BACKGROUND: This experimental, comparative, controlled study was conducted to assess whether morphine given locally could block the development of hyperalgesia and allodynia in a guinea pig bone damage model METHODS: Withdrawal responses to mechanical and thermal stimuli applied to the plantar surface of the hind paw were measured before and after bone damage. In separate groups of rats, the effects of administering morphine 150 mcg into the marrow cavity, and on the development of hyperalgesia and allodynia after bone damage were assessed. In another group of rats, naloxone 40 mcg (a mu-opioid anatagonist) was injected into the marrow cavity followed by morphine. RESULTS: In animals that received no treatment, hyperalgesia and allodynia peaked 2 hours after bone injury. Injection of morphine into the marrow cavity immediately after bone injury prevented the development of hyperalgesia and allodynia. Naloxone given into the marrow cavity before giving morphine blocked the antihyperalgesic effect of morphine. CONCLUSION: These findings provide further evidence that local application of morphine at the time of orthopedic surgery, bone graft or marrow harvesting may reduce the amount of postoperative pain. (Author)
Animal ; HYPERALGESIA ; MORPHINE ; GUINEA PIGS