You perform a palmar digital nerve block and an abaxial sesamoid block and neither improve lameness. You then perform a low four-point block and the horse becomes sound. Where is the most likely origin of the lameness?

You perform a palmar digital nerve block and an abaxial sesamoid block and neither improve lameness. You then perform a low four-point block and the horse becomes sound. Where is the most likely origin of the lameness?

• A. Carpal joint
• B. Metacarpophalangeal joint
• C. Proximal suspensory region
• D. Dorsal process of the third carpal bone

Answer: (B)

The scenario tests how to localize lameness by using nerve blocks to map pain to a specific region. Blocking the palmar digital nerves desensitizes the distal digit, including the coffin joint and navicular area; if that block doesn't change the gait, the problem isn’t in those distal structures. The abaxial sesamoid block aims a bit more proximally around the fetlock to desensitize the structures from the pastern upward, but if there’s still no improvement, the source lies proximal to that region, i.e., near the fetlock or above. A low four-point block then targets the fetlock region itself, desensitizing the/metacarpophalangeal joint and adjacent structures. When the horse becomes sound after this block, the most likely source is the fetlock joint. So the lesion is at the metacarpophalangeal joint rather than the carpal region or proximal suspensory area, or specifically the dorsal process of the third carpal bone, which would be addressed with blocks aimed at the carpus.

The scenario tests how to localize lameness by using nerve blocks to map pain to a specific region. Blocking the palmar digital nerves desensitizes the distal digit, including the coffin joint and navicular area; if that block doesn't change the gait, the problem isn’t in those distal structures. The abaxial sesamoid block aims a bit more proximally around the fetlock to desensitize the structures from the pastern upward, but if there’s still no improvement, the source lies proximal to that region, i.e., near the fetlock or above. A low four-point block then targets the fetlock region itself, desensitizing the/metacarpophalangeal joint and adjacent structures. When the horse becomes sound after this block, the most likely source is the fetlock joint.

So the lesion is at the metacarpophalangeal joint rather than the carpal region or proximal suspensory area, or specifically the dorsal process of the third carpal bone, which would be addressed with blocks aimed at the carpus.