Is injecting a local anesthetic into neck muscles appropriate for treating muscular spasm associated with straightening of the cervical spine, and what are the recommended dosage and technique?

Intramuscular Local Anesthetic Injection for Neck Muscle Spasm is NOT Recommended

Based on the most recent and highest quality evidence, intramuscular injection of local anesthetic for chronic neck pain and muscular spasm should NOT be routinely performed, as the 2025 BMJ clinical practice guideline found low certainty evidence showing little to no effect on pain relief compared to sham procedures 1.

Evidence Quality and Hierarchy

The 2025 BMJ guideline 1 represents the highest quality evidence available, systematically reviewing interventional procedures for chronic spine pain including neck pain. This guideline specifically evaluated intramuscular injection of local anesthetic (with or without steroids) and found:

• Low certainty evidence that intramuscular local anesthetic injections have little to no difference in pain relief versus sham procedures
• When combined with steroids, intramuscular injections actually showed increased pain compared to sham
• No high certainty evidence exists for important pain relief from any interventional procedure for chronic spine pain
• Procedures carry potential serious adverse events including death, spinal cord infarction, paraplegia, and stroke (though these were primarily associated with epidural injections)

Contradictory Research Evidence

While older research studies suggest potential benefit, they are of lower quality and smaller scale:

• A 2015 study 2 found lidocaine injection into the intramuscular innervation zone (not trigger points) reduced neck pain at 6 months, but this was a small observational study without blinding
• A 2019 meta-analysis 3 showed 1.6-point VAS improvement with local anesthetic versus dry needling at 1-4 weeks, but when limited to double-blinded studies, this effect disappeared (P=0.331)
• A 2007 Cochrane review 4 found limited evidence for intramuscular lidocaine in myofascial trigger points from only two trials

The guideline evidence supersedes these individual studies due to its comprehensive systematic approach, recent publication (2025), network meta-analysis methodology, and rigorous certainty assessment.

Clinical Decision Algorithm

If considering injection for neck muscle spasm:

1. First-line approach: Non-interventional management (physical therapy, oral medications, activity modification)

2. If interventional procedure requested by patient: Counsel that moderate-to-low certainty evidence shows little to no benefit compared to placebo injections

3. If proceeding despite evidence (patient preference after informed consent):

   • Target intramuscular innervation zones rather than trigger points (S-shaped belt in mid-muscle belly of trapezius) 2
   • Use 0.5% lidocaine, 4 mL per injection site 2
   • Avoid adding steroids (associated with increased pain) 1
   • Limit to once weekly for maximum 4 weeks 2

4. Monitor for adverse events: Pain increase, infection, bleeding, neurological symptoms

Critical Caveats

• "Straightening of neck spine" (loss of cervical lordosis) is often an incidental radiographic finding that may not correlate with clinical symptoms
• The guideline found no evidence of subgroup effects based on clinical condition, meaning even if you believe a specific patient type might benefit, the evidence suggests this is unlikely 1
• Approximately 50% of trials failed to report adverse events, meaning safety data is incomplete 1
• The procedure is costly with questionable benefit-to-burden ratio 1

When Injection Might Be Considered

The only scenario with moderate certainty evidence showing benefit is acute whiplash within 8 hours using intravenous (not intramuscular) methylprednisolone, which reduced pain at one week 4. This is a completely different clinical scenario than chronic muscular spasm.

For chronic neck muscle spasm associated with straightening of cervical spine, the evidence does not support routine use of intramuscular local anesthetic injections 1.