What is a nerve block?

Nerve block, also known as regional anaesthetic, is an injection of local anaesthetic by your anaesthetist to “block” the nerve or a group of nerves that supply the area of your body where your operation will be.

How is a nerve block used?

Nerve blocks for leg, foot and ankle surgery can be made to last up to 24 hours. The nerve block may be part of your general anaesthetic to give you pain relief after your operation.

Some operations can be done under nerve blocks alone. Sedation can be given with this to make you feel relaxed and comfortable.

Certain drugs or medical conditions may make blocks unsuitable for you. Your anaesthetist will discuss these with you on the day of your operation.

What nerves are blocked?

In the case of leg, foot and ankle surgery, the nerves run from the lower part of your back coming together in a


large nerve at the back of your leg, a smaller one at the front and a ring of several nerves around the foot. These nerves can be blocked at different sites from lower back (“lumbar plexus”) to hip region (“sciatic”) to behind the knee (“popliteal”) or in the ring around the ankle (“ankle block”) where they pass close to the skin. The best block for you will depend on the site of your operation and will be explained by your anaesthetist.

What are the benefits of having a nerve block?

These include:

• Better pain relief. You are less likely to need strong pain killers after your operation, avoiding their side effects like nausea or sleepiness and confusion.

• If your operation can be done under a block alone, you can avoid the risks and side effects of a general anaesthetic.

• You are more likely to go home on the same day after your operation if your pain is well-controlled after a block.


How are blocks performed?

You should prepare for your operation by following the instructions from pre-operative assessment clinic. This includes following the fasting advice.

The nerve block is usually performed in the anaesthetic room. Your heart rate, blood pressure and breathing will be monitored and a cannula (“a drip”) placed into a vein before the block. Most blocks are performed awake before your general anaesthetic.

Depending on where the block injection is, an assistant will help you to get into the correct position. This may involve turning over to lie on your front or side. Some blocks may be done when you are under general anaesthetic; your anaesthetist will discuss this with you on the day.

The skin will be cleaned and the area numbed before the injection. The nerves are located using an ultrasound machine or a very small machine that makes your leg muscles twitch. A very fine block needle is used to give the local anaesthetic to block the nerves.

For most patients, the injection is no more painful than having the cannula in your vein or bloods taken. Once the injection is done, your leg or foot may start to feel warm, tingly or numb but it can take 20 to 40 minutes for the block to work fully.

What are the risks and side effects of having a block?

Block injections are generally very safe but there are still risks to be aware of. Common side effects including bruising or discomfort around the injection site are usually short-lived.

These symptoms go away within 4 to 6 weeks in most cases (95%) and within a year in majority (99%). Swelling after the operation, or conditions such as diabetes can make nerve damage more likely.

What happens after the operation?

Your leg may be numb for between 4 to 24 hours after your block. It is likely that you will be going home with the foot/leg still numb.

Therefore, it is important to avoid injury by taking precautions whilst the block is still working.

• If you are assessed as needing a walking aid, use it as instructed by the physiotherapist or nurses.

• Do not drive for at least 48 hours and until your block has worn off completely. Your surgeon will give you instructions about when you can drive depending on the type of surgery.

• Take extra special care when walking if your foot dressing comes loose until the numbness has worn off to avoid cuts, burns or scalding.

• Do not put your blocked leg/foot near a radiator, stove or oven.
Other side effects are related to the spread of local anaesthetic around the injection site or the placement of the block needle. Bleeding may occur if a blood vessel is damaged but can usually be treated by putting pressure on the injection site.

More specific side effects to be aware of:

For injection of nerve behind your knee or further up your leg: Your leg will become numb and the power to move it is also affected. You will not be able to reliably balance without the assistance of crutches or a stick. The physiotherapists will assess your safety and provide you with an appropriate aid. For many of the operations for which the block is useful, you will not be weight-bearing (able to stand on the operated leg) for a period afterwards to help healing. A block should not compromise the speed of return to the normal mobilisation which aids recovery. These sensory and motor symptoms usually get better as the block wears off. In rare cases, weakness of the foot affecting your ability to walk and/or numbness can last for a prolonged period or be permanent. (See Nerve injury below).

Very rare: life-threatening reactions such as a fit or seizure in reaction to the local anaesthetic are very rare. These require emergency treatments. Your anaesthetist can discuss these with you if you wish to know more.

Nerve injury: nerves can be damaged during surgery, general anaesthetic or a block. It is estimated to happen between 1 in 700 to 1 in 5000 cases where a block is performed. There may be a long lasting numbness patch or tingling after the operation. Uncommonly, there may be weakness in one or more muscles and persistent pain.

What happens if a block is not done?

It is perfectly acceptable if you do not choose to have a block for your operation. Occasionally, the block may not work as well as planned. In some cases, it may not be a suitable option. Uncommon risks may affect people differently. If you have an occupation which could be adversely affected by occurrence of an uncommon risk it is important you consider all the options before you decide to include a block in your post operative pain relief plan.

Your anaesthetist and surgeon can discuss other options with you. These include local anaesthetic (but not a nerve block) injected by the surgeon around the operation site during the operation as well as different types of pain killers.

Pain killers after surgery

As the block wears off, you may feel pins and needles sensation in your leg.

It is important to begin taking regular pain killers as instructed so that they can start to work before the block wears off completely. You are advised to take your post operative painkillers before bed on the night of surgery and to continue to take them regularly. They are to give you enough pain relief to be able to move as instructed by the physiotherapist. Different people will need different amounts of pain killers to achieve this and the amount you require will reduce in the days following surgery.

This will help reduce the pain when the block has worn off.


For video information on blocks,
For more information on nerve damage:
For other patient information on anaesthetics
For local information See our preparing for surgery pages [link below]


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