A multicenter retrieval study of the taper interfaces of modular hip prostheses

Oxide degradation precedes additively manufactured Ti-6Al-4V selective dissolution: An unsupervised machine learning correlation of impedance and dissolution compared to Ti-29Nb-21Zr

Additively manufactured (AM) Ti-6Al-4V devices are implanted with increasing frequency. While registry data report short-term success, a gap persists in our understanding of long-term AM Ti-6Al-4V corrosion behavior. Retrieval studies document β phase selective dissolution on conventionally manufactured Ti-6Al-4V devices. Researchers reproduce this damage in vitro by combining negative potentials (cathodic activation) and inflammatory simulating solutions (H2O2-phosphate buffered saline). In this study, we investigate the effects of these adverse electrochemical conditions on AM Ti-6Al-4V impedance and selective dissolution. We hypothesize that cathodic activation and H2O2 solution will degrade the oxide, promoting corrosion. First, we characterized AM Ti-6Al-4V samples before and after a 48 h -0.4 V hold in 0.1 M H2O2/phosphate buffered saline. Next, we acquired nearfield electrochemical impedance spectroscopy (EIS) data. Finally, we captured micrographs and EIS during dissolution. Throughout, we used AM Ti-29Nb-21Zr as a comparison. After 48 h, AM Ti-6Al-4V selectively dissolved. Ti-29Nb-21Zr visually corroded less. Structural changes at the AM Ti-6Al-4V oxide interface manifested as property changes to the impedance. After dissolution, the log-adjusted constant phase element (CPE) parameter, Q, significantly increased from -4.75 to -3.84 (Scm-2(s)α) (p = .000). The CPE exponent, α, significantly decreased from .90 to .84 (p = .000). Next, we documented a systematic decrease in oxide polarization resistance before pit nucleation and growth. Last, using k-means clustering, we established a structure-property relationship between impedance and the surface's dissolution state. These results suggest that AM Ti-6Al-4V may be susceptible to in vivo crevice corrosion within modular taper junctions.

Are Corrosion and Material Loss a Threat for Titanium-Titanium Tapers in Total Hip Arthroplasty Modular Acetabular Components?

BACKGROUND

Extensive research has reported on fretting corrosion and material loss for a variety of metal taper interfaces in orthopedic devices. For modular acetabular shell-liner constructs, the interfaces studied thus far have consisted of mixed-metal pairings, and the risk of fretting corrosion and material loss for the all-titanium (Ti) shell-liner taper junction in one ceramic-on-ceramic (COC) design remains poorly understood. We asked: do Ti shell-liner taper interfaces in COC total hip arthroplasty devices show in vivo evidence of (1) fretting and/or corrosion, and (2) quantifiable potential material loss?

METHODS

We examined 22 shell-liner pairs and 22 single liners from retrieved COC components. The taper interface surfaces were assessed for fretting corrosion using a semiquantitative scoring method and imaged with scanning electron microscopy. A subcohort of components was measured with a coordinate measuring machine, and volumetric material loss and maximum wear depth were calculated.

RESULTS

Fretting corrosion at the taper interfaces was minimal to mild for 95% of liners and 100% of shells. Imaging revealed fretting marks within a band of corrosion on some implants and evidence of corrosion not in the proximity of mechanical damage. Estimated material loss ranged from 0.2 to 1.3 mm3 for liners, and 0.5 to 1.1 mm3 for shells. Maximum wear depth for all components was 0.03 mm or less.

CONCLUSIONS

Our results indicate that, compared to other taper junctions in total joint arthroplasty, the risk of corrosion and material loss may be minimal for Ti shell-liner interfaces.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The influence of surgical technique guidance and surgeon's experience on the femoral head assembly in total hip arthroplasty

INTRODUCTION

The importance of the assembly procedure on the taper connection strength is evident. However, existent surgical technique guides frequently lack comprehensive and precise instructions in this regard. The aim of our experimental study was to evaluate the influence of the surgical technique guide on the femoral head assembly procedure in surgeons with differing levels of experience in total hip arthroplasty.

MATERIALS AND METHODS

Twenty-eight participants, divided into four groups based on their lifetime experience in total hip arthroplasty, conducted a femoral head assembly procedure in a simulated intraoperative environment before and after reviewing the surgical technique guide. Demographic information and the number of hammer blows were documented. Hammer velocity and impaction angle were recorded using an optical motion capturing system, while the impaction force was measured using a dynamic force sensor within the impactor.

RESULTS

We observed a high variation in the number of hammer blows, maximum force, and impaction angle. Overall, the number of hammer blows decreased significantly from 3 to 2.2 after reviewing the surgical technique guide. The only significant intragroup difference in the number of hammer blows was observed in the group with no prior experience in total hip arthroplasty. No correlation was found between individual factors (age, weight, height) or experience and the measured parameters (velocity, maximum force and angle).

CONCLUSIONS

The present study demonstrated a high variation in the parameters of the femoral head assembly procedure. Consideration of the surgical technique guide was found to be a limited factor among participants with varying levels of experience in total hip arthroplasty. These findings underline the importance of sufficient preoperative training, to standardize the assembly procedure, including impaction force, angle, and use of instruments.

Performance of Austenitic High-Nitrogen Steels under Gross Slip Fretting Corrosion in Bovine Serum

Modular artificial hip joints are a clinical standard today. However, the release of wear products from the head-taper interface, which includes wear particles in the nm size range, as well as metal ions, have raised concerns. Depending on the loading of such taper joints, a wide variety of different mechanisms have been found by retrieval analyses. From these, this paper concentrates on analyzing the contribution of gross slip fretting corrosion at ultra-mild wear rates using a bovine calf serum solution (BCS) as the lubricant. The parameters were chosen based on biomechanical considerations, producing wear rates of some ng/m wear path. In parallel, the evolution of tribomaterial (third bodies) was analyzed as to its constituents and generation rates. It has already been shown earlier that, by an advantageous combination of wear mechanisms and submechanisms, certain constituents of the tribomaterial remain inside the contact area and act like extreme-pressure lubricant additives. For the known wear and corrosion resistance of austenitic high-nitrogen steels (AHNSs), which outperform CoCrMo alloys even under inflammatory conditions, we hypothesized that such steels will generate ultra-mild wear rates under gross slip fretting. While testing AHNSs against commercially available biomedical-grade materials of CoCrMo and TiAlV alloys, as well as zirconia-toughened alumina (ZTA) and against itself, it was found that AHNSs in combination with a Ti6Al4V alloy generated the smallest wear rate under gross slip fretting corrosion. This paper then discusses the wear behavior on the basis of ex situ analyses of the worn surfaces as to the acting wear mechanisms and submechanisms, as well as to the tribological reaction products.

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.

Trunnionosis and prosthesis dissociation after total hip arthroplasty

Femoral neck trunnion dissociations are rare complications of total hip replacements. This hardware failure is often due to underlying trunnionosis which is important to recognize. We present a case of a patient with dissociation at the femoral head-neck junction of a total hip arthroplasty (THA) with a Stryker Accolade TMZF femoral stem. There was no significant preceding trauma. The complication was visualized on radiography and confirmed during revision arthroplasty.

Understanding the role of head size and neck length in micromotion generation at the taper junction in total hip arthroplasty

Modular hip implants allow intra-operative adjustments for patient-specific customization and targeted replacement of damaged elements without full implant extraction. However, challenges arise from relative micromotions between components, potentially leading to implant failure due to cytotoxic metal debris. In this study magnitude and directions of micromotions at the taper junction were estimated, aiming to understand the effect of variations in head size and neck length. Starting from a reference configuration adhering to the 12/14 taper standard, six additional implant configurations were generated by varying the head size and/or neck length. A musculoskeletal multibody model of a prothesized lower limb was developed to estimate hip contact force and location during a normal walking task. Following the implant assembly, the multibody-derived loads were imposed as boundary conditions in a finite element analysis to compute the taper junction micromotions as the relative slip between the contacting surfaces. Results highlighted the L-size head as the most critical configuration, indicating a 2.81 μm relative slip at the mid-stance phase. The proposed approach enables the investigation of geometric variations in implants under accurate load conditions, providing valuable insights for designing less risky prostheses and informing clinical decision-making processes.

Association of Total Hip Arthroplasty Flexural Rigidity With Magnetic Resonance Imaging and Histological Findings

BACKGROUND

Modular connections in total hip arthroplasty (THA) offer surgical advantages, but can contribute to implant fretting and corrosion due to micromotion at the head-stem interface. Previous studies implicated lower flexural rigidity as a key contributing factor to THA corrosion and fretting, but none associated flexural rigidity with direct histological evaluation or magnetic resonance imaging (MRI) outcomes. The purpose of this study was to determine how implant flexural rigidity is associated with MRI imaging metrics and histopathological outcomes in patients who have a failed THA.

METHODS

Patients requiring revision THA surgery underwent preoperative MRIs with 3-dimensional multispectral imaging techniques to suppress metal artifacts. The MRI images were graded for adverse local tissue reactions. For each hip, trunnion flexural rigidity was measured from the retrieved femoral stem, and a periprosthetic tissue sample was retrieved and evaluated using semiquantitative histology. Generalized linear models and analyses of variance were used to assess associations between flexural rigidity and MRI and histology outcomes.

RESULTS

A total of 106 THA stems were retrieved (46 women and 60 men, age: 68 years (range, 60 to 73 years). After adjustment for length of implantation, flexural rigidity was negatively correlated with histologic aseptic lymphocyte-dominant vasculitis-associated lesion severity (β = -26.27, P = .018), Fujishiro lymphocyte grading (β = -13.4, P = .039), perivascular lymphocyte layers (β = -17.8, P = .022), the grade of tissue organization (β = -22.5, P = .009), the presence of diffuse synovitis (β = -66.5, P = .003), and the presence of lymphoid aggregates (β = -75.9, P = .022). No association was found between MRI metrics and flexural rigidity.

CONCLUSIONS

Among these implants, decreased trunnion stiffness was associated with increased histologic features of adverse host-mediated soft tissue reactions.

Is taper corrosion in modular revision hip stem junctions associated with patient or implant specific factors? A retrieval analysis

Implant modularity within revision total hip arthroplasty (THA) offers multiple implant configurations and allows surgeons a high intraoperative flexibility to restore functionality to the patients joint, even in complex revision cases. However, a rare but devastating complication for patients, clinicians and manufacturers presenting a breakage of the taper junction between the distal stem and the proximal implant part. Aside from implant and patient specific risk factors, corrosion and fretting at the stem junctions have been associated with taper failure. Whether corrosive processes are a precursor of failure or rather an accompaniment of material fatigue is thereby still unclear. Therefore, this study aims to investigate the incidence of taper corrosion in a collection of 17 retrievals from a single type (MRP-Titan, Peter Brehm GmbH) and on the correlation of taper corrosion to implant and patient specific factors. None of the implants was revised for problems related to the taper junction, corrosion or the implant itself. The modular stem junction of all retrievals was visually rated with respect to corrosion, fretting and surface contamination. Additionally, the stability of taper junctions of retrievals where the proximal part with the neck was still assembled to the stem was determined by measuring the loosening moment of the securing screw and the push-out-force for taper dissociation. There was no difference between the mean push-out-force of the retrievals (14 kN ± 1.2 kN) and new reference samples (12.6 kN ± 0.5 kN). Approximately one third of the investigated retrievals showed considerable taper corrosion. The extent of corrosion increased with time in vivo and contamination of the neck piece, while it decreased with the loosening moment of the locking screw. The parameters femoral head offset, neck piece length, lateralized neck pieces, obesity of patients and septic/aseptic revision were not correlated to taper corrosion. Taper corrosion seems to occur regularly in modular taper junctions and is not necessarily connected to taper failure. A correct assembly of the junction and avoiding taper surface contamination during revision surgery is mandatory.

The effect of trunnionosis on the risk of re-revision following femoral head exchange in hip arthroplasty

BACKGROUND

Fretting corrosion at modular junctions contributes to arthroplasty failure. Currently, no evidence-based guidelines are available regarding the acceptable level of trunnion corrosion that can occur in vivo. We aimed to examine the relationship between trunnion corrosion and risk of re-revision to assist surgeons with intraoperative decision making.

METHOD

Grading by 3 independent examiners of revised and re-revised head components was performed using a modified Goldberg corrosion scale. Samples were separated into low-grade (LG) and high-grade (HG) corrosion. Mechanical testing determined the relationship between corrosion severity and pull-off strength at the head-stem junction.

RESULTS

529 retrieved femoral heads were analysed. A positive association was detected between males and HG corrosion (OR 2.07; 95% CI, 1.45-2.94; p < 0.001). No difference between the survivorship of LG and HG heads was detected (p-value = 0.247). In the re-revised sample, the first implant had a time in situ that was on average 7.97 years longer (95% CI, 5.4-10.6) than that of the subsequent re-revised femoral head. Severe corrosion on the first head was associated with a 37.5 (95% CI, 4.00-1944) fold increase of HG on the subsequent head (p < 0.001). Femoral disassembly force had a positive correlation with stem taper corrosion grade (p = 0.001).

CONCLUSIONS

A well-fixed stem with corrosion may remain in situ.

In vivo corrosion on retrieved hip endoprostheses and in vitro effects of corrosion products on bone mineralization

In vivo corrosion of modular endoprostheses remains a great concern, as the release of heavy metal ions can impair the implant's service life and the wellbeing of the patient. The detailed corrosion mechanisms that occur in vivo are so far not completely understood. In this context, the effects of implant released cobalt (Co) and chromium (Cr) ions on osteoblast mineralization and gene expression have not been investigated extensively. This comprehensive study aimed at furthering the understanding of in vivo implant corrosion from the clinical signs via prosthesis retrievals and histology of the synovial membranes down to the molecular processes instigated by corrosion products and its effects on bone mineralization. A detailed in vivo failure analysis was performed investigating 22 retrieved hip endoprostheses from different manufacturers and taper material combinations. The aim was to find a correlation of taper damage and especially corrosion to susceptible biomedical alloys and its effect on periprosthetic tissue as well as the clinical implant performance with regard to revision diagnosis and presence of radiolucent lines (RLL). A second part investigated the effects of Co and Cr ions on the in vitro mineralization process of osteoblasts. Cell cultures were exposed to relevant concentrations of CoCl2 and CrCl3 (0 μM, 100 μM, 200 μM) with and without addition of phosphate. Mineralization behavior was analyzed with Alizarin Red assay and Von Kossa staining of calcium depots, alkaline phosphatase activity of osteoblasts and gene expression was analyzed with real time quantitative PCR. The retrieval study provides evidence of in vivo fretting and crevice corrosion on all metallic tapers combined with either ceramic or metal femoral heads. Within the modular taper junctions, selective dissolution of the α phase occurred in wrought TiAl6V4 alloys, and etching of the fine-grained wrought CoCr28Mo6 alloy implants was observed in formed crevices. In addition, significant amounts of wear particles and corrosion products were detected in retrieved synovial membranes. An increased risk for the occurrence of a RLL in the proximal zones was determined for patients with a corroded mixed metal taper. Whereas Co ions have hardly any effects on mineralization, Cr ions cause a significant concentration dependent decrease in mineralization rate of osteoblasts. However, this effect is alleviated by addition of a phosphate source. Our data reveal that Cr ions depleted dissolved phosphates by forming an insoluble complex (CrPO4), which inhibits the phosphate dependent mineralization process. No significant effect of the heavy metal ions on osteoblast activity by means of alkaline phosphate activity as well as on gene expression is determined. This study broadens the understanding of in vivo corrosion of metallic modular implants and its clinically relevant effects on mineralization. Based on these findings, in vivo corrosion of CoCr28Mo6 endoprostheses should be limited to avoid inhibitory effects of Cr3+ on bone mineralization which can contribute to premature implant failure.

Metallosis in Total Hip Arthroplasty

» Metallosis is a rare but significant complication that can occur after total hip arthroplasty (THA) for a variety of reasons but most commonly in patients with metal-on-metal implants.» It is characterized by the visible staining, necrosis, and fibrosis of the periprosthetic soft tissues, along with the variable presence of aseptic cysts and solid soft tissue masses called pseudotumors secondary to the corrosion and deposition of metal debris.» Metallosis can present with a spectrum of complications ranging from pain and inflammation to more severe symptoms such as osteolysis, soft tissue damage, and pseudotumor formation.» Workup of metallosis includes a clinical evaluation of the patient's symptoms, imaging studies, serum metal-ion levels, and intraoperative visualization of the staining of tissues. Inflammatory markers such as erythrocyte sedimentation rate and C-reactive protein along with intraoperative frozen slice analysis may be useful in certain cases to rule out concurrent periprosthetic joint infection.» Management depends on the severity and extent of the condition; however, revision THA is often required to prevent rapid progression of bone loss and tissue necrosis.

Evaluating trunnionosis in modular anatomic shoulder arthroplasties: a retrieval study

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Additively manufactured Ti-29Nb-21Zr shows improved oxide polarization resistance versus Ti-6Al-4V in inflammatory simulating solution

Retrieval studies in the past two decades show severe corrosion of titanium and its alloys in orthopedic implants. This damage is promoted by mechanically assisted crevice corrosion (MACC), particularly within modular titanium-titanium junctions. During MACC, titanium interfaces may be subject to negative potentials and reactive oxygen species (ROS), generated from cathodic activation and/or inflammation. Additive manufacturing (AM) may be able to produce new, corrosion-resistant titanium alloys and admixtures that are less susceptible to these adverse electrochemical events. In this study, we characterize the impedance and corrosion properties of three new AM titanium materials, including Ti-6Al-4V with added 1% nano-yttria stabilized ZrO2 , admixed Ti-29Nb-21Zr, and pre-alloyed Ti-29Nb-21Zr. We aim to elucidate how these materials perform when subjected to high ROS solutions. We include conventionally and additively manufactured Ti-6Al-4V in our study as comparison groups. A 0.1 M H2 O2 phosphate-buffered saline (PBS) solution, simulating inflammatory conditions, significantly increased biomaterial OCP (-0.14 V vs. Ag/AgCl) compared to PBS only (-0.38 V, p = .000). During anodic polarization, Ti-6Al-4V passive current density more than doubled from 1.28 × 10-7 to 3.81 × 10-7  A/cm2 when exposed to 0.1 M H2 O2 . In contrast, Ti-29Nb-21Zr passive current density remained relatively unchanged, slightly increasing from 7.49 × 10-8 in PBS to 9.31 × 10-8 in 0.1 M H2 O2 . Ti-29Nb-21Zr oxide polarization resistance (Rp ) was not affected by 0.1 M H2 O2 , maintaining a high value (1.09 × 106 vs. 1.89 × 106  Ω cm2 ), while Ti-6Al-4V in 0.1 M H2 O2 solution had significantly diminished Rp (4.38 × 106 in PBS vs. 7.24 × 104  Ω cm2 in H2 O2 ). These results indicate that Ti-29Nb-21Zr has improved corrosion resistance in ROS containing solutions when compared with Ti-6Al-4V based biomaterials.

A convolutional neural network for high throughput screening of femoral stem taper corrosion

Corrosion at the modular head-neck taper interface of total and hemiarthroplasty hip implants (trunnionosis) is a cause of implant failure and clinical concern. The Goldberg corrosion scoring method is considered the gold standard for observing trunnionosis, but it is labor-intensive to perform. This limits the quantity of implants retrieval studies typically analyze. Machine learning, particularly convolutional neural networks, have been used in various medical imaging applications and corrosion detection applications to help reduce repetitive and tedious image identification tasks. 725 retrieved modular femoral stem arthroplasty devices had their trunnion imaged in four positions and scored by an observer. A convolutional neural network was designed and trained from scratch using the images. There were four classes, each representing one of the established Goldberg corrosion classes. The composition of the classes were as follows: class 1 (n = 1228), class 2 (n = 1225), class 3 (n = 335), and class 4 (n = 102). The convolutional neural network utilized a single convolutional layer and RGB coloring. The convolutional neural network was able to distinguish no and mild corrosion (classes 1 and 2) from moderate and severe corrosion (classes 3 and 4) with an accuracy of 98.32%, a class 1 and 2 sensitivity of 0.9881, a class 3 and 4 sensitivity of 0.9556 and an area under the curve of 0.9740. This convolutional neural network may be used as a screening tool to identify retrieved modular hip arthroplasty device trunnions for further study and the presence of moderate and severe corrosion with high reliability, reducing the burden on skilled observers.

Evaluation of Mechanically-Assisted Crevice Corrosion of Different Modular Dual Mobility Constructs

BACKGROUND

Modular dual mobility (MDM) acetabular component use is rising in total hip arthroplasty. However, concern of mechanically-assisted crevice corrosion (MACC) at the shell-liner interface remains. We investigated shell-liner corrosion using retrieval analyses and corrosion chamber testing.

METHODS

We analyzed fretting and corrosion on 10 matched pairs of two commercial modular dual mobility constructs (MDM1 and MDM2). Also, pristine pairs of Ti6Al4V shells and CoCrMo liners from three commercial dual mobility systems (MDM1, MDM2, MDM3) were tested in vitro to model MACC performance. Three pairs of each were placed into an electrochemical chamber with stepwise increasing cyclic compression loads, while measuring currents generated at the shell-liner taper. Onset fretting loads and fretting currents were calculated.

RESULTS

Corrosion damage scores on retrieved components were low, but higher in the MDM2 to MDM1 liners (P = 0.006), specifically outside the taper region (P = 0.00003). Fretting currents were higher in the MDM2 than in MDM1 or MDM3 (P = 0.011). Onset loads were also higher in the MDM2 (P = 0.001).

CONCLUSION

Among retrieved liners, MDM2 tapers seem prone to non-mechanical corrosion modes. Higher onset loads and fretting currents in MDM2 tapers indicate greater MACC resistance, but higher severity once corrosion begins. Differences among the devices were likely due to taper design and surface finish. Currents in all three were <5 μA, much lower than those observed with head-neck tapers. Our findings suggest that among the types of corrosion observed in these MDM designs, mechanically driven corrosion may not be the most significant.

Predicting Corrosion Damage in the Human Body Using Artificial Intelligence: In Vitro Progress and Future Applications

Artificial intelligence (AI) is used in the clinic to improve patient care. While the successes illustrate AI's impact, few studies have led to improved clinical outcomes. In this review, we focus on how AI models implemented in nonorthopedic fields of corrosion science may apply to the study of orthopedic alloys. We first define and introduce fundamental AI concepts and models, as well as physiologically relevant corrosion damage modes. We then systematically review the corrosion/AI literature. Finally, we identify several AI models that may be implemented to study fretting, crevice, and pitting corrosion of titanium and cobalt chrome alloys.

An Atypical Adverse Local Tissue Reaction Seen With Metal-On-Metal Total Hip Arthroplasty Utilizing Polyethylene Liners With Metal Inlays

Adverse local tissue reaction (ALTR) is a frequently described, although uncommon, complication of metal-on-metal total hip arthroplasty. Here in we report on 2 patients with unique metal-inlay polyethylene liners who suffered from ALTR that required revision arthroplasty. In 2 of 3 cases the femoral trunnion was noted to have minimal corrosion and the stem was salvaged with a titanium adapter. In one case there was catastrophic femoral stem failure and an extended trochanteric osteotomy was required to remove the unique lateral flare stem. The surgeon must pay special attention when scrutinizing radiographs to identify a metal inlay polyethylene liner and when performing revision arthroplasty to prevent greater trochanter fracture in a patient who likely already has compromised abductor function due to ALTR.

Can severity of trunnion damage be estimated by visual inspection alone?

Taper corrosion has been widely reported to be problematic for modular total hip arthroplasty implants. A simple and systematic method to evaluate taper damage with sufficient resolution is needed. We introduce a semiquantitative grading system for modular femoral tapers to characterize taper corrosion damage. After examining a unique collection of retrieved cobalt-chromium (CoCr) taper sleeves (n = 465) using the widely-used Goldberg system, we developed an expanded six-point visual grading system intended to characterize the severity, visible material loss, and absence of direct component contact due to corrosion. Female taper sleeve damage was evaluated by three blinded observers using the Goldberg scoring system and the expanded system. A subset (n = 85) was then re-evaluated following destructive cleaning, using both scoring systems. Material loss for this subset was quantified using metrology and correlated with both scoring systems. There was substantial agreement in grading among all three observers with uncleaned (n = 465) and with the subset of cleaned (n = 85) implants. The expanded scoring criteria provided a wider distribution of scores which ultimately correlated well with corrosion material loss. Cleaning changed the average scores marginally using the Goldberg criteria (p = 0.290); however, using the VGS, approximately 40% of the scores for all observers changed, increasing the average score from 4.24 to 4.35 (p = 0.002). There was a strong correlation between measured material loss and new grading scores. The expanded scoring criteria provided a wider distribution of scores which ultimately correlated well with corrosion material loss. This system provides potential advantages for assessing taper damage without requiring specialized imaging devices.

Wear estimation of hip implants with varying chamfer geometry at the trunnion junction: a finite element analysis

The hip joint helps the upper body to transfer its weight to lower body. Along with age, there are various reasons for the degeneration of the hip joint. The artificial hip implant replaces the degenerated hip. Wear between the joints is the primary cause of the hip implant becoming loose. The wear can occur due to various reasons. Due to this revision surgery are most common in young and active patients. In the design phase of the implant if this is taken care then life expectancy of the implant can be improved. Small design changes can significantly enhance the implant's life. In this work, elliptical-shaped hip implant stem is designed, and linear wear is estimated at trunnion junction. In this work, a 28 mm diameter femoral head with a 4 mm thick acetabular cup and a 2 mm thick backing cup is used. The top surface taper radiuses are changed. Solid works was used to create the models. Ansys was used to perform the analysis. It was found that as the radius of the TTR decreased, the wear rate decreased. The least wear rate was found in 12/14 mm taper with a value of 1.15E^-02mm year^-1for the first material combination and with a value of 1.23E^-02mm year^-1for the second material combination. In the comparison between the models with 1 mm chamfer and no chamfer, it was found that the wear rate was lower for the models with 1 mm chamfer. When the chamfer was increased (more than 1 mm), the linear wear increased. Wear is the main reason for the loosening of hip implants, which leads to a revision of an implant. It was found that with a decrease in TTR, there was a small increase in the linear wear rate. Overall, the implant with TTR 6 mm and a chamfer of 1 mm was found to have the least wear rate. To validate these results, the implant can be 3D printed and tested on a hip simulator.

Trunnions and Modularity in Total Hip Arthroplasty: A Historical Review With Current Clinical Implications

Trunnion in total hip arthroplasty refers to the interface between the neck of a femoral stem and the femoral head. Clinical complications arising from damage to this junction, whether it be due to mechanical wear, corrosion, or a combination, are referred to as mechanically assisted crevice corrosion (MACC), also commonly known as trunnionosis. With the use of modular hip prostheses, which help customize offset and leg length to an individual patient's anatomy, the incidence of MACC and revision due to MACC has increased in recent years. Although the cause of MACC is multifactorial, with patient factors and technique factors contributing to this condition, taper design and geometry, metallurgical properties of implants, and size mismatch of the bearing couple are some of the implant factors that have also been implicated in this clinical phenomenon. Understanding the history of taper design and geometry, the track record of older implants, and the rationale behind the development of current prostheses can help surgeons choose the right implants for their patients and accurately assess the pros and cons of new implants being introduced to the market each year.

Interaction of surface topography and taper mismatch on head-stem modular junction contact mechanics during assembly in modern total hip replacement

Implant failure due to fretting corrosion at the head-stem modular junction is an increasing problem in modular total hip arthroplasty. The effect of varying microgroove topography on modular junction contact mechanics has not been well characterized. The aim of this study was to employ a novel, microgrooved finite element (FEA) model of the hip taper interface and assess the role of microgroove geometry and taper mismatch angle on the modular junction mechanics during assembly. A two-dimensional, axisymmetric FEA model was created using a modern 12/14 taper design of a CoCrMo femoral head taper and Ti6Al4V stem taper. Microgrooves were modeled at the contacting interface of the tapers and varied based on height and spacing measurements obtained from a repository of measured retrievals. Additionally, taper angular mismatch between the head and stem was varied to simulate proximal- and distal-locked engagement. Forty simulations were conducted to parametrically evaluate the effects of microgroove surface topography and angular mismatch on predicted contact area, contact pressure, and equivalent plastic strain. Multiple linear regression analysis was highly significant (p < 0.001; R2  > 0.74) for all outcome variables. The regression analysis identified microgroove geometry on the head taper to have the greatest influence on modular junction contact mechanics. Additionally, there was a significant second order relationship between both peak contact pressure (p < 0.001) and plastic strain (p < 0.001) with taper mismatch angle. These modeling techniques will be used to identify the implant parameters that maximize taper interference strength via large in-silico parametric studies.

What Patient and Implant Factors Affect Trunnionosis Severity? An Implant Retrieval Analysis of 664 Femoral Stems

BACKGROUND

Corrosion at the modular head-neck taper interface of total and hemiarthroplasty hip implants (trunnionosis) is a cause of implant failure and thus a clinical concern. Patient and device factors contributing to the occurrence of trunnionosis have been investigated in prior implant retrieval studies but generally with limited sample sizes and a narrow range of models. The purpose of the present investigation was to determine which patient and device factors were associated with corrosion damage on the femoral stem taper across a large collection of different implant models retrieved following revision hip arthroplasty.

METHODS

A retrieval study of 664 hip arthroplasty modular stem components was performed. Patient and device information was collected. Trunnions were imaged under digital microscopy and scored for corrosion damage using a scaling system. Damage was related to patient and device factors using regression analyses.

RESULTS

Greater duration of implantation (P = .005) and larger head size (P < .001) were associated with an elevated corrosion class. Older age at index surgery (P = .035), stainless steel stem material (P = .022), indication for revision as bone or periprosthetic fracture (P = .017), and infection (P = .018) and certain larger taper geometries were associated with a decreased corrosion class.

CONCLUSION

Factors identified as contributing to a higher or lower risk of more severe corrosion are consistent with most prior smaller retrieval studies. Surgeons should be aware of these risk factors when selecting implants for their patients and when diagnosing trunnionosis in symptomatic hip arthroplasty patients.

Surface Analysis of Ti-Alloy Micro-Grooved 12/14 Tapers Assembled to Non-Sleeved and Sleeved Ceramic Heads: A Comparative Study of Retrieved Hip Prostheses

Ti6Al4V titanium alloy (Ti-alloy) sleeved ceramic heads have become widely used in revision surgery when the hip stem is left in situ. This solution guarantees a new junction between the bore of the ceramic head and the Ti-alloy sleeve, regardless of any possible, slight surface damage to the Ti-alloy taper of the stem. However, this solution introduces an additional Ti-alloy/Ti-alloy interface pairing, which is potentially susceptible to mechanically assisted crevice corrosion. This study evaluated both qualitatively and quantitatively the damage that occurred in vivo on Ti-alloy micro-grooved 12/14 tapers of (i) primary implants with non-sleeved ceramic heads (Group 1), (ii) secondary implants with non-sleeved ceramic heads (Group 2), and (iii) secondary implants with sleeved ceramic heads (Group 3). A total of 45 explants-15 for each group, including short-, medium- and long-neck heads-underwent optical evaluation for surface damage (Goldberg scoring), surface roughness analysis, and SEM/EDX analysis. The Goldberg scores did not reveal different patterns in the tapers' surface damage; surface damage was classified as absent or mild (surface damage score ≤2) in 94%, another 94%, and 92% of the analysed regions for Group 1, Group 2, and Group 3, respectively. Small but significant differences in morphological changes occurred in the tapers of the three groups: reductions no greater than a few percentage points in median values of roughness parameters were found in Group 1 and Group 2, while negligible changes were found in Group 3. SEM/EDX analysis revealed little (i.e., a slight increase in the oxygen content) to undetectable changes in the chemical composition on the Ti-alloy surface independently of the group. These results suggest that the Ti-alloy/Ti-alloy sleeve/taper junction is only mildly susceptible to mechanically assisted crevice corrosion. Assembling a sleeved ceramic head, with variable neck lengths up to a "long-neck", to a Ti-alloy micro-grooved 12/14 taper of a stem left in situ does not seem to increase the risk of revision due to trunnionosis, as long as junction stability (i.e., the proper seating of the sleeved ceramic head on the 12/14 taper) is achieved intraoperatively.

High risk of elevated metal concentrations with 9/10-mm stem trunnions and highly cross-linked polyethylene grafted with poly(2-methacryloyloxyethyl phosphorylcholine) in total hip arthroplasty

BACKGROUND

The risks of metal release due to fretting and corrosion at the head-neck junction and consequent adverse local tissue reaction (ALTR) have concerns in metal-on-polyethylene (MoP) total hip arthroplasty (THA). Although trunnions have become thinner in diameter to increase the range of motion, it has remained unclear whether this change affects metal release and ALTR in vivo. This study aimed to investigate serum metal concentrations and the prevalence of ALTR in MoP THA with a 9/10-mm stem trunnion.

PATIENTS AND METHODS

A consecutive series of 37 hips that underwent THA using MoP grafted with poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) with a 9/10-mm trunnion stem were retrospectively reviewed. Serum metal levels were assessed and compared with those in MoP THA with a 10/12-mm trunnion stem. ALTR was diagnosed with serum metal levels and cross-sectional images. The factors associated with serum metal levels were also assessed.

RESULTS

The median serum cobalt and chromium levels were 1.5 μg/L and 1.0 μg/L in the 9/10-mm group and 0.2 μg/L and 0.4 μg/L in the 10/12-mm group, respectively. ALTR was found in 5 hips of 3 patients. Revision surgery was performed in 4 hips, and all stem trunnions and femoral heads showed severe corrosion. Postoperative walking ability was associated with serum metal levels.

CONCLUSION

It was found that a 9/10-mm stem trunnion with MoP grafted with PMPC had high risks of metal release in primary THA. Careful follow-up and cross-sectional imaging are needed to detect ALTR for early revision.

Fretting corrosion testing of acetabular modular tapers for total hip replacements: A comparison of two designs

Acetabular components (DePuy Pinnacle (A) and Stryker Trident (B), Ti-6Al-4V shells and CoCrMo liners) with varying geometries were assembled under a 4 kN seating load. Liner-displacement was recorded. Cyclic compression to 4 kN, R = 0.01, 9 Hz was applied for three million cycles to evaluate fretting corrosion currents (n = 5). Fretting currents, load-displacement, ion dissolution, and disassembly loads were used to compare device performance. Data were analyzed using ANOVA with Tukey post hoc comparisons (p < 0.05). Liner seating displacements were not significantly different between groups. Fretting currents averaged over the initial 10 h and over three million cycles were 0.17 μA (A) and 0.55 μA (B) and 0.05 μA (A) and 0.17 μA (B), respectively (p = 0.19). No variation in ion averages between A and B (0.23 and 0.45 ppm for Ti [p = 0.21], 0.63 and 0.85 ppm for Co [p = 0.47]) existed. Average push-out forces, -2.41 (A) and -2.42 kN (B), were not significantly different (p = 0.97). SEM and EDS showed some titanium and metal oxide transfer from the shell to the liner in both designs. Overall, both implant designs exhibited very minor MACC in these experiments. This study demonstrates quantitative measures of in vitro fretting corrosion over the course of three million cycles and the minimal degree of acetabular taper damage. Clinical Significance: Retrieval studies show dual mobility acetabular shell-liner tapers with metal-on-metal contacts are susceptible to fretting corrosion in vivo.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A novel method to improve femoral head and stem taper stability intraoperatively in total hip arthroplasty - a proof of concept study

BACKGROUND

Mechanically assisted crevice corrosion (MACC) has been associated with the compromised durability and fixation of modular total hip implants, adverse reaction of local tissue, and other undesirable clinical outcomes in total hip arthroplasty (THA). MACC is primarily caused by the relative motion between the femoral head and stem. To minimize the relative motion the taper connection between the two components must be strong enough. The current study addressed the following questions: (1) Does increasing the mass of the femoral stem improve the taper connection strength intraoperatively? (2) Does increasing the mass of the femoral stem reduce the risk of periprosthetic tissue damage intraoperatively?

HYPOTHESIS

Increasing the mass of the femoral stem improve the taper connection strength intraoperatively.

MATERIALS AND METHODS

During the experiment, femoral heads were impacted onto the stem tapers with and without an additional weight attached to the stem. The femoral heads were then pulled off to investigate the strength of the taper connection. The stem displacement and acceleration at impaction were also measured to evaluate the risk of periprosthetic tissue damage.

RESULTS

The results showed that the pull-off force was increased by 24% (p=0.011, n=6) when an additional weight was attached to the stem. The additional weight also reduced the maximum stem acceleration and maximum stem displacement by 37% (p<0.001, n=6) and 14% (p=0.094, n=6), respectively.

DISCUSSION

These findings suggest that the femoral head and stem taper connection strength can be significantly improved and the risk of periprosthetic tissue damage significantly reduced intraoperatively by attaching an additional weight to the stem to increase its mass.

LEVEL OF EVIDENCE

III, comparative in vitro mechanical investigation.

An Overview of the Stability and Fretting Corrosion of Microgrooved Necks in the Taper Junction of Hip Implants

Fretting corrosion at the head-neck interface of modular hip implants, scientifically termed trunnionosis/taperosis, may cause regional inflammation, metallosis, and adverse local tissue reactions. The severity of such a deleterious process depends on various design parameters. In this review, the influence of surface topography (in some cases, called microgrooves/ridges) on the overall performance of the microgrooved head-neck junctions is investigated. The methodologies together with the assumptions and simplifications, as well as the findings from both the experimental observations (retrieval and in vitro) and the numerical approaches used in previous studies, are presented and discussed. The performance of the microgrooved junctions is compared to those with a smooth surface finish in two main categories: stability and integrity; wear, corrosion, and material loss. Existing contradictions and disagreements among the reported results are reported and discussed in order to present a comprehensive picture of the microgrooved junctions. The current research needs and possible future research directions on the microgrooved junctions are also identified and presented.

Trabecular titanium cups in acetabular revision arthroplasty: analysis of 10-year survivorship, restoration of center of rotation and osteointegration

AIMS

In case of severe bone loss, acetabular revision can be challenged using extra porous pure trabecular titanium (TT) revision cups designed to ensure enhanced iliac and ischiatic purchase. Aim of the study is to report on the clinical and radiological results of a TT acetabular component, evaluating functional outcome, restoration of the hip center of rotation and osteointegration.

METHODS

85 patients, who underwent acetabular revision with a TT revision cup system between October 2009 and December 2018, were included in a retrospective study. Clinical outcome were assessed with Harris Hip Score (HHS). The hip rotation center was measured using the Pierchon method on the AP pelvis film. Loosening of the cup was determined according to the Kosashvili modification of Gill's criteria. Kaplan- Meier survivorship curve was performed. Results The mean follow-up was 6.12 years. The average HHS improved from 54.7 points to 89.7 points (p < 0.05). Two acetabular components (2.3%) were re-revised after a mean of 5.6 years, for aseptic loosening and for infection, with a progressive radiolucency and a > 5 mm vertical migration, respectively. The radiographic evaluation of the position of the hip rotation center revealed a statistically significant difference (p < 0.05) between the pre- and post-operative values. The hip rotation center was correctly restored within 5% of the reference Pierchon values in a percentage of 85.4% relative to horizontal parameters and within 8% in a percentage of 66.7% relative to vertical parameters. 5-year and 10-year survivorships were, respectively, 100% and 88%.

CONCLUSIONS

In case of severe bone loss, TT revision cup system allows for good restoration of center of rotation and osteointegration showing good 10-year survival rate.

Do total shoulder arthroplasty implants corrode?

BACKGROUND

Total shoulder arthroplasty (TSA) has become the gold-standard treatment to relieve joint pain and disability in patients with glenohumeral osteoarthritis who do not respond to conservative treatment. An adverse reaction to metal debris released due to fretting corrosion has been a major concern in total hip arthroplasty. To date, it is unclear how frequently implant corrosion occurs in TSA and whether it is a cause of implant failure. This study aimed to characterize and quantify corrosion and fretting damage in a single anatomic TSA design and to compare the outcomes to the established outcomes of total hip arthroplasty.

METHODS

We analyzed 21 surgically retrieved anatomic TSAs of the same design (Tornier Aequalis Pressfit). The retrieved components were microscopically examined for taper corrosion, and taper damage was scored. Head and stem taper damage was quantitatively measured with a non-contact optical coordinate-measuring machine. In selected cases, damage was further characterized at high magnifications using scanning electron microscopy. Energy-dispersive x-ray spectroscopy and metallographic evaluations were performed to determine underlying alloy microstructure and composition. Comparisons between groups with different damage features were performed with independent-samples t tests; Mann-Whitney tests and multivariate linear regression were conducted to correlate damage with patient factors. The level of statistical significance was set at P < .05.

RESULTS

The average material loss for head and stem tapers was 0.007 mm3 and 0.001 mm3, respectively. Material loss was not correlated with sex, age, previous implant, or time in situ (P > .05). We observed greater volume loss in head tapers compared with stem tapers (P = .002). Implants with evidence of column damage had larger volumetric material loss than those without such evidence (P = .003). Column damage aligned with segregation bands within the alloy (preferential corrosion sites). The average angular mismatch was 0.03° (standard deviation, 0.0668°), with negative values indicating distal engagement and positive values indicating proximal engagement. Implants with proximal engagement were significantly more likely to have column damage than those with distal engagement (P = .030).

DISCUSSION

This study has shown not only that the metal components of TSA implants can corrode but also that the risk of corrosion can be reduced by (1) eliminating preferential corrosion sites and (2) ensuring distal engagement to prevent fluid infiltration into the modular junction.

A Review of Biomaterials and Associated Performance Metrics Analysis in Pre-Clinical Finite Element Model and in Implementation Stages for Total Hip Implant System

Total hip replacement (THR) is a common orthopedic surgery technique that helps thousands of individuals to live normal lives each year. A hip replacement replaces the shattered cartilage and bone with an implant. Most hip implants fail after 10–15 years. The material selection for the total hip implant systems is a major research field since it affects the mechanical and clinical performance of it. Stress shielding due to excessive contact stress, implant dislocation due to a large deformation, aseptic implant loosening due to the particle propagation of wear debris, decreased bone remodeling density due to the stress shielding, and adverse tissue responses due to material wear debris all contribute to the failure of hip implants. Recent research shows that pre-clinical computational finite element analysis (FEA) can be used to estimate four mechanical performance parameters of hip implants which are connected with distinct biomaterials: von Mises stress and deformation, micromotion, wear estimates, and implant fatigue. In vitro, in vivo, and clinical stages are utilized to determine the hip implant biocompatibility and the unfavorable local tissue reactions to different biomaterials during the implementation phase. This research summarizes and analyses the performance of the different biomaterials that are employed in total hip implant systems in the pre-clinical stage using FEA, as well as their performances in in vitro, in vivo, and in clinical studies, which will help researchers in gaining a better understanding of the prospects and challenges in this field.

No Change in Serum Metal Ions Levels After Primary Total Hip Replacement With an Additively Manufactured Dual Mobility Acetabular Construct

Background

Modular junctions of mixed metals have been associated with fretting and corrosion, and in extreme circumstances, adverse local tissue reactions. Since modular dual mobility (MDM) hip constructs involve a titanium shell with a modular cobalt-chromium liner, the aim of this study was to evaluate serum metal ions at minimum 1 year following total hip arthroplasty (THA) in a cohort of patients with these types of implants.

Methods

A single surgeon enrolled 30 patients in a prospective study in which all patients were evaluated preoperatively with serum cobalt, chromium, and titanium metal ion levels. Patients underwent primary THA with an additively manufactured titanium acetabular shell, MDM cobalt-chromium liner, titanium cementless stem, and ceramic head. A “Four Quadrant Test” was used to ensure proper liner seating intraoperatively. At minimum 1 year following surgery, clinical and radiographic evaluation was conducted, and repeat metal ion levels were collected. Patient-reported outcome measures were collected preoperatively and postoperatively.

Results

Twenty-five patients completed 1-year follow-up. All patients had normal metal ion levels for cobalt (<1 μg/L), chromium (<5 μg/L), and titanium (sensitivity test) preoperatively and postoperatively. Patient-reported outcome measures improved significantly after primary THA: Veterans RAND-12 Physical Component Score (31.05 to 45.02, P < .001), Visual Analogue Scale Pain score (70.68 to 7.77, P < .001), Hip Disability and Osteoarthritis Outcomes Score, Joint Replacement (51.99 to 86.97, P < .001).

Conclusions

No significant elevation was detected in serum metal ion levels 16 months following THA using an additively manufactured titanium acetabular shell, a cobalt-chromium MDM liner, and titanium stem with a ceramic head.

Metal-on-metal total hip arthroplasty: does increasing modularity affect clinical outcome?

BACKGROUND

Modularity of metal-on-metal (MoM) implants has come under scrutiny due to concerns regarding additional sources of metal debris. This study is a retrieval analysis of implants from the same manufacturer with the same MoM bearing surface. The difference between the implants was presence or absence of modular junctions.

METHODS

This is a retrospective study of 31 retrieved implants from 31 patients who received a Conserve Wright Medical MoM hip prosthesis. The 31 implants consisted of 16 resurfacings and 15 implants with modular junctions; 4 conventional THAs and 11 modular-neck THAs.

RESULTS

43% of pre-revision MRI scans performed on resurfacing implants and 91% performed on the modular implants illustrated evidence of an adverse local tissue reaction. There was no difference in pre-revision blood metal ion levels or bearing surface wear between the resurfacings and modular implants. The neck-head tapers of the modular group showed low levels of material loss. However, the neck-stem tapers showed increased severity of corrosion and material loss.

CONCLUSIONS

The modular implants had an increased incidence of adverse local tissue reaction. This could be related to the presence of modular junctions, particular the neck-stem junction which showed increased susceptibly to corrosion.

Insights into Imprinting: How Is the Phenomenon of Tribocorrosion at Head-Neck Taper Interfaces Related to Corrosion, Fretting, and Implant Design Parameters?

BACKGROUND

Wear and corrosion at modular neck tapers in THA can lead to major clinical implications such as periprosthetic osteolysis, adverse local tissue reactions, or implant failure. The material degradation processes at the taper interface are complex and involve fretting corrosion, third-body abrasion, as well as electrochemical and crevice corrosion. One phenomenon in this context is imprinting of the head taper, where the initially smooth surface develops a topography that reflects the rougher neck taper profile. The formation mechanism of this specific phenomenon, and its relation to other observed damage features, is unclear. An analysis of retrieved implants may offer some insights into this process.

QUESTIONS/PURPOSES

(1) Is imprinting related to time in situ of the implants and to the taper damage modes of corrosion and fretting? (2) Are implant design parameters like neck taper profile, stem material, or head seating associated with the formation of imprinting? (3) Is imprinting created by an impression of the neck taper profile or can a different mechanistic explanation for imprinting be derived?

METHODS

Thirty-one THAs with cobalt-chromium-molybdenum-alloy (CoCrMo) heads retrieved between 2013 and 2019 at revision surgery from an institutional registry were investigated. Inclusion criteria were: 12/14 tapers, a head size of 36 mm or smaller, time in situ more than 1 year, and intact nonmodular stems without sleeve adaptors. After grouping the residual THAs according to stem type, stem material, and manufacturer, all groups of three or more were included. Of the resulting subset of 31 retrievals, nine THAs exhibited a still assembled head-neck taper connection. The median (range) time in situ was 5 years (1 to 23). Two stem materials (21 titanium-alloy and 10 stainless steel), three kinds of bearing couples (11 metal-on-metal, 13 metal-on-polyethylene, and seven dual-mobility heads), and two different neck taper profiles (six wavy profile and 25 fluted profile) were present in the collection. Four THAs exhibited signs of eccentric head seating. The 31 investigated THAs represented 21% of the retrieved THAs with a CoCrMo alloy head during the specified period.At the head tapers, the damage modes of corrosion, fretting, and imprinting were semiquantitatively rated on a scale between 0 (no corrosion/fretting/imprinting) and 3 (severe corrosion/fretting/imprinting). Corrosion and fretting were assessed applying the Goldberg score, with the modification that the scale started at 0 and not at 1. Imprinting was assessed with a custom scoring system. Rating was done individually at the proximal and distal head taper half and summed to one total damage score for each retrieval and damage mode. Correlations between the damage modes and time in situ and between the damage modes among each other, were assessed using the Spearman rank order correlation coefficient (ρ). Associations between imprinting and implant design parameters were investigated by comparing the total imprinting score distributions with the Mann-Whitney U-test. Metallographically prepared cross-sections of assembled head-neck taper connections were examined by optical microscopy and disassembled head and neck taper surfaces were assessed by scanning electron microscopy (SEM).

RESULTS

The imprinting damage score increased with time in-situ (ρ = 0.72; p < 0.001) and the corrosion damage score (ρ = 0.63; p < 0.001) but not with the fretting damage score (ρ = 0.35; p = 0.05). There was no difference in total imprinting score comparing neck taper profiles or stem materials, with the numbers available. Eccentric head seating had elevated total imprinting score (median 6 [interquartile range 0]) compared with centric seating (median 1 [2]; p = 0.001). Light optical investigations showed that imprinting can be present on the head taper surfaces even if the depth of abraded material exceeds the neck taper profile height. SEM investigations showed bands of pitting corrosion in the imprinted grooves.

CONCLUSION

The microscopic investigations suggest that imprinting is not an independent phenomenon but a process that accompanies the continuous material degradation of the head taper surface because of circular damage on the passive layer induced by grooved neck tapers.

CLINICAL RELEVANCE

Material loss from head-neck taper connections involving CoCrMo alloy heads is a source of metal ions and could potentially be reduced if hip stems with smooth neck tapers were used. Surgeons should pay attention to the exact centric seating of the femoral head onto the stem taper during joining of the parts.

Metal Articulations as a Source of Total Hip Arthroplasty Pain

The consensus systematic risk stratification algorithm from the American Association of Hip and Knee Surgeons, the American Academy of Orthopaedic Surgeons, and The Hip Society summarizes clinical challenges in evaluation and treatment of metal-on-polyethylene total hip arthroplasty (THA) patients with adverse local tissue reaction (ALTR) due to mechanically assisted crevice corrosion (MACC), reviews up-to-date evidence, and identifies the areas for future research in order to provide a useful resource for orthopedic surgeons providing care to these patients. A painful THA has various intrinsic and extrinsic causes. ALTR is one of the intrinsic causes in patients with painful THA. The occurrence of ALTR due to MACC at modular junctions is likely to be multifactorial, including implant, surgical, and patient factors. Therefore, a systematic evaluation needs to involve a focused clinical history, detailed physical examination, laboratory tests, and imaging in order to identify potential differential diagnoses. There should be a low threshold to perform a systematic evaluation of patients with painful non-metal-on-metal THA, including patients with metal-on-polyethylene THA, and modular dual-mobility THA with the CoCr metal acetabular insert, as early recognition and diagnosis of ALTR due to MACC will facilitate initiation of appropriate treatment prior to significant adverse biological reactions. Specialized tests such as blood metal analysis and metal artifact reduction sequence magnetic resonance imaging are important modalities in evaluation and management of ALTR in patients with painful THA.

Cathodic activation and inflammatory species are critical to simulating in vivo Ti-6Al-4V selective dissolution

In vivo retrievals of metallic orthopedic implants have shown selective dissolution of Ti-6Al-4V, where the vanadium-rich β phase preferentially corrodes from the surface. This damage, typically observed in crevices, is not directly caused by wear mechanics and the underlying electrochemical mechanism remains poorly understood. Previous studies show that fretting corrosion can cause negative potential drops, resulting in a decrease in surface oxide passivation resistance and the electrochemical generation of reactive oxygen species (ROS) at metallic surfaces. In this study, we combine cathodic activation and hydrogen peroxide to induce selective dissolution in vitro. After a 600 s -1 V hold and 4 h recovery in 20 °C 1 M H₂O₂ solution, the Ti-6Al-4V β phase was preferentially dissolved. An initial activation threshold of -0.5 V induced a significant increase in β dissolution (p = 0.000). Above this threshold, little selective dissolution occurred. In an Arrhenius-like fashion, decreasing solution concentration to 0.1 M required 72 h to generate β dissolution instead of 4 h at 1 M. Heating 0.1 M solution to body temperature (37 °C) resulted in a decrease in the time needed to replicate a similar level of β dissolution (>90%). Electrochemical impedance shows that both cathodic activation and inflammatory species are necessary to induce selective dissolution, where the combinatorial effect causes a significant drop in oxide passivation resistance from 10⁶ to 10² (p = 0.000). STATEMENT OF SIGNIFICANCE: Though hip arthroplasties are considered a successful procedure, revision rates of 2-4% result in tens of thousands of additional surgeries within the United States, subjecting patients to increased risk of complications. Corrosion is associated with implant failure and retrieval studies show that titanium and its alloys can severely corrode in vivo in ways not yet duplicated in vitro. Here, we reproduce selective dissolution of Ti-6Al-4V β phase simulating key characteristics of in vivo degradation observed in orthopedic retrievals. We establish both cathodically activated corrosion, a relatively unexplored concept, and the presence of inflammatory species as prerequisites, furthering our understanding of this clinically relevant damage mode. We introduce an Arrhenius-based approach to assess the concentration-temperature-time interactions present.

Pre-clinical evaluation of fretting-corrosion at stem-head and stem-cement interfaces of hip implants using in vitro and in silico models

Prior to clinical use, the corrosion resistance of new prosthesis system must be verified. The fretting-corrosion mechanisms of total hip arthroplasty (THA) implants generate metal debris and ions that can increase the incidence of adverse tissue reactions. For cemented stems, there are at least two interfaces that can be damaged by fretting-corrosion: stem-head and stem-cement. This investigation aimed to evaluate, through in vitro and in silico analyses, fretting-corrosion at the stem-head and stem-cement interfaces, to determine which surface is most affected in pre-clinical testing and identify the causes associated with the observed behavior. Unimodular stems and femoral heads of three different groups were evaluated, defined according to the head/stem material as group I (SS/SS), group II (CoCr/SS), and group III (CoCr/CoCr). Seven pairs of stems and heads per group were tested: three pairs were subjected to material characterization, three pairs to in vitro fretting-corrosion testing, and one pair to geometric modeling in the in silico analysis. The absolute area of the stem body degraded was more than three times higher compared with the trunnion, for all groups. These results were corroborated by the in silico analysis results, which revealed that the average micromotion at the stem-cement interface (9.65-15.66 μm) was higher than that at the stem-head interface (0.55-1.08 μm). In conclusion, the degradation of the stem-cement interface is predominant in the pre-clinical set, indicating the need to consider the fretting-corrosion at the stem-cement interface during pre-clinical implant evaluations.

Taper Material Loss in Total Hip Replacements: Is It Affected by Joint Friction?

BACKGROUND

Metal debris and corrosion products generated from the taper junctions of modular joint replacements have been recognized as contributors to failure. Therefore, understanding the factors associated with increased taper wear and corrosion is fundamental to improving implant performance.

METHODS

A cohort of 85 large-diameter metal-on-metal heads and cups retrieved at revision surgery, after 10 to 96 months of service, was evaluated. First, metrology was conducted to quantify head taper material loss and implant articular surface wear. Then, joint frictional moments for each retrieved head-and-cup pair were measured during 10 cycles of simulated physiological gait in a biomechanical model. Taper material loss was evaluated for correlations with frictional moments, articular wear, head diameter, head-cup clearance, and time in vivo.

RESULTS

Peak resultant frictional moments ranged from 9.1 to 26.3 Nm, averaging 17.3 ± 2.7 Nm. Fretting and corrosion damage during in vivo service resulted in material loss from the head tapers ranging between 0.04 and 25.57 mm3, compared with combined head and cup articular wear of 0.80 to 351.75 mm3 in this cohort. Taper material loss was not correlated with higher frictional moments (R = -0.20 to 0.11, p = 0.07 to 0.81). Higher frictional moments from axial rotation were correlated with higher head and cup wear (R = 0.33, p < 0.01). The correlation between taper material loss and head diameter was weak and did not reach statistical significance (R = 0.20, p = 0.07). Taper material loss was not correlated with nominal head-cup clearance (R = 0.06, p = 0.6). Finally, taper material loss increased significantly over time (R = 0.34, p < 0.01).

CONCLUSIONS

Despite serious concerns regarding trunnionosis, volumes of head taper wear were generally lower than those of articular surface wear. There was no statistical correlation between taper wear and frictional moments. Therefore, the results suggest that high friction in metal-on-metal implants does not contribute to higher material loss at the head taper, despite high bending moments.

CLINICAL RELEVANCE

The amount of metal debris and corrosion products from taper junctions of the joint arthroplasties, widely recognized as an insidious cause of failure, was not correlated with joint frictional moments. Multiple factors affect taper wear: implant design, material, size, surface finish, and patient weight and activity level. However, in the present cohort, high friction of metal-on-metal total hip replacements likely did not contribute to increased volume of material loss at taper interfaces, despite increased moments at the locations of taper material loss.

Revision Total Hip Arthroplasty Using the Modular Proximal Stem Modified for Asians: Medium-Term Clinical Results and Perioperative Complications

BACKGROUND

This study aimed to examine the medium-term clinical and radiological outcomes of revision THA using the S-ROM-A stem, a modification of the S-ROM stem intended for Asians.

METHODS

Femoral reconstruction using the S-ROM-A stem was performed in 126 hips that underwent revision THA. All patients were followed for perioperative complications. In addition, clinical and radiographic outcomes at a mean of 8 (range 5-14) years postoperatively were evaluated in 96 hips of 86 patients (76%).

RESULTS

The most common perioperative complication was a femoral fracture, occurring in 16 hips (13%), including 11 intraoperative and 5 postoperative fractures. Dislocation occurred in five hips (4.0%), infection in three hips (2.4%), and trunnionosis in two hips (1.6%), including late complications. The total second stem revision was performed in two hips while stem only second revision preserving the bone ingrown sleeve was performed in four hips. With a second revision for aseptic loosening as the endpoint, the 13-year stem survival rate was 100%. Hip function as assessed by the Japanese Orthopedic Association score improved from a mean of 48 points preoperatively to 87 points 8 years postoperatively (P < .05). Radiological evaluation at the final follow-up showed that 95 hips (99%) achieved bone ingrowth fixation and one hip (1%) achieved fibrous stable status.

CONCLUSION

Revision THA using the S-ROM-A stem resulted in good medium-term outcomes. Although modifications of the stem length and shape may be effective in preventing fractures in Asians with relatively small body sizes, attention should be paid to the occurrence of trunnionosis, which may be associated with the decreased taper size.

In vitro testing for hip head-neck taper tribocorrosion: A review of experimental methods

In vitro test methods are challenged by the multi-factorial nature of head-neck taper connection tribocorrosion due to the consequences of simplification. Incorrect study design and misinterpretation of results has led to contradictory findings regarding important factors affecting head-neck taper tribocorrosion. This review seeks to highlight important considerations when developing in vitro test methods, to help researchers strengthen their study design and analyze the implications of others' design decisions. The advantages, disadvantages, limitations and procedural considerations for finite element analyses, electrochemical studies and in vitro simulations related to head-neck taper connection tribocorrosion are discussed. Finite element analysis offers an efficient method for studying large ranges of mechanical parameters. However, they are limited by neglecting electrochemical, biological and fluid flow factors. Electrochemical studies may be preferred if these factors are considered important. Care must be taken in interpreting data from electrochemical studies, particularly when different materials are compared. Differences in material valence and toxicity affect clinical translation of electrochemical studies' results. At their most complex, electrochemical studies attempt to simulate all aspects of headneck taper connection tribocorrosion in a bench top study. Effective execution requires in-depth knowledge of the tribocorrosion phenomenon, the involved mechanisms, and their measures such that each study design decision is fully informed.

Semi-quantitative histology confirms that the macrophage is the predominant cell type in metal-on-metal hip tissues

Numerous studies have examined the histology of metal-on-metal hip tissues for evidence of a dose response to metal wear but have often reported inconclusive or contradictory findings. The aim of the present study was to address these discrepancies using multiple histological scoring methods to characterize the tissue features of one large group of revised metal-on-metal total hips. Periprosthetic tissues from 165 metal-on-metal hip revisions were examined for features of aseptic lymphocytic vasculitis associated lesions (ALVAL) as rated using two scoring systems as well as rankings for macrophage and lymphocyte numbers, intracellular wear debris and necrosis. Correlations between histological features and clinical variables including gender and time to revision and implant variables including articular surface wear volume or visual taper corrosion scores were examined. Both ALVAL scores reflected the macrophage dominated histology with average scores of 5.9/10 and 1.5/3. There was a statistically significant correlation between the original ALVAL score and wear rate per year (correlation coefficient = 0.17, p = .05) and a moderate correlation between the number of macrophages and wear particles and wear volume. There was no statistically significant correlation between wear and any other feature including lymphocytic inflammation or necrosis. Strong correlations between combined cup and ball wear volume and histological characteristics were not observed, although the number of macrophages was more closely correlated with wear than lymphocytes or necrosis.

Tribocorrosion is Common, but Mild in Modular Humeral Components in Shoulder Arthroplasty: An Implant Retrieval Analysis

Background

Wear and corrosion at the junctions of modular implants are increasingly recognized issues in the design of hip and knee arthroplasty prostheses, yet less is known about their significance in shoulder arthroplasty.

Methods

A query of paired total shoulder implant specimens (eg, humeral head and stem components from the same patient) was performed using an institutional implant retrieval registry. Implants were examined under a stereomicroscope and evaluated for evidence of fretting and corrosion using the modified Goldberg scoring system. Available electronic medical records of included specimens were reviewed to report relevant clinical characteristics and identify potential associations with the presence of tribocorrosion.

Results

Eighty-three paired total shoulder implant specimens, explanted at a single institution between 2013 and 2020, were analyzed. Corrosion was identified in 52% (43/83) of humeral head components and 40% (33/83) of humeral stem components. Fretting was identified in 29% (24/83) of humeral head components and 28% (23/83) of humeral stem components. Of the 56 paired implants for which clinical data were available, the duration of implantation (DOI) was less than 2 years in 29% of paired implants and greater than 5 years in 36% of implants. The presence of corrosion or fretting was not associated with DOI, a male humeral head taper, or periprosthetic infection as the indication for revision.

Conclusion

Mild tribocorrosion was present in more than half of the retrieved humeral implant specimens. However, trunnionosis did not manifest as a clinical cause of revision surgery in our study.

Importance of surgical assembly technique on the engagement of 12/14 modular tapers

Fretting-corrosion at the modular taper junction in total hip replacements (THR), leading to implant failure, has been identified as a clinical concern and has received increased interest in recent years. There are many parameters thought to affect the performance of the taper junction, with the assembly process being one of the few consistently identified to have a direct impact. Despite this, the assembly process used by surgeons during THR surgery differs from a suggested 'ideal' process. For example, taper junctions of cutting tools should be pushed together rather than impacted, while ensuring as much concentricity as possible between the male and female taper and loading axis. This study devised six simple assembly methodologies to investigate how surgical variations affect the success of the compressive fit achieved at the taper interface compared to a controlled assembly method, designed to represent a more 'ideal' scenario. Key findings from this study suggest that a more successful and repeatable engagement can be achieved by quasi-statically loading the male and female taper concentrically with the loading axis. This was shown by a greater disassembly to assembly force ratio of 0.626 ± 0.07 when assembled using the more 'ideal' process, compared to 0.480 ± 0.05 when using a method closer to that used by a surgeon intraoperatively. Findings from this study can be used to help inform new surgical instrumentation and an improved surgical assembly method.