Validation of the accuracy of needle placement as used in diagnostic local analgesia of the maxillary nerve for investigation of trigeminally mediated headshaking in horses.
Authors: Wilmink S, Warren-Smith C M R, Roberts V L H
Journal: The Veterinary record
Summary
# Editorial Summary: Maxillary Nerve Blocks for Equine Headshaking Diagnosis Diagnostic local analgesia of the maxillary nerve is routinely used to identify trigeminal involvement in equine headshaking, yet the actual accuracy of needle placement during this technique had never been formally validated. Wilmink and colleagues performed bilateral maxillary nerve blocks on 30 horse cadaver heads across three operator experience levels, then used computed tomography to verify contrast medium placement around the target site. Only 53.3% of injections successfully deposited anaesthetic in the correct location, though experienced operators achieved accurate placement in 80% of attempts compared with just 40% in less and non-experienced practitioners—a statistically significant difference. This finding carries important clinical weight: a negative response to maxillary nerve analgesia cannot reliably exclude facial dysaesthesia as a cause of headshaking, as false negatives arising from misplaced injections may mask the condition's true aetiology. Practitioners should recognise that technique proficiency directly impacts diagnostic validity, and repeated procedural experience or mentorship from skilled colleagues appears essential for reliable application of this diagnostic tool.
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Practical Takeaways
- •A negative response to maxillary nerve diagnostic local anaesthesia does not rule out facial dysaesthesia as a cause of headshaking, as nearly half of injections may miss the target even with experienced operators
- •Proper training and experience with this diagnostic technique is critical; less experienced practitioners should recognize their higher failure rate (60%) and consider referral to experienced colleagues or additional training
- •When investigating suspected trigeminally mediated headshaking, clinicians should understand the technique's limitations and consider CT confirmation if available, particularly when clinical suspicion remains despite negative diagnostic results
Key Findings
- •Contrast medium was successfully deposited around the maxillary nerve target site in only 53.3% (32/60) of injections across all operators
- •Experienced operators achieved accurate needle placement in 80% (16/20) of cases compared to 40% (16/40) for less and non-experienced performers
- •Operator experience significantly influences success rate of diagnostic local anaesthesia of the maxillary nerve (p<0.05)
- •False negative diagnostic results may occur due to failed needle placement rather than absence of facial dysaesthesia