The effects of perineural and intrasynovial anaesthesia of the equine foot on subsequent magnetic resonance images.
Authors: Black B, Cribb N C, Nykamp S G, Thomason J J, Trout D R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Anaesthesia and MRI Artefacts in the Equine Foot When diagnostic nerve blocks or intra-articular injections precede MRI examination of the equine foot, clinicians need to understand whether the anaesthetic procedure itself creates imaging artefacts that could confound diagnosis. Black and colleagues investigated this question by performing baseline MRI scans on 15 horses, then injecting mepivacaine around the palmar digital nerves and into three synovial structures (podotrochlear bursa, distal interphalangeal joint, and digital flexor tendon sheath) in one forelimb per horse, with repeat MRI imaging at 24 and 72 hours post-injection. Perineural anaesthesia of the digital nerves and intrasynovial injection into the podotrochlear bursa and distal interphalangeal joint produced no detectable changes on MRI at either timepoint; however, injection into the digital flexor tendon sheath caused a significant and sustained increase in synovial fluid volume that remained visible at 72 hours. The authors recommend delaying MRI examination for more than three days following digital flexor tendon sheath anaesthesia, whilst diagnostic imaging can safely proceed within this timeframe if only nerve blocks or other synovial structures have been anaesthetised—an important practical distinction for clinicians coordinating regional analgesia with diagnostic imaging protocols.
Read the full abstract on PubMed
Practical Takeaways
- •Avoid MRI evaluation within 3 days of intrasynovial anaesthesia to the digital flexor tendon sheath, as anaesthetic-induced fluid accumulation mimics pathology and can be misinterpreted
- •Perineural anaesthesia and injections into other structures (podotrochlear bursa, DIP joint) are safe to perform immediately before MRI without compromising image interpretation
- •Document all regional anaesthetic procedures and timing when scheduling MRI, particularly for digital flexor tendon sheath injections, to prevent diagnostic errors
Key Findings
- •Perineural anaesthesia of palmar digital nerves and intrasynovial anaesthesia of podotrochlear bursa and distal interphalangeal joint did not significantly alter MRI findings at 24 or 72 hours post-injection
- •Intrasynovial mepivacaine injection into the digital flexor tendon sheath caused significant iatrogenic increase in synovial fluid detectable on MRI at both 24 and 72 hours post-injection
- •MRI artefacts from perineural and intrasynovial anaesthesia persist for at least 72 hours in the digital flexor tendon sheath, potentially confounding pathological interpretation