14
46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
part of the metacarpo- and metatarsophalangeal joint’s scutum proximale. The ISL is a
thick collagenous structure that is firmly attached to the PSBs, creating a firm union
between the two bones (Denoix et al. 1997).
In the majority of cases, only one limb is affected (Formston & Serth 1968; Sedrish et
al. 1996) with a suspected predisposition for the hind limbs. Five out of eight horses
in a study by Dabareiner et al., (2001) and five out of seven horses in a study by
Wisner (1991) had hind limb involvement. Both PSBs of a limb are commonly
affected (Wisner et al. 1991). Wisner's (1991) study found three out of seven horses
to have bilaterally affected fetlock joints, but only one case was identified on
radiographs whereas the other two needed computed tomography for identification.
Clinical examination may reveal fetlock joint or digital flexor tendon sheath (DFTS)
distension, pain on flexion of the metacarpo or metatarsophalangeal joints and
variable degrees of lameness (Wisner et al. 1991). Diffuse cellulitis over the affected
joint has also been described (Dabareiner et al. 2001).
Perineural (abaxial sesamoid and low palmar/plantar blocks), intra-articular and intrathecal (DFTS) anaesthesia do not seem to provide consistent improvement of
lameness in these cases, with literature reporting opposing findings (Dabareiner et al.
2001; Sedrish et al. 1996; Wisner et al. 1991). It is speculated that variation in
communication between the plantar or palmar pouch of the metacarpo- and
metatarsophalangeal joint with the digital flexor tendon sheath may be the reason
thereof. It appears that it may be helpful to perform anaesthesia of all three
compartments to obtain a diagnosis (Dabareiner et al. 2001).
Four standard radiographic views of the fetlock are recommended for evaluation of
the PSBs, including dorsoproximal-palmaro/plantarodistal oblique (DPr-Pa/PlDiO,
which best demonstrates the lesions), lateromedial (LM), and two oblique views –
dorsomedial-palmaro/plantarolateral oblique (DM-Pa/PlLO) and dorsolateralpalmaro/plantaromedial oblique (DL-Pa/PlMO) (Butler et al. 2000; Wisner et al.
1991). A fifth view, the flexed lateromedial, is often obtained at the Onderstepoort
Veterinary Academic Hospital in order to visualise the articular margins of the PSBs.
It is important to increase kilovoltage settings for the dorso-palmar/plantar views in
order to visualise the axial borders of the PSBs (Butler et al. 2000), and poor
radiographic technique may be a reason for not visualising these lesions. Bony
changes may not be apparent when radiographs are first taken, as up to 30-60% of
mineral content must be lost, and 7 to 10 days is needed before changes become
detectable (Dennis et al. 2010).
Radiological findings are typical, if not pathognomonic, for axial osteitis. Lesions
consist of bone lysis at the apical to mid-body axial margins of the PSBs, although the
entire axial border can be involved. Variable degrees of joint effusion may be
present. Lesions may be symmetrical or asymmetrical between the two PSBs, and
may either appear cystic or erosive, and are exclusively destructive in nature
(Wisner et al. 1991). Sequestrum formation has been described but is uncommon
(Dabareiner et al. 2001; Dunkerley et al. 1997).
Ultrasound is a valuable tool to visualise the ISL ligament, abaxial margins of the
PSBs, digital flexor sheath and flexor tendons. Abnormalities detected by ultrasound
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