Residency · Residency · Chronic Pain Management
Local Anesthetic Injection Techniques for Chronic Pain
Introduction
Local anesthetic (LA) injections are foundational tools in chronic pain management, used for both diagnostic and therapeutic purposes. Understanding LA pharmacology, concentration selection, toxicity thresholds, and region-specific techniques is essential for safe and effective practice. Lidocaine remains the workhorse agent for trigger point injections (TPIs) and peripheral nerve blocks, while bupivacaine and ropivacaine are preferred when longer duration is needed. A notable clinical observation is that the analgesic benefit of many LA-based procedures outlasts the pharmacologic duration of the block -- a phenomenon attributed to central modulation and interruption of pain-spasm cycles.
Local Anesthetic Pharmacology for the Pain Physician
Mechanism of Action
Local anesthetics work by blocking voltage-gated sodium channels, preventing axonal depolarization and nerve impulse propagation. An important clinical principle is differential blockade: small unmyelinated C-fibers (which carry pain signals) are blocked before larger myelinated A-alpha fibers (which carry motor signals), allowing analgesia without complete motor blockade at lower concentrations. Both peripheral and central mechanisms contribute to LA analgesia -- local anesthetics reduce ectopic discharge, dorsal horn wind-up, and peripheral sensitization.
Commonly Used Agents
| Agent | Class | Onset | Duration (plain) | Duration (with epi) | Max Dose (plain) | Max Dose (with epi) |
|---|---|---|---|---|---|---|
| Lidocaine | Amide | 2-5 min | 60-120 min | 2-4 hrs | 4.5 mg/kg (≤300 mg) | 7 mg/kg (≤500 mg) |
| Bupivacaine | Amide | 5-15 min | 4-8 hrs | 6-12 hrs | 2.5 mg/kg (≤175 mg) | 3 mg/kg (≤225 mg) |
| Ropivacaine | Amide | 5-15 min | 4-6 hrs | 6-10 hrs | 3 mg/kg (≤200 mg) | — |
| Procaine | Ester | 2-5 min | 30-60 min | 60-90 min | 7 mg/kg (≤500 mg) | — |
Concentration Selection
Concentration selection depends on the clinical target. Dilute lidocaine (0.25-0.5%) is used for trigger points and perineural infiltration where minimal motor effect is desired. Standard 1% lidocaine (10 mg/mL) is appropriate for most TPIs and superficial nerve blocks -- 30 mL of 1% lidocaine equals 300 mg, the maximum plain dose. Two percent lidocaine is reserved for deeper nerve blocks, dental blocks, and some peripheral nerve targets. For longer-duration needs, 0.25% bupivacaine is used for fascial plane blocks (erector spinae plane, quadratus lumborum), while 0.5% bupivacaine is used for peripheral nerve blocks requiring prolonged analgesia.
Why Lidocaine Over Bupivacaine for Trigger Points
Bupivacaine has significantly greater myotoxicity than lidocaine, causing more histologic muscle fiber damage, particularly with repeated dosing. Lidocaine's shorter duration is rarely a disadvantage for trigger point injections because the sustained benefit derives from non-anesthetic mechanisms -- mechanical disruption of the taut band and washout of inflammatory mediators. Procaine (an ester) has even lower myotoxicity but is less widely available.
Local Anesthetic Systemic Toxicity (LAST)
Recognition
Early signs of LAST include perioral numbness, tinnitus, metallic taste, lightheadedness, agitation, and circumoral tingling. Late signs include seizures, loss of consciousness, cardiovascular collapse, and arrhythmias. Bupivacaine is more cardiotoxic than lidocaine, and symptoms may present without the classic progression -- cardiac toxicity can be the first sign with bupivacaine.
Prevention
Prevention starts before the syringe is drawn up: calculate and respect the maximum dose. Aspirate before every injection and inject in slow, divided aliquots. Use the lowest effective concentration and volume. Epinephrine serves both as an intravascular marker (causing tachycardia if injected intravascularly) and to slow systemic absorption. Ultrasound guidance for deeper blocks reduces the risk of inadvertent intravascular injection.
Treatment (ASRA LAST Checklist)
If LAST is suspected, stop the injection immediately and call for help. Manage the airway with 100% oxygen and secure the airway if needed. Treat seizures with benzodiazepines (midazolam 0.1 mg/kg IV) and avoid propofol because of its cardiac depressant effects. The definitive treatment is 20% lipid emulsion (Intralipid): administer a 1.5 mL/kg bolus over 1 minute, followed by a 0.25 mL/kg/min infusion, and repeat the bolus up to two additional times if cardiovascular collapse persists. Avoid vasopressin, calcium channel blockers, beta-blockers, and local anesthetics (including lidocaine for arrhythmia). Prolonged CPR may be required, but LA-induced cardiac arrest is survivable with prompt lipid rescue.
<image>Infographic-style poster summarizing Local Anesthetic Systemic Toxicity (LAST) recognition and treatment. Left column shows a human figure with early CNS symptoms labeled (perioral numbness, tinnitus, metallic taste, visual disturbance, agitation) progressing to late symptoms (seizures, LOC, respiratory arrest). Right column shows cardiovascular toxicity progression (hypotension, bradycardia, conduction block, asystole). Bottom panel shows the ASRA LAST treatment algorithm: stop injection, airway management, seizure treatment with midazolam, and 20% lipid emulsion dosing protocol (1.5 mL/kg bolus then 0.25 mL/kg/min infusion) with a drawing of an Intralipid bag. Clean medical education style with color-coded severity zones (yellow for early, red for late).</image>
Trigger Point Injection Technique
Identification of Trigger Points
A trigger point is identified by four cardinal features. The taut band is a palpable firm band of muscle fibers containing the trigger point. Referred pain is elicited when compression of the trigger point reproduces the patient's characteristic pain in a predictable distribution. The local twitch response (LTR) is a brief contraction of the taut band elicited by snapping palpation or needle insertion -- a useful but not essential confirmatory sign. The jump sign occurs when the patient flinches or withdraws in response to trigger point pressure.
Injection Protocol
Position the patient to relax the target muscle and identify the taut band, isolating it between two fingers using pincer or flat palpation. Use a 25-27 gauge needle, 1.5 inches in length (longer for gluteal, lumbar paraspinal, or quadratus lumborum targets). Aspirate, then inject 0.5-2 mL of 0.5-1% lidocaine per trigger point. The fanning technique involves redirecting the needle through the taut band in multiple passes to mechanically disrupt the contracted sarcomeres. Eliciting local twitch responses during needling correlates with better outcomes in some studies. Limit treatment to 3-5 trigger points per session to stay well under the maximum LA dose. Apply pressure after injection and have the patient perform immediate gentle stretching of the treated muscle.
Mechanism of Benefit
The therapeutic benefit of trigger point injections involves multiple mechanisms working together. Mechanical disruption breaks up contracted sarcomeres and the taut band. Washout clears accumulated inflammatory mediators (substance P, CGRP, bradykinin, TNF-alpha) from the motor endplate region. Sodium channel blockade by the local anesthetic interrupts the pain-spasm-pain cycle. Reflex relaxation occurs through interruption of afferent nociceptive input to the spinal cord. Dry needling achieves comparable outcomes in many RCTs, but the addition of local anesthetic provides faster onset of relief and less post-procedure soreness.
<image>Step-by-step illustration of trigger point injection technique. Panel A: cross-sectional anatomy of a skeletal muscle showing normal muscle fibers alongside a taut band containing a trigger point nodule with surrounding contraction knots, with the motor endplate labeled. Panel B: flat palpation technique — two fingers pinning the taut band against underlying bone, with a 25-gauge needle inserted at 30-degree angle into the trigger point, aspirating. Panel C: fanning technique diagram showing the needle redirected through the taut band in 4-5 different trajectories from the same skin entry point, with small aliquots of lidocaine deposited at each pass. Panel D: the local twitch response — a brief visible contraction of the taut band upon needle contact. Clean anatomical illustration style with labeled structures and numbered steps.</image>
Region-Specific Applications
Head and Neck
The greater occipital nerve (GON) block targets the GON as it emerges medial to the occipital artery, approximately one-third of the distance from the external occipital protuberance to the mastoid process. One to two milliliters of 1-2% lidocaine, with or without steroid, is injected. The analgesic effect often outlasts the anesthetic duration by days to weeks, likely through trigeminocervical complex modulation. The lesser occipital nerve (LON) block uses the same technique but targets a more lateral point along the posterior border of the sternocleidomastoid. The sphenopalatine ganglion (SPG) block uses transnasal 2-4% lidocaine via cotton applicator or catheter device and is useful for cluster headache and migraine. Cervical and upper trapezius trigger point injections are high-yield for myofascial neck pain, posture-related pain, and tension headache; the needle trajectory should be kept tangential to the chest wall to avoid the pleural dome.
Thorax and Abdominal Wall
The erector spinae plane (ESP) block involves injection into the fascial plane deep to the erector spinae muscle and superficial to the transverse process, using 15-30 mL of dilute LA (0.25% bupivacaine or 0.5% lidocaine). The injectate spreads to dorsal and ventral rami, providing multilevel analgesia. Indications include post-thoracotomy syndrome, post-mastectomy pain, chronic rib pain, and post-herpetic neuralgia. Intercostal nerve blocks use 3-5 mL of LA per level for chronic rib pain and post-herpetic neuralgia, with a pneumothorax risk of approximately 0.5-1%.
Lumbopelvic
Lumbar paraspinal and quadratus lumborum trigger point injections are common for mechanical low back pain with a myofascial component; gluteus medius/minimus and piriformis trigger points frequently coexist. The quadratus lumborum (QL) block is an ultrasound-guided injection targeting the QL fascia, useful for chronic abdominal wall and flank pain. Piriformis injection, performed under ultrasound or fluoroscopy guidance, addresses piriformis syndrome with sciatic irritation.
Extremity
The suprascapular nerve block addresses chronic shoulder pain, adhesive capsulitis, and post-stroke shoulder pain. Genicular nerve blocks serve as diagnostic blocks before radiofrequency ablation for chronic knee osteoarthritis. Pudendal nerve blocks treat chronic pelvic pain and pudendal neuralgia. Ilioinguinal and iliohypogastric blocks address chronic post-hernia-repair groin pain.
Corticosteroid Adjuvants: When to Add and When to Avoid
When Steroid Adds Value
Corticosteroid adjuvants are beneficial when there is an inflammatory or neuritic component: occipital neuralgia, radiculopathy, post-herpetic neuralgia, frozen shoulder, and bursitis. They are also appropriate for joint and tendon sheath injections in inflammatory arthropathies and for some chronic facetogenic pain through intra-articular injections.
When Steroid Should Be Avoided
Steroids should be avoided for pure myofascial trigger points, where there is no inflammatory substrate and where steroids risk local fat atrophy, skin depigmentation, and tissue thinning. They must be avoided in diagnostic medial branch blocks because the steroid confounds diagnostic accuracy and invalidates the test. Tendon body injections (Achilles, patellar) should not include steroid due to tendon rupture risk. Cervical transforaminal injections should never use particulate steroids because of the risk of catastrophic spinal cord or brainstem infarction from particulate embolism; only non-particulate dexamethasone should be used.
Particulate vs Non-Particulate
Particulate steroids (methylprednisolone, triamcinolone, betamethasone) provide a longer-lasting depot effect but carry the risk of embolic events if inadvertently injected intra-arterially. Non-particulate dexamethasone is safer for transforaminal and cervical injections, with a shorter duration but no embolic risk.
Integrating Injections with Rehabilitation
Injections produce their best outcomes when integrated with a rehabilitation program. On the day of injection, the analgesic window should be used for gentle range of motion, posture correction, and activation of inhibited muscles. During the first one to two weeks, structured physical therapy should focus on stretching the involved muscles, strengthening antagonists, and implementing ergonomic modifications. Over the medium term, treatment should address upstream drivers such as cervical posture for headache or hip mechanics for low back pain. Repeat injection is appropriate when there is a partial response with clear functional gains during the analgesic window, but not as a substitute for addressing unresolved mechanical or behavioral perpetuating factors. Injections without concurrent rehabilitation consistently show diminishing returns over serial sessions.
<image>Clinical decision algorithm flowchart for local anesthetic injection selection in chronic pain. Top node: "Chronic pain with identifiable peripheral pain generator." First branch: "Myofascial trigger point?" leading to "Lidocaine 0.5-1% TPI with fanning technique — avoid bupivacaine (myotoxicity) — no steroid needed." Second branch: "Peripheral nerve target?" leading to sub-branches for "Diagnostic block (use small-volume lidocaine only, no steroid)" and "Therapeutic block (lidocaine +/- steroid if neuritic component)." Third branch: "Fascial plane block?" leading to "ESP or QL block with dilute bupivacaine/ropivacaine for longer duration." Each endpoint includes key safety reminders (max dose, LAST precautions, ultrasound guidance). Bottom panel shows a timeline: "Post-injection rehabilitation integration" with milestones at Day 0 (gentle ROM), Week 1-2 (structured PT), and Month 1-3 (address perpetuating factors). Clean flowchart style with color-coded pathways.</image>
Clinical Pearls
Lidocaine is preferred over bupivacaine for trigger point injections due to bupivacaine's greater myotoxicity -- the shorter duration of lidocaine is irrelevant since sustained TPI benefit is predominantly mechanical. Always calculate the maximum LA dose before the procedure; a common error is exceeding limits when injecting multiple trigger points or performing bilateral blocks in the same session. The analgesic benefit of peripheral nerve blocks frequently outlasts the pharmacologic duration by days to weeks, likely through central modulation of the trigeminocervical complex and dorsal horn processing. Twenty percent lipid emulsion must be immediately available for any LA injection procedure -- LAST is rare but survivable with prompt treatment. Steroid adjuvants are not one-size-fits-all: they help with neuritic and inflammatory pain but add no benefit and potential harm for pure myofascial trigger points and diagnostic medial branch blocks. Erector spinae plane blocks offer multilevel analgesia with a more favorable safety profile than paravertebral or epidural approaches for chronic thoracic and abdominal wall pain. Injections work best as part of a rehabilitation program -- capitalize on the analgesic window for functional gains rather than relying on serial injections alone.
References
- Neal JM, Barrington MJ, Fettiplace MR, et al. The Third American Society of Regional Anesthesia and Pain Medicine Practice Advisory on Local Anesthetic Systemic Toxicity. Reg Anesth Pain Med. 2018;43(2):113-123.
- Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual. 2nd ed. Williams & Wilkins; 1999.
- Forero M, Adhikary SD, Lopez H, et al. The Erector Spinae Plane Block: A Novel Analgesic Technique in Thoracic Neuropathic Pain. Reg Anesth Pain Med. 2016;41(5):621-627.
- Chou R, Hashimoto R, Friedly J, et al. Pain Management Injection Therapies for Low Back Pain. Technology Assessment Report. AHRQ. 2015.
