What is knee replacement surgery and how does it work?
In a healthy knee, both the ends of the thigh and shin bones are covered with hard cartilage which allows the bones to move against each other without any friction. Arthritis damages and the hard cartilage become thin. It leads, the cartilage wears away so that the bones rub against each other and here comes the pain.
In a knee replacement operation, the surgeon removes the worn ends of the bones and damaged hard cartilage and replaces them with metal and plastic parts(Artificial Knee). The plastic acts like hard cartilage, helping the joint to move freely. The interlocking parts of the artificial joint allow the knee to bend and also making it more stable.
What are the different types of knee replacement surgery?
There are different kinds of artificial knee joint and its surgical techniques. Your doctor help you to choose the best option for you, taking into account the condition of your knee.
Total knee replacement
Most total knee replacement involve replacing the joint surfaces at the end of the thigh bone (femur) and at the top of the shin bone (tibia).
A total knee replacement may also involve replacing the undersurface of the kneecap (patella) with a smooth plastic dome. Some surgeons prefer to preserve the natural patella.
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 technique is to use a mobile plastic bearing which isn’t firmly fixed to the metal parts. This may help to reduce wear on the new joint.
Unicompartmental (partial) knee replacement
There are three compartments of the knee, the inner (medial), the outer (lateral) and the kneecap . 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.
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. Partial knee replacement isn’t suitable for everyone because you need to have strong, healthy ligaments within your knee.
Recent research shows that patients who have partial knee replacements are more likely to have the knee revised than patients who have a total knee replacement – about 1 person in 10 needs further surgery after 10 years. Partial knee replacement can be considered at any age. For younger patients it offers the opportunity to preserve more bone, which is helpful if a revision is needed at a later stage. For older patients, it is good because it’s a less stressful operation with less risk of bleeding and less pain. The outcome of the surgery depends on the type of arthritis, rather than your age.
Kneecap replacement (patellofemoral arthroplasty)
It’s possible to replace just the under-surface of the kneecap and its groove (the trochlea) if these are the only parts of your knee affected by arthritis. This is also called a patellofemoral joint arthroplasty The operation has a higher rate of failure than total knee replacement – which may be caused by the arthritis progressing to other parts of the knee. Some Doctors prefer a total knee replacement as the results are more successful. More research is needed to understand which patients are more likely to do well with this operation.
Complex or revision knee replacement
Sometimes more complex type of knee replacement is needed. The 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 implant to be more precisely fixed into the bone cavity. The components may also interlock in the centre of the knee, forming a hinge to give greater stability. A complex knee replacement may be necessary 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.