PRIMARY TOTAL KNEE REPLACEMENT PROSTHESIS(Implant):
A General information for the Patients.
Dr. Ankur Saurav
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:
Here I will be explaining you only about the implants used in Primary Total Knee Replacement.
- 1.Implant used in patients undergoing primary(first) total knee replacement.
- 2. Implant used in patients undergoing Revision(Replaced knee being replaced again) knee replacement.
- Total Knee Replacement Prosthesis (Implant) consists of 3 main components:
- 1. The Femoral Component: The component which attaches to the lower part of your thigh bone.
- 2. 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:
- 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:
- 1. It allows small amount of rotation that a normal knee experiences when becoming fully extended.
- 2. 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:
- 1. 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.
- 2. 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.