Acute pain and chronic pain are not the same phenomenon. They arise through different mechanisms, serve different biological purposes, and respond to different interventions. Treating them identically is why so many people remain in pain despite months or years of treatment.
Acute Pain: The Protective Signal
Acute pain is a biological alarm. It is triggered by tissue damage or threat of damage, mediated by nociceptors in the peripheral tissue, and proportional to the actual or potential injury. It is the pain you feel when you sprain an ankle or burn your hand. It serves a protective function: to withdraw from the source of harm and protect the injured area during healing. Appropriate management includes rest, protection, and gradual return to loading as the tissue heals.
Chronic Pain: The Malfunctioning Alarm
Chronic pain persists beyond tissue healing time, which is typically three months or less for most musculoskeletal injuries. By this point, the pain is no longer primarily driven by tissue damage. It is maintained by changes in the peripheral nervous system, including sensitised nociceptors, and in the central nervous system, including changes to descending pain inhibition and cortical mapping. The alarm is still ringing, but the fire has gone out.
Why This Changes Treatment
- Rest, which is appropriate for acute pain, worsens chronic pain by reinforcing avoidance and reducing tissue tolerance
- Imaging such as MRI is rarely useful for chronic pain management because the findings rarely change the clinical approach
- Progressive graded exposure to feared movements is the most evidence-based approach for most chronic musculoskeletal pain
- Addressing central sensitisation requires sleep, stress management, and psychological approaches alongside physical treatment