"Mobile Bearing Gold Knee " By Dr. Gaurav Sawhney
We at Indus Hospital are proud to announce that we have been offering the facility of state of the art knee replacement surgery with the use of latest technological innovations to provide patients with superior knee replacement solutions.
We are presenting a recent case operated at Indus International Hospital, Dera Bassi.
Patient was a 58 year old female with severe degenerative joint disease also known as osteoarthritis of the knee.
She had difficulty walking even 100 metres and had pain during the day as well as night. Her X rays showed varus deformity of both knees with total loss of medial joint space on both sides.
She was operated upon by team of our specialist joint replacement surgeons Dr Gaurav Sawhney and Dr V P S Sandhu where in mobile bearing specially coated PorEx knees (also known as mobile bearing or rotating platform gold knee) were implanted on both sides in the same surgery.
PorEx is a special surface modification where the chromium cobalt components are coated with special alloy of titanium niobium nitride. This coating is hypoallergenic meaning that it releases approximately 95% less allergenic ions compared to chromium cobalt surface which is the common material used in knee prosthesis. Therefore patients who may be allergic or suspected to be allergic to metals are ideal candidates for receiving these special implants. There is also least risk of chromium or cobalt toxicity to the patient because of reduced release of chromium and cobalt ions into the body.
Other major advantage of this special coating is that it makes the surface of the implant ceramic like with increased hardness and smoothness of the articulating surface. Articulating surface is a surface which moves against the polyethylene allowing motion at the knee joint. This increased smoothness and hardness improves the wear properties of the implant. By wear properties we mean that when the metallic implant moves against the ultra high molecular weight polyethylene there is reduced friction and there by reduced particle generation. This increases the expected life of the knee prosthesis. We must keep in mind that during the lifetime of the implant the metallic component would move against the ultra high molecular weight polyethylene many millions of times. Therefore improving the wear characteristics of the metal component has a major role in increasing the longevity of implanted knee.
Preoperative X-rays PostoperativeX-rays Mobile Bearing Gold Knee
This titanium niobium nitride coating looks like gold and therefore in common parlance these knees are also known as gold knees.
In this particular case, not only were these knees carrying a special coating, they were also mobile bearing.
Let us explain the concept of mobile bearing. Most of the knee prosthesis which are used currently are fixed bearing knees. By fixed bearing we mean that these knee prosthesis have a polyethylene which is fixed on top of the tibial metallic component that is the lower leg bone component. When the upper femoral metallic component moves against this fixed bearing polyethylene there is friction and wear of the polyethylene. In addition to the wear of polyethylene on top surface there is friction and wear at its lower surface where the polyethylene rubs against the rough top of the tibial metallic component. During the lifetime of the patient and the implant this motion will occur millions of times generating innumerable small particles from the upper surface of the polyethylene. These particles get into the surrounding tissue and incite an inflammatory reaction ultimately causing loosening of the implant. Therefore to increase the lifespan of the implanted knee prosthesis it is imperative to reduce particle generation from the polyethylene. The special coating as well as mobile bearing are an attempt to attain this particular aim.
To decrease this wear of the polyethylene, concept of mobile bearing is used. In mobile bearing knee prosthesis the ultra high molecular weight polyethylene rotates over the fixed tibial metallic component in addition to the motion against the specially coated femoral implant. This articulation between the metallic component and the polyethylene is made highly polished and smooth to prevent back side wear which is often a problem with fixed bearing implants. At the same time the articulation between femoral metallic component (that is the component fixed to the thigh bone) and the polyethylene is made highly congruent to prevent and decrease the wear between metallic component and polyethylene. Therefore using the mobile bearing concept, wear of polyethylene is reduced on both upper and lower sides of the polyethylene. This helps increase the life of knee prosthesis.
When special coating of titanium niobium nitride is combined with mobile bearing, expected longevity of the implanted knee prosthesis is increased.
Another advantage is the increased natural rotation which can be achieved by the patient during flexion of the knee which is a result of polyethylene being able to rotate over the tibial metallic base plate component. This increased rotation helps give a more natural feeling knee to the patient.
Dr. Gaurav Sawhney
M.B.B.S. M.S. (Orthopedic)
Indus International Hospital