What area of the distal equine limb is anesthetized with a Palmar Digital Nerve (PDN) block?

Areas Anesthetized by a Palmar Digital Nerve (PDN) Block in the Equine Limb

A Palmar Digital Nerve (PDN) block anesthetizes the palmar/plantar aspect of the foot, including the heel bulbs, frog, and sole of the equine distal limb. 1

Anatomical Coverage

The PDN block specifically desensitizes:

• The palmar/plantar aspect of the foot
• Both heel bulbs
• The frog
• The sole of the foot
• The navicular region
• The distal interphalangeal joint (coffin joint)

Technical Aspects of PDN Block

Block Location

• The block is performed by injecting local anesthetic over each palmar digital nerve
• Injection sites are located just proximal to the collateral cartilages of the foot
• The nerves run along each side of the digital flexor tendons at the level of the proximal sesamoid bones

Efficacy and Duration

• PDN blocks are fully effective between 15 minutes and 1 hour after administration 1
• The analgesic effect begins to diminish between 1-2 hours post-injection
• Some residual analgesia may persist beyond 2 hours, affecting gait characteristics
• By 24 hours, the block effect completely resolves and lameness returns to pre-block values 1

Volume Requirements

• Recent research shows that a low volume of 0.75 mL of 2% mepivacaine per nerve is as effective as the traditionally used higher volume of 1.5 mL 2
• Using lower volumes may help achieve more precise localization of pain

Clinical Applications

PDN blocks are primarily used for:

1. Diagnostic purposes to localize lameness in the distal limb
2. Identifying navicular syndrome (horses with navicular syndrome show significant improvement after PDN block) 1
3. Providing analgesia for painful conditions of the foot

Important Considerations

• When performing sequential nerve blocks for lameness diagnosis, it's crucial to perform lameness evaluations between 15 minutes and 1 hour after PDN block to ensure effective nerve blockade 1
• Subsequent blocks should be delayed for at least 3 hours following PDN block to avoid confounding results
• The block does not affect structures innervated by the dorsal branches of the digital nerves

Potential Complications

• Intravascular injection (can be minimized with proper technique)
• Temporary swelling at the injection site
• Potential for nerve damage with improper technique
• Continuous perineural infusion may cause limb swelling, suggesting careful consideration of drug and infusion regimens is needed 3

PDN blocks remain one of the most commonly used diagnostic nerve blocks in equine practice due to their reliability in identifying foot pain as a source of lameness.