Particulate Debris Released From Breast Implant Surfaces Is Highly Dependent on Implant Type

BACKGROUND

Although breast implants (BIs) have never been safer, factors such as implant debris may influence complications such as chronic inflammation and illness such as ALCL (anaplastic large cell lymphoma). Do different types of BIs produce differential particulate debris?

OBJECTIVES

The aim of this study was to quantify, investigate, and characterize the size, amount, and material type of both loosely bound and adherent surface particles on 5 different surface types of commercial BIs.

METHODS

Surface particles from BIs of 5 surface types (n = 5/group), Biocell, Microcell, Siltex, Smooth, SmoothSilk, and Traditional-Smooth, were: (1) removed by a rinsing procedure and (2) removed with ultrapure adhesive carbon tabs. Particles were characterized (ASTM 1877-16) by scanning electron microscopy and energy-dispersive X-ray chemical analysis.

RESULTS

Particles rinsed from Biocell, Microcell and Siltex were <1 μm in diameter whereas SmoothSilk and Traditional-Smooth surfaces had median sizes >1 μm (range, 0.4-2.7 μm). The total mass of particles rinsed from the surfaces indicated Biocell had >5-fold more particulate compared with all other implants, and >30-fold more than SmoothSilk or Traditional-Smooth implants (>100-fold more for post-rinse adhesion analysis). Energy-dispersive X-ray analysis indicated that the particulate material for Biocell, Microcell, and Siltex was silicone (>50%), whereas particulates from SmoothSilk and Traditional-Smooth implants were predominantly carbon-based polymers, eg, polycarbonate-urethane, consistent with packaging (and were detected on all implant types). Generally, SmoothSilk and Traditional-Smooth implant groups released >10-fold fewer particles than Biocell, Microcell, and Siltex surfaces. Pilot ex vivo tissue analysis supported these findings.

CONCLUSIONS

Particulate debris released from BIs are highly dependent on the type of implant surface and are a likely key determinant of in vivo performance.

LEVEL OF EVIDENCE: 5

Metal-induced delayed type hypersensitivity responses potentiate particle induced osteolysis in a sex and age dependent manner

It is widely recognized that innate macrophage immune reactions to implant debris are central to the inflammatory responses that drive biologic implant failure over the long term. Less common, adaptive lymphocyte immune reactions to implant debris, such as delayed type hypersensitivity (DTH), can also affect implant performance. It is unknown which key patient factors, if any, mediate these adaptive immune responses that potentiate particle/macrophage mediated osteolysis. The objective of this investigation was to determine to what degree known adaptive immune responses to metal implant debris can affect particle-induced osteolysis (PIO); and if this pathomechanism is dependent on: 1) innate immune danger signaling, i.e., NLRP3 inflammasome activity, 2) sex, and/or 3) age. We used an established murine calvaria model of PIO using male and female wild-type C57BL/6 vs. Caspase-1 deficient mice as well as young (12–16 weeks old) vs. aged (18–24 months old) female and male C57BL/6 mice. After induction of metal-DTH, and Cobalt-alloy particle (ASTM F-75, 0.4um median diameter) calvaria challenge, bone resorption was assessed using quantitative micro-computed tomography (micro-CT) analysis and immune responses were assessed by measuring paw inflammation, lymphocyte transformation test (LTT) reactivity and adaptive immune cytokines IFN-gamma and IL-17 (ELISA). Younger aged C57BL/6 female mice exhibited the highest rate and severity of metal sensitivity lymphocyte responses that also translated into higher PIO compared to any other experimental group. The absence of inflammasome/caspase-1 activity significantly suppressed DTH metal-reactivity and osteolysis in both male and female Caspase-1 deficient mice. These murine model results indicate that young female mice are more predisposed to metal-DTH augmented inflammatory responses to wear debris, which is highly influenced by active NLRP3 inflammasome/caspase-1 danger signaling. If these results are clinically meaningful for orthopedic patients, then younger female individuals should be appropriately assessed and followed for DTH derived peri-implant complications.

Investigation of CoCrMo material loss in a novel bio-tribometer designed to study direct cell reaction to wear and corrosion products

Wear and corrosion in total hip replacement negatively impact implant service-life and patient well-being. The aim of this study was to generate a statistical response surface of material loss using an apparatus, capable of testing the effect of wear and corrosion products in situ on cells, such as macrophages. The test chamber of a ball-on-flat tribometer operating inside a CO₂ incubator was integrated with an electrochemical setup and adapted for cell culture work. A 20-test series, following a 2-level 3-factor design of experiments, was performed with a ceramic head in reciprocating rotational motion against a CoCrMo-alloy disc, under constant load. The lubricant was cell culture medium (RPMI-1640+10vol% bovine serum). Response surfaces were generated, which statistically showed the influence of motion amplitude, load, and potential on the total mass loss and wear scar volume of the metallic discs. Potential had the highest impact on the total mass loss, while motion amplitude and load significantly influenced the wear scar volume. The concentrations of the alloy elements found in the lubricants reflected the bulk-alloy stoichiometry. The total concentration of Co released into the lubricant (2.3-63 ppm by total mass loss, 1.5 to 62 ppm by ICP-MS) corresponded well with the known range to trigger cell response. Tribocorrosion tests in the presence of cells and tissues, such as macrophages, lymphocytes and/or synovium, will be carried out in the future.

The Inflammatory Effects of Breast Implant Particulate Shedding: Comparison With Orthopedic Implants

Currently, there is a dearth of information regarding the degree of particle shedding from breast implants (BIs) and what are the general biological consequences of BI debris. Thus, it is unclear to what degree BI debris compromises the long-term biological performance of BIs. For orthopedic implants, it is well established that the severity of biological reactivity to implant debris governs long-term clinical performance. Orthopedic implant particulate debris is generally in the range of 0.01 to 100 μm in diameter. Implant debris-induced bioreactivity/inflammation is mostly a peri-implant phenomenon caused by local innate immune cells (eg, macrophages) that produce proinflammatory cytokines such as tumor necrosis factor-α, interleukin-1β, interleukin-6, and prostaglandin 2 (PGE2). In orthopedics, there have been few systemic concerns associated with polymeric implant debris (like silicone) other than documented dissemination to remote organs (eg, liver, spleen, etc.) with no known associated pathogenicity. This is not true of metal implant debris where normal (well-functioning) implants can induce systemic reactions such as delayed type hypersensitivity. Diagnostic analysis of orthopedic tissues has focused on innate (macrophage mediated) and adaptive (lymphocyte-mediated hypersensitivity) immune responses. Orthopedic implant debris-associated lymphocyte cancers have not been reported in over 40 years of orthopedic literature. Adaptive immune responses such as hypersensitivity reactions to orthopedic implant debris have been dominated by certain implant types that produce specific kinds of debris (eg, metal-on-metal total joint prostheses). Orthopedic hypersensitivity responses and atypical BI bioreactivity such as BI-associated anaplastic large cell lymphoma share crossover markers for diagnosis. Differentiating normal innate immune reactivity to particles from anaplastic large cell lymphoma reactions from delayed type hypersensitivity reactions to BI-associated implant debris remains unclear but vital to patients and surgeons.

CoCrMo alloy vs. UHMWPE Particulate Implant Debris Induces Sex Dependent Aseptic Osteolysis Responses In Vivo using a Murine Model

Background:

The rate of revision for some designs of total hip replacements due to idiopathic aseptic loosening has been reported as higher for women. However, whether this is environmental or inherently sex-related is not clear.

Objective:

Can particle induced osteolysis be sex dependent? And if so, is this dependent on the type of implant debris (e.g. metal vs polymer)? The objective of this study was to test for material dependent inflammatory osteolysis that may be linked to sex using CoCrMo and implant grade conventional polyethylene (UHMWPE), using an in vivo murine calvaria model.

Methods:

Healthy 12 week old female and male C57BL/6J mice were treated with UHMWPE (1.0um ECD) or CoCrMo particles (0.9um ECD) or received sham surgery. Bone resorption was assessed by micro-computed tomography, histology and histomorphometry on day 12 post challenge.

Results:

Female mice that received CoCrMo particles showed significantly more inflammatory osteolysis and bone destruction compared to the females who received UHMWPE implant debris. Moreover, females challenged with CoCrMo particles exhibited 120% more inflammatory bone loss compared to males (p<0.01) challenged with CoCrMo implant debris (but this was not the case for UHMWPE particles).

Conclusion:

We demonstrated sex-specific differences in the amount of osteolysis resulting from CoCrMo particle challenge. This suggests osteo-immune responses to metal debris are preferentially higher in female compared to male mice, and supports the contention that there may be inherent sex related susceptibility to some types of implant debris.

Fretting-corrosion in Hip Implant Modular Junctions: New Experimental Set-up and Initial Outcome

Modern hip prostheses feature a modular implant design with at least one tapered junction. This design can lead to several complications due to the introduction of additional interfaces, which are subjected to various loading conditions and micromotion. The main objective of current study is to develop a fretting corrosion apparatus, which is able characterize the mechanical and electrochemical behaviour of various existing metal alloy couples during fretting motion. This study describes the design and the main considerations during the development of a novel fretting corrosion apparatus, as well as determination of the machine compliance and the initial testing results. Machine compliance considerations and frictional interactions of the couples are discussed in detail. For the preliminary tests, metal alloy pins, made of Ti6Al4V and wrought high-carbon CoCrMo were mechanically polished to a surface roughness of less than 20nm. 2 pins (Diameter = 11mm) of either Ti6Al4V or CoCrMo were loaded onto a Ti6Al4V alloy rod at a normal force of 200N. The interface types included: Ti6Al4V-Ti6Al4V-Ti6Al4V, Ti6Al4V-Ti6Al4V-CoCrMo, and CoCrMo-Ti6Al4V-CoCrMo. The Ti6Al4V rod articulated against the metal alloy pins in a sinusoidal fretting motion with a displacement amplitude of ±50μm. Bovine calf serum (30g/L of protein content) was selected as a lubricant and tested at 2 different pH levels (pH 3.0 and 7.6). In all cases, current and friction energy were monitored during the fretting process. The results indicated distinct, material-specific current evolutions and friction energies. No significant differences were observed in electrochemical or mechanical behaviour in response to pH change. In general, Ti6Al4V-Ti6Al4V-Ti6Al4V couples displayed the earliest passivation and superior electrochemical behaviour compared to Ti6Al4V-Ti6Al4V-CoCrMo and CoCrMo-Ti6Al4V-CoCrMo under fretting conditions. In addition, fluctuations in current were observed in specific regions at all instances where Ti6Al4V was coupled with Ti6Al4V. These fluctuations were not observed in instances where Ti6Al4V was coupled with CoCrMo. These findings suggest transitions in the degradation mechanisms at the modular junction as a function of material couples/contacts. The findings may assist in improving the current hip modular junctions.

Design of a tribocorrosion bioreactor for the analysis of immune cell response to in situ generated wear products

Adverse local tissue reactions to wear debris and corrosion products have lead to a sharp decline in the use of metal-on-metal (MOM) total hip athroplasties (THAs) clinically. Today, approximately 1 million patients are still carrying such a device. To gain a better understanding of the effect of wear and corrosion products on cells within the joint environment, it is important to generate conditions in vitro that resemble the in vivo system as closely as possible. In this paper, we present a novel tribocorrosion bioreactor that enables the simultaneous conduction of tribocorrosion and cell-culture experiments. In this setup, macrophage cell cultures are located in direct proximity to a tribological interface mimicking the sliding conditions of THA and are exposed to wear and corrosion products as they are generated. These products may include meta-stable species and metallo-organic complexes that have not been considered in earlier studies. The combination of standard tribological, electrochemical, and biological techniques is associated with several challenges that are described here in detail.

Implant debris particle size affects serum protein adsorption which may contribute to particle size-based bioreactivity differences

Biologic reactivity to orthopedic implant debris mediates long-term clinical performance of total joint arthroplasty implants. However, the reasons that some facets of implant debris (e.g., particle size, shape, base material, etc.) are more pro-inflammatory remain controversial. This precludes accurate prediction and optimal design of modern total joint replacements. We hypothesized that debris particle size can influence adsorbed protein film composition and affect subsequent bioreactivity. We measured size-dependent proteinfilm adsorption, and adsorbed protein-film-dependent cytokine release using equal surface areas of different sized cobalt-chromium alloy (CoCr-alloy) particles and in vitro challenge of human macrophages (THP-1 and human primary). Smaller (5 μm diameter) versus larger (70 μm diameter) particles preferentially adsorbed more serum protein in general (p<0.03), where higher molecular weight serum proteins consistent with IgG were identified. Additionally, 5-μm CoCr-alloy particles pre-coated with different protein biofilms (IgG vs. albumin) resulted in a difference in cytokine expression in which albumin-coated particles induced more TNF-α release and IgG-coated particles induced more IL-1β release from human monocytes/macrophages. In these preliminary in vitro studies, we have demonstrated the capability of equal surface areas of different particle sizes to influence adsorbed protein composition and that adsorbed protein differences on identical particles can translate into complex differences in bioreactivity. Together, these findings suggest that adsorbed protein differences on different-sized particles of the same material may be a contributing mechanism by which certain particles induce different reactivities.

Osteoclasts lose innate inflammatory reactivity to metal and polymer implant debris compared to monocytes/macrophages

Long-term aseptic failures of joint replacements are generally attributed to implant debris-induced inflammation and osteolysis. This response is largely mediated by immune and bone cells (monocytes/macrophages and osteoclasts, respectively), that in the presence of implant debris (e.g. metal particles and ions), release pro-inflammatory cytokines such as IL-1β, TNF-α, and IL-6. The relative degree to which implant debris can illicit inflammatory response(s) from osteoclasts vs monocytes/macrophages is unknown, i.e. are osteoclasts a viable target for anti-inflammatory therapy for implant debris? We investigated relative monocyte versus osteoclast inflammatory responses in a side-by-side comparison using implant debris from the perspective of both danger signaling (IL-1β) and pathogenic recognition (TNF-α) reactivity (Challenge Agents: Cobalt-alloy, Titanium-alloy, and PMMA particles, 0.9-1.8um-dia ECD and Cobalt, and Nickel-ions 0.01-0.1mM, all with and without LPS priming). Human monocytes/macrophages reacted to implant debris with >100 fold greater production of cytokines compared to osteoclast-like cells. Particulate Co-alloy challenge induced >1000 pg/ml of IL-1β and TNF-α, in monocytes and <50pg/mL IL-1β and TNF-α in osteoclasts. Cobalt ions induced >3000pg/mL IL-1β and TNF-α in monocytes/macrophages and <50pg/mL IL-1β and TNF-α in osteoclasts. The paracrine effect of supernatants from debris-treated monocytes/macrophages was capable of inducing greater osteoclastogenesis (TRAP+, p<0.06) and inflammation than direct debris challenge on osteoclasts. Our results indicate that as monocytes/macrophages differentiate into osteoclasts, they largely lose their innate immune reactivity to implant debris and thus may not be as relevant a therapeutic target as monocytes/macrophages for mitigating debris-induced inflammation.

Asymptomatic prospective and retrospective cohorts with metal-on-metal hip arthroplasty indicate acquired lymphocyte reactivity varies with metal ion levels on a group basis

Some tissues from metal-on-metal (MoM) hip arthroplasty revisions have shown evidence of adaptive-immune reactivity (i.e., excessive peri-implant lymphocyte infiltration/activation). We hypothesized that, prior to symptoms, some people with MoM hip arthroplasty will develop quantifiable metal-induced lymphocyte reactivity responses related to peripheral metal ion levels. We tested three cohorts (Group 1: n = 21 prospective longitudinal MoM hip arthroplasty; Group 2: n = 17 retrospective MoM hip arthroplasty; and Group 3: n = 20 controls without implants). We compared implant position, metal-ion release, and immuno-reactivity. MoM cohorts had elevated (p < 0.01) amounts of serum Co and Cr compared to controls as early as 3 months post-op (Group 1:1.2 ppb Co, 1.5 ppb Cr; Group 2: 3.4 ppb Co, 5.4 ppb Cr; Group 3: 0.01 ppb Co, 0.1 ppb Cr). However, only after 1-4 years post-op did 56% of Group 1 develop metal-reactivity (vs. 5% pre-op, metal-LTT, SI > 2), compared with 76% of Group 2, and 15% of Group 3 controls (patch testing was a poor diagnostic indicator with only 1/21 Group 1 positive). Higher cup-abduction angles (50° vs. 40°) in Group 1 were associated with higher serum Cr (p < 0.07). However, sub-optimal cup-anteversion angles (9° vs. 20°) had higher serum Co (p < 0.08). Serum Cr and Co were significantly elevated in reactive versus non-reactive Group-1 participants (p < 0.04). CD4+CD69+ T-helper lymphocytes (but not CD8+) and IL-1β, IL-12, and IL-6 cytokines were all significantly elevated in metal-reactive versus non-reactive Group 1 participants. Our results showed that lymphocyte reactivity to metals can develop within the first 1-4 years after MoM arthroplasty in asymptomatic patients and lags increases in metal ion levels. This increased metal reactivity was more prevalent in those individuals with extreme cup angles and higher amounts of circulating metal.

Quantifying subtle but persistent peri-spine inflammation in vivo to submicron cobalt-chromium alloy particles

PURPOSE

We evaluated the consequences of cobalt-chromium alloy (CoCr) wear debris challenge in the peri-spine region to determine the inflammation and toxicity associated with submicron particulates of CoCr-alloy and nickel on the peri-spine.

METHODS

The lumbar epidural spaces of (n = 50) New Zealand white rabbits were challenged with: 2.5 mg CoCr, 5.0 mg CoCr, 10.0 mg CoCr, a positive control (20.0 mg of nickel) and a negative control (ISOVUE-M-300). The CoCr-alloy and Ni particles had a mean diameter of 0.2 and 0.6 μm, respectively. Five rabbits per dose group were studied at 12 and 24 weeks. Local and distant tissues were analyzed histologically and quantitatively analyzed immunohistochemically (TNF-α and IL-6).

RESULTS

Histologically, wear particles were observed in all animals. There was no evidence of toxicity or local irritation noted during macroscopic observations in any CoCr-dosed animals. However, Ni-treated control animals experienced bilateral hind leg paralysis and were euthanized at Day 2. Histopathology of the Ni particle-treated group revealed severe neuropathy. Quantitative immunohistochemistry demonstrated a CoCr-alloy dose-dependent increase in cytokines (IL-6, TNF-α, p < 0.05) at 12 and 24 weeks.

CONCLUSIONS

Subtle peri-spine inflammation associated with CoCr-alloy implant particles was dose dependent and persistent. Neuropathy can be induced by highly reactive Ni particles. This suggests peri-spine challenge with CoCr-alloy implant debris (e.g., TDA) is consistent with past reports using titanium alloy particles, i.e., mild persistent inflammation.

In vivo response to cross-linked polyethylene and polycarbonate-urethane particles

This study was undertaken to examine macrophage response to polycarbonate-urethane, a proposed alternative material to polyethylene in acetabular components of total hip arthroplasty. Polyethylene wear debris from total joint replacements has been linked to osteolysis and implant lifespan. It has been shown in vitro, that polyethylene particles cleaned of endotoxin generate less of an inflammatory cytokine response than endotoxin bound particles. Comparative particle induced effects on implant fixation were tested using endotoxin free cross-linked ultra-high molecular weight polyethylene (x-UHMWPE) and polycarbonate-urethane (PCU) particles with and without intraperitoneal injection (IP) of lipopolysaccharide (LPS) using a Ti-alloy femoral intramedullary nail rat model. MicroCT and mechanical testing assessment of peri-implant bone indicated significantly less bone and lower fixation strength, respectively, when the implant was surrounded by xUHMWPE particles compared to PCU particles (with and without LPS IP). This indicates particles of PCU may be less disruptive to bone-implant fixation than x-UHMWPE in vivo, under both LPS free and challenged conditions.

In vitro macrophage response to polyethylene and polycarbonate-urethane particles

This study was undertaken to compare macrophage response to polycarbonate-urethane (PCU), a proposed alternative material to polyethylene in acetabular components of total hip arthroplasty to cross-linked ultra-high molecular weight polyethylene (xUHMWPE) in the presence or absence of endotoxin. Polyethylene wear debris that is generated by total hip and knee replacements has been linked to osteolysis and limiting the lifespan of the implant. We added both lipopolysaccharide (LPS)-free and endotoxin-associated xUHMWPE and PCU particles to a human monocyte cell line (TH1) in culture and measured cell viability and tumor necrosis factor (TNF)alpha, interleukin (IL)-1beta, and prostaglandin E(2) (PGE(2)) in the medium after 24 h. Results indicate that particles (both xUHMWPE and PCU) free of endotoxin did not significantly induce secretion of TNFalpha, IL-1beta, or PGE(2) above basal levels. However, endotoxin-exposed PCU particles induced significantly less TNFalpha and IL-1beta than endotoxin-exposed xUHMWPE particles. This indicates that if endotoxin is available for binding to particles in vivo, then xUHMWPE may be more inflammatory to periprosthetic tissue and bone in part because of its affinity/reactivity with endotoxin when compared with PCU.

In vitro reactivity to implant metals demonstrates a person-dependent association with both T-cell and B-cell activation

Hypersensitivity to metallic implants remains relatively unpredictable and poorly understood. We initially hypothesized that metal-induced lymphocyte proliferation responses to soluble metal challenge (ions) are mediated exclusively by early T-cell activation (not B-cells), typical of a delayed-type-hypersensitivity response. We tested this by comparing proliferation (6 days) of primary lymphocytes with early T-cell and B-cell activation (48 h) in three groups of subjects likely to demonstrate elevated metal reactivity: group 1 (n = 12) history of metal sensitivity with no implant; group 2a (n = 6) well performing metal-on-metal THRs, and group 2b (n = 20) subjects with poorly performing metal-on-polymer total joint arthroplasties (TJA). Group 1 showed 100% (12/12) metal reactivity (stimulation index > 2) to Ni. Groups 2a and 2b were 83% (5/6) and 75% (15/22) metal reactive (to Co, Cr, or Ni), respectively. Of the n = 32 metal-reactive subjects to Co, Cr, or Ni (SI > 2), n = 22/32 demonstrated >2-fold elevations in % of T-cell or B-cell activation (CD25+, CD69+) to metal challenge when compared with untreated control. 18/22 metal-activated subjects demonstrated an exclusively T-cell or B-cell activation response to metal challenge, where 6/18 demonstrated exclusively B-cell activation and 12/18 demonstrated a T-cell only response, as measured by surface activation markers CD25+ and CD69+. However, there was no direct correlation (R(2) < 0.1) between lymphocyte proliferation and % T-cell or B-cell activation (CD25+:CD69+). Proliferation assays (LTT) showed greater ability to detect metal reactivity than did subject-dependent results of flow-cytometry analysis of T-cell or B-cell activation. The high incidence of lymphocyte reactivity and activation indicate that more complex than initially hypothesized immune responses may contribute to the etiology of debris-induced osteolysis in metal-sensitive individuals.

Early failure of metal-on-metal bearings in hip resurfacing and large-diameter total hip replacement: A consequence of excess wear

Early failure associated with adverse reactions to metal debris is an emerging problem after hip resurfacing but the exact mechanism is unclear. We analysed our entire series of 660 metal-on-metal resurfacings (Articular Surface Replacement (ASR) and Birmingham Hip Resurfacing (BHR)) and large-bearing ASR total hip replacements, to establish associations with metal debris-related failures. Clinical and radiological outcomes, metal ion levels, explant studies and lymphocyte transformation tests were performed. A total of 17 patients (3.4%) were identified (all ASR bearings) with adverse reactions to metal debris, for which revision was required. This group had significantly smaller components, significantly higher acetabular component anteversion, and significantly higher whole concentrations of blood and joint chromium and cobalt ions than asymptomatic patients did (all p < 0.001). Post-revision lymphocyte transformation tests on this group showed no reactivity to chromium or cobalt ions. Explants from these revisions had greater surface wear than retrievals for uncomplicated fractures. The absence of adverse reactions to metal debris in patients with well-positioned implants usually implies high component wear. Surgeons must consider implant design, expected component size and acetabular component positioning in order to reduce early failures when performing large-bearing metal-on-metal hip resurfacing and replacement.

A review of the biologic effects of spine implant debris: Fact from fiction

BACKGROUND

Biologic-reactivity to implant-debris is the primary determinant of long-term clinical performance. The following reviews: 1) the physical aspects of spinal-implant debris and 2) the local and systemic biologic responses to implant debris.

METHODS

Methods included are: 1) gravimetric wear analysis; 2) SEM and LALLS; 3) metal-ion analysis; 4) ELISA, toxicity testing, patch testing; and 5) metal-lymphocyte transformation testing (metal-LTT).

RESULTS

Wear and corrosion of spine-implants produce particles and ions. Particles (0.01-1000 μm) are generally submicron ( <1 µm). Wear rates of metal-on-polymer and metal-on-metal disc arthroplasties are approximately 2-20 and 1 mm(3)/yr, respectively. Metal-on-metal total disc replacement components have significant increases in circulating metal (less than 10-fold that of controls at 4 ppb-Co and 3 ppb-Cr or ng/mL). Debris reactivity is local and systemic. Local inflammation is caused primarily by ingestion of debris by local macrophages, which produce pro-inflammatory cytokines TNFα, IL-1β, IL-6, and PGE2. Systemic responses associated with implant-debris have been limited to hypersensitivity reactions. Elevated amounts of in the liver, spleen, etc of patients with failed TJA have not been associated with remote toxicological or carcinogenic pathology to date. Implant debris are differentially bioreactive. Greater numbers are pro-inflammatory; the smaller-sized debris are more bioreactive by virtue of their greater numbers (dose) for a given amount of implant mass loss (one 100-μm-diameter particle is equivalent in mass to 1 million 1-μm-diameter particles). Elongated particles are pro-inflammatory (ie, aspect ratio of greater than 3). Metal particles are more proinflammatory than polymers, ceteris paribus.

CONCLUSION

Spinal arthroplasty designs have been in use for more than 20 years internationally; therefore, concerns about neuropathology, toxicity, and carcinogenicity are mitigated. Debris-induced inflammation still depends on the individual and the type of debris. The consequence of debris-induced inflammation is continued; vigilance by physicians is recommended monitoring of spinal implants using physical exams and testing of metal content and bioreactivity, as is planning for the likelihood of revision in younger individuals.

Th1 type lymphocyte reactivity to metals in patients with total hip arthroplasty

BACKGROUND

All prostheses with metallic components release metal debris that can potentially activate the immune system. However, implant-related metal hyper-reactivity has not been well characterized. In this study, we hypothesized that adaptive immunity reaction(s), particularly T-helper type 1 (Th1) responses, will be dominant in any metal-reactivity responses of patients with total joint replacements (TJAs). We tested this hypothesis by evaluating lymphocyte reactivity to metal "ions" in subjects with and without total hip replacements, using proliferation assays and cytokine analysis.

METHODS

Lymphocytes from young healthy individuals without an implant or a history of metal allergy (Group 1: n = 8) were used to assess lymphocyte responses to metal challenge agents. In addition, individuals (Group 2: n = 15) with well functioning total hip arthroplasties (average Harris Hip Score = 91, average time in-situ 158 months) were studied. Age matched controls with no implants were also used for comparison (Group 3, n = 8, 4 male, 4 female average age 70, range 49-80). Group 1 subjects' lymphocyte proliferation response to Aluminum+3, Cobalt+2, Chromium+3, Copper+2, Iron+3, Molybdenum+5, Manganeese+2, Nickel+2, Vanadium+3 and Sodium+2 chloride solutions at a variety of concentrations (0.0, 0.05, 0.1, 0.5, 1.0 and 10.0 mM) was studied to establish toxicity thresholds. Mononuclear cells from Group 2 and 3 subjects were challenged with 0.1 mM CrCl3, 0.1 mM NiCl2, 0.1 mM CoCl2 and approx. 0.001 mM titanium and the reactions measured with proliferation assays and cytokine analysis to determine T-cell subtype prominence.

RESULTS

Primary lymphocytes from patients with well functioning total hip replacements demonstrated a higher incidence and greater magnitude of reactivity to chromium than young healthy controls (p < 0.03). Of the 15 metal ion-challenged subjects with well functioning total hip arthroplasties, 7 demonstrated a proliferative response to Chromium, Nickel, Cobalt and/or Titanium (as defined by a statistically significant >2 fold stimulation index response, p < 0.05) and were designated as metal-reactive. Metals such as Cobalt, Copper, Manganese, and Vanadium were toxic at concentrations as low as 0.5 mM while other metals, such as Aluminum, Chromium, Iron, Molybdenum, and Nickel, became toxic at much higher concentrations (>10 mM). The differential secretion of signature T-cell subsets' cytokines (Th1 and Th2 lymphocytes releasing IFN-gamma and IL-4, respectively) between those total hip arthroplasty subjects which demonstrated metal-reactivity and those that did not, indicated a Th1 type (IFN-gamma) pro-inflammatory response.

CONCLUSION

Elevated proliferation and production of IFN-gamma to metals in hip arthroplasty subjects' lymphocytes indicates that a Th1 (vs. Th2) type response is likely associated with any metal induced reactivity. The involvement of an elevated and specific lymphocyte response suggests an adaptive (macrophage recruiting) immunity response to metallic implant debris rather than an innate (nonspecific) immune response.

Saline irrigation does not affect bone formation or fixation strength of hydroxyapatite/tricalcium phosphate-coated implants in a rat model

Intramembranous bone regeneration is critical to implant fixation. In cementless joint replacement (as opposed to cemented joint replacement), saline irrigation is not typically performed during surgery so that the osteogenic stimulus provided by the marrow is preserved. Several groups are now using the rat marrow ablation model to study intramembranous bone regeneration and implant fixation. In this model, the marrow contents are mechanically disrupted, and debris is often cleared by saline irrigation, a step that appears inconsistent with the clinical situation. Furthermore, in contrast to conventional wisdom, it has been reported that saline irrigation enhanced bone-implant contact and peri-implant bone formation in the rat model (Ishizaka et al. Bone 1996;19:589-594), although mechanical fixation of the implant was not investigated. Accordingly, the present study was performed to determine if saline irrigation leads to enhanced mechanical fixation of implants in the rat model. Forty-eight 400 to 450 g male rats were divided equally into two groups. The treatment group, in contrast to the control group, received saline irrigation in the ablated medullary canal prior to placement of hydroxyapatite/tricalcium phosphate-coated implants. Eight animals in each group were killed at 2, 4, or 8 weeks after implantation, at which time the specimens were analyzed by micro computed tomography to measure bone formation around the implant, followed by a mechanical pull-out test to measure the strength of fixation of the implant. As expected, there was increased fixation strength over time, but there were no significant differences in peri-implant bone volume, bone-implant contact, or implant fixation strength between the two groups. Thus, we found no effect of saline irrigation on bone formation or implant fixation strength in this study in which the implant had an osteoconductive coating.

Effects of soluble metals on human peri-implant cells

Despite reports associating tissue necrosis with implant failure, the degree to which processes, such as metal toxicity, negatively impact implant performance is unknown. We evaluated representative human peri-implant cells (i.e., osteoblasts, fibroblasts, and lymphocytes) when challenged by Al+3, Co+2, Cr+3, Fe+3, Mo+5, Ni+2, and V+3 chloride solutions (and Na+2 as a control) over a wide range of concentrations (0.01-10.0 mM). Cell responses were measured using proliferation assays, viability assays, and microscopic cell morphology assessments. Differential effects were found to be less a function of the cell type than of the composition and concentration of metal challenge. No preferential immunosuppression was demonstrated. Below 0.01 mM, no metal was toxic. The most toxic metals (i.e., Co, Ni, and V) reduced proliferation (IC50), and viability (LC50) and cell morphology of osteoblasts, fibroblasts, and lymphocytes by <50% at challenge concentrations <1 mM. All other metals tested required >5 mM to exact the same responses. Below 1 mM, these toxic metals also induced alterations in all cell morphology consisting of loss of filopodia or lamellipodia or changes in cell shape. Metals that were toxic at clinically relevant concentrations (less than previously reported values in peri-implant tissues/fluids) include Co (0.6 mM), Ni (0.8 mM), V (0.5 mM) for lymphocytes and Co (0.8 mM), V (0.3 mM), Al (1-5 mM), Fe (1-5 mM) for fibroblasts, and Co (0.8 mM), Ni (0.7 mM), V (0.1 mM) for osteoblasts. Only Co and V were toxic in vitro at concentrations below that detected in vivo in synovial fluid (V at 0.1 mM and Co at 0.8 mM for fibroblasts, and V at 0.4 mM and Co at 0.8 mM on osteoblasts). Thus, soluble Co and V released from Co- and Ti-based alloys, respectively, could be implicated as the most likely to mediate cell toxicity in the periprosthetic milieu.

Lymphocyte responses in patients with total hip arthroplasty

How lymphocyte-mediated metal sensitivity affects orthopaedic implant performance remains poorly understood. Do patients with implants exhibit elevated lymphocyte reactivity to metals and is this reactivity more generalized or more implant-alloy specific? We investigated these questions by measuring lymphocyte responses to implant metals (Cr(+3), Co(+2), Ni(+2) at 0.1mM, and Ti(+4) at 0.001 mM) in six subject groups: Group 1a=young controls, Group 1b=age matched controls, Group 2a=subjects with osteoarthritis (OA) and no history of metal sensitivity, Group 2b=OA subjects with history of metal sensitivity, Group 3a=total hip arthroplasty (THA) subjects with no to mild radiographic osteolysis, and Group 3b=THA subjects with moderate osteolysis. Lymphocyte proliferation, using Lymphocyte Transformation Testing (LTT), and cytokine release provided quantitative reactivity measurement, where a stimulation index of >2 indicated metal sensitivity. OA subjects with a history of metal sensitivity (Group 2b) were more metal reactive to Ni than any other group, as expected (66% incidence and Stimulation Index >20). However, THA subjects (Groups 3a and b) were >3 fold more reactive to Cr (p<0.04), than were controls (Groups 1a & b) or OA subjects (Groups 2a & b). THA subjects with moderate vs mild osteolysis (Group 3b vs 3a) were more reactive to Co (43% vs 0% incidence). Only osteolytic THA subjects demonstrated increased cytokine responses with >two-fold (p<0.05) increases in soluble interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) levels in response to Cr challenge. This elevated incidence and averaged level of lymphocyte reactivity supports a metal-specific adaptive immune response and suggests involvement in the pathogenesis of poor implant performance, e.g. aseptic osteolysis.

Immune responses correlate with serum-metal in metal-on-metal hip arthroplasty

Cell-mediated hypersensitivity associated with metal components may be related to levels of implant debris. We tested this hypothesis by comparing lymphocyte reactivity to soluble Co, Cr, Ni, and Ti of patients with metal-on-polyethylene and metal-on-metal arthroplasties with healthy controls, and patients with osteoarthritis. The metal-on-metal group (n=9) demonstrated significantly elevated serum Co and Cr concentrations (13- and 58-fold, P<.05, respectively) and significantly elevated lymphocyte reactivity to Co (SI>5, P<.004) and Ni (SI>2.5, P<.01) when compared to controls (n=12) and subjects with metal-on-poly implants (n=7). These elevated in vivo metal levels demonstrated positive linear correlation with lymphocyte reactivity supporting our hypothesis that lymphocyte metal-induced reactivity increases with increased metal exposure. These results represent the first direct link between in vivo metal exposure and lymphocyte reactivity. Whether this lymphocyte reactivity to metal debris is etiologically linked to poor implant performance remains uncertain.

The combination of pamidronate and calcitriol reverses particle- and TNF-α-induced altered functions of bone-marrow-derived stromal cells with osteoblastic phenotype

Periprosthetic bone loss after total joint arthroplasty is a major clinical problem resulting in aseptic loosening of the implant. Among many cell types, osteoblasts play a crucial role in the development of peri-implant osteolysis. In this study, we tested the effects of calcitriol (1α,25-dihydroxy-vitamin-D3) and the bisphosphonate pamidronate on titanium-particle- and TNF-α-induced release of interleukin-6 and suppression of osteoblast-specific gene expressions in bone-marrow-derived stromal cells with an osteoblastic phenotype. We monitored the expression of procollagen α1[1], osteocalcin, osteonectin and alkaline phosphatase mRNAs by Northern blots and real-time reverse transcription and polymerase chain reaction analyses. The release of various cytokines was also analysed by ELISA.

We found that calcitriol or pamidronate could only partially recover the altered functions of osteoblasts when added alone. Only a combination of these compounds restored all the tested functions of osteoblasts. The local delivery of these drugs may have therapeutic potential to prevent or to treat periprosthetic osteolysis and aseptic loosening of implants.

Differences in the fretting corrosion of metal-metal and ceramic-metal modular junctions of total hip replacements

The use of modular interlocking components is a central design feature of total joint replacements. In this investigation we hypothesized that clinically available ceramic-metal modular connections used in total hip arthroplasty release more metal through fretting corrosion than traditional metal-metal modular connections. This was investigated using an in vitro comparison of ceramic (zirconia, ZrO2) and metal (Co-alloy) femoral-head fretting upon Co-alloy stem components. In vitro fretting corrosion testing consisted of potentiodynamic monitoring and analysis of metal release from zirconia and Co-alloy 28 mm femoral heads with similar surface roughnesses (Ra=0.46 microm) on identical Co-alloy stems at 2.2 kN for 1x10(6) cycles at 2 Hz. In contrast to our original hypothesis, we found greater metal release (approximately 11-fold increase in Co and 3-fold increase in Cr) and potentiodynamic fretting of metal-metal modular junctions when compared to ceramic-metal. Potentiodynamic testing demonstrated that lower initial voltages (-266<153 mV), greater maximum voltage changes (116>56 mV, p<0.05, t-test) and voltage variability (3>0.5 mV, p<0.05, t-test) were associated with the open circuit potentials of Co-alloy on Co-alloy junctions when compared to zirconia on Co-alloy junctions. In this study of a single total hip replacement stem and head design, zirconia heads mated with Co-alloy stems produced less fretting than Co-alloy heads mated with Co-alloy stems. Although further studies are necessary with a variety of implant designs and under different experimental conditions, the evidence presented here should, in part, alleviate concerns of increases in fretting corrosion at modular junctions of ceramic-metal coupled components.

Lymphocyte Transformation Testing for Quantifying Metal-Implant-Related Hypersensitivity Responses

Hypersensitivity to metallic implants has been documented in case reports and cohort studies. However, this phenomenon remains unpredictable and poorly understood. There is continuing concern about the extrapolation of dermal patch testing to the periimplant environment. The utility of lymphocyte transformation testing (LTT) for predicting implant-related sensitivity in orthopedic patients was evaluated by contrasting LTT and patch-testing protocols and examining original cohort LTT data of subjects with and without implants. LTT of peripheral blood lymphocytes was performed, using four groups: (1) age-matched controls; (2) patients with osteoarthritis (preimplant), with and without dermal metal sensitivity; and (3) patients with total hip arthroplasty. A stimulation index of greater than 2 ( p < .05) indicated metal sensitivity. Patients with osteoarthritis and a history of metal sensitivity were more reactive to nickel than were those of any other group, as expected (ie, 66% incidence and average stimulation index of > 20). However, subjects with implants (group 3) were threefold more reactive to chromium (p < .04) than were controls (group 1) or subjects with osteoarthritis (group 2). Quantifiable lymphocyte reactivity as exemplified by increased incidence and average reactivity levels was metal implant specific (characteristic of adaptive immune responses) and suggests that LTT may be useful in the determination of implant-specific sensitivity. Advantages of LTT include quantitative results and the facilitation of multichallenge agent and dose testing. Thus, LTT (provided by laboratories fully disclosing testing methods) may be an additional tool in the armamentarium of physicians.

Interfacial kinetics of titanium- and cobalt-based implant alloys in human serum: metal release and biofilm formation

The biocompatibility of metallic implant surfaces is governed in large part by the interfacial kinetics associated with metal release and protein binding. The kinetics of metal release from, and protein binding to, cobalt- and titanium-based implant alloys in human serum were investigated by (1). measuring the temporal release of Cr and Ti into serum from Co-Cr-Mo (ASTM F-75) and Ti implant alloys (Ti-6Al-4V: ASTM F136, and commercially pure Ti, cpTi: ASTM F67), respectively; (2). examining the composition of human serum proteins adsorbed onto the surfaces of Co- and Ti-based implant alloys; and (3). identifying the serum proteins associated with the binding of soluble Cr and Ti degradation products. Analysis of metal dissolution kinetics found that Cr was released from Co-based implant alloy at an order of magnitude higher than Ti was released from Ti-based implant alloys. Serum became saturated with soluble CR and Ti at levels as high as 3250 ng/mL Ti from cpTi; 3750 ng/mL Ti from Ti-6Al-4V; and 35400 ng/mL Cr from Co-Cr-Mo degradation. The observation that human serum binds more released metal from Co-based alloy dissolution was consistent with the observed differences in biofilm composition between the two alloys, where additional serum protein(s) of approximately approximately 140 (kDa) molecular weight were detected on Co-based implant alloy surfaces. However, both Cr and Ti released from Co- and Ti-based alloys exhibited a bimodal binding pattern to both low molecular weight serum protein(s) (<32 kDa), and to higher molecular weight protein(s) in the 180-250 kDa range. Identification of metal alloy-dependent biofilm compositions and dissolution products provides the basis for understanding the bioavailability and bioreactivity of these implant alloys and their degradation products.

Concentration- and composition-dependent effects of metal ions on human MG-63 osteoblasts

Metal debris from implants has been shown to alter the function of osteoblasts in cell cultures. Its remains unclear, however, if specific forms of released ionic metals are involved in the pathogenesis of periprosthetic osteolysis. We evaluated the relative effects of ionic forms of implant metals by treating human osteoblast-like MG-63 osteosarcoma cells with eight concentrations (0.001-10.0 mM) of Cr(+3), Mo(+5), Al(+3), Ta(+5), Co(+2), Ni(+2), Fe(+3), Cu(+2), Mn(+2), Mg(+2), Na(+2), and V(+3) chloride solutions. The results demonstrated that the metal ions differentially affected osteoblast proliferation, viability, type-I collagen gene expression, and cytokine release. The metal ions were ranked in order from least to most toxic (based on a 50% reduction in viability) as follows: Na < Cr < Mg < Mo < Al < Ta < Co < Ni < Fe < Cu < Mn < V. Metal-induced decreases in osteoblast proliferation were similar in ranking. Nontoxic concentrations of metals had no effect on procollagen alpha1[I] gene expression; only at toxic concentrations did metals produce a decrease in gene expression. The most toxic metals (V, Mn, Fe, and Ni) were also the only metals found to induce IL-6 secretion on a per cell basis (of the cytokines tested, interleukin 6 (IL-6), interleukin beta 1 (IL-1beta), transforming growth factor beta 1 (TGF-beta1), and tumor necrosis factor alpha (TNF-alpha), only IL-6 was detectable in the culture medium after 48 h for any metal at any concentration). Less toxic metals (e.g., Co and Cr) had little effect on IL-6 release, even at high concentrations. In general, metal ions reduced osteoblast function (i.e., proliferation and collagen gene expression) in proportion to the degree of toxicity. These results support the hypothesis that adverse local cellular responses (particularly necrotic responses) associated with metal debris from implanted metallic devices may be due in part to metal ions released from implants or from particulate debris.

Osteolysis: basic science

Since the recognition of aseptic loosening by Charnley in the early 1960s, much information has been gained on the basic science of periprosthetic bone loss. Initially termed cement disease, it now generally is accepted that, in most instances, osteolysis is a manifestation of an adverse cellular response to phagocytosable particulate wear and corrosion debris, possibly facilitated by local hydrodynamic effects. Tissue explant, animal, and cell culture studies have allowed us to compile an appreciation of the complexity of cellular interactions and chemical mediators involved in osteolysis. Cellular participants have been shown to include the macrophage, osteoblast, fibroblast, and osteoclast. The plethora of chemical mediators that are responsible for the cellular responses and effects on bone include prostaglandin E2, tumor necrosis factor-alpha, interleukin-1, and interleukin 6. However, an increasing number of other proinflammatory and antiinflammatory cytokines, prostenoids, and enzymes have been shown to play important roles in this process. The ultimate goal of basic research is to develop novel strategies for evaluation and treatment of patients with osteolysis. Although initial animal studies are promising for possible pharmacologic treatment and prevention of osteolysis, well-controlled human trials are required before agents such as bisphosphonates can be recommended for general clinical use.

The potential role of the osteoblast in the development of periprosthetic osteolysis: review of in vitro osteoblast responses to wear debris, corrosion products, and cytokines and growth factors

Limited information is available on the responses of osteoblasts to wear debris, corrosion products, and cytokines and on the roles of altered osteoblast functions in the development of periprosthetic bone loss. Wear debris-challenged osteoblasts exhibit altered functions resulting in the loss of their capacity to produce bone matrix and to replace the resorbed bone. Also, osteoblasts may secrete cytokines, which act in a paracrine fashion to recruit inflammatory cells into the periprosthetic space and to stimulate osteoclastic bone resorption. These effects may be mediated in part by ionic metal dissolution products. We review the mechanisms by which altered osteoblast functions, in response to particulate wear debris, corrosion products, and cytokines and growth factors, may contribute to the development and the progression of periprosthetic osteolysis.

Differential lymphocyte reactivity to serum-derived metal-protein complexes produced from cobalt-based and titanium-based implant alloy degradation

The lymphocyte response to serum protein complexed with metal from implant alloy degradation was investigated in this in vitro study using primary human lymphocytes from healthy volunteers (n = 10). Cobalt chromium molybdenum alloy (Co-Cr-Mo, ASTM F-75) and titanium alloy (Ti-6Al-4V, ASTM F-136) beads (70 microm) were incubated in agitated human serum at 37 degrees C to simulate naturally occurring metal implant alloy degradation processes. Particulate free serum samples that had been incubated with metal were then separated into molecular weight based fractions. The amounts of soluble Cr and Ti within each serum fraction were measured and correlated with lymphocyte proliferation response to the individual serum fractions. Lymphocytes from each subject were cultured with 11 autologous molecular weight based serum fractions either with or without added metal. Two molecular weight ranges of human serum proteins were associated with the binding of Cr and Ti from Co-Cr-Mo and Ti implant alloy degradation (at <30 and 180-250 kDa). High molecular weight serum proteins ( approximately 180 kDa) demonstrated greater lymphocyte reactivity when complexed with Cr alloy and Ti alloy than low (5-30 kDa) and midrange (30-77 kDa) serum proteins. When the amount of lymphocyte stimulation was normalized to both the moles of metal and the moles of protein within each fraction (metal-protein complex reactivity index), Cr from Co-Cr-Mo alloy degradation demonstrated approximately 10-fold greater reactivity than Ti in the higher molecular weight serum proteins ( approximately 180 kDa). This in vitro study demonstrated a lymphocyte proliferative response to both Co-Cr-Mo and Ti alloy metalloprotein degradation products. This response was greatest when the metals were complexed with high molecular weight proteins, and with metal-protein complexes formed from Co-Cr-Mo alloy degradation.

Orthopaedic implant related metal toxicity in terms of human lymphocyte reactivity to metal-protein complexes produced from cobalt-base and titanium-base implant alloy degradation

Metal toxicity from sources such as orthopaedic implants was investigated in terms of immune system hyper-reactivity to metal implant alloy degradation products. Lymphocyte response to serum protein complexed with metal from implant alloy degradation was investigated in this in vitro study using primary human lymphocytes from healthy volunteers (n = 10). Cobalt chromium molybdenum alloy (Co-Cr-Mo, ASTM F-75) and titanium alloy (Ti-6Al-4V, ASTM F-136) beads (70 microm) were incubated in agitated human serum at 37 degrees Celsius to simulate naturally occurring metal implant alloy degradation processes. Particulate free serum samples, which were incubated with metal, were then separated into molecular weight based fractions. The amounts of soluble Cr and Ti within each serum fraction were measured and correlated with lymphocyte proliferation response to the individual serum fractions. Lymphocytes from each subject were cultured with 11 autologous molecular weight based serum fractions either with or without added metal. Two molecular weight ranges of human serum proteins were associated with the binding of Cr and Ti from Co-Cr-Mo and Ti implant alloy degradation (at < 30 and 180-330 kDa). High molecular weight serum proteins (approximately 180 kDa) demonstrated greater lymphocyte reactivity when complexed with metal released from Co-Cr-Mo alloy and Ti alloy than with low (5-30 kDa) and midrange (30-77 kDa) serum proteins. When the amount of lymphocyte stimulation was normalized to both the moles of metal and the moles of protein within each fraction (Metal-Protein Complex Reactivity Index, MPCRI), Cr from Co-Cr-Mo alloy degradation demonstrated approximately 10 fold greater reactivity than Ti in the higher molecular weight serum proteins (approximately 180-250 kDa). This in vitro study demonstrated a lymphocyte proliferative response to both Co-Cr-Mo and Ti alloy metalloprotein degradation products. This response was greatest when the metals were complexed with high molecular weight proteins, and with metal-protein complexes formed from Co-Cr-Mo alloy degradation.

Evaluation of metallic and polymeric biomaterial surface energy and surface roughness characteristics for directed cell adhesion

Directed cell adhesion remains an important goal of implant and tissue engineering technology. In this study, surface energy and surface roughness were investigated to ascertain which of these properties show more overall influence on biomaterial-cell adhesion and colonization. Jet impingement was used to quantify cellular adhesion strength. Cellular proliferation and extracellular matrix secretion were used to characterize colonization of 3T3MC fibroblasts on: HS25 (a cobalt based implant alloy, ASTM F75), 316L stainless steel, Ti-6Al4V (a titanium implant alloy), commercially pure tantalum (Ta), polytetrafluoroethylene (PTFE), silicone rubber (SR), and high-density polyethylene (HDPE). The metals exhibited a nearly five-fold greater adhesion strength than the polymeric materials tested. Generally, surface energy was proportional to cellular adhesion strength. Only polymeric materials demonstrated significant increased adhesion strength associated with increased surface roughness. Cellular adhesion on metals demonstrated a linear correlation with surface energy. Less than half as much cellular proliferation was detected on polymeric materials compared to the metals. However the polymers tested demonstrated greater than twice the amount of secreted extracellular matrix (ECM) proteins on a per cell basis than the metallic materials. Thus, surface energy may be a more important determinant of cell adhesion and proliferation, and may be more useful than surface roughness for directing cell adhesion and cell colonization onto engineered tissue scaffoldings.

A triple assay technique for the evaluation of metal-induced, delayed-type hypersensitivity responses in patients with or receiving total joint arthroplasty

The determination of biocompatibility has been dominated historically by the characterization of candidate materials based upon the observation of adverse host responses. However, some adverse responses are subtle in clinical settings and continue to foster debate and investigation. One of these responses is "metal allergy" or hypersensitivity to metallic biomaterials. Current methods used to diagnose hypersensitivity reactions, such as dermal patch testing and migration inhibition assays, are not well accepted in orthopedic practice as a means for the characterization of hypersensitivity to metallic joint-replacement components. An increasing need to resolve whether metal sensitivity may be a significant and/or predisposing factor for eliciting an over-aggressive immune response in patients with metallic implant components requires improved and standardized widespread study. Here we present three in vitro methodologies: (1) a proliferation assay, (2) cytokine analysis using ELISA, and (3) a migration inhibition assay. When in conjunction with one another, these assays may be used to more comprehensively quantify metal-induced hypersensitivity responses. Therefore, these methodologies are detailed with the intent of facilitating multi-center large-scale studies. In the following cases, a multi-assay approach for measuring the prevalence of delayed-type hypersensitivity in orthopedic patients shows the propensity to yield a more comprehensive and, therefore, more conclusive determination than currently employed patch testing or single assay techniques.

Systemic metal-protein binding associated with total joint replacement arthroplasty

The distribution of titanium [Ti] and chromium [Cr] in serum protein fractions of patients with and without total joint replacements containing Cr and Ti was studied. Three groups were evaluated: 10 patients with cobalt-chromium [CoCr] alloy prostheses and known elevated levels of Cr; 10 patients with Ti containing implants and known elevated levels of Ti; and 10 age matched controls without prostheses. Metal-protein binding was also examined by adding various concentrations of Cr(+3) (CrCl(3)) to control serum. Cr and Ti were bound to serum proteins within specific molecular weight ranges in both patient groups. Two molecular weight ranges were found to bind Cr (at approximately 70 and approximately 180 kDa) in patients with CoCr alloy prostheses, whereas a single molecular weight range (at approximately 70 kDa) was found to bind Ti in patients with Ti alloy implants. This metal-protein binding was reproduced in vitro by adding CrCl(3) at concentrations of approximately 100 and 1000 ppb Cr, which is orders of magnitude higher than that contained in the serum of patients with CoCr alloy implants ( approximately 3 ppb Cr). This suggests that protein binding is initiated in the periprosthetic space where metal concentrations are typically 2-3 orders of magnitude higher than that observed systemically in the serum. In vitro, high molecular weight proteins including immunoglobulins demonstrated the highest affinity to Cr. Determination of specific protein carriers of metal degradation products is an essential component in the assessment of the long-term biological affects of total joint replacement devices.

Metal release and excretion from cementless titanium alloy total knee replacements

Concentrations of titanium, aluminum, and vanadium were measured in the serum and urine of patients with titanium alloy cementless primary total knee arthroplasty components. Patients were categorized in one of five groups. In Group 1, the patellar and tibial articulating surfaces were made of carbon fiber reinforced ultrahigh molecular weight polyethylene. In Group 2, the patellar and tibial surfaces were made of ultrahigh molecular weight polyethylene. In Group 3, the femoral titanium alloy articulating surface was nitrogen ion implanted with ultrahigh molecular weight polyethylene patellar and tibial articulating surfaces. Patients in Group 4 had failed patellar components, and Group 5 was comprised of age and gender matched control subjects without implants. Serum concentrations of titanium were approximately 50 times greater in patients with failed patellar components (Group 4) and approximately 10 times greater in patients with carbon fiber reinforced polyethylene bearing surfaces (Group 1) when compared with Groups 2 and 3 and the control subjects (Group 5). For aluminum and vanadium, no detectable differences were observed among any of the groups. In addition, analysis of 24-hour urine samples showed no significant differences in titanium, aluminum, or vanadium concentrations among any of the groups. Elevated serum titanium levels may serve as a marker of patellar component failure or accelerated femoral component wear in total knee replacements with titanium alloy bearings. The toxicologic ramifications of these findings are unknown.

Metal release in patients who have had a primary total hip arthroplasty. A prospective, controlled, longitudinal study

There is an increasing recognition that, in the long term, total joint replacement may be associated with adverse local and remote tissue responses that are mediated by the degradation products of prosthetic materials. Particular interest has centered on the metal-degradation products of total joint replacements because of the known toxicities of the metal elements that make up the alloys used in the implants. We measured the concentrations of titanium, aluminum, cobalt, and chromium in the serum and the concentration of chromium in the urine of seventy-five patients during a three-year prospective, longitudinal study. Twenty patients had had a so-called hybrid total hip replacement (insertion of a modular cobalt-alloy femoral stem and head with cement and a titanium acetabular cup without cement), fifteen had had insertion of an extensively porous-coated cobalt-alloy stem with a cobalt-alloy head and a titanium-alloy socket without cement, and twenty had had insertion of a proximally porous-coated titanium-alloy stem with a cobalt-alloy head and a titanium socket without cement. The remaining twenty patients did not have an implant and served as controls. The results of our study showed that, thirty-six months postoperatively, patients who have a well functioning prosthesis with components containing titanium have as much as a threefold increase in the concentration of titanium in the serum and those who have a well functioning prosthesis with cobalt-alloy components have as much as a fivefold and an eightfold increase in the concentrations of chromium in the serum and urine, respectively. The predominant source of the disseminated chromium-degradation products is probably the modular head-neck junction and may be a function of the geometry of the coupling. Passive dissolution of extensively porous-coated cobalt-alloy stems was not found to be a dominant mode of metal release.

CLINICAL RELEVANCE

Increased concentrations of circulating metal-degradation products derived from orthopaedic implants may have deleterious biological effects over the long term that warrant investigation. This is a particularly timely concern because of recent clinical trends, including the reintroduction of metal-on-metal bearing surfaces and the increasing popularity of extensively porous-coated devices with large surface areas of exposed metal. Accurate monitoring of the concentrations of metal in the serum and urine after total hip replacement also can provide insights into the mechanisms of metal release. Our findings suggest that fretting corrosion at the head-neck coupling is an important source of metal release that can lead to increased concentrations of chromium in the serum. Determinations of the concentrations of metal in the serum and urine may be useful in the diagnosis of patients who are symptomatic after a total joint replacement as increased levels are indicative of at least one mode of mechanical dysfunction (for example, fretting corrosion) of the device.

Cell adhesion to biomaterials: correlations between surface charge, surface roughness, adsorbed protein, and cell morphology

Adhesion of cells to a biomaterial surface can be a major factor mediating its biocompatibility. In this investigation, jet impingement techniques were used to quantify strength of cellular adhesion to various material surfaces. The metals tested: HS25 (a cobalt-based alloy similar to F75), 316L stainless steel, Ti-6Al-4V, and commercially pure tantalum, exhibited nearly a fivefold increase in adhesion strength above that characteristic of the polymeric materials tested (PTFE, silicone rubber, and HDPE). The present study examines physical and biological factors that might influence fibroblast adhesion to the biomaterial surface. The relation between surface charge and cellular adhesion was investigated in a controlled manner by measuring adhesion strength over a range of charge densities. The cells showed charge and electrical potential-dependent adhesion maxima, suggesting that surface alloying for optimum adherence may be possible. In a preliminary series of experiments adsorbed serum protein layers on a series of materials of differing adherence were investigated using gel electrophoresis to assess protein composition. Analysis of adsorbed proteins revealed little difference in relative abundance or total adsorption quantity. SEM micrographs of cells on Ti-6Al-4V and silicone rubber (high and low adhesion materials, respectively) demonstrated differences in cell morphology and cell density.