Alleviating Acute and Chronic Hind Limb Pain

"Musculoskeletal pain associated with acute and chronic hind limb injuries is common in equine practice," said Laurie Goodrich, DVM, MS, Dipl. ACVS, of Cornell University, during her presentation at the 2003 American Association of Equine Practitioners' convention. "Unabated pain can result in complications such as gastrointestinal disorders and supporting limb laminitis. Pain management is critical to decrease suffering, to decrease peri-surgical (before surgery) stress responses, to promote early ambulation (movement), and to minimize the devastating effects of contralateral (opposite front or hind) limb laminitis," she continued.

Goodrich discussed a technique for pain management used by veterinarians at Cornell University's hospital. The technique involves administering a combination of the opioids morphine and detomidine given epidurally (in the spinal canal). Epidural opioids (drugs possessing some properties characteristic of opiate narcotics, but not derived from opium) have been used successfully for analgesia (pain relief) for years. Goodrich said recent studies in horses using morphine with an alpha-2 agonist, such as detomidine, have resulted in prolonged and profound analgesia. "Most importantly," she said, "motor function is not affected.

"Administering epidural morphine and detomidine for hind limb analgesia through an epidurally placed catheter ensures proper administration of the drug and ease of repeated administration. Furthermore, the catheter may allow drugs to reach farther cranially (toward the head) into the epidural space, which provides analgesia to the upper limits of the hind limbs," Goodrich continued. "Long-term epidural catheterization is also not associated with any adverse systemic effects."

Goodrich described the technique in which a catheter is sutured in place in the skin above the tail and an elastic wrap is attached over the catheter. Twenty-six research horses at Cornell University had the catheters placed two to 24 hours before arthroscopic surgery to debride a cartilage and subchondral bone defect on the femur. The morphine and detomidine combination was administered before surgery and from zero to three times after surgery as needed to manage pain and discomfort. For 20-30 minutes after administration, the horses were sedated, as shown by a head droop, a drop in heart rate, and swaying; however, all horses were able to walk. After that time, analgesia effects lasted a minimum of six hours. Those horses were compared with horses treated with saline as a control.

Horses which received the morphine-detomidine combination had a significant improvement in lameness score and a significant decrease in heart rate for eight to 10 hours after treatment, said Goodrich. She said with this method, repeated doses can easily be administered for several weeks if necessary.

In a separate study, Goodrich evaluated the effects of the analgesia technique on clinical cases. Out of 35 horses presented to the hospital for various lamenesses between 1996 and 2003 which underwent the procedure, analgesia was considered good to excellent for all of them. Goodrich said catheters were maintained from 24 hours to four weeks. The catheters were placed with ease, and the efficacy of medication depended on the severity of the pain, duration of the pain before administration, and progression of the disease process, she said.

She found that analgesia was achieved for 48 hours in cases with mild pain and for six to eight hours in horses with severe pain. The average time for pain relief was 18-24 hours. Goodrich noted that signs of infection, rejection, or irritation to the catheter were not seen.

"The analgesia effects on clinical cases were profound," she said. "We feel that supporting limb laminitis was abated in many cases; the horses were able to bear weight on the painful limb during the resolution of the disease process. Some of the horses were released from the hospital with the catheter in place so that drugs could be administered by the referring veterinarian."

With this method of analgesia, horses with acute or chronic hind limb lameness can have their pain managed, thus preventing laminitis of the supporting limb. This analgesia allows the horse to go through any necessary surgery and recover from surgery easier and with less pain and complications.

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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