Overview of Sural Nerve Block
A sural nerve block is a type of local anesthetic often used for foot and ankle surgeries. The technique is chosen as an alternative or supplement to general anesthesia. The sural nerve is easily accessible as it is located just beneath the skin, near the ankle. This makes it relatively easy to administer anesthetic to it.
This particular method was first introduced by a doctor named McCutcheon in 1965. At that time, there was a 10% chance of the method not working as intended.
Another more advanced method is the ultrasound-guided sural nerve block. This technique uses an ultrasound to better locate the sural nerve. However, since the sural nerve is so small, it can be difficult to see, even with an ultrasound. Approaches that focus on the blood vessels might increase the chances of the block being successful.
A standard ankle block often involves numbing four major nerves in the ankle – the superficial peroneal, deep peroneal, saphenous, and tibial nerves. Whether to apply the sural nerve block as well depends on the surgical plan. However, it is often recommended to apply the sural nerve block no matter where the surgery is happening within the foot. This is because numbing the deep sensory nerve of the side of the foot and ankle (which is responsible for sensing vibrations) can help make patients more comfortable during the procedure.
Anatomy and Physiology of Sural Nerve Block
The sciatic nerve, located at the back of your leg, splits into two main nerves above the fold of your knee. These two nerves are called the tibial nerve and the common peroneal nerve. The tibial nerve continues down your leg, giving rise to the medial sural nerve and posterior tibial nerve. These nerves mainly control feeling in the back of your leg and the soles of your feet.
The medial sural nerve travels between the parts of your calf muscle, comes up to the surface about halfway down your leg, and continues to the side of your ankle under a band of tissue called the extensor retinaculum.
It’s worth noting that the sural nerve is purely sensory, meaning it helps you feel, but not move. Doctors can use an ultrasound to view this nerve, but can also block it using just knowledge of where it should be in the body. At the level of your ankle, deep-set nerves include the tibial and deep peroneal nerves, while close-to-the-surface or “superficial” nerves called include the superficial peroneal, sural, and saphenous nerves. All of these nerves stem from the sciatic nerve, except for the saphenous nerve, which is a sensory branch of the femoral nerve located in your thigh.
Why do People Need Sural Nerve Block
A sural nerve block is a method used to numb certain parts of the body for surgeries or to manage pain after an operation. Specifically, it is typically used for procedures involving the back and outer side of the calf or the top and outer side of the fifth toe (the little toe).
When a Person Should Avoid Sural Nerve Block
Some conditions could prevent a doctor from performing a sural nerve block. This procedure involves blocking the nerves in your leg to help control pain. But in certain cases, it can’t be done. Reasons might include:
If the patient doesn’t want the procedure, it can’t be done. Similarly, if a patient is allergic to the medications used to numb the area, the procedure can’t be performed. If there’s an infection at or near where the injection would be given, doing the procedure could potentially spread the infection. Similarly, if the patient has a widespread infection or cancer at the needle entry site, a sural nerve block is not the right option. Certain blood conditions, known as coagulopathy, could also prevent this procedure because they might make it hard to control bleeding.
Moreover, if a patient already has issues with feeling or movement in the area of the block, the procedure is generally not recommended. Caution is necessary for patients who are on blood-thinning medication. However, doctors consider certain parts of the leg, like the ankle and side, as safe to target because they can be easily compressed to control bleeding.
Equipment used for Sural Nerve Block
The tools your doctor will need include:
* Chlorhexidine gluconate or povidone-iodine. These are skin cleaning agents used before the procedure to prevent infection.
* An ultrasound probe which uses high-frequency sound waves to create images of body parts. This will be covered with a sterile cover and used with a type of liquid called gel.
* A local anesthetic, usually 1% lidocaine, will be used to numb the area on the surface of the skin where the procedure will be done.
* A regional block local anesthetic solution is used to numb a large area of your body. This helps manage the pain after surgery. It may include Bupivacaine (0.5%) or Ropivacaine (0.5%) for more extended pain relief or Lidocaine (2%) or Mepivacaine (1.5%) if the doctor wants the anesthetic to start working more quickly.
* A syringe (10-20 mL) with extension tubing. This is a small tube that will be used to inject the anesthetic.
* A short bevel block needle (2 inches, 22-gauge). This is a specific type of short, thin needle that will be used to inject the anesthetic.
Who is needed to perform Sural Nerve Block?
For this particular procedure, it’s best to have a specialist doctor known as an anesthesiologist, who has specific training in a type of pain relief called regional anesthesia. Furthermore, there are other valuable members of the healthcare team, like nurses who have been trained in sedation. They can really help during the procedure.
Preparing for Sural Nerve Block
Before starting a medical procedure, your doctor will explain what will happen and ask for your agreement to go ahead – this is known as ‘informed consent’. After you’ve agreed, the doctor will then have you lie in a certain way to make the side of your leg easy to reach.
Depending on your comfort level and your doctor’s decision, you might be given medication to help you relax during the procedure. To make sure everything remains clean and reduces any chances of infection, the doctor will apply a special disinfecting solution to the area where they’re going to work. This could be a 2% chlorhexidine gluconate or a povidone-iodine solution.
A sterile gel is then added to the ultrasound probe, a special device that uses sound waves to create a live picture of the inside of your body. This probe is covered with a clean, unused cover to keep everything sterile. This meticulous level of cleanliness is called ‘aseptic technique’, and it’s important to ensure no germs are introduced into your body.
How is Sural Nerve Block performed
The sural nerve block is a type of injection performed around the ankle region in order to numb pain. This procedure can be conducted using an ultrasound to guide the process. The doctor first identifies certain features on your ankle, including the back edge of the outside ankle bone and the Achilles tendon. The point where the injection will be given is marked. It is found next to the Achilles tendon and behind the outside bone of your ankle.
A device known as a high-frequency ultrasound probe (operating between 10 and 18 MHz) is then placed over this point. This helps the doctor see the lesser saphenous vein (a small vein in your leg). The doctor then uses an out-of-plane approach. In this method, they inject a local anesthetic, which is a drug that numbs a particular area of your body, typically around 5 mL. This anesthetic surrounds the lesser saphenous vein. Alternatively, they may use an in-plane technique, where the injection is administered from the back to the front direction towards the sural nerve—a nerve that runs near the veins in your legs.
Making the calf muscle tight or positioning the leg lower might be done to enlarge the aforementioned vein size, thereby making the sural nerve easier to spot.
While an ultrasound can decrease the total volume of the local anesthetic used and lessen potential risks of injecting the nerve or blood vessels, a traditional approach using manual identification (landmark-based technique) is also often used. In this, the doctor feels for the Achilles tendon and outer ankle bone. They then insert the needle at the uppermost edge of the outside ankle bone, beside the Achilles tendon, with the needle aiming towards the outside ankle bone. If a tingling sensation, known medically as paresthesia, is felt, the process of moving the needle forward stops, and a local anesthetic (typically 3 to 5 mL) is injected after confirming that it doesn’t withdraw. If no feeling of paresthesia is detected, the needle continues to advance until it touches the outside ankle bone, followed by an injection of a local anesthetic after the needle retreats.
Success of the procedure might be implied through anesthesia in the calf’s back, outside, and the outside of your fifth toe. Additionally, losing sympathetic tone – the balance between the body’s stress response and relaxation response, might also indicate success. This can be seen as changes in foot color and foot redness.
Possible Complications of Sural Nerve Block
Although it’s not very likely, there might be some side effects from an injection. These could include feeling pain when the injection is given, bleeding, getting an infection, or having allergic reactions. If the injection was accidentally given into a blood vessel, this could cause a reaction to the local anesthesia. If the needle tip accidentally hits certain areas around or within the nerve, it could cause nerve damage and a lot of pain.
What Else Should I Know About Sural Nerve Block?
The sural nerve, which feeds sensation to side and back of your calf and foot, doesn’t get a lot of attention in scientific research. This is probably because this nerve doesn’t play a major role in certain foot surgeries. But, according to a research study, when doing surgery on the inner half of the foot, bypassing the sural nerve seems to have no effect on patients’ comfort during surgery.
The technique to numb or “block” the sural nerve can be done in two ways: using an ultrasound for guidance or using traditional anatomical landmarks. A study comparing these two ways found that using ultrasound and referring to a vein called the lesser saphenous vein, created a more effective and longer-lasting block than the traditional way.
There are differences in opinion on how much local anesthetic, the medicine that numbs a specific area, is needed for a successful sural nerve block. Earlier, it was thought that 1 to 2 mL of anesthetic was sufficient. But now, most recommendations are for 5 to 7 mL. However, doctors are careful not to use more than 10 mL, as there could be a risk of blocking blood flow and causing a condition called compartment syndrome, which entails painful pressure build-up from internal bleeding or swelling of tissues.
