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\begin{document}

\title{Rib fractures in horses}



\author[1]{Yvonne Hall}%
\author[1]{Russell Parker}%
\affil[1]{The Liphook Equine Hospital}%


\vspace{-1em}



  
  \date{June 09, 2024}


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EVE Clinical Commentary

The case report by describes an interesting case of rib fracture in a
race horse with an attributable hindlimb lameness. This case is the
first to suggest that caudal rib fractures are a cause of hindlimb
lameness and peri regional diagnostic analgesia of a rib fracture can be
used to alleviate hindlimb lameness.

A recent retrospective study reported 73 horses diagnosed with a rib
fracture of which 56\% (41/73) presented due to poor performance with a
fewer number of horses presenting with lameness as a primary complaint
(21/73). Undoubtedly rib fractures are painful in the acute stages of
injury, with the most common site for rib fracture in a horse being
dorsally (5-15cm from the costovertebral junction) on the
18\textsuperscript{th} rib (Hall et. al. 2022). In this study, not all
horses with caudal rib fractures were found to have lameness those that
were lame had a variable pattern of lameness. All of the horses which
underwent diagnostic analgesia were found to have lameness independent
to the rib fracture. However only a small percentage of horses underwent
diagnostic analgesia, a limitation of a retrospective study.

An alternative retrospective case series of 50 rib fractures reported 5
fractures of the first rib which all occurred in racing thoroughbreds
(age 2-7 years with a median age of 3), all of which had ipsilateral
forelimb lameness. In the absence of a traumatic incident the authors
suggested that fractures of the 1\textsuperscript{st} rib may represent
fatigue fracture pathology associated with training. A similar aetiology
is possible for caudal rib fractures but is considered unlikely as this
injury is not over represented in racing Thoroughbreds compared with a
general population of horses and trauma remains the most likely cause.

Ribs can be imaged in detail with nuclear scintigraphy given the
relatively small amount of overlying soft tissue. Orthogonal images
(lateral, dorsal and oblique) should be used to localise region, extent,
pattern and origin of increased radiopharmaceutical uptake. Nuclear
scintigraphy is highly sensitive in identifying osteoblastic activity
but has low specificity for identifying the nature of the pathological
process. Fractures show increased radiopharmaceutical uptake within
24-72 hours post injury, making nuclear scintigraphy highly sensitive in
the acute stage of disease verses radiographic signs which may not be
seen for around 7-10 days unless the fracture is displaced. The
appearance of a fracture on nuclear scintigraphy includes 5-7 days of
diffuse intense uptake, 1-4 weeks of focal intense uptake (figure 1.)
and then a gradual decrease of radiopharmaceutical uptake over the next
6-12 months. This prolonged visibility on scintigraphy means that is
difficult to age a fracture based on scintigraphy alone. Ultrasonography
is potentially more suitable to monitor fracture healing and identify
those cases which are non-healing and requiring intervention.
Costochondral junctions normally have a moderate increased
radiopharmaceutical uptake on nuclear scintigraphy and should not be
mistaken for a rib fracture (figure 1.). The caudal ribs overly the
kidney (figure 1.) but in most instances have a mild to moderate diffuse
region of increased radiopharmaceutical uptake. The use of furosemide
one hour before imaging has been advocated to improve soft tissue
clearance and improve image count to background ratio. This was
evaluated in a recent study where 1mg/kg furosemides was administered
intravenously 1 h post 99m Tc-HDP administration and the image quality
was assessed subjectively and semi-quantitively. There was no
significant difference in image quality or radiation dose rate to
handler, with a minimum distance of 30cm distance having the most effect
on reducing handler dose rate by 65\% .

Ultrasonographic examination is highly sensitive and specific in
identifying rib fractures (Hall et. al. 2022). If a rib fracture is
suspected in the initial stages of examination, then survey
ultrasonographic examination of the ribs is recommended, especially the
caudal ribs. However, rib fractures rarely result in focal localising
pain on palpation and so even a detailed clinical examination may be
unrewarding. Ultrasonography of the ribs is a simple technique; clipping
isn't required and discontinuity and callus within the lateral cortex of
the ribs is easy to identify (Figure 2) but should not be confused with
the costochondral junction (figures 3 and 4). The costochondral junction
is identified by the presence of hypoechoic cartilage and it should be
noted that the margins of adjacent ribs are normally irregular at this
site. In contrast, a rib fracture does not contain hypoechoic cartilage,
though the rib margins are likely to be irregular and commonly
periosteal new bone may be seen.

In this case of hindlimb lameness due to fracture of the
18\textsuperscript{th} rib , the horse took 12 months to recover and
resume ridden exercise with conservative therapy. Ultrasonographic
examination can monitor fracture healing and is useful in identifying
non-healing fractures which may represent surgical candidates. Hall and
colleagues (2022) reported six horses which underwent surgery due to
failed initial conservative management which resulted in continued
fracture instability, callus at the fracture site or fracture
displacement causing impingement on adjacent ribs. One horse which
underwent wedge ostectomy and internal fixation with a locking
compression plate returned to its previous level of exercise. All other
surgically managed cases (5/73) underwent partial rib resection. Most
horses in this study were managed conservatively (67/73). Given the very
small number of surgically managed cases it is not possible to determine
if fracture healing or outcome would have been improved if surgical
intervention had been performed in more cases.

Peri-regional analgesia of a rib fracture is commonly used in human
medicine as a therapeutic aid and is easy to perform in the horse. In
this instance the ipsilateral hindlimb lameness was partially alleviated
by this technique in the acute stage of lameness and completely
abolished in the chronic stage of lameness. Perineural analgesia can
result in increased radiopharmaceutical uptake within the soft tissues
on bone phase scintigraphy, up to 7 days post blocking , with 50\% of
horses having uptake at the site of a tibial perineural injection one
day post injection, 25\% of horses at the block site 3 days post
injection and 1 horse with increased radiopharmaceutical uptake 7 days
post injection. An appropriate washout period is recommended prior to
scintigraphy if perineural analgesia has been performed to prevent false
positive results.

Although rib fractures are largely under reported in adult horses this
case report and recent retrospective studies confirm they should be
considered a differential diagnosis for cases of poor performance and
both fore and hind limb lameness. Diagnostic analgesia could be used to
determine significance of the rib fracture in cases of hind limb
lameness.

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\verb`EVE Clinical Commentary figure 2.docx`  available at \url{https://authorea.com/users/646481/articles/684026-rib-fractures-in-horses}

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\verb`EVE Clinical Commentary Figure 4.docx`  available at \url{https://authorea.com/users/646481/articles/684026-rib-fractures-in-horses}

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