Evidence of bias affecting the interpretation of the results of local anaesthetic nerve blocks when assessing lameness in horses.
Authors: Arkell M, Archer R M, Guitian F J, May S A
Journal: The Veterinary record
Summary
# Editorial Summary: Bias in Lameness Assessment Following Nerve Blocks Observer bias significantly influences how lameness is graded during diagnostic nerve blocks—a finding with important implications for clinical decision-making. Arkell and colleagues asked 18 observers (comprising orthopaedic specialists, general practitioners, and final-year veterinary students) to grade lameness in eight horses on a 0–10 scale, then reassessed them after being informed that a nerve block had been performed. Results revealed a mean upward shift of 0.4 grades in lameness scoring simply from knowing a block had been administered, with agreement between assessors varying considerably depending on expertise; orthopaedic specialists achieved reasonable consensus (±1 grade), whilst non-specialists and students showed significantly poorer agreement. The individual consistency within observers was good (0.6 grade difference on re-assessment), confirming the bias was systematic rather than due to general unreliability. This research underscores the value of blinded assessment protocols when evaluating nerve block responses and highlights how expectation bias can subtly skew clinical interpretation—a crucial consideration for veterinarians, physiotherapists and coaches relying on lameness grades to guide diagnosis and treatment decisions.
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Practical Takeaways
- •Blinding the observer to nerve block administration is critical for valid lameness assessment; knowing a block has been done can artificially inflate improvement scores by 0.4 grades
- •Lameness grading should ideally be performed by experienced orthopaedic specialists, as non-experts show significantly poorer inter-observer agreement and greater susceptibility to bias
- •Standardized, blinded assessment protocols are essential when evaluating diagnostic blocks to avoid expectation bias influencing clinical decision-making
Key Findings
- •Observer knowledge of nerve block administration introduced systematic bias, increasing mean lameness grade by 0.4 on a 0-10 scale
- •Individual observer consistency was good with average intra-observer difference of 0.6 grades between repeat assessments
- •Agreement between orthopaedic experts was reasonable (±1 grade) but significantly poorer for non-experts and veterinary students
- •Different observer groups were influenced to different extents by knowledge of nerve block administration