If a horse is ¾ lame and a palmar nerve block resolves the lameness, which structure is likely unaffected?

When a horse is diagnosed as ¾ lame, it indicates a significant degree of lameness, suggesting pain or discomfort originating from a specific area in the horse's limb. A palmar nerve block is typically used to anesthetize nerves supplying structures in the palmar aspect of the hoof, which can help to localize the source of pain.

In this case, if the palmar nerve block successfully resolves the lameness, it suggests that the source of the pain is likely located in the structures innervated by the blocked nerves. These structures include the distal sesamoid bone (navicular bone), the distal interphalangeal joint, and some of the soft tissues in the area.

P3 (the pedal bone or coffin bone) is a key structure that typically lies deeper and is not primarily innervated by the palmar nerves. While P2 (the short pastern bone) and the navicular bone may be impacted by conditions that produce lameness and can be alleviated through a palmar nerve block, P3 is more likely to remain unaffected as it does not receive direct sensory innervation from the nerves targeted by this block.

Therefore, in the scenario where lameness is resolved by a pal