EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2017
521
Critically Appraised Topic
Should I use magnetic resonance imaging to evaluate horses with foot penetrations?
L. Meehan* School of Veterinary Sciences, University of Bristol, Langford, Somerset, UK. *Corresponding author email:
lucy.meehan@
bristol.ac.uk
Summary
Introduction and history Solar penetrations are common and potentially life threatening. The location, depth and direction of the injury are important in determining the structures involved. The use of diagnostic imaging is instrumental in diagnosis. Radiography and contrast radiography have been shown to be useful; however, in recent years the use of magnetic resonance imaging (MRI) has been advocated.
Search method A population, intervention, comparator, outcome (PICO) question was constructed. In (horses with foot penetrations) does (MRI imaging) provide additional information compared to (radiography and contrast radiography) for (treatment and prognosis)? Searches of CAB abstracts and Medline were performed using the following search terms:
• (Horse OR horses OR equine) AND (MRI or ‘magnetic resonance imaging’) AND (feet OR foot OR hooves OR hoof) AND (‘solar penetration’ OR streetnail OR ‘street nail’ OR penetrat* wound OR lesion OR ‘wound infection’)
• (Horse OR horses OR equine) AND (X-ray OR ‘x ray’ OR radiogra* OR contrast) AND (feet OR foot OR hooves OR hoof) AND (‘solar penetration’ OR streetnail OR ‘street nail’ OR penetrat* OR wound OR lesion OR ‘wound infection’)
The search results were evaluated by title and abstract for
relevance to the PICO question and nine references selected for further evaluation.
Quality of evidence The studies included comprised four case series; two retrospective clinical studies and three review articles. The review articles were excluded and six references evaluated.
Radiography The use of plain radiographs (Richardson and O’Brien 1985) and contrast bursography (Smith and Schramme 1992) have been described for investigation of solar penetration in the horse. With plain radiographs, 66% of horses had no evidence of radiographic changes at the time of presentation (mean interval between injury to examination 20 days). At surgery, 50% had abnormalities consistent with navicular bone (NB) osteomyelitis. The use of a metallic probe aided determination of depth and direction of the tract. Repeat radiography of horses without evidence of osteomyelitis revealed evidence of bony lesions in 50% of cases. A total of nine horses had subluxation of the distal interphalangeal joint
(DIPJ), correlating with deep digital flexor tendon (DDFT) rupture and five of 32 horses had ‘satisfactory’ outcome in this case series. Three cases were described using contrast bursography
and arthrography to identify communication between the penetrating tract and synovial structures (Smith and Schramme 1992). Only one case had demonstrable communication between the navicular bursa and penetrating injury. All three cases evaluated by contrast bursography had lesions associated with the DDFT, which were not visible radiographically; however, these were detected at surgery or post-mortem. All three horses were subjected to euthanasia.
Magnetic resonance imaging There have been two previous case series which have described the use of low field standing MRI in identifying penetrating injuries to the foot. Kinns and Mair (2005) described three cases that were imaged 48 h to 6 weeks after initial injury. All cases had radiography and contrast bursography performed prior to MRI and were negative for synovial sepsis. All cases had DDFT pathology confirmed on MRI. One case was imaged at 48 h post-injury, at which time the tract was identified, but no DDFT lesion was apparent; however, repeat MRI 2 weeks later showed a lesion. A further case series reported the MRI findings in two horses with chronic forelimb lameness (Boado et al. 2005). A penetrating tract and a lesion within the DDFT were identified on high field MRI examination in both horses. A larger scale retrospective study (del Junco et al. 2012)
evaluated the imaging findings in 55 horses that underwent standing low-field MRI examination following solar penetration. A total of 14 of these horses had radiographic abnormalities, the nature of which is not described. A clear signal void tract corresponding to the penetrating injury was seen in 35/55 horses. In total, 37 of the 55 cases had DDFT damage. No information is given regarding the presence or absence of synovial sepsis and whether this could be detected on MRI examination. A poor correlation between MRI findings and surgical findings was described. A further large retrospective study evaluated the
outcome for horses with solar penetration wounds that underwent surgery for synovial sepsis (Findley et al. 2014). These authors stated that the majority of horses sustained injuries to three structures, most commonly DDFT, DIPJ and NB. It was not stated how the DDFT injuries were confirmed and only 31 horses in this study underwent MRI; the findings of the MRI examination are not described. Similarly, radiography was used to ‘aid diagnosis’ in 73 cases, but details of examination are not available. The presence or absence of abnormalities on imaging studies is not used in the regression models to describe outcome. Involvement of the distal
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