Overview of Lumbar Plexus Block
The idea of local anesthesia that can numb the entire lower back nerves, known as a lumbar plexus block (LPB), has been around for nearly 50 years. It was first used in a technique described by Winnie and his team in 1973, which they referred to as the “3 in 1 technique”. They believed that injecting a large amount of anesthesia into the sheath covering the femoral nerve could create a numbing effect on other connected nerves including the obturator, lateral femoral cutaneous and other nerves in the lumbar plexus. However, it was later discovered that this method only numbed the femoral and lateral femoral cutaneous nerves.
In 1976, another procedure was proposed by Chayen and his team named the “posterior lumbar plexus block,” also known as “psoas compartment block.” This method was found to be more effective in numbing all the nerves in the lumbar plexus with a single injection. It was shown to effectively numb the femoral, lateral femoral cutaneous, and importantly also the obturator nerve. Today, the term “lumbar plexus block” is usually associated with the posterior method, not the original inguinal femoral nerve block.
Since the introduction of the posterior lumbar plexus block, several variations of the technique have been introduced. Most just have minor changes in the needle insertion point or the particular level of the lower back where the procedure is done. The most significant change has been in determining when the numbness has been achieved. Initially, the procedure relied on a “loss of resistance” but then moved towards the use of a nerve stimulator (typically looking for a muscle twitch in the thigh). Nowadays, ultrasound-guided techniques are commonly used. However, currently, there is no decisive evidence to suggest that any one ultrasound-guided technique is better than the others.
Anatomy and Physiology of Lumbar Plexus Block
The lumbar plexus is a network of nerves located in a large muscle in your back, the psoas muscle. This network is formed by nerve roots from the four vertebrae in your lower back, known as the lumbar vertebrae L1 to L4. In some people, it also includes a nerve root from the last thoracic vertebra, T12. There are quite a few individuals, between 20% to 40%, who have some variations in how this network forms. However, it’s not clear whether these differences have any practical implications.
The psoas muscle, where the lumbar plexus resides, has two main portions: an anterior and posterior portion. These portions are divided by a sheath-like structure, forming a space where the nerve roots come together to form the lumbar plexus. This network of nerves then goes in different directions, each penetrating the psoas muscle and branching into different areas.
The main branches of the lumbar plexus include the Iliohypogastric nerve, the Ilioinguinal nerve, and the Genitofemoral nerve. The Iliohypogastric and Ilioinguinal nerves are formed by L1, playing roles in different areas like the muscles of the abdomen. The Genitofemoral nerve, principally formed by L1 and L2, is responsible for enervating several areas, including the skin of specific areas of the leg, and some muscles of the male reproductive system.
There are also the Lateral femoral cutaneous nerve, the Femoral nerve, and the Obturator nerve. The Lateral femoral cutaneous nerve provides sensation to the skin of the thigh, the Femoral nerve plays a crucial role in moving the thighs and provides sensations to the knee and part of the leg, and the Obturator nerve is involved in movements of the inner thigh muscles and sensations to the hip and knee joints.
The lumbar plexus takes a triangular shape and spreads according to the distribution of the nerves. If a blockage occurs in the psoas muscle, it often influences the internal plane and spreads to the lumbar nerve roots. The depth from the skin to the lumbar plexus is around 9 to 10 cm and slightly deeper in males. Nevertheless, inserting needles too deep into this area might increase the risk of injury.
Why do People Need Lumbar Plexus Block
The lumbar plexus block (LPB) is a type of medical procedure that helps in managing pain during and after surgery. They’re particularly useful if you’re undergoing surgeries involving the hip or thigh. Let’s break down more technical terms: a ‘block’ is a procedure where a medication is injected at a specific site to numb the area and manage pain; the ‘lumbar plexus’ is a network of nerves in the lower back region.
You might get an LPB if you’re undergoing surgical procedures like hip replacement, knee replacement, hip arthroscopy, or treatments for certain fractures in the hip or thigh. This procedure is also useful in managing long-term pain conditions like Shingles (Herpes zoster).
It’s worth noting, however, that for a hip replacement surgery, an LPB alone might not be enough to numb the entire area. This is due to the fact that certain parts of the hip are regulated by different nerves – the sacral plexus and sciatic nerve. Therefore, in some cases, another procedure called a ‘sciatic nerve block’ might be combined with the LPB.
When a Person Should Avoid Lumbar Plexus Block
There are some situations where performing a lumbar plexus block, a type of regional pain-block technique, might not be recommended. These include:
– If the patient does not want the procedure (patient refusal)
– If the patient is allergic to the medications used to numb the area (local anesthetics)
– If there is an ongoing infection at the intended site of the procedure
– If the patient is on strong blood thinners with a measure known as INR above 1.5, or hasn’t stopped using the blood thinners long enough prior to the procedure (this can increase the risk of bleeding).
Furthermore, there are situations where a different procedure might be considered instead, these include:
– If the patient has a device that delivers pain relief substances into the spinal fluid (intrathecal pump) or an electrical device to manage pain (spinal cord stimulator)
– If the patient has a significant abnormal curvature or deformation of the lower spine (major lumbar spine deformity)
– If the patient has previously undergone major back surgery involving inserted devices, or spinal fusion
– If the patient already has some form of nerve or sensory issues (preexisting neurological deficit).
Equipment used for Lumbar Plexus Block
Neurostimulation Technique
This technique uses a specialized needle with a protective covering to stimulate the nerves. The needle is typically 10 cm long. (Please note that a 15 cm needle is rarely required.)
It leverages a device known as a peripheral nerve block stimulator along with a surface electrode.
For numbing the skin, a 23 to 25-gauge needle – that’s quite a small, thin needle – is used.
In some scenarios, an 8 to 10 cm 25 gauge spinal needle is also required.
The doctor will then apply 20 mL of local anesthetic – a medication that numbs the area.
They’ll then use a pack of gauze that measures 4-inches x 4-inches to apply pressure and stop any bleeding after the procedure.
A solution containing Chlorhexidine gluconate is used to disinfect your skin before the procedure.
The doctor will also wear sterile gloves for infection prevention, and they’ll use a marking pen for precise mark-ups.
Ultrasound-guided Technique
In this technique, a curved probe called a transducer is used. This probe produces low-frequency waves between 5 to 10 Hz to capture images.
Just like in the neurostimulation technique, a 23 to 25-gauge needle is used for numbing the skin.
Following that, the doctor would apply 20 mL of a local anesthetic to numb the area.
A pack of gauze measuring 4-inches x 4-inches is used to control bleeding.
Similarly, the skin is disinfected using a Chlorhexidine gluconate solution.
Of course, the doctor wears sterile gloves, and markings are made using a pen, for precision.
Who is needed to perform Lumbar Plexus Block?
A lumbar plexus block is a type of anesthesia that numbs the lower part of your body. It’s a complicated procedure and should only be performed by doctors who have received special training in this area. Nurses with training in this area also help out during the procedure. They work with the doctor to provide the anesthesia and also help to make sure the patient is relaxed and comfortable.
Preparing for Lumbar Plexus Block
Before any procedure that involves anesthesia, it’s important for the doctor to carry out a comprehensive health check-up. They’ll study your medical history, do a physical examination, check your airway, and review tests you might have taken. Certain aspects are specially important – if you are allergic to anything, if you have neurological conditions, bleeding disorders, or if you generally suffer from chronic pain. The doctors will also note down any current medications you are on, specially pain relievers and blood thinners.
The doctor will also explain to you about the Lumbar Plexus Block – this is a procedure that helps in managing pain after leg and hip surgeries. They would give you details about what this procedure means for you, its advantages, and potential risks. They’ll take your consent to go ahead with the procedure after you understand all aspects about it. Like all procedures, the Lumbar Plexus Block is done in a fully equipped setting, with constant monitoring, oxygen support, suction capabilities, and emergency equipment for patient safety.
How is Lumbar Plexus Block performed
Sometimes, doctors use a technique called “neurostimulation” to locate a nerve called the “femoral nerve” which is inside an area of the body called the “psoas”. This nerve is important because it controls the “quadriceps muscle” in your thigh. The doctor uses a special tool to produce a small electrical current, which causes your quadriceps muscle to twitch. This helps the doctor to identify exactly where the femoral nerve is. Although there are several ways to do this, we’ll describe one common method.
Firstly, you’ll be monitored in the standard way recommended by the American Society of Anesthesiologists. You’ll lie on your side with the side being operated on facing upwards. Your knee on that side will be bent at a right angle and your hip slightly bent too. The doctor marks a point on your back that is 4-5 centimeters to the side of the middle of your back and level with the top part of your hip bone known as the iliac crest. The area is cleaned and sterile towels are placed around it. A “safety time-out” is performed where the patient, nurse, and doctor all confirm the patient’s identity and the procedure to be followed.
Because this procedure might be uncomfortable, you will likely be given a mild sedative to help you relax. A local anaesthetic (usually lidocaine) is injected at the chosen site to numb the area. The doctor will then introduce a thin needle, trying to locate a small bony feature of your spine called the “transverse process”. If the doctor can’t find the transverse process immediately, they will adjust the angle of the needle slightly until they can locate it.
Once the transverse process has been located, a device called a “neurostimulator” is used. This device generates an electrical current that is passed through the needle and an EKG pad on your skin. The needle is placed alongside the first one and directed towards the transverse process. The neurostimulator is used to produce a twitch in your quadriceps muscle, which lets the doctor know the needle is in the right place. The anaesthetic is then injected slowly and carefully.
Sometimes, a tube called a “catheter” is left in the area for a continuous supply of anaesthetic. This helps to provide excellent pain relief but must be done carefully to avoid the catheter being placed incorrectly. The amount of anaesthetic can be adjusted depending on how well your pain is controlled. If you start to experience a “foot drop” (a weakness that causes you to drag the toes of one foot) it could be due to a surgical complication and should be addressed urgently. An ultrasound scanning technique can also be used, but that goes beyond the scope of this explanation.
Possible Complications of Lumbar Plexus Block
Problems that might arise from a procedure called a lumbar plexus block – which is done to block pain in certain areas – are quite rare. Sometimes, the medicine used to numb the area might spread to the space around your spinal cord called the epidural space. You might feel weakness on both sides of your body, have low blood pressure, or face problems with urination. But at the University of Pittsburgh, we’ve found that these symptoms are extremely uncommon. Certain techniques, like inserting the needle closer to the middle of your lower back and towards your head (the L3 area), might raise the chance of this happening.
More rare side effects include accidental injection into the spinal cord and anesthesia affecting your spinal cord. As these don’t happen often, we don’t know exactly how common they are. Reviewing different cases, there were only 5 major problems out of 394 patients that had lumbar plexus block. However, at the University of Pittsburgh, we’ve performed thousands of these blocks in the last 20 years and have seen almost no complications, and only one instance of a catheter being accidentally placed into the spinal sac.
A kidney injury such as a subcapsular hematoma, which is like a bruise on the kidney, is also a very rare side effect. This side effect might be more likely if the injection is done higher up in the lower back (at the L3 level). That’s why we generally aim for an area on the lower back that lines up with the top of your hip bones, as it guides us to inject around the L4 or L5 area of your spine. To prevent this kind of injury, we also make sure not to insert the needle too deep. Be aware that there’s also a small chance that a large amount of the numbing medicine could get into your blood quickly or that too much of it is used. The response to this would be to immediately give you a treatment to limit the effects of the medicine.
Very serious side effects, like a psoas compartment hematoma, which is a buildup of blood in a space in your body, or other injuries to blood vessels near your lower back, can happen but are very, very rare. These complications might cause more concern if it’s hard to put pressure on and check the bleeding site. Patients who take anticoagulants, which are medicines that help prevent blood clots, or patients who might have problems with blood clotting may not be good candidates for this procedure.
A lot of patients ask about the chance of a nerve injury. Thankfully, this is also a very rare complication. Long-term nerve injuries only happen in about 2 to 4 out of every 10,000 nerve blocks. Specifically, the risk of nerve injury from a lumbar plexus block might be as low as 0.1%. If a low amount of electric current is required to make a muscle twitch, it might show a higher chance for nerve damage. If this occurs, the needle should be pulled back a bit to increase the required current.
What Else Should I Know About Lumbar Plexus Block?
A lumbar plexus block is a specialized way to numb the lower body, often used when performing surgeries on the lower limbs. For many years, it has been effectively used and proven to be safe, especially in hospitals where this method is commonly used.
From our experience, using a lumbar plexus block for pain management after lower limb surgery can be very beneficial. It can help reduce the amount of pain medication needed, make the patient feel more comfortable, and help the patient start walking and doing physical therapy sooner after surgery. It can be especially useful when recovering from hip surgery.
In order to use this method safely and effectively, it’s important for anesthesia doctors and pain specialists to understand the anatomy of the lumbar plexus, which is a network of nerves in the lower back, and the different ways to perform the block. They should also know when this method is appropriate to use and when it’s not.
