"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