What type of anaesthesia might you have ahead of your knee replacement operation? And what factors influence the choice of anaesthetic? YKC’s Jim Newman tackles some quick-fire questions.

Will my knee replacement be carried out under anaesthetic?

Yes! There are a couple of options in terms of which anaesthetic you’ll receive [see below], but every knee replacement is carried out under anaesthetic, so you won’t feel any pain during the operation.

Which anaesthetic will I receive?

You’ll likely have either a general anaesthetic or a spinal anaesthetic – a combination of local anaesthetic and a morphine derivative which is injected into the spine – which will numb you from the waist down.

Both of these are very often combined with a nerve block in the thigh which numbs the sensory nerve that supplies feeling to the knee. This will help provide pain relief after your operation.

How do you choose between the two anaesthetic options?

Traditionally we’ve used spinal anaesthetic as the ‘go-to’ option for knee replacement, but as we increasingly move towards day case joint replacement surgery we are switching to performing many more procedures under general anaesthetic.

That’s because general anaesthetic doesn’t affect motor function in the same way as spinal – so the nerves to the muscles are unaffected. If you’re spending the night in hospital, a temporary effect on your leg muscles isn’t a major problem. If, however, you’re aiming to send patients home the same day, motor function matters, because it means we can get you up and about much quicker.

It’s also the case the even short-acting spinal anaesthetics can increase the risk of hypotension (a drop in blood pressure) when you stand up. Again, that presents problems for day case surgery.

Whether you are suitable for day case knee replacement depends on several factors, such as your fitness, comorbidities (that is, other conditions you may have) and your expectations for discharge, but if you are suitable for same day discharge, you’re much more likely to have a general anaesthetic with a nerve block.