ACCIS

Hemispherical vs equatorial press fit hemispherical:

An hemispherical designed cup, will require, to enable sufficient press fit that the acetabulum is "underreamed" 1-3 mm smaller than the intended cup	When the cup is impacted the impacting force is distributed evenly over the hemispherical surface	Action = reaction : the acetabulum will exercise a force trying to withstand the impaction force.	When the cup is seated the push back force will try to push the actebaulum component out jeopardizing its primary fixation

An design with an equatorial press fit (see here below) does niot reuire underreaming . The implant is widened at the equator. Upon impaction the forces at the equator are higher than at the spherical area	Action = reaction : the acetabulum will exercise a force trying to withstand the impaction force but this forces is highest at the equator.	When the cup is seated the major force is at the equator , increasing the "holding force" rather than pushing back

The Accis design The press fit fixation by equatorial over-sizing is different from the fixation principle of over-sizing with spherical cups. While spherical cups run the considerable risk of being pushed out of the acetabulum due to the forces around the whole cup, called the rebound effect (46) , fixation of cups with equatorial
over -sizing is enhanced by compression forces only
Two fins are added near the equator of the ACCIS®acetabular components to support rotational stability (arrow in figure ).
The outside of the cup is coated with a plasma spray of pure Titanium (cpTi) according to the ISO standard 5832-2. The pore diameter is 75-350 micron, the coating thickness 300 +/- 50 micron and the roughness RA is 50 micron. The solidity of the fixation is specified as Rh = 45 MPa, while a minimal strength of 22 MPa is required according to the “FDA-Guidance for the industry”. The metal surface of the inner side of the acetabular component is engineered with the ceramic TiNbN by PVD.

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