design, newer models more closely mimic the rolling and gliding
motion of the joint. Most standard knee implants are made up of 3
components that cover different bone surfaces:
• The metal femoral component curves around the lower end of the
femur.
• The tibial component is made up of a metal platform with a poly-
ethylene cushion insert. It is attached to the top surface of the tibia.
• The patellar piece is a dome-shaped implant made of polyethylene
that covers the back surface of the patella and mimics the shape of
the kneecap.
Typically, manufacturers design these components to work as metal-
on-plastic (usually cobalt-chromium or titanium with polyethylene).
This provides smooth movement and minimal wear. There are cur-
rently more than 150 knee implant designs on the market, so when
choosing which device to use surgeons consider several key differ-
ences, including:
• Cruciate-retaining vs. posterior-
stabilized. Cruciate-retaining implants let the surgeon preserve the
patient's posterior cruciate ligament, if it's still intact. These implants
have a small groove that allows for flexion of the ligament. Posterior-
stabilized implants let the surgeon remove the ligament and replace it
with a cam-and-post system that prevents the thighbone from sliding
too far forward on the shinbone when the knee is bent.
• Cemented vs. cementless. While some implants are attached using fast-
curing bone cement, cementless prostheses are made of a material
that attracts new bone growth to keep the device in place. Both
approaches work well, though more surgeons are moving to cement-
less options since they allow for a relatively easier surgery, take less
time to place and — especially in younger patients — seem to be a
better fit.
J A N U A R Y 2 0 1 6 • O U T PA T I E N TS U R G E R Y. N E T • 5 5
