There are several nerves very close to the femoral nerve that go to the hip. The nerves are called the ‘obturator’ and the ‘lateral cutaneous nerve of the thigh’. By putting anaesthetic around the femoral nerve, these other nerves are blocked too. This is helpful for people who are having broken hips fixed, or new joints put in.
The nerve block may be used with a general anaesthetic, in which case you will be asleep for the nerve block. If the block is instead of a general anaesthetic, you will be awake or sedated (sleepy). This is not usually done.
The block usually lasts for several hours. The leg will be numb and feel heavy during this time. One advantage of the block is that it reduces the amount of other strong painkillers, such as morphine, needed during and after the operation.
The aim is that you feel no pain during the operation. The block will provide pain relief during the operation and for several hours afterwards. Your anaesthetist will talk to you before doing the block and explain whether you will be awake, asleep or sedated during the operation.
There are a number of benefits. You may have other serious medical conditions, such as heart or lung disease. In this case a general anaesthetic may have slightly more risk than normal. Doing the block, instead of using a general anaesthetic alone, will cause less stress to your medical condition and be safer.
It is more common to perform a femoral nerve block with a general anaesthetic. This gives excellent pain relief both during and after surgery. This means that the anaesthetist does not need to give as much anaesthetic or strong painkillers. This means a faster recovery and less sickness after the operation.
Are there any alternatives?
There are several alternatives to a femoral nerve block. These are all listed below. The problem is that they all have additional risks involved. It may not be reasonable to expose you to these risks. For example, it is not reasonable to have a full general anaesthetic to remove a small skin tag. This is a tiny flap of skin less than a fingernail in size. This should be easy to do with a local anaesthetic block and sedation.
General anaesthetic: You can have your general anaesthetic, where you are completely asleep throughout, but without the femoral nerve block. Other strong painkillers, such as morphine, can be given to keep you comfortable when you wake up.
Epidural: It may be possible to perform an epidural where the lower part of the body goes numb and is pain free. This involves placing a plastic tube next to the nerves in the spine, so that drugs can be injected, making the nerves stop working temporarily. This is a higher risk procedure for a small operation on the thigh, for instance.
Spinal: Alternatively a single injection, like an epidural, but without putting the plastic tube in, can be used. This single injection is called a spinal. It does not last as long as an epidural. This is also a more risky procedure for a small operation.
Local anaesthetic: Sometimes, if the surgery is minor, local anaesthetic injections can be used to numb the operation area only.
If you are to have one of these procedures there is another information leaflet that will tell you more about it.
Who should have it done?
Patients needing surgery on the hip, thigh or knee can have this type of anaesthetic for their operation.
Who should not have it done?
Each patient has the final decision to proceed or not. If you are unhappy about the procedure for any reason, you should not continue. There are specific medical situations when a femoral nerve block should not be done and they are as follows:
Medication that prevents your blood from clotting, such as Warfarin; this would lead to more bleeding than normal. Bleeding around the nerves in the leg is a serious problem and must be avoided.
An illness that prevents your blood from clotting, such as haemophilia; this would lead to more bleeding around the nerves in the leg.
Infection of the skin over the site where the needle needs to be put in; this could lead to further infection in the deeper tissues and possibly blood poisoning. This could also cause infection around the nerves.
Unusual or difficult anatomy; this would make it difficult to put the needle in the correct place.
Previous injury or disease affecting your femoral nerve; perhaps you have had a previous injury to your upper leg, or groin. This could make it unsafe to do this type of block.
Author: Dr Sean White FRCA. Consultant in pain and anaesthesia
© Dumas Ltd 2006