Background
Cold therapy is a popular non-pharmacological intervention used following musculoskeletal injuries and many surgical procedures. The primary aim of cold therapy is the removal of heat energy via conduction from the site of injury, in order to facilitate a therapeutic effect.1 Cold therapy produces a number of physiological effects to the human body including a reduction in blood flow, oedema, haemorrhage,2 cellular metabolic rate, hypoxia, enzymatic activity and tissue damage.3 Cold therapy has also been demonstrated to significantly increase the pain threshold and pain tolerance by reducing nerve conduction velocity and muscle spasm.4
Cold therapy application varies with modality, duration and frequency.5–7 A number of different cold therapy modalities are currently used for the treatment of musculoskeletal trauma, ranging from bags of ice8 to electrically powered continuous cold therapy devices.9 The recommendations for the usage of the cold therapy modalities range from 10 to 20 min (2–4 times a day)10 up to 45 min every 2 h.11 To date a gold standard cold therapy protocol for the acute management of musculoskeletal trauma, which includes an optimum modality with the most effective treatment protocol, has not been established.
During cold therapy the dermal layer cools first. Deeper tissue and tissue adjacent to the modality gradually decrease in temperature, as heat is transferred via conduction to rewarm the superficial skin surface close to the modality.12 There is a high correlation between skin surface temperature and intra-articular temperature during cold therapy. Skin surface cools in a very similar fashion to the deeper tissues, and therefore the skin surface temperature is a useful tool in measuring the effectiveness of cold therapy modalities.2 An effective cold therapy modality is one, which reduces skin surface temperatures quickly, not causing tissue damage and maintains these reduced temperatures over an extended period of time.
Many clinical studies have compared the effectiveness of cold therapy modalities on skin surface temperature of healthy participants with a single 20 min application per modality.1 ,2 ,13 ,14 However, repeated application of ice and gel packs is perceived to yield a more therapeutic effect, constantly withdrawing heat energy in the attempt to reduce inflammation.15 In the postoperative setting, bandages used after knee surgery, have been shown to significantly impede the effects of cold therapy.16
We conducted a study involving cold therapy with compression on a rubber model of a human knee and compared the effectiveness of a gel pack (DonJoy-Orthopaedic Pty Ltd, Normanhurst, New South Wales, Australia) frozen at six different temperatures (1 824 364 860 and 72 h at −20°C) with an ice bag (ICE'N'EASY, Bokarina, Queensland, Australia) by measuring surface temperature. The cryotherapy was applied on top of a standardised surgical dressing. Results showed that gel packs were more effective at cooling than ice and water combinations, on average by 2.6°C (p<0.05).17
There have also been recent advances in technology to deliver cold therapy. Whole body cryotherapy (WBC) involves short exposures to air temperatures below −100°C in a chambers containing two rooms. The first room contains a precooling room and then a cryogenic chamber. Cold water immersion (CWI) is a modality used by patients with rheumatic disease and athletes before and after sporting activity. A recent study compared the effect of 4 min of WBC 110°C with CWI at 8°C on knee skin temperature, and if the modalities could achieve skin surface temperature required for analgesic purposes (<13°C), however, neither modality were able to achieve these levels.18
Commercial devices, such as Game Ready (CoolSystems, Inc., Concord, California, USA)19 have been used more often in the outpatient setting. This device provides intermittent pneumatic compression while delivering cryotherapy to the patient. A recent study compared the effects of Game Ready (CoolSystems, Inc., Concord, California, USA) versus ice wrap on pain in patients in the postoperative week, following subacromial decompression and rotator cuff repair. The results showed that Game Ready (CoolSystems, Inc., Concord, California, USA) was not superior over the ice wrap in reducing pain or narcotic use.19
Another study compared the cooling effects of six different modalities on quadriceps intramuscular temperature.20 These included Game Ready (CoolSystems, Inc., Concord, California, USA), ice and ice wrap. This study concluded that ice and ice wrap should be used as modalities in the treatment of injuries given that they produced intramuscular temperatures lower than that of Game Ready (CoolSystems, Inc., Concord, California, USA).
To our knowledge, however, there have been no studies, which measure the progressive effect of ice bags and gel packs on human knee skin surface temperature of healthy participants, with a surgical dressing, for more than 3 h. While there are numerous studies, which only tested one application of each cryotherapy, the effect of multiple applications on skin surface temperature is not known.
The aim of this study, therefore, was to compare the effectiveness of gel packs and ice bags at reducing the skin surface temperature of healthy human knees, with a surgical dressing.