What is the likely diagnosis and appropriate management for a patient with left-sided low back pain that worsens with movement after mowing the lawn, without red-flag symptoms?

Acute Mechanical Low Back Pain (Likely Musculoskeletal Strain)

This is most likely nonspecific mechanical low back pain from a musculoskeletal strain sustained during lawn mowing, and you should treat it conservatively with NSAIDs, activity modification (not bed rest), and reassurance about the excellent prognosis—over 90% of patients improve within the first month without any imaging or specialized interventions. 1

Diagnostic Classification

Your patient fits into the "nonspecific low back pain" category, which accounts for more than 85% of low back pain presentations in primary care. 1 The key features supporting this diagnosis include:

• Mechanical nature: Pain triggered by specific movements (mowing) and worsened by certain positions 2
• Absence of red flags: No mention of progressive neurologic deficits, bowel/bladder dysfunction, fever, unexplained weight loss, or history of cancer 1
• Unilateral presentation: Left-sided sharp pain without bilateral symptoms or saddle anesthesia 1

The probability of serious pathology is extremely low: cancer (0.7%), compression fracture (4%), spinal infection (0.01%), and cauda equina syndrome (0.04%). 1

Critical Red Flags to Exclude (But Likely Absent Here)

Before proceeding with conservative management, quickly verify the absence of these red flags that would mandate immediate imaging and specialist referral:

• Cauda equina syndrome: Urinary retention (90% sensitivity), fecal incontinence, bilateral leg weakness, saddle anesthesia 1
• Progressive motor deficits: Foot drop, weakness at multiple levels 1, 3
• Cancer risk factors: History of cancer (increases probability from 0.7% to 9%), unexplained weight loss, age >50 years, failure to improve after 1 month 1
• Infection indicators: Fever, IV drug use, recent infection, immunosuppression 1, 4
• Fracture risk: Significant trauma, osteoporosis, prolonged corticosteroid use 1, 4

Immediate Management (No Imaging Required)

Do NOT order imaging at this stage. 1 Routine imaging for nonspecific low back pain provides no clinical benefit, increases healthcare costs, and often identifies abnormalities (disc bulges, degenerative changes) that are present in 29-43% of completely asymptomatic individuals. 1, 5

Pharmacologic Treatment

• NSAIDs: First-line medication with moderate evidence of benefit for short-term pain control 2, 6
• Muscle relaxants: Consider for associated muscle spasms 5, 2
• Acetaminophen: May be used, though evidence is weaker than for NSAIDs 2, 7
• Avoid routine opioids: Reserve only for severe, refractory pain and use judiciously for short duration 5, 2

Non-Pharmacologic Treatment (Essential)

• Advise to remain active: This is more effective than bed rest—patients should continue normal activities as tolerated 1, 5
• Activity modification: Avoid aggravating movements temporarily, but do NOT prescribe complete rest 5, 2
• Heat therapy: Apply as needed for symptomatic relief 5, 7
• Patient education: Explain the favorable natural history—90% of acute low back pain resolves within 1 month 1, 8, 7

Reassurance is Therapeutic

Tell the patient explicitly that most low back pain improves substantially within the first month, and that the absence of red flags means serious pathology is extremely unlikely. 1, 7 This reassurance itself improves outcomes.

When to Escalate Care

Reevaluation Timeline

• Reassess at 1 month if symptoms persist or worsen 1
• Consider earlier follow-up (within 2 weeks) if pain becomes severe or disabling 5

Indications for Imaging (Only After Conservative Failure)

MRI or CT should only be ordered after 6 weeks of failed conservative therapy in patients who are potential candidates for surgery or epidural steroid injection. 1, 5 Earlier imaging is appropriate only if:

• Red flags develop (progressive motor deficits, cauda equina symptoms, suspected malignancy/infection) 1, 3
• Radicular symptoms with motor involvement emerge (e.g., foot drop, significant weakness) 3
• Symptoms persist beyond 6 weeks AND patient is a surgical candidate 1, 5

Specialist Referral Criteria

• Immediate referral: Progressive neurologic deficits, cauda equina syndrome, suspected malignancy/infection 3, 5
• Within 2 weeks: Severe, disabling radicular pain preventing normal activities 5
• Within 3 months: Persistent symptoms despite conservative management 5

Common Pitfalls to Avoid

1. Ordering premature imaging: Plain radiographs or MRI before 6 weeks (without red flags) provides no benefit and may lead to unnecessary interventions based on incidental findings 1, 5

2. Prescribing bed rest: This is counterproductive—staying active accelerates recovery 1, 5

3. Over-medicalizing the condition: Attempting to identify specific anatomical diagnoses in nonspecific low back pain has not been validated and does not improve outcomes 1

4. Missing red flags: Always screen for cauda equina syndrome (urinary retention is the most sensitive finding at 90%), progressive motor deficits, and cancer risk factors 1

5. Delaying physiotherapy: If symptoms persist beyond 2 weeks or are severe, initiate physiotherapy immediately—do not wait for imaging 5

Expected Clinical Course

The natural history strongly favors spontaneous improvement: 90% of patients with acute mechanical low back pain recover within 1 month with conservative management alone. 1, 8, 7 Even disc herniations show spontaneous reabsorption or regression by 8 weeks in the majority of cases. 5, 4