Cemented total hip stem design influence on adaptative cortical thickness and femoral morphology

Five-year following total hip implantation femur adaptive morphology was compared between two groups differing only in their femoral stem design.

Group 1, recruited prospectively, included 51 Dédicace stems(Stryker-Howmedica) and group 2, retrospectively matched to group 1, comprised 51 Kerboull MK3 stems (Stryker-Howmedica). While MK3 prosthetic system increases in size homogeneously (widening along the whole length as the implant dimension increases), the Dédicace prosthetic system provides various metaphyseal widths for a given diaphyseal size. We opted for primary fixation (press fit according to the "French paradox") prior to cementing in both cases, despite the risk of discontinuity in the cement mantle. The homogeneous dimensioning of the MK3 stem enables distal primary fixation, whereas the Dédicace range allows differentiated adaptation to diaphyseal length and metaphyseal caliber. The following parameters were measured and calculated: Noble index, femoral cortical thickness score of Barnett and Nordindiaphyseal filling and stress-shielding at three levels around the stem.

Bone-remodeling, assessed on X-ray, was without clinical impact, whether it took the form of spongialization or stress-shielding. The sole factor tending to induce stress-shielding was a high degree of canal filling by the distal third of the stem, more frequently encountered with the MK3 model. Metaphyseal filling was equivalent with all stems. In the matched series on the contralateral healthy side, femoral spongialization was comparable.

Level III; case/control study.