3 in 1 block , PENG block , Lumbosacral block techniques with diagramatic view explanation in MD Anaesthesia. With possible,e viva questions
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3 in 1 femoral nerve block ultrasound anatomy diagram
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PENG pericapsular nerve group block hip ultrasound
This educational medical graphic illustrates the innervation and regional anesthesia techniques for the hip. The top section features an anatomical diagram of the pelvis and upper thigh in two views: an anterior superficial view showing the Lateral Femoral Cutaneous, Femoral, and Obturator nerves, and a deep view showing the Trochanteric nerve. The bottom section presents three ultrasound images demonstrating specific regional nerve blocks. 1) Obturator Nerve Block: Shows the anterior and posterior branches of the obturator nerve (ObN Ant. Br. and ObN Post Br.). 2) Femoral Nerve Block: Displays the needle tip approaching the femoral nerve, adjacent to the femoral artery, femoral vein, and psoas muscle under the fascia iliaca. 3) PENG (Pericapsular Nerve Group) Block: Highlights landmarks including the Femoral Artery (FA), Pectineus muscle (PE), iliopectineal ligament (LA), and iliacus muscle (M). The diagram serves as a clinical guide for anesthesiology and pain management, comparing traditional nerve blocks with the newer PENG technique for hip analgesia.
This diagnostic ultrasound image demonstrates the ultrasound-guided technique for a Pericapsular Nerve Group (PENG) block, a regional anesthesia procedure used for hip analgesia. The transverse view identifies key musculoskeletal and vascular landmarks. On the left, the anterior inferior iliac spine (AIIS) appears as a hyperechoic bony prominence. Centrally, the iliopubic eminence (IPE) is visible as a deep bony landmark. Superior to the IPE, the psoas tendon (PT) is visualized as an oval hyperechoic structure. To the right, the femoral artery (FA) appears as an anechoic circular lumen. A significant hyperechoic area labeled LA (local anesthetic) is seen deposited in the fascial plane between the psoas tendon and the iliopubic eminence, which is the target site for the PENG block to provide sensory blockade of the articular branches of the femoral, obturator, and accessory obturator nerves.
This composite educational image illustrates the Pericapsular Nerve Group (PENG) block, a regional anesthesia technique for hip analgesia. Panel A shows the clinical setup, including the patient’s supine position and the transverse orientation of a curved-array ultrasound probe at the level of the inguinal crease. Panel B presents the corresponding sonographic anatomy. Key landmarks include the hyperechoic bony contours of the anterior inferior iliac spine (AIIS) and the iliopubic eminence (IPE). The psoas tendon (PT) is identified as a hypoechoic oval structure resting between these bony prominences. The femoral artery (FA) is visualized medially as an anechoic, pulsatile vessel. A dashed red arrow demonstrates the in-plane needle trajectory, targeting the fascial plane between the psoas tendon and the pubic ramus. This block specifically targets the articular branches of the femoral nerve, obturator nerve, and accessory obturator nerve to provide sensory blockade of the anterior hip capsule without significant motor impairment.
Diagnostic ultrasound images illustrating the Pericapsular Nerve Group (PENG) block for regional anesthesia. The composite contains two panels showing the cross-sectional anatomy of the anterior hip region. The left panel identifies key landmarks: the femoral artery (FA), femoral vein (FV), and femoral nerve (FN) located medially and superiorly. Deep to these lie the psoas tendon (PT), iliopubic eminence (IPE), and anterior inferior iliac spine (AIIS). The right panel demonstrates the clinical implementation of the block, where hypoechoic local anesthetic (AL) is seen spreading within the fascial plane between the psoas tendon and the underlying bony cortex (IPE and AIIS). The images highlight the anatomical plane containing sensory branches of the femoral, obturator, and accessory obturator nerves targeted for hip fracture analgesia. Orientation arrows indicate anterior and medial directions, emphasizing the deep approach required to reach the periarticular space while avoiding superficial neurovascular structures.
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Regional Anaesthesia: 3-in-1 Block, PENG Block & Lumbosacral Block
MD Anaesthesia Reference Guide with Viva Questions
PART 1: THREE-IN-ONE (3-IN-1) BLOCK
Concept & Rationale
The 3-in-1 block (Winnie, 1973) uses a single inguinal injection of a large volume of local anaesthetic to block three nerves simultaneously:
- Femoral nerve (L2-L4, posterior divisions)
- Lateral femoral cutaneous nerve (L2-L3)
- Obturator nerve (L2-L4, anterior divisions)
The anatomical basis is that all three nerves share a continuous fascial sheath (the fascia iliaca compartment) which communicates proximally. A large volume injected under distal compression tracks proximally into this sheath, blocking all three nerves.
"The femoral nerve runs down the thigh in a fascial sheath that is continuous with the nerve sheath that contains all three nerves more proximally. If a large amount of local anesthetic is injected into this sheath, it will track proximally, medially, and laterally and thereby block all three nerves."
- Roberts and Hedges' Clinical Procedures in Emergency Medicine
Anatomy
Anatomy of the three nerves targeted by the 3-in-1 block, shown emerging from the psoas muscle at L2-L5.
| Nerve | Origin | Course | Sensory Territory |
|---|---|---|---|
| Femoral | L2-L4 (posterior div.) | Lateral to femoral artery under inguinal ligament | Anterior thigh, femoral shaft, medial leg (saphenous) |
| Lateral femoral cutaneous | L2-L3 | 1-2 cm medial to ASIS, under inguinal ligament | Anterolateral thigh to knee |
| Obturator | L2-L4 (anterior div.) | Medial border of psoas, obturator canal | Medial thigh, hip joint capsule |
The coverage for lower limb:
Sensory distribution of lumbar plexus blocks (pink = femoral + LFCN + obturator; green = sciatic territory).
Indications
- Primary: Hip fracture analgesia (NOF fractures), especially elderly patients
- Anterior thigh and knee surgeries
- ORIF of femoral shaft
- Supplement to general/neuraxial anaesthesia for knee arthroplasty
- Patients with respiratory compromise (reduces opioid requirement)
Technique
Landmark / Nerve Stimulator Method:
- Patient supine
- Palpate femoral artery 2 cm distal to the inguinal ligament
- Mark injection point 1-2 cm lateral to the femoral artery (NAVEL: Nerve-Artery-Vein-Empty space-Lymphatics, lateral to medial)
- Raise a subcutaneous wheal of local anaesthetic
- Insert a 22-25G, 3.75 cm needle at 45-60° angle to skin, directed cephalad
- Advance until:
- "Pop" / loss of resistance as fascia lata penetrated, OR
- Paraesthesia elicited, OR
- Needle pulsates laterally (proximity to nerve)
- Inject 25-30 mL of local anaesthetic (larger volume than femoral block alone)
- Apply digital pressure distal to injection site to force fluid to track proximally
Key difference from simple femoral block: Volume is 25-30 mL (vs. 20 mL for femoral alone), and distal compression is essential for spread.
Ultrasound-Guided Technique:
- High-frequency linear probe placed transversely below the inguinal ligament
- Identify femoral artery, vein, fascia iliaca, and femoral nerve (hyperechoic, lateral to artery)
- Insert needle in-plane (lateral to medial)
- Confirm local anaesthetic spread under fascia iliaca, circumferentially around femoral nerve
Local Anaesthetic Doses
| Drug | Concentration | Volume |
|---|---|---|
| Bupivacaine | 0.375-0.5% | 25-30 mL |
| Ropivacaine | 0.5% | 25-30 mL |
| Levobupivacaine | 0.375-0.5% | 25-30 mL |
| Lidocaine (with epinephrine) | 1.5-2% | 25-30 mL |
Complications
- Femoral artery/vein puncture (hence ASIS lateral landmark important)
- Local anaesthetic systemic toxicity (LAST)
- Nerve injury
- Haematoma
- Infection
- Quadriceps weakness (motor block - fall risk in elderly)
- Incomplete obturator block (common - in ~50% cases the obturator remains unblocked)
PART 2: PENG (PERICAPSULAR NERVE GROUP) BLOCK
Concept & Background
Described by Girón-Arango et al. (2018), the PENG block is a fascial plane block targeting the articular branches (not the main trunks) of:
- Femoral nerve (articular branches)
- Obturator nerve (articular branches via accessory obturator nerve)
- Accessory obturator nerve
The local anaesthetic is deposited in the musculofascial plane between the psoas tendon and the pubic ramus (deep to the iliopubic eminence), where these articular branches travel.
Key advantage: Near-complete motor sparing - quadriceps strength preserved, enabling early ambulation.
Anatomical diagram of hip innervation (top) and comparison of femoral nerve block vs PENG block on ultrasound (bottom). PENG targets LA deposition between psoas tendon (PT) and iliopubic eminence (IPE).
Anatomy
| Structure | US Appearance | Role |
|---|---|---|
| Anterior inferior iliac spine (AIIS) | Hyperechoic bony prominence (lateral) | Lateral landmark |
| Iliopubic eminence (IPE) | Hyperechoic bony prominence (central) | Medial landmark, target plane above |
| Psoas tendon (PT) | Oval hyperechoic structure | Superficial to IPE, needle goes lateral to it |
| Femoral artery (FA) | Anechoic, pulsatile (medial) | Safety landmark - avoid |
| Target plane | Between PT superiorly and pubic ramus | Site of local anaesthetic deposition |
Indications
- Hip fracture (NOF, intertrochanteric, subtrochanteric) - pre-op and post-op analgesia
- Total hip arthroplasty
- Hip arthroscopy
- When motor preservation is essential (early mobilisation, fall risk)
- Alternative when fascia iliaca block is contraindicated
Technique
PENG block setup and ultrasound anatomy. Panel A: patient position and probe placement. Panel B: needle trajectory (red dashed arrow) targeting the plane between psoas tendon (PT) and iliopubic eminence (IPE).
Step-by-step:
- Patient supine
- Place curved-array (low-frequency) or linear (high-frequency) probe at the level of the inguinal crease, parallel to the inguinal ligament
- Probe orientation: from ASIS laterally to pubic tubercle medially
- Identify on US: AIIS, IPE (bony prominences), psoas tendon (oval, hyperechoic, between AIIS and IPE), femoral artery (pulsatile, medial)
- Insert 22G, 10 cm needle in-plane, lateral to medial
- Advance until needle tip contacts the pubic ramus lateral to psoas tendon
- Negative aspiration
- Inject 20 mL of local anaesthetic (e.g., 0.2-0.5% ropivacaine, 3 mg/kg up to 20 mL)
- Confirm spread: hypoechoic pool should lift the psoas tendon off the pubic ramus - "hydrodissection" of the fascial plane
Critical point: If injection is intramuscular (into the psoas), slight needle retraction is needed before re-injecting.
Ultrasound Anatomy (Labeled Image)
PENG block US view: PT = psoas tendon, IPE = iliopubic eminence, AIIS = anterior inferior iliac spine, FA = femoral artery, LA = local anaesthetic deposited in target fascial plane.
Local Anaesthetic
- Ropivacaine 0.2-0.5%, 20 mL (3 mg/kg in children)
- Bupivacaine 0.25-0.5%, 20 mL
Advantages over 3-in-1 / Femoral Block
| Feature | Femoral / 3-in-1 | PENG |
|---|---|---|
| Motor block | Yes (quadriceps) | No (motor sparing) |
| Fall risk | High | Low |
| Obturator coverage | Variable | Articular branches covered |
| Technique | Relatively simple | Requires US skills |
| Evidence level | Strong (RCTs) | Emerging (case series, small RCTs) |
Complications
- Haematoma (femoral vessels adjacent)
- Intramuscular injection into psoas
- Incomplete analgesia (only articular branches, not all hip pain pathways)
- Femoral nerve palsy (if injected too superficially/laterally)
- LAST
PART 3: LUMBOSACRAL BLOCK
The lumbosacral block encompasses blocking the lumbar plexus (posterior approach / psoas compartment block) and the sacral plexus (parasacral block). Together, they provide anaesthesia for the entire lower limb.
A. POSTERIOR LUMBAR PLEXUS BLOCK (Psoas Compartment Block)
Anatomy:
The lumbar plexus (L1-L4) forms within the body of the psoas major muscle, between its anterior and posterior laminae. Terminal branches: femoral nerve, obturator nerve, lateral femoral cutaneous nerve, genitofemoral nerve, and ilioinguinal nerve.
Sagittal view - lumbar plexus within psoas major, in close proximity to aorta, vena cava, and kidneys.
Indications:
- Hip surgery (arthroplasty, ORIF)
- Femoral shaft fracture
- Anterior thigh surgery
- Combined with sciatic block: complete lower limb anaesthesia
Technique - Landmark (Winnie / Chayen approach):
- Patient lateral decubitus (operative side up) or prone
- Draw a line connecting both iliac crests (intercristal line ≈ L4 level)
- Draw a parasagittal line through the posterior superior iliac spine (PSIS)
- Injection point: intersection of the intercristal line with the lateral third of the distance between midline and PSIS
- Insert a long (10-15 cm), insulated stimulating needle perpendicular to the skin
- Advance until transverse process is contacted, then "walk off" caudally
- Never insert >3 cm past the transverse process depth
- Endpoint: quadriceps contraction (femoral motor response)
- Inject 20-30 mL local anaesthetic
Technique - Ultrasound Guided:
Posterior lumbar plexus block US view. The "trident sign" - acoustic shadows of L2, L3, L4 transverse processes with psoas between them. Plexus (yellow oval) visible as hyperechoic density in the posterior psoas.
- Large curvilinear probe, parasagittal orientation, lateral to lumbar spinous processes
- Identify the "trident sign": acoustic shadows of L2, L3, L4 transverse processes
- Psoas muscle visible between shadows (striated appearance)
- Lumbar plexus = hyperechoic density in posterior part of psoas
- Needle in-plane, between L3-L4 transverse processes
- Inject 20 mL into the nerve root plane
Local Anaesthetic:
- Ropivacaine 0.5%, 20-30 mL
- Bupivacaine 0.375-0.5%, 20-30 mL
Complications (highest complication rate among peripheral nerve blocks):
- Retroperitoneal haematoma (most serious - cannot compress)
- Epidural / intrathecal spread (bilateral block, total spinal)
- Intravascular injection (aorta, inferior vena cava, renal vessels proximity)
- Renal capsular puncture
- Nerve injury
- Contraindicated in anticoagulated patients
B. SACRAL PLEXUS BLOCK (PARASACRAL BLOCK)
Anatomy:
The sacral plexus arises from L4-S4, formed on the anterior surface of the piriformis muscle. Terminal branches: sciatic nerve, posterior femoral cutaneous nerve (PFCN), superior/inferior gluteal nerves, pudendal nerve.
The parasacral block is the only peripheral block that reliably anesthetizes ALL terminal branches of the sacral plexus, including the PFCN. (Morgan & Mikhail)
Indications:
- Combined with lumbar plexus block for complete lower limb anaesthesia (hip disarticulation, extensive thigh surgery)
- Perineal surgeries
- When PFCN coverage is needed
Technique:
- Patient lateral decubitus, operative side up
- Draw a vertical line from PSIS to ischial tuberosity
- Mark a point 6 cm inferior to PSIS along this line
- Insert long stimulating needle perpendicular to skin (parasagittal orientation)
- Advance until motor response in leg or foot is elicited (usually at ~7 cm depth)
- Inject 15-20 mL local anaesthetic
- Caution: Pelvic viscera are at risk at this depth
Combined Lumbosacral Block: Coverage Summary
| Block Component | Nerves Blocked | Coverage |
|---|---|---|
| Posterior lumbar plexus | Femoral, LFCN, Obturator, genitofemoral | Anterior + medial thigh, hip |
| Parasacral / sciatic | Sciatic (tibial + common peroneal), PFCN | Posterior thigh, entire leg below knee |
| Combined | All major lower limb nerves | Complete lower limb (except perineum) |
QUICK COMPARISON TABLE
| Feature | 3-in-1 Block | PENG Block | Lumbar Plexus Block |
|---|---|---|---|
| Target | Femoral, LFCN, Obturator (main trunks) | Articular branches of femoral/obturator/AON | Lumbar plexus (L1-L4) within psoas |
| Approach | Anterior (inguinal) | Anterior (inguinal crease) | Posterior (paravertebral) |
| Motor block | Yes (quadriceps) | No (motor sparing) | Yes |
| Volume | 25-30 mL | 20 mL | 20-30 mL |
| US needed | Helpful, not mandatory | Mandatory | Strongly recommended |
| Key complication | Quadriceps weakness/fall risk | Haematoma, intramuscular injection | Retroperitoneal haematoma, epidural spread |
| Evidence | Strong (RCTs) | Emerging | Strong |
VIVA QUESTIONS - MD ANAESTHESIA
3-in-1 Block
Q1. What is the anatomical basis for the 3-in-1 block?
A: The femoral nerve sheath is continuous with the fascia iliaca compartment, which also contains the LFCN and obturator nerves more proximally. A large volume with distal compression spreads proximally within this compartment, blocking all three nerves from a single injection point.
Q2. Why does the obturator nerve frequently escape block in a 3-in-1 technique?
A: The obturator nerve exits the psoas medially at the pelvic brim and enters the obturator canal, which is anatomically distant from the inguinal injection site. The fascial continuity is inconsistent, and the obturator nerve lies deepest and most medially - spread rarely reaches it reliably. Failure rates for obturator block with 3-in-1 technique approach 50%.
Q3. What is the NAVEL mnemonic and how does it relate to femoral nerve block?
A: NAVEL = Nerve (femoral), Artery (femoral), Vein (femoral), Empty space, Lymphatics - from lateral to medial in the femoral triangle. The femoral nerve is LATERAL to the femoral artery; the injection point is 1-2 cm lateral to the pulsating femoral artery.
Q4. What is the volume of local anaesthetic for a 3-in-1 block vs a simple femoral nerve block?
A: Femoral nerve block alone = 20 mL; 3-in-1 block = 25-30 mL. The additional volume and distal pressure are essential to achieve proximal spread.
Q5. What is the key modification in technique compared to a simple femoral nerve block?
A: Application of firm digital pressure distal to the injection site immediately after injection, to force the local anaesthetic to track proximally rather than distally.
Q6. Which patients benefit most from a 3-in-1 block in the ED?
A: Elderly patients with hip fractures (NOF fractures) and those with respiratory compromise, COPD, or opioid intolerance - the block provides excellent analgesia without opioid-related respiratory depression or sedation.
PENG Block
Q7. Who described the PENG block and in which year?
A: Girón-Arango et al., described in 2018 in Regional Anesthesia and Pain Medicine.
Q8. What nerves does the PENG block target, and why is it motor sparing?
A: It targets only the articular branches of the femoral nerve, obturator nerve, and accessory obturator nerve as they innervate the anterior hip joint capsule. Because it does NOT block the main femoral nerve trunk, the quadriceps motor function is preserved.
Q9. Describe the key US landmarks for a PENG block.
A: (1) Anterior inferior iliac spine (AIIS) - lateral hyperechoic bony prominence; (2) Iliopubic eminence (IPE) - medial bony landmark; (3) Psoas tendon (PT) - oval hyperechoic structure between AIIS and IPE; (4) Femoral artery (FA) - anechoic, pulsatile, medial. The needle targets the plane between the PT and the pubic ramus.
Q10. What is the correct needle direction for the PENG block?
A: In-plane, from lateral to medial, until the needle tip contacts the pubic ramus lateral to the psoas tendon.
Q11. What volume and drug are used for a PENG block?
A: 20 mL of ropivacaine 0.2-0.5% (3 mg/kg in children, up to 20 mL) or bupivacaine 0.25-0.5%.
Q12. What is the clinical significance of the PENG block over the fascia iliaca block for hip fractures?
A: The PENG block is motor sparing (preserves quadriceps function), reducing fall risk in elderly post-op patients. It also targets specifically the articular branches responsible for hip joint pain, making it more targeted. However, its evidence base (primarily case series and small RCTs) is less robust than the fascia iliaca block.
Q13. What are the limitations of the PENG block?
A: (1) Does not reliably cover trochanteric branches (superior gluteal nerve), so posterior hip pain after arthroplasty may be inadequate; (2) Evidence is still emerging; (3) Requires US skill; (4) Cannot provide complete hip anaesthesia alone - supplement needed for posterior capsule/trochanteric pain.
Lumbosacral Block
Q14. What constitutes a "complete lower limb block"?
A: Posterior lumbar plexus block (blocks femoral, LFCN, obturator nerves) + sciatic nerve block OR parasacral block. This covers essentially all motor and sensory innervation of the lower limb except the perineum (pudendal nerve).
Q15. Why does the posterior lumbar plexus block have the highest complication rate among peripheral nerve blocks?
A: Because the psoas muscle lies in close proximity to the aorta, inferior vena cava, kidneys, renal vessels, and the epidural/intrathecal space. The needle is deep (8-12 cm), increasing risk of vascular puncture, retroperitoneal haematoma, inadvertent epidural/intrathecal injection, and renal injury.
Q16. What is the "trident sign" on ultrasound for lumbar plexus block?
A: The acoustic shadows cast by the transverse processes of L2, L3, and L4 on a parasagittal US view resemble the three prongs of a trident. The psoas muscle lies between these shadows, and the lumbar plexus appears as a hyperechoic density within the posterior psoas.
Q17. What is the endpoint of nerve stimulation for a posterior lumbar plexus block?
A: Quadriceps contraction (patella "kick") - indicating proximity to the femoral nerve component of the lumbar plexus within the psoas compartment.
Q18. Why is the posterior lumbar plexus block contraindicated in anticoagulated patients?
A: Because a retroperitoneal haematoma is a serious complication, and unlike a femoral haematoma, it cannot be detected or compressed from outside. It can accumulate silently and cause haemodynamic compromise or femoral nerve compression.
Q19. What is the parasacral block, and what makes it unique?
A: The parasacral block (also called the true sacral plexus block) blocks all terminal branches of the sacral plexus (L4-S4), including the sciatic nerve AND the posterior femoral cutaneous nerve - which sciatic nerve blocks from subgluteal or popliteal approaches may miss. It is the only peripheral block that reliably blocks the PFCN.
Q20. What is the injection depth for the parasacral block, and what is the key risk?
A: Approximately 7 cm from the skin surface, 6 cm below the PSIS on a line from PSIS to ischial tuberosity. The key risk is injury to pelvic viscera (rectum, bladder, pelvic vessels) given the depth and proximity to the pelvis.
Q21. Describe the Chayen landmark for posterior lumbar plexus block.
A: The injection point is at the intersection of (1) the intercristal line (connecting both iliac crests, corresponding to L4) and (2) a parasagittal line drawn through the PSIS. The needle enters at the junction of the lateral and middle thirds between the midline and PSIS parasagittal line.
Q22. What is the maximum safe volume for a lumbar plexus block and why?
A: 20-30 mL. Volumes exceeding 20 mL increase the risk of bilateral epidural spread and contralateral limb involvement, as the local anaesthetic can track along the psoas fascia toward the epidural space.
Integrated / High-Order Questions
Q23. A 78-year-old with NOF fracture and COPD needs pre-operative analgesia. Compare 3-in-1 block, fascia iliaca block, and PENG block.
A: All three are acceptable. Fascia iliaca block (suprainguinal) has the best evidence for hip fracture analgesia. 3-in-1 block is similar but less reliable for obturator coverage; volume-dependent. PENG block is ideal if early mobilisation is planned (motor sparing), though evidence is emerging. In an anticoagulated patient, PENG or fascia iliaca (anterior approaches) are preferred over posterior lumbar plexus block (retroperitoneal risk). Given COPD, all are preferable to systemic opioids.
Q24. Why might the PENG block fail to provide complete analgesia after total hip arthroplasty?
A: The PENG block covers only the anterior hip capsule (articular branches of femoral/obturator nerves). The posterior capsule is innervated by the superior gluteal nerve and branches from the sciatic nerve. Additionally, trochanteric pain (greater trochanter) and femoral shaft pain are not covered. A supplementary block or infiltration is often needed.
Q25. What are the differences between the 3-in-1 block and the fascia iliaca compartment block (FICB)?
A: Both target femoral and LFCN via the fascia iliaca compartment. The FICB is injected more laterally (lateral to femoral nerve, 2/3 of the way from pubic tubercle to ASIS), relying entirely on diffusion. The 3-in-1 block injects adjacent to the femoral nerve laterally with distal compression. The FICB more reliably blocks the LFCN but neither reliably blocks the obturator nerve.
Sources: Roberts and Hedges' Clinical Procedures in Emergency Medicine; Morgan and Mikhail's Clinical Anesthesiology, 7e; Miller's Anesthesia, 10e; Barash, Cullen and Stoelting's Clinical Anesthesia, 9e
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