| CHRIS SERVANT |
| KNEE REPLACEMENT |
What is the knee joint? |
| The knee is a joint that is actually formed by three separate joints or compartments.
The hinge joint between the femur (thigh bone) and the tibia (shin bone) forms a medial (inner) compartment and
a lateral (outer) compartment. At the front of the knee there is the third compartment – the patellofemoral
compartment, which is located under the patella (kneecap).
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| The medial compartment is on the left side of your right knee and the right side of
your left knee. The lateral compartment is on the right side of your right knee and the left side of your left knee.
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What is a knee replacement? |
| A knee replacement is an artificial joint that replaces an arthritic knee joint.
Basically a knee replacement is a re-surfacing of the arthritic joint surfaces. The joint surfaces are removed
and replaced by a metal and plastic replacement (or prosthesis).
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A total knee replacement |
The usual components of the prosthesis are:
- A curved metal component (made of a cobalt-chromium alloy) is fitted to the end of the femur.
- A flat metal component (made of a titanium alloy) is fitted to the tibia. A press-fit plastic insert
(made of a high-density polyethylene) is attached to this metal component. The plastic insert does not show
up on X-ray.
- If the kneecap is resurfaced, the under surface of the kneecap is removed and replaced with a plastic
‘button’
The components are usually fixed to the cut bone surfaces with a thin layer of acrylic bone cement. Together
the metal and plastic components of the prosthesis form a smooth, low-friction and durable joint surface.
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Depending on which joint surfaces are worn, there are three main types of knee replacement:
- Total knee replacement (TKR) – the surfaces of both the medial and lateral compartments are
replaced and occasionally the kneecap (patella) is resurfaced as well
- Unicompartmental knee replacement (UKR) – only the medial compartment is worn and needs replacing,
so the prosthesis is often referred to as a ‘half knee replacement’
- Patellofemoral joint replacement (PFJR) – only the kneecap compartment is replaced
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