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Knee Replacement Implants


The orthopaedic surgeon would replace the damaged knee with artificial components during the knee replacement surgery. Different types of implants are available and the one used for the surgery would depend on factors like the needs based on the problem and the anatomy of the knee, including the age, weight, the general health and activity level the performance of the implant and the cost the experience of the doctor and the familiarity with the device. The surgeon discusses the type of implant that would be required for the knee replacement surgery.

What are the components of the implants?
The implants can be made of ceramic material, metal alloys or strong plastic parts. As many as three bone surfaces might be replaced in the total knee replacement.
The top surface of the tibia - This part is generally a flat metal component with a cushion made from polyethene. There might be designs that attach the polyethylene directly to the bone.
The back of the patella - This portion is generally made from polyethylene, imitating the shape of the patella. It does not need to be resurfaced always.
The lower surface of the femur - The metal component curves around the femur. The kneecap can smoothly move up and down against the bone.

Ceramic Implants
The ceramic components were employed first as alternatives to the polyethylene bearings. The bearings made from ceramics, i.e. aluminium oxide (alumina) and zirconium oxide (zirconia) have extremely low wear properties making them very suitable for knee replacement surgeries. The superior wear characteristics of these ceramics have been verified through numerous experimental and clinical studies. There have hardly been any problems in the long-term clinical outcomes.
1. Alumina Ceramics - This is the most commonly used type among the ceramic bearings. The coefficient of friction is very low in alumina and is thus the appropriate choice for an orthopaedic bearing surface. It also has proven biocompatibility. The vivo ageing does not affect the material properties of the substance.
2. Zirconia ceramics - This type of ceramics have as much as 2 to 3 times more flexural strength and toughness against fracture. These types are much more resistance to fractures. These bearings were introduced in order to reduce the risk of catastrophic failures while retaining the superior wear properties of the alumina heads.

Oxinium Implants
The oxinium is a patented metal alloy and is produced by Smith & Nephew. It is a zirconium metal alloy and is oxidized through a patented process, turning the metal surface into ceramic. The substance has the surface of that of ceramic and the structure of metal. The metal alloy offers a combination of smoothness, hardness and scratch resistance. The surface is twice as hard and scratch resistant as the cobalt-chrome alloys.
It has been found through experimental studies and research that the surface made from oxinium reduces wear by as much as 50%. The material is much less brittle compared to ceramic. Thus the risk of brittle fractures is reduced. There is minimal nickel content, reducing the chances of metal sensitiveness in patients. The femoral component is generally made of oxinium.

The implants have their own characteristics and different wear and tear properties. Also, the biocompatibility of these implants vary.

Authored By: Dr. S. V. Santpure

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