Primary Total Knee Replacement Prosthesis(Implant)

A General information for the Patients

 Written By :

Dr. Ankur Saurav
Sr.Orthopedic Surgeon
Fellowship in Joint Replacement (Germany),  Fellowship in Sports Medicine (ISAKOS)

  • Knee prosthesis or commly called as knee implants that is used in total knee replacement can be broadly classified into two types:
  • Implant used in patients undergoing primary(first) total knee replacement.
  • Implant used in patients undergoing Revision(Replaced knee being replaced again) knee replacement.

Here I will be explaining you only about the implants used in Primary Total Knee Replacement.

  • Total Knee Replacement Prosthesis (Implant) consists of 3 main components:
  • The Femoral Component: The component which attaches to the lower part of your thigh bone.
  • The Tibial component: The Plastic Spacer(Polyethylene): This lies between the femoral and tibial component.

The model below is showing the different components in Knee Replacement:​

Fig.1 :Knee model seen from front.​

Fig 2: Knee Model seen from side

Your surgeon in his basket has variety of implant types and the one to be used in you depends on lots of factors like:

  • Your particular Anantomy
  • Amount of knee deformity
  • Ligament Stability
  • Quality of soft tissue around knee
  • Another method of classifying the Knee Replacement Implant is:
  • Type 1:

Plastic Component is Fixed to the tibial Component. This implant is also called as Fixed Bearing implants.

  • Type 2:

Plastic Component is Rotating on the tibial component. This is also known as Rotating Platform implant

  • Which type of Implant will be used in a particular patient depends on lots of factor and one the important factor is surgeons experience.
  • ROTATING PLATFORM IMPLANT has some of the theoretical advantages like:
  • It allows small amount of rotation that a normal knee experiences when becoming fully extended.
  • Less shear stress on the top of the plastic, where femoral component bends.
  • There are some disadvantages also in Rotating platform also as it is more dependent on soft tissue, more chances of dislocation and need more expertise from surgeon.
  • I use Rotating Platform implants in young and and active patients.
  • Long term studies show similar survivorship of Rotating platform and fixed bearing Implants.
  • Another category of implants relates to how the Posterior Cruciate Ligament(One the four main ligaments of the knee)is treated during the surgery:
  • Cruciate Retaining(CR): Your Posterior Cruciate Ligament(PCL) is not removed during surgery. This is done if your PCLis healthy and functional. This cuts less bone.
  • Posterior Stabilised(PS) Implant:In this type the PCL is removed and implant has a box and post in the design which stabilize the knee. This cuts more bone than the CR implant.
  • Both these designs have its own advantages and it depends on your surgeon what is he going to use
  • I personally use mostly Posteriorly Stabilized implant as in India we get mostly very deformed and damaged knee in which these PCL is almost nonfunctional.
  • In some of the cases your knee cap(Patella) is also replaced.
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