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Complex Revision-Surgery of Knee Prosthesis and associated problems

With prosthesis loosening but also with substance losses after sled prosthesises both, a bone compensation and a stronger anchoring than by the first implantation are necessary.

In order to treat defects in the range of the femoral bone, spongy chips and blocks from the iliac crest , donor bones but also metal blocks come into effect. The grafts (bone blocks) must ingrow which is why the foundation of a surface replacement has to be reinforced due to diversely shanks which differ in their thickness and length.
The pairing is different to the pure surface replacement. At this a polyethylene pin is embedded into the corresponding configuration of the femoral component. Thus results a beautiful guided motion with high stability.

Within prosthesis loosening and the abrasion of the polyethylene ligament instability is very common, thereby a stronger guidance is requested. The newest prosthesis designs include rotational components with a higher posterior stabilization,so that here too, wear and tear in rotational mpovements can be prevented. More over there is the so-called “Hyperflex” polyethylene component which allows full diffraction.

Figure 1: Revision Knee Sytsem Legion (Smith & Nephew)

Figure 2: X-ray: Legion Prosthesis 3 days post-op

Major defects after mulitple revisions, severe infections, substance loss due to heavy polyethelene abrasion and serious ligament instability indicate endoprosthetics. This allows a hiogher guidiance and thereby compensades the ligament weakness.

The implants resemble mechanically the beginning of the development, coupled prosthesis. Hereby a complete thinning due to serious misalingments can be stabilized. The disadvantage of pure hinge joint is the flux in the bone caused by the shafts and rotational movements which can lead to loosening. This forces can be countervailed due to sagittal hinges. In modern systems it is therefore under development to include rotation. The prosthesis we use have the design of a coupled roation prosthesis, so that we can assure a long service life.