The pain experience is classically divided into two different categories
a) Acute
b) Chronic.
You may be familiar with the terms but do you know what the difference is? At it’s core, the predominant difference is the length of the pain experience, however, it is actually a lot more complicated than simply the duration of the pain symptoms.
Acute pain is defined as a sudden onset of pain that lasts less than 12 weeks.
Chronic pain is recognised as long-term pain of more than 12 weeks, or after the time that healing would have been thought to have occurred in pain after trauma or surgery.
Acute pain is predominately due to tissue damage &/or inflammation caused by trauma, surgery, infection or arthritis – this stimulates nocioceptors (our pain sensitive nerve receptors) These pain signals are transmitted to the brain stem where the pain signals are interpreted. The function of acute pain is as an “indicator” or “protective mechanism” to prevent further pain & injury i.e avoid certain movements, do not touch hot objects or rest if over training. Acute pain should last for the duration of time it takes for the affected tissue to heal & inflammation to settle.
Chronic Pain however does not have a specific length of time & frequently outlasts the time required for adequate tissue healing following the initial onset of the symptoms. There is more research being conducted into the mechanisms of chronic pain, as the pain experience exceeds the tissue injury. One of the explanations for the persistence of symptoms is neuroplasticity
Neuroplasticity is a neurophysiological theory that explains that changes in the structure, function and organisation of the nervous system occur continuously throughout a person’s lifetime.
Musculoskeletal injuries which result in localised tissue damage and inflammation, also result in the stimulation of pain-sensitive sensory receptors. Persistent, prolonged stimulation of these nerve endings can subsequently have an effect on their structure. These changes can include increases in excitability, meaning that nerve endings are more easily stimulated, or their stimulation exceeds the ideal duration or the nerve ending can proliferate resulting in an increased number of pain receptors relaying information to the Central Nervous System (CNS). It is these factors that can contribute to the pain experience/or pain interpretation extending longer or being inappropriate to the associated damaged tissue.
Chronic pain can also have a greater association with psychological or behavioural responses to pain that contribute significantly to the clinical presentation, including but not limited to fatigue, unrefreshing sleep, fear avoidance, and mood disturbances.