Objective: To assess the effects of heat and cold on quantifiable pain behaviors in an animal model of arthritis that minimizes the motivational-affective component of pain.
Design: The effects of superficial heat (40 degrees C) and cold (4 degrees C) on pain behaviors in rats with knee joint inflammation were tested before and after induction of inflammation and after treatment with heat or cold.
Subjects: Joint inflammation was induced in male Sprague-Dawley rats by intra-articular injection of the knee joint with 3% kaolin and 3% carrageenan.
Main outcome measures: Withdrawal latency to heat applied to the paw (PWL) assessed secondary hyperalgesia; spontaneous pain behaviors assessed degree of weight bearing/ guarding; and joint circumference assessed joint swelling.
Results: Cold treatment of the inflamed knee joint significantly reversed the PWL immediately after treatment (p = .003) without affecting spontaneous pain behaviors orjoint circumference. In contrast, heat treatment produced a small but significant decrease in spontaneous pain behaviors (p = .03) without affecting PWL or joint circumference.
Conclusion: Acute arthritic pain can be treated with either superficial heat for reducing guarding or with cold for reducing pain or hyperalgesia outside the injury site.