Retrieval Analysis of Titanium Nitride Coatings for Orthopaedic Implants.

BACKGROUND: The first generation of titanium nitride (TiN) coatings for orthopaedic implants was clinically introduced in the 1990s because of their promising biocompatibility, wear resistance, and corrosion resistance. This study evaluated the in vivo performance of early TiN-coated knee and hip implants, focusing on the bearing surfaces and mechanisms of in vivo damage. METHODS: There were 13 TiN-coated implants (5 knee and 8 hip) retrieved from 8 patients as part of a multi-institutional implant retrieval program. The average implantation time was 4.25 years for knees and 17.5 years for hips. Implant revisions occurred for various reasons, including polyethylene wear, loosening, pain, infection, and instability. Components were examined using a semiquantitative scoring method, and surface roughness measurements were performed using white-light interferometry. Surface morphology, chemistry, and particle characterization were also assessed by scanning electron microscopy. RESULTS: For hips, mild corrosion was found on femoral head tapers, along with severe scratching on certain femoral heads. Knee implants exhibited low burnishing and scratching for both mechanisms. Roughness measurements (Sa) were 37.3 nm (interquartile range = 22.0 to 62.4) for hips and 85.3 nm (interquartile range = 66.3 to 110) for knees. The observed scratch depth in both hip and knee implants due to third-body particles ranged from 0.3 to 1.3 µm. The coating coverage remained intact in the majority of the implants, with 2 cases of small, localized cohesive chipping and substrate exposure. CONCLUSIONS: The results of this study confirm the potential in vivo durability of early TiN coatings and will be useful in benchmarking wear tests for modern TiN-coated orthopaedic implants.

Oxidation and Damage Mechanisms of Second-Generation Highly Cross-Linked Polyethylene Tibial Inserts.

BACKGROUND: After clinical introduction in 2005, sequentially annealed, highly cross-linked polyethylene (SA HXLPE) was studied for retrievals with short implantation times; however, long-term follow-ups are lacking. The objective of this study was to examine and compare the revision reasons, damage mechanisms, and oxidation indices of SA HXLPE and conventional gamma inert-sterilized (Gamma Inert) ultra-high-molecular-weight polyethylene tibial inserts implanted for >5 years. METHODS: There were 74 total knee arthroplasty tibial inserts (46 SA HXLPEs, 28 Gamma Inerts) implanted for >5 years (mean 7 ± 2 years) retrieved as part of a multicenter retrieval program. Cruciate-retaining implants comprised 44% of the SA HXLPEs and 14% of the Gamma Inerts. Patient factors and revision reasons were collected from revision operating notes. A semiquantitative scoring method was used to assess surface damage mechanisms. Oxidation was measured using Fourier transform infrared microscopy according to American Society for Testing and Materials 2102. Differences between cohorts were assessed with Mann-Whitney U-tests. RESULTS: Loosening (Gamma Inert: 17 of 28, SA HXLPE: 15 of 46) and instability (Gamma Inert: 6 of 28, SA HXLPE: 15 of 46) were the most common revision reasons for both cohorts. The most prevalent surface damage mechanisms were burnishing, pitting, and scratching, with burnishing of the condyles being higher in Gamma Inert components (P = .022). Mean oxidation was higher in the SA HXLPE inserts at the articulating surface (P = .002) and anterior-posterior faces (P = .023). No difference was observed at the backside surface (P = .060). CONCLUSIONS: Revision reasons and surface damage mechanisms were comparable in the Gamma Inert and SA cohorts. Further studies are needed to continue to assess the in vivo damage and clinical relevance, if any, of oxidation in SA HXLPE over longer implantation times, particularly for implants implanted for more than 10 years.

Femoral Head Penetration Rates and Oxidation of Highly Cross-Linked Polyethylene Hip Liners Implanted More Than 10 Years.

BACKGROUND: Highly cross-linked polyethylene (HXLPE) was introduced to improve wear in total hip arthroplasty, with manufacturers implementing different thermal treatments to reduce oxidation. It is important to understand how long-term time in vivo affects the wear of these materials. The purpose of this study was to investigate the wear and oxidative performance of first-generation HXLPE hip inserts implanted for greater than 10 years and compare annealed and remelted HXLPE formulations. METHODS: There were 49 total hip arthroplasty liners retrieved during routine revision surgery as part of an institutional review board-approved implant retrieval program. Penetration rates for the liners were calculated as the difference between the thickness of the unloaded and loaded regions divided by implantation time. Oxidation indices for the rim, locking mechanism, articulating surface, and backside regions were measured using Fourier-transform infrared spectroscopy according to American Society for Testing and Materials 2102. Mann-Whitney U tests were used to determine the statistical difference between annealed and remelted components. RESULTS: The cohort had an average implantation time of 13.1 ± 2.6 years for annealed and 12.1 ± 1.7 years for remelted components. The components were revised most often for polyethylene wear, instability, and loosening. The penetration rate averaged 0.0177 ± 0.014 mm/year for annealed components and 0.015 ± 0.022 mm/year for remelted components. Penetration rates did not differ between the remelted and annealed cohorts (P = .28). Oxidation indices were found to be significantly higher in the annealed cohort for all regions of interest (P < .001). CONCLUSIONS: Oxidation was found to be higher in the annealed HXLPE; however, this does not seem to be associated with greater wear as we found the average penetration rates for the cohorts were low, and the penetration rates were similar between the annealed and remelted cohorts.

Short-Term Surface Damage Mechanisms of Retrieved Highly Cross-Linked Polyethylene Patellar Components.

BACKGROUND: Previous retrieval studies of patellar components for total knee arthroplasty focused on historical designs and polyethylene materials that are no longer clinically relevant. Therefore, this study aimed to compare revision reasons and surface damage mechanisms of conventional, gamma inert sterilized polyethylene and highly cross-linked polyethylene (HXLPE) patellar components in contemporary designs from a single manufacturer. METHODS: A total of 114 gamma inert and 76 HXLPE patellar components were gathered in a multicenter orthopaedic implant retrieval program. Patient age and body mass index were similar between cohorts (P = .27 and P = .42, respectively); however, the gamma inert cohort was implanted longer (µdifference = 3.1 years; P = .005). A matched subset was created based on the total knee arthroplasty design, patellar shape, and implantation time. Revision reasons were gathered from revision operating notes, and surface damage was examined via the Hood scoring method. Differences between HXLPE and gamma inert cohorts were evaluated using Mann-Whitney U-tests. RESULTS: The most common revision reasons were infection, loosening, and instability, with the most common patellar complication resulting in revision being patellar loosening for both cohorts with similar incidences for both (chi-square; P = .60, P = .59). The most common surface damage modes were burnishing, scratching, and pitting in both cohorts. Total surface damage was significantly higher in the gamma inert components (P = .02), but not in the matched subset (P = .46). CONCLUSION: Overall, the clinical performance of HXLPE was similar to that of conventional polyethylene for patellar components with short implantation times. While this study provides much needed information on the performance of HXLPE patellae in short-term retrievals, long-term studies are still needed.

Fretting Corrosion, Third-Body Polyethylene Damage, and Cup Positioning in Primary vs Revision Dual Mobility Total Hip Arthroplasty.

BACKGROUND: Dual mobility (DM) articulations were introduced for total hip arthroplasty to reduce the risk of instability for patients who have a high risk of dislocation. The use of DM constructs in both primary and revision total hip arthroplasty has been steadily increasing, leading to concerns regarding potential risks of fretting corrosion, polyethylene wear, metal release, and failure due to component positioning. METHODS: A total of 56 retrieved DM constructs were collected. The inner and outer polyethylene liner surfaces were assessed for 7 damage mechanisms, and fretting corrosion was evaluated for the femoral stem, head, and modular liner. Three polyethylene liners with the greatest amounts of embedded debris were examined using scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to determine the elemental content of the debris. Acetabular cup orientation was analyzed radiographically using the EBRA (Einzel-Bild-Roentgen-Analyse) method. RESULTS: The devices were revised most frequently for infection (36%), loosening (21%), and instability/dislocation (18%). The most common polyethylene damage mechanisms were scratching, pitting, burnishing, and embedded debris, and no difference in total damage was found between primary and revision cases. Scanning electron microscopy/energy-dispersive X-ray spectroscopy revealed that debris morphology and composition were consistent with porous titanium coating, resulting from cup loosening or broken screws and augments. A total of 71% and 50% of the constructs were determined to be within the Lewinnek safe zone for inclination and anteversion, respectively. CONCLUSION: The most notable mechanisms of surface damage were due to third-body debris, especially for the polyethylene surfaces which articulate against cobalt-chromium femoral heads and acetabular liners. Scratching of the femoral head and the metal liner from this debris may support the clinical use of ceramic for DM bearing surfaces in the future.

A systematic review of preclinical in vivo testing of 3D printed porous Ti6Al4V for orthopedic applications, part I: Animal models and bone ingrowth outcome measures.

For Ti6Al4V orthopedic and spinal implants, osseointegration is often achieved using complex porous geometries created via additive manufacturing (AM). While AM porous titanium (pTi) has shown clinical success, concerns regarding metallic implants have spurred interest in alternative AM biomaterials for osseointegration. Insights regarding the evaluation of these new materials may be supported by better understanding the role of preclinical testing for AM pTi. We therefore asked: (a) What animal models have been most commonly used to evaluate AM porous Ti6Al4V for orthopedic bone ingrowth; (b) What were the primary reported quantitative outcome measures for these models; and (c) What were the bone ingrowth outcomes associated with the most frequently used models? We performed a systematic literature search and identified 58 articles meeting our inclusion criteria. We found that AM pTi was evaluated most often using rabbit and sheep femoral condyle defect (FCD) models. Additional ingrowth models including transcortical and segmental defects, spinal fusions, and calvarial defects were also used with various animals based on the study goals. Quantitative outcome measures determined via histomorphometry including ''bone ingrowth'' (range: 3.92-53.4% for rabbit/sheep FCD) and bone-implant contact (range: 9.9-59.7% for rabbit/sheep FCD) were the most common. Studies also used 3D imaging to report outcomes such as bone volume fraction (BV/TV, range: 4.4-61.1% for rabbit/sheep FCD), and push-out testing for outcomes such as maximum removal force (range: 46.6-3092 N for rabbit/sheep FCD). Though there were many commonalities among the study methods, we also found significant heterogeneity in the outcome terms and definitions. The considerable diversity in testing and reporting may no longer be necessary considering the reported success of AM pTi across all model types and the ample literature supporting the rabbit and sheep as suitable small and large animal models, respectively. Ultimately, more standardized animal models and reporting of bone ingrowth for porous AM materials will be useful for future studies.

Quantitative ultrahigh-molecular-weight polyethylene wear in total elbow retrievals.

BACKGROUND: The purpose of this study was to evaluate ultrahigh-molecular-weight polyethylene (UHMWPE) wear and damage from retrieved total elbow arthroplasty components and compare in vivo wear with wear produced in vitro. METHODS: Explanted total elbow components were collected at revision surgery. UHMWPE damage was characterized visually, whereas penetration and wear were quantified using micro-computed tomography and gas pycnometry. Volumetric wear rates were compared with historical hip data, and wear data were compared with reported in vitro wear test data. RESULTS: Humeral bushing damage primarily occurred in the form of burnishing, scratching, and pitting at the articular face in the region of contact with the ulnar component. Wear of the ulnar bushings was concentrated on the edge of the component at the point of contact with the axis pin. Pitting and embedded debris were dominant damage modes, in addition to burnishing and delamination. Backside wear was negligible. The median linear penetration rates of the lateral, medial, and ulnar bushings were 0.14 mm/yr (range, 0.01-0.78 mm/yr), 0.12 mm/yr (range, 0.03-0.55 mm/yr), and 0.11 mm/yr (range, 0.01-0.69 mm/yr), respectively. The volumetric wear rates of the lateral, medial, and ulnar bushings were 5.5 mm3/yr (range, 0.7-37.2 mm3/yr), 5.9 mm3/yr (range, 0.6-25.5 mm3/yr), and 5.5 mm3/yr (range, 1.2-51.2 mm3/yr), respectively. CONCLUSIONS: The observed wear rates were similar to those reported in well-functioning total hip replacement patients with conventional UHMWPE bearings. We found limitations in reported in vitro testing resulting in wear that was not consistent with our retrieval data. We recommend further investigation to clinically validate in vitro simulation to provide appropriate loading protocols for elbow wear simulation.

Retrieval Analysis of Cruciate-Retaining and Posterior-Stabilized Total Knee Arthroplasty and Correlations to Laxity and Wear.

BACKGROUND: Total knee arthroplasty (TKA) with posterior-stabilized (PS) or posterior cruciate-retaining (CR) implants has high success rates and survivorship. However, it is uncertain how laxity and constraint are associated with long-term polyethylene wear under physiological conditions. METHODS: To answer this question, we measured the laxity patterns of 47 harvested cadaver specimens with primary TKAs in a custom knee-testing machine at full extension and at 30°, 60°, and 90° of flexion. The wear patterns of the tibial inserts were assessed using a semiquantitative method which is a modified approach of that proposed by Hood et al in 1983. RESULTS: Statistical analysis found that the PS TKA cohort had a statistically significant increase in varus laxity at 60° and 90° of flexion, as well as total coronal laxity at 60° of flexion when compared to the CR cohort. Furthermore, analysis demonstrated a significant correlation between increased PS coronal laxity and increased tibial wear, a trend that was not seen in the CR specimens. CONCLUSION: Our findings suggest that greater laxity in flexion after primary TKA may increase the wear realized over time and that PS TKAs may be more susceptible due to the loss of support the PCL affords to the flexion space. Whether a CR or PS TKA is used, surgeons need to avoid the pitfalls that may create greater flexion laxity during the procedure to optimize long-term polyethylene wear.

Thermal Localization Improves the Interlayer Adhesion and Structural Integrity of 3D printed PEEK Lumbar Spinal Cages.

Additive manufacturing (AM) is a potential application for polyetheretherketone (PEEK) spinal interbody fusion cages, which were introduced as an alternative to titanium cages because of their biocompatibility, radiolucency and strength. However, AM of PEEK is challenging due to high melting temperature and thermal gradient. Although fused filament fabrication (FFF) techniques have been shown to 3D print PEEK, layer delamination was identified in PEEK cages printed with a first generation FFF PEEK printer [1]. A standard cage design [2] was 3D printed with a second generation FFF PEEK printer. The effect of changing layer cooling time on FFF cages' mechanical strength was investigated by varying nozzle sizes (0.2 mm and 0.4 mm), print speeds (1500 and 2500 mm/min), and the number of cages printed in a single build (1, 4 and 8). To calculate the porosity percentage, FFF cages were micro-CT scanned prior to destructive testing. Mechanical tests were then conducted on FFF cages according to ASTM F2077 [2]. Although altering the cooling time of a layer was not able to change the failure mechanism of FFF cages, it was able to improve cages' mechanical strength. Printing a single cage per build caused a higher ultimate load than printing multiple cages per build. Regardless of the cage number printed per build, cages printed with bigger nozzle diameter achieved higher ultimate load compared to cages printed with smaller nozzle diameter. Printing with a bigger nozzle diameter resulted in less porosity, which might have an additional affect on the interlayer delamination failure mechanism.

Acoustic Parameters for Optimal Ultrasound-Triggered Release from Novel Spinal Hardware Devices.

Post-operative infection is a catastrophic complication of spinal fusion surgery, with rates as high as 10%, and existing preventative measures (i.e., peri-operative antibiotics) are only partially successful. To combat this clinical problem, we have designed a drug delivery system around polyether ether ketone clips to be used for prophylactic post-surgical release of antibiotics upon application of ultrasound. The overall hypothesis is that antimicrobial release from this system will aggressively combat post-surgical bacterial survival. This study investigated a set of acoustic parameters optimized for in vitro ultrasound-triggered coating rupture and subsequent release of encapsulated prophylactic antibiotics. We determined that a transducer frequency of 1.7 MHz produced the most consistent burst release and that, at this frequency, a pulse repetition frequency of 6.4 kHz and acoustic output power of 100% (3.41 MPa) produced the greatest release, representing an important proof of principle and the basis for continued development of this novel drug delivery system.

Does annealing improve the interlayer adhesion and structural integrity of FFF 3D printed PEEK lumbar spinal cages?

Polyaryletheretherketone (PEEK) has been commonly used for interbody fusion devices because of its biocompatibility, radiolucency, durability, and strength. Although the technology of PEEK Additive Manufacturing (AM) is rapidly developing, post-processing techniques of 3D printed PEEK remain poorly understood. AM of PEEK has been challenging because of its high melt temperature (over 340 °C) and requires specialized equipment which was not commercially available until recently. A lumbar fusion cage design, used in ASTM interlaboratory studies, was 3D printed with a medical grade PEEK filament via Fused Filament Fabrication (FFF) under two different print speeds. PEEK cages were then annealed above the PEEK's glass transition temperature, at 200 °C or 300 °C. AM cages were CT scanned to determine the porosity before and after annealing. Mechanical tests were conducted on cages according to ASTM F2077 (ASTM F2077, 2014). SEM images helped to evaluate the cages' surface morphology before and after heat treatment. It was observed that annealing did not produce markedly better mechanical properties at either temperature, however, it had an effect on the cages' mechanical properties at lower printing speed under all loading conditions. Although the structure of the pores changed after annealing, annealing conditions examined here as a post-processing method were not able to decrease the undesired porosity formed during the 3D printing process or change the failure mechanism, which is due interlayer debonding.

Reasons for Revision, Oxidation, and Damage Mechanisms of Retrieved Vitamin E-Stabilized Highly Crosslinked Polyethylene in Total Knee Arthroplasty.

BACKGROUND: In order to improve oxidation resistance, antioxidants such as vitamin-E are added to polyethylene used in the bearing surfaces of orthopedic components. Currently, little is known about the efficacy of this treatment in vivo. This study therefore reports on the reasons for revision, surface damage mechanisms, and oxidation of retrieved vitamin E-stabilized highly crosslinked polyethylene (HXLPE) for total knee arthroplasty. METHODS: We examined 103 retrieved knee inserts fabricated from vitamin E (VE)-stabilized HXLPE and 67 fabricated from remelted HXLPE as a control. The implantation times were 1.2 ± 1.3 and 1.5 ± 1.3 years for the VE and control cohorts, respectively. The inserts were evaluated for 7 surface damage mechanisms using a semiquantitative scoring method and analyzed for oxidation using Fourier-transform infrared spectroscopy. Reasons for revision were also assessed using operative notes created at time of retrieval. RESULTS: Both groups were revised primarily for instability, infection, and loosening. Burnishing, pitting, and scratching were the most common damage mechanisms observed, with the VE cohort demonstrating less surface damage than the control. Measured oxidation for the cohort was low, with a median oxidation index of 0.09 ± .05 for the articulating surface, 0.05 ± 0.06 for the backside, 0.08 ± 0.06 for the anterior/posterior surfaces, and 0.08 ± 0.05 for the stabilizing post. As compared to the control cohort, oxidation tended to be less for the VE group at the articulating (P < .001) and backside (P = .003) surfaces, although the median differences were minimal and may not be clinically significant. CONCLUSION: The results indicate positive fatigue damage resistance and oxidation resistance for the retrieved VE-stabilized total knee arthroplasty inserts.

Structure-Property Relationships for 3D printed PEEK Intervertebral Lumbar Cages Produced using Fused Filament Fabrication.

Recent advances in additive manufacturing technology now enable fused filament fabrication (FFF) of Polyetheretherketone (PEEK). A standardized lumbar fusion cage design was 3D printed with different speeds of the print head nozzle to investigate whether 3D printed PEEK cages exhibit sufficient material properties for lumbar fusion applications. It was observed that the compressive and shear strength of the 3D printed cages were 63-71% of the machined cages, whereas the torsion strength was 92%. Printing speed is an important printing parameter for 3D printed PEEK, which resulted in up to 20% porosity at the highest speed of 3000 mm/min, leading to reduced cage strength. Printing speeds below 1500 mm/min can be chosen as the optimal printing speed for this printer to reduce the printing time while maintaining strength. The crystallinity of printed PEEK did not differ significantly from as-machined PEEK cages from extruded rods, indicating that the processing provides similar microstructure.

What Is the Incidence of Cobalt-Chromium Damage Modes on the Bearing Surface of Contemporary Femoral Component Designs for Total Knee Arthroplasty?

BACKGROUND: The purpose of this study was to determine the incidence of metal release in contemporary total knee arthroplasty and the patient-related factors associated with this release. METHODS: In total, 256 retrieved cobalt-chromium femoral components were collected through a multi-institutional orthopedic implant retrieval program (implanted: 1-15 years). Implants were mainly revised for loosening (84/256), instability (62/256), and infection (46/256). Third-body damage was assessed using a semiquantitative scoring method. Microscale electro-corrosion damage (MECD) was evaluated using digital optical microscopy. Radii of curvature were measured from representative components to calculate anterior-posterior and medial-lateral ratios. Femoral component surface roughness was measured using a white light interferometer. Using a multivariable linear model, associations between damage score, implant, and patient factors were tested. Spearman's ρ correlation tests were performed to determine the association between roughness measurements and damage score. RESULTS: Mild to severe damage was observed in 52% (134/256) of the components. In the multivariable linear model, anterior-posterior ratio (ß = -8.07; P < .001), loosening (ß = -0.52; P = .006), and patient weight (ß = 0.01; P = .007) were associated with damage score. Suspected MECD damage was observed in 82% (209/256) of components. The Ra value (ρ = 0.196; P = .002) and Rq value (ρ = 0.157; P = .012) increased as the damage score increased. CONCLUSION: The findings of this retrieval study support that similar damage mechanisms exist in contemporary and long-term total knee arthroplasty devices. Additionally, we observed associations between loosening, anterior-posterior conformity, and patient weight with increased surface damage.

Oxidation, Damage Mechanisms, and Reasons for Revision of Sequentially Annealed Highly Crosslinked Polyethylene in Total Knee Arthroplasty.

BACKGROUND: Sequentially annealed, highly crosslinked polyethylene (HXLPE) has been used clinically in total knee arthroplasty (TKA) for over a decade. However, little is known about the revision reasons; its surface damage mechanisms; or its in vivo oxidative stability relative to conventional polyethylene. We asked whether retrieved HLXPE tibial inserts exhibited: (1) similar revision reasons; (2) improved resistance to surface damage; and (3) improved oxidative stability, when compared with conventional gamma inert sterilized polyethylene inserts. METHODS: A total of 456 revised tibial inserts were collected in a multicenter retrieval program between 2000 and 2016. The implantation time for the HXLPE components was 1.8 ± 1.8 years, and for the control inserts it was 3.4 ± 2.7 years. Revision reasons were assessed based on medical records, radiographs, and examinations of the retrieved components. Surface damage was assessed using a semi-quantitative scoring method. Oxidation was measured using Fourier transform infrared spectroscopy. RESULTS: The tibial inserts in both cohorts were revised most frequently for loosening, infection, and instability. The most commonly observed surface damage modes were burnishing, pitting, and scratching. Oxidation of the HXLPE inserts was, on average, low and similar to the control inserts at the bearing surface and the stabilizing post. CONCLUSIONS: We observed evidence of in vivo oxidation in both HXLPE and control tibial inserts. We found no association between the levels of oxidation and the clinical performance of the HXLPE tibial components. The findings of this study document the revision reasons, surface damage modes, and oxidative behavior of sequentially annealed HXLPE for TKA.

Fretting and Corrosion Damage in Taper Adapter Sleeves for Ceramic Heads: A Retrieval Study.

BACKGROUND: During revision surgery with a well-fixed stem, a titanium sleeve can be used in conjunction with a ceramic head to achieve better stress distribution across the taper surface. In vitro testing suggests that corrosion is not a concern in sleeved ceramic heads; however, little is known about the in vivo fretting corrosion of the sleeves. The purpose of this study was to investigate fretting corrosion in sleeved ceramic heads in retrieved total hip arthroplasties. METHODS: Thirty-seven sleeved ceramic heads were collected during revision. The femoral heads and sleeves were implanted 0.0-3.3 years. The implants were revised predominantly for instability, infection, and loosening. Fifty percent of the retrievals were implanted during a primary surgery. Fretting corrosion was assessed using the Goldberg-Higgs semiquantitative scoring system. RESULTS: Mild-to-moderate fretting corrosion scores (score = 2-3) were observed in 92% of internal tapers, 19% of external tapers, and 78% of the stems. Severe fretting corrosion was observed in 1 stem trunnion that was previously retained during revision surgery and none of the retrieved sleeves. There was no difference in corrosion damage of sleeves used in primary or revision surgery. CONCLUSION: The fretting corrosion scores in this study were predominantly mild and lower than reported fretting scores of cobalt-chrome heads in metal-on-polyethylene bearings. Although intended for use in revisions, we found that the short-term in vivo corrosion behavior of the sleeves was similar in both primary and revision surgery applications. From an in vivo corrosion perspective, sleeves are a reasonable solution for restoring the stem taper during revision surgery.

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.

Corrosion Damage and Wear Mechanisms in Long-Term Retrieved CoCr Femoral Components for Total Knee Arthroplasty.

BACKGROUND: Metal debris and ion release has raised concerns in joint arthroplasty. The purpose of this study was to characterize the sources of metallic ions and particulate debris released from long-term (in vivo >15 years) total knee arthroplasty femoral components. METHODS: A total of 52 CoCr femoral condyles were identified as having been implanted for more than 15 years. The femoral components were examined for incidence of 5 types of damage (metal-on-metal wear due to historical polyethylene insert failure, mechanically assisted crevice corrosion at taper interfaces, cement interface corrosion, third-body abrasive wear, and inflammatory cell-induced corrosion [ICIC]). Third-body abrasive wear was evaluated using the Hood method for polyethylene components and a similar method quantifying surface damage of the femoral condyle was used. The total area damaged by ICIC was quantified using digital photogrammetry. RESULTS: Surface damage associated with corrosion and/or CoCr debris release was identified in 51 (98%) CoCr femoral components. Five types of damage were identified: 98% of femoral components exhibited third-body abrasive wear (mostly observed as scratching, n = 51/52), 29% of femoral components exhibited ICIC damage (n = 15/52), 41% exhibited cement interface damage (n = 11/27), 17% exhibited metal-on-metal wear after wear-through of the polyethylene insert (n = 9/52), and 50% of the modular femoral components exhibited mechanically assisted crevice corrosion taper damage (n = 2/4). The total ICIC-damaged area was an average of 0.11 ± 0.12 mm2 (range: 0.01-0.46 mm2). CONCLUSION: Although implant damage in total knee arthroplasty is typically reported with regard to the polyethylene insert, the results of this study demonstrate that abrasive and corrosive damage occurs on the CoCr femoral condyle in vivo.

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.