Biomechanics of a calcar loading and a shortened tapered femoral stem: Comparative in-vitro testing of primary stability and strain distribution

Abstract

Purpose The most common femoral short stems available on the market can, in principle, be divided with regard to their anchoring concepts into a calcar loading and a shortened tapered design. The purpose of this study was to compare the primary stability and stress-shielding of two short stems, which correspond to these two different anchoring concepts. Methods Using seven paired fresh frozen human cadaver femurs, primary axial and rotational stabilities under dynamic load (100–1600 N) were evaluated by miniature displacement transducers after 100,000 load cycles. Changes in cortical strains were measured before and after implantation of both stem types to detect implant-specific load transmission and possible stress-shielding effects. Results Reversible and irreversible micromotions under dynamic load displayed no significant differences between the two implants. Implantation of either stem types resulted in a reduction of cortical strains in the proximal femur, which was less pronounced for the calcar loading implant. Conclusions Both short stems displayed comparable micromotions far below the critical threshold above which osseointegration may disturbed. Neither short stem could avoid proximal stress-shielding. This effect was less pronounced for the calcar loading short stem, which corresponds to a more physiological load transmission.

A scoring system to evaluate stability of percutaneous osseointegrated implants for transfemoral amputation with validation in the ITAP clinical trial

“…With respect to implant alignment and IF scores in participants where in vivo implant alignment was not true (N ax or N g ) there appeared to be no detrimental effect to IF score and the bone remodelled as necessary that is, where the stem tip was close or touching the endosteal wall, the bone thickened and where gaps were initially identified, over time bone formation filled them. Furthermore, it seems that cemented fixation IF scores (mean = 8.00, SD = 6.34) were more successful than pressfit IF scores (mean = 0.50, SD = 8.99) aligning with current trends in THR 51 however this is not common practice in POI fixation.…”