Knee replacement
is surgery for people with severe knee damage. Knee replacement can relieve
pain and allow you to be more active. It is a surgical procedure to
replace the weight-bearing surfaces of the knee joint to relieve the pain and
disability of osteoarthritis.[1]
It may be performed for other knee diseases such as rheumatoid arthritis and psoriatic
arthritis. In patients with severe deformity from advanced rheumatoid arthritis, trauma, or long
standing osteoarthritis, the surgery may be more complicated and carry higher
risk. Osteoporosis does not typically cause knee pain, deformity, or
inflammation and is not a reason to perform knee replacement.
Knee replacement
surgery can be performed as a partial or a total knee replacement.[2]
In general, 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.
Technique:
The surgery involves exposure
of the front of the knee, with detachment of part of the quadriceps muscle 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 then impacted onto the bone or fixed using polymethylmethacrylate cement. Alternative techniques exist that
affix the implant without cement. These cement-less techniques may involve osseointegration,
including porous metal prostheses.
Total knee replacement hardware, including femoral
head, tibial plate, patellar plate, and menisus replacement plate.
A round ended
implant is used for the femur, mimicking the natural shape of the joint. On the
tibia the component is flat, although it sometimes has a stem which goes down
inside the bone for further stability. A flattened or slightly dished high
density polyethylene surface is then inserted onto the tibial component so
that the weight is transferred metal to plastic not metal to metal. During the
operation any deformities must be corrected, and the ligaments balanced so that
the knee has a good range of movement and is stable and aligned. In some cases
the articular surface of the patella is also removed and replaced by a
polyethylene button cemented to the posterior surface of the patella. In other
cases, the patella is replaced unaltered.
Partial knee replacement:
Unicompartmental
arthroplasty (UKA), also called partial knee replacement, is an option for some
patients. The knee is generally divided into three "compartments":
medial (the inside part of the knee), lateral (the outside), and patellofemoral
(the joint between the kneecap and the thighbone). Most patients with arthritis
severe enough to consider knee replacement have significant wear in two or more
of the above compartments and are best treated with total knee replacement. A minority
of patients (the exact percentage is hotly debated but is probably between 10
and 30 percent) have wear confined primarily to one compartment, usually the
medial, and may be candidates for unicompartmental knee replacement. Advantages
of UKA compared to TKA include smaller incision, easier post-op rehabilitation,
better post-operative range of motion, shorter hospital stay, less blood loss,
lower risk of infection, stiffness, and blood clots, but a harder revision if
necessary. While most recent data suggests that UKA in properly selected
patients has survival rates comparable to TKA, most surgeons believe that TKA
is the more reliable long term procedure. Persons with infectious or
inflammatory arthritis or marked
deformity are not candidates for this procedure.
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