An Alternative Approach to Palmar Digital Nerve Blocks

An Alternative Approach to Palmar Digital Nerve Blocks

Anesthetic that numbs out areas higher on the limb or misses relevant nerves altogether could otherwise confound interpretation of the diagnostic nerve block portion of a lameness exam.

Photo: Erica Larson, News Editor

Injecting anesthetic in a slightly different location than used with a traditional nerve block technique could be a more effective approach to pinpointing the cause of equine foot pain during lameness exams, noted a past-president of the American Association of Equine Practitioners (AAEP).

Marvin Beeman, DVM, of the Littleton Equine Medical Center, in Colorado, renowned performance horse practitioner, described this approach at the organization’s 2013 convention, held Dec. 7-11 in Nashville, Tenn. He presented during a session consisting of past-presidents sharing practice tips from their many years of clinical experience.

Beeman reminded his audience that the palmar digital nerve (PDN) block is the most common regional anesthetic block used to diagnose lameness in the horse. Usually, veterinarians place this block near the ungual (collateral) cartilages on the sides of the pastern, but Beeman said he prefers to place the needle lower, on the midline between the bulbs of the heel. He does this while holding the horse’s front leg held between his knees or bracing the hind limb on his thigh and extending the limb as far back as possible.

Beeman explained that inserting and infusing the anesthetic as low as possible on the foot offers several benefits:

  • The horse only needs one needle stick between the heel bulbs rather than two sticks (one on either side of the lower pastern);
  • Anesthetic agents do not migrate up or down the limb as much as the traditional approach (which can anesthetize lesions above the front of the coronary band and in the pastern region), particularly if the practitioner places a thumb over the nerve- vascular bundle while injecting;
  • The practitioner is less likely to inadvertently invade the digital artery or vein because the needle is not placed directly on or near the nerve-vascular bundle; and
  • He or she is also less likely to invade the distal (lower) synovial sheath (that encloses the tendons) because the injection site is below where the sheath ends.

He said this lower, midline block eliminates confusion that can arise when variant nerve branches between the palmar or plantar digital nerves are not anesthetized using a PDN block over the lateral and medial nerves at a slightly higher site; in other words, the traditional approach can miss variant nerve branches and not completely block the desired region.

Beeman said he believes this approach is far more predictable than anesthetizing at the higher site for the migration reasons described. To gauge the block's success, Beeman advised veterinarians to check sensation from the heel bulbs to the widest part of the foot with a blunt instrument. And, he reminded the audience to reevaluate the hoof tester response and flexion tests after blocking the relevant portions of the distal limb with anesthesia.

Beeman's concluded that this method can more accurately block areas of the lower limb with less chance of anesthetic diffusing higher up into the pastern or fetlock region. In addition, it is more likely that lower variant nerves will be blocked by placing anesthetic at a low point between the heel bulbs. Anesthetic that numbs out areas higher on the limb or misses relevant nerves altogether could otherwise confound interpretation of the diagnostic nerve block portion of a lameness exam.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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