Acute pain is a signal to protect ourselves from further injury and occurs following inflammation of damaged tissue. The inflamed area becomes hypersensitive causing movements that are not normally painful to be painful. This protection mechanism allows healing. Tissue can be damage by thermal, chemical or mechanical energy known as “noxious stimulus”. Sensory nerve endings in the body tissue detect this and are known as nociceptors. Nociceptive neurons detect damage or the potential of damage at the periphery and convey messages to the central nervous system, pain perception can either be increased to immobilise an area, or inhibited to allow movement.
However if pain is allowed to continue it can have adverse effects, causing neuroplastic changes within the CNS leading to hypersensitivity and chronic pain. Ice is commonly applied to painful swollen injuries to help manage pain. This use of ice is known as cryotherapy, and is defined as the therapeutic application of a substance to the body which decreases tissue temperature by 10° to 15° Celsius, 2 - 4cm below the skin.
Application can be by an ice pack, vapo-coolant spray, ice massage, and ice bath immersion. This cooling of the body tissues is able to produce an analgesic effect via a variety of mechanisms. Including; reduced nerve conduction velocity, inhibition of nociceptors via the gate control theory, reduction in muscle spasm, vasoconstriction and reduction in enzyme activity / cellular metabolism.
Nerve conduction velocity referrers to the speed that messages are passed along the nociceptive pain fibres, a reduction in their speed means that less painful stimulus reaches the central nervous system. Algafy and George (2007) demonstrated significant reduction in nerve conduction velocity up to 33%. This resulted in 89% increase in pain threshold and 76% increase in pain tolerance. That initially unpleasant feeling of applying ice to your skin can produce a counter irritate. This means that the nociceptive pain fibres are inhibited at the spinal cord by the new stimulation of the unpleasant cold, masking the original pain. This is know as the gate control theory.
Vasoconstriction is the narrowing of blood vessel and can reduce inflammatory mediators by reducing the blood flow and enzyme activity. This is directly reducing tissue damage at the painful area. Due to the effects of vasoconstriction, it is most appropriate to use cryotherapy clinically for acute injury/trauma which has caused swelling, muscle spasm, and delayed onset of muscle soreness. Cryotherapy can be used following major orthopaedic surgery like knee replacement and hip replacement with good effect for these reasons.
Precautions of using cryotherapy need to be taken when there is insufficient circulation, and decreased sensation or comprehension (Nadler, 2004). Adverse effects include ice burn, nerve damage, and frostbite (Bleakley et al., 2004; Nadler, 2004).
Melzack, R., and Wall, P. (2003). Handbook of Pain Management. A clinical companion to the Wall and Melzack's Textbook of Pain. London: Churchill Livingston.
Algafly, A. A., & George, K. P. (2007). The effect of cryotherapy on nerve conduction velocity, pain threshold and pain tolerance. British Journal of Sports Medicine, 41(6), 365-369. doi:10.1136/bjsm.2006.031237
Nadler, S. F., Weingand, K. and Kruse, R.J. . (2004). The Physiologic Basis and Clinical Applications of Cryotherapy and Thermotherapy for the Pain Practitioner. Pain Physician, 7(3), 395-399.