maintain consistency. To facilitate
detection of abnormal findings it is advised to orientate them in a
standard manner for viewing, for example; laterolateral views should be
assessed with the cranial aspect of the animal to the interpreter's left
(Thrall, 2018). In addition, always make sure you look at a radiograph
in the same way, starting from the outside of the anatomy working
inwards as per anatomical structure or from cranial to caudal and/or
dorsal to ventral. Image interpretation should be done remotely and not
in the field with day light blurring your image interpretation. Make
sure you choose a quiet isolated place without distraction (Thrall,
2018). Nowadays DICOM images can easily be transferred to such places
and they allow, on the contrary to JPEG files, the reader to manipulate
the orientation, size, blackness and contrast (Thrall, 2018).

Radiographic abnormalities

Very common radiographic abnormalities associated with the thoracolumbar
spine are those associated with the SP. They can show a huge variability
in their size, shape and margin but also in radiopacity and interspinous
space width (Figures 4 and 5) (Looijen et al., 2022a; M. Zimmerman et
al., 2012). The main location of narrow interspinous spaces is the
caudal saddle region and the cranial lumbar spine (T14--L2), which is
reported consistently in the literature (Butler, Janet A. et al., 2017;
Haussler et al., 1999; Henson, F. M.D.Kidd, 2009; Jeffcott, 1979, 1980;
Townsend et al., 1986). How these changes arise and/or develop remains
unclear. As does the question of what the true incidence of pain arising
from abnormal SP is (Henson, F.M.D., Kidd, 2009). The anatomical
abnormality itself is however, extremely common (Henson, F.M.D., Kidd,
2009). Unfortunately, little is known about its congenital and
developmental features. One study revealed that in foals at a young age,
barely any radiographic changes were found within the thoracolumbar
spine(Sinding \& Berg, 2010). Which conflicts with Pressanto et al.
2023, who stated that the absence of difference in occurrence of
radiographic findings of the SP between yearlings and older horses
supported a developmental rather than acquired aetiology (Pressanto et
al., 2023).

Post-mortem research revealed that horses with overriding SP were found
in 86\% and 92\% of the cases, unrelated to their clinical presentation
(Haussler et al., 1999; Townsend et al., 1986). Radiographic incidence
of abnormalities was found in 34\% of normal horses and 33\% in horses
with a history of thoracolumbar pain (Jeffcott, 1979, 1980).
Histopathology of the interspinous ligament in horses with impingement
revealed altered collagen fibre alignment and ligamentous layers. They
also found evidence of a significant increase in the number of nerves
located within the ligament suggesting a possible explanation for
thoracolumbar pain (Ehrle et al., 2019). Unfortunately, the control
group described horses with the absence of thoracolumbar pathology on
radiography and pathology and therefore did not involve non-clinical
horses with radiographic abnormalities. This made a comparison between
clinically unaffected horses with impingement and those with clinical
symptoms and radiographic changes impossible.

Grading systems

Over the years multiple grading systems have been designed, all trying
to encompass the many different radiographic findings of multiple SP,
allowing interpretation the thoracolumbar spine as a whole (Figure 6)
(Cousty et al., 2010; De Graaf et al., 2015; Denoix, J-M., Dyson, 2011;
Gerhards, H., Hertsch, B., Jahn, P., \& Brunken, 2007; Pettersson, H.,
B. Strömberg, 1987; Sager, 1997; Marieke Zimmerman et al., 2011). These
studies have described common radiographic abnormalities of the SP;
however, they unfortunately have some pitfalls. For example, not all
studies have compared diseased to non-diseased animals, they have not
been validated amongst different observers and they have not established
a `'cut-off'' grade for those which may have an increased likelihood of
having clinical symptoms of primary back pain associated with
radiographic findings. A limited number of studies described a grading
system originating from a sum of grades per SP rather than a generalised
summary of abnormalities (Erichsen et al., 2004; Marieke Zimmerman et
al., 2011). Only until recently has it been described that inter- and
intra-observer agreement on the severity of radiographic abnormalities
offers only selective reliability when grading SP (Looijen et al.,
2022). Most of all, a general consensus of its clinical relevance has
never been established (Looijen et al., 2022).

Clinical relevance of impingement of spinous processes

A limited number of studies have compared clinically unaffected horses
to those with clinical signs of back pain and their radiographic changes
within the thoracolumbar spine. Both studies found \selectlanguage{english} that there is a
wide range of radiographic abnormalities of the SP seen in horses with
or without back pain, and \selectlanguage{english}the severity of the lesions of the SP was
significantly associated with the presence of osteoarthritis of the
articular process joints and clinical symptoms (Cousty et al., 2010;
Marieke Zimmerman et al., 2011). Another study, without comparison,
found widespread variation of radiographic and scintigraphic changes in
riding horses without clinical signs of back problems which lead to the
conclusion that clinically significant changes are not easily
interpretated (Erichsen et al., 2004). These findings are supported by
multiple studies which also revealed a lack of correlation between
radiographic findings of SP and clinical symptoms (Geiger \& Gerhards,
2015; Holmer et al., 2007; Ranner \& Gerhards, 2002; Rieland, 2002).
Another body of evidence is also present showing good correlation
between impingement of SPs and back pain and therefore a true scientific
consensus is absent (Cousty et al., 2010; Hendrickson, 2020; Turner,
2011; M. Zimmerman et al., 2012). Zimmerman et al. 2012, found that in
horses with primary back pain, there was no significant difference in
radiographic abnormalities (M. Zimmerman et al., 2012). However, horses
with severe radiographic abnormalities (above grade 5 out of a scale of
0-7) presented with a combination of back and sacroiliac pain, with and
without hindlimb lameness, or sacroiliac pain with hind limb lameness
(M. Zimmerman et al., 2012). In the group of clinically normal horses,
40\% had medium-grade radiographic abnormalities of the SP(M. Zimmerman
et al., 2012).

Pre-purchase examinations and impingement of spinous processes

Studies which investigated radiographic abnormalities of SP during PPE
are limited. There is only one study performed in Germany and one in the
Netherlands which compared radiographic alterations of the thoracolumbar
spine without clinical signs of back pain on PPE (De Graaf et al., 2015;
Holmer et al., 2007). The majority of horses in these studies had
radiological abnormalities however, these were predominantly mild with
only a few horses having higher grades (De Graaf et al., 2015; Holmer et
al., 2007). Unpublished data of at least one thousand Warmblood horses,
mainly used for dressage, showed potential correlation between mild
radiographic abnormalities and age, gender and height. With taller and
older horses, as well as geldings, being more prone to radiographic
abnormalities. In addition, no differences were found in the future
athletic results of horses with different grades of abnormal SP. On the
contrary, follow-up done by De Graaf et al. 2015, found that there was
no significant association between gender, age and discipline and
clinical signs of developing back pain (De Graaf et al., 2015). A high
grade of abnormal SP (3 out of 0-3) was associated with an increased
risk of clinical symptoms on follow-up, however the sensitivity of a
grade 3 in their study was low. Grade 3 changes involved impinging or
overlapping SP with combined increased opacity, radiolucencies and
severe remodelling and/or fusion (De Graaf et al., 2015). This study
concluded that there was a high risk of developing clinical symptoms
when having a grade 3 abnormality however, no warranty can be offered
for absence of clinical signs for grade 0-2 (De Graaf et al., 2015). 
\selectlanguage{english}Holmer et al. 2007, stated that radiographic abnormalities were
frequent even among clinically healthy horses and they stated that
recent court decisions in Germany had decided that radiographic
abnormalities unaccompanied by clinical symptoms in a horse are not seen
as material defects and are therefore insignificant (Holmer et al.,
2007). They argue whether radiographic examination of the SP as part of
a general exam at PPE makes sense at all without a clinical suspicion of
back pain (Holmer et al., 2007).

Thoracolumbar articular process joints

The articular process joints of the thoracolumbar spine are another
region which should be closely investigated in horses with back pain or
other clinical signs which may lead to further investigation of the
thoracolumbar spine. According to Girodroux et al. 2009, osteoarthritis
of the articular process joints may contribute to back pain, with or
without association of other osseous abnormalities (Girodroux et al.,
2009). Unfortunately, in this study there was no control group to
investigate the prevalence of osteoarthritis in healthy horses. As
previously stated, the severity of impinging SP has been associated with
osteoarthritis of the articular process joints (Zimmerman et al., 2011).
Horses with osteoarthritis of the articular process joints were more
likely to have thoracolumbar pain than those with SP lesions alone,
however, those with concurrent lesions of the SP and osteoarthritis of
the articular process joints were associated with the highest likelihood
of thoracolumbar pain (Zimmerman et al., 2012). As mentioned previously,
high quality radiography with additional views to assess these joints is
necessary and may be potentially challenging. This is mainly due to the
variation in shape of these joints within the thoracic region as well as
morphological differences between thoracic and lumbar articular process
joints (Denoix et al., 2018). Within the cranial thoracic region, the
joint spaces are oriented obliquely whereas further caudally they become
more vertical (Beaumont et al., 2022). Within the caudal thoracolumbar
area, the joints are more rounded with curved joint space (Beaumont et
al., 2022). A mammillary process is dorsocranially present, elongating
the shape of the cranial articular process (Beaumont et al., 2022). In
the oblique views, this often overlies the joint space, making it
difficult to distinguish new bone formation along the base of the
interspinous space (which is commonly seen) from a normal mammillary
process (Beaumont et al., 2022; Manso-Diaz et al., 2018). Denoix
proposed a grading system for the radiographic abnormalities associated
with these articular process joints, however the fact remains that
limited evidence is established for radiographic abnormalities within
these low-motion joints (Cousty et al., 2010).

Other thoracolumbar anatomy

Other lesions associated with the thoracolumbar spine include
spondylosis, stress fractures, traumatic fractures, intervertebral disc
lesions and/or muscle injury. Spondylosis deformans occurs at a low
prevalence in horses with back pain (Meehan et al., 2009). Similar to
osteoarthritis of the articular process joints, spondylosis deformans
can be found alone or in combination with other osseous abnormalities
(Meehan, 2017). Lesions often are seen in the mid to caudal thoracic
spine (T10-T14) and the majority of horses have more than one
lesion(Meehan et al., 2009). In Zimmerman et al., they also found that
the severity of spinous process lesions were significantly associated
with the presence of spondylosis (Zimmerman et al., 2011). They state
that this is an important feature and highlights the need for high
quality and comprehensive radiographic evaluation of the thoracolumbar
spine (Zimmerman et al., 2011). Infectious discospondylitis, on the
other hand, is a much more severe condition during which horses often
show additional neurological signs (Alward et al., 2007; Vandekerckhove
et al., 2023). Radiographic signs of spondylosis and discospondylitis
may be similar but often the latter encompasses aggressive radiographic
signs such as cortical lysis, mottled punctate trabecular pattern and/or
periosteal remodelling (Alward et al., 2007; Vandekerckhove et al.,
2023). Other intervertebral disc lesions, with or without associated
radiographic abnormalities of the opposing end-plates, may be found
further cranially (in the cervical spine) but have been described in the
cranial thoracic spine and show a big variety of clinical signs (Dyson
et al., 2019).

More uncommon lesions such as thoracolumbar fractures of either the SP
or the vertebral bodies, often encompass severe clinical symptoms and
are unlikely to be found at PPE (Collar et al., 2015; Ferguson, 1996;
Frers et al., 2023; Mangla et al., 2022). However, one should consider
the diagnosis of chronic fractures during PPE. Quite often those of the
withers, which may look severely malformed and misshapen (Figure 7), can
be found. Another reason for the presence of similar abnormalities found
during PPEs, maybe due to preventative iatrogenic shortening performed
in ponies for height limitations at FEI competitions. Rib fractures as a
cause of poor performance has recently been described (Hall et al.,
2023). They carry a fair prognosis and should be managed conservatively
in most cases, ultrasonography and scintigraphy are useful tools but
they have also been diagnosed on radiographs when apparent in their most
dorsal portion (Hall et al., 2023). Rib fractures were most commonly
diagnosed in the caudal ribs (Hall et al., 2023).

Neoplasia's of the thoracolumbar spine or of its associated soft tissues
often carries a guarded prognosis with severe clinical symptoms of
ataxia (Finding et al., 2014; Nikolaou et al., 2015). However, one case
report described surgical removal of an osteoma involving two SP which
had a good prognosis and only clinical symptoms of back pain (Owen et
al., 2019). \selectlanguage{english}Radiographical findings included the presence of a circular
area of increased radiopacity at the level of  \selectlanguage{english}the interspinous space
of T12 and T13 (Owen et al., 2019).

Conclusion

PPE are performed by many equine clinicians all over the world and as
stated by the German Equine Veterinary Association: ``The most important
aspect of assessing the current physical condition of a horse during the
pre-purchase assessment is a thorough clinical examination. The
radiographic examination is a complementary examination and represents
only a small section of the range of findings during a pre-purchase
examination''(R\selectlanguage{ngerman}öntgen-Leitfaden (2018) - Leitfaden Fu\selectlanguage{english}r Die
R\selectlanguage{ngerman}öntgenologische Beurteilung Bei Der Kaufuntersuchung Des Pferdes,
2018). The latter statement thoroughly summarises what every equine
practitioner should bear in mind while performing a PPE. They should use
this in every aspect and part of the examination before advising
positively or negatively. Unfortunately, questions asked by clients such
as: ``Do these radiographic abnormalities indicate current disease? Are
these radiographic abnormalities indicators of increased risk of
disease? Is there a risk for resale of this horse?'', cannot be answered
yet and will regrettably remain difficult to answer in the future. The
need for more studies involving follow-up of radiographic alterations,
in combination with comparison of those with and without back pain, is
important. A consensus for a reliable and repeatable grading system is
of high priority. Due to the previously described limitations using
different grading systems on PPE, the interpretation might be variable,
non-repeatable and therefore at risk of being unreliable. The
combination of growing evidence of a lack of correlation in between
clinical symptoms and radiographic abnormalities of the thoracolumbar
spine makes us conclude that taking radiographs of the back during PPE
should not be performed unless clinical examination indicates otherwise.
A ridden examination of the horse, with a familiar and well-experienced
rider, is advised for an objective point on view.

Acknowledgements

The authors would like to thank Gabriel Manso Diaz, the co-authors and
the publisher of `'A practical guide to equine radiography for their
contribution of the figures.

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Beaumont, A., Bertoni, L., \& Denoix, J. M. (2022). Ultrasonographic
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Figures

Figure 1: Laterolateral radiographs of the caudal thoracic (a) and
cranial lumbar (b) spine. Cranial is to the left. Articular process
joint (black circle), intervertebral disc space (also known as the
intercentral joint) (three black lines). Note the metallic markers
placed on the skin dorsal to T11-T12 and T17-T18 interspinous spaces.

Figure 2: a. Oblique radiograph of the thoracolumbar spine, with a
magnified view of the articlar process joint. b. Transverse computed
tomographic (CT) image of the thoracic spine to demonstrate how the
projection is acquired. Cranial is to the left on the radiograph, the
camera is on the left of the horse in the CT image. Left intervertebral
foramen (*) and right intervertebral foramen (**).

Figure 3: Positioning of radiopaque markers (a) to correctly obtain and
overlap sequential LL views of the caudal thoracic spine (b). This
figure is modified from the textbook A Practical Guide To Equine
Radiography (Manso-Diaz et al., 2018).

Figure 4: Laterolateral radiographs of the thoracolumbar spine with
multiple mild radiographic abnormalities shown. This figure is modified
from Looijen et al,. 2022 (Looijen et al., 2022). Cranial is to the
left. (a) Interspinous space with impingement of the SP (box). (b) Small
osseous cyst-like lesion (circle), mild narrowing of the interspinous
spaces (small rectangular boxes) and dorsal remodelling of the spinous
process (rectangular box). (c) Isolated opacities dorsal to the SP
(rectangular boxes) and a small area of radioluceny and remodelling at
the cranial margin of the spinous process (circle).

Figure 5: Laterolateral radiographs of the thoracolumbar spine with
multiple moderate radiographic abnormalities shown. This figure is
modified from Looijen et al,. 2022 (Looijen et al., 2022). Cranial is to
the left. (a) Beak shaped remodelling at the craniodorsal aspect of the
spinous process suggestive of enthesopathy of the supraspinous ligament
(circle) and remodelling at the craniodorsal aspect of the spinous
process suggestive of enthesopathy of the interspinous ligament
(rectangular boxes). (b) Large osseous cyst-like lesion within the mid
portion of a spinous process (circle) and severe remodelling and
sclerosis of the spinous processses (rectangular box).

Figure 6: Overview of the several different grading systems of the SP of
the thoracolumbar spine. This figure is modified from Petterson et al.,
1987, mod. Petterson (1996), Sager (1997), Denoix and Dyson (2003),
Gerhards (2007), Cousty et al., 2009 and Zimmerman et al., 2011

Figure 7: Laterolateral radiograph of the cranial thoracic SP (withers)
showing severe remodelling of the dorsal aspect of the SP likely
indicating multiple chronic healed fractures.

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