What:
- Knee replacement,
or knee arthroplasty,
is a surgical procedure to
replace the weight-bearing surfaces of
the knee joint. - A round ended implant is used for the femur,
mimicking the natural shape of the joint. - The tibia component is flat,
it sometimes has a stem
which goes down inside the bone for further stability. - A flattened or slightly dished
high density polyethylene surface is
inserted onto the tibial component,
so that the weight is transferred metal to plastic not metal to metal. - The articular surface of the patella is removed and replaced by a polyethylene button cemented to the posterior surface of the patella.
Why:
- To relieve pain and disability.
How:
- The surgery consists of
replacing the diseased or damaged joint surfaces of the knee
with metal and plastic components
shaped to allow continued motion of the knee. - During the operation
deformities must be corrected,
and the ligaments balanced
so that the knee has a good range of movement
and is stable and aligned. - The operation involves substantial postoperative pain,
and includes vigorous physical rehabilitation. - The recovery period may be
6 weeks or longer
and may involve the use of mobility aids,
such as walking frames, canes, and crutches,
to enable the return to preoperative mobility.
Algorithm:
- Expose the front of the knee,
detach part of the quadriceps muscle, aka vastus medialis, from the patella. - The patella is displaced
to one side of the joint,
allowing exposure of
the distal end of the femur and
the proximal end of the tibia. - The ends of these bones are then accurately cut to shape
using cutting guides
oriented to the long axis of the bones. - The cartilages and the anterior cruciate ligament are removed;
the posterior cruciate ligament may also be removed
but the tibial and fibular collateral ligaments are preserved. - Metal components are impacted onto the bone
or fixed using
polymethylmethacrylate (PMMA) cement.
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