There are several kinds of replacement knee joint as well as different surgical methods. Your doctor and orthopaedic surgeon should help you to choose the best option for you, taking into account the condition of your knee and your general health.
Total knee replacement
A total knee replacement may also involve replacing the under-surface of your kneecap (patella) with a smooth plastic dome. Some surgeons prefer to preserve the natural patella if possible, but sometimes the decision will need to be made during the operation.
If you’ve had a previous operation to remove the patella altogether (patellectomy), this won’t stop you having a knee replacement, but it may affect the type of replacement part (prosthesis) your surgeon uses.
The new parts are normally cemented in place. If cement is not used then the surface of the component facing the bone is textured or coated to encourage bone to grow onto it, forming a natural bond.
Another common technique is to use a mobile plastic bearing which isn’t firmly fixed to the metal parts. This may help to reduce wear on your new joint, though it isn’t hasn’t been shown to provide better long-term results.
Unicompartmental (partial) knee replacement
There are three compartments of the knee – the inner (medial), the outer (lateral) and the kneecap (patellofemoral). If arthritis affects only one side of your knee – usually the inner side – it may be possible to have a half-knee replacement (sometimes called unicompartmental or partial replacement). Because this involves less interference with the knee than a total knee replacement, it usually means a quicker recovery and better function.
Partial knee replacements can be carried out through a smaller cut (incision) than a total knee replacement, using techniques called reduced invasive or minimally invasive surgery. A smaller incision may further reduce the recovery time.
Partial knee replacement isn’t suitable for everyone because you need to have strong, healthy ligaments within your knee. Sometimes this won’t be known until the time of surgery.
Research shows that people who have partial knee replacements are more likely to have the knee revised than people who have a total knee replacement – about 1 person in 10 needs further surgery after 10 years. Even though the operation involves less interference with the knee it is often a more complex operation than total knee replacement. Your surgeon may therefore prefer to offer you a more predictable total knee replacement.
Partial knee replacement can be considered at any age. For younger people, it offers the opportunity to preserve more bone, which is helpful if you need revision surgery at a later stage. For older people, partial knee replacement is a less stressful operation with less pain and less risk of bleeding. The outcome of the surgery, however, depends on the type of arthritis, rather than your age.
Complex or revision knee replacement
Some people may need a more complex type of knee replacement. The usual reasons for this are:
- major bone loss due to arthritis or fracture
- major deformity of the knee
- weakness of the main knee ligaments.
These knee replacements usually have a longer stem, which allows the component to be more securely fixed into the bone cavity. The components may also interlock in the centre of the knee to form a hinge to give greater stability. Extra pieces of metal and/or plastic may be used to make up for any removed or badly damaged bone.
This type of operation may be needed if you’re having a second or third joint replacement in the same knee, and could be better from the start if you have very severe arthritis.