Cryotherapy, sometimes known as cold therapy, is the local or general use of low temperatures in medical therapy. Cryotherapy may be used to treat a variety of tissue lesions.^[1] The most prominent use of the term refers to the surgical treatment, specifically known as cryosurgery or cryoablation. Cryosurgery is the application of extremely low temperatures to destroy abnormal or diseased tissue and is used most commonly to treat skin conditions.

Cryotherapy is used in an effort to relieve muscle pain, sprains and swelling after soft tissue damage or surgery. When a musculoskeletal injury occurs, the body sends signals to our inflammatory cells, macrophages, which release IGF-1. IGF-1 is a hormone-insulin-like growth factor which initiates the termination of damaged tissue. In some cases, this inflammatory response can be aggravated and cause increased swelling and edema, which can actually prolong the recovery process.^[2] For decades, it has been commonly used to accelerate recovery in athletes after exercise. Cryotherapy decreases the temperature of tissue surfaces to minimize hypoxic cell death, edema accumulation, and muscle spasms. Minimising each or all of these ultimately alleviates discomfort and inflammation.^[3] It can involve a range of treatments, from the application of ice packs or immersion in ice baths (generally known as cold therapy), to the use of cold chambers.

Cryotherapy chamber

There are two types of cryochamber which differ in their mechanisms of action and their use. Partial-body cryotherapy makes use of liquid nitrogen to lower the temperature. The chamber used is an individual, tube-shaped enclosure that covers a person's body, but it has an open top to keep the head at room temperature.^[4]

In contrast, the temperature of a whole body cryotherapy chamber is reduced electrically, and the user fully enters it, head included.

Cryotherapy is a specific type of low-temperature treatment used to reduce inflammation and its associated pain.^[5]

Cryotherapy was developed in the 1970s by Japanese rheumatologist Toshima Yamaguchi^[6][7] and introduced to Europe, US and Australia in the 1980s^[8][9] and 1990s.^[10] Both types of cryochamber decrease the skin temperature, but lower temperatures are achieved with whole-body cryotherapy than with partial-body cryotherapy, and might be considered more effective.^[11]

Mechanism of action

When the body is subjected to extreme cooling, the blood vessels are narrowed which reduces blood flow to the areas of swelling. Once outside the cryogenic chamber, the vessels expand, and an increased presence of anti-inflammatory proteins (IL-10) is established in the blood.^[12] The treatment typically involves exposing the individual to freezing, dry temperatures (at −40 °C) for 2 to 4 minutes in one of these chambers.^[13] While in the cryotherapy chamber, blood flow is reduced in that injured area. This will reduce muscle spasms and soreness. This is important to activate the circulatory system to encourage healing and regenerate muscle fibers.^[14]

Main uses

Proponents say that cryotherapy may reduce pain and inflammation, help with mental disorders, support exercise recovery and improve joint function. Cryotherapy chambers belong to the group of equipment associated with sports rehabilitation and wellness.

• Reducing the symptoms of eczema^[15]

Cryosurgery

Cryosurgery is the application of extreme cold to destroy abnormal or diseased tissue. The application of ultra-cold liquid causes damage to the treated tissue due to intracellular ice formation. The degree of damage depends upon the minimum temperature achieved and the rate of cooling.^[16] Cryosurgery is used to treat a number of diseases and disorders, most especially skin conditions like warts, moles, skin tags and solar keratoses. Liquid nitrogen is usually used to freeze the tissues at the cellular level. The procedure is used often as it is relatively easy and quick, can be done in the doctors surgery, and is deemed quite low risk. If a cancerous lesion is suspected then excision rather than cryosurgery may be deemed more appropriate.^[17] Contraindications to the use of cryosurgery include but are not limited to; using it over a neoplasm, someone with conditions that are worsened by exposure to cold (i.e. Raynaud's, urticaria), and poor circulation or no sensation in the area.^[18] There are some precautions to using cryosurgery. They include someone with collagen vascular disease, dark-skinned individuals (due to high risk of hypopigmentation), and impaired sensation at the area being treated.^[19]

Ice pack therapy

Ice pack therapy is a treatment of cold temperatures to an injured area of the body. Though the therapy is extensively used, and it is agreed that it alleviates symptoms, testing has produced conflicting results about its efficacy and possibility of producing undesirable results.^{[20][21][22][23]}

An ice pack is placed over an injured area and is intended to absorb heat of a closed traumatic or Edematous injury by using conduction to transfer thermal energy. The physiologic effects of cold application include immediate vasoconstriction with reflexive vasodilation, decreased local metabolism and enzymatic activity, and decreased oxygen demand. Cold decreases muscle spindle fiber activity and slows nerve conduction velocity; therefore, it is often used to decrease spasticity and muscle guarding. It is commonly used to alleviate the pain of minor injuries, as well as decrease muscle soreness. The use of ice packs in treatment decreases the blood flow most rapidly at the beginning of the cooling period,^[24] this occurs as a result of vasoconstriction, the initial reflex sympathetic activity. Although the use of cryotherapy has been shown to aid in muscle recovery, some studies have highlighted that the degree of muscle cooling in humans is not significant enough to produce a considerable effect on muscle recovery. Based on previous research comparing human and animal models, the insufficient degree of cooling is due to larger limb size, more adipose tissue, and a higher muscle diameter in humans.^[25]

Ice is not commonly used prior to rehabilitation or performance because of its known adverse effects to performance such as decreased myotatic reflex and force production, as well as a decrease in balance immediately following ice pack therapy for 20 minutes.^[26] However, if ice pack therapy is applied for less than 10 minutes, performance can occur without detrimental effects. If the ice pack is removed at this time, athletes are sent back to training or competition directly with no decrease in performance.^[27] Ice has also been shown to possibly slow and impair muscle protein synthesis and repair in recreational athletes. This is especially true for cold water immersion, but equivalent controlled studies have not been done to see if the same effects hold true for ice packs. Regardless, ice has been shown in studies to inhibit the uptake of dietary protein post-muscle conditioning exercise.^{[citation needed]}

Although there are many positive effects of cryotherapy in athletes' short-term recovery, in recent years, there has been much controversy regarding whether cryotherapy is actually beneficial or may be causing the opposite effect. While inflammation that occurs post-injury or from a damaging exercise may be detrimental to secondary tissue, it is beneficial for the structural and functional repair of the damaged tissue. Therefore, some researchers are now recommending that ice not be used so as not to delay the natural healing process following an injury. The original RICE (rest, ice, compression, elevation) method was rescinded because the inflammatory response is necessary for the healing process, and this practice may delay healing instead of facilitating it. Animal studies also show that a disrupted inflammatory stage of healing may lead to impaired tissue repair and redundant collagen synthesis.^[28]

There is a study that concludes that cryotherapy has a positive impact on the short-term recovery of athletes. Cryotherapy helped manage muscle soreness and facilitate recovery within the first 24 hours following a sport-related activity. Athletes who use cryotherapy within the first 24 hours to alleviate pain recovered at a faster rate than athletes who did not use cryotherapy after their sport-related activity.^[3]

Cryotherapy following total knee replacement

Post-surgical management following total knee replacement surgery may include cryotherapy with the goal of helping with pain management and blood loss following surgery.^[29] Cryotherapy is applied using ice, cold water, or gel packs, sometimes in specialized devices that surround the skin and surgical site (but keeps the surgical site clean).^[29] Evidence from clinical trials regarding the effectiveness of cryotherapy is weak and because of this, the use of cryotherapy may not be justified.^[29] Weak evidence indicates that cryotherapy used postoperatively may be associated with a small decrease in blood loss and pain following the surgery. No clinically significant improvements in range of motion have been reported. There are not many side effects or adverse effects reported with this intervention.^[29]

Traditional vs continuous cryotherapy after total knee arthroplasty

Cryotherapy, the withdrawal of heat from an individual's body via the application of cold modalities to reduce tissue temperature, has been known as a treatment intervention for the overall management of musculoskeletal injuries, especially when it comes to relieving pain and improving functional outcomes after total knee arthroplasty. Over the years, new cryotherapy devices that aim to maintain a fixed temperature for a prolonged time have become more apparent, thereby questioning both the efficacy and therapeutic outcomes of continuous cryotherapy with the ones of traditional cryotherapy.^[30]

The most concurrent systematic review and meta-analysis aimed to compare continuous and traditional applications of cryotherapy on patients who have undergone total knee arthroplasty, specifically in pain intensity, analgesics consumption, swelling, blood loss, postoperative range of motion (PROM), and length of hospital stay. According to the study's findings, there were no statistically significant differences in pain intensity, analgesic consumption, swelling, blood loss, PROM, and length of hospital stay between the continuous and traditional cryotherapy groups. At the same time, the study acknowledges its limitations, including lack of blinding, substantial heterogeneity, and modest sample sizes in eligible trials.^[30]

In addition to such findings, the study compared the financial implications of both continuous cryotherapy and traditional cryotherapy. They found that continuous cryotherapy may be subject to additional costs not covered by insurance. In contrast, the cost of traditional cryotherapy is nearly negligible.^[30]

With that in mind, continuous cryotherapy was shown to have produced similar clinical effects to traditional cryotherapy; the only difference being the additional costs that insurance companies do not cover with continuous cryotherapy. Therefore, the researchers state the current evidence isn’t substantial enough to support the theoretical cost-effectiveness of continuous cryotherapy after total knee arthroplasty.^[30]

Cold spray anesthetics

In addition to their use in cryosurgery, several types of cold aerosol sprays are used for short-term pain relief. Unlike other cold modalities, it does not produce similar physiological effects due to the fact it decreases skin temperature, not muscle temperature. It reflexively inhibits underling muscle by using evaporation to cool the area.^[31] Ordinary spray cans containing tetrafluoroethane, dimethyl ether, or similar substances, are used to numb the skin prior to or possibly in place of local anesthetic injections, and prior to other needles, small incisions, sutures, and so on. Other products containing chloroethane are used to ease sports injuries, similar to ice pack therapy. Cold aerosol spray could also be used to relieve trigger points and improve range of motion. After applying the cold spray, one can stretch the muscle and will then have improved mobility and a decrease in pain immediately.^[32][33][34] However, this is only a short-term effect as the pain relief and improved range of motion can wear off within a minute.^[35]

Whole body cryotherapy

An increasing amount of research is done on the effects of whole-body cryotherapy on exercise, beauty, and health. Research is often inconsistent because of the usage of the different types of cryo-chambers, and different treatment periods. However, it becomes increasingly clear that whole body cryotherapy has a positive effect on muscle soreness and decreases the recovery time after exercise.^[36] Some older papers show inconsistencies in the effects.^[10]

Cryotherapy is also increasingly used as a non-drug treatment against rheumatoid arthritis, stress, anxiety, or chronic pain, multiple sclerosis and fibromyalgia.^[4] Studies for these, and other diseases (Alzheimer's, migraines), are ongoing although more evidence becomes available on the positive effects of Whole Body Cryotherapy. The FDA points out that the effects of Whole Body Cryotherapy lacks evidence and should be researched more.^[37]

Cryotherapy treatment involves exposing individuals to extremely cold dry air (below −100 °C) for two to four minutes. Yet, three to four minute exposure to whole body cryotherapy is different from a one to two minute exposure. It is more beneficial to expose for a shorter amount of time to increase therapeutic benefits. Longer durations have negative effects on thermal sensation, tissue oxygenation, and blood volume. Also, the amount of sessions is an important part of the healing process. Just one session will not exhibit significant effects. A minimum of twenty sessions is required. Thirty sessions is recommended for optimal effects though.^[38] To achieve the subzero temperatures required for whole body cryotherapy, two methods are typically used: liquid nitrogen and refrigerated cold air. During these exposures, individuals wear minimal clothing, which usually consists of shorts for males, and shorts and a crop top for females. Gloves, a woollen headband covering the ears, and a nose and mouth mask, in addition to dry shoes and socks, are commonly worn to reduce the risk of cold-related injury. The first whole body cryotherapy chamber was built in Japan in the late 1970s, introduced to Europe in the 1980s, and has been used in the US and Australia in the past decade.^[10]

Adverse effects

Reviews of whole-body cryotherapy have called for research studies to implement active surveillance of adverse events, which are suspected of being underreported.^[10][39] If the cold temperatures are produced by evaporating liquid nitrogen, there is the risk of inert gas asphyxiation as well as frostbite.^[40] However, these risks are irrelevant in the electronically operated chambers.

Contraindications

Contraindications include patients with cardiovascular disease, arterial hypertension, acute infectious diseases, seizures, cold allergy, and some psychiatric disorders.^[41]

Partial body

Partial body cryotherapy devices also exist. If the cold temperatures are produced by evaporating liquid nitrogen, there is the risk of inert gas asphyxiation as well as frostbite.^[40]