A guide for patients on local anaesthetic

What are local anaesthetics?

Local anaesthetics are a class of drug that act locally on the nerves in our bodies by blocking the sensation of pain.

Is local anaesthetic safe?

Local anaesthetics are very safe; the risk of an adverse reaction is very low.

Complications of local anaesthetic include:

• allergic reaction to the anaesthetic (less than one person per 10,000)
• toxic reaction to the drug (less than one person per 2,000 across all injections)
• irritation or damage to the nerves at the injection sites (very rare)
• bruising around the injection site (one person in 20)

For foot and ankle surgery, many different types of blocks/injections can be given. This is dependent on the type of surgery you are having done. They include:

Ring/toe blocks

These involve an injection to either side of the toe around its base. This type of injection only numbs the toe. It will last about nine hours.

Ankle block

With an ankle block, four to five injections are given around the level of the ankle. The reason for the increased number of injections is because of the number of nerves entering the foot. This block lasts about nine hours.

Popliteal block 

This consists of one injection behind the back of the knee and one at the front of the ankle. A popliteal block can last between 24 and 72 hours. In some cases, the block can last less than 24 hours.

A special needle is used that sends out a small electrical signal to the nerve. The signal makes your foot twitch; patients liken the sensation to someone tapping the sole of their foot. The electrical impulse helps the podiatric surgeon in finding the nerve. The experience is generally not painful, but can feel a bit peculiar, especially when the foot begins to twitch. When the anaesthetic is injected a cold sensation can be felt down the leg.

The whole experience lasts about 10 minutes and requires you to be on your stomach and keep as still as possible. Moving around can prolong the injection time.

Once the injection has finished, your leg (beneath the knee), will become numb and you will not be able to move your foot. Once this has happened, your leg will not be able to support your body. If you need to get up for whatever reason you will need help. This will be the case until the block wears off.

The injection at the front of the ankle is used to block a nerve, which is inaccessible from the back of the leg. This is a traditional injection and involves no electrical impulse.

Following the popliteal block, an ankle block may also be needed as the popliteal block can take a while before it goes completely numb, whereas the ankle block makes the foot numb a lot faster. To see if you need the ankle block, a quick test of your foot’s sensation will be carried out.

Your questions

If you have any further questions about the anaesthetic, please mention this at your appointment before your surgery. You might want to write your questions down beforehand and bring them with you.