Background To our knowledge there has been no research that has compared the effectiveness of two popular cold therapy modalities applied to healthy human knees, with a surgical dressing, over a 4 h period.

Hypothesis To determine whether gel packs are more effective than ice bags at reducing skin surface temperature in humans.

Study design This was a randomised, repeated measures crossover study, which included nine healthy participants.

Level of evidence Level 2.

Methods Two cold therapy modalities—a gel pack (DonJoy-Orthopaedic Pty Ltd, Normanhurst, New South Wales, Australia) and an ice bag (ICE'N'EASY, Bokarina, Queensland, Australia)—were applied on top of a surgical dressing, covering the knee. Each participant randomly received two cold therapy treatments, in separate sessions, at least 4 days apart. Each session utilised the time protocol of 20 min application on the hour, for 4 h. Skin surface temperature was recorded throughout the session at 1 min intervals.

Results In the first application, the ice bag (5°C±1.7°C) was more effective at reducing skin surface temperature (p<0.04) from baseline than the gel pack (4°C±0.9°C), and had a significantly greater cooling rate (p<0.02). On the subsequent three applications, both modalities were just as effective at reducing skin surface from baseline, and had similar cooling rates.

Conclusions An ice bag initially was more effective than the gel pack at reducing skin surface temperature of healthy knees, with a surgical dressing. Over a 4 h period both gel packs and ice bags were just as effective at reducing skin surface temperature and at maintaining these lower temperatures.