Does Diagnostic Analgesia in the Distal Aspect of the Limb of Horses Performed in a Clinical Situation Less Than 12 or 36 Hours Before Magnetic Resonance Imaging Result in Artifacts?

Abstract

The potential effect of diagnostic analgesia performed <24 hours before magnetic resonance imaging (MRI) has not been assessed. It is not known whether perineural or intrasynovial analgesia performed in a clinical setting in unsedated horses might result in more tissue trauma and consequently artifacts than in sedated horses in an experimental setting. The aims of this study were to assess whether diagnostic analgesia (using mepivacaine) in the distal aspect of the limb in a clinical setting in unsedated horses, performed on the day of (<12 hours) or the day before (<36 hours) high-field and low-field MRI, results in artifacts that could confound image interpretation. Cases were limbs which had undergone diagnostic analgesia in the distal aspect of the limb <36 hours before high-field (n = 17) or low-field (n = 55) MRI. Controls had MRI of the same region as cases but had not undergone diagnostic analgesia in the distal aspect of the limb <36 hours before MRI. The regions of possible injection sites were assessed for alteration in signal intensity and/or in the contour of the limb, altered tissue architecture, or a needle tract. Distension of the dorsal pouch of the distal interphalangeal joint and of the digital flexor tendon sheath was measured. There were no artifacts resulting from diagnostic analgesia performed within 12 or 36 hours preceding low-field or high-field MRI that could confound image interpretation. Results suggest that it is reasonable and safe (from an imaging point of view) to perform diagnostic analgesia in the distal aspect of the limb shortly before MRI.