What is the role of lidocaine (local anesthetic) injections in the subacromial space for relieving pain associated with subacromial impingement syndrome?

Lidocaine Injections for Subacromial Impingement Syndrome Pain Relief

Subacromial lidocaine injections can provide short-term pain relief for subacromial impingement syndrome, but should not be used as a standalone treatment as they are less effective than a comprehensive approach including exercise therapy and NSAIDs. 1

Efficacy of Subacromial Lidocaine Injections

• Lidocaine injections into the subacromial space can provide immediate short-term pain relief for patients with subacromial impingement syndrome 2
• When used as a diagnostic test before corticosteroid injections, lidocaine significantly improves treatment outcomes - 65% of patients receiving a lidocaine test injection before corticosteroid showed at least 50% improvement at 3 weeks compared to only 42% in those receiving direct subacromial corticosteroid injections 2
• The pain relief from lidocaine alone is typically short-lived (hours) compared to the longer-lasting effects when combined with corticosteroids or other treatments 3

Treatment Algorithm for Subacromial Impingement Syndrome

1. First-line treatment (0-6 weeks): 1

   • Exercise therapy focusing on gentle, progressive stretching and range of motion exercises
   • NSAIDs (oral or topical) for pain and inflammation
   • Activity modification to reduce movements that exacerbate symptoms

2. Second-line treatment (if inadequate response after 4-6 weeks): 1

   • Subacromial corticosteroid injection (with lidocaine)
   • Continue exercise program
   • Consider lidocaine test injection to determine optimal injection site before administering corticosteroid 2

3. Third-line options (if minimal improvement after 3-6 months): 1

   • Consider surgical consultation

Evidence for Injection Techniques

• Lidocaine with corticosteroid: Subacromial injection of combined corticosteroid with lidocaine provides significant pain reduction for up to 12 weeks 3, 4
• Low vs. high volume: Low-volume (4 cc) lidocaine with corticosteroid injections are non-inferior to high-volume (10 cc) injections for pain relief 5
• Lidocaine test approach: Using a 1 ml of 1% lidocaine test injection before corticosteroid administration increases success rates by helping determine the optimal injection site 2
• Alternative to injection: The heated lidocaine/tetracaine patch has shown similar efficacy to subacromial corticosteroid injections for SIS pain relief 6

Comparative Effectiveness

• Interscalene nerve blocks provide better pain scores and lower opioid consumption than subacromial infusions 3
• Subacromial injection of ropivacaine and morphine provides better immediate pain relief (at 2 hours) than IV analgesics, but IV analgesics provide better pain control at 12-48 hours 3
• Subacromial bupivacaine 0.5% infusion has shown lower pain scores at 18 hours and reduced opioid consumption compared to saline infusion 3

Important Considerations and Pitfalls

• Diagnostic value: Lidocaine injections have diagnostic utility - significant pain relief following injection supports the diagnosis of subacromial impingement 7
• Temporary relief only: Lidocaine alone provides only short-term relief and should not replace comprehensive treatment 1
• Avoid overreliance: Repeated injections without concurrent exercise therapy may lead to poorer long-term outcomes 1
• Predictors of poor response: Patients with more severe disease, longer symptom duration (>3 months), and type II or III acromion morphology may respond less favorably to conservative treatments including injections 7

Long-term Management

• Most cases (>90%) of subacromial impingement syndrome have good prognosis with appropriate conservative management 1
• Exercise therapy remains the cornerstone of treatment, with injections serving as adjunctive therapy for pain control during rehabilitation 1
• Surgical interventions have not demonstrated clinically important benefits over non-operative management in most cases 1