Neck loosening
Static mechanical strength
Fretting and corrosion
Fatigue mechanical strength
Neck loosening
Tests have shown that locking strength of the stem / neck junction is higher than the V40™ head / monolithic stem junction. To date, no issue has been reported regarding this matter. We have tested different loading conditions: static load, manual gentle impaction, few millions cycles of loading.
Static mechanical strength
Because the hip has to endure daily life activities, we need to care about peak loads. Bergman et al have reported high peak load during stumbling, up to 8.7 times the body weight. The graph below shows that the maximum yield strength of the ABG™II Modular, which is much higher than this maximum load. This graph also offers a comparison with the standard ABG™II cementless stem (for which no such failure has ever been reported, after 10 years of implantations).
Fretting and corrosion
In order to accomodate a modural neck on the smallest ABG™II sizes, the junction dimensions have been reduced compared to some implants already available on the Market.
Viceconti et al reported that reduced contact surfaces may produce higher fretting; despite these reduced dimensions, and thanks to the ABG™II Modular proprietary material properties and manufacturing processes, fretting level remains quite low and equivalent to what has been reported by Viceconti et al as shown on the graph on the right.
Overall, neck + stem fretting wear remain under the 5 mg for 5 million cycle estimated by Viceconti et al as the upper limit for modular implants.
Furthermore, our MEB and EDS analysis have demonstrated that all the components were undamaged, except at the surface contact area. No corrosion was observed.
Being very low, fretting wear did not have any effect on the mechanical function of the test samples. No fatigue fractures were observed and the necks remained securely joined to the stems.
Fatigue mechanical strength
Being made of TMZF® for the stem and GADS Vitalium® for the neck, it has been possible to push the mechanical testing much further than most of the common tests reported on the market: not only both stem resistance and neck resistance have been tested (by potting the stem at a level such that it has to withstand 100% of the load), but the test were run at loads much higher than the norm request.
Such a potting (just below the bottom of the connexion) creates the worst case conditions regarding stresses in the modular junction as it negates any shielding effects of the potting media to the stem components and connection.
The worst stem/neck combinations in term of stress have been tested with a minimum load equivalent to 6 times the mean body weight (from 4500 to 5300 depending of stem size).
Finally, despite the thin width of the neck, and thanks to GADS Vitallium® material, samples tested to simulate deepflexion and loaded with 2300N, passed 1 million cycles without any failure.
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