Recently, our lab has made observations of metal damage patterns from retrieval studies that appeared to be cellular in nature [1]. This type of damage presented on about 74% of the retrieved implants and was attributed to inflammatory cells (termed ICI corrosion) [1]. An alternate hypothesis arose surrounding the use of electrosurgery in total joint arthroplasty (TJA). In TJA, where surgery occurs around metallic devices, the interactions of the high voltage, high frequency current created by an electrosurgical generator and the implant need to be better understood. In order to explore the effects electrosurgical currents have on metal implants, the interaction of a model system of highly polished metal disks and a standard electrosurgical generator (ConMed, Utica, NY) was evaluated in various modes and power settings. The disks were made of CoCrMo or Ti-6Al-4V alloys and were polished to a mirror finish for use and placed directly on the return electrode pad used in patients. Both coagulation and cut modes were evaluated, as well as both monopolar and bipolar configurations in wet and dry conditions using a blade-shaped tip. In wet cases, the disks were wet with phosphate buffered saline prior to the test to simulate body fluids in contact with the implant during current application. In all cases, surface damage was generated on both surfaces and was readily observed as a direct result of the current interacting with the metal (Fig. 1 and 2). Direct contact with the metal, regardless of a dry or wet surface, resulted in pitting and oxide buildup at the contact area. Non-contact activation in proximity to the surface or contact with fluid on the surface caused arcing and created damage that was more widespread over the area of fluid contact with the surface. The damage patterns created on the wetted surface by the electrosurgical unit looked very similar to the patterns we previously attributed to inflammatory cells. More specifically, it produced circular, ruffled areas with centralized pits and occasionally presented trail- and weld-like features (Fig. 2). While these results show that some of the damage previously reported to be from ICI corrosion is indeed the result of electrosurgery, there are still cases in retrievals that cannot be explained by this process and the corrosion reaction to alloys exposed to ROS-based molecules demonstrate significant acceleration of corrosion. Thus, ICI corrosion is still a viable hypothesis. Surgeons utilizing electrosurgical systems in proximity to metallic orthopedic implants need to exercise caution as the discharge of electrical energy through these implants can induce localized surface damage and may result in other adverse effects to the metal implants. Ultimately, we would like to update the community on the nature of the damage we previously reported and more importantly bring to light the possibility of surgeon-induced damage to the implant as a result of electrosurgical methods

Introduction. Dual mobility (DM) total hip arthroplasty (THA) prostheses are designed to increase stability. In the setting of primary and revision THA, DM THA are used most frequently for dysplasia and instability diagnoses, respectively. As the use of DM THA continues to increase, with 8,031 cases logged in the American Joint Replacement Registry from 2012–2018, characterizing in vivo damage and clinical failure modes are important to report. Methods. Under IRB-approved implant retrieval protocol, 43 DM THA systems from 41 patients were included. Each DM THA component was macroscopically examined for standard damage modes. Clinically-relevant data, including patient demographics and surgical elements, were collected from medical records. Fretting and corrosion damage grading is planned, according to the Goldberg et al. classification system. Results. In this 43-retrieved implant series, there were 23 female and 17 male patients (n=1, unknown), with an average body mass index of 29 (range, 19–49), and average ages at index and revision of 63 years (range, 34–80) and 64 years (range, 38–88), respectively. The average duration of implantation was 12.9 months (range, 0.1–72.0). Reasons for revision included infection (n=11, 26%), mechanical complication (n=10, 23%), intraprosthetic dislocation (n=6, 14%), periprosthetic fracture (n=5, 12%), pain (n=4, 9%), acetabular-associated loosening (n=3, 7%), unknown (n=3, 7%), hematoma (n=2, 5%), leg length discrepancy (n=1, 2%), and inflammatory reaction (n=1, 2%); some cases included multiple reasons for revision. On articular surfaces, scratching was the most commonly observed damage mode on all components, with more than 40% of acetabular cup and femoral heads showing scratching damage (Figure 1A). Abrasion, burnishing, and pitting damage were also observed in more than 10% of acetabular cup and acetabular liner components; further, approximately 20% of polyethylene acetabular liners exhibited edge deformation damage. On backside surfaces, polyethylene acetabular liners showed the greatest damage, with more than 60% of components exhibiting abrasion, scratching, or pitting damage (Figure 1B). Conclusion. This series showed various reasons for revision as well as in vivo damage of retrieved DM systems following short-to-midterm implantation. Damage was observed on both articular and backside surfaces of the five components of DM THA. Modularity of DM THA prostheses may amplify rates of in vivo damage. Future studies are needed to confirm these results and clinical significance. For any figures or tables, please contact the authors directly

Introduction. Corrosion products from modular taper junctions of hip prostheses have been implicated in adverse local tissue reactions after THR. Numerous factors have been proposed as the root causes of this phenomenon, including implant design and materials, manufacturing variables, intraoperative assembly, and patient lifestyle. As significant taper damage only occurs in a few percent of cases of THR, we have addressed this complication using a “forensic” examination of retrieval specimens to gain insight into the factors initiating the cascade leading to irreversible damage of the modular interface. In this study we report the categorization of over 380 retrievals into groups having shared damage patterns, metallic composition, and interface surface geometries to isolate the genesis of mechanically-assisted corrosion and its relation to intraoperative assembly, manufacturing, and postoperative loading. Methods. A total of 384 femoral components were examined after retrieval at revision THR. The implants were produced by a diverse range of manufacturers, 271 in CoCr, and 113 in TiAlV, with both smooth (253) and machined (131) tapers. Initially, the implants were sorted into groups based on composition and taper roughness. Each trunnion was then cleaned to remove organic deposits and examined by stereomicroscopy at X6-X31. After an initial pilot study, we developed a classification system consisting of 8 basic patterns of damage (Table 1). We then classified all 384 trunnions according to this 8-group system. The prevalence of each pattern was calculated on the basis of both composition and surface texture of the trunnion. Results. Overall, 81% of the trunnions had visible areas of surface damage, which varied as a function of composition (CoCr: 77%; TiAlV: 90%; p=0.002) and finish (smooth: 88%; machined: 67%; p<0.001). The most common pattern of damage was a circumferential ring at the base of the taper (24%) followed by a group with slight fretting or assembly damage distributed over the entire taper (19%). Damage to one quadrant at the bottom third was seen in approximately 18%. When combining material types, 41% of smooth tapers had circumferential patterns of damage corresponding to groups 2, 3, and 5. Conversely, 77% of the machined tapers had damage limited to one side or on two opposite sides (Patterns 4, 6, 7, 8, and 9). Discussion. Our results show that the pattern and location of damage is influenced not only by composition and surface texture, but can also be an indicator of component fit. The damage patterns observed on almost half (45%) of the trunnions were not circumferential (Chart 2), suggesting that misalignment of the head during assembly may be responsible for initiating the corrosion cascade in stems with machined taper surfaces. Summary. We categorized over 380 implant retrievals into groups having shared damage patterns, metallic composition, and interface surface geometries to isolate the genesis of corrosion

Introduction. Previous studies of CoCr alloy femoral components for total knee arthroplasty (TKA) have identified 3. rd. body abrasive wear, and apparent inflammatory cell induced corrosion (ICIC) [1] as potential damage mechanisms. The association between observed surface damage on the femoral condyle and metal ion release into the surrounding tissues is currently unclear. The purpose of this study was to investigate the damage on the bearing surface in TKA femoral components recovered at autopsy and compare the damage to the metal ion concentrations in the synovial fluid. Methods. 12 autopsy TKA CoCr femoral components were collected as part of a multi-institutional orthopedic implant retrieval program. The autopsy components included Depuy Synthes Sigma Mobile Bearing (n=1) and PFC (n=1), Stryker Triathlon (n=1) and Scorpio (n=3), and Zimmer Nexgen (n=4) and Natural Knee (n=2). Fluoro scans of all specimens prior to removal was carried out to assure no signs of osteolysis or aseptic loosening were present. Third-body abrasive wear of CoCr was evaluated using a semi-quantitative scoring method similar to the Hood method [2]. ICIC damage was reported as location of affected area and confirmed using a digital optical microscope with 4000X magnification. Synovial fluid was aspirated from the joint capsule prior to removal of the TKA device. The synovial fluid was spun at 1600 rpm for 20 minutes in a centrifuge with the cell pellet removed. The supernatant was analyzed in 1 mL quantities for ICP-MS (inductively coupled plasma mass spectrometry) by Huffman Hazen Laboratories. Data was expressed as ppb. Results. Mild to severe damage (Damage Score ≥ 2) was observed on 92% of the components in at least one quadrant, with no severe damage (Damage Score = 4) observed. ICIC damage was observed on three components in three different regions (the posterior lateral, anterior, and medial bearing surface). These observations were confirmed with digital optical microscopy, where we observed as interconnecting pits and indentations with a spiraling or trailing region, consistent with prior observation of ICIC in retrievals (Figure 1). Cobalt was detected in 7 cases, however the metal levels were not as high as levels observed in patients with a failed joint replacement (Table 1). There was no correlation between the metal ion concentration and the damage score on the CoCr femoral condyle. Discussion. This study documents the damage mechanics and associated metallic release into the synovial fluid of “well-functioning” TKA components retrieved at autopsy. It has been suggested that ICIC damage is actually damage from electrocautery during surgery. However, we observed ICIC damage on autopsy retrievals in which the use of electrocautery is unlikely. The damage mechanisms observed on the autopsy TKA components were similar but less severe compared to mechanisms observed in long-term TKA components from revision surgery [1]. More research is needed to better understand the metal release from CoCr femoral components and periprosthetic tissue reactions in TKA

Introduction. The use of bone cement as a fixation agent has ensured the long-term functionality of THA implants . 1. However, some studies have shown the undesirable effect of wear of stem-cement interface, due to the release of metals and polymeric debris lead to implant failure . 2,3. Debris is generated by the micromotion together with a severely corrosive medium present in the crevice of stem-cement interface . 3,4. FEA studies showed that micromotion can affect osseointegration and fretting wear . 5,6. The aim of this research is to investigate if the micromotions measures from in silico analysis of the stem-cement correlate with the fretting-corrosion damage observed on in vitro testing. Methods. The in vitro fretting-corrosion testing was made with positioning and loading based on ISO 7206-4 and ISO 7206-6. It was used Exeter stems embedded in bone cement (PMMA) and immersed in a saline solution (9.0 g/L of NaCl). A fatigue testing system (Instron 8872, USA) was used to conduct the test, applying a sinusoidal cyclic load at 5.0 Hz. The tests were finished after 10 million cycles and images of stem surfaces were taken with a photographic camera (Canon EOS Rebel T6i, Japan) and a stereoscope (Leica M165C, Germany). For the computational analysis, the same testing configurations were modeled on software ANSYS. The analysis was performed using linear isotropic elasticity for both stem (E=193GPa; ⱱ=0.27; σ. y. =400MPa) and PMMA cement (E=2.7GPa; ⱱ=0.35; σ. u. =76MPa). 7,8. . A second-order tetrahedral element was used to mesh all components with a size of 0.5 mm in the stem-cement contact area, increasing until 1.0 mm outside from them. A frictional contact (µ=0.25) with an augmented Lagrange formulation was used. The third cycle of loading was evaluated and a variation of sliding distance less than 10% was set as convergence criteria. The micromotion was measured as the sliding distance on the stem-cement interface. Results and Discussion. The in silico analysis showed the presence of areas almost without micromotion in the proximal lateral and distal medial regions. In these regions, there is no evidence of fretting-corrosion after the in vitro testing. The lack of micromotion is caused by the debonding due to testing configurations and implant design. The absence of contact doesn't allow wear by abrasion or third body, avoiding the fretting-corrosion damage. For the regions distal lateral and proximal medial, it is possible to observe fretting-corrosion due to micromotions, which is supported by the in silico analysis results. The region proximal medial had the highest micromotion on computational analysis and the fretting-corrosion was more severe on laboratory testing, reinforcing the relevance of micromotion in the fretting-corrosion damage on the stem-cement interface. Conclusion. The results indicate a correlation of micromotion calculated by in silico analysis and fretting-corrosion damage observed on in vitro testing. The developed FEA model may be a useful tool to predict the fretting-corrosion damage on the THA implants on pre-clinical testing. Additional efforts are needed to apply this tool on bone-implant systems to predict fretting-corrosion damage observed in vivo. For any figures or tables, please contact authors directly

Introduction. Corrosion at modular junctions of total hip replacements has been identified as a potential threat to implant longevity, resulting in efforts to determine appropriate countermeasures. Visual scoring and volumetric material loss measurements have been useful tools to elucidate various clinical and design factors associated with corrosion damage. However, corrosion involves electron exchange that results in chemical changes to biomedical alloys, and electrochemical assessment may therefore be a more appropriate approach to understand the phenomenon. The purpose of this pilot study was to electrochemically distinguish the severity of corrosion in retrieved femoral heads. A secondary goal was to identify the potential of electrochemical impedance spectroscopy (EIS) as a method to identify different forms of corrosion damage. Methods. Twenty femoral heads were identified from a larger study of total hip replacements, obtained as part of an ongoing multi- center IRB-approved retrieval program. Using a previously established 4-point scoring method, components were binned by taper damage: 10 components were identified as having severe damage, 7 with moderate damage and 2 with mild damage. One (1) unimplanted control was included to represent minimal corrosion damage. All components were then characterized using electrochemical impedance spectroscopy under the frequency domain: a 10 mV sinusoidal voltage, ranging from 20 kHz to 2 mHz, was applied to the taper of a femoral head (working electrode) filled with a 1M solution of PBS, a platinum counter electrode and a chlorided silver reference electrode. Absolute impedance at 2 mHz (|Z. 0.002. |), and max phase angle (θ) were assessed relative to taper damage severity. After least-squares fitting of the EIS data to a Randles circuit with a constant phase element, circuit elements: polarization resistance (Rp), CPE-capacitance, and CPE-exponent were also evaluated. The seven (7) most severely corroded components were further examined with scanning electron microscopy to identify corrosion modes. For all statistical analyses, significance was determined at alpha=0.05. Results. Taper damage was strongly correlated with both |Z. 0.002. | (ρ = −0.857, p<0.001) and CPE-capacitance (ρ=0.913, p<0.001). Taper damage was moderately associated with max phase angle (ρ= −0.483, p=0.031), CPE-exponent (ρ= −0.653, p=0.002) and Rp (ρ=0.556, p=0.011). Log-log plots of the strongest predictors of taper damage (|Z. 0.002. | and CPE- capacitance) identified some clustering among severely corroded components. SEM analysis identified evidence of grain/phase boundary corrosion on four components, all with log CPE-capacitance ≥ −4.4. Discussion. The results of this pilot study highlight that electrochemical impedance spectroscopy is useful in determining corrosion severity in retrieved femoral heads, and may also identify intergranular corrosion attack. For an undamaged taper, the self- passivating behavior of CoCrMo creates a surface that opposes charge transfer, but greater corrosion appears to compromise this barrier. The observed trend of low impedance but high capacitance for severely corroded components with intergranular corrosion may signal charge storage at the boundaries of individual grains. Additional work is underway to characterize this behavior

Introduction. The release of metal debris and ions has raised concerns in joint arthroplasty. In THA metal debris and ions can be generated by wear of metal-on-metal bearing surfaces and corrosion at modular taper interfaces, currently understood to be mechanically assisted crevice corrosion (MACC) [1]. More recently, inflammatory-cell induced corrosion (ICIC) has been identified as a possible source of metal debris and/or ions [2]. Although MACC has been shown to occur at modular junctions in TKA, little is known about the prevalence of other sources. The purpose of this study was to determine the sources of metallic debris and ion release in long-term implanted (in vivo > 15y) TKA femoral components. Specific attention was paid to instances of ICIC as well as damage at the implant-bone interface. Methods. 1873 retrieved TKA components were collected from 2002–2013 as part of a multi-center, IRB-approved retrieval program. Of these, 52 CoCr femoral condyles were identified as long term TKA (Average: 17.9±2.8y). These components were predominantly revised for loosening, PE wear and instability. 40/52 of the components were primary surgeries. Components were examined using optical microscopy to confirm the presence of 5 damage mechanisms (polyethylene failure, MACC corrosion of modular tapers, corrosion damage between cement and backside, third-body wear, and ICIC). Third-body wear was evaluated using a semi-quantitative scoring method based on the percentage of damaged area. A score of 1 had minimal damage and a score of 4 corresponded to severe damage. Polyethylene components were scored using the Hood method and CoCr components were scored similarly to quantify metal wear. The total area damaged by ICIC was quantified using photogrammetry. Images were taken using a digital SLR with a calibrated ruler in the same focal plane. Using known pixel dimensions, the ICIC damaged area was calculated. Results. Surface damage indicative of corrosion and/or CoCr debris release was identified in 92% (n=48) of the components. Third-body wear was the most prevalent damage mechanism identified in 77% (n=40/52; Figure 1) of these components. ICIC was identified in 38% (n=20/52, figure 2) of the components. The polyethylene damage scores were predominantly a score of 4 out of a maximum score of 4 (89%). The corresponding femoral components had moderate to severe damage scores, with 39% with a score of 2, 37% scoring 3 and 22% scoring 4 out of a maximum score of 4. The total ICIC damaged area was an average of 0.11 ± 0.12 mm. 2. (Range: 0.01–0.46mm. 2. ). Discussion. In this study, we sought to identify mechanisms that could lead to the release of CoCr debris/ions in TKA. Five different mechanisms of potential metal release were observed. The most prevalent were third-body wear and ICIC damage. However the clinical implications remain unclear for several mechanisms because none of the devices were revised due to adverse local tissue reactions or biologic reactions to CoCr. Although we documented the prevalence of each damage mechanism, the quantity of metal removal was not investigated, warranting future studies

Background. Sequentially annealed, highly crosslinked polyethylene (HXLPE) has been used clinically in total knee arthroplasty (TKA) for over a decade[1]. However, little is known about the reasons for HXLPE revision, its surface damage mechanisms, or its in vivo oxidative stability relative to conventional polyethylene. We asked whether retrieved sequentially annealed HLXPE tibial inserts exhibited: (1) similar reasons for revision; (2) enhanced resistance to surface damage; and (3) enhanced oxidative stability, when compared with tibial inserts fabricated from conventional gamma inert sterilized polyethylene (control). Methods. Four hundred and fifty-six revised tibial inserts in two cohorts (sequentially annealed and conventional UHMWPE control) were collected in a multicenter retrieval program between 2000 and 2016. We controlled for implantation time between the two cohorts by excluding tibial inserts with a greater implantation time than the longest term sequentially annealed retrieval (9.5 years). The mean implantation time (± standard deviation) for the sequentially annealed components was 1.9 ± 1.7 years, and for the control inserts, 3.4 ± 2.7 years (Figure 1). Reasons for HXLPE revision were assessed based on medical records, radiographs, and examinations of the retrieved components. Surface damage mechanisms were assessed using the Hood method[2]. Oxidation was measured at the bearing surface, the backside surface, the anterior and posterior faces, as well as the post (when available) using FTIR (ASTM F2102). Surface damage and oxidation analyses were available for 338 of the components. We used nonparametric statistical testing to analyze for differences in oxidation and surface damage when adjusting for polyethylene formulation as a function of implantation time. Results. The tibial inserts in both cohorts were revised most frequently for loosening, infection, and instability. Instability was observed more frequently in inserts without a stabilizing post. In both cohorts, the most commonly observed surface damage mechanisms were burnishing, pitting, and scratching. Delamination was rare and only observed in 2 sequentially annealed inserts and 7 inserts in the control cohort. We observed six cases of posterior condyle fracture, which was always associated with instability (Figure 2). 5/6 of the fracture cases did not have a stabilizing post. Oxidation indices of the sequentially annealed inserts were, on average, low (ASTM oxidation index < 1) and not significantly different than the control inserts on the bearing surface and anterior/posterior face (Figure 3). Discussion. The findings of this study document the reasons for revision, surface damage mechanisms, and oxidative behavior of sequentially annealed HXLPE for TKA. We observed evidence of low in vivo oxidation in both retrieved sequentially annealed HXLPE and control tibial inserts. We found no association between the levels of oxidation and clinical performance of the HXLPE tibial components. However, because of the short-term follow-up, analysis of longer-term retrievals may be appropriate

As a treatment for end-stage elbow joint arthritis, total elbow replacement (TER) results in joint motions similar to the intact joint; however, bearing wear, excessive deformations and/or early fracture may necessitate early revision of failed implant components. Compared to hips, knees and shoulders, very little research has been focused on the evaluation of the outcomes of TER, possible failure mechanisms and the development of optimal designs. The current study aims to develop computational models of TER implants in order to analyze implant behaviour; considering contact stresses, plastic deformations and damage progression. A geometrical model of a TER assembly was developed based on measurements from a Coonrad-Morrey TER implant (Zimmer, Inc., Warsaw, IN). Ultra high molecular weight polyethylene (UHMWPE) nonlinear elasto-plastic material properties were assigned to the humeral and ulnar bushings. A frictional penalty contact formulation with a coefficient of friction of 0.04 was defined between all of the surfaces of the model to take into account every possible interaction between different implant components in vivo. The loading scenario applied to the model includes a flexion-extension motion, a joint force reaction with variable magnitude and direction and a time varying varus-valgus (VV) moment with a maximum magnitude of 13 N.m, simulating a chair-rise scenario as an extreme loading condition. An explicit dynamic finite element solver was used (ABAQUS Explicit, Dassault Systèmes, Vélizy-Villacoublay, France), due to improved capabilities when performing large deformation analyses. Model results were compared directly with corresponding experimental data. Experimental wear tests were performed on the abovementioned implants using a VIVO (AMTI, Watertown, MA) six degree-of-freedom (6-DOF) joint motion simulator apparatus. The worn TER bushings were scanned after the test using micro computed tomography (µCT) imaging techniques, and reconstructed as 3D models. Comparisons were made based on the sites of damage and deformed geometries between the numerical results and experimental test data. In addition to that, parametric geometrical models were developed using worn geometry of the retrievals in order to account for primary wear and deformations while simulating long-term contact stress and secondary damage progression on the bushings (Fig. 1). Contact pressure distributions on the humeral and ulnar bushings correlate with the sites of damage as represented by the µCT data and gross observation of clinical retrievals. Furthermore, deformation patterns and kinematics of the components are in good agreement with the experimental results (Fig.2). Excessive plastic deformations are evident in both the numerical and the experimental results close to the regions with high contact pressures. Simulating parametric initially-worn geometries results in the formation of secondary damage zones, as well as redistribution of contact stresses and contact locations (Fig. 3). The results demonstrate UHMWPE bushing damage due to different loading protocols. Numerical results demonstrate strong agreement with experimental data based on the location of deformation and creep on bushings and exhibit promising capabilities for predicting the damage and failure mechanisms of TER implants. For figures/tables, please contact authors directly.

INTRODUCTION. Due to increasing interest into taper corrosion observed primarily in hip arthroplasty devices with modular tapers, efforts towards characterizing the corrosion byproducts are prevalent in the literature [1–4]. As a result of this motivation, several studies postulate cellular induced corrosion due to the presence of remarkable features in the regions near taper junction regions and articulating surfaces [3–5]. Observations made on explanted devices from a retrieval database as well as laboratory tests have led to the alternative proposal of electrocautery-electrosurgery damage as the cause of these features. These surgical instruments are commonly used for hemostasis or different degrees of tissue dissection. METHODS. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to evaluate the features observed on retrieved devices. Retrieved devices consisted of OXINIUM and cobalt-chromium-molybdenum (CoCrMo) femoral implants, a Titanium-alloy hip stem, and a CoCrMo metal-on-metal femoral head. Electrocautery-electrosurgery damage was created using a SurgiStat II (Valleylab, Colorado) onto various components (CoCrMo, OXINIUM femoral heads as well as Ti-6Al-4V and CoCrMo alloy test stem constructs). Test components were evaluated using the same methods as the retrieved devices. RESULTS. Remarkable features were present on retrieved devices (Figure 1) which were similar to previous studies (3–5). The appearance of these features could be described as crater-like, pitted, scratched, molten or splattered material, and ruffled. These features were present on articulating and non-articulating regions as well as near taper junctions. Testing performed on samples using the SurgiStat II, created features that were similar in appearance (Figure 1). Additionally, material transfer that included an iron peak based on EDS in addition to the cobalt and chromium (present due to native material) was detected in the regions of contact (Figure 2). CONCLUSIONS. It was possible to re-create damage features similar to those previously characterized as remarkable features created by cellular-induced corrosion [3–5]. It is theorized that the high-voltage based electrocautery (commonly Bovie) or high-frequency based electrosurgical devices can result in localized degradation/alteration of oxides and passive regions of commonly used orthopaedic alloys. These surgical instruments, specifically the cutting electrodes, are frequently made of stainless steels which can result in iron transfer during contact with the device. During the surgical use of the electrocautery-electrosurgery instrument, it may be necessary to remove tissue, bone, or cauterize near the implant or explant which may have led to the damage features noted in this study and the previous literature [3–5]. If this damage occurs during the initial implantation of the devices, it may further exacerbate corrosion in the damaged region and/or alter the mechanical integrity of the constructs (i.e. fatigue performance)

Magnetic resonance imaging (MRI) scans are widely used in the assessment of knees, often prior to arthroscopic procedures. The reporting of chondral damage on MRI scans can be variable. The correlation between MRI reports of chondral damage and that found at arthroscopy is often inconsistent. The aim of this study was to identify how well MRI reports correlated with the extent of chondral damage found at arthroscopy. A retrospective case-note review of a single-surgeon series of 175 arthroscopic procedures was performed. 83 patients were included in the study. The remainder were excluded if an MRI scan had not been performed, or had been performed more than 3 months prior to surgery. The condition of the articular cartilage demonstrated by MRI was compared to that found at arthroscopy. Data was analysed for presence and extent of chondral damage. Comparison between MRI and arthroscopy findings showed high Specificity (90%) and Negative Predictive Values (89%) for chondral damage, but low Sensitivity (46%). Cohen's kappa values < 0.2 revealed very poor correlation for the extent of damage. This study demonstrates that MRI is good at describing whether articular damage is present but does not reliably describe the extent of the damage

The primary stability of an uncemented femoral total knee replacement component is provided by press-fit forces at the bone-implant interface. This press-fit is achieved by resecting the bone slightly larger than the inner dimensions of the implant, resulting in a so-called interference fit. Previous animal studies have shown that an adequate primary stability is required to minimize micromotions at the bone-implant interface to achieve bone-ingrowth, which provides the secondary (long-term) fixation. It is assumed that during implantation a combination of elastic and plastic deformation and abrasion of the bone will occur, but little is known about what happens at the bone-implant interface and how much interference fit eventually is achieved. Purpose of this study was therefore to assess the actual and effective interference fit and the amount of bone damage during implantation of an uncemented femoral knee component. In this study, five cadaveric distal femora were prepared and femoral knee components were implanted by an experienced surgeon. Micro-CT scans and conventional CT-scans were obtained pre- and post-implantation for geometrical measurements and to measure bone mineral density. In addition, the position of the implant with respect to the bone was determined by optical scanning of the reconstructions (Figure.1). By measuring the differences in surface geometry, assessments were made of the cutting error, the actual interference fit, the amount of bone damage, and the effective interference fit. Our analysis showed an average cutting error of 0.67± 0.17 mm, which pointed mostly towards bone under-resections. We found an average actual AP interference fit of 1.48± 0.27 mm, which was close to the nominal value of 1.5 mm. We observed combinations of bone damage and elastic deformation in all bone specimens (Figure. 2), which showed a trend to be related with bone density. Higher bone density tended to lead to lower bone damage and higher elastic deformation (Figure. 3). The results of the current study indicate different factors that interact while implanting an uncemented femoral knee component. This knowledge can be used to fine-tune design criteria of femoral components and obtain adequate primary stability for all patients in a more predictable way

Introduction. Wear of the ultra-high molecular weight polyethylene (UHWMPE) component and the subsequent aseptic loosening remains a primary reason for late revision of total knee replacements (TKRs).[1] While improved measurement techniques have provided more quantitative information on the wear of surgically retrieved inserts, it is not well understood how observed damage patterns translate to volume loss of polyethylene in vivo. The overall purpose of this study is to investigate the relationship of damage patterns and volume loss at the articular surface of total knee replacements. We hypothesize that damage patterns are reliable predictors of volume loss. Methods. Two different investigators independently analyzed damage patterns and volume loss on 43 revision- and 21 postmortem-retrieved MG II (Zimmer Inc.) tibial UHMWPE components. Areas of damage patterns on the articular surfaces were outlined with a video microscope (SmartScope, OGP) and were separated into four spatially exclusive categories (Fig. 1): delamination, pitting, striations and polishing. Articular surfaces were digitized with a low-incidence laser coordinate measuring machine (SmartScope, OGP). Autonomous reconstruction, a previously described and validated method,[2] calculated volume loss on the medial and lateral sides of each component. To investigate the predictability of volume loss using observed patterns, stepwise linear regression models were rendered in PASW Statistics 18 (SPSS Inc). Results. Components with total volume loss higher than 300 mm3 exhibited the jagged and flaky surface topography characteristic of severe delamination. Excluding delaminated components, the population's total wear rate (±95% CI) was 12.9 ± 5.97 mm3/year (Pearson's r = 0.527, p < 0.001), which accounted for volume loss due to creep (Figure 2). The wear rates on the medial side (6.56 ± 3.91 mm3/year, Pearson's r = 0.434, p = 0.002) and on the lateral side (6.32 ± 3.44 mm3/year, Pearson'sr = 0.467, p < 0.001) were not significantly different (p = 0.926). Linear regression models that included delaminated components revealed that delaminated and striated areas were significant predictors of volume (Figure 3 - Table 1). Pitted area was also a significant factor on the total part, but fell out of the medial and lateral models. When delaminated components were excluded, volume loss was similarly explained by striated and pitted areas on the medial side and total part. However, the adjusted R2 of these models was low − 0.177 and 0.166, respectively. Discussion. We found that damage patterns were not reliable surrogates for material volume loss. Other than delamination, area of striated patterns best predicted volume loss. However, the large reduction in adjusted R2 of the linear regression model indicates that delaminated areas were essential to explaining variations in the volume loss. While other groups have reported striations on retrievals [3], this damage pattern remains widely unrecognized in retrieval and knee simulator studies, with the mechanism poorly understood. To view tables/figures, please contact authors directly

Introduction. In an effort to provide a TKA bearing material that balances resistance to wear, mechanical failure and oxidation, manufacturers introduced antioxidant polyethylene. In many designs, this is accomplished through pre-blending the polymer with the antioxidant before consolidation and radiation crosslinking. This study reports the wear performance (in terms of thickness change) of a hindered phenol (PBHP) UHMWPE from analysis of an early series of knee retrievals and explores these questions: 1) What is early-time performance of this new bearing material? 2) Is there a difference in performance between fixed and mobile bearings in this design? 3) How does quantitative surface analysis help understand performance at the insert-tray modular interface?. Methods. A series of 100 consecutive Attune™ knee inserts (DePuy Synthes, Warsaw, IN) received at revision by an IRB approved retrieval laboratory between September 2014 and March 2019 were investigated. In vivo duration was 0–52 months. Both the fixed bearing design (n=74) and the rotating platform mobile bearing design (n=26) were included. Dimensional change was determined by measurement of each insert and compared to the as-manufactured dimensions, provided by the manufacturer. The insert-tray interfaces under the loaded bearing zones were analyzed with light interferometry using an optical surface profiler (NewView™ 7300, Zygo, Middlefield, CT). Statistical analyses to explore relationships between measured variables were conducted using SPSS. Results. Mean total through-thickness change of the inserts was 0.052 mm. Mean rate of thickness change for all inserts having in vivo duration > 12 months was 0.038 mm/year (fixed bearing 0.042, mobile bearing 0.029 mm/year). The rate of thickness change for all inserts showed a decreasing trend with duration that was not statistically significant, (rho -.244, p=.094); however, the mobile bearing cohort alone showed a significant decrease in thickness change rate with duration (rho= −.659; p=.014). Surface roughness (Sa) of the distal surface of the UHMWPE inserts under the bearing areas averaged 1.24 µm (range 0.12 – 8.53) and peak-to-valley height (PV) averaged 27.1 µm (range 4 – 95). Sa and PV both showed a decreasing trend with duration in vivo in the mobile bearing inserts, but that trend did not reach statistical significance (p= 0.05 criterion). Neither Sa nor PV showed correlation with measured thickness change. Discussion. This study indicates that the rate of thickness change of a relatively new antioxidant cross-linked bearing material is very similar to other reported wear rates of crosslinked knee inserts. Lower wear rate of mobile bearing inserts compared to fixed bearings also is consistent with earlier published studies. Direct comparison between quantitative thickness change and objective, quantitative surface metrology on the same series brings new information to the arena of measuring and reporting “wear” of UHMWPE and underscores the importance of the distinction between visual damage and actual thinning of the bearing. The systematic surface analysis of the modular interfaces showing that surface roughness (Sa) and total damage feature topography (PV) trend downward with in vivo duration of mobile bearings supports the hypothesis that relative motion at that interface may ‘polish out’ the surface topography over time. For any figures or tables, please contact authors directly

Background. In total hip arthroplasty (THA), the importance of preserving muscles is widely recognized; therefore, muscle-sparing approaches are widely used. Recently, we reported that there are bony impressions, that we called the obturator attachment (OA), on the greater trochanter that indicate the insertions of the short external rotator tendons. In this study, we used a three-dimensional (3-D) template to evaluate damage to the insertions of the short external rotator muscles during a femoral procedure. Methods. We investigated 12 hips in 10 patients who underwent THA. Preoperative CT imaging of the hip was performed, and 3-D reconstruction of the greater trochanter was used to visualize the bony impressions that indicate the insertions of the obturator internus and externus muscles (Fig 1A). We performed preoperative 3-D templating of two different femoral prosthesis (flat tapered-wedge stem: J-Taper, cylindrical straight stem: PerFix910) and then evaluated the extent of damage to the OA during the stem placement (Fig 1B, 1C). The extent of damage to the OA was classified using the following scale: grade 0, no damage of the insertion area; grade 1, less than 1/3; grade 2, equal to or more than 1/3–2/3; grade 3, equal to or more than 2/3; grade 4, complete. Results. The attachment area of the obturator internus tendon was damaged in 9 hips (7 hips: grade 1, 2 hips: grade 2) using J-Taper and all hips (8 hips: grade 2, 4 hip: grade 3) using PerFix910. The attachment area of the obturator externus tendon was not damaged in any hip using J-Taper but was damaged in 5 hips (5 hips: grade 1) using PerFix910. Conclusions. The tendon insertion site for the obturator internus was more likely to be damaged by rasping or reaming. The tapered-wedge type stem was considered to be superior to the straight, cylindrical stem for preserving the tendon insertions on the greater trochanter. Fig.1 Three-dimensional reconstructed images of the left greater trochanter, after removal of the femoral head. A: The deep depression in the anterior part of the trochanteric fossa (blue area) indicates the insertion of the obturator internus, and the posterior depression in the trochanteric fossa (red area) indicates the insertion of the obturator externus. B: Preoperative 3-D templating of the J-taper (Kyocera, Kyoto, Japan) was performed. The insertion area of the obturator internus was damaged (Grade 1), while the insertion area of the obturator externus was not damaged. C: Preoperative 3-D templating of the PerFix910 (Kyocera, Kyoto, Japan) was performed. The most of the insertion area of the obturator internus was damaged (Grade 3), while the insertion area of the obturator externus was not damaged. Oi = obturator internus, Oe = obturator externus, Lt = lessor trochanter, Sup = superior, and Ant = anterior

Introduction. When third body particles originating from bone cement or bone void fillers become trapped between articulating surfaces of joint replacements, contact surfaces may be damaged leading to accelerated wear and premature failure of the implant. In this study, the damage to cobalt chrome counterfaces by third body particles from PMMA bone cement (GMV, DePuy) and various bone void fillers was investigated; then wear tests of UHMWPE were carried out against these surfaces. Methods. Third body particles of polymerised GMV bone cement and the bone void fillers; OsteoSet (with tobramycin), Stimulan and Stimulan+ (with vancomycin and tobramycin) (provided by Biocomposites Ltd.) were trapped between an UHMWPE pin and a highly polished cobalt chrome plate. A load of 120N was applied to the pin and using an Instron materials testing machine, the plate was pulled beneath the pin to recreate third body damage [1]. The resulting surface topography of the plate was analysed using white light interferometry (Bruker NPFLEX). Pin on plate wear tests of GUR 1020 UHMWPE pins were carried out against the plates perpendicular to the direction of damage for 500,000 cycles in 25% bovine serum using a 6-station multi-axial reciprocating rig under conditions to replicate the kinematics in total knee replacement. Wear of the pins was determined by gravimetric analysis and results were compared to negative (highly polished) control plates and positive controls scratched with a diamond stylus (lip height 2µm). Statistical analysis was carried out using one-way ANOVA with significance taken at p<0.05. Results. Following damage simulation with Stimulan and Stimulan+, no scratches could be seen on the surface of the cobalt chrome plates using a stereomicroscope under 63× magnification (Figure 1). Table 1 shows that OsteoSet caused surface damage with the highest density of scratches, which had a greater mean lip height than those caused by the other third body materials. Stimulan+ caused significantly (p=0.002) fewer scratches than Osteoset and the surface damage caused by Stimulan was below the resolution of the surface analysis measurement technique used. The pin on plate wear test showed that under the test conditions used, the wear of UHMWPE was similar (p=0.108) for negative control plates and plates scratched with third body particles and a significant (p<0.001) increase in wear was only observed against the positive control plates [2]. Discussion. This study shows that third body particles originating from bone cement and bone void fillers can damage the surface of highly polished cobalt chrome plates and that materials of similar composition can cause varying severity of damage. Wear tests against plates damaged with third body particles did not significantly affect the wear of UHMWPE and to significantly increase wear, scratches needed to have a lip height of 2µm or above

Introduction:. Cemented femoral components have been used in hip replacement surgery since its inception. For many patients this works well, but recent retrieval studies. 1–4. and more fundamental studies. 5, 6. have highlighted the issues of damage and material loss from the both matt and polished cemented stems. Materials and methods:. This study will focus on a cohort of retrievals from the Southampton Orthopaedics Centre for Arthroplasty Retrieval Surgery (SOCARS). The cohort consisted of a number of hybrid modular total hip replacements with cemented femoral components, both from mixed and matched manufacturer stem and head combinations. Femoral stems were polished, collarless, tapered designs; head sizes ranged from 28–54 mm. For each femoral stem, samples of Palacos R + G cement (Heraeus Medical GmbH, Hanau, Germany) were retrieved from the proximal region of the cement mantle (Gruen zones 1 and 7), corresponding to both macroscopically damaged and undamaged surfaces of the stem. The areas of damage were determined using calibrated digital photography; damaged surfaces were then imaged in detail using an Alicona InfiniteFocus microscope (Alicona Imaging GmbH, Graz, Austria). The technique uses optical microscopy and focus variation technology to extract 3D morphology and depth information from the surface with a resolution of 10 nm. A series of measurements were made and two different analysis routes were used to provide volumetric material loss measurements from the stem surface. High-resolution microscopy and elemental analysis of the cement and stem surfaces was conducted via SEM and EDX to identify the mechanisms leading to material loss at the cement-stem interface. Results:. The results demonstrate that material loss from polished femoral stems results from a progressive tribocorrosion process; the major damage mechanism is thought to be the micro-motion between the femoral stem surface and zirconium dioxide radiopacifier agglomerates originating from the cement. No significant link was found between the extent of damage to the femoral stem and either the head size or the amount of wear occurring at the head-cup bearing surface. The scale of stem damage varied between implants but often exceeded the volumetric material loss measured at the bearing surfaces. Conclusions:. Tribo-corrosive damage to the femoral stems of cemented total hip prostheses is a major potential source of material loss in vivo; in severely affected arthroplasties, measurements of volumetric wear of the stem at the cement-stem interface were greater than at either the head-cup bearing surface or the taper junction. The mechanism of material loss in this study was identified as a wear-dominated tribocorrosion interaction between the cement and stem, with zirconium dioxide radiopacifier agglomerates within the cement providing the hard particles which damaged the surface of cobalt-chrome femoral stems

Wear of the polyethylene (PE) insert in total knee replacements can lead to wear-particle and fluid-pressure induced osteolysis. One major factor affecting the wear behaviour of the PE insert in-vivo is the surface characteristics of the articulating femoral components. Contemporary femoral components available in Canada are either made of cast Cobalt Chromium (CoCr) alloy or have an oxidized zirconium surface (Oxinium). The latter type of femoral components have shown to have increased abrasive wear resistance and increased surface wettability, thus leading to reduced PE wear in-vitro compared with conventional cast CoCr components. Although surface damage has been reported on femoral components in general, there have been no reports in the literature as to what extent the recommended operating techniques affect the surface tribology of either type of femoral component. Twenty-two retrieved total knee replacements were identified with profound surface damage on the posterior aspect of the femoral condyles. The femoral components were of three different knee systems: five retrievals from the NexGen(r) total knee system (Zimmer Inc., Warsaw, IN), twelve retrievals from the Genesis II(r) total knee system (CoCr alloy or Oxinium; Smith & Nephew Inc., Memphis, TN), and five retrievals from the Duracon(r) total knee system (Stryker Inc., Mahwah, NJ). Reasons for revision were all non-wear-related and included aseptic loosening in two cases, painful flexion instability, and chronic infection. All retrieved femoral components showed evidence of surface damage on the condyles, at an average of 99° flexion (range, 43° – 135° flexion). Titanium (Ti) alloy transfer and abrasive surface damage were evident on all retrieved CoCr alloy femoral components that came in contact with Ti alloy tibial trays. Surface damage on the retrieved Oxinium femoral components was gouging, associated with the removal and cracking of the oxide and exposure of the zirconium alloy substrate material. CoCr alloy femoral components that had unintended contact with CoCr alloy tibial trays also showed evidence of gouging and abrasive wear. All femoral components showed severe surface damage in the posterior aspect of the condyles. The femoral surface was heavily scratched and the oxidized zirconium coating surface appeared removed. The surface analysis suggested that the surface damage most likely occurred during the time of initial implantation. In particular, it appeared that the femoral condyles were resting on the posterior aspect of the tibial tray in flexion, thus scratching the femoral components. Such scratches could potentially lead to accelerated PE insert wear and reduced implant longevity, thus making expensive revisions surgery necessary. The authors strongly suggest a revision of the current operating techniques recommended by the implant manufacturer to prevent this type of surface damage from occurring

Introduction. Wear of the UHMWPE tibial component remains a major reason for aseptic loosening and subsequent revision or failure of TKAs [1]. Many retrieval studies measure surface damage patterns as surrogates for the severity of wear, but little is known about how these patterns relate to the volume of material lost. This study (a) examines the wear rate of a cruciate retaining TKA design and (b) relates observed wear patterns to volume loss on the surface. We hypothesize that damage patterns are good predictors for volumetric wear. Methods. 43 revision and 21 postmortem-retrieved MG II (Zimmer Inc.) tibial UHMWPE components were included in this study. Wear scars and damage patterns on the superior articular surfaces were digitized using a video microscope (SmartScope, OGP). Patterns were parsed into four spatially exclusive categories: delamination, polishing, striations and pitting. The surfaces were measured at 100×100µm using a low-incidence laser on a coordinate measuring machine (SmartScope, OGP). Autonomous mathematical reconstruction of the original surface was used [2] to calculate volume changes on the medial and lateral surfaces as an estimate of wear volume [Fig. 1] Total volume loss was calculated within the observed wear scar, and volume loss under each pattern was calculated and normalized to the total volume loss of its insert. Results. Excluding delaminated components, total wear correlated linearly with time in situ (Pearson's r=0.53) with a volumetric wear rate of 13.0±2.9 mm. 3. /year. Total wear area correlated linearly with total wear volume (Pearson's r=0.44), while delaminated area correlated strongly with total wear volume (Pearson's r=0.80). Excluding delaminated components, striated areas correlated more strongly to total volume loss (Pearson's r=0.54) than did total wear scar area (Pearson's r=0.34), while other patterns showed no correlation [Fig. 2]. When present, delaminated areas contributed most to total volume loss in postmortem- and revision-retrievals (58.3% and 38.7% respectively), striations second most (36.2% and 30.7%) and polished areas third most (24.6% and 27.6%), although significant differences were not observed [Fig. 3]. Pitted areas contributed significantly less (heteroscedastic t-test p=0.010) to total wear on postmortem- (1.3±1.7%) than on revision-retrievals (11.3±19.6%), although they were observed with a slightly higher frequency in the postmortem group (81% vs. 76%). Discussion. We found that damage patterns were not reliable surrogates for material volume loss. Other than delamination, area of striated patterns best predicted and contributed most to volume loss. Furthermore, our data suggests that polished and striated patterns in the absence of pitting are markers of a well-functioning UHWMPE TKR. While other groups have reported striations on retrievals [3], this damage pattern remains widely unrecognized in retrieval and knee simulator studies, with the mechanism poorly understood. The higher contribution of pitting to total wear volume in revision-retrieved TKR suggests that the fatigue wear mechanism leading to pitting contributes to the need for the early revision of the implant

Purpose. The objective of this study was to compare the wear characteristics and damage scores in highly crosslinked (XLPE) and conventional polyethylene (CPE) acetabular liners. Methods. This was a retrieval analysis of 13 XLPE liners obtained from patients who underwent revision surgery from 1999 to 2011. These patients were matched on patient demographics (age, BMI, side, sex, and length of implantation) and implant characteristics (inner diameter, outer diameter, and lip angle) to another group with CPE who underwent revision in the same time period. The only difference between implants was the use of XLPE. Wear analysis was performed with micro-computed tomography (micro-CT), provided thickness measurements across four quadrants of the bearing surface. Surface damage was scored and the pattern documented. The mean duration of implantation was 5.00 ± 3.36 years in the XLPE group and 5.19 ± 3.69 years in the CPE group (p = 0.12), with the longest duration exceeding 10 years. Results. CPE demonstrated more wear at time of retrieval with a mean thickness of 8.18 ± 1.50 mm compared to XLPE with a mean thickness of 8.91 ± 1.76 mm (p < 0.001). Damage scoring was not significantly different between the two groups, with a total damage score of 13.77 ± 3.95 in XLPE and 15.23 ± 4.63 in CPE (p = 0.18). There was no difference in the distribution of wear and damage. Conclusion. XLPE undergoes less wear than CPE, however this may not be apparent by using damage scoring alone, which is the most common retrieval analysis technique. The superior wear properties of XLPE may reduce the need for revision surgery as a result of decreased wear and osteolysis