Diffusion of Anesthetic After a Low Palmar Nerve Block on the Forelimb

1. Introduction
The low palmar nerve block (LPB) or low four-point block desensitizes the medial and lateral branches of the palmar metacarpal nerves and palmar nerves. The LPB is thought to desensitize all structures distal to the splint bones, and it has been noted to improve lameness in horses with proximal suspensory desmitis. We hypothesized that diffusion of local anesthetic to the proximal suspensory region would occur after a LPB.

2. Materials and Methods
Bilateral LPBs were performed in nine adult horses using a 50:50 solution of mepivicane and iohexol. For each nerve, 2 ml of solution were used in one forelimb and 4 ml were used in the opposite forelimb. Lateral radiographs of both metacarpi were taken at 0, 5, 15, 30, 60, 90, and 120 min. Diffusion of anesthetic above and below the injection sites, intrasynovial contrast deposition, and proximal diffusion of contrast were noted.

3. Results
Evidence of the contrast agent was noted in the proximal metacarpal region in 94% (n = 17) of the limbs. Contrast was seen in the fetlock joint in 44% (n = 8) of limbs and in the digital tendon sheath in 39% (n = 7) of the limbs. [...]