The study of any cementless hip system is essentially based on three concepts: initial stability, secondary biological stability and factors regarding the reliability of this stability.
Initial Stability relies on optimal bone fill with press-fit support on the cortical bone. For the acetabular component, this is best achieved with a hemispherical form. Femoral support is assured by a triple cortical contact in the metaphyseal zone. A triple support requires a stem with a sagittal bow.
Secondary stability must account for a compromise between fixation and extractability. The sand-blasted titanium surface provides this possibility. Bone on-growth produces a sheath around the metal, similar to cement, from the fourth week onwards.
Reliability. Reliabe stability of the a cetabular cup is favored by the hemispherical form of the s hell and the ample thickness of polyethylene which distribute adverse forces. Femur stability is provided through pure metaphyseal fixation. Metaphysodiaphyseal fixation often becomes plain diaphyseal fixation with all its inherent problems.
Initial results with a minimum follow-up of one year (320 cases with an average follow-up of 2 years) seem to confirm the efficient nature of the biological fixation by the total absence of pain. Only the future will tell us if our concepts are entirely effective.
