Adverse Local Tissue Reaction due to Mechanically Assisted Crevice Corrosion Presenting as Late Instability Following Metal-on-Polyethylene Total Hip Arthroplasty.

BACKGROUND: Mechanically assisted crevice corrosion (MACC) at modular junctions can cause a spectrum of adverse local tissue reactions (ALTRs) in patients who have undergone total hip arthroplasty (THA). The purpose of this study is to describe the presentation, treatments, and related complications of a cohort of patients presenting with late instability following metal-on-polyethylene THA due to underlying MACC and ALTR. METHODS: This multicenter retrospective case series presents 17 patients (12 women, mean age 62.6, range 42-73) presenting with late instability secondary to ALTR and MACC. All patients had a metal (Cobalt Chrome)-on-polyethylene bearing surface. Patients experienced a mean 2.7 dislocations (range 1-6) at mean 4.3 years (range 0.4-17.0) following their index surgery. Serum metal levels (n = 12) demonstrated a greater elevation of cobalt (mean 6.9, range 0.13-20.88 ng/mL) than chromium (mean 1.9, range 0.13-3.23 ng/mL). RESULTS: Patients were revised for instability at a mean of 6.8 years (range 2.1-19.4) following their index surgery. ALTR was encountered in every case and the modular head-neck junction demonstrated visible corrosion. An exchange of the CoCr head to a ceramic head with a titanium sleeve and placement of a constrained liner was performed for a majority of patients (n = 15, 88.2%). Five patients (29.4%) had complications postoperatively including peroneal palsy (n = 2), periprosthetic joint infection (n = 2), and ALTR recurrence (n = 1). CONCLUSION: Recurrent instability in the setting of otherwise well-positioned THA components and without another obvious cause should raise concern for ALTR as a potential underlying etiology.

Fourier transform infrared spectroscopic imaging of wear and corrosion products within joint capsule tissue from total hip replacements patients.

Implant debris generated by wear and corrosion is a prominent cause of joint replacement failure. This study utilized Fourier transform infrared spectroscopic imaging (FTIR-I) to gain a better understanding of the chemical structure of implant debris and its impact on the surrounding biological environment. Therefore, retrieved joint capsule tissue from five total hip replacement patients was analyzed. All five cases presented different implant designs and histopathological patterns. All tissue samples were formalin-fixed and paraffin-embedded. Unstained, 5 µm thick sections were prepared. The unstained sections were placed on BaF2 windows and deparaffinized with xylene prior to analysis. FTIR-I data were collected at a spectral resolution of 4 cm-1 using an Agilent Cary 670 spectrometer coupled with Cary 620 FTIR microscope. The results of study demonstrated that FTIR-I is a powerful tool that can be used complimentary to the existing histopathological evaluation of tissue. FTIR-I was able to distinguish areas with different cell types (macrophages, lymphocytes). Small, but distinct differences could be detected depending on the state of cells (viable, necrotic) and depending on what type of debris was present (polyethylene [PE], suture material, and metal oxides). Although, metal oxides were mainly below the measurable range of FTIR-I, the infrared spectra of tissues exhibited noticeable difference in their presence. Tens of micrometer sized polyethylene particles could be easily imaged, but also accumulations of submicron particles could be detected within macrophages. FTIR-I was also able to distinguish between PE debris, and other birefringent materials such as suture. Chromium-phosphate particles originating from corrosion processes within modular taper junctions of hip implants could be identified and easily distinguished from other phosphorous materials such as bone. In conclusion, this study successfully demonstrated that FTIR-I is a useful tool that can image and determine the biochemical information of retrieved tissue samples over tens of square millimeters in a completely label free, nondestructive, and objective manner. The resulting chemical images provide a deeper understanding of the chemical nature of implant debris and their impact on chemical changes of the tissue within which they are embedded.

Healing bone lesion defects using injectable CaSO4 /CaPO4 -TCP bone graft substitute compared to cancellous allograft bone chips in a canine model.

CaSO4 /CaPO4 -TCP bone graft substitute has been shown to be effective for treatment of bone lesion defects, but its mechanical, histological, and radiographic characteristics have not been studied in direct comparison with a conventional treatment such as cancellous allograft bone. Thirteen canines had a critical-size axial defect created bilaterally into the proximal humerus. CaSO4 /CaPO4 -TCP bone graft substitute (PRO-DENSE™, Wright Medical Technology) was injected into the defect in one humerus, and an equal volume of freeze-dried cancellous allograft bone chips was placed in the contralateral defect. The area fraction of new bone, residual graft, and fibrous tissue and the compressive strength and elastic modulus of bone within the defects were determined after 6, 13, or 26 weeks and correlated with radiographic changes. The data were analyzed using Friedman and Mann-Whitney tests. There was more bone in defects treated with the CaSO4 /CaPO4 -TCP bone graft substitute compared to defects treated with cancellous bone allograft at all three time points, and the difference at 13 weeks was significant (p = 0.025). The new bone was significantly stronger and stiffer in defects treated with the CaSO4 /CaPO4 -TCP bone graft substitute compared to defects treated with cancellous bone allograft at 13 (p = 0.046) and 26 weeks (p = 0.025). At 26 weeks, all defects treated with CaSO4 /CaPO4 -TCP bone graft substitute demonstrated complete healing with new bone, whereas healing was incomplete in all defects treated with cancellous allograft chips. The CaSO4 /CaPO4 -TCP bone graft substitute could provide faster and significantly stronger healing of bone lesions compared to the conventional treatment using freeze-dried cancellous allograft bone. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 408-414, 2019.

Metal wear particles in hematopoietic marrow of the axial skeleton in patients with prior revision for mechanical failure of a hip or knee arthroplasty.

Wear particles generated by hip and knee arthroplasties disseminate to the liver and spleen with the highest concentrations observed in subjects who have had a failed arthroplasty. We asked to what extent metallic particles could also disseminate to remote hematopoietic bone marrow. Cored samples of red marrow from the axial skeleton and proximal humerus were obtained postmortem from four males and two females aged 79-92 years. Seven to seventeen years prior to their demise, each subject had undergone successful revision of their arthroplasty for mechanical failure in which an unintended wear condition had generated a large volume of metal particles. The marrow samples were analyzed using stained histological sections and energy dispersive X-ray analysis. Intracellular metal alloy particles were detected in the bone marrow of the cranium, proximal humerus, sternum, ribs, lumbar vertebrae, and the iliac crest. The components previously revised for mechanical failure were confirmed to be the predominant source of the disseminated wear debris. Particles of either Ti, Ti6Al4V, CoCrMo, FeCrNi alloys, or BaSO4 were identified in 24 of the 25 marrow samples examined. The particles ranged in size from 50 nm (the limit of resolution of our technique) to 6 µm. Metallic wear particles generated by hip and knee arthroplasties can disseminate widely to hematopoietic bone marrow throughout the axial skeleton and proximal humerus, especially in cases with a history of severe wear. The hematopoietic microenvironment is potentially sensitive to metallic degradation products. However, actual medical sequelae from disseminated wear debris is a rare occurrence. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1930-1936, 2019.

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.

Alloy Microstructure Dictates Corrosion Modes in THA Modular Junctions.

BACKGROUND: Adverse local tissue reactions (ALTRs) triggered by corrosion products from modular taper junctions are a known cause of premature THA failure. CoCrMo devices are of particular concern because cobalt ions and chromium-orthophosphates were shown to be linked to ALTRs, even in metal-on-polyethylene THAs. The most common categories of CoCrMo alloy are cast and wrought alloy, which exhibit fundamental microstructural differences in terms of grain size and hard phases. The impact of implant alloy microstructure on the occurring modes of corrosion and subsequent metal ion release is not well understood. QUESTIONS/PURPOSES: The purpose of this study was to determine whether (1) the microstructure of cast CoCrMo alloy varies broadly between manufacturers and can dictate specific corrosion modes; and whether (2) the microstructure of wrought CoCrMo alloy is more consistent between manufacturers and has low implications on the alloy's corrosion behavior. METHODS: The alloy microstructure of four femoral-stem and three femoral-head designs from four manufacturers was metallographically and electrochemically characterized. Three stem designs were made from cast alloy; all three head designs and one stem design were made from wrought alloy. Alloy samples were sectioned from retrieved components and then polished and etched to visualize grain structure and hard phases such as carbides (eg, M23C6) or intermetallic phases (eg, σ phase). Potentiodynamic polarization (PDP) tests were conducted to determine the corrosion potential (Ecorr), corrosion current density (Icorr), and pitting potential (Epit) for each alloy. Four devices were tested within each group, and each measurement was repeated three times to ensure repeatable results. Differences in PDP metrics between manufacturers and between alloys with different hard phase contents were compared using one-way analysis of variance and independent-sample t-tests. Microstructural features such as twin boundaries and slip bands as well as corrosion damage features were viewed and qualitatively assessed in a scanning electron microscope. RESULTS: We found broad variability in implant alloy microstructure for both cast and wrought alloy between manufacturers, but also within the same implant design. In cast alloys, there was no difference in PDP metrics between manufacturers. However, coarse hard phases and clusters of hard phases (mainly intermetallic phases) were associated with severe phase boundary corrosion and pitting corrosion. Furthermore, cast alloys with hard phases had a lower Epit than those without (0.46 V, SD 0.042; 0.53 V, SD 0.03, respectively; p = 0.015). Wrought alloys exhibited either no hard phases or numerous carbides (M23C6). However, the corrosion behavior was mainly affected by lattice defects and banded structures indicative of segregations that appear to be introduced during bar stock manufacturing. Alloys with banding had a lower Ecorr (p = 0.008) and higher Icorr (p = 0.028) than alloys without banding (-0.76 V, SD 0.003; -0.73 V, SD 0.009; and 1.14 × 10-4 mA/cm2, SD 1.47 × 10-5; 5.2 × 10-5 mA/cm2, SD 2.57 × 10-5, respectively). Alloys with carbides had a slightly higher Ecorr (p = 0.046) than those without (-0.755 V, SD 0.005; -0.761 V, SD 0.004); however, alloys with carbides exhibited more severe corrosion damage as a result of phase boundary corrosion, hard phase detachment, and subsequent local crevice corrosion. CONCLUSIONS: The observed variability in CoCrMo alloy microstructure of both cast and wrought components in this study appears to be an important issue to address, perhaps through better standards, to minimize in vivo corrosion. The finding of the banded structures within wrought alloys is especially concerning because it unfavorably influences the corrosion behavior independent of the manufacturer. The findings suggest that a homogeneous alloy microstructure with a minimal hard phase fraction exhibits more favorable corrosion behavior within the in vivo environment of modular taper junctions, thus lowering metal ion release and subsequently the risk of ALTRs to corrosion products. Also, the question arises if hard phases fulfill a useful purpose in metal-on-polyethylene bearings, because they may come with a higher risk of phase boundary corrosion and pitting corrosion and the benefit they provide by adding strength is not needed (unlike in metal-on-metal bearings). CLINICAL RELEVANCE: Implant failure resulting from corrosion processes within modular junctions is a major concern in THA. Our results suggest that implant alloy microstructure is not sufficiently standardized and may also dictate specific corrosion modes and subsequent metal ion release.

Adverse Local Tissue Responses to Failed Temporomandibular Joint Implants.

PURPOSE: The purpose of this study was to determine whether failed alloplastic temporomandibular joint replacement (TMJR) devices can elicit the aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) reaction seen in some patients with metal-on-metal hip arthroplasties. MATERIALS AND METHODS: This study involved analysis of paraffin-embedded sections of peri-implant tissue from failed TMJ implant cases obtained from 3 independent sources. Hematoxylin and eosin staining, conventional and polarized light microscopy, back-scattered electron imaging, and energy-dispersive x-ray analysis were used. Immunohistochemical methods were used to identify T and B lymphocytes and macrophages. RESULTS: The total TMJR device specimens showed primary macrophage and lymphocytic responses similar to responses reported previously for failed total hip implants, including ALVAL. No chronic or acute inflammation was apparent in the failed hemiarthroplasty TMJR cases. CONCLUSION: In this limited preliminary study, the local tissue responses to the failed TMJR implants showed similar primary macrophage and lymphocyte responses to previously reported failed metal-on-metal and metal-on-polyethylene orthopedic total joint replacement devices. No such local inflammatory responses were seen with the failed TMJR hemiarthroplasty devices.

Nanoscale surface modification by anodic oxidation increased bone ingrowth and reduced fibrous tissue in the porous coating of titanium-alloy femoral hip arthroplasty implants.

Hip arthroplasty femoral stems coated with Ti6Al4V beads were treated by anodic oxidation in H3 PO4 for enhanced bioactivity and were studied in a 6-month canine model to determine the effects of the treated surface on the ingrowth of bone and soft tissues. The area fractions of bone, marrow, and fibrous tissue in the porous coating of seven treated and seven untreated control implants were determined using histomorphological techniques. The area fraction of bone within the porous coating was greater for anodic oxide treated (23.6 ± 8.3%) compared to control implants (l2.7 ± 4.7%) (p = 0.013), and there was less fibrous tissue in the treated implants (18.0 ± 9.5%) compared to the controls (33.1 ± 7.9%) (p = 0.006). XPS, XRD, TEM, and SEM analyses of the treated implants revealed a 400 nm-thick titanium oxide layer of low crystallinity with an undulating surface, populated with more than 25 nm-size pores per square micrometer. There was no detectable increase in serum titanium or in generation of particulates locally compared to the control implants. Micro and nanoscale surface modification by anodic oxidation increased bone ingrowth and reduced fibrous tissue, which may extend the longevity of fixation, limiting pathways for particle migration, and impeding the progression of osteolysis and aseptic loosening of arthroplasty components. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 283-290, 2017.

Aseptic Lymphocytic-Dominated Vasculitis-Associated Lesions Scores Do Not Correlate With Metal Ion Levels or Unreadable Synovial Fluid White Blood Cell Counts.

BACKGROUND: Failed metal-on-metal (MoM) bearings are being increasingly encountered with little information to guide evaluation for aseptic lymphocytic-dominated vasculitis-associated lesions (ALVAL). It is often assumed that elevated metal ion levels correlate with the occurrence of ALVAL. Our purpose was to determine the utility of the erythrocyte sedimentation rate, C-reactive protein, synovial white blood cell count, differential (%PMN), and serum metal ion levels in diagnosing ALVAL. METHODS: We identified 80-failed MoM total hip arthroplasties. Tissue was examined under light microscopy and graded on a scale of ALVAL severity. Mean laboratory values were compared between groups and receiver operating curves generated with an area under the curve to determine test performance and optimal cutoffs. RESULTS: ALVAL scores were graded as low in 30 (37.5%), moderate in 39 (49%), and severe in 8 (10%), with 3 being unreadable. No clear cutoff values for erythrocyte sedimentation rate, C-reactive protein, or synovial white blood cell count could be determined to reliably diagnose moderate or severe ALVAL. Furthermore, serum metal levels had no correlation with ALVAL score. The best test to diagnose ALVAL was the synovial fluid monocyte percentage with an optimal cutoff value of 39% and area under the curve of 69% (moderate testing performance). CONCLUSION: The diagnosis of ALVAL remains challenging, with most of the screening tests being unreliable. Although serum metal ion levels are typically elevated in failed MoM bearings, higher levels do not appear to correlate with ALVAL grade. Elevated synovial fluid monocytes may provide diagnostic utility for ALVAL, suggesting a possible delayed-type hypersensitivity reaction.

Does Surface Topography Play a Role in Taper Damage in Head-neck Modular Junctions?

BACKGROUND: There are increasing reports of total hip arthroplasty failure subsequent to modular taper junction corrosion. The surfaces of tapers are machined to have circumferential machining marks, resulting in a surface topography of alternating peaks and valleys on the scale of micrometers. It is unclear if the geometry of this machined surface topography influences the degree of fretting and corrosion damage present on modular taper junctions or if there are differences between modular taper junction material couples. QUESTIONS/PURPOSES: (1) What are the differences in damage score and surface topography between CoCr/CoCr and CoCr/Ti modular junctions? (2) How are initial surface topography, flexural rigidity, taper angle mismatch, and time in situ related to visual taper damage scores for CoCr/CoCr couples? (3) How are initial surface topography, flexural rigidity, taper angle mismatch, and time in situ related to visual taper damage scores for CoCr/Ti couples? METHODS: Damage on stem and head tapers was evaluated with a modified Goldberg score. Differences in damage scores were determined between a group of 140 CoCr/CoCr couples and 129 CoCr/Ti couples using a chi-square test. For a subgroup of 70 retrievals, selected at random, we measured five variables, including initial stem taper machining mark height and spacing, initial head taper roughness, flexural rigidity, and taper angle mismatch. All retrievals were obtained at revision surgeries. None were retrieved as a result of metal-on-metal failures or were recalled implants. Components were chosen so there was a comparable number of each material couple and damage score. Machining marks around the circumference of the tapers were measured using white light interferometry to characterize the initial stem taper surface topography in terms of the height of and spacing between machining mark peaks as well as initial head taper roughness. The taper angle mismatch was assessed with a coordinate measuring machine. Flexural rigidity was determined based on measurements of gross taper dimensions and material properties. Differences of median or mean values of all variables between material couples were determined (Wilcoxon rank-sum tests and t-tests). The effect of all five variables along with time in situ on stem and head taper damage scores was tested with a multiple regression model. With 70 retrievals, a statistical power of 0.8 could be achieved for the model. RESULTS: Damage scores were different between CoCr/CoCr and CoCr/Ti modular taper junction material couples. CoCr/CoCr stem tapers were less likely to be mildly damaged (11%, p = 0.006) but more likely to be severely damaged (4%, p = 0.02) than CoCr/Ti stem tapers (28% and 1%, respectively). CoCr/CoCr couples were less likely to have moderately worn head tapers (7% versus 17%, p = 0.003). Stem taper machining mark height and spacing and head taper roughness were 11 (SD 3), 185 (SD 46), and 0.57 (SD 0.5) for CoCr/CoCr couples and 10 (SD 3), 170 (SD 56), and 0.64 (SD 0.4) for CoCr/Ti couples, respectively. There was no difference (p = 0.09, p = 0.1, p = 0.16, respectively) for either factor between material couples. Larger stem taper machining mark heights (p = 0.001) were associated with lower stem taper damage scores, and time in situ (p = 0.006) was associated with higher stem taper damage scores for CoCr/CoCr material couples. Stem taper machining marks that had higher peaks resulted in slower damage progression over time. For CoCr/Ti material couples, head taper roughness was associated with higher stem (p = 0.001) and head taper (p = 0.003) damage scores, and stem taper machining mark height, but not time in situ, was associated with lower stem taper damage scores (p = 0.007). CONCLUSIONS: Stem taper surface topography was related to damage scores on retrieved head-neck modular junctions; however, it affected CoCr/CoCr and CoCr/Ti couples differently. CLINICAL RELEVANCE: A taper topography of circumferential machining marks with higher peaks appears to enable slower damage progression and, subsequently, a reduction of the reported release of corrosion products. This may be of interest to implant designers and manufacturers in an effort to reduce the effects of metal release from modular femoral components.

How Does Wear Rate Compare in Well-functioning Total Hip and Knee Replacements? A Postmortem Polyethylene Liner Study.

BACKGROUND: The longevity of total hip (THR) and knee replacements (TKR) that used historical bearing materials of gamma-in-air sterilized UHMWPE was affected more by osteolysis in THRs than in TKRs, although osteolysis remains a concern in TKRs. Therefore, the study of polyethylene wear is still of interest for the knee, particularly because few studies have investigated volumetric material loss in tibial knee inserts. For this study, a unique collection of autopsy-retrieved TKR and THR components that were well-functioning at the time of retrieval was used to compare volumetric wear differences between hip and knee polyethylene components made from identical material. QUESTIONS/PURPOSES: The following questions were addressed: (1) How much did the hip liners wear and what wear patterns did they exhibit? (2) How much did the knee inserts wear and what wear patterns did they exhibit? (3) What is the ratio between TKR and THR wear after controlling for implantation time and patient age? METHODS: We compared 23 THR components (Harris-Galante [HG] and HG II) and 20 TKR components (Miller-Galante [MG II]) that were retrieved postmortem. The components were made from the same polyethylene formulation and with similar manufacturing and sterilization (gamma-in-air) processes. Twenty-one patients (12 males, nine females) had THRs and 16 (four males, 12 females) had TKRs. Patients who had TKRs had an older (p = 0.001) average age than patients who had THRs (age, 75 years; SD, 10, versus 66 years; SD, 12, respectively). Only well-functioning components were included in this study. Therefore, implants retrieved postmortem from physically active patients and implanted for at least 2 years were considered. In addition, only normally wearing TKR components were considered, ie, those with fatigue wear (delamination) were excluded. The wear volume of each component was measured using metrology. For the tibial inserts an autonomous mathematic reconstruction method was used for quantification. RESULTS: The acetabular liners of the THR group had a wear rate of 38 mm(3) per year (95% CI, 29-47 mm(3)/year). Excluding patients with low-activity, the wear rate was 47 mm(3) per year (95% CI, 37-56 mm(3)/year). The wear rate of normally wearing tibial inserts was 17 mm(3) per year (95% CI, -6 to 40 mm(3)/year). After controlling for the relevant confounding variable of age, we found a TKR/THR wear rate ratio of 0.5 (95% CI, 0.29-0.77) at 70 years of age with a slightly increasing difference with increasing age. CONCLUSIONS: Excluding delamination, TKRs exhibited lower articular wear rates than THRs for historical polyethylene in these two unique cohorts of postmortem retrievals. CLINICAL RELEVANCE: The lower TKR wear rate is in line with the lower incidence of osteolysis in TKRs compared with THRs.

Modern trunnions are more flexible: a mechanical analysis of THA taper designs.

BACKGROUND: There is renewed concern surrounding the potential for corrosion at the modular head-neck junction to cause early failure in contemporary THAs. Although taper corrosion involves a complex interplay of many factors, a previous study suggested that a decrease in flexural rigidity of the femoral trunnion may be associated with an increased likelihood of corrosion at retrieval. QUESTIONS/PURPOSES: By analyzing a large revision retrieval database of femoral stems released during a span of three decades, we asked: (1) how much does flexural rigidity vary among different taper designs; (2) what is the contribution of taper geometry alone to flexural rigidity of the femoral trunnion; and (3) how have flexural rigidity and taper length changed with time in this group of revised retrievals? METHODS: A dual-center retrieval analysis of 85 modular femoral stems released between 1983 and 2012 was performed, and the flexural rigidity and length of the femoral trunnions were determined. These stems were implanted between 1991 and 2012 and retrieved at revision or removal surgery between 2004 and 2012. There were 10 different taper designs made from five different metal alloys from 16 manufacturers. Digital calipers were used to measure taper geometries by two independent observers. RESULTS: Median flexural rigidity was 228 N-m(2); however, there was a wide range of values among the various stems spanning nearly an order of magnitude between the most flexible (80 N-m(2)) and most rigid (623 N-m(2)) trunnions, which was partly attributable to the taper geometry and to the material properties of the base alloy. There was a negative correlation between flexural rigidity and length of the trunnion and release date of the stem. CONCLUSIONS: There is wide variability in flexural rigidity of various taper designs, with a trend toward trunnions becoming shorter and less rigid with time. CLINICAL RELEVANCE: This temporal trend may partly explain why taper corrosion is being seen with increasing frequency in modern THAs.

Adverse local tissue reaction arising from corrosion at the femoral neck-body junction in a dual-taper stem with a cobalt-chromium modular neck.

BACKGROUND: Femoral stems with dual-taper modularity were introduced to allow additional options for hip-center restoration independent of femoral fixation in total hip arthroplasty. Despite the increasing availability and use of these femoral stems, concerns exist about potential complications arising from the modular neck-body junction. METHODS: This was a multicenter retrospective case series of twelve hips (eleven patients) with adverse local tissue reactions secondary to corrosion at the modular neck-body junction. The cohort included eight women and three men who together had an average age of 60.1 years (range, forty-three to seventy-seven years); all hips were implanted with a titanium-alloy stem and cobalt-chromium-alloy neck. Patients presented with new-onset and increasing pain at a mean of 7.9 months (range, five to thirteen months) following total hip arthroplasty. After serum metal-ion studies and metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) revealed abnormal results, the patients underwent hip revision at a mean of 15.2 months (range, ten to twenty-three months). Tissue specimens were examined by a single histopathologist, and the retrieved implants were studied with use of light and scanning electron microscopy. RESULTS: Serum metal levels demonstrated greater elevation of cobalt (mean, 6.0 ng/mL) than chromium (mean, 0.6 ng/mL) or titanium (mean, 3.4 ng/mL). MRI with use of MARS demonstrated adverse tissue reactions in eight of nine patients in which it was performed. All hips showed large soft-tissue masses and surrounding tissue damage with visible corrosion at the modular femoral neck-body junction. Available histology demonstrated large areas of tissue necrosis in seven of ten cases, while remaining viable capsular tissue showed a dense lymphocytic infiltrate. Microscopic analysis was consistent with fretting and crevice corrosion at the modular neck-body interface. CONCLUSIONS: Corrosion at the modular neck-body junction in dual-tapered stems with a modular cobalt-chromium-alloy femoral neck can lead to release of metal ions and debris resulting in local soft-tissue destruction. Adverse local tissue reaction should be considered as a potential cause for new-onset pain in patients with these components, and early revision should be considered given the potentially destructive nature of these reactions. A workup including serologic studies (erythrocyte sedimentation rate and C-reactive protein), serum metal levels, and MARS MRI can be helpful in establishing this diagnosis.

Implantation of a titanium partial limb prosthesis in a white-naped crane (Grus vipio).

A female white-naped crane (Grus vipio) was presented with an open, oblique fracture of the distal right tarsometatarsus and concomitant vascular and nerve damage. Conventional fracture fixation repairs failed, which led to implantation of a custom titanium limb prosthesis. After subsequent revisions with 2 different prosthetic devices, limb function was ultimately restored but a later yolk embolism caused a circulatory compromise in the opposite leg, which necessitated euthanasia. Histopathologic results revealed limited ingrowth of bone into the porous coated implant, which indicated that a limb prosthesis may provide salvage for long-legged, heavy-bodied birds with fractures of the tarsometatarsus.

Successful long-term fixation and progression of osteolysis associated with first-generation cementless acetabular components retrieved post mortem.

BACKGROUND: Primary cementless acetabular reconstruction has shown durable long-term fixation. Late failures secondary to aseptic loosening are rare but may occur in patients with previously well-fixed components. In the present study, the histopathological characteristics of postmortem specimens were correlated with wear damage and radiographic data in an attempt to better understand the long-term events in the periacetabular tissue around well-functioning devices. METHODS: Seventeen primary cementless Harris-Galante I acetabular components with adjacent tissues were harvested after a mean of eleven years (range, four to twenty-five years) from patients whose implants were well functioning at the time of death. Undecalcified and paraffin sections were used to quantify the extent of bone and soft tissues within the porous coating and at the interface between the coating and the surrounding bone. Wear particles were identified with use of polarized light microscopy and energy-dispersive x-ray analysis. Bearing-surface volumetric wear and backside wear damage of the polyethylene liner were assessed. RESULTS: All of the components were fixed by bone ingrowth (mean extent, 33% ± 21%). Particle-induced granulomas were present in the porous coating and along the interface and progressed through screw holes, ballooning into the retroacetabular bone in the longer-term specimens. Particles of femoral and acetabular origin were identified in the granulomas. Bearing-surface volumetric wear (mean, 41.6 mm3/year) increased with duration and correlated with increasing extent of granuloma in the porous coating and the increasing size of pelvic granulomas. Radiolucencies on radiographs correlated with the extent of bone and fibrous tissue ingrowth. Of the six pelvic granulomas that were identified histologically, only one was apparent on routine radiographs. CONCLUSIONS: Acetabular fixation by bone ingrowth can be successful into the third decade after implantation. Osteolysis and secondary replacement of bone with particle-induced granuloma are commonly seen in the presence of excellent clinical function. Strategies designed to minimize bearing-surface wear and backside damage are important to maintain long-term bone ingrowth fixation.

In vivo oxide-induced stress corrosion cracking of Ti-6Al-4V in a neck-stem modular taper: Emergent behavior in a new mechanism of in vivo corrosion.

In vivo modular taper corrosion in orthopedic total joint replacements has been documented to occur for head-neck tapers, modular-body tapers, and neck-stem tapers. While the fretting corrosion mechanism by which this corrosion occurs has been described in the literature, this report shows new and as yet unreported mechanisms at play. A retrieved Ti-6Al-4V/Ti-6Al-4V neck-stem taper interface, implanted for 6 years is subjected to failure analysis to document taper corrosion processes that lead to oxide driven crack formation on the medial side of the taper. Metallurgical sectioning techniques and scanning electron microscopy analysis are used to document the taper corrosion processes. The results show large penetrating pitting attack of both sides of the taper interface where corrosion selectively attacks the beta phase of the microstructure and eventually consumes the alpha phase. The pitting attack evolves into plunging pits that ultimately develop into cracks where the crack propagation process is one of corrosion resulting in oxide formation and subsequent reorganization. This process drives open the crack and advances the front by a combination of oxide-driven crack opening stresses and corrosion attack at the tip. The oxide that forms has a complex evolving structure including a network of transport channels that provide access of fluid to the crack tip. This emergent behavior does not appear to require continued fretting corrosion to propagate the pitting and cracking. This new mechanism is similar to stress corrosion cracking where the crack tip stresses arise from the oxide formation in the crack and not externally applied tensile stresses.

Early failure of metal-on-metal artificial disc prostheses associated with lymphocytic reaction: diagnosis and treatment experience in four cases.

STUDY DESIGN: Report of four collected cases. OBJECTIVE: The purpose of this report is to describe the presentation, diagnostic workup, treatment, and pathologic findings in four cases of lymphocytic reaction in patients receiving a metal-on-metal total disc replacement (TDR). SUMMARY OF BACKGROUND DATA: Metal-on-metal designs in hip arthroplasty have gained popularity because of decreased volumetric wear rates and theoretically increased implant longevity. Systemic metal ions produced have not been associated with adverse clinical sequelae, although there have been reports of local soft-tissue reactions leading to early prosthetic failure. Histologic evaluation in these cases suggested a cell-mediated delayed-type hypersensitivity reaction. Metal-on-metal bearings have also emerged in lumbar and cervical TDR. METHODS: This report is on four patients, from three centers, who underwent TDR, using a metal-on-metal implant, and later presented with symptoms that were determined to be due to lymphocytic reaction. Details of their symptoms, diagnostic work-up, treatment, and outcomes were compiled. RESULTS: All four patients initially had a good surgical outcome, followed by the onset and worsening of axial pain, and/or radicular symptoms months later. All patients had imaging findings of a mass lesion with neurologic impingement. All three of the lumbar patients underwent a decompressive posterior procedure before the eventual device removal and fusion. Intraoperatively, in all the lumbar cases, a thick, yellowish, avascular soft-tissue mass was found to be responsible for an epidural-mass effect on the thecal sac. In the cervical case, there was a gray-tinged soft-tissue response around the implant, suggestive of metallosis. Independent laboratory analysis confirmed a lymphocytic reaction to the implant. Three of the patients had a good outcome after the explant and revision surgery. The remaining patient continued to have residual symptoms related to the neural compression caused by the mass. CONCLUSIONS: In this group of patients from three centers, a metal-on-metal TDR resulted in a lymphocytic reaction causing subsequent failure of the surgery. This phenomenon has previously been recognized with metal bearings in hip arthroplasty. Surgeons using metal-on-metal TDRs should be aware of this possible occurrence.

Metal-on-metal bearing surfaces.

Metal-on-metal bearing couples remain a popular option in total hip arthroplasty and are the only currently available option for surface replacement arthroplasty. In general, the intermediate-term clinical performance of metal-on-metal bearings has been favorable. There are, however, lingering concerns about the biologic consequences of metal release from these bearings in terms of both local tissue effects, including delayed-type hypersensitivity reactions in a subset of patients, and potential systemic effects as a consequence of chronic elevations in serum cobalt and chromium content. Advances in the understanding of the operant wear mechanisms in these bearings provide strategies for reducing the burden of metal released into the periprosthetic milieu, which in turn will mitigate the concerns about the biologic response to the metal debris. Continued surveillance of patients with these bearings is warranted to determine whether metal-on-metal bearing couples provide a long-term survivorship advantage over other bearing couple options and to evaluate whether chronic elevations in the body burden of cobalt and chromium is well tolerated over the long term.

In vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip-implants.

Titanium alloys are widely used in total-joint replacements due to a combination of outstanding mechanical properties, biocompatibility, passivity, and corrosion resistance. Nevertheless, retrieval studies have pointed out that these materials can be subjected to localized or general corrosion in modular interfaces when mechanical abrasion of the oxide film (fretting) occurs. Modularity adds large crevice environments, which are subject to micromotion between contacting interfaces and differential aeration of the surface. Titanium alloys are also known to be susceptible to hydrogen absorption, which can induce precipitation of hydrides and subsequent brittle failure. In this work, the surface of three designs of retrieved hip-implants with Ti-6Al-4V/Ti-6Al-4V modular taper interfaces in the stem were investigated for evidence of severe corrosion and precipitation of brittle hydrides during fretting-crevice corrosion in the modular connections. The devices were retrieved from patients and studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analysis. The surface qualitative investigation revealed severe corrosion attack in the mating interfaces with evidence of etching, pitting, delamination, and surface cracking. In vivo hydrogen embrittlement was shown to be a mechanism of degradation in modular connections resulting from electrochemical reactions induced in the crevice environment of the tapers during fretting-crevice corrosion.

Vertebroplasty comparing injectable calcium phosphate cement compared with polymethylmethacrylate in a unique canine vertebral body large defect model.

BACKGROUND CONTEXT: Vertebroplasty was developed to mechanically reinforce weakened vertebral bodies. Polymethylmethacrylate (PMMA) bone cement has been most commonly used but carries risks of thermal injury and respiratory and cardiovascular complications. Calcium phosphate (CaP) offers the potential for biological resorption and replacement with new bone, restoring vertebral body mass and height. PURPOSE: To compare compressive strength, elastic modulus of the adjacent motion segments, and histologic response of vertebral bodies injected with either CaP or PMMA in a canine vertebroplasty model. STUDY DESIGN: By using a canine vertebroplasty model, two level vertebroplasties were performed at L1 and L3 and studied for 1 month (n=10) and 6 months (n=10). In each canine, one vertebral defect was randomly injected with either CaP cement (BoneSource; Stryker, Freiberg, Germany) or PMMA. METHODS: Twenty dogs had an iatrogenically created cavitary lesion at two nonadjacent levels injected with either CaP or PMMA. Canines from each group were tested mechanically (n=5) and histologically (n=5). Histology consisted of axial sections of the L1 and L3 vertebral bodies and high-resolution contact radiographs. Sections from each specimen were embedded in plastic without decalcification to study the bone-cement interface. Bone-cement interfaces were compared for evidence of necrosis, fibrosis, foreign body response, cement resorption, and new bone formation between the PMMA and CaP treatments groups. Mechanical compression testing was performed on specimens from the 1-month (n=5) and 6-month (n=5) time periods. The T13 vertebral body was used as an intact control for the destructive compression testing of L1 and L3. Each vertebral body was compressed to 50% of its original height under displacement control at 15 mm/min to simulate a nontraumatic loading situation. Force and displacement data were recorded in real time. RESULTS: Vertebral sites containing PMMA were characterized by a thin fibrous membrane. PMMA was detected within the trabeculae, vascular channels, and the spinal canal. Unlike PMMA, CaP underwent resorption and remodeling with vascular invasion and bone ingrowth. Woven and lamellar bone was found on the CaP cement surface, within the remodeled material, and on the surrounding trabeculae. Vertebral body compression strength testing revealed no significant difference in vertebral body height and compressive strength between PMMA and CaP. There was a trend for CaP-treated vertebrae to increase in compressive strength from 1 month to 6 months, whereas PMMA decreased compressive strength when compared with adjacent nontreated vertebrae. CONCLUSION: For both short and intermediate time periods, the injection of CaP cement can be an effective method to treat large vertebral defects. Early results indicate that CaP remodeling might result in the resorption of the majority of the cement with replacement by lamellar bone.