Pericapsular Nerve Group Block

Anatomy and Physiology

The PENG block appears to be the suprainguinal version of the articular branches of the femoral nerve, which has the added benefit of blocking the accessory obturator nerve and the obturator nerve. The femoral nerve is the longest branch of the lumbar plexus, originating from the ventral rami of L2 to L4 spinal nerves. This nerve emerges from the lateral border of the psoas muscle to descend between the iliacus and psoas muscles. The nerve then divides into 2 major branches—the anterior and posterior branches, which provide motor innervation to the hip flexors and knee extensors, and sensory branches, which innervate the anteromedial part of the thigh and the medial sides of the leg and foot. The femoral nerve gives rise to a motor branch that innervates the iliac before passing under the inguinal ligament.

Articular branches at the hip joint originate at a higher level along the course of the nerve, explaining why the femoral or fascia iliaca compartment block remains insufficient for hip analgesia. The obturator nerve is formed from the lumbar plexus, specifically the L2, L3, and L4 anterior divisions. This nerve descends through the fibers of the psoas major, traveling posteriorly to the common iliac arteries and laterally along the pelvic wall. In the obturator canal, it divides into 2 branches—anterior and posterior branches. The anterior branch pierces the fascia lata to become the cutaneous branch of the obturator nerve, supplying the skin of the middle part of the medial thigh.

The accessory obturator nerve, present in 10% to 30% of patients, originates from the third and fourth lumbar nerves (derived from the L2 to L4 ventral rami) and often innervates the hip joint and adductor longus. The nerve innervates the medial capsule with sensory fibers.[9][10] An anatomic study by Short et al demonstrated that high branches of both the femoral and obturator nerves and the accessory obturator nerve provide innervation to the anterior hip capsule because the anterior hip capsule receives the major sensory innervation, whereas the posterior and inferior capsules have no sensory fibers.

The hip capsule is divided into 2 sections—anterior and posterior parts. The anterior portion has nociceptive fibers, whereas the posterior part contains mechanoreceptors.[11] The anatomical pathways of the femoral, obturator, and accessory obturator nerves, along with their relationship to the inferomedial acetabulum and the space between the anterior inferior iliac spine and iliopubic eminence, may indicate potential sites for regional analgesia. These findings suggest the deposition of local anesthetics in the fascial plane between the psoas muscle and the upper pubic branch contributes to anesthesia of these nerves, thereby enhancing analgesic coverage for hip surgery.[12]

Indications

The PENG block is a novel regional analgesia technique that can reduce pain following hip surgery and fractures, providing better analgesia compared to other peripheral blocks used in these procedures. The block is typically used to provide analgesia following injuries or surgeries of the hip or thigh, such as acetabular fractures, femoral neck or mid-shaft fractures, hip replacement, hip arthroscopy, and knee surgery. A recent report demonstrated effective surgical anesthesia with a PENG block for a medial thigh lesion.[13] Other studies described using the block in vascular operations, such as stripping to target several dermatomes.[14] The PENG block cannot be offered as the only anesthesia for hip surgery due to the innervation of the posteromedial hip capsule deriving from branches of the sacral plexus and sciatic nerve.[15]

Contraindications

The contraindications for PENG block include:

• Patient refusal
• Infection at the injection site
• Allergy to local anesthetics
• Systemic anticoagulation (international normalized ratio >1.5 or inadequate time since cessation of anticoagulant, according to the American Society of Regional Anesthesia and Pain Medicine guidelines)

Equipment

The PENG block is performed under ultrasound guidance and requires the following equipment (see Image. Standard Nerve Block Tray):

• Ultrasound guidance with a low-frequency curvilinear probe, sterile sleeve, and gel
• A 23- to 25-gauge needle for skin infiltration
• 20 mL of local anesthetic
• 80 mm B-bevel nerve block needle
• 1 pack of 4-inch × 4-inch gauze
• Chlorhexidine gluconate solution for skin asepsis
• Sterile gloves
• Marking pen

Personnel

Only trained clinicians should perform the PENG block, a regional anesthesia technique. Sedation is recommended for patient comfort. A nurse trained in regional anesthesia can assist with the block and administer sedation to the patient.

Preparation

A preoperative evaluation must be carried out according to World Health Organization guidelines before administering the regional nerve block. This evaluation should include medical history, physical examination, airway assessment, and analysis of preoperative tests. The current treatment should also be noted, including using analgesics and anticoagulants to minimize bleeding risk. The patient should be informed about the risks and benefits of the PENG block, which involves a detailed description of the procedure to obtain informed consent. Finally, this procedure should be performed in a clinical center with appropriate monitoring equipment.

Technique or Treatment

The PENG block is performed exclusively under ultrasound guidance using a low-frequency probe. Two main techniques are distinguished:

Out-of-Plane Technique

After adequate premedication, the patient is positioned supine and hip extended. After sterile preparation, 3 mL of 2% lidocaine is injected at the insertion site using a hyperechoic needle (designed for regional anesthesia) guided by ultrasound using a low-frequency probe. At the anterior superior iliac spine level, the probe is placed parallel to the inguinal fold, and scanning is performed with a gradual movement of the probe head. When the lower anterior inferior iliac spine is observed, the probe is rotated slightly median until a continuous hyperechoic shadow of the upper pubic ramus is visible. This maneuver allows us to identify the psoas muscle with a prominent tendon above the pubic ramus. The target is located in the plane between these 2 structures. The pubic ramus should be aligned in the center of the image to target the pubic ramus just inside the anterior inferior iliac spine. A 100-mm nerve block needle can be introduced, and 20 mL of local anesthetic is administered using the ultrasound-guided out-of-plane technique.[16]

In-Plane Technique

With the patient positioned supine, a low-frequency curvilinear ultrasound probe is placed in a transverse plane over the anterior superior iliac spine. Once the anterior superior iliac spine is identified, the transducer is aligned with the pubic ramus and rotated approximately 45° parallel to the inguinal crease. The transducer is then slid medially along this axis until the anterior inferior iliac spine, iliopubic eminence, and psoas tendon are visualized as anatomic landmarks. Sliding the probe distally or gently tilting it caudally exposes the head of the femur.

After returning to the initial starting position, the femoral artery and iliopubic eminence are visualized. Using an in-plane technique, a 100-mm nerve block needle is inserted from lateral to medial using a skin wheal at a 30° to 45° angle toward the ultrasound beam. The needle is advanced in the plane between the psoas tendon anteriorly and the pubic ramus posteriorly. Approximately 15 to 20 mL of a long-lasting local anesthetic, for example, 0.5% ropivacaine, is deposited in this space, ensuring the psoas tendon is lifted. Care should be taken to avoid puncturing the psoas tendon (see Image. Relevant Sonoanatomy for PENG Block).[12]

Complications

Regional anesthesia techniques require a thorough knowledge of the potential complications associated with each procedure. The complications related to peripheral nerve blocks include infection, bleeding, nerve damage, and local anesthetic toxicity. Systemic toxicity of local anesthetics is related to either intravascular injection or an excessive dose beyond the toxic dose limits. Treatment in this emergency includes the immediate administration of intravenous intralipid and hemodynamic supportive measures.

The Second American Society of Regional Anesthesia and Pain Medicine Practice Advisory on Neurologic Complications Associated With Regional Anesthesia and Pain Medicine sheds particular light on the complications associated with mechanical, ischemic, or neurotoxic lesions of the peripheral nervous system. As the PENG block is a new regional anesthesia technique, epidemiological data on specific complications are limited. However, with ultrasound-guided administration, the risk of femoral nerve or vascular damage (with hematoma) is minimal. Long-term peripheral nerve damage incidence represents 2 to 4 cases per 10,000 peripheral nerve blocks.[17]

Clinical Significance

The PENG block is a new and alternative regional analgesic technique for hip surgery. This block can be combined with other regional anesthesia techniques to effectively target the anterior hip capsule by blocking the articular branches of the femoral nerve and accessory obturator nerve. The PENG block can be an alternative to the femoral nerve or lumbar plexus block to prevent quadriceps weakness and facilitate early postoperative revalidation. The use of multimodal analgesia combined with regional analgesia, including nerve blocks and periarticular infiltration techniques, is associated with the decreased postoperative use of opioids and improved by reducing morbidity and length of hospital stay. To evaluate the efficacy of PENG block for hip surgery, a review was carried out using the Joanna Briggs Institute framework; adult and pediatric studies were included, and database searches identified 345 articles. The author concluded that current evidence of using PENG block for hip surgery or hip pain is limited to only case reports and case series. Double-blind, randomized controlled trials are needed to better understand the analgesic efficacy and adverse effects of the PENG block.[8] 

In a retrospective review that compares the analgesic benefit of adding the PENG block to local infiltration anesthetic after primary total hip arthroplasty, Kiran Mysore MD et al identified 123 patients who met the inclusion criteria; 47 received and 76 did not receive the PENG block. Results showed that the PENG block was associated with reduced 24-hour hydromorphone consumption.[18] Following Girón et al's publication, which was the first author to discover this block, Ueshima and Otake documented their clinical experience using the PENG technique in 4 patients to manage perioperative pain after reduction of hip dislocation and replacement. They reported that the PENG block technique effectively covered both the femoral and obturator nerves, making it a valuable analgesic option for hip surgery.[19][20]

Enhancing Healthcare Team Outcomes

Effective acute pain management following hip surgery necessitates the collaborative efforts of interprofessional and multidisciplinary teams throughout the preoperative, intraoperative, and postoperative phases. The PENG block, a specialized regional anesthesia technique, is typically performed by an anesthesiologist trained in this area, with assistance from a nurse. Clear communication among team members is vital to ensure optimal patient care. Before the procedure, a timeout should be conducted to verify the patient's identity, confirm the procedure, and ensure that the surgical site is accurately marked. Maintaining a sterile technique throughout the process is crucial, as is preparedness for any potential emergencies. All team members should be well-acquainted with the possible complications that can arise during the procedure and be ready to respond effectively.

Postoperatively, training nursing and surgical staff in pain assessment methods, such as Visual Analog Scales (VAS) and Numeric Rating Scales (NRS), and in effective pain management strategies is essential. This training plays a critical role in the patient's recovery process, ensuring that pain is managed effectively and that any adjustments to the pain management plan can be made promptly. An interprofessional approach enhances the overall quality of care, promoting patient comfort and satisfaction while reducing the risk of complications related to inadequate pain management.

Nursing, Allied Health, and Interprofessional Team Interventions

A nursing team qualified for the operating room and postoperative pain management is necessary and required to perform regional anesthetic procedures safely.

Nursing, Allied Health, and Interprofessional Team Monitoring

The PENG block must be performed like any regional anesthetic procedure. The ideal location is within a hospital center equipped with cardiovascular and respiratory monitoring equipment to ensure optimal monitoring of vital parameters and proper resuscitation.