Objective
The purpose of this study is to evaluate the effects of the cold air application on the subjective pain threshold of knee joint pain.

Method
We recorded the changes of the pain threshold in 60 patients before and after cold air application who complaint of knee joint pain. Patients were divided into 3 groups randomly with each 20 patients and each group received cold air application for 30 seconds, 1 minute, 3 minutes. Cold air of CRAis (Kyung-won Century, Korea) was applied to the anterior portion of the knee with a temperature of ⁣30^oC. The changes of the pain threshold was estimated by visual analogue scale.

Results
In 30 seconds treating group, VAS score was lowered 2.25±1.16 and 2.26±1.13 immediately after, and 30 minutes after cold air application, respectively (P＜0.05). In 1 minutes treating group, VAS score was lowered 1.65±2.58 and 2.41±2.59 immediately after and 30 minutes after cold air application, respectively (P＜0.05). In 3 minutes treating group, VAS score was lowered 1.94±1.80 and 2.10±2.3 immediately after and 30 minutes after cold air application, respectively (P＜0.05). The VAS score was lowered significantly after cold air application in all groups, but there's no significant correlation between change of VAS score and cold air application time. In group with initial VAS score greater than 5, the VAS score was more decreased after cold air application.

Conclusion
Cold air application for 30 seconds using CRAis machine is useful treatment method for knee joint pain.