Non-original abutments differ in design of the connecting surfaces and material and demonstrate higher rotational misfit. These differences may result in unexpected failure modes.

Today's implant quality stainless steels contain up to 16 wt% nickel although nickel ions are the most widespread skin contact allergens. Previously sensitized persons may develop allergic reactions when nickel is released from stainless steel medical implants. New low-nickel stainless steels combine the benefits of excellent mechanical properties with virtual absence of nickel. Miniature bone plates and corresponding 2.0 mm screws for the fixation of small bone fragments were produced of a low-nickel stainless steel. The implants were tested in a static reverse-bending setup and under dynamic conditions, and compared to commercially pure (CP) titanium and standard 316L implant steel counterparts. The low-nickel plate could withstand over 200 cycles of bending, whereas the titanium plate broke at 26 cycles. This confirms the higher tolerance of the low-nickel plate to multiple contouring during surgery. Nevertheless, high cycle fatigue tests under physiologic conditions showed that the low-nickel steel plates exhibit lower resistance to cyclic loads than titanium and 316L plates. SEM investigations of the fatigue fractures confirmed that the cracks preferentially propagate along grain boundaries leading to intergranular fracture of the low-nickel steel. It is suggested that the intergranular crack initiation facilitates the early failure under high cycle fatigue conditions, whereas plastic bending properties are not affected. The tendency to intergranular crack initiation in the low-nickel steel could stem from surface deformation (work hardening) introduced during machining and related embrittlement in the surface zone.

Purpose Fixation of periprosthetic hip fractures with intracortical anchorage might not be feasible in cases with bulky implants and/or poor bone stock. Methods Rotational stability of new plate inserts with extracortical anchorage for cerclage fixation was measured and compared to the stability found using a standard technique in a biomechanical setup using a torsion testing machine. In a synthetic PUR bone model, transverse fractures were fixed distally using screws and proximally by wire cerclages attached to the plates using "new" (extracortical anchorage) or "standard" (intracortical anchorage) plate inserts. Time to fracture consolidation and complications were assessed in a consecutive series of 18 patients (18 female; mean age 81 years, range 55-92) with periprosthetic hip fractures (ten type B1, eight type CVancouver) treated with the new device between July 2003 and July 2010. Results The "new" device showed a higher rotational stability than the "standard" technique (p <0.001). Fractures showed radiographic consolidation after 14±5 weeks (mean ± SD) postoperatively in patients. Revision surgery was necessary in four patients, unrelated to the new technique. Conclusion In periprosthetic hip fractures in which fixation with intracortical anchorage using conventional means might be difficult due to bulky revision stems and/or poor bone stock, the new device may be an addition to the range of existing implants.

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