Acute Low Back Pain:
What to Do When Your Back "Goes"

What acute low back pain is

Low back pain is pain between the lower edge of the ribs and the creases of the buttocks. It is called acute when an episode has lasted less than about six weeks, subacute up to twelve weeks, and chronic beyond that. It is extraordinarily common: the Global Burden of Disease study estimated that 619 million people worldwide had low back pain in 2020, and it remains the leading cause of years lived with disability globally (GBD 2021 Low Back Pain Collaborators, Lancet Rheumatology, 2023).

For the great majority of people, no single structure can be confidently identified as the source of pain. Doctors call this non-specific low back pain. Muscles, ligaments, the small facet joints and the intervertebral discs may all contribute, but tests cannot reliably pinpoint which one. Only a small proportion of people have a specific, well-understood cause such as a vertebral fracture, infection or cancer (Hartvigsen et al., Lancet, 2018). "Non-specific" does not mean the pain is imaginary or minor — it means that the treatment approach does not depend on finding one damaged structure.

Common triggers and risk factors

An episode often starts with an ordinary movement — bending, lifting, twisting, or a sneeze — and sometimes with no clear trigger at all. The movement is usually the last straw rather than the cause of damage. Factors associated with a higher risk of low back pain include physically demanding work, smoking, obesity, and physical and mental health conditions such as depression (Hartvigsen et al., 2018). In Tokyo, long commutes, prolonged desk work, carrying heavy bags on stairs and lifting children or luggage are familiar settings.

Symptoms

Typical features are aching or sharp pain across the lower back, sometimes more on one side; muscle spasm and stiffness; difficulty standing up straight, getting out of a chair or rolling over in bed; and pain that changes with movement and position. Pain may spread into the buttock or upper thigh. Pain that travels below the knee, especially with numbness or tingling, suggests irritation of a nerve root (sciatica), which is discussed in a separate column.

Warning signs that need prompt medical care

Serious causes are rare. In an Australian study of 1,172 consecutive patients seeing primary care for acute low back pain, only 11 (0.9%) had serious pathology over the following year, most often a vertebral fracture. Most patients had at least one traditional "red flag", so individual flags on their own were often misleading; the more informative signs for fracture were older age (over 70), significant trauma and prolonged corticosteroid use (Henschke et al., Arthritis & Rheumatism, 2009). Even so, some symptoms should never be ignored.

Symptom	Why it matters	What to do
New difficulty passing urine, loss of bladder or bowel control, or numbness around the genitals or buttocks ("saddle" area)	Possible compression of the nerves at the base of the spine (cauda equina syndrome)	Emergency care the same day
Progressive leg weakness or foot drop	Significant nerve compression	Urgent assessment
Fever, feeling unwell, recent infection, injecting drug use or a weakened immune system	Possible spinal infection	Urgent assessment
History of cancer, unexplained weight loss, or pain that is constant and worse at night	Possible spread of cancer to the spine	Prompt assessment
Significant fall or accident, older age, osteoporosis or long-term steroid use	Possible vertebral fracture	Prompt assessment, often with imaging

Diagnosis: why a scan is often not needed

Assessment is mainly a careful history and physical examination, including a check of leg strength, sensation and reflexes, aimed at excluding the warning signs above and identifying nerve-root involvement. When none of these features are present, guidelines advise against routine imaging in the early weeks.

One reason is that spine scans frequently show changes that are a normal part of ageing. A systematic review of imaging in 3,110 people without back pain found disc degeneration in 37% of 20-year-olds rising to 96% of 80-year-olds, and disc bulges in 30% of 20-year-olds rising to 84% of 80-year-olds (Brinjikji et al., American Journal of Neuroradiology, 2015). Seeing these findings on a report can cause worry and lead to unnecessary treatment, even though they may have nothing to do with the current pain. Imaging is appropriate when warning signs are present, when symptoms are not improving as expected, or when a procedure is being considered for a specific diagnosis.

What helps

Because most episodes improve over time whatever is done, the aim of treatment is to relieve pain enough to keep moving while recovery happens.

Stay active — avoid bed rest

Bed rest was once routine advice. It is no longer recommended. A Cochrane review found that, for acute low back pain, advice to stay active produced small improvements in pain and function compared with advice to rest in bed (Dahm et al., Cochrane Database of Systematic Reviews, 2010). In practice this means continuing normal daily activities — including work, where possible — as much as pain allows, changing position frequently, and short walks. It is fine to rest briefly when pain is severe; the point is to avoid prolonged immobility.

Heat and simple non-drug measures

The American College of Physicians guideline recommends that, because most acute and subacute low back pain improves regardless of treatment, patients and clinicians should first choose non-drug options: superficial heat (moderate-quality evidence), or massage, acupuncture or spinal manipulation (low-quality evidence) (Qaseem et al., Annals of Internal Medicine, 2017). A heat pack or warm bath is inexpensive and widely available. Reassurance and accurate information are themselves an important part of care.

Medicines

If medication is wanted, the same guideline suggests a non-steroidal anti-inflammatory drug (NSAID) such as ibuprofen or loxoprofen, or a skeletal muscle relaxant (moderate-quality evidence). NSAIDs are not suitable for everyone — for example people with certain kidney, stomach or heart conditions, or those on blood thinners — so check with a doctor or pharmacist. Topical NSAID patches and gels (シップ) are commonly used in Japan.

Physiotherapy, injections and surgery

For a first, uncomplicated episode, formal physiotherapy is not always necessary, but guidance on safe movement and a gradual return to activity can help, particularly if pain is slow to settle or fear of movement is holding recovery back. Injections and surgery have no established role in non-specific acute low back pain. Surgery is considered only for specific diagnoses — for example, a disc herniation causing cauda equina syndrome or progressive weakness, an unstable fracture, infection or tumour — and these are managed by spine specialists.

What to expect: recovery and recurrence

Recurrence is common but not inevitable. Among 353 people who had recovered from an episode of acute low back pain, about a quarter (24%) reported a recurrence within a year; a previous history of back pain was the only factor that consistently predicted it (Stanton et al., Spine, 2008). A minority of people develop persistent pain; high initial pain intensity, psychological distress and pain in several body sites are associated with a higher risk (Hartvigsen et al., 2018). If pain is not clearly improving after a few weeks, a review with a doctor is worthwhile.

Reducing the risk of another episode

A systematic review of 21 randomised trials (30,850 participants) found moderate-quality evidence that exercise combined with education reduced the risk of a new episode of low back pain over the following year (relative risk 0.55), and lower-quality evidence that exercise alone also helped. Education alone, back belts and shoe insoles did not appear to prevent low back pain (Steffens et al., JAMA Internal Medicine, 2016). No single type of exercise has been shown to be clearly best; the most useful programme is one you will keep doing — walking, strengthening, Pilates, yoga or swimming are all reasonable choices. Stopping smoking and maintaining a healthy weight are sensible for general health and are associated with a lower risk.

When to see a doctor

Seek emergency care immediately for any bladder or bowel changes, numbness in the saddle area, or rapidly worsening leg weakness. See a doctor promptly if back pain follows a significant fall or injury, if you are older or have osteoporosis, if you have a history of cancer, fever or unexplained weight loss, if pain is severe and constant even at rest or at night, or if pain spreads below the knee with numbness or weakness. Otherwise, it is reasonable to manage a typical episode with activity, heat and simple measures, and to see a doctor if it is not improving after two to four weeks or keeps coming back. In Tokyo, a general orthopaedic clinic (整形外科) is usually an appropriate first contact; many can arrange imaging and refer to a spine specialist (脊椎外科) when needed.