Clinical management of bone loss in cervical total disc arthroplasty: literature review and treatment recommendations.

PURPOSE: Cervical total disc replacement (cTDR) has been established as an alternative treatment for degenerative cervical radiculopathy and myelopathy. While the rate of complications for cTDR is reasonably low, recent studies have focused on bone loss after cTDR. The purpose of this work is to develop a clinical management plan for cTDR patients with evidence of bone loss. To guide our recommendations, we undertook a review of the literature and aimed to determine: (1) how bone loss was identified/imaged, (2) whether pre- or intraoperative assessments of infection or histology were performed, and (3) what decision-making and revision strategies were employed. METHODS: We performed a search of the literature according to PRISMA guidelines. Included studies reported the clinical performance of cTDR and identified instances of cervical bone loss. RESULTS: Eleven case studies and 20 cohort studies were reviewed, representing 2073 patients with 821 reported cases of bone loss. Bone loss was typically identified on radiographs during routine follow-up or by computed tomography (CT) for patients presenting with symptoms. Assessments of infection as well as histological and/or explant assessment were sporadically reported. Across all reviewed studies, multiple mechanisms of bone loss were suspected, and severity and progression varied greatly. Many patients were reportedly asymptomatic, but others experienced symptoms like progressive pain and paresthesia. CONCLUSION: Our findings demonstrate a critical gap in the literature regarding the optimal management of patients with bone loss following cTDR, and treatment recommendations based on our review are impractical given the limited amount and quality evidence available. However, based on the authors' extensive clinical experience, close follow-up of specific radiographic observations and serial radiographs to assess the progression/severity of bone loss and implant changes are recommended. CT findings can be used for clinical decision-making and further follow-up care. The pattern and rate of progression of bone loss, in concert with patient symptomatology, should determine whether non-operative or surgical intervention is indicated. Future studies involving implant retrieval, histopathological, and microbiological analysis for patients undergoing cTDR revision for bone loss are needed.

Fretting and Tribocorrosion of Modular Dual Mobility Liners: Role of Design, Microstructure, and Malseating.

BACKGROUND: Modular dual mobility (DM) bearings have a junction between a cobalt chrome alloy (CoCrMo) liner and titanium shell, and the risk of tribocorrosion at this interface remains a concern. The purpose of this study was to determine whether liner malseating and liner designs are associated with taper tribocorrosion. METHODS: We evaluated 28 retrieved modular DM implants with a mean in situ duration of 14.6 months (range, 1 to 83). There were 2 manufacturers included (12 and 16 liners, respectively). Liners were considered malseated if a distinct divergence between the liner and shell was present on postoperative radiographs. Tribocorrosion was analyzed qualitatively with the modified Goldberg Score and quantitatively with an optical coordinate-measuring machine. An acetabular shell per manufacturer was sectioned for metallographic analysis. RESULTS: There were 6 implants (22%) that had severe grade 4 corrosion, 6 (22%) had moderate grade 3, 11 (41%) had mild grade 2, and 5 (18.5%) had grade 1 or no visible corrosion. The average volumetric material loss at the taper was 0.086 ± 0.19 mm3. There were 7 liners (25%) that had radiographic evidence of malseating, and all were of a single design (P = .01). The 2 liner designs were fundamentally different from one another with respect to the cobalt chrome alloy type, taper surface finish, and shape deviations. Malseating was an independent risk factor for increased volumetric material loss (P = .017). CONCLUSIONS: DM tribocorrosion with quantifiable material loss occurred more commonly in malseated liners. Specific design characteristics may make liners more prone to malseating, and the interplay between seating mechanics, liner characteristics, and patient factors likely contributes to the shell/liner tribocorrosion environment. LEVEL OF EVIDENCE: Level III.

Has Wrought Cobalt-Chromium-Molybdenum Alloy Changed for the Worse Over Time?

BACKGROUND: Total hip arthroplasty (THA) failure due to tribocorrosion of modular junctions and resulting adverse local tissue reactions to corrosion debris have seemingly increased over the past few decades. Recent studies have found that chemically-induced column damage seen on the inner head taper is enabled by banding in the alloy microstructure of wrought cobalt-chromium-molybdenum alloy femoral heads, and is associated with more material loss than other tribocorrosion processes. It is unclear if alloy banding represents a recent phenomenon. The purpose of this study was to examine THAs implanted in the 1990s, 2000s, and 2010s to determine if alloy microstructure and implant susceptibility to severe damage has increased over time. METHODS: Five hundred and forty-five modular heads were assessed for damage severity and grouped based on decade of implantation to serve as a proxy measure for manufacturing date. A subset of heads (n = 120) was then processed for metallographic analysis to visualize alloy banding. RESULTS: We found that damage score distribution was consistent over the time periods, but the incidence of column damage significantly increased between the 1990s and 2000s. Banding also increased from the 1990s to 2000s, but both column damage and banding levels appear to recover slightly in the 2010s. CONCLUSION: Banding, which provides preferential corrosion sites enabling column damage, has increased over the last 3 decades. No difference between manufacturers was seen, which may be explained by shared suppliers of bar stock material. These findings are important as banding can be avoidable, reducing the risk of severe column damage to THA modular junctions and failure due to adverse local tissue reactions.

Are Damage Modes Related to Microstructure and Material Loss in Severely Damaged CoCrMo Femoral Heads?

BACKGROUND: Fretting and corrosion in metal-on-polyethylene total hip arthoplasty (THA) modular junctions can cause adverse tissue reactions that are responsible for 2% to 5% of revision surgeries. Damage within cobalt-chromium-molybdenum (CoCrMo) alloy femoral heads can progress chemically and mechanically, leading to damage modes such as column damage, imprinting, and uniform fretting damage. At present, it is unclear which of these damage modes are most detrimental and how they may be linked to implant alloy metallurgy. The alloy microstructure exhibits microstructural features such as grain boundaries, hard phases, and segregation bands, which may enable different damage modes, higher material loss, and the potential risk of adverse local tissue reactions. QUESTIONS/PURPOSES: In this study, we asked: (1) How prevalent is chemically dominated column damage compared with mechanically dominated damage modes in severely damaged metal-on-polyethylene THA femoral heads made from wrought CoCrMo alloy? (2) Is material loss greater in femoral heads that underwent column damage? (3) Do material loss and the presence of column damage depend on alloy microstructure as characterized by grain size, hard phase content, and/or banding? METHODS: Surgically retrieved wrought CoCrMo modular femoral heads removed between June 2004 and June 2019 were scored using a modified version of the Goldberg visually based scoring system. Of the total 1002 heads retrieved over this period, 19% (190 of 1002) were identified as severely damaged, exhibiting large areas of fretting scars, black debris, pits, and/or etch marks. Of these, 43% (81 of 190) were excluded for metal-on-metal articulations, alternate designs (such as bipolar, dual-mobility, hemiarthroplasty, metal adaptor sleeves), or previous sectioning of the implant for past studies. One sample was excluded retroactively as metallurgical analysis revealed that it was made of cast alloy, yielding a total of 108 for further analysis. Information on patient age (57 ± 11 years) and sex (56% [61 of 108] were males), reason for removal, implant time in situ (99 ± 78 months), implant manufacturer, head size, and the CoCrMo or titanium-based stem alloy pairing were collected. Damage modes and volumetric material loss within the head tapers were identified using an optical coordinate measuring machine. Samples were categorized by damage mode groups by column damage, imprinting, a combination of column damage and imprinting, or uniform fretting. Metallurgical samples were processed to identify microstructural characteristics of grain size, hard phase content, and banding. Nonparametric Mann-Whitney U and Kruskal-Wallis statistical tests were used to examine volumetric material loss compared with damage mode and microstructural features, and linear regression was performed to correlate patient- and manufacturer-specific factors with volumetric material loss. RESULTS: Chemically driven column damage was seen in 48% (52 of 108) of femoral heads, with 34% (37 of 108) exhibiting a combination of column damage and imprinting, 12% (13 of 108) of heads displaying column damage and uniform fretting, and 2% (2 of 108) exhibiting such widespread column damage that potentially underlying mechanical damage modes could not be verified. Implants with column damage showed greater material loss than those with mechanically driven damage alone, with median (range) values of 1.2 mm3 (0.2 to 11.7) versus 0.6 mm3 (0 to 20.7; p = 0.03). Median (range) volume loss across all femoral heads was 0.9 mm3 (0 to 20.7). Time in situ, contact area, patient age, sex, head size, manufacturer, and stem alloy type were not associated with volumetric material loss. Banding of the alloy microstructure, with a median (range) material loss of 1.1 mm3 (0 to 20.7), was associated with five times higher material loss compared with those with a homogeneous microstructure, which had a volume loss of 0.2 mm3 (0 to 4.1; p = 0.02). Hard phase content and grain size showed no correlation with material loss. CONCLUSION: Chemically dominated column damage was a clear indicator of greater volume loss in this study sample of 108 severely damaged heads. Volumetric material loss strongly depended on banding (microstructural segregations) within the alloy. Banding of the wrought CoCrMo microstructure should be avoided during the manufacturing process to reduce volumetric material loss and the release of corrosion products to the periprosthetic tissue. CLINICAL RELEVANCE: Approximately 30% of THAs rely on wrought CoCrMo femoral heads. Most femoral heads in this study exhibited a banded microstructure that was associated with larger material loss and the occurrence of chemically dominated column damage. This study suggests that elimination of banding from the alloy could substantially reduce the release of implant debris in vivo, which could potentially also reduce the risk of adverse local tissue reactions to implant debris.

Do Battlefield Injury-acquired Indwelling Metal Fragments Induce Metal Immunogenicity?

BACKGROUND: A battlefield-related injury results in increased local and systemic innate immune inflammatory responses, resulting in wound-specific complications and an increased incidence of osteoarthritis. However, little is known about whether severe injuries affect long-term systemic homeostasis, for example, immune function. Moreover, it also remains unknown whether battlefield-acquired metal fragments retained over the long term result in residual systemic effects such as altered immune reactivity to metals. QUESTIONS/PURPOSES: Does a retained metal fragment from a battlefield injury contribute to increased (1) adaptive metal-specific immune responses, (2) systemically elevated metal ion serum levels, and (3) serum immunoglobulin levels compared with combat injuries that did not result in a retained metal fragment? METHODS: In this pilot study, we analyzed metal-immunogenicity in injured military personnel and noninjured control participants using lymphocyte transformation testing (LTT, lymphocyte proliferation responses to cobalt, chromium and nickel challenge at 0.001, 0.01 and 0.1-mM concentrations in triplicate for each participant), serum metal ion analysis (ICP-mass spectroscopy), and serum immunoglobulin analysis (IgE, IgG, IgA, and IgM ). Military personnel with a battlefield-sustained injury self-recruited without any exclusion for sex, age, degree of injury. Those with battlefield injury resulting in retained metal fragments (INJ-FRAG, n = 20 male, mean time since injury ± SD was 12 ± 10 years) were compared with those with a battlefield injury but without retained metal fragments (INJ-NO-FRAG, n = 12 male, mean time since injury ± SD was 13 ± 12 years). A control group comprised of male noninjured participants was used to compare measured immunogenicity metrics (n = 11, males were selected to match battlefield injury group demographics). RESULTS: Military participants with sustained metal fragments had increased levels of metal-induced lymphocyte responses. The lymphocyte stimulation index among military participants with metal fragments was higher than in those with nonretained metal fragments (stimulation index = 4.2 ± 6.0 versus stimulation index = 2.1 ± 1.2 (mean difference 2.1 ± 1.4 [95% confidence interval 5.1 to 0.8]; p = 0.07) and an average stimulation index = 2 ± 1 in noninjured controls. Four of 20 participants injured with retained fragments had a lymphocyte proliferation index greater than 2 to cobalt compared with 0 in the group without a retained metal fragment or 0 in the control participants. However, with the numbers available, military personnel with retained metal fragments did not have higher serum metal ion levels than military participants without retained metal fragment-related injuries or control participants. Military personnel with retained metal fragments had lower serum immunoglobulin levels (IgG, IgA, and IgM) than military personnel without retained metal fragments and noninjured controls, except for IgE. Individuals who were metal-reactive positive (that is, a stimulation index > 2) with retained metal fragments had higher median IgE serum levels than participants who metal-reactive with nonmetal injuries (1198 ± 383 IU/mL versus 171 ± 67 IU/mL, mean difference 1027 ± 477 IU/mL [95% CI 2029 to 25]; p = 0.02). CONCLUSIONS: We found that males with retained metal fragments after a battlefield-related injury had altered adaptive immune responses compared with battlefield-injured military personnel without indwelling metal fragments. Military participants with a retained metal fragment had an increased proportion of group members and increased average lymphocyte reactivity to common implant metals such as nickel and cobalt. Further studies are needed to determine a causal association between exposure to amounts of retained metal fragments, type of injury, personnel demographics and general immune function/reactivity that may affect personal health or future metal implant performance. LEVEL OF EVIDENCE: Level IV, therapeutic study.

What Surgeons Need to Know About Adverse Local Tissue Reaction in Total Hip Arthroplasty.

Adverse local tissue reactions (ALTRs) were first associated with patients with failed metal-on-metal surface replacements and total hip arthroplasty (THA). However, an increasing number of cases of ALTR in metal-on-polyethylene (MOP) THA patients is being reported. Clinically, ALTR appears as benign, aseptic masses or bursae in the periprosthetic tissues. Histopathologically, ALTRs are distinguished by an intense lymphocyte infiltrate, destruction of the synovial surfaces, widespread necrosis, and fibrin exudate. Tribocorrosion of modular junctions appears to be the cause of ALTR in MOP patients. The various tribocorrosion damage modes occurring at modular junctions produce metal ions and a diversity of particulates in relation to size, chemical composition, and structure. The mechanisms by which these various products of tribocorrosion lead to ALTR are still a matter of considerable research. This review clarifies what constitutes ALTR, its relationship to implant factors, and highlights current methods for diagnosis and management of patients with ALTR in the setting of MOP THA.

Echocardiographic Changes in the Context of Metal-on-Metal Versus Nonmetal-on-Metal Total Hip Arthroplasty.

BACKGROUND: The purpose of this study is to determine if there is a difference in echocardiographic results between patients with metal-on-metal (MoM) vs non-MoM total hip arthroplasty (THA) and to determine if a correlation exists between serum metal levels and echocardiographic outcomes. METHODS: Seventy-five patients with the same modular THA enrolled in this prospective cohort study, and 49 had MoM bearings. All patients had serum cobalt, chromium, and titanium levels drawn at 2 study visits with a transthoracic echocardiogram at the second visit. Serum metal concentrations and echocardiographic parameters were compared with 2-way t-tests. Multiple linear regression analyses identified any significant predictors of echocardiographic outcomes. RESULTS: Mean serum cobalt and chromium levels were significantly greater in the MoM group at both time-points (P < .001 and P < .05, respectively). Titanium levels were similar between groups (P > .05). MoM patients had significantly lower global longitudinal strain compared with the non-MoM group (18.4% vs 20.2%; P = .026). Serum cobalt concentration was found to be an independent predictor of tricuspid annular plane systolic excursion (P = .02). CONCLUSION: MoM THA bearings are associated with increased serum cobalt and chromium levels. Patients with MoM THAs had decreased global longitudinal strain, a measure of left ventricular function, but both groups remained within normal range. The clinical impact of the positive association between serum cobalt concentration and tricuspid annular plane systolic excursion, a marker of right ventricular function, deserves further study. These findings can reassure physicians and patients that metal-induced cardiomyopathy is not typical in the setting of MoM THA. LEVEL OF EVIDENCE: Level II, Prospective Cohort Study.

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.

High Failure at a Minimum 5-Year Follow-Up in Primary Total Hip Arthroplasty Using a Modular Femoral Trunnion.

BACKGROUND: Modular femoral trunnions enable the surgeon to independently adjust offset, leg length, and anteversion in total hip arthroplasty (THA). However, modularity may result in an increased risk of fretting and corrosion along with a higher risk of implant dissociation or fracture. The purpose of this study is to evaluate mid-term survivorship of THAs using a cementless modular system. METHODS: A consecutive series of 221 patients who underwent a primary THA using the ALFA II modular stem by a single surgeon between 2002 and 2004 were reviewed. Survivorship of the ALFA II modular hip system was evaluated at a minimum of 5 years postoperatively. RESULTS: Of the 221 patients, 28 (12.7%) died from causes unrelated to the surgery before adequate follow-up, and 64 (29.0%) patients were lost to follow-up. The remaining 129 patients had a mean 6.5-year (range: 5-8 years) follow-up. All-cause survivorship of the modular stem system was 81% (95% confidence interval = 69-90) at a mean 6.5-year follow-up. Of the 25 (19.4%) cases requiring revision surgery, 52.0% was for dissociation of the modular components, 32.0% was for fracture of the prosthesis, 12.0% was for instability/multiple dislocations, and 4.0% was for chronic septic THA. Body mass index (odds ratio = 1.080) and offset (odds ratio = 1.254) were independent risk factors for mechanical failures of the modular stem system. CONCLUSION: The modular stem hip system of interest in this study demonstrates a high failure rate at mid-term follow-up, and we caution against the use of similar designs in primary THAs.

Mathematical model of perineural tumor spread: a pilot study.

BACKGROUND: Perineural spread (PNS) of pelvic cancer along the lumbosacral plexus is an emerging explanation for neoplastic lumbosacral plexopathy (nLSP) and an underestimated source of patient morbidity and mortality. Despite the increased incidence of PNS, these patients are often times a clinical conundrum-to diagnose and to treat. Building on previous results in modeling glioblastoma multiforme (GBM), we present a mathematical model for predicting the course and extent of the PNS of recurrent tumors. METHODS: We created three-dimensional models of perineurally spreading tumor along the lumbosacral plexus from consecutive magnetic resonance imaging scans of two patients (one each with prostate cancer and cervical cancer). We adapted and applied a previously reported mathematical model of GBM to progression of tumor growth along the nerves on an anatomical model obtained from a healthy subject. RESULTS: We were able to successfully model and visualize perineurally spreading pelvic cancer in two patients; average growth rates were 60.7 mm/year for subject 1 and 129 mm/year for subject 2. The model correlated well with extent of PNS on MRI scans at given time points. CONCLUSIONS: This is the first attempt to model perineural tumor spread and we believe that it provides a glimpse into the future of disease progression monitoring. Every tumor and every patient are different, and the possibility to report treatment response using a unified scale-as "days gained"-will be a necessity in the era of individualized medicine. We hope our work will serve as a springboard for future connections between mathematics and medicine.

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.

Diagnosing Taper Corrosion: When Is It the Taper and When Is It Something Else?

There has been an increasing use of modularity at the head-neck junction in total hip arthroplasty to more closely mimic the native anatomy, allowing for optimal leg length and stability. Corrosion at this junction in metal-on-polyethylene bearings can lead to an adverse local tissue reaction (ALTR). This increasingly prevalent condition should be considered in the differential diagnosis of hip pain and difficulty ambulating. A recent symposium by the American Academy of Hip and Knee Surgeons described the diagnosis, etiology, management, and prevention of taper corrosion. This article describes the history, physical, plain and advanced imaging findings, laboratory tests, and other diagnoses that should be taken into consideration when diagnosing taper corrosion. The presence of ALTR due to taper corrosion can mimic other diagnoses such as periprosthetic joint infection, instability, or aseptic loosening. Serum metal levels have been found to be the most effective screening tool for identifying corrosion, but other common causes of hip pain and difficulty ambulating should always be ruled out with the use of radiographs and common laboratory techniques before diagnosing ALTR due to corrosion.

Risk Adjustment Is Necessary in Medicare Bundled Payment Models for Total Hip and Knee Arthroplasty.

BACKGROUND: Concerns exist that high-risk patients in alternative payment models may face difficulties with access to care without proper risk adjustment. The purpose of this study is to identify the effect of medical and orthopedic specific risk factors on the cost of a 90-day episode of care following total hip (THA) and knee arthroplasty (TKA). METHODS: We queried the Medicare 5% Limited Data Set for all patients undergoing primary THA and TKA from 2010 to 2014. To evaluate the cost of an episode of care, we calculated all claims for 90 days following surgery. Multivariate analysis was performed to quantify the added episode-of-care costs for demographic variables, geography, medical comorbidities, and orthopedic specific risk factors. RESULTS: Of the 58,809 TKA patients, the median 90-day Medicare costs was $23,800 (interquartile range, $18,900-$32,300), while the median of the 27,293 THA patients was $24,000 (interquartile range, $18,500-$33,900). Independent risk factors (all P < .05) resulting in at least a 10% increase in episode-of-care costs following TKA included malnutrition, age over 85, male gender, pulmonary disorder, failed internal fixation, Northeast region, lower socioeconomic status, neurologic disorder, and rheumatoid arthritis. Independent risk factors (all P < .05) resulting in at least a 10% increase in episode-of-care costs following THA included malnutrition, male gender, age over 85, failed internal fixation, hip dysplasia, Northeast region, neurologic disorder, lower socioeconomic status, conversion THA, avascular necrosis, and depression. CONCLUSION: Certain comorbidities and orthopedic risk factors increase 90-day episode-of-care costs in the Medicare population. The current lack of proper risk stratification could be a powerful driver of decreased access to care for our most medically challenged members of society.

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.

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.

Serum Metal Levels for Diagnosis of Adverse Local Tissue Reactions Secondary to Corrosion in Metal-on-Polyethylene Total Hip Arthroplasty.

BACKGROUND: Recently, corrosion at the head-neck junction in metal-on-polyethylene bearing surface total hip arthroplasty (THA) has been recognized as a cause of adverse local tissue reactions (ALTRs). Serum metal levels have been advocated as a tool for the diagnosis of ALTR; however, no prior studies have specifically examined their utility. The purpose of this study was to determine the optimal cutoff values for serum cobalt and chromium levels in diagnosing ALTR after metal-on-polyethylene bearing surface THA. METHODS: We reviewed 447 consecutive patients with serum metal levels tested at our institution and identified 64 patients with a metal-on-polyethylene bearing who had axial imaging or underwent reoperation to confirm the presence or absence of ALTR. Receiver-operating characteristic curves were produced to identify cutoff thresholds to optimize sensitivity, and diagnostic test performance was characterized. RESULTS: Forty-four of the 64 patients (69%) were positive for an ALTR. The best test for the diagnosis of ALTR was the serum cobalt level (area under the curve [AUC] = 99%). A threshold cutoff of ≥1.0 ng/mL had a sensitivity of 100%, specificity of 90%, positive predictive value (PPV) of 96%, and negative predictive value (NPV) of 100%. Serum chromium levels were also diagnostic (AUC = 87%). A threshold cutoff of ≥0.15 ng/mL had a sensitivity of 100%, specificity of 50%, PPV of 81%, and NPV of 100%. Finally, serum cobalt-to-chromium ratio was also helpful for diagnosis (AUC = 90%). A threshold cutoff value of 1.4 for the cobalt-to-chromium ratio offered a sensitivity of 93%, specificity of 70%, PPV of 87%, and NPV of 82%. CONCLUSION: Measurement of serum cobalt level with a threshold value of 1.0 ng/mL in our experience is the best test for identifying the presence of ALTR in patients with a metal-on-polyethylene THA. Measurement of chromium level and the ratio of cobalt-to-chromium levels are also of value.

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.

Corrosion at the Head-Neck Junction: Why Is This Happening Now?

While mechanically-assisted crevice corrosion (MACC) at the head/neck junction of modular total hip arthroplasty (THA) femoral components was first described over two decades ago, it is only within the last few years that investigators have observed that adverse local tissue reactions (ALTRs) associated with MACC are an increasingly prevalent mode of failure of contemporary THAs. As yet, the incidence, etiology and pathogenesis of MACC-associated ALTR are not well understood. In this review, possible implant-, patient-, and surgeon-related factors are considered in the context of a small but growing body of evidence from laboratory simulations, implant and tissue retrieval studies and clinical case series. It is likely that MACC-associated ALTR is a multifactorial process and that ongoing research will lead to multiple strategies that will facilitate early diagnosis and ultimately prevention of the adverse clinical sequelae of this phenomenon.

Diagnosis and Management of Adverse Local Tissue Reactions Secondary to Corrosion at the Head-Neck Junction in Patients With Metal on Polyethylene Bearings.

We reviewed 27 patients who underwent revision for an adverse local tissue reaction (ALTR) secondary to corrosion at the head-neck junction with MoP bearings. Serum cobalt and chromium levels were elevated in all cases, with a mean cobalt of 11.2 ppb and chromium of 2.2 ppb. Patients underwent modular bearing exchange, including a ceramic head with a titanium sleeve in 23 of 27 cases with only one recurrence of ALTR in one of the four patients not treated with a ceramic head. The diagnosis of ALTR secondary to corrosion is associated with cobalt levels of >1 ppb with cobalt levels elevated above chromium. Retention of a well-fixed stem and modular exchange to a ceramic head leads to resolution of symptoms and decreases in metal levels.

Do Complication Rates Differ by Gender After Metal-on-metal Hip Resurfacing Arthroplasty? A Systematic Review.

BACKGROUND: Although metal-on-metal (MoM) bearing surfaces provide low rates of volumetric wear and increased stability, evidence suggests that certain MoM hip arthroplasties have high rates of complication and failure. Some evidence indicates that women have higher rates of failure compared with men; however, the orthopaedic literature as a whole has poorly reported such complications stratified by gender. QUESTIONS/PURPOSES: This systematic review aimed to: (1) compare the rate of adverse local tissue reaction (ALTR); (2) dislocation; (3) aseptic loosening; and (4) revision between men and women undergoing primary MoM hip resurfacing arthroplasty (HRA). METHODS: Systematic MEDLINE and EMBASE searches identified all level I to III articles published in peer-reviewed journals, reporting on the outcomes of interest, for MoM HRA. Articles were limited to those with 2-year followup that reported outcomes by gender. Ten articles met inclusion criteria. Study quality was evaluated using the Modified Coleman Methodology Score; the overall quality was poor. Heterogeneity and bias were analyzed using a Mantel-Haenszel statistical method. RESULTS: Women demonstrated an increased odds of developing ALTR (odds ratio [OR], 5.70 [2.71-11.98]; p<0.001), dislocation (OR, 3.04 [1.2-7.5], p=0.02), aseptic loosening (OR, 3.18 [2.21-4.58], p<0.001), and revision (OR, 2.50 [2.25-2.78], p<0.001) after primary MoM HRA. CONCLUSIONS: A systematic review of the currently available literature reveals a higher rate of complications (ALTR, dislocation, aseptic loosening, and revision) after MoM HRA in women compared with men. Although femoral head size has been frequently implicated as a prime factor in the higher rate of complication in women, further research is necessary to specifically probe this relationship. Retrospective studies of data available (eg, registry data) should be undertaken, and moving forward studies should report outcomes by gender (particularly complications). LEVEL OF EVIDENCE: Level III, therapeutic study.