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MC²® is a mobile plate prothesis for the tri-compartment re-surfacing of the knee.
The mobility of the plate is exclusively rotational.
These is no medio-lateral or antero-posterior mobility that can interfere with the kinematics induced by the design of the prothesis.
This mobile plate is designed to provide maximum safety without the risk of dislocation.
The congruence is wide : between 0° and 60°, developed on both lateral surfaces, it varies from 800 to 1400 mm².
When walking (between 0° and 30°), the system of postero-stabilisation is not required, thereby reducing the level of the antero-posterior stress.
As of 60° , the postero-stabilisation cam is called on, and provides a surface contact, that takes the relay from the congruence provided from 0° to 60° by the lateral coils.
The amplitude of intrinsic flexion, determined by the design and positioning of the postero-stabilisation cam, as well as by the design of the posterior prothetic condyle is 130°.
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The Femoral Component
It consists of two lateral condyles and a central condyle (or third condyle), coming into contact with the central cam of the mobile plate as of 60°.
As with the mobile plate, the junction between the third condyle and the lateral condyles was studied in order to provide a gentle transition, improving the polishing possibilities and limiting the risk of wear of the polyethylene.
The space required by the postero-stabilisation central chamber was optimised in order to resect as little bone as possible both in height and in width.
The roof of this chamber is open, reducing the burden of the femur and also making the retrograde centro-medullar pinning possible in case of supra condylar fracture.
The thickness of the distal condyle, like that of the posterior condyle, is 9 mm.
The cutting angle of the throchlea is 6°. This sharp obliqueness is used to create the anterior section while avoiding the risk of stair gait.
The design of the femoral component was concerned with lightening this component.
The recess in the lateral condyles in the MC²® femur is used to reduce the mass by 30 %.
Ribs guarantee the good positioning of the implant, while providing the role of adjustment on the bone sections.
The trochlea is deep, wide and its recess is continued as distally as possible, so as to give the prosthetic patella good congruence up to 100° of flexion.
Like the tibial base, the femoral component is derived from a chrome cobalt foundry procedure that is rectified and highly polished.
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The Mobile Plate
The mobile plate has two lateral surfaces that are perfectly congruent with the between - 5° and 60° of flexion.
The postero-stabilisation cam is positioned at the centre.
The junction of this cam and the lateral slide surfaces have been especially optimised, in order to avoid any abrupt connection that may generate matter due to wear by friction with the femoral component.
The lower hub, joined with the tibial keel, presents a portion of cylinder 10 mm high, then continues with a cone-shaped segment of 14.5mm (for a toyal height of 24.5 mm).
This cylindrical portion is justified by the need to stabilise the mobile plate if it is raised with respect to the base, a situation observed when the lateral ligaments are relaxed, or distracted when walking.
In fact, if the entire height of the hub was cone-shaped, the raising of the mobile plate would enable detrimental front or sagittal swing movements as this may favour the wear and flow of the polyethylene.
In front, the mobile plate is highly scalloped to avoid all contact with the patellar tendon or the point of the patella in hyperflexion.
The size of the mobile plate compared with the tibial base was studied to allow for considerablerotation (over 15°), while avoiding contact with the soft parts (lateral ligaments, patellar tendon, popliteral tendon).
In fact, in several models of mobile plate prostheses, the rotary amplitude, if it isn't controlled by a stop device, is limited by the friction of the mobile plate with the soft parts. This friction can generate anterior (patellar tendon), lateral (LLI/LLE) or postero -lateral (popliteal tendo,) pain.
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The Tibial Base
The shape is anatomic and can be adapted to the re-cut surface of the tibia, without the necessity of a right or left component.
The thickness of the base was minimised by the use of of a keel comprising two fins, playing the role of a prop. Thekeel is cone-shaped, suitable for a preparation by milling or recessing, and the centre is emptied to receive the hub from the mobile plate.
The tibial base is made of cobalt chrome, a material whose behaviour in friction is known. The characteristicsof friction are optimised by the restification of the plate and keel, and a high level of polishing.
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The Patellar
It consists of a portion of sphere, that is then re-cut in an oval shape, to adapt to the edge of the patellar section as well as possible.
It is equipped with two sealing hubs.
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LEXA® - Hinge total knee prosthesis
- Modular
- Metal / metal rotation axis
- Limited rotation
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MERCURY - Double mobility acetabular cup
The double mobility principal has clinically demonstrated its ability to reduce :
- the risks of dislocation
- the risk of loosening
- the wear of the polyethylene
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