Distal limb desensitisation following analgesia of the digital flexor tendon sheath in horses using four different techniques.
Authors: Jordana M, Martens A, Duchateau L, Vanderperren K, Saunders J, Oosterlinck M, Pille F
Journal: Equine veterinary journal
Summary
# Editorial Summary When performing diagnostic analgesia of the digital flexor tendon sheath (DFTS) during lameness evaluation, practitioners must recognise that local anaesthetic can inadvertently block the palmar or plantar digital nerves, creating false-positive responses that obscure the true source of pain. Jordana and colleagues conducted a controlled crossover study in nine horses, comparing four injection techniques (proximal recess, axial to the lateral sesamoid, at the sesamoid base, and distal mid-pastern) to quantify this effect using dynamometry to measure skin sensitivity at the heel bulbs before and up to 120 minutes post-injection. The proximal approach carried substantially higher risk of unintended digital nerve desensitisation, causing complete loss of heel bulb sensitivity in 10 of 72 injections compared with only three to five limbs using other techniques; notably, the proximal technique was four times more likely to produce desensitisation in forelimbs and three times more likely in hindlimbs. Although desensitisation was typically unilateral (affecting only the lateral heel bulb in most cases), occurring in roughly 31% of injections overall, these findings carry clear clinical implications: practitioners should routinely assess skin sensitivity at the heel bulbs following DFTS analgesia to distinguish genuine analgesia of intra-sheath structures from artefactual desensitisation caused by inadvertent nerve blockade, and should preferentially adopt axial or distal injection techniques to minimise this confounding effect during diagnostic work-ups.
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Practical Takeaways
- •Always test heel bulb skin sensitivity after DFTS analgesia to avoid misinterpreting nerve block effects as pain relief from deep structures—this is critical for accurate lameness diagnosis
- •Use axial, base, or distal injection techniques preferentially over proximal technique to minimize inadvertent desensitisation of palmar/plantar digital nerves
- •Recognize that unilateral lateral heel bulb desensitisation is a common expected finding and does not necessarily indicate successful diagnostic analgesia of the primary pain source
Key Findings
- •Complete desensitisation of heel bulbs occurred in 30.6% of limbs (22/72) after DFTS analgesia, with an additional 9.7% showing partial desensitisation
- •Proximal injection technique resulted in 4× higher probability of forelimb desensitisation and 3× higher in hindlimbs compared to axial and base techniques
- •Desensitisation was almost exclusively unilateral (lateral heel bulb only) in 35/36 affected limbs, with only 5 limbs showing bilateral involvement
- •Skin desensitisation showed significant differences between injection techniques only at 30 minutes post-injection