M.D. Roach

Failure of Emperion modular femoral stem with implant analysis

Modularity in total hip arthroplasty provides multiple benefits to the surgeon in restoring the appropriate alignment and position to a previously damaged hip joint. The vast majority of modern implants incorporate modularity into their design with some implants having multiple modular interfaces. There is the potential for failure at modular junctions because of fretting and crevice corrosion in combination with mechanical loading. This case report details the failure of an Emperion (Smith and Nephew, Memphis, TN) femoral stem in a 67-year-old male patient 6 years after total hip replacement. Analysis of the implant revealed mechanically assisted crevice corrosion that likely accelerated fatigue crack initiation in the hip stem. The benefits of modularity come with the potential drawback of a combination of fretting and crevice corrosion at the modular junction, which may accelerate fatigue, crack initiation and ultimately reduce the hip longevity.

Alpha plus beta annealed and aged Ti-15 Mo alloy for high strength implant applications.

Management of femur fractures requires titanium alloy implants that provide a good combination of static strength and ductility plus sufficient high cycle fatigue strength to resist repetitive loading. A research program was initiated to determine whether aging treatments could increase the strength of alpha + beta Ti-15Mo while maintaining acceptable tensile ductility. A pilot heat treating study indicated the best combination of strength and ductility was obtained using an α + β annealing temperature of 705°C ± 10°C followed by an aging treatment of 482°C ± 10°C. EBSD data for four suppliers revealed that the alpha phase ratios ranged from 16.3% to 18.6% and the beta phase ratios ranged from 81.4% to 83.7%. Mean beta grain size diameters ranged between 1.42 and 1.78 µm. Tensile testing qualification data from four suppliers was statistically analyzed and reviewed. Minimum reproducible tensile values were established and incorporated into ASTM F2066-13 implant material standard. Cantilever fatigue testing was performed with proximal femoral nail implants that were fabricated into fully finished implant constructs. Fatigue results for 125°, 130°, and 135° implant constructs met the acceptance criteria regarding the fatigue runout load limits and failure modes that were identified.

A comparison of the stress corrosion cracking susceptibility of commercially pure titanium grade 4 in Ringer's solution and in distilled water: a fracture mechanics approach.

From the results of laboratory investigations reported in the literature, it has been suggested that stress corrosion cracking (SCC) mechanisms may contribute to early failures in titanium alloys that have elevated oxygen concentrations. However, the susceptibility of titanium alloys to SCC in physiological environments remains unclear. In this study, a fracture mechanics approach was used to examine the SCC susceptibility of CP titanium grade 4 in Ringers solution and distilled de-ionized (DI) water, at 37°C. The study duration was 26 weeks, simulating the non-union declaration of a plated fracture. Four wedge loads were used corresponding to 86-95% of the alloys ligament yield load. The longest cracks were measured to be 0.18 mm and 0.10 mm in Ringers solution and DI water, respectively. SEM analysis revealed no evidence of extensive fluting and quasi-cleavage fracture features which, in literature reports, were attributed to SCC. We thus postulate that the Ringers solution accelerated the wedge-loaded crack growth without producing the critical stresses needed to change the fracture mechanism. Regression analysis of the crack length results led to a significant best-fit relationship between crack growth velocity (independent variable) and test electrolyte, initial wedge load, and time of immersion of specimen in electrolyte (dependent variables).

Photofunctionalization of anodized titanium surfaces using UVA or UVC light and its effects against Streptococcus sanguinis

UV light preirradiation of anodized titanium oxide layers has recently been shown to produce a photocatalytic effect that may reduce early bacterial attachment on titanium surfaces. Streptococcus species have been identified as primary early colonizers and contribute to early biofilm formation on dental implant surfaces. Anodized layers with primarily amorphous, primarily anatase, primarily rutile, and mixtures of anatase and rutile phase oxides were preirradiated with UVA or UVC light for 10 min. Nanoscale surface roughness and pre- and post-UV-irradiated wettability were measured for each anodization group. Sample groups were subjected to streptococcus sanguinis for a period of 24 h. Bacterial attachment and killing efficacy were measured and compared to the corresponding non-UV control groups. UVA treatments showed trends of at least a 20% reduction in bacterial attachment regardless of the crystallinity, or combination of oxide phases present. Anodized layers consisting of primarily anatase phase on the outermost surface were shown to have a killing efficacy of at least 50% after preirradiation with UVA light. Anodized layers containing disperse mixtures of anatase and rutile phases at the outermost surface showed at least a 50% killing efficacy after pre-irradiation with either UVA or UVC light.