Aims. 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. Methods. 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. Results. 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. Conclusion. 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. Cite this article: Bone Joint Res 2023;12(3):155–164

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

Fracture of contemporary femoral stems is a rare occurrence. Earlier THR stems failed due to design issues or post manufacturing heat treatments that weakened the core metal. Our group identified and analyzed 4 contemporary fractured femoral stems after revision surgery in which electrochemical welds contributed to the failure. All four stems were proximally porous coated titanium alloy components. All failures occurred in the neck region post revision surgery in an acetabular cup exchange. All were men and obese. The fractures occurred at an average of 3.6 years post THR redo (range, 1.0–6.5 years) and 8.3 years post index surgery (range, 5.5–12.0 years). To demonstrate the effect of electrocautery on retained femoral stems following revision surgery, we applied intermittent electrosurgical currents at three intensities (30, 60, 90 watts) to the polished neck surface of a titanium alloy stem under dry conditions. At all power settings, visible discoloration and damage to the polished neck surface was observed. The localized patterns and altered metal surface features exhibited were like the electrosurgically-induced damage priorly reported. The neck regions of all components studied displayed extensive mechanical and/or electrocautery damage in the area of fracture initiation. The use of mechanical instruments and electrocautery was documented to remove tissues in all 4 cases. The combination of mechanical and electrocautery damage to the femoral neck and stem served as an initiation point and stress riser for subsequent fractures. The electrocautery and mechanical damage across the fracture site observed occurred iatrogenically during revision surgery. The notch effect, particularly in titanium alloys, due to mechanical and/or electrocautery damage, further reduced the fatigue strength at the fractured femoral necks. While electrocautery and mechanical dissection is often required during revision THA, these failures highlight the need for caution during this step of the procedure in cases where the femoral stem is retained

In 2020 almost 90% of femoral heads for total hip implants in Germany were made of ceramic. Nevertheless, the cellular interactions and abrasion mechanisms in vivo have not been fully understood until now. Metal transfer from the head-neck taper connection, occurring as smear or large-area deposit, negatively influences the surface quality of the articulating bearing. In order to prevent metal transfer, damage patterns of 40 Biolox delta ceramic retrievals with CoC and CoPE bearings were analysed. A classification of damage type and severity for each component (n=40) was done according to an established scoring system. To investigate the physical properties, the surface quality was measured using confocal microscopy, quantitative analysis of phase composition were performed by Raman spectroscopy and qualitative analysis of metal traces was done by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). The periprosthetic tissue was analysed for abrasion particles with SEM and EDX. Both bearing types show different damage patterns. Dotted/ drizzled metal smears were identified in 82 % of CoC (n=16) and 96 % of CoPE (n=24) bearings. Most traces on the ceramic heads were identified in the proximal area while they were observed predominantly in the distal area for the ceramic inlays. The identified marks are similar to those of metallic bearings. Metallic smears lead to an increase of up to 30 % in the monoclinic crystalline phase of the ceramic. The roughness increases by up to six times to Ra=48 nm. Ceramic and metallic wear particles from the articulating surfaces or head neck taper junctions were found in the periprosthetic tissue. Damage patterns on CoC hip implants seem to be similar to those of metallic implants. More detailed analysis of CoC implants are needed to understand the described damage patterns and provide advice for prevention

Aims. Arthroplasty has become increasingly popular to treat end-stage ankle arthritis. Iatrogenic posterior neurovascular and tendinous injury have been described from saw cuts. However, it is hypothesized that posterior ankle structures could be damaged by inserting tibial guide pins too deeply and be a potential cause of residual hindfoot pain. Methods. The preparation steps for ankle arthroplasty were performed using the Infinity total ankle system in five right-sided cadaveric ankles. All tibial guide pins were intentionally inserted past the posterior tibial cortex for assessment. All posterior ankles were subsequently dissected, with the primary endpoint being the presence of direct contact between the structure and pin. Results. All pin locations confer a risk of damaging posterior ankle structures, with all posterior ankle structures except the flexor hallucis longus tendon being contacted by at least one pin. Centrally-aligned transcortical pins were more likely to contact posteromedial neurovascular structures. Conclusion. These findings support our hypothesis that tibial guide pins pose a considerable risk of contacting and potentially damaging posterior ankle structures during ankle arthroplasty. This study is the first of its kind to assess this risk in the Infinity total ankle system. Cite this article: Bone Jt Open 2021;2(7):503–508

Introduction and Objective. Traditionally, osteoarthritis (OA) has been associated mostly with degradation of cartilage only. More recently, it has been established that other joint tissues, in particular bone, are also centrally involved. However, the link between these two tissues remains unclear. This relationship is particularly evident in post-traumatic OA (PTOA), where bone marrow lesions (BMLs), as well as fluctuating levels of inflammation, are present long before cartilage degradation begins. The process of bone-cartilage crosstalk has been challenging to study due to its multi-tissue complexity. Thus, the use of explant model systems have been crucial in advancing our knowledge. Thus, we developed a novel patellar explant model, to study bone cartilage crosstalk, in particular related to subchondral bone damage, as an alternative to traditional femoral head explants or cylindrical core specimens. The commonly used osteochondral explant models are limited, for our application, since they involve bone damage during harvest. The specifics aim of this study was to validate this novel patellar explant model by using IL-1B to stimulate the inflammatory response and mechanical stimulation to determine the subsequent developments of PTOA. Materials and Methods. Lewis rats (n=48) were used to obtain patellar and femoral head explants which were harvested under an institutional ethical approval license. Explants were maintained in high glucose media (containing supplements), under sterile culture conditions. Initially, we characterised undamaged patellar explants and compared them with the commonly used femoral head. First, tissue viability was assessed using an assay of metabolic activity and cell damage. Second, we created chemical and mechanical damage in the form of IL-1B treatment, and mechanical stimulation, to replicate damage. Standard biochemical assays, histological assays and microstructural assays were used to evaluate responses. For chemical damage, explants were exposed to 10ng/ml of IL-1B for 24 hours at 0, 1, 3 and 7 days after harvesting. For mechanical damage, tissues were exposed to mechanical compression at 0.5 Hz, 10 % strain for 10 cycles, for 7 days. Contralateral patellae served as controls. In both groups, sGAG, ADAMTS4, and MMP-13 were measured as an assessment of representative cartilage responses while ALP, TRAP and CTSK were assessed as a representative of bone responses. In addition to this, histomorphometric, and immunohistochemical, evaluations of each explant system were also carried out. Results. Our results confirm that the patellar explant system is an excellent ex vivo model system to study bone-cartilage crosstalk, and one which does not induce any bone damage at the time of tissue harvest. We successfully established culture conditions to maintain viability in these explants for up to 28 days. Rat IL-1B treatment resulted in increased both proteoglycan content and bone metabolism markers after 7 days when compared with the controls. To confirm this finding, qualitative immunohistochemical staining showed chondrocytes increased expression of MMP13 after treatment with IL-1B. Furthermore, we observed that the levels of ADAMTS4 decreased in 48 hours after IL-1B exposure. Contrastingly IL-1B treatment had the opposite effect on CTSK markers when compared with the control. Mechanically compressed patellae showed a decrease in compressive moduli from day 3 to day 7, suggesting that tissue remodelling may have taken place as a compensatory mechanism in response to damage. In addition, MMP13 release decreased over 48 hours after mechanical compression, while TRAP levels were increased compared with the control. Conclusions. Thus, we successfully demonstrated that IL-1B and mechanical stimulation affects both bone and cartilage tissues independently in this system, which may have relevance in the understanding of bone-cartilage crosstalk after injury and how this is involved in PTOA development

Abstract. Objectives. A damaged vertebral body can exhibit accelerated ‘creep’ under constant load, leading to progressive vertebral deformity. However, the risk of this happening is not easy to predict in clinical practice. The present cadaveric study aimed to identify morphometric measurements in a damaged vertebral body that can predict a susceptibility to accelerated creep. Methods. Mechanical testing of 28 human spinal motion segments (three vertebrae and intervening soft tissues) showed how the rate of creep of a damaged vertebral body increases with increasing “damage intensity” in its trabecular bone. Damage intensity was calculated from vertebral body residual strain following initial compressive overload. The calculations used additional data from 27 small samples of vertebral trabecular bone, which examined the relationship between trabecular bone damage intensity and residual strain. Results. Calculations from trabecular bone samples showed a strong non-linear relationship between residual strain and trabecular bone damage intensity (R. 2. = 0.78, P < 0.001). In damaged vertebral bodies, damage intensity as calculated from residual strain was then related to vertebral creep rate (R. 2. = 0.39, P = 0.001). This procedure enabled accelerated vertebral body creep to be predicted from morphological changes (residual strains) in the damaged vertebral body. Conclusion. These findings suggest that morphometric measurements obtained from fractured vertebrae can be used to quantify vertebral damage intensity and hence to predict progressive vertebral deformity

Introduction. Pitting damage on implants has been reported and attributed to use of electrocautery. This study aimed to distinguish how different TKA bearing surfaces are susceptible to this type of damage and whether surgeons were aware that this damage can occur. Methods. A survey was sent to Hip and Knee Society members to determine what percentage of adult reconstructive surgeons use electrocautery after implantation of components. Three bearing surfaces for primary TKA were selected: CoCr, Oxinium, and zirconium nitride (ZrN) to be damaged by electrocautery with a monopolar (MP, Bovie) and bipolar (BP, Aquamantys) electrocautery with three different energy settings. A comparison of surface damage and backscatter elemental analysis using SEM was performed. Average roughness (Ra), maximal peak-to-valley height (Rz,), kurtosis (Rk), and skewness (Rsk) measurements were collected using a profilometer (DektakXT, Bruker, Tucson, AZ) with a 2.5µm radius stylus to assess an area of 3.8mm by 3.2mm in the central portion of the area for each MP and BP energy setting used to impart damage to the bearing surfaces. A similar undamaged area for each bearing surface was also measured for roughness parameter comparison. Results. Median Rz and Ra measurements were larger for BP damaged areas compared to MP for all bearing surfaces.(Table 1) The Oxinium surface had the greatest increase in roughness parameters of all three bearing surfaces tested. Survey results indicate that a significant percentage of adult reconstructive surgeons use the electrocautery after implants are in place and are not aware of this type of damage. Backscatter SEM analysis found significant changes for BP damage compared to MP. Conclusion. Our in vitro study determined surface damage caused by electrocautery can have significant effects on the bearing surfaces of implants. Our survey determined many arthroplasty experts are unaware that this damage can occur. For any figures or tables, please contact the authors directly

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

Ligaments and tendons are connective tissues with a highly hierarchical structure, from collagen fibres, to fibrils and fascicules. Their intricate structural arrangement produces an anisotropic non-linear elastic mechanical behaviour and a complex damage pattern before failure. Recent constitutive models have been developed with all parameters describing the structure of the tissue, with the advantage that they can in theory be measured on the tissue rather than being phenomenologically-derived. This is an ideal framework to model damage as its onset and propagation can be associated to changes in the structure directly. In this preliminary study, the possibility to identify damage mechanisms in the tissue structure using in silico models was analysed for both the anterior cruciate ligament, with fascicules forming a helix with its longitudinal axis, and the patellar tendon, with fascicules co-aligned with its longitudinal axis. Tissues of interest were modelled as cylinders submitted to uniaxial tension. Damage was modelled as either a reduction of collagen volume fraction with increased strain, assuming the number of collagen fibres sustaining load decreases as fibres fail, or a reduction of the modulus of the fibres, assuming pre-failure damage of the fibres. Each damage mechanism was associated with a damage variable with different fibre stretch threshold for damage initiation and assuming linear variation of damage until an arbitrary failure point. The apparent behaviour of the modelled tissues was significantly different as damage thresholds, damage mechanisms, type of fascicules were varied. This preliminary work showed that using a structural constitutive model to describe occurrence and propagation of structural damage in an in silico model of hierarchical connective tissues is a framework that can clearly differentiate at a macroscopic level between different values of damage threshold and different damage mechanisms for tissue with co-aligned or helical fascicules

Primary implant stability is critical for osseointegration and subsequent implant success. Small displacements on the screw/bone interface are necessary for implant success, however, larger displacements can propagate cracks and break anchorage points which causes the screw to fail. Limited information is available on the progressive degradation of stability of an implanted bone screw since most published research is based on monotonic, quasi-static loading [1]. This study aims to address this gap in knowledge. A total of 100 implanted trabecular screws were tested using multi-axial loading test set-up. Screws were loaded in cycles with the applied force increasing 1N in each load cycle. In every load cycle, Peak forces, displacements, and stiffness degradation (calculated in the unloading half of the cycle) where recorded. 10 different loading configurations where tested. The damage vs displacement shows a total displacement at the point of failure between 0.3 and 0.4 mm while an initial stiffness reduction close to 40%. It is also shown that at a displacement of ~0.1 mm, the initial stiffness of every sample had degraded by 20% (or more) meaning that half of the allowable degradation occurred in the first 25-30% of the total displacement. Other studies on screw overloading [1] suggests similar results to our concerning initial stiffness degradation at the end of the loading cycle. Our results also show that the initial stiffness degrades faster with relatively small deformations suggesting that the failure point of an implanted screw might occur before the common failure definition (pull-out force, for example). These results are of great significance since primary implant stability is better explained by the stiffness of the construct than by its failure point

Objectives. Bone void fillers are increasingly being used for dead space management in arthroplasty revision surgery. The aim of this study was to investigate the influence of calcium sulphate bone void filler (CS-BVF) on the damage and wear of total knee arthroplasty using experimental wear simulation. Methods. A total of 18 fixed-bearing U2 total knee arthroplasty system implants (United Orthopedic Corp., Hsinchu, Taiwan) were used. Implants challenged with CS-BVF were compared with new implants (negative controls) and those intentionally scratched with a diamond stylus (positive controls) representative of severe surface damage (n = 6 for each experimental group). Three million cycles (MC) of experimental simulation were carried out to simulate a walking gait cycle. Wear of the ultra-high-molecular-weight polyethylene (UHMWPE) tibial inserts was measured gravimetrically, and damage to articulating surfaces was assessed using profilometry. Results. There was no significant difference (p  >  0.05) between the wear rate of implants challenged with CS-BVF (3.3 mm. 3. /MC (95% confidence interval (CI) 1.8 to 4.8)) and the wear rate of those not challenged (2.8 mm. 3. /MC (95% CI 1.3 to 4.3)). However, scratching the cobalt-chrome (CoCr) significantly (p < 0.001) increased the wear rate (20.6 mm. 3. /MC (95% CI 15.5 to 25.7)). The mean surface roughness of implants challenged with CS-BVF was equivalent to negative controls both after damage simulation (p = 0.98) and at the conclusion of the study (p = 0.28). Conclusion. When used close to articulating surfaces, a low-hardness, high-purity CS-BVF had no influence on wear. When trapped between the articulating surfaces of a total knee arthroplasty, CS-BVF did not scratch the surface of CoCr femoral components, nor did it increase the wear of UHMWPE tibial inserts compared with undamaged negative controls. Cite this article: R. M. Cowie, S. S. Aiken, J. J. Cooper, L. M. Jennings. The influence of a calcium sulphate bone void filler on the third-body damage and polyethylene wear of total knee arthroplasty. Bone Joint Res 2019;8:65–72. DOI: 10.1302/2046-3758.82.BJR-2018-0146.R1

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

Background. Intervertebral disc (IVD) degeneration is a major cause of low back pain (LBP). Degenerate discs are associated with accelerated cellular senescence. Cell senescence is associated with a secretory phenotype characterised by increased production of catabolic enzymes and cytokines. However to date, the mechanism of cell senescence within disc degeneration is unclear. Senescence can be induced by increased replication or induced by stress such as reactive oxygen species or cytokines. This study investigated the association of cellular senescence with markers of DNA damage and presence of cytoplasmic DNA (which in cancer cells has been shown to be a key regulator of the secretory phenotype), to determine mechanisms of senescence in disc degeneration. Methods and Results. Immunohistochemistry for the senescence marker: p16. INK4A. was firstly utilised to screen human intervertebral discs for discs displaying at least 30% immunopostivity. These discs were then subsequently analysed for immunopostivity for DNA damage markers γH2AX and cGAS and the presence of cytoplasmic DNA. The number of immunopositive cells for p16. INK4A. positively correlated with the expression of γH2AX and cGAS. Senescent cells were also associated with the presence of cytoplasmic DNA. Conclusions. These new findings elucidated a role of cGAS and γH2AX as a link from genotoxic stress to cytokine expression, which is associated with senescent cells. The findings indicate that cellular senescence in vivo is associated with DNA damage and presence of cytoplasmic DNA. Whether this DNA damage is a result of replicative senescence or stress induced is currently being investigated in vitro. No conflicts of interest. Sources of funding: Funded by ARUK and MRC

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

Intervertebral disc (IVD) degeneration is a major cause of low back pain (LBP). Degenerate discs are associated with accelerated cellular senescence. Cell senescence is associated with a secretory phenotype characterised by increased production of catabolic enzymes and cytokines. However, to date, the mechanism of cell senescence within disc degeneration is unclear. Senescence can be induced by increased replication or induced by stress such as reactive oxygen species or cytokines. This study investigated the association of cellular senescence with markers of DNA damage and presence of cytoplasmic DNA (which in cancer cells has been shown to be a key regulator of the secretory phenotype), to determine mechanisms of senescence in disc degeneration. Immunohistochemistry for the senescence marker: p16INK4A was firstly utilised to screen human intervertebral discs for discs displaying at least 30% immunopostivity. These discs were then subsequently analysed for immunopostivity for DNA damage markers γH2AX and cGAS and the presence of cytoplasmic DNA. The number of immunopositive cells for p16 INK4A positively correlated with the expression of γH2AX and cGAS. Senescent cells were also associated with the presence of cytoplasmic DNA. These new findings elucidated a role of cGAS and γH2AX as a link from genotoxic stress to cytokine expression which is associated with senescent cells. The findings indicate that cellular senescence in vivo is associated with DNA damage and presence of cytoplasmic DNA. Whether this DNA damage is a result of replicative senescence or stress induced is currently being investigated in vitro

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