hta_ knee intro.qxp - Ministero della Salute

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• a tibial component: a metallic plate (also called tibial tray) that is applied to the proximal
part of the tibia;
• an insert: a plastic layer that is inserted onto the tibial plate and articulates with the
femoral component. It presents a toroidal surface and may have a raised central
ridge.
Sometimes a patellar component is used to replace the natural patella. It consists of a block of
plastic (usually polyethylene) having the form of a cupola that imitates the shape of the patella.
The choice of the prosthesis is based on the patient’s characteristics (e.g. age, weight, activity
level), the implant’s characteristics (e.g. design, materials), and the surgeon’s experience and
familiarity with the device (see totaljoints website; Pritchett, 2004; Kuster, 2002).
Prostheses for total knee replacement can also be classified according to other factors:
• the method of fixation of the components (cemented, uncemented or hybrid);
• the retention or the sacrifice of the posterior cruciate ligament;
• the type of plastic insert (that can be made by different types of polyethylene, fixed
or mobile, and posterior stabilized or not).
Metal alloys are commonly used for femoral and tibial component, the insert is usually made
of plastic and the patella may be all-plastic or metal-backed.
The selection of the best implant is quite complex: the variability of knee conditions is great
and the number of choices in prosthesis types are significant.
Figure A1.1: Schematisation of a total knee implant. The plastic insert is not visible in radiographic
images. Images were from www.sxc.hu