User:Vulpecula Rubra/sandbox

Use in horses
Short-term nerve blocks are useful in regionalizing the source of pain during lameness examinations in horses. A local anesthetic alone is injected perineurally to desensitize tissues beyond the site of injection. When the painful area is blocked, the lameness should temporarily improve or resolve. For example, the palmar digital nerves can be blocked to investigate pain arising from the sole and heel area of the hoof. If pain is arising from this area, the horse will stop limping. If the source of lameness arises from higher up in the leg, the horse will continue to limp, and a nerve block can be performed higher up the leg. Because there are essentially no motor neurons in the lower limbs of horses, the risk of weakness or ataxia is negligible.

Types
Certain nerve blocks are commonly used in horses and are usually performed in the order they appear below. Each block involves the palmar nerve or its branches which are located in the forelimb.

Palmar digital nerve block - The palmar digital nerves (formerly known as the posterior digital nerves) run down the back of the pastern, one on each side of the deep flexor tendon. These nerves provide feeling to the back third of the horse's foot including: This block is one technique used to diagnose navicular disease because the navicular bone and associated structures are typically desensitized though other structures desensitized by the block may be contributing to the lameness.
 * sensitive tissues of the hoof wall, sole, and frog
 * coronet and heel bulbs
 * lower half of the pastern (back part only)
 * deeper structures of the foot (digital cushion, back third of the coffin bone, lateral cartilages, navicular bone and bursa, deep flexor tendon and its sheath)

Low palmar nerve block - The low palmar (also known as the abaxial sesamoidian) block desensitizes the palmar nerves. Blocking both the medial and lateral palmar nerves near the base of the sesamoid bones desensitizes the entire foot and at least half of the pastern. Blocking above the sesamoid bones may desensitize part of the fetlock and sesamoid bones with variable success.

4-point nerve block - The 4-point nerve block involves the two palmar nerves and the palmar metacarpal nerves. Blocking these four nerves desensitizes the foot, pastern, and entire fetlock joint, including the sesamoid bones.

Other nerve blocks - Nerves above the knee or hock may be blocked to desensitize these joints and the entire lower leg though these blocks are more difficult to perform. Due to the large area that is desensitized these blocks are not very helpful in localizing lameness and may cause the horse to stumble.

Effectiveness
The effectiveness of a nerve block is tested by checking the skin for loss of sensation. This is usually done with a pointed but dull object such as the tip of a pen. Some veterinarians use a needle though this may cause bleeding as well as unnecessary pain and irritation if the site is not completely blocked. Another nerve block must be performed if skin sensation has not been lost. Block failure is usually due to not enough anesthetic being absorbed which may be influenced by the following factors:
 * injection too far away from the nerve
 * not enough anesthetic injected for the size of the nerve
 * testing the skin too soon after injection

Most commonly used local anesthetic drugs take 10-15 minutes to desensitize a nerve. The block may last 1-2 hours depending on the product used and volume injected.