Glossary
Diagnostic analgesia (nerve block).
Direct answer
Diagnostic analgesia is a technique in which local anaesthetic is placed next to a nerve, or inside a joint, tendon sheath or bursa, in order to desensitise a defined region for a limited time. If lameness then improves markedly, the pain source most probably lies within that region.
Blocks usually proceed from the lower limb upwards, one step at a time. The commonest interpretation error concerns spread: the agent does not stay exactly where it was placed and may reach neighbouring nerves or structures. Onset time, duration of effect and partial rather than complete improvement make the reading harder still.
The comparison with human medicine is instructive. Diagnostic blocks are used in people too, but the patient reports directly whether and how much the pain eases. In the horse the answer is read from gait, that is, through a subjective detour. This is why the technique is increasingly paired with objective measurement of movement asymmetry.
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.