Understanding Chronic Pain: Why Pain Persists After Injury
Chronic pain is not simply acute pain that has lasted longer than expected. In many cases, pain persists even after tissues have healed, due to changes in how the nervous system processes pain signals. This phenomenon, often referred to as central sensitisation, involves increased sensitivity within the brain and spinal cord, leading to amplified pain responses.
Understanding chronic pain as a condition of altered nervous system function helps explain why imaging findings do not always correlate with symptom severity and why multidisciplinary treatment is often required.
Chronic pain can persist long after an injury has healed because the nervous system itself can become overly sensitive and continue to generate pain signals, even when tissues look “normal.”
This process, called central sensitisation, helps explain why scan or X-ray findings often do not match the severity of symptoms and why multidisciplinary treatment is usually needed rather than relying on medications or surgery alone. Understanding this shift—from “tissue damage” pain to “nervous system” pain—can be a powerful first step in regaining control.[1][2][3][4]
WHAT IS CHRONIC PAIN?
Chronic pain is generally defined as pain that lasts longer than three months or beyond the expected time of tissue healing after an injury, surgery, or illness. In chronic pain, the original trigger (for example, a sprain or surgery) may have improved or resolved, yet pain continues or spreads. Importantly, chronic pain is now recognised as a disease of the nervous system in its own right, not just “ongoing acute pain.”[4][5][1]
FROM ACUTE INJURY TO PERSISTENT PAIN
Acute pain is usually a protective alarm system: nerve endings in injured tissue send danger messages to the spinal cord and brain, prompting rest and healing. When the body heals as expected, this nociceptive (injury-related) pain normally settles as tissues repair and inflammation decreases. In some people, however, repeated or intense pain signals, high stress, poor sleep, or emotional trauma can drive lasting changes in the spinal cord and brain’s pain networks, “turning up the volume” on pain and setting the stage for chronic pain.[6][1][4]
WHAT IS CENTRAL SENSITISATION?
Central sensitisation refers to an increased responsiveness of pain-processing neurons in the spinal cord and brain to normal or even minor inputs. In this state, the central nervous system becomes hyperexcitable, so that ordinary signals (or even no external stimulus at all) can trigger pain, and existing pain feels more intense and widespread. Research shows that central sensitisation can persist even after the original tissue problem has healed and may underlie conditions such as chronic low back pain, fibromyalgia, whiplash-associated disorders, osteoarthritis pain, and some forms of headache.[2][7][5][1][4][6]
HOW CENTRAL SENSITISATION CHANGES PAIN
Everyday touch, movement, or pressure can become painful (allodynia), and painful stimuli hurt more than expected (hyperalgesia).[4][6]
Pain may spread beyond the original injury site, feel disproportionate to findings on examination, or move around the body over time.[1][2]
People often report other sensitivities, such as to light, sound, temperature, or chemicals, along with fatigue, poor sleep, and “brain fog,” reflecting the broader impact on sensory and regulatory systems.[2][1]
WHY PAIN CAN PERSIST AFTER HEALING
In central sensitisation, the link between pain and tissue damage becomes loosened: pain is no longer a direct measure of what is happening in muscles, joints, or discs. Functional brain imaging and sensory testing show that people with chronic low back pain and similar conditions often have heightened pain responses and altered brain activation patterns, even when structural imaging is mild or normal. These findings emphasise that chronic pain is driven by altered pain processing within the nervous system, rather than “imagined” or “all in the head.”[8][7][1][4]
IMAGING FINDINGS VS SYMPTOM SEVERITY
It is common for scans (X-rays, CT, MRI) to show degenerative changes such as disc bulges, arthritis, or tendon wear that are also seen in many people without pain. Studies in chronic low back pain demonstrate that the degree of structural change often does not correlate with pain intensity, disability, or quality of life, supporting a major role for central sensitisation and other non-structural factors. This mismatch can be confusing but also reassuring; severe pain does not necessarily mean severe damage or ongoing harm.[7][9][8][1][2]
THE ROLE OF THE BRAIN, MOOD, AND STRESS
Pain is always produced by the brain as a protective response, integrating signals from the body with thoughts, emotions, memories, and context. Psychological factors such as anxiety, depression, trauma history, and pain catastrophising (fearing the worst about pain) are linked to greater central sensitisation and higher pain intensity in conditions like chronic low back pain. Sleep disturbance, ongoing stress, and reduced physical activity can further “train” the nervous system to remain in a sensitised state, creating a vicious cycle of pain, distress, and disability.[10][3][8][1][4]
WHY THIS IS NOT “JUST PSYCHOLOGICAL”
Although mood and thoughts influence pain, central sensitisation is grounded in measurable biological changes, including altered neurotransmitters, receptor sensitivity, and functional connectivity in pain-related brain networks. Psychological and social factors act as amplifiers or dampeners of these neural processes, which is why addressing them can meaningfully reduce pain even when scans do not change. Understanding this bio-psycho-social model reduces stigma and opens the door to more effective, integrated care.[3][10][7][6][1][4]
RECOGNISING FEATURES OF CENTRAL SENSITISATION
Clinicians look for a pattern of symptoms and examination findings that suggest central rather than purely tissue-based pain. Common features include:[9][2]
Pain that is widespread, migratory, or out of proportion to identifiable tissue injury.[9][1][2]
Heightened sensitivity to touch, pressure, temperature, or movement, often with allodynia and hyperalgesia on examination.[6][2]
Co-occurring symptoms like fatigue, sleep problems, cognitive difficulties, and sensory sensitivities (e.g. noise, light, odours).[1][2]
Symptoms persisting despite structurally focused treatments such as repeated injections or surgeries, or minimal findings on imaging.[3][2]
These features help identify “nociplastic” pain—a category where pain arises from altered nociception despite no clear ongoing tissue damage or nerve injury—driven largely by central sensitisation.[5][6]
WHY MULTIDISCIPLINARY TREATMENT IS OFTEN NEEDED
Because chronic pain with central sensitisation involves biological, psychological, and social processes, a multimodal and multidisciplinary approach is recommended by guidelines and expert reviews. No single medication, procedure, or therapy addresses all the mechanisms; instead, combining strategies that target the nervous system, mind, body, and environment is more effective for improving function and quality of life.[10][2][3][6][1]
KEY ELEMENTS OF A MULTIMODAL PLAN
Pain neuroscience education: Learning how pain and central sensitisation work can reduce fear, catastrophising, and perceived threat, which in turn reduces pain intensity and disability.[2][3][1]
Graded physical activity and exercise: Carefully paced, progressive exercise (aerobic, strength, and flexibility) helps desensitise the nervous system, improve confidence in movement, and reduce fatigue.[3][6]
Psychological therapies: Cognitive-behavioural therapy and acceptance and commitment therapy have evidence for improving coping, mood, and function in central sensitisation syndromes, even when effects on pain intensity are modest.[10][1][3]
Sleep and stress management: Addressing insomnia, stress, and relaxation through behavioural sleep strategies, mindfulness, or other techniques can dampen central sensitisation and improve pain outcomes.[6][1][3]
Medication as one part: Some medications (e.g. certain antidepressants or anticonvulsants) can help modulate nervous system sensitivity in selected patients, but their effects are usually partial and work best alongside non-drug therapies.[3][6]
Interdisciplinary programs: Structured pain rehabilitation programs that integrate medical, psychological, and physical therapies show benefits for function, distress, and self-management in chronic pain and central sensitisation.[1][10][3]
MOVING FROM DAMAGE TO SENSITIVITY
Reframing chronic pain as a problem of a sensitised nervous system rather than ongoing injury allows more realistic expectations and more targeted care. Instead of searching endlessly for a “fix” on scans or with repeated procedures, the focus shifts to calming the system, rebuilding strength and confidence, improving sleep and mood, and reconnecting with valued activities. This shift does not minimise the reality of pain; rather, it explains why pain after injury can persist and how a coordinated, multidisciplinary approach can gradually help the nervous system become less sensitive over time.[4][2][6][1][3]
