For Knee Replacement
No food for 6 hours before your operation.
It is okay to drink clear fluids up to 2 hours before surgery (water, clear fruit juice, black tea/coffee) until arrival at the hospital.
Take all your usual medications. If diabetic and taking insulin, take half your usual dose the night before and no insulin or diabetic tablets on the morning of your operation. Discuss use of blood thinners with your surgeon or anaesthetist especially if you have cardiac stents. Aspirin can be continued. Lyrica will usually be offered to all patients as a ‘pre-med’ (unless you have had prior problems with this medication).
The typical anaesthetic sequence is listed below. This may be altered to suit your requirements. Firstly, all patients will be asleep for the operation with a full general anaesthetic, unless otherwise requested. In addition to this we will use three types of local anaesthetic, the first two will be done before you go to sleep.
- A spinal injection
- A local anaesthetic catheter in your leg
- Local anaesthetic in your knee joint, placed by the surgeon
This is a simple single injection in the lower back designed to keep your legs numb for several hours after your operation. It is not an “epidural”. It is done in the sitting position or lying on your side. The main benefits of a spinal injection is total pain relief for several hours after the operation and a marked reduction in the amount of morphine based pain medications used during this period. This often means less side effects relating to morphine medications such as nausea, drowsiness and itch. The effect of the injection is to put both legs to sleep so that you will not be able to feel or move them at all for a few hours. This is a very safe technique and complications are uncommon. Serious complications are rare. The spinal injection is recommended but optional. It does not contribute to low back pain and is considered quite safe however if you do not wish to have this injection please discuss this with your anaesthetist. If you have had spinal fusion surgery it may be more technically difficult and may not be offered.
Local Anaesthetic Catheter
This is a small catheter, which will be placed into your thigh muscle using ultrasound guidance. It may be done before you go to sleep with sedation. The catheter will be connected to a portable pump, which will trickle local anaesthetic into your leg for 3-5 days after your surgery. The effect is to reduce pain from your knee. Muscle strength may be affected by this infusion but should be sufficient to allow you to walk. You may feel a numb sensation around the knee and down the inside of your leg as far as the ankle while the infusion is running. The catheter will provide continuous pain relief in the background but you will need additional pain relief tablets. Simply speak to your nurse if your pain relief is not adequate. The pain catheter may also be ‘topped up’ by pressing the button attached to it when you feel like you need extra pain relief such as when you are going to walk or do physiotherapy however it may or may not be effective. Please note that the pain catheter will not block pain from the back of the knee or the thigh muscles which can be sore in the first 24 hours due to the application of a tourniquet during surgery. The top up button is available every 4 hours. If pressing the button does not assist with pain relief ask for a pain tablet from the nurses.
Direct Local Anaesthetic Injection
When you are asleep, the surgeon will inject a large amount of local anaesthetic directly into your knee joint. This is very effective at reducing pain after surgery and will last 12 to 24 hours after your operation.
After Your Operation
If you have had a spinal injection, you will wake up with numb legs and be unable to move them for at least 2-3 hours. As the spinal wears off you may notice some pain in your knee. For most people it wears off gradually and they will be comfortable at rest. Occasionally the pain may come on quickly and can be severe. To help prevent this the surgeon will have injected a large amount of local anaesthetic directly into your knee joint while you were asleep. We will also give you a slow release pain tablet (PALEXIA SR) before the spinal injection wears off.
If you do start to feel pain call the nurse for a pain tablet, usually a quick release strong pain reliever such as PALEXIA IR. You may also try pressing the button attached to your local anaesthetic catheter. This gives you a ‘top-up’ of local anaesthetic. It may help but does not affect pain at the back of the knee. It is available to press once every 4 hours. It is unlikely to be needed on the day of surgery but it may be useful the following day before or after physiotherapy. Even if you don’t get relief the first time you press the button you may get relief on subsequent attempts so you can try to press it again.
There are a range of medications used to help with pain management. It is important that you get to understand what these are and how they make you feel as all of these can have side effects. You will also need to know about these tablets as you will be taking some home following discharge.
Most patients are relatively comfortable at rest but will experience moderate or occasionally more severe pain when bending the knee or walking. The most common pain score while walking is 4 out of 10 but the range is wide with some patients almost completely pain free and others with moderate to severe pain. Approximately 1 in 20 will experience a lot more pain and consume more pain tablets than other patients. We have ward rounds daily by a pain team supervised by a pain specialist who can help by putting stronger local anaesthetic into your leg catheters, performing additional nerve blocks or changing your medications to help make you comfortable.
For more information visit www.betterpainrelief.org