Lucan · Conditions

Mechanical low back pain

Australian guidance: RACGP Low Back Pain + eTG Pain & Analgesia

1. Definition and epidemiology

Mechanical low back pain refers to pain located between the lower rib margins and the inferior buttock crease that does not have an identified specific or serious pathological cause; it is also described as non-specific, musculoskeletal, or undiagnosed low back pain, and may be accompanied by referred leg pain. Approximately 1 in 6 Australians report back problems, and back problems are the second most common reason Australians seek care from their general practitioner and the leading cause of lost work productivity and early retirement in Australia. Serious underlying pathology accounts for fewer than 1% of primary care presentations, with non-specific low back pain representing 90 to 95% of cases, and radicular pain or neurogenic claudication comprising 5 to 10%.

2. Pathophysiology

The lumbar spine bears the majority of axial load transmitted from the trunk, with forces concentrated at the L4/5 and L5/S1 intervertebral levels. Under repetitive or excessive compressive and shear forces, the nucleus pulposus of the intervertebral disc undergoes progressive proteoglycan loss and dehydration, reducing its capacity to distribute load uniformly; this accelerates annular fissuring and, in some cases, disc herniation with irritation of adjacent nerve roots. Facet joints, which are true synovial joints, develop cartilage erosion and capsular hypertrophy in response to altered segmental mechanics, generating nociceptive afferent input via the medial branches of the dorsal rami. Paraspinal muscle spasm is a secondary phenomenon driven by reflex protective co-contraction, which further compresses the segment and perpetuates a pain cycle. Central sensitisation can develop when peripheral nociceptive input is sustained, lowering pain thresholds and contributing to the chronic pain phenotype. Psychosocial factors including fear-avoidance behaviour, negative affect, and poor social support modulate descending inhibitory pathways and substantially influence recovery trajectories beyond the purely structural changes visible on imaging.

3. Clinical presentation and diagnostic criteria

Low back pain is diagnosed clinically. The history should characterise onset, duration, aggravating and relieving factors, radiation, and functional impact, alongside a targeted screen for alerting features of serious pathology. Acute low back pain is defined as lasting fewer than 6 weeks; subacute between 6 and 12 weeks; and chronic beyond 12 weeks. On examination, a postural assessment, bony and soft tissue palpation for tenderness and tone, and movement assessment for range and associated pain should be performed. A focused neurological examination including straight leg raise, deep tendon reflexes, and strength and sensation testing is warranted when there is clinical suspicion of neurological impairment. Alerting features that raise concern for serious pathology include: fever with elevated inflammatory markers (spinal infection); history of significant trauma or older age with minor trauma and corticosteroid use (vertebral fracture); prior malignancy, unexplained weight loss, age greater than 50 years, failure to improve with treatment, or rest pain (malignancy); new urinary retention, faecal incontinence, or saddle anaesthesia (cauda equina syndrome); and younger age, prolonged morning stiffness with night pain, and improvement with exercise (axial spondyloarthritis). When none of these alerting features is present, the diagnosis of mechanical low back pain is made clinically without the need for investigation.

4. Investigations and AU-specific cutoffs

Routine investigation is not indicated for mechanical low back pain in the absence of alerting features for serious pathology. When alerting features are present, the following apply:

• MRI lumbar spine: preferred modality when serious pathology is suspected (infection, malignancy, cauda equina syndrome, severe neurological deficits). Note that MRI is not covered by the Medicare Benefits Schedule if requested by a general practitioner, physiotherapist, or chiropractor without specialist involvement in most circumstances; early specialist referral facilitates access.
• Plain radiography: recommended as first-line imaging when vertebral fracture is suspected, given a pre-test probability of 0.5%; post-test probability rises to approximately 1% with 1 risk factor, 7% with 2 risk factors, and 52% with 3 or more risk factors. If plain radiography is negative but clinical suspicion persists, MRI is the next step.
• CT lumbar spine: limited role; may be used when MRI is unavailable or contraindicated, or when early specialist referral is not possible.
• Blood tests: C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and full blood count when spinal infection or malignancy is suspected. ESR greater than or equal to 100 mm/h is a weaker risk factor for malignancy.
• The ACSQHC imaging decision flow chart distinguishes between conditions requiring immediate MRI (cauda equina syndrome, spinal infection, severe or progressive neurological deficits, cancer with major risk) and those where imaging should be deferred after a trial of therapy (axial spondyloarthritis, radiculopathy in surgical candidates, spinal stenosis in surgical candidates).
• Degenerative changes on imaging (disc degeneration, disc bulge, facet degeneration, spondylolisthesis) are highly prevalent in asymptomatic individuals and increase with age; their presence does not confirm a causal relationship with pain and should be contextualised for the patient.

5. Management

The ACSQHC Low Back Pain Clinical Care Standard (2022) defines an eight-component pathway.

Initial assessment within 0 to 2 weeks combines clinical and psychosocial assessment, screening for serious pathology, and arrangement of follow-up. Validated psychosocial screening tools such as the STarT Back Screening Tool or the Orebro Musculoskeletal Pain Screening Questionnaire should be used early to stratify patients by risk of poor functional outcome and guide intensity of intervention.

Patient education is a core treatment component. Patients should be informed that serious causes account for fewer than 5% of presentations, that acute episodes typically resolve within 6 weeks with appropriate primary care management, and that imaging rarely changes management in the absence of alerting features. Addressing fear-avoidance beliefs and pain catastrophising through motivational interviewing or targeted communication reduces the risk of chronicity.

Self-management and maintained physical activity are the cornerstone of management. Patients are encouraged to stay active, continue or return to usual activities and work as soon as feasible, and avoid prolonged bed rest, which is associated with worse outcomes.

Physical and psychological interventions should be offered based on clinical and psychosocial assessment findings. Physiotherapy-directed exercise programmes, cognitive behavioural therapy, and multidisciplinary pain programmes are appropriate for patients at higher risk of poor outcome or with persistent symptoms.

Review at 2 to 6 weeks allows reassessment of symptom progress and adjustment of the management plan. Referral to a multidisciplinary team or specialist review is considered for persisting or worsening symptoms, progressive neurological deficits, or new alerting features at 6 to 12 weeks. Emergency assessment is indicated for signs of cauda equina syndrome, spinal cord compression with rapidly progressive neurology, suspected spinal infection, spinal tumour, or trauma with fracture.

6. Pharmacology and AU PBS notes

Pharmacotherapy is a second-line adjunct to self-management and physical activity, intended to enable function rather than eliminate pain.

First-line analgesia: Non-steroidal anti-inflammatory drugs (NSAIDs) are recommended as first-line pharmacotherapy for patients at low risk of gastrointestinal or cardiovascular harm. Options available in Australia include ibuprofen (Nurofen, Brufen), naproxen (Naprosyn, Anaprox), and diclofenac (Voltaren). NSAIDs are available over the counter at standard doses and on the PBS at higher doses; no PBS streamlined authority code applies specifically to low back pain. Paracetamol (Panadol; generic brands widely available) may be used for mild to moderate pain, though evidence for efficacy in non-specific low back pain is weaker than for NSAIDs.

Second-line analgesia: When NSAIDs are insufficient or contraindicated, short-term muscle relaxants such as diazepam (Valium) may be considered, though the evidence base is limited and dependence risk is significant; benzodiazepines as a class are generally to be avoided given their risk profile. Duloxetine (Cymbalta, Milnor; PBS item for depression and diabetic neuropathic pain but not specifically for low back pain) has emerging evidence for chronic low back pain. Tricyclic antidepressants are occasionally trialled for centralised chronic pain.

Medications to avoid: Anticonvulsants, benzodiazepines, and antidepressants as a class carry risks that often outweigh benefits in low back pain and are not recommended per ACSQHC guidance. Opioid analgesics (e.g. oxycodone, codeine) are considered only in carefully selected patients, at the lowest effective dose and for the shortest duration possible, using immediate-release formulations for short-term use. Opioid prescribing in Australia is subject to state and territory regulatory requirements, and the Opioid Analgesic Stewardship in Acute Pain Clinical Care Standard provides additional guidance.

7. Complications and monitoring

Transition to chronic low back pain (duration greater than 12 weeks) occurs in approximately 10 to 15% of patients and is associated with substantially greater disability, healthcare utilisation, and psychosocial burden. Psychosocial factors identified at the initial assessment, including fear-avoidance behaviour, low mood, job dissatisfaction, and poor social support, are the strongest predictors of chronicity and should trigger early targeted intervention rather than waiting for spontaneous resolution.

Opioid-related complications require active monitoring: dependence, constipation, respiratory depression (particularly in older patients or those with concurrent central nervous system depressants), and opioid-induced hyperalgesia. Where opioids are initiated, a clear stopping goal and review date should be documented at prescription.

Monitoring schedule: Review at 2 to 6 weeks after initial presentation for all patients; reassess pain scores, functional status, and psychosocial factors using validated tools at each visit; consider multidisciplinary or specialist referral if symptoms persist or worsen beyond 6 to 12 weeks. Repeat imaging is not warranted for patients with unchanged symptoms who have had previous spinal imaging.

Cauda equina syndrome is the critical surgical emergency: new urinary retention or incontinence, faecal incontinence, and saddle anaesthesia mandate immediate emergency referral regardless of prior investigations.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.