Psoas Compartment Block - Anatomy, Indications, Contraindications and Complications

Introduction

A Psoas Compartment Block (PCB) is a local anesthesia technique used to numb specific nerves in the lower back. These nerves are part of the lumbar plexus, transmitting sensation from the lower body. During the block, Anesthesia is injected into a precise location between the quadratus lumborum and the psoas major muscles. The primary lumbar plexus nerves, including the femoral, lateral femoral cutaneous, and obturator nerves, become numb, relieving discomfort.

What Is Psoas Compartment Block?

A Psoas Compartment Block (PCB) is anesthesia that numbs specific lower back nerves. It targets the femoral, lateral femoral cutaneous, and obturator nerves within the psoas major muscle. The block involves injecting anesthesia between two muscles, the posterior lumbar plexus block.

There are two approaches to blocking the nerves: one from the front (Winnie technique) and one from the back (psoas compartment block). The psoas compartment block has shown better success in numbing the obturator nerve, improving pain relief for the hip and knee areas.

Anatomy:

A lumbar plexus is a group of nerves in the lower back that provides sensation and movement to the abdomen, thigh, and genital area. The primary nerves include:

• The femoral nerve (front thigh).

• Obturator nerve (adductors and hip/knee sensation).

• Iliohypogastric/ilioinguinal nerves (abdomen/genitals).

• Genitofemoral nerve (genital region).

These nerves run within the psoas major muscle.A psoas compartment block is a procedure that targets the lumbar plexus for pain relief. It involves injecting anesthesia under ultrasound guidance to numb these nerves. The block is safe and effective for managing certain lower back and leg pains.

What Are the Indications for Psoas Compartment Block?

• The Psoas Compartment Block (PCB) is used for anesthesia and pain relief during hip or knee surgeries.

• Anesthesia is injected close to the nerves in the lower back that regulate leg sensation and movement.

• When used in conjunction with a sciatic nerve block, the PCB effectively numbs the entire lower leg, which is especially useful for hip surgeries and cases where general anesthesia is not ideal.

• It can be combined with IV opioids or other types of nerve blocks to reduce postoperative pain.

• Pediatric children undergoing hip or femoral operations benefit from the PCB as well.

• Mainly used for analgesia (pain relief) after significant hip or knee surgeries, providing excellent pain relief for up to 48 hours after the operation.

• It lessens the need for painkillers after surgery.

• The block targets nerves in the lower back to numb the leg and improve patient comfort during and after surgery.

What Is the Procedure for Insertion of Psoas Compartment Block?

Equipment used for a psoas compartment block includes:

• A special ultrasound probe for imaging.

• Chlorhexidine for cleaning the skin.

• A small needle and numbing medication for numbing the skin.

• Sterile gloves and towels for a clean environment.

• A cover for the ultrasound probe.

• A stimulating catheter, a special needle, and a syringe for inserting a catheter (if needed).

• A neurostimulator to help locate the nerves.

• An insulated needle of a specific length.

• A local anesthetic medication.

• The patient is positioned on their side with the hip bent. The whole lower leg is exposed to observe muscle movement, mainly if the neurostimulator is used with ultrasound guidance or the loss of resistance technique.

Techniques used in insertion for psoas compartment block:

The block can be done using two different techniques:

Traditional Neurostimulation and Loss of Resistance Technique:

1. Lines are drawn on the skin to locate the L4-L5 level and the tips of the lumbar transverse processes.

2. After cleaning the region, numbing cream is given to the skin.

3. A needle is inserted near the transverse process and directed slightly up or down.

4. The lumbar plexus is located and stimulated to ensure correct needle placement.

5. An anesthetic medication is injected to numb the area.

Ultrasound-Guided Technique:

1. An ultrasound probe is used to visualize the spine and surrounding structures.

2. The probe is moved to locate the L4-L5 intervertebral space and the lumbar transverse process.

3. A needle is carefully inserted towards the lumbar plexus, guided by the ultrasound image.

4. The needle is checked to ensure it is in the right place using stimulation if needed.

5. The anesthetic medication is injected to provide pain relief.

6. The ultrasound-guided approach allows accurate needle placement with the help of real-time images. It also helps avoid accidental injection into the spinal canal, making the procedure safer.

7. Both techniques are effective in providing pain relief, and the choice between them depends on the preference of the medical team and the patient's condition.

Who Are Not Eligible for Psoas Compartment Block?

• Patient's opposition to the procedure or need to know its advantages and risks.

• Patients on blood thinners or with blood clotting disorders (coagulopathy) may not be suitable candidates due to the risk of bleeding.

• Local or systemic infections in the body can also be a contraindication for the block.

• Allergy to the local anesthetic used for the block.

• Patients with sepsis (a severe infection) may not be suitable for the block, mainly when a catheter is used for prolonged pain relief.

• Patients with fixed cardiac output or weak cardiac function should exercise caution because the block can harm the heart.

• Patients with significant coagulopathy may not be suitable for the block due to the risk of bleeding.

• Patients with severe lumbar spine deformity may have deformed anatomy, making the block difficult or dangerous.

How Is Psoas Block Given Continuously?

After hip or knee replacement procedures, a continuous Psoas Compartment Block (PCB) approach can help relieve pain. Patients report low pain levels during the first 48 hours after the operation. To perform a continuous block, a catheter is inserted near the nerves in the lower back and connected to a pump that continuously delivers a small amount of numbing medication.

The catheter must be positioned correctly because the intrathecal and epidural areas are close. It's essential to ensure the catheter is in the right place. The doctor checks for blood or cerebrospinal fluid before starting the medication. If needed, a small test dose is given first to verify the correct position of the catheter. An infusion of a local anesthetic is used to maintain pain relief over time. The doctor closely watches the patient to prevent any potential adverse effects, such as those that could impact both sides or modify blood pressure.

A continuous psoas compartment block involves inserting a small tube near the nerves in the lower back to relieve pain with medication after hip or knee surgeries. The doctor takes precautions to ensure the catheter is in the right place and adjusts the medication to manage pain effectively.

What Are the Undesirable Side Effects and Complications?

The Psoas Compartment Block (PCB) has some potential side effects and complications, including rare but serious ones. The most common side effect is the spread of the numbing medication to the surrounding areas, which can happen in about 3% to 27% of cases. This may cause additional numbness or affect other nerves.

Epidural diffusion is more likely to occur with specific insertion points and approaches. Using a larger volume of medication may also increase the risk of unwanted effects. High injection pressure during the block can lead to bilateral (both sides) numbness and increase the risk of affecting the spine.

Rare but severe complications include the unintentional injection of medication into blood vessels or the spinal canal. This can lead to severe problems like seizures or cardiac arrest. However, precautions like aspiration before injection and slow, careful administration can help reduce these risks.

Hemorrhagic consequences (bleeding) have been recorded occasionally, particularly in individuals using blood thinners. However, many people taking such drugs can undergo PCB without any problems.

Conclusion:

Ultrasound-guided psoas compartment block is a safe and effective pain relief technique for certain surgeries. It's an excellent alternative to other methods and can target specific nerves. However, serious complications are possible, so careful monitoring and injection are crucial. Its use is expected to increase, especially for postoperative pain relief after hip surgeries, even in patients on anticoagulants. Some patients can even receive this block at home with a portable infusion pump. It's a valuable technique, but caution is essential to avoid complications.