A femoral nerve block is an injection of local anaesthetic into the groin. 

There are several nerves that run very close to the femoral nerve and go to the hip. 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.

Nerve blocks are usually used with a general anaesthetic or strong sedative to make you sleepy, which means that you will be asleep for when the nerve block is inserted. 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 as these drugs can make you feel sick and light headed. And because you feel better, it can make it easier to commence your rehabilitation sooner.

There are a number of benefits to having a nerve block. You may have other serious medical conditions, such as heart or lung disease in which case a general anaesthetic may have slightly more risk than normal. Doing a block, instead of using a general anaesthetic alone, will cause less stress to your medical condition and be safer.

Having a numb limb can feel a little strange, especially when you have no muscle control. Be careful when getting up with the nurse or physiotherapist, as you may not have enough power in the limb to support yourself. Before getting out of bed for the first time muscle strength should be assessed.

There are several alternatives to a femoral nerve block. These are all listed below.  All operations and anaesthetics carry potential risks. Your anaesthatist can discuss the best options for you.

• 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.

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 could 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 could lead to more bleeding around the nerves in the leg and permanent damage.
• Infection of the skin over the site where the needle needs to be put in could lead to further infection in the deeper tissues, possibly blood poisoning or infection around the nerves.
• An unusual or difficult anatomy could make it difficult to put the needle in the correct place.
• Previous injury or disease affecting your femoral nerve could make it difficult or unsafe to do this type of block.