Quantification of trunnion damage in a series of intact total hip arthroplasty femoral stems previously identified to be at risk of catastrophic failure

BACKGROUND

Corrosion at the head-neck junction of femoral stems is a rare complication of total hip arthroplasty (THA) with manifestations ranging from subclinical wear to failure. Prior studies have identified a single femoral component design with an increased propensity for catastrophic trunnion failure. The purpose of the present study was to quantify trunnion damage of this femoral component retrieved from patients undergoing revision THA for non-trunnionosis indications.

METHODS

24 femoral components from a single manufacturer were identified for study inclusion. Each prosthesis underwent stereomicroscopic inspection. Corrosion and fretting scores were assigned per the Goldberg criteria to quadrants of the trunnion. Material loss was calculated based on cone angles across trunnion quadrants. This was carried out using a coordinate measuring machine that digitised each trunnion surface. Stems were compared to a series of femoral stems with the same trunnion design.

RESULTS

20 of the 24 (83%) trunnions demonstrated corrosion, all 24 trunnions demonstrated fretting. Corrosion scores did not statistically differ with respect to trunnion zone (p = 0.53), while fretting scores were higher in the inferior compared to the superior zones (p < 0.001). There was no significant difference in cone angles assessing material loss between stems (p = 0.25).

CONCLUSIONS

Evidence of trunnion damage was observed in each stem retrieved for non-trunnionosis revision. Fretting occurred more frequently about the inferior quadrants. However, digitised trunnion shapes were similar between compared stems exhibiting no material loss. Therefore, it is possible that previous reports of trunnion failures for this implant are not a systemic issue, and that further investigation is required.

Microstructure Evolution and Fretting Wear Mechanisms of Steels Undergoing Oscillatory Sliding Contact in Dry Atmosphere

Variations in the microstructure and the dominant fretting wear mechanisms of carbon steel alloy in oscillatory sliding contact against stainless steel in a dry atmosphere were evaluated by various mechanical testing and microanalytical methods. These included scanning electron microscopy and energy dispersive spectrometry with corresponding elemental maps of the wear tracks, in conjunction with cross-sectional transmission electron microscopy of samples prepared by focused ion beam machining to assess subsurface and through-thickness changes in microstructure, all as a function of applied load and sliding time. Heavily dislocated layered microstructures were observed below the wear tracks to vary with both the load and sliding time. During the accumulation of fretting cycles, the subsurface microstructure evolved into stable dislocation cells with cell walls aligned parallel to the surface and the sliding direction. The thickness of the damaged subsurface region increased with the load, consistent with the depth distribution of the maximum shear stress. The primary surface oxide evolved as Fe2O3 and Fe3O4 with increasing sliding time, leading to the formation of a uniform oxide scale at the sliding surface. It is possible that the development of the dislocation cell structure in the subsurface also enhanced oxidation by pipe diffusion along dislocation cores. The results of this study reveal complex phase changes affecting the wear resistance of steels undergoing fretting wear, which involve a synergy between oxidative wear, crack initiation, and crack growth along dislocation cell walls due to the high strains accumulating under high loads and/or prolonged surface sliding.

Fretting and Fretting Corrosion Behavior of Additively Manufactured Ti-6Al-4V and Ti-Nb-Zr Alloys in Air and Physiological Solutions

Additive manufacturing (AM) of orthopedic implants has increased in recent years, providing benefits to surgeons, patients, and implant companies. Both traditional and new titanium alloys are under consideration for AM-manufactured implants. However, concerns remain about their wear and corrosion (tribocorrosion) performance. In this study, the effects of fretting corrosion were investigated on AM Ti-29Nb-21Zr (pre-alloyed and admixed) and AM Ti-6Al-4V with 1% nano yttria-stabilized zirconia (nYSZ). Low cycle (100 cycles, 3 Hz, 100 mN) fretting and fretting corrosion (potentiostatic, 0 V vs. Ag/AgCl) methods were used to compare these AM alloys to traditionally manufactured AM Ti-6Al-4V. Alloy and admixture surfaces were subjected to (1) fretting in the air (i.e., small-scale reciprocal sliding) and (2) fretting corrosion in phosphate-buffered saline (PBS) using a single diamond asperity (17 µm radius). Wear track depth measurements, fretting currents and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis of oxide debris revealed that pre-alloyed AM Ti-29Nb-21Zr generally had greater wear depths after 100 cycles (4.67 +/- 0.55 µm dry and 5.78 +/- 0.83 µm in solution) and higher fretting currents (0.58 +/- 0.07 µA). A correlation (R2 = 0.67) was found between wear depth and the average fretting currents with different alloys located in different regions of the relationship. No statistically significant differences were observed in wear depth between in-air and in-PBS tests. However, significantly higher amounts of oxygen (measured by oxygen weight % by EDS analysis of the debris) were embedded within the wear track for tests performed in PBS compared to air for all samples except the ad-mixed Ti-29Nb-21Zr (p = 0.21). For traditional and AM Ti-6Al-4V, the wear track depths (dry fretting: 2.90 +/- 0.32 µm vs. 2.51 +/- 0.51 μm, respectively; fretting corrosion: 2.09 +/- 0.59 μm vs. 1.16 +/- 0.79 μm, respectively) and fretting current measurements (0.37 +/- 0.05 μA vs. 0.34 +/- 0.05 μA, respectively) showed no significant differences. The dominant wear deformation process was plastic deformation followed by cyclic extrusion of plate-like wear debris at the end of the stroke, resulting in ribbon-like extruded material for all alloys. While previous work documented improved corrosion resistance of Ti-29Nb-21Zr in simulated inflammatory solutions over Ti-6Al-4V, this work does not show similar improvements in the relative fretting corrosion resistance of these alloys compared to Ti-6Al-4V.

Evaluating trunnionosis in modular anatomic shoulder arthroplasties: a retrieval study

BACKGROUND

Shoulder arthroplasty procedures are widely indicated, and the number of shoulder arthroplasty procedures has drastically increased over the years. Rapid expansion of the utilization of reverse total shoulder arthroplasty has outpaced the more modest growth of anatomic total shoulder arthroplasty (aTSA) while shoulder hemiarthroplasty (HA) has trended down. Recently, shoulder prostheses have transitioned to increasingly modular systems offering more individualized options with the potential for decreased pain and increased range of motion. However, increased primary procedures has resulted in increased revision surgeries, with one potential cause being fretting and corrosion damage within these modular systems.

METHODS

Following institutional review board approval, 130 retrieved aTSA and 135 HA explants were identified through database query. Humeral stem and head components were included in all 265 explants, whereas 108 included polyethylene glenoid liner components. All explanted components were macroscopically evaluated for standard damage modes, and taper junctions were microscopically examined for fretting/corrosion using a modified Goldberg-Cusick classification system that was 4-quadrant graded for both the male and female component. Medical records were reviewed for patient demographics and surgical information.

RESULTS

In this series, 158 of explants were from female patients (male = 107), and 162 explants were from the right shoulder. Average age at implantation was 61 years (range: 24-83), average age at explanation was 66 years (range, 32-90), and average duration of implantation was 61.4 months (range, 0.5-240). Scratching, edge deformation, and burnishing were the most commonly observed standard damage modes. Of the 265 explants, 146 had a male stem component vs. 118 with a female stem component. Average summed fretting grades on male and female stem components were 8.3 and 5.9, respectively (P < .001). Average summed corrosion grades for male and female stem components were 8.2 and 6.2, respectively (P < .001). Wider male tapers (>11 mm) showed significantly less fretting and corrosion (P < .001). Lastly, mismatched metal compositions between the head and stem components showed greater fretting and corrosion damage (P = .002).

CONCLUSION

In this series of 265 aTSA and HA explants, there was substantial damage present on the explanted components. All components demonstrated macroscopic damage. In this retrieval study, small-tapered male stems with small, thin female heads and mismatched metal composition between components were risk factors for increased implant wear. As shoulder arthroplasty volume increases, optimizing design is paramount for long-term success. Additional work could determine the clinical significance of these findings.

Modeling Fretting Wear Resistance and Shakedown of Metallic Materials with Graded Nanostructured Surfaces

In applications involving fretting wear damage, surfaces with high yield strength and wear resistance are required. In this study, the mechanical responses of materials with graded nanostructured surfaces during fretting sliding are investigated and compared to homogeneous materials through a systematic computational study. A three-dimensional finite element model is developed to characterize the fretting sliding characteristics and shakedown behavior with varying degrees of contact friction and gradient layer thicknesses. Results obtained using a representative model material (i.e., 304 stainless steel) demonstrate that metallic materials with a graded nanostructured surface could exhibit a more than 80% reduction in plastically deformed surface areas and volumes, resulting in superior fretting damage resistance in comparison to homogeneous coarse-grained metals. In particular, a graded nanostructured material can exhibit elastic or plastic shakedown, depending on the contact friction coefficient. Optimal fretting resistance can be achieved for the graded nanostructured material by decreasing the friction coefficient (e.g., from 0.6 to 0.4 in 304 stainless steel), resulting in an elastic shakedown behavior, where the plastically deformed volume and area exhibit zero increment in the accumulated plastic strain during further sliding. These findings in the graded nanostructured materials using 304 stainless steel as a model system can be further tailored for engineering optimal fretting damage resistance.

Larger-diameter trunnions and bolt-reinforced taper junctions are associated with less tribocorrosion in reverse total shoulder arthroplasty

BACKGROUND

Morse taper junction tribocorrosion is recognized as an important failure mode in total hip arthroplasty. Although taper junctions are used in almost all shoulder arthroplasty systems currently available in the United States, with large variation in design, limited literature has described comparable analyses of taper damage in these implants. In this study, taper junction damage in retrieved reverse total shoulder arthroplasty (RTSA) implants was assessed and analyzed.

METHODS

Fifty-seven retrieved RTSAs with paired baseplate and glenosphere components with Morse taper junctions were identified via database query; 19 of these also included paired humeral stems and trays or spacers with taper junctions. Components were graded for standard damage modes and for fretting and corrosion with a modified Goldberg-Cusick classification system. Medical records and preoperative radiographs were reviewed. Comparative analyses were performed assessing the impact of various implant, radiographic, and patient factors on taper damage.

RESULTS

Standard damage modes were commonly found at the evaluated trunnion junctions, with scratching and edge deformation damage on 76% and 46% of all components, respectively. Fretting and corrosion damage was also common, observed on 86% and 72% of baseplates, respectively, and 23% and 40% of glenospheres, respectively. Baseplates showed greater moderate to severe (grade ≥ 3) fretting (43%) and corrosion (27%) damage than matched glenospheres (fretting, 9%; corrosion, 13%). Humeral stems showed moderate to severe fretting and corrosion on 28% and 30% of implants, respectively; matched humeral trays or spacers showed both less fretting (14%) and less corrosion (17%). On subgroup analysis, large-tapered implants had significantly lower summed fretting and corrosion grades than small-tapered implants (P < .001 for both) on glenospheres; paired baseplate corrosion grades were also significantly lower (P = .031) on large-tapered implants. Factorial analysis showed that bolt reinforcement of the taper junction was also associated with less fretting and corrosion damage on both baseplates and glenospheres. Summed fretting and corrosion grades on glenospheres with trunnions (male) were significantly greater than on glenospheres with bores (female) (P < .001 for both).

CONCLUSIONS

Damage to the taper junction is commonly found in retrieved RTSAs and can occur after only months of being implanted. In this study, tribocorrosion predominantly occurred on the taper surface of the baseplate (vs. glenosphere) and on the humeral stem (vs. tray or spacer), which may relate to the flexural rigidity difference between the titanium and cobalt-chrome components. Bolt reinforcement and the use of large-diameter trunnions led to less tribocorrosion of the taper junction. The findings of this study provide evidence for the improved design of RTSA prostheses to decrease tribocorrosion.

Interfacial compliance, energy dissipation, frequency effects, and long-term fretting corrosion performance of Ti-6Al-4V/CoCrMo interfaces

Fretting corrosion in modular orthopedic implants is a well-documented process that may be associated with adverse local tissue reactions, pain, and revisions. Engineering modular junction interfaces to withstand applied fretting motion without surface abrasion could prevent implant degradation and surface damage. Previous work on geometrically modified Ti-6Al-4V/CoCrMo interfaces with increased compliance showed reduced fretting currents and surface damage during short term, variable-load in vitro testing. This study assesses the same interfaces under long-term conditions using an in vitro pin-on-disk fretting corrosion test apparatus. Preliminary variable-load frequency testing of typical control pin geometries showed a frequency-dependent current response, with underlying contact conditions of metal-metal interfaces that remained unchanged. One-million-cycle testing showed diminished fretting currents in all groups by 5 × 10⁵  cycles, but consistently lower currents in the high-compliance group. Corresponding fretting currents and work of fretting measurements of high-compliance pins confirmed that minimal fretting was experienced at the interface, with elastic bending of the pin accounting for almost all applied displacement. Debris generated during testing were composed of titanium and chromium oxides, small amounts of cobalt and molybdenum oxides, and sodium and phosphate originating from the surrounding test solution. Post-test analyses of sample surfaces revealed substantially more surface damage on CoCrMo disks than Ti-6Al-4V pins, thought to be a result of adhesive wear of mixed oxide debris on the pin and abrasion of the disk by the oxide debris layer. Surface damage to high-compliance pins suggests some abrasion is unavoidable with geometric modifications.

Assessing Taper Geometry, Head Size, Head Material, and Their Interactions in Taper Fretting Corrosion of Retrieved Total Hip Arthroplasty Implants

BACKGROUND

Decreased fretting and corrosion damage at the taper interface of retrieved ceramic-on-polyethylene total hip arthroplasty (THA) implants has been consistently reported; however, resultant fretting corrosion as a function of femoral head size and taper geometry has not been definitively explained.

METHODS

Eight cohorts were defined from 157 retrieved THA implants based on femoral head composition (n = 95, zirconia-toughened alumina, ZTA vs n = 62, cobalt-chromium alloy, CoCr), head size (n = 56, 32mm vs n = 101, 36mm), and taper geometry (n = 84, 12/14 vs n = 73, V40). THA implants were evaluated and graded for taper fretting and corrosion. Data were statistically analyzed, including via a 2³ factorial modeling.

RESULTS

Factorial-based analysis indicated the significant factors related to both resultant (summed) fretting and corrosion damage were head material and taper geometry; head material-taper geometry interaction was also a significant factor in resultant corrosion damage. Lower rates of moderate-to-severe fretting and corrosion damage were exhibited on ZTA heads (ZTA = 13%, CoCr = 38%), smaller heads (32mm = 18%, 36mm = 26%), and 12/14 tapers (12/14 = 13%, V40 = 35%). ZTA+32mm heads demonstrated the lowest rates of moderate-to-severe fretting and corrosion damage (12/14 = 2%, V40 = 7%), whereas CoCr heads with V40 tapers demonstrated the greatest rates of moderate-to-severe damage (32mm = 47%, 36mm = 59%).

CONCLUSION

In this series, retrieved implants with ZTA, 32-mm heads paired with 12/14 tapers exhibited lower rates of moderate-to-severe damage. Factorial analysis showed head material, taper geometry, and their interactions were the most significant factors associated with resultant damage grades. Isolating implant features may provide additional information regarding factors leading to fretting and corrosion damage in THA.

LEVEL OF EVIDENCE

IV (case series).

In vivo corrosion and damages in modular shoulder prostheses

Wear and corrosion at taper junctions of orthopaedic endoprostheses remain of great concern and are associated with adverse clinical reactions. Whereas tribocorrosion of hip tapers was extensively investigated, there is only little knowledge regarding the clinical performance of modular total shoulder prostheses. This retrieval study evaluated 35 modular taper junctions of anatomical shoulder explants using stereomicroscopy, confocal microscopy, as well as optical and scanning electron microscopy to determine the damage modes as well as the effects of taper topography and alloy microstructure. Among all humeral head tapers, 89% exhibited material degradation. Different overlapping wear mechanisms were identified such as plastic deformation, adhesive material transfer, microploughing, and fretting damage. Only CoCrMo cast alloy heads showed a susceptibility to electrochemically dominated fretting in comparison to CoCrMo wrought alloy. Moreover, corundum blasted stem tapers show a significantly increased incidence rate for microploughing. To date, this is the most comprehensive study on the damage types of modular taper junctions of anatomical shoulder arthroplasty proving the existence of fretting even on less weight-bearing implants. This study revealed critical fretting factors, such as the surface finish and the alloy type that are essential for the development of countermeasures that avoid any taper corrosion.

Negative influence of biofilm on CoCrMo corrosion

Minimal studies exist investigating biofilm-induced corrosion of orthopaedic implants. This study investigates potential contributions of Pseudomonas aeruginosa and Staphylococcus aureus biofilms on corrosion resistance of CoCrMo under static and fretting conditions. Biofilms were cultured on CoCrMo coupons for either 4 weeks (static culture) or 6 days (fretting culture; pin-on-disk with a Ti6Al4V hemispherical tip pin). Morphology of biofilms and corrosion of coupon surfaces were analyzed via SEM. Open circuit potential and electrochemical impedance spectroscopy measurements were collected for corrosion performance evaluation. Results showed no visible corrosion on coupon surfaces in static culture, which suggests these biofilms alone do not induce severe corrosion under the conditions of this study. However, electrochemical data showed biofilm presence lowered coupon electrochemical impedance in static and fretting cultures, suggesting resistive and capacitive characteristics of the metal oxide-biofilm-media interface were altered. Under fretting, the P. aeruginosa group exhibited a distinct damage morphology and Co:Cr:Mo ratio within the wear scar when compared with S. aureus and the bacteria-free control. These differences suggest the presence of P. aeruginosa biofilms may negatively impact corrosion resistance at the fretting interface. Taken together these results demonstrate biofilms can contribute to implant corrosion by influencing the electrochemical impedance of implant metal surfaces.

The Effect of Disc Surface Topography on the Dry Gross Fretting Wear of an Equal-Hardness Steel Pair

Experimental investigations were carried out with an Optimol SRV5 tribological tester in a flat-on-sphere scheme. The balls co-acted with the discs in a gross sliding fretting regime. The balls and discs were made from the same steel with a very similar hardness. Tests were conducted at 25–35% relative humidity, 30 °C, and a constant normal load and number of cycles (18,000). The discs had different textures after various machining treatments. It was found that the total wear level of the tribological assembly was proportional to the disc surface amplitude. The influence of the disc roughness on the coefficient of friction was evident only for the smallest stroke of 0.1 mm, and the frequency of oscillation affected this dependency.

Is There Material Loss at the Conical Junctions of Modular Components for Total Knee Arthroplasty?

BACKGROUND

Clinical concern exists regarding fretting corrosion and material loss from taper junctions in orthopedic devices, with previous research focusing on the modular components from total hip arthroplasty. Comparatively little has been published regarding the fretting corrosion and material loss in modular knee devices. The purpose of this study is to evaluate fretting corrosion damage and quantify material loss for conical total knee arthroplasty taper interfaces.

METHODS

Stem tapers of 166 retrieved modular knee devices were evaluated for fretting corrosion using a semiquantitative scoring method. High precision profilometry was then used to determine volumetric material loss and maximum wear depth for a subset of 37 components (implanted for 0.25-18.76 years). Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the observed damage.

RESULTS

Mild to severe fretting corrosion was observed on the majority of tapers, with 23% receiving a maximum visually determined damage score of 4. The median rate of volumetric material loss was 0.11 mm³/y (range 0.00-0.76) for femoral components (both cone and bore taper surfaces combined) and 0.01 mm³ (range 0.00-8.10) for tibial components. Greater rates of material loss were associated with mixed metal pairings. There was a strong correlation between visual fretting corrosion score and calculated material loss (ρ = 0.68, P < .001). Scanning electron microscopy revealed varying degrees of scratching, wear, fretting corrosion, and instances of cracking with morphology not consistent with fretting corrosion, wear, or fatigue.

CONCLUSION

Although visual evidence of fretting corrosion damage was prevalent and correlated with taper material loss, the measured volumetric material loss was low compared with prior reports from total hip arthroplasty.

Does Taper Design Affect Taper Fretting Corrosion in Ceramic-on-Polyethylene Total Hip Arthroplasty? A Retrieval Analysis

BACKGROUND

Ceramic-on-polyethylene (CoP) implants have exhibited lower fretting and corrosion scores than metal-on-polyethylene implants. This study aims at investigating the effect of taper design on taper corrosion and fretting in modular CoP total hip arthroplasty (THA) systems.

METHODS

Under an institutional review board--approved protocol, a query of an implant retrieval library from 2002 to 2017 identified 120 retrieved CoP THA systems with zirconia toughened alumina femoral heads. Femoral stem trunnions were visually evaluated and graded for fretting, corrosion, and damage at the taper interface. Medical records were reviewed for patient demographics and implant characteristics. Data were statistically analyzed using Spearman correlation and rank-sum tests with a Dunn's post hoc test, with a significance level of α = 0.05.

RESULTS

Four different taper designs were evaluated: 11/13 (n = 18), 12/14 (n = 53), 16/18 (n = 21), and V40 (n = 28). There were no statistically significant demographic differences between taper groups for duration of implantation, laterality, patient age, and patient sex, but patients with 16/18 tapers had a higher body mass index than V40 tapers (P = .012). Duration of implantation had a weak positive correlation with both trunnion fretting (ρ = 0.224, P = .016) and corrosion (ρ = 0.253, P = .006). Summed fretting and corrosion scores were significantly greater on the V40 and 16/18 tapers compared with the 12/14 tapers (all P ≤ .001).

CONCLUSION

Taper fretting and corrosion were observed in CoP THA implants and were greatest with V40 and 16/18 tapers and lowest with 12/14 tapers. Differences in taper design characteristics may lead to greater micromotion at the taper-head interface, leading to increased fretting and corrosion.

Fretting and Corrosion Damage of Retrieved Dual-Mobility Total Hip Arthroplasty Systems

BACKGROUND

Dual-mobility (DM) total hip arthroplasty (THA) systems are designed to increase stability while potentially avoiding problems associated with large femoral heads. Complications of these systems are not yet fully understood. This study aims at characterizing in vivo performance of DM hip systems and assessing modes of clinical failure.

METHODS

Under an institutional review board-approved implant retrieval protocol, 18 DM THA systems from 17 patients were included. Implants were graded at the head-neck junction for fretting and corrosion based on the system of Goldberg et al. Components were also macroscopically examined for different damage modes. Demographics and surgical data were collected from medical records, and radiographs were assessed for component positioning. Data were analyzed through Spearman rank-order correlation and Mann-Whitney U-tests, with α = 0.05.

RESULTS

The average length of implantation was 13.4 months with mild to moderate fretting corrosion damage. Polyethylene (PE) liners exhibited edge deformation, scratching, and pitting damage. Metallic components exhibited burnishing and scratching damage. Summed fretting and corrosion scores were strongly correlated (ρ = 0.967, P < .0001). Summed corrosion score was moderately correlated with presence of embedding on the PE liner (ρ = 0.690, P = .017). PE liner abrasion and edge deformation of the femoral stem taper were moderately positively correlated (ρ = 0.690, P = .017). Fretting and corrosion damage were not significantly correlated with patient demographics or radiographic positioning of implants. There were no differences in scores between modular and monoblock designs.

CONCLUSION

These findings demonstrate that dual-mobility THA systems may be susceptible to the same fretting and corrosion damage observed in traditional modular THA systems. Future studies are needed to confirm these results and clinical significance.

Design, Material, and Seating Load Effects on In Vitro Fretting Corrosion Performance of Modular Head-Neck Tapers

BACKGROUND

The short-term corrosion and micromechanical behavior of 32 unique head-neck taper design/material/assembly conditions was tested using an incremental cyclic fretting corrosion (ICFC) test method previously developed.

METHODS

Seven materials, design, and simulated surgical parameters were evaluated, each being assigned 2 conditions for testing, using a 2^7-2 (7 factor, quarter factorial) design of experiments test matrix. The factors explored were (1) seating load, (2) head-neck offset, (3) material combination, (4) taper diameter, (5) taper roughness, (6) angular mismatch/engagement, and (7) taper length. Each sample underwent assembly, ICFC testing, pull off.

RESULTS

Low seating load and high head offset correlated with increased fretting corrosion (P < .05). High head offset also contributed to a lower onset load for fretting current and higher micromotion (P < .05). Head subsidence measured over the ICFC test for samples seated at 100 N was significantly higher than samples seated at 4000 N. Micromotion for 12-mm head offsets was statistically higher than samples with a 1.5-mm head offset. A number of interactive effects were observed. For example, samples seated at 4000 N were less sensitive to head offset than samples seated at 100 N in terms of the resulting fretting current.

CONCLUSION

Taper locking position, material combination, taper engagement length, taper roughness, and taper dimensions all had weak or no correlation with fretting current and taper micromotion. This test method and experimental design is a versatile means of assessing potential new taper designs in the future.

Management of the Implant With Taper Corrosion: What to Change and What to Change It to?

Management of implant corrosion remains a challenge for the revision arthroplasty surgeon. Our field continues to gain insight in to how to manage this clinical scenario but there are still gaps in what is known to be considered to be the standard of care. There is a significant amount of effort going in to determining the best means of managing this issue but more work is needed. There is no doubt more studies are needed to further delineate the appropriate treatment algorithms for this clinical problem.

What Factors Drive Taper Corrosion?

Adverse local tissue reactions to corrosion products can lead to total hip arthroplasty failure. Although this problem has been well known for more than 25 years, it has seemingly increased in frequency over the recent years. The occurrence of corrosion is multifactorial-depending on implant, patient, and surgeon factors. As of now, there is no "one-size-fits-all" solution to prevent corrosion in total hip arthroplasty devices. Thus, it is imperative to fully understand the exact mechanisms of modular junction corrosion to prevent premature implant failure. This review highlights a few key concepts that need to be explored to minimize the impact of corrosion. The key concepts include (1) the prevention of micromotion, (2) the role of implant alloy metallurgy in the corrosion process, (3) the in vivo generation of a corrosive environment, and (4) potential unanticipated problems.

Effects of Seating Load Magnitude on Incremental Cyclic Fretting Corrosion in 5°40' Mixed Alloy Modular Taper Junctions

BACKGROUND

Mechanically assisted crevice corrosion of modular tapers continues to be a concern in total joint arthroplasties. A surgical factor that may affect taper fretting corrosion during cyclic loading is seating load magnitude. In this study, modular head-neck taper junctions were seated, capturing load-displacement, over a range of axially oriented loads, and electrochemical and micromotion data were captured during short-term incremental cyclic fretting corrosion (ICFC) tests. The hypothesis is low seating loads result in greater motion and fretting corrosion in ICFC tests. The effect of assembly load on pull-off force post-ICFC testing was also evaluated.

METHODS

The study employed custom-built test fixtures which measured head-neck micromotion and an electrochemical chamber to monitor electrochemical reactions. Head-neck motion measurements were captured using 2 noncontact differential variable reluctance transducers mounted to the head. Seating experiments ranged from 1000 to 8000 N.

RESULTS

Significant differences due to seating loads were reported in seating displacement, ICFC subsidence, and fretting current at 4000 N cyclic load. Seating load decreased but did not eliminate currents. Fretting onset load remained fixed (approximately 1200 N) for tapers seated above 2000 N. Fretting subsidence was negligible for seating loads of 4000 N or higher, and increased subsidence was observed below 4000 N.

CONCLUSION

This short-term test method evaluated the acute performance of modular implants which were assembled under various loads and demonstrated the link between seating loads, fretting motions, and electrochemical reactions. While increased seating loads reduced fretting corrosion and taper subsidence, it did not prevent fretting corrosion even at 8 kN seating.

Fretting and Corrosion Damage in Retrieved Metal-on-Polyethylene Modular Total Hip Arthroplasty Systems: What Is the Importance of Femoral Head Size?

BACKGROUND

Fretting and corrosion at the modular femoral head-femoral neck (taper) interface have been reported in retrieved total hip arthroplasty (THA) prostheses. This study investigated associations among implant design, radiographic factors, and patient factors with corrosion and fretting at the taper interface in retrieved metal-on-polyethylene modular THA prostheses.

METHODS

Ninety-two retrieved primary metal-on-polyethylene THA implants were evaluated and graded for fretting, corrosion, and damage at the taper interface, including the femoral stem trunnion and femoral head. Preoperative radiographs were assessed for osteolysis and femoral stem alignment; and medical records were reviewed for demographic data.

RESULTS

Male patients had greater head corrosion (P = .037), patient age at revision had a weak, negative correlation with trunnion corrosion (ρ = -0.20, P = .04), and both body mass index and duration of implantation had weak, positive correlations with head fretting (ρ = 0.26, P = .01 and ρ = 0.33, P = .001, respectively). A weak, negative correlation was found between femoral head size and both head fretting and head corrosion (ρ = -0.26, P = .007 and ρ = -0.21, P = .028, respectively), and a weak, positive correlation was found between head offset and trunnion fretting (ρ = 0.23, P = .030). Varus femoral stem alignment was associated with greater head fretting (P = .038).

CONCLUSION

Larger femoral head sizes were correlated with less severe head corrosion and head fretting, with 28-mm heads exhibiting more moderate-to-severe damage. Other factors, such as head-taper engagement and geometry, rather than head size, may affect rates of corrosion and fretting damage at the taper interface.

Does the Additional Articulation in Retrieved Bipolar Hemiarthroplasty Implants Decrease Trunnionosis Compared to Total Hip Arthroplasty?

BACKGROUND

Trunnionosis at the modular head-neck taper interface in metal-on-polyethylene total hip arthroplasty (MoP THA) has been shown to occur, and represents a potential mode of MoP THA failure. The purpose of the present investigation is to elucidate differences in fretting and corrosion at the head-neck taper interface of prostheses retrieved from bipolar hemiarthroplasty (BH) and MoP THA.

METHODS

A retrieval analysis of BH and MoP THA prostheses featuring a single taper design from a single manufacturer and in vivo for a minimum 2 years was performed. Fifteen femoral heads of 28-mm diameter and corresponding femoral stems retrieved from BH were compared with MoP THA implants matched based on time in vivo and head length (28 mm, -3 mm to 28 mm, +8 mm). Fretting and corrosion damage scoring was completed under stereomicroscopic visualization.

RESULTS

Femoral head bore tapers retrieved from BH exhibited decreased overall fretting (P = .02), when compared to those retrieved from MoP THA. Total corrosion scores for all retrieved implants were positively correlated with implantation time (ρ = 0.54, P < .02).

CONCLUSION

Femoral heads retrieved from BH exhibit decreased fretting damage compared to those retrieved from MoP THA. The added articulation in BH implants may decrease torque produced at the head-neck taper junction, thereby decreasing fretting. Increased fretting damage in implants from MoP THA is not associated with increased corrosion in 28-mm heads of this taper design. The longer a BH or MoP THA prosthesis is implanted, the greater the risk of damage due to corrosion.

Alarmingly High Rate of Implant Fractures in One Modular Femoral Stem Design: A Comparison of Two Implants

BACKGROUND

Reports of implant fracture at the modular junction have been seen in modular neck designs, stem-sleeve modular femoral stems, and diaphyseal engaging bi-body modular stems. To date, however, there has never been a direct comparison between 2 different implant designs from the same modular family. The purpose of this study is to compare the rate of implant failure of 2 such stem-sleeve modular femoral stem designs, the S-ROM and Emperion, to further identify factors which increase the risk of this mode of failure.

METHODS

A retrospective, single surgeon, review of our institutional database was performed to compare the 2 groups of patients.

RESULTS

A total of 1168 total hip arthroplasty procedures were included in our analysis, 547 (47%) with Emperion and 621 (53%) with S-ROM. Eight (1.5%) fractures in 7 patients occurred in the Emperion group compared to 1 (0.2%) fracture in the S-ROM group (P = .015).

CONCLUSION

The precise cause of the stem fractures in our study remains unknown and is likely multifactorial. Given the unexpectedly high rate of catastrophic implant failures in the form of stem fracture at the stem-sleeve junction, we recommend more judicious use of modularity in primary total hip arthroplasty.

Ceramic Bearings with Titanium Adapter Sleeves Implanted During Revision Hip Arthroplasty Show Minimal Fretting or Corrosion: a Retrieval Analysis

BACKGROUND

The BIOLOX® option system, consisting of a BIOLOX® delta ceramic femoral head with a titanium alloy adapter sleeve, is being increasingly utilized in revision hip arthroplasty. The sleeve protects the ceramic head from fracture and improper motion about the stem trunnion when a damaged trunnion is encountered at revision surgery. Corrosion and fretting due to metal-metal contact at the taper region of hip prosthesis create the potential of causing periprosthetic osteolysis and adverse local tissue reactions.

QUESTIONS/PURPOSES

The objective of this study was to identify the type and extent of damage to retrieved sleeves and ceramic heads to determine their in vivo performance.

METHODS

Twenty-four ceramic heads with titanium alloy sleeves were examined. The articular and taper surfaces for each ceramic head were assessed for metal transfer using a subjective grading system. All surfaces of the 24 titanium sleeves and stem trunnions (only available for 7 of 24 cases) were assessed for corrosion and fretting using an established grading system. Scanning electron microscopy and energy dispersive X-ray analysis were conducted on representative sample of sleeves.

RESULTS

Fretting and corrosion were higher at the inner surface of the taper sleeve than the outer sleeve. Mean fretting scores at the inner taper and outer taper sleeve surfaces were 1.8 and 1.2, respectively. The mean corrosion score at the inner taper surface was 1.8; no corrosion was observed on the outer surface of any taper sleeve. SEM and EDS analyses provided further indications of low levels of damage.

CONCLUSION

Fretting and corrosion were less severe than previously reported for conventional THA metal-metal taper connections, indicating that a ceramic head and titanium sleeve is a safe alternative in revision THA.

Mechanical, chemical and biological damage modes within head-neck tapers of CoCrMo and Ti6Al4V contemporary hip replacements

Total hip replacement (THR) failure due to mechanically assisted crevice corrosion within modular head-neck taper junctions remains a major concern. Several processes leading to the generation of detrimental corrosion products have been reported in first generation modular devices. Contemporary junctions differ in their geometries, surface finishes, and head alloy. This study specifically provides an overview for CoCrMo/CoCrMo and CoCrMo/Ti6Al4V head-neck contemporary junctions. A retrieval study of 364 retrieved THRs was conducted which included visual examination and determination of damage scores, as well as the examination of damage features using scanning electron microscopy. Different separately occurring or overlapping damage modes were identified that appeared to be either mechanically or chemically dominated. Mechanically dominated damage features included plastic deformation, fretting, and material transfer, whereas chemically dominate damage included pitting corrosion, etching, intergranular corrosion, phase boundary corrosion, and column damage. Etching associated cellular activity was also observed. Furthermore, fretting corrosion, formation of thick oxide films, and imprinting were observed which appeared to be the result of both mechanical and chemical processes. The occurrence and extent of damage caused by different modes was shown to depend on the material, the material couple, and alloy microstructure. In order to minimize THR failure due to material degradation within modular junctions, it is important to distinguish different damage modes, determine their cause, and identify appropriate counter measures, which may differ depending on the material, specific microstructural alloy features, and design factors such as surface topography. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1672-1685, 2018.

Metal-on-Metal Compared With Metal-on-Polyethylene: The Effect on Trunnion Corrosion in Total Hip Arthroplasty

BACKGROUND

Trunnion tribocorrosion in total hip arthroplasties is concerning, but retrieval studies often are subjective or lack comparison groups. Quantitative comparisons of clinically relevant implants are required. The purpose of this investigation was to evaluate material loss in metal-on-metal (MoM) and metal-on-polyethylene (MoP) total hip articulations while controlling for trunnion design and head size.

METHODS

The 166 retrieved femoral heads from 2 manufacturers were analyzed. Four cohorts based on head size, trunnion design, manufacturer, and articulation type (MoM vs MoP) were created. Corrosion was measured by a coordinate measurement machine, and material loss was assessed (MATLAB).

RESULTS

Retrieved femoral heads from MoP articulations had 5 times less trunnion material loss than MoM articulations, on average, for both manufacturers. There was no difference in material loss between large modular head (>40 mm) and 36-mm MoM hip trunnion. Implants with a material loss above the detectable limit demonstrated a correlation with time in vivo only in MoP articulations.

CONCLUSION

Retrieved femoral heads from MoP bearing couples had a lower magnitude of material loss than MoM couples, independent of head diameter. A time in vivo effect was only seen in MoP bearings.

Retrieval Analysis of Neck-Stem Coupling in Modular Hip Prostheses

BACKGROUND

Dual-taper modular stems have suffered from high revision rates caused by adverse local tissue reactions secondary to fretting and corrosion. We compared the fretting and corrosion behavior of a group of modular neck designs to that of a design that had been recalled for risks associated with fretting and corrosion at the modular neck junction.

METHODS

We previously analyzed fretting and corrosion on 60 retrieved Rejuvenate modular neck-stem implants. Here we compare those results to results from 26 retrieved implants from 7 other modular neck designs. For the 26 additional cases, histology slides of tissue collected at revision were reviewed and graded for aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL). Multivariate analyses were performed to assess differences in fretting and corrosion, adjusting for confounding factors (eg, length of implantation).

RESULTS

The Rejuvenate design had higher damage and corrosion scores than the other 7 designs (P < .01). Histologic samples from the recalled design were 20 times more likely to show ALVAL than samples from the other designs (P < .01). Mixed metal couples had higher fretting (P < .01) and corrosion (P = .02) scores than non-mixed metal couples.

CONCLUSION

Fretting and corrosion occurred on all modular neck-stem retrievals regardless of design. However, mixed metal couples suffered more corrosion than homogenous couples. This may be due to the lower modulus of the titanium alloy used for the stem, allowing for increased metal transfer and surface damage when loaded against a cobalt alloy modular neck, which in turn could account for the higher ALVAL and corrosion scores. Due to increased corrosion risk with mixed metals and increased neck fracture risk with non-mixed metal stem and necks, we suggest that clinicians avoid implantation of modular neck-stem systems.

Assessment of Corrosion, Fretting, and Material Loss of Retrieved Modular Total Knee Arthroplasties

BACKGROUND

Modular junctions in total hip arthroplasties have been associated with fretting, corrosion, and debris release. The purpose of this study is to analyze damage severity in total knee arthroplasties of a single design by qualitative visual assessment and quantitative material loss measurements to evaluate implant performance and patient impact via material loss.

METHODS

Twenty-two modular knee retrievals of the same manufacturer were identified from an institutional review board-approved database. Junction designs included tapers with an axial screw and tapers with a radial screw. Constructs consisted of 2 metal alloys: CoCr and Ti6Al4V. Components were qualitatively scored and quantitatively measured for corrosion and fretting. Negative values represent adhered material. Statistical differences were analyzed using sign tests. Correlations were tested with a Spearman rank order test (P < .05).

RESULTS

The median volumetric material loss and the maximum linear depth for the total population were -0.23 mm³ and 5.84 μm, respectively. CoCr components in mixed metal junctions had higher maximum linear depth (P = .007) than corresponding Ti components. Fretting scores of Ti6Al4V alloy components in mixed metal junctions were statistically higher than the remaining groups. Taper angle did not correlate with material loss.

CONCLUSION

Results suggest that CoCr components in mixed metal junctions are more vulnerable to corrosion than other components, suggesting preferential corrosion when interfacing with Ti6Al4V. Overall, although corrosion was noted in this series, material loss was low, and none were revised for clinical metal-related reaction. This suggests the clinical impact from corrosion in total knee arthroplasty is low.

Do Stem Taper Microgrooves Influence Taper Corrosion in Total Hip Arthroplasty? A Matched Cohort Retrieval Study

BACKGROUND

Previous studies identified imprinting of the stem morphology onto the interior head bore, leading researchers to hypothesize an influence of taper topography on mechanically assisted crevice corrosion. The purpose of this study was to analyze whether microgrooved stem tapers result in greater fretting corrosion damage than smooth stem tapers.

METHODS

A matched cohort of 120 retrieved head-stem pairs from metal-on-polyethylene bearings was created controlling for implantation time, flexural rigidity, apparent length of engagement, and head size. There were 2 groups of 60 heads each, mated with either smooth or microgrooved stem tapers. A high-precision roundness machine was used to measure and categorize the surface morphology. Fretting corrosion damage at the head-neck junction was characterized using the Higgs-Goldberg scoring method. Fourteen of the most damaged heads were analyzed for the maximum depth of material loss and focused ion beam cross-sectioned to view oxide and base metal.

RESULTS

Fretting corrosion damage was not different between the 2 cohorts at the femoral head (P = .14, Mann-Whitney) or stem tapers (P = .35). There was no difference in the maximum depths of material loss between the cohorts (P = .71). Cross-sectioning revealed contact damage, signs of micro-motion, and chromium-rich oxide layers in both cohorts. Microgroove imprinting did not appear to have a different effect on the fretting corrosion behavior.

CONCLUSION

The results of this matched cohort retrieval study do not support the hypothesis that taper surfaces with microgrooved stems exhibit increased in vivo fretting corrosion damage or material release.

Fretting and Corrosion at the Backside of Modular Cobalt Chromium Acetabular Inserts: A Retrieval Analysis

BACKGROUND

Adverse local tissue reaction formation has been suggested to occur with the Modular Dual Mobility (MDM) acetabular design. Few reports in the literature have evaluated fretting and corrosion damage between the acetabular shell and modular metal inserts in this modular system. We evaluated a series of 18 retrieved cobalt chromium MDM inserts for evidence of fretting and corrosion.

METHODS

We assessed the backsides of 18 MDM components for evidence of fretting and corrosion in polar and taper regions based on previously established methods. We collected and assessed 30 similarly designed modular inserts retrieved from metal-on-metal (MoM) total hip arthroplasties as a control.

RESULTS

No specific pattern of fretting or corrosion was identified on the MDM inserts. Both fretting and corrosion were significantly greater in the MoM cohort than the MDM cohort, driven by higher fretting and corrosion scores in the engaged taper region of the MoM inserts.

CONCLUSION

MoM components demonstrated more fretting and corrosion than MDM designs, specifically at the taper region, likely driven by differences in the taper engagement mechanism and geometry among the insert designs. The lack of significant fretting and corrosion observed in the MDM inserts are inconsistent with recent claims that this interface may produce clinically significant metallosis and adverse local tissue reactions.

Corrosion of the Head-Stem Taper Junction-Are We on the Verge of an Epidemic?: Review Article

BACKGROUND

The modular head taper junction has contributed to the success of total hip arthroplasty (THA) greatly. Taper corrosion and wear problems reported for large and extra-large metal-on-metal bearings as well as for bi-modular THA stems have cast doubt on the benefit of the taper interface. Presently, corrosion problems are being reported for nearly all kinds of artificial hip joints incorporating metal heads, questioning taper connections in general.

QUESTIONS/PURPOSES

This study aimed to review the mechanical and electrochemical relationships that may lead to taper corrosion, which have been reported more commonly in recent literature, and to also review the contribution of patient characteristics and surgical techniques involved in taper assembly that may contribute to the problem.

METHODS

The search criteria "(corrosion) AND (hip arthroplasty) AND (taper OR trunnion)" and "(hip arthroplasty) AND ((pseudotumor) OR (pseudo-tumor))" in PubMed and the JAAOS were used for the literature search. In addition, the arthroplasty registers were considered.

RESULTS

Most studies acknowledge the multifactorial nature of the problem but concentrate their analysis on taper and implant design aspects, since this is the only factor that can be easily quantified. The sometimes conflicting results in the literature could be due to the fact that the other two decisive factors are not sufficiently considered: the loading situation in the patient and the assembly situation by the surgeon. All three factors together determine the fate of a taper junction in THA. There is no single reason as a main cause for taper corrosion. The combined "outcome" of these three factors has to be in a "safe range" to achieve a successful long-term taper fixation.

CONCLUSION

No, this is not the beginning of an epidemic. It is rather the consequence of disregarding known mechanical and electrochemical relationships, which in combination have recently caused a more frequent occurrence-and mainly reporting-of corrosion issues.

The effect of fretting associated periodic cathodic potential shifts on the electrochemistry and in vitro biocompatibility of commercially pure titanium

This study explored how periodic cathodic polarization of commercially pure titanium (cpTi) alters its electrochemical properties and biocompatibility. MC3T3-E1 preosteoblast cells were cultured directly on cpTi samples and maintained at open circuit potential (OCP) for 24 h followed by an additional 24-h sequence of periodic cathodic polarization to -1000 or -750 mV (vs. Ag/AgCl) for 1 s followed by a 5-s recovery at OCP. Control experiments were performed where the samples were maintained at OCP throughout the entire test. Subsequent electrochemical impedance spectroscopy revealed both of the periodic cathodic polarization conditions significantly reduced the polarization resistance (R_p ), while only the -1000 mV condition significantly increased the capacitance (C) as compared to the controls. Scanning electron micrographs showed that the cells were fragmented and balled up on the samples periodically shifted to -1000 mV as compared to the cells that were well spread on the controls and samples periodically shifted to -750 mV. Additionally, live/dead fluorescence microscopy revealed that periodic polarizations to -1000 mV reduced cell viability to around 12% as compared to the greater than 95% cell viability observed on the controls and samples periodically polarized to -750 mV. This work showed that periodic cathodic potential shifts can notably alter the electrochemical behavior of cpTi and the viability and morphology of cells seeded directly onto its surface. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1591-1601, 2016.

Trunnionosis: Does Head Size Affect Fretting and Corrosion in Total Hip Arthroplasty?

BACKGROUND

Wear and tribocorrosion at the modular head-neck taper interface may be a cause of failure in metal-on-polyethylene total hip arthroplasty (THA). The present investigation endeavored to elucidate the effect of femoral head diameter on fretting and corrosion in retrieved head-neck tapers.

METHODS

A retrieval analysis of THA prostheses in vivo for a minimum of 1 year was performed. Twenty-three femoral heads of 32-mm diameter were matched with 28-mm heads based on time in vivo and head length (-3 mm to +8 mm). All included implants featured a single taper design from a single manufacturer. Fretting and corrosion damage scoring was performed for each implant under stereomicroscopic visualization.

RESULTS

Head diameter was observed to affect fretting (P = .01), with 32-mm femoral heads exhibiting greater total fretting scores than 28-mm heads. Fretting damage was greatest (P = .01) in the central concentric zone of the femoral head bore tapers, regardless of head diameter, length, or stem offset. No significant effect on total corrosion scores was observed for any head or stem variable. Retrieved implant total corrosion scores were positively correlated (ρ = 0.51, P < .001) with implantation time.

CONCLUSION

Increased femoral head diameter in THA may produce greater fretting damage owing to and increased head-neck moment arm. There is no associated increase in corrosion with 28-mm and 32-mm heads of this taper design. The longer a THA prosthesis is implanted, the greater the risk of damage due to corrosion.

Effect of wire fretting on the corrosion resistance of common medical alloys

Metallic medical devices such as intravascular stents can undergo fretting damage in vivo that might increase their susceptibility to pitting corrosion. As a result, the US Food and Drug Administration has recommended that such devices be evaluated for corrosion resistance after the devices have been fatigue tested in situations where significant micromotion can lead to fretting damage. Three common alloys that cardiovascular implants are made from [MP35N cobalt chromium (MP35N), electropolished nitinol (EP NiTi), and 316LVM stainless steel (316LVM)] were selected for this study. In order to evaluate the effect of wire fretting on the pitting corrosion susceptibility of these medical alloys, small and large fretting scar conditions of each alloy fretting against itself, and the other alloys in phosphate buffered saline (PBS) at 37°C were tested per ASTM F2129 and compared against as received or PBS immersed control specimens. Although the general trend observed was that fretting damage significantly lowered the rest potential (E_r ) of these specimens (p < 0.01), fretting damage had no significant effect on the breakdown potential (E_b , p > 0.05) and hence did not affect the susceptibility to pitting corrosion. In summary, our results demonstrate that fretting damage in PBS alone is not sufficient to cause increased susceptibility to pitting corrosion in the three common alloys investigated. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2487-2494, 2017.

The Contact Ageing Effect on Fretting Damage of an Electro-Deposited Coating against an AISI52100 Steel Ball

This article investigates the effect of contact ageing on fretting damage of an epoxy-based cathodic electro-deposited coating for use on automotive seat slide tracks (made of cold-rolled high strength steel). Static normal load was induced at the contact between the coating and an AISI52100 ball for a certain duration. It was identified that plastically deformed contact area increased logarithmically as a function of time when the contact was under static normal load. Fretting tests after various durations of static contact were conducted using a ball-on-flat plate apparatus. All fretting tests were halted when the friction coefficient reached a critical value of 0.5, indicating complete coating failure. The total number of fretting cycles to the critical friction coefficient was found to vary with the duration of static contact before fretting. It was identified that the number of cycles to the critical friction coefficient decreased with the increased duration of static contact. Meanwhile, the friction coefficient at steady-state sliding was not greatly affected by the duration of static contact before fretting. Finally, the relation between coating thickness after indentation creep and the number of cycles to the critical friction coefficient was found to be linear. Obtained results show that the duration of static contact before fretting has an influence on the fretting lifetime of an electro-deposited coating.

Does Taper Size Have an Effect on Taper Damage in Retrieved Metal-on-Polyethylene Total Hip Devices?

BACKGROUND

Taper design has been identified as a possible contributor to fretting corrosion damage at modular connections in total hip arthroplasty systems, but variations in as-manufactured taper interfaces may confound this analysis. This study characterized taper damage in retrievals with 2 different taper sizes but comparable taper surface finishes and investigated if fretting and corrosion damage is related to taper size in the context of a multivariable analysis for metal-on-polyethylene bearings.

METHODS

A total of 252 cobalt chromium femoral heads were identified in a collection of retrievals: 77 with taper A and 175 with taper B. Implantation time averaged 5.4 ± 6.0 years (range, 0-26 years). Explants were cleaned and analyzed using a 4-point semiquantitative method. Clinical and device factors related to head taper fretting corrosion damage were assessed using ordinal logistic regression with forward stepwise control. Components were then selected to create 2 balanced cohorts, matched on significant variables from the multivariable analysis.

RESULTS

Increased head offset (P < .001), longer implantation time (P = .002), heavier patients (P < .001), and more flexible tapers (P < .001) were associated with increased taper fretting and corrosion damage. When damage scores were compared between the balanced groups, no significant differences were found.

CONCLUSION

These results suggest that fretting and corrosion damage is insensitive to differences in taper size. The final model derived explains almost half of the fretting corrosion damage observed and identifies contributing factors that are consistent with other in vitro and retrieval studies.

The Effect of Impact Location on Force Transmission to the Modular Junctions of Dual-Taper Modular Hip Implants

BACKGROUND

The purpose of this study was to investigate the effect that off-axis impaction has on stability of dual-taper modular implants as measured by forces delivered to and transmitted through the head-neck and neck-stem tapers, respectively.

METHODS

One hundred forty-four impact tests were performed using 6 different directions: one on-axis and five 10° off-axes. Four different simulations were performed measuring the head-neck only and 3 different neck angulations: 0°, 8°, and 15°. A drop tower impactor delivered both on- and off-axis impaction from a constant height. Load cells positioned in the drop mass and at the head-neck (HN) or neck-stem (NS) junction measured the impact and joint forces, respectively.

RESULTS

Impact force of the hammer on the head ranged from 3800-4500 N. Greatest impact force delivered to the head was typically with axial impact. However, greatest force transmission to the neck-stem junction was not necessarily with axial impacts. There was limited variability in the force measured at the NS junction for all impaction directions seen in the 8° neck, whereas the 15° neck had greater forces transmitted to the NS junction with off-axes impactions directed in the proximal and posterior-proximal directions.

CONCLUSION

The location of the impact significantly influences the force transmitted to the head-neck and neck-stem junctions in dual-taper modular hip implants. Although axial impacts proved superior to off-axis impacts for the straight 0° neck, greater force transmission with off-axis impacts for the angled necks suggests that off-axis impacts may potentially compromise the stability of dual-taper components.

Fretting Fatigue Behaviour of Pin-Loaded Thermoset Carbon-Fibre-Reinforced Polymer (CFRP) Straps

This paper focuses on the fretting fatigue behaviour of pin-loaded carbon-fibre-reinforced polymer (CFRP) straps studied as models for rigging systems in sailing yachts, for suspenders of arch bridges and for pendent cables in cranes. Eight straps were subjected to an ultimate tensile strength test. In total, 26 straps were subjected to a fretting fatigue test, of which ten did not fail. An S–N curve was generated for a load ratio R of 0.1 and a frequency f of 10 Hz, showing a fatigue limit stress of the straps around the matrix fatigue limit, corresponding to 46% of the straps’ ultimate tensile strength (σ_UTS). The fatigue limit was defined as 3 million load cycles (N = 3 × 10⁶), but tests were even conducted up to N = 11.09 × 10⁶. Catastrophic failure of the straps was initiated in their vertex areas. Investigations on the residual strength and stiffness properties of straps tested around the fatigue limit stress (for N ≥ 1 × 10⁶) showed little influence of the fatigue loading on these properties. Quasi-static finite element analyses (FEA) were conducted. The results obtained from the FEA are in good agreement with the experiments and demonstrate a fibre parallel stress concentration in the vertex area of factor 1.3, under the realistic assumption of a coefficient of friction (cof) between pin and strap of 0.5.

Tribocorrosion in shoulder arthroplasty humeral component retrievals

BACKGROUND

Tribocorrosion at the modular taper connections of total hip implants has been associated with trunnionosis and adverse local tissue reactions. Modularity is also widely used in shoulder arthroplasty implants, but little information exists about the potential for tribocorrosion. This study hypothesized that there would be mild or no tribocorrosion in a series of retrieved shoulder implants.

METHODS

A total of 28 implants with a mean implantation time of 6.2 ± 6.0 years were evaluated using a validated damage scoring method. Implant tapers on the head and stem were divided into upper (deepest) and lower zones and independently scored for fretting and corrosion damage from 1 (none) to 4 (severe).

RESULTS

Corrosion was present on 32% of heads and 38% of stems, whereas fretting was present on 36% of heads and 46% of stems. There was significantly greater (P = .02) corrosion in the lower zone of the retrieved stems (1.4 ± 0.5) than there was in the upper zone (1.1 ± 0.3). Correlation between the head and stem corrosion for lower zone was moderate (r = 0.41; P = .04).

DISCUSSION

Tribocorrosion was present on the heads and stems of some of the retrieved shoulder implants examined in this study. The incidence of tribocorrosion in shoulder implants was lower than in reported cases of retrieved hip implants. The greatest damage was in the lower zone of the taper, where the connection may be exposed to the surrounding joint fluid. It remains to be seen whether this leads to any clinical presentation of trunnionosis.

Adverse reactions to metal debris in metal-on-polyethylene total hip arthroplasty using a titanium-molybdenum-zirconium-iron alloy stem

We report a series of three patients who underwent uncemented total hip arthroplasty with a modular titanium-molybdenum-zirconium-iron stem and a cobalt-chrome-molybdenum head on an ultra-high molecular weight highly cross-linked polyethylene liner bearing. All three cases subsequently developed pain and adverse reaction to metal debris, leading to revision of the implants within thirty-six months. They were subsequently found to have hypersensitivity to cobalt or chromium. However where tested, blood metal ion levels were within MHRA guideline limits. Corrosion was noted at the taper-trunnion junction. It is possible, that the multi alloy head-neck combination may lead to corrosion. Hypersensitivity to metal ions may result to ARMD at lower metal ion levels. The use of ceramic heads may help avoid this risk.

Mechanically assisted taper corrosion in modular TKA

The purpose of this study was to characterize the prevalence of taper damage in modular TKA components. One hundred ninety-eight modular components were revised after 3.9±4.2 years of implantation. Modular components were evaluated for fretting corrosion using a semi-quantitative 4-point scoring system. Design features and patient information were assessed as predictors of fretting corrosion damage. Mild-to-severe fretting corrosion (score ≥2) was observed in 94/101 tapers on the modular femoral components and 90/97 tapers on the modular tibial components. Mixed alloy pairs (p=0.03), taper design (p<0.001), and component type (p=0.02) were associated with taper corrosion. The results from this study supported the hypothesis that there is taper corrosion in TKA. However the clinical implications remain unclear.

The reliability of a scoring system for corrosion and fretting, and its relationship to material loss of tapered, modular junctions of retrieved hip implants

It has been suggested that corrosion and fretting at the tapered, modular junctions of hip arthroplasties may contribute to implant failure. In this study the reliability of a commonly used peer-reviewed scoring system for visual assessment of corrosion and fretting at these junctions was evaluated. Volumetric material loss at the tapered head surface was measured and associations with the visual scores were investigated. We found that the inter-observer reproducibility and single-observer repeatability of the corrosion scores were substantial using Cohen's weighted Kappa statistic (k = 0.64-0.71). The reproducibility and repeatability of the fretting scores however were slight to fair (k = 0.18-0.31). Taper corrosion scores were significantly and moderately correlated with the volume of material loss measured (Spearman's r = 0.59; P < 0.001). We recommend the continued use of this scoring system but it should not be a substitute for measurement of material loss.

Friction and solid-solid adhesion on complex metallic alloys

The discovery in 1987 of stable quasicrystals in the Al-Cu-Fe system was soon exploited to patent specific coatings that showed reduced friction in ambient air against hard antagonists. Henceforth, it was possible to develop a number of applications, potential or commercially exploited to date, that will be alluded to in this topical review. A deeper understanding of the characteristics of complex metallic alloys (CMAs) may explain why material made of metals like Al, Cu and Fe offers reduced friction; low solid-solid adhesion came later. It is linked to the surface energy being significantly lower on those materials, in which translational symmetry has become a weak property, that is determined by the depth of the pseudo-gap at the Fermi energy. As a result, friction is anisotropic in CMAs that builds up according to the translation symmetry along one direction, but is aperiodic along the other two directions. A review is given in this article of the most salient data found along these lines during the past two decades or so.

Is increased modularity associated with increased fretting and corrosion damage in metal-on-metal total hip arthroplasty devices?: a retrieval study

This retrieval study documents taper damage at modular interfaces in retrieved MOM THA systems and investigates if increased modularity is associated with increased fretting and corrosion. One hundred thirty-four (134) heads and 60 stems (41 modular necks) of 8 different bearing designs (5 manufacturers) were analyzed. Damage at the shell-liner interface of 18 modular CoCr acetabular liners and the corresponding 11 acetabular shells was also evaluated. The results of this study support the hypothesis that fretting and corrosion damage occurs at a variety of modular component interfaces in contemporary MOM THAs. We also found that modularity of the femoral stem was associated with increased damage at the head. An analysis of component and patient variables revealed that dissimilar alloy pairing, larger head sizes, increased medio-lateral offsets and longer neck moment arms were all associated with increased taper damage at the modular interfaces.

Pseudotumour formation due to tribocorrosion at the taper interface of large diameter metal on polymer modular total hip replacements

We present an in-depth failure analysis of two large diameter bearing metal-on-polymer (MoP) modular total hip replacements, which have required revision surgery due to pseudotumour formation. The failure analysis showed a discrete pattern of material loss from the distal end of the head taper/stem trunnion interface. We postulate that the use of a proximal contacting taper design had provided insufficient mechanical locking between the head and the stem, enabling the head to toggle on the trunnion. In addition, the difference in angle between the taper and the trunnion formed a crevice between the two components. Through a combination of crevice environment, mechanically assisted corrosion, mechanical wear and erosion; debris and metal-ions have been released resulting in the adverse local tissue reactions (ALTR).

Fretting fatigue behaviour of Ni-free high-nitrogen stainless steel in a simulated body fluid

Fretting fatigue behaviour of Ni-free high-nitrogen steel (HNS) with a yield strength of about 800 MPa, which was prepared by nitrogen gas pressurized electroslag remelting, was studied in air and in phosphate-buffered saline (PBS(-)). For comparison, fretting fatigue behaviour of cold-rolled SUS316L steel (SUS316L(CR)) with similar yield strength was examined. The plain fatigue limit of HNS was slightly lower than that of SUS316L(CR) although the former had a higher tensile strength than the latter. The fretting fatigue limit of HNS was higher than that of SUS316L(CR) both in air and in PBS(-). A decrease in fatigue limit of HNS by fretting was significantly smaller than that of SUS316L(CR) in both environments, indicating that HNS has better fretting fatigue resistance than SUS316L(CR). The decrease in fatigue limit by fretting is discussed taking into account the effect of friction stress due to fretting and the additional influences of wear, tribocorrosion and plastic deformation in the fretted area.