How is a pericapsular nerve group (PENG) block performed, including recommended local anesthetic dosage and alternative superficial techniques?

PENG Block: Technique, Evidence, and Clinical Role

The PENG block is a motor-sparing ultrasound-guided technique that targets hip joint capsule pain but does NOT cover surgical incision pain; therefore, femoral or fascia iliaca blocks remain the evidence-based standard of care for hip fracture analgesia. 1

What the PENG Block Targets

The PENG block deposits local anesthetic around the articular branches of the femoral, obturator, and accessory obturator nerves that supply the anterior hip joint capsule—the primary source of pain in hip fractures. 1 This anatomically focused approach explains both its strengths (excellent joint pain relief with motor preservation) and its critical limitation (no coverage of the surgical incision). 1

Current Guideline Position

The Association of Anaesthetists explicitly states that PENG blocks have NOT been compared in trials with fascia iliaca or femoral nerve blocks and do NOT provide analgesia to the surgical incision site. 2, 1 Consequently:

• Femoral or fascia iliaca blocks remain the recommended first-line peripheral nerve blocks for hip fracture analgesia. 2, 1
• Single-shot nerve blocks should be provided in the Emergency Department and at the time of surgery (provided 6 hours has passed between blocks). 2
• Ultrasound-guided placement increases accuracy and adequacy of analgesia. 2
• Peripheral nerve blocks should routinely supplement general or spinal anesthesia. 2

How to Perform the PENG Block

Ultrasound-Guided Technique (Standard Approach)

• Patient positioning: Supine with the hip in neutral position. 3
• Probe placement: High-frequency linear ultrasound probe positioned in a transverse oblique plane over the anterior inferior iliac spine. 3
• Anatomical landmarks: Identify the iliopsoas muscle and tendon, the iliopubic eminence, and the femoral artery. 3
• Needle approach: In-plane or out-of-plane technique to deposit local anesthetic in the musculofascial plane between the psoas tendon anteriorly and the pubic ramus posteriorly. 3
• Local anesthetic dosage: 20 mL of 0.25-0.5% levobupivacaine or bupivacaine is the most commonly reported volume and concentration. 4, 5, 6

Alternative Landmark-Based Technique

A feasibility study demonstrated successful PENG block placement using nerve stimulator guidance when ultrasound is unavailable:

• Landmarks: Anterior superior iliac spine and pubic tubercle are used to identify the injection site. 5
• Technique: Nerve stimulator-guided approach with 20 mL of 0.25% bupivacaine plus 8 mg dexamethasone. 5
• All 10 patients achieved successful blocks with significant pain reduction (NRS at rest from 6-9 to 0-2; on limb elevation from 8-10 to 2-4). 5
• This technique is feasible but should be considered only when ultrasound is truly unavailable, as ultrasound guidance remains the gold standard. 5

Evidence Quality: Critical Gaps

The evidence base for PENG blocks consists entirely of case reports and case series—representing low-quality evidence. 1, 7, 6 Key limitations include:

• No randomized controlled trials comparing PENG to femoral or fascia iliaca blocks exist. 2, 1, 7
• A 2021 scoping review identified only 20 articles describing a combined total of 74 patients, all case reports or small case series. 7
• A 2021 narrative review found 57 publications, but 36 were case reports/series and 12 were letters—no RCTs were identified. 6

Motor-Sparing Advantage: The One Clear Benefit

The strongest evidence for PENG blocks comes from a 2021 RCT comparing PENG to suprainguinal fascia iliaca block in 40 total hip arthroplasty patients. 4 This study demonstrated:

• Significantly lower incidence of quadriceps motor block with PENG at 3 hours (45% vs 90%, p<0.001) and 6 hours (25% vs 85%, p<0.001). 4
• Better preservation of hip adduction at 3 hours (p=0.023). 4
• Decreased sensory block of anterior, lateral, and medial thighs at all measurement intervals (all p≤0.014). 4
• However, NO clinically significant differences in postoperative pain scores, opioid consumption, ability to perform physiotherapy, or length of hospital stay. 4

This means PENG preserves motor function better but does not improve pain control or functional outcomes compared to fascia iliaca block. 4

Clinical Bottom Line and Algorithm

For Hip Fracture Analgesia (Standard Practice):

1. Use femoral or fascia iliaca blocks as first-line (fascia iliaca may provide better incisional analgesia). 2, 1
2. Administer in the Emergency Department on admission. 2
3. Repeat at time of surgery if ≥6 hours has passed since the first block. 2
4. Use ultrasound guidance to maximize accuracy. 2

Potential Role for PENG Block:

• Consider PENG only when isolated hip joint pain relief is the primary goal and incisional coverage is not required (e.g., pre-positioning for spinal anesthesia, non-surgical hip pain). 1
• PENG may be useful for posterior surgical approaches where lateral cutaneous nerve coverage is less critical. 2
• PENG offers motor-sparing advantages that may theoretically facilitate earlier mobilization, but this has not translated to improved functional outcomes in trials. 4

Common Pitfalls and Caveats

• Do not use PENG as a substitute for fascia iliaca or femoral blocks in hip fracture surgery—it will not cover incisional pain. 2, 1
• Transient motor side effects can occur if local anesthetic is deposited in an unintended location (reported in 2 cases). 7
• The Association of Anaesthetists describes PENG as a "promising new technique that merits attention and deserves further investigation" but emphasizes it is not yet standard of care. 1
• More than 50 peer-reviewed articles have been published since the block's introduction in 2018, reflecting growing interest, but high-quality comparative RCTs are urgently needed. 1, 6

Research Imperative

Randomized controlled trials directly comparing PENG to established peripheral nerve blocks are required to define its true effectiveness and optimal clinical role. 1, 7, 6 Until such evidence exists, PENG remains an investigational technique that should not replace guideline-recommended blocks for hip fracture analgesia. 2, 1