The efficacy of antibiotic-eluting material in a two-stage model of periprosthetic joint infection.

Periprosthetic joint infections occur in about 2% of patients who undergo primary total joint arthroplasty, a procedure performed over 1 million times in the United States. The gold standard of treatment is a two-stage revision. This study aimed to establish a two-stage procedure in a preclinical small animal model (rat) to test and compare the efficacy of an antibiotic-eluting material in managing infection. Joint replacement was simulated by transchondylarly implanting a polyethylene (PE) plug into the distal femur and a titanium screw in the proximal tibia. Methicillin-sensitive Staphylococcus aureus (MSSA) 108 CFU/mL was injected into the tibial canal and the joint space before wound closure. The control groups were killed on postoperative day (POD) 18 (n = 12) and on POD 42 (n = 4) to assess both early and later-stage outcomes in the control group. The test group underwent revision surgery on POD 18 for treatment using gentamicin-eluting polyethylene (GPE, n = 4) and was observed until POD 42 to evaluate the efficacy of treatment. Our results showed that the bone loss for the treatment group receiving GPE was significantly less than that of the control (p < 0.05), which was supported by the histology images and an AI-tool assisted infection rate evaluation. Gait metrics duty factor imbalance and hindlimb temporal symmetry were significantly different between the treatment and control groups on Day 42. This animal model was feasible for evaluating treatments for peri-prosthetic joint infections (PJI) with a revision surgery and specifically that revision surgery and local antibiotic treatment largely hindered the peri-prosthetic bone loss. Statement of clinical significance: This revision model of peri-prosthetic infection has the potential of comparatively evaluating prophylaxis and treatment strategies and devices. Antibiotic-eluting UHMWPE is devised as at tool in treating PJI while providing weight bearing and joint space preservation.

The use of deep learning enables high diagnostic accuracy in detecting syndesmotic instability on weight-bearing CT scanning.

PURPOSE: Delayed diagnosis of syndesmosis instability can lead to significant morbidity and accelerated arthritic change in the ankle joint. Weight-bearing computed tomography (WBCT) has shown promising potential for early and reliable detection of isolated syndesmotic instability using 3D volumetric measurements. While these measurements have been reported to be highly accurate, they are also experience-dependent, time-consuming, and need a particular 3D measurement software tool that leads the clinicians to still show more interest in the conventional diagnostic methods for syndesmotic instability. The purpose of this study was to increase accuracy, accelerate analysis time, and reduce interobserver bias by automating 3D volume assessment of syndesmosis anatomy using WBCT scans. METHODS: A retrospective study was conducted using previously collected WBCT scans of patients with unilateral syndesmotic instability. One-hundred and forty-four bilateral ankle WBCT scans were evaluated (48 unstable, 96 control). We developed three deep learning models for analyzing WBCT scans to recognize syndesmosis instability. These three models included two state-of-the-art models (Model 1-3D Convolutional Neural Network [CNN], and Model 2-CNN with long short-term memory [LSTM]), and a new model (Model 3-differential CNN LSTM) that we introduced in this study. RESULTS: Model 1 failed to analyze the WBCT scans (F1 score = 0). Model 2 only misclassified two cases (F1 score = 0.80). Model 3 outperformed Model 2 and achieved a nearly perfect performance, misclassifying only one case (F1 score = 0.91) in the control group as unstable while being faster than Model 2. CONCLUSIONS: In this study, a deep learning model for 3D WBCT syndesmosis assessment was developed that achieved very high accuracy and accelerated analytics. This deep learning model shows promise for use by clinicians to improve diagnostic accuracy, reduce measurement bias, and save both time and expenditure for the healthcare system. LEVEL OF EVIDENCE: II.

Defining and predicting radiographic knee osteoarthritis progression: a systematic review of findings from the osteoarthritis initiative.

PURPOSE: The purposes of this systematic review were to (1) identify the commonly used definitions of radiographic KOA progression, (2) summarize the important associative risk factors for disease progression based on findings from the OAI study and (3) summarize findings from radiographic KOA progression prediction modeling studies regarding the characterization of progression and outcomes. METHODS: A systematic review was performed by conducting a literature search of definitions, risk factors and predictive models for radiographic KOA progression that utilized data from the OAI database. Radiographic progression was further characterized into "accelerated KOA" and "typical progression," as defined by included studies. RESULTS: Of 314 studies identified, 41 studies were included in the present review. Twenty-eight (28) studies analyzed risk factors associated with KOA progression, and 13 studies created or validated prediction models or risk calculators for progression. Kellgren-Lawrence (KL) grade based on radiographs was most commonly used to characterize KOA progression (50%), followed by joint space width (JSW) narrowing (32%) generally over 48 months. Risk factors with the highest odds ratios (OR) for progression included periarticular bone mineral density (OR 10.40), any knee injury within 1 year (OR 9.22) and baseline bone mineral lesions (OR 7.92). Nine prediction modeling studies utilized both clinical and structural risk factors to inform their models, and combined models outperformed purely clinical or structural models. CONCLUSION: The cumulative evidence suggests that combinations of structural and clinical risk factors may be able to predict radiographic KOA progression, particularly in patients with accelerated progression. Clinically relevant and feasible prediction models and risk calculators may provide valuable decision-making support when caring for patients at risk of KOA progression, although standardization in modeling and variable identification does not yet exist.

Do total hip arthroplasty polyethylene liners without free radicals oxidize in vivo or ex vivo?

Crosslinking substantially reduces the wear of ultra-high molecular weight polyethylene (UHMWPE) used in total hip arthroplasty (THA) but some reports have indicated that first generation liners manufactured without antioxidants may be vulnerable to in vivo oxidation. This study evaluated maximum oxidation using Fourier transform infrared spectroscopy per ASTM F2102-06ε1 and linear head penetration using a coordinate measuring machine among 66 revision-retrieved THA components with in vivo durations ranging from 0.02 to 24.6 years. These included 30 liners crosslinked with 5 Mrad of gamma radiation and then melted, 13 non-crosslinked, never-irradiated liners sterilized with gas plasma and 23 non-crosslinked, never-irradiated liners sterilized with ethylene oxide. All liners were vacuum-sealed and stored at -20°C prior to analysis with the exception of three retrievals of each material type that were stored in air for 9.9 to 21.5 years. All 57 vacuum-sealed and frozen retrievals demonstrated good oxidative stability with maximum oxidation indices (OIs) less than 1.0 and 75% (43/57) of these liners had maximum OIs less than 0.1. Linear penetration measurements were lower in the crosslinked liners compared to non-crosslinked retrievals. Although instances of oxidation and embrittlement were found after ex vivo storage in air among liners that did not have free radicals at the time of implantation, in vivo oxidation does not appear to be a clinical concern through the first decade of service for crosslinked liners and at up to 25 years after surgery for non-crosslinked liners.

Assessing the utility of deep neural networks in predicting postoperative surgical complications: a retrospective study.

BACKGROUND: Early detection of postoperative complications, including organ failure, is pivotal in the initiation of targeted treatment strategies aimed at attenuating organ damage. In an era of increasing health-care costs and limited financial resources, identifying surgical patients at a high risk of postoperative complications and providing personalised precision medicine-based treatment strategies provides an obvious pathway for reducing patient morbidity and mortality. We aimed to leverage deep learning to create, through training on structured electronic health-care data, a multilabel deep neural network to predict surgical postoperative complications that would outperform available models in surgical risk prediction. METHODS: In this retrospective study, we used data on 58 input features, including demographics, laboratory values, and 30-day postoperative complications, from the American College of Surgeons (ACS) National Surgical Quality Improvement Program database, which collects data from 722 hospitals from around 15 countries. We queried the entire adult (≥18 years) database for patients who had surgery between Jan 1, 2012, and Dec 31, 2018. We then identified all patients who were treated at a large midwestern US academic medical centre, excluded them from the base dataset, and reserved this independent group for final model testing. We then randomly created a training set and a validation set from the remaining cases. We developed three deep neural network models with increasing numbers of input variables and so increasing levels of complexity. Output variables comprised mortality and 18 different postoperative complications. Overall morbidity was defined as any of 16 postoperative complications. Model performance was evaluated on the test set using the area under the receiver operating characteristic curve (AUC) and compared with previous metrics from the ACS-Surgical Risk Calculator (ACS-SRC). We evaluated resistance to changes in the underlying patient population on a subset of the test set, comprising only patients who had emergency surgery. Results were also compared with the Predictive OpTimal Trees in Emergency Surgery Risk (POTTER) calculator. FINDINGS: 5 881 881 surgical patients, with 2941 unique Current Procedural Terminology codes, were included in this study, with 4 694 488 in the training set, 1 173 622 in the validation set, and 13 771 in the test set. The mean AUCs for the validation set were 0·864 (SD 0·053) for model 1, 0·871 (0·055) for model 2, and 0·882 (0·053) for model 3. The mean AUCs for the test set were 0·859 (SD 0·063) for model 1, 0·863 (0·064) for model 2, and 0·874 (0·061) for model 3. The mean AUCs of each model outperformed previously published performance metrics from the ACS-SRC, with a direct correlation between increasing model complexity and performance. Additionally, when tested on a subgroup of patients who had emergency surgery, our models outperformed previously published POTTER metrics. INTERPRETATION: We have developed unified prediction models, based on deep neural networks, for predicting surgical postoperative complications. The models were generally superior to previously published surgical risk prediction tools and appeared robust to changes in the underlying patient population. Deep learning could offer superior approaches to surgical risk prediction in clinical practice. FUNDING: The Novo Nordisk Foundation.

Comparing the performance of a deep convolutional neural network with orthopedic surgeons on the identification of total hip prosthesis design from plain radiographs.

PURPOSE: A crucial step in the preoperative planning for a revision total hip replacement (THR) surgery is the accurate identification of the failed implant design, especially if one or more well-fixed/functioning components are to be retained. Manual identification of the implant design from preoperative radiographic images can be time-consuming and inaccurate, which can ultimately lead to increased operating room time, more complex surgery, and increased healthcare costs. METHOD: In this study, we present a novel approach to identifying THR femoral implants' design from plain radiographs using a convolutional neural network (CNN). We evaluated a total of 402 radiographs of nine different THR implant designs including, Accolade II (130 radiographs), Corail (89 radiographs), M/L Taper (31 radiographs), Summit (31 radiographs), Anthology (26 radiographs), Versys (26 radiographs), S-ROM (24 radiographs), Taperloc Standard Offset (24 radiographs), and Taperloc High Offset (21 radiographs). We implemented a transfer learning approach and adopted a DenseNet-201 CNN architecture by replacing the final classifier with nine fully connected neurons. Furthermore, we used saliency maps to explain the CNN decision-making process by visualizing the most important pixels in a given radiograph on the CNN's outcome. We also compared the CNN's performance with three board-certified and fellowship-trained orthopedic surgeons. RESULTS: The CNN achieved the same or higher performance than at least one of the surgeons in identifying eight of nine THR implant designs and underperformed all of the surgeons in identifying one THR implant design (Anthology). Overall, the CNN achieved a lower Cohen's kappa (0.78) than surgeon 1 (1.00), the same Cohen's kappa as surgeon 2 (0.78), and a slightly higher Cohen's kappa than surgeon 3 (0.76) in identifying all the nine THR implant designs. Furthermore, the saliency maps showed that the CNN generally focused on each implant's unique design features to make a decision. Regarding the time spent performing the implant identification, the CNN accomplished this task in ~0.06 s per radiograph. The surgeon's identification time varied based on the method they utilized. When using their personal experience to identify the THR implant design, they spent negligible time. However, the identification time increased to an average of 8.4 min (standard deviation 6.1 min) per radiograph when they used another identification method (online search, consulting with the orthopedic company representative, and using image atlas), which occurred in about 17% of cases in the test subset (40 radiographs). CONCLUSIONS: CNNs such as the one developed in this study can be used to automatically identify the design of a failed THR femoral implant preoperatively in just a fraction of a second, saving time and in some cases improving identification accuracy.

Detecting total hip replacement prosthesis design on plain radiographs using deep convolutional neural network.

Identifying the design of a failed implant is a key step in the preoperative planning of revision total joint arthroplasty. Manual identification of the implant design from radiographic images is time-consuming and prone to error. Failure to identify the implant design preoperatively can lead to increased operating room time, more complex surgery, increased blood loss, increased bone loss, increased recovery time, and overall increased healthcare costs. In this study, we present a novel, fully automatic and interpretable approach to identify the design of total hip replacement (THR) implants from plain radiographs using deep convolutional neural network (CNN). CNN achieved 100% accuracy in the identification of three commonly used THR implant designs. Such CNN can be used to automatically identify the design of a failed THR implant preoperatively in just a few seconds, saving time and improving the identification accuracy. This can potentially improve patient outcomes, free practitioners' time, and reduce healthcare costs.

Longitudinal Model of Periprosthetic Joint Infection in the Rat.

The majority of periprosthetic joint infections occur shortly after primary joint replacement (<3 months) and require the removal of all implant components for the treatment period (~4 months). A clinically relevant animal model of periprosthetic infection should, therefore, establish an infection with implant components in place. Here, we describe a joint replacement model in the rat with ultrahigh molecular weight polyethylene (UHMWPE) and titanium components inoculated at the time of surgery by methicillin-sensitive Staphylococcus aureus (S. aureus), which is one of the main causative microorganisms of periprosthetic joint infections. We monitored the animals for 4 weeks by measuring gait, weight-bearing symmetry, von Frey testing, and micro-CT as our primary endpoint analyses. We also assessed the infection ex vivo using colony counts on the implant surfaces and histology of the surrounding tissues. The results confirmed the presence of a local infection for 4 weeks with osteolysis, loosening of the implants, and clinical infection indicators such as redness, swelling, and increased temperature. The utility of specific gait analysis parameters, especially temporal symmetry, hindlimb duty factor imbalance, and phase dispersion was identified in this model for assessing the longitudinal progression of the infection, and these metrics correlated with weight-bearing asymmetry. We propose to use this model to study the efficacy of using different local delivery regimens of antimicrobials on addressing periprosthetic joint infections. Statement of clinical significance: We have established a preclinical joint surgery model, in which postoperative recovery can be monitored over a multi-week course by assessing gait, weight-bearing, and allodynia. This model can be used to study the efficacy of different combinations of implant materials and medication regimens. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1101-1112, 2020.

Delivery of bupivacaine from UHMWPE and its implications for managing pain after joint arthroplasty.

Total joint replacement is a widely used and successful surgical approach. Approximately 7 million US adults are currently living with a hip or knee replacement. However, the surgical procedures for total joint replacement are associated with significant postoperative pain, and current strategies do not adequately address this pain, which leads to patient dissatisfaction, reduced mobility, and increased risk of opioid addiction. We hypothesized that the ultra-high-molecular-weight polyethylene (UHMWPE) bearing surfaces used in total joint prosthetics could provide sustained release of the local anesthetic bupivacaine to provide relief from joint pain for an extended period of time after surgery. In this paper, we describe the production of bupivacaine-loaded UHMWPE (BPE) and measure the in vitro bupivacaine release kinetics of BPE. We found that bupivacaine could be released from BPE at clinically relevant rates for up to several days and that BPE possesses antibacterial effects. Therefore, bupivacaine-loaded UHMWPE is a promising material for joint replacement prostheses, and future studies will evaluate its safety and efficacy in in vivo models. STATEMENT OF SIGNIFICANCE: Total joint replacement is associated with significant pain and risk of infection. In our paper, we introduce bupivacaine-loaded ultra-high-molecular-weight polyethylene (BPE), which releases bupivacaine, a pain-treating drug, at doses comparable to currently used doses. Additionally, BPE inhibits the growth of infection-causing bacteria. Therefore, BPE may be able to reduce both postsurgical pain and risk of infection, potentially treating two of the most prominent complications associated with total joint replacement. To our knowledge, this is the first development of a material that can address both complications, and devices incorporating BPE would represent a significant advancement in joint arthroplasty prosthetics. More generally, the incorporation of therapeutic agents into ultra-high-molecular-weight polyethylene could impact many orthopedic procedures owing to its ubiquity.

The Role of Crosslinked Polyethylene in Reducing Aggregated Costs of Total Hip Arthroplasty in the United States.

BACKGROUND: Widespread adoption of crosslinked polyethylene for the acetabular articular surface for total hip arthroplasty has substantially reduced revision rates and dislocation rates. We aim to provide estimates of the resulting magnitude of the annual reduction in aggregated costs of total hip arthroplasty surgery in the United States. METHODS: After we obtained, from the literature, the contrasting mid-term rates of revisions and dislocations of total hip arthroplasty using conventional polyethylene vs those using crosslinked polyethylene, specifically from only registry studies and prospective, randomized controlled studies, we multiplied these incidence figures by the cost estimates of these failures to generate approximations of the cost savings in the United States from the use of crosslinked polyethylene. RESULTS: The estimates suggest that in the United States these savings might be one billion dollars per annual cohort over a 15-year duration. CONCLUSION: The use of crosslinked polyethylene has reduced substantially the overall costs of total hip arthroplasty surgery in the United States.

Cadaver-Specific Models for Finite-Element Analysis of Iliopsoas Impingement in Dual-Mobility Hip Implants.

BACKGROUND: Joint dislocation is a major cause of failure in total hip arthroplasty. Dual-mobility implants provide a femoral head diameter that can match the native hip size for greater stability against dislocation. However, such large heads are prone to impingement against surrounding soft tissues. To address this concern, the concept of an anatomically contoured dual-mobility implant was evaluated using cadaver-specific finite-element analysis (FEA). METHODS: The stiffness of 10 iliopsoas tendons was measured and also 3D bone models, contact pressure, and iliopsoas tendon stress were evaluated for 2 implant designs according to a previous cadaveric experiment. The iliopsoas interaction with an anatomically contoured and conventional dual-mobility implant was analyzed throughout hip flexion. RESULTS: The tensile test of cadaveric iliopsoas tendons revealed an average linear stiffness of 339.4 N/mm, which was used as an input for the FEA. Tendon-liner contact pressure and tendon von Mises stress decreased with increasing hip flexion for both implants. Average contact pressure and von Mises stresses were lower in the anatomically contoured design compared with the conventional implant across all specimens and hip flexion angles. CONCLUSIONS: This study was built upon a previous cadaver study showing reduced tenting of the iliopsoas tendon for an anatomically contoured design compared with a conventional dual-mobility implant. The present cadaver-specific FEA study found reduced tendon-liner contact pressure and tendon stresses with contoured dual-mobility liners. Anatomical contoured design may be a solution to avoid anterior soft-tissue impingement when using hip prostheses with large femoral heads.

In-vitro oxidation model for UHMWPE incorporating synovial fluid lipids.

Post-irradiation melting of ultra-high molecular weight polyethylene (UHMWPE) reduced the oxidation potential of UHMWPE in vivo. After mid-term (5-10 years) use in vivo, there is detectable oxidation in irradiated and melted joint implant retrievals. The absorption of the synovial fluid lipid squalene was identified as a possible factor initiating oxidation. We investigated the role of lipids in UHMWPE oxidation by asking: (1) Do other synovial fluid lipids initiate oxidation in irradiated and melted UHMWPE?; (2) What is the effect of the absorption of multiple lipids on UHMWPE oxidation?; (3) How does lipid-initiated oxidation in vitro compare to what is observed in long-term retrievals? We diffused emulsified single and mixed lipids into irradiated and melted UHMWPE and accelerated aged them. We analyzed the oxidation in these samples and in four long-term highly crosslinked, irradiated, and melted Longevity™ UHMWPE liner retrievals (in vivo for up to 190 months) using Fourier Transform Infrared Spectroscopy (FTIR). We showed that lipids other than squalene could initiate oxidation in UHMWPE and that the types of absorbed lipids determined the amount of resultant oxidation. Although mixed lipids doping and accelerated aging reproduced the average and maximum oxidation values and oxidation products observed in vivo, the oxidation depth profile and its effect on cross-link density was different. One reason for this was the variability of oxidation in retrievals, suggesting additional factors contributing to oxidation. The understanding of oxidative processes in vivo and the development of clinically relevant in vitro protocols to evaluate implant materials is crucial for their long-term performance. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1833-1839, 2018.

Inferior Radiographic and Functional Outcomes With Modular Stem in Metal-on-Metal Total Hip Arthroplasty.

BACKGROUND: Data on the association between stem type and metal-on-metal (MoM) total hip arthroplasty (THA) performance are limited. The aim of this study is to investigate the effect of stem type on the prevalence of osteolysis and radiolucency, blood metal ion levels, and functional outcomes in patients with Articular Surface Replacement THA (ASR XL), a type of MoM THA. METHODS: We analyzed 539 unilateral MoM THAs coupled with Summit (48%), Corail (35%), or S-ROM (17%) hip stems at a mean follow-up of 6.4 years. Fifty-four percent of the patients were male, and the mean age was 60 years. We studied radiographs, patient-reported outcome measures, and ion levels. RESULTS: Patients with S-ROM hip stems were 3.8 times more likely to have osteolysis (P = .003) and 7.6 times more likely to have radiolucency (P < .001) than those treated with Summit hip stems. In addition, patients treated with S-ROM hip stems scored worse than those with Summit hip stems in 4 of the 5 patient-reported outcome measures: Harris Hip Score, Visual Analog Scale pain, University of California at Los Angeles activity, and EQ-5D index. All these differences were statistically significant and ranged from 5% to 10%, which is clinically significant. CONCLUSION: Patients with S-ROM hip stems had inferior functional and radiographic results compared to patients with Summit hip stems. Retrieval studies on large diameter head MoM THA and close follow-up of these patients with hip stems are needed to understand the mechanism causing the differences in outcomes between these stem types.

Risk factors for mid-term revision surgery in patients with articular surface replacement total hip arthroplasty.

INTRODUCTION: This study assessed the associations between gender and implant survival, as well as adverse local tissue reaction (ALTR), in patients with articular surface replacement (ASR) XL total hip arthroplasty (THA). Secondly, we sought to report the differences between genders in metal ion levels and patient reported outcome measures (PROMs) in these patients. METHODS: 563 unilateral ASR XL THA patients were enrolled in a multicentre follow-up study at a mean of 6.4 years after index surgery. All patients had blood metal ion levels and PROMs obtained annually, and a valid anteroposterior pelvis radiograph. A sub-set of patients from a single centre had annual MRI performed and were analysed for the presence of moderate-to-severe ALTR. RESULTS: 60 hips (11%) were revised during the study period. The only variables found to be associated with revision surgery in patients with unilateral THA were VAS pain (hazard ratio [HR], 1.35; p<0.001) and elevated cobalt metal ion levels (HR, 1.05; p<0.001). No variables assessed were found to be associated with prevalence of ALTR. Chromium concentrations were greater in female patients than males, while cobalt levels were similar between genders. Males reported higher HHS, EQ-5D and UCLA scores than females. CONCLUSIONS: Both males and females with metal-on-metal THA implants should be followed with equal vigilance as gender does not appear to be associated with poor outcomes, such as revision surgery and presence of ALTR.

ACL substitution may improve kinematics of PCL-retaining total knee arthroplasty.

PURPOSE: One of the key factors responsible for altered kinematics and joint stability following contemporary total knee arthroplasty (TKA) is resection of the anterior cruciate ligament (ACL). However, ACL retention can present several technical challenges, and in some cases may not be viable due to an absent or nonfunctional ACL. Therefore, the goal of this research was to investigate whether substitution of the ACL through an anterior post mechanism could improve kinematic deficits of contemporary posterior cruciate ligament (PCL) retaining implants. METHODS: Kinematic analysis of different implant types was done using KneeSIM, a previously established dynamic simulation tool. Walking, stair-ascent, chair-sit, and deep knee bend were simulated for an ACL-substituting (PCL-retaining) design, a bi-cruciate-retaining and ACL-sacrificing (PCL-retaining) implant, as well as the native knee. The motion of the femoral condyles relative to the tibia was recorded for kinematic comparisons. RESULTS: The ACL-substituting and ACL-retaining implants provided similar kinematic improvements over the ACL-sacrificing implant, by reducing posterior femoral shift in extension and preventing paradoxical anterior sliding. During all simulated activities, the ACL-sacrificing implant showed between 7 and 8 mm of posterior shift in extension in contrast to the ACL-retaining implant and the ACL-substituting design, which showed overall kinematic trends similar to the native knee. CONCLUSION: The absence of ACL function has been linked to abnormal kinematics and joint stability in patients with contemporary TKA. ACL-substituting implants could be a valuable treatment option capable of overcoming the limitations of contemporary TKA, particularly when retaining the native ACL is not feasible or is challenging.

Increased oxidative protection by high active vitamin E content and partial radiation crosslinking of UHMWPE.

Vitamin E stabilization successfully improved long-term oxidation resistance of wear-resistant ultra-high-molecular-weight polyethylene (UHMWPE) used for joint implants. Stabilization can be achieved by blending an antioxidant into the UHMWPE resin powder before consolidation and irradiation. Balancing the wear resistance and vitamin E content in the blend is the current challenge with this approach, because vitamin E hinders crosslinking of UHMWPE during irradiation, which decreases wear resistance. The vitamin E concentration in the blend is generally limited to less than 0.3 wt%. Wear- and oxidation-resistant UHMWPE has been obtained previously by consolidating blends of pre-irradiated UHMWPE powders (XPE) into an unmodified polyethylene matrix (PE), where the improvement in wear rate depended on the radiation dose and fraction of XPE. We hypothesized that increasing the vitamin E content in the unirradiated matrix would not compromise wear and would further improve the oxidative stability of XPE/PE blends. Pin-on-disk wear testing showed that the XPE/PE blends containing 0.1-1.0 wt% vitamin E in the matrix had comparable wear rates. We used an aggressive accelerated aging test in the presence of the pro-oxidant squalene and oxidation induction time (OIT) test and found that higher amounts of vitamin E resulted in stronger oxidation resistance for XPE/PE blends. The mechanical strength and toughness of the blends were not affected by changing the vitamin E content in the matrix. Stabilizing UHMWPE with higher vitamin E content may extend the service life of UHMWPE implants. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1860-1867, 2018.

Effects of vitamin E-diffused highly cross-linked UHMWPE particles on inflammation, apoptosis and immune response against S. aureus.

Particle-induced osteolysis and periprosthetic joint infection (PJI) are closely associated with periprosthetic tissue immune function. The objective of this study was to determine the effects of polyethylene particles on inflammation and response against S. aureus. Effects that vitamin E-diffused cross-linked UHMWPE (VE-PE) particles had on apoptosis, inflammation, and bactericidal activities compared to virgin cross-linked UHMWPE (control PE) particles were examined. Murine RAW 264.7 macrophages exposed to VE-PE particles in vitro were less apoptotic, secreted less tumor necrosis factor (TNF)-α, and responded more effectively against lipopolysaccharide or S. aureus compared to control PE particles. Implantation of VE-PE particles in murine calvaria in vivo caused less reactive oxygen species generation, less apoptosis, and less osteolysis compared to control PE particles. Implantation of PE particles in mice calvaria for 28 days, followed by inoculation with S. aureus in the same site where PE particles were implanted, demonstrated enhanced S. aureus clearance in the VE-PE group at day 33 after inoculation. These findings indicate that VE-PE particles might be less inflammatory and might preserve innate immunity of local tissue, allowing for enhanced clearance of bacteria.

An intraluminal stent facilitates light-activated vascular anastomosis.

BACKGROUND: Photochemical tissue bonding (PTB) is a sutureless, light-activated technique that produces a watertight, microvascular repair with minimal inflammation compared to standard microsurgery. However, it is practically limited by the need for a clinically viable luminal support system. The aim of this study was to evaluate a hollow biocompatible stent to provide adequate luminal support to facilitate vascular anastomosis using the PTB technique. METHODS: Forty rats underwent unilateral femoral artery transection. Five rats were used to optimize the stent delivery method, and the remaining 35 rats were randomized into three groups: (1) standard suture repair with 10-0 nylon microsuture (SR), (2) standard suture repair over the stent (SR + S), or (3) PTB repair over stent (PTB + S). For the PTB group, a 2-mm overlapping cuff was painted with 0.1% (wt/vol) Rose Bengal then illuminated for 30 seconds on each side (532 nm, 0.5 W/cm, 30 J/cm). Anastomotic leak and vessel patency (immediate, 1 hour, and 1 week postoperatively) were assessed. RESULTS: Vessels in all three groups were patent immediately and at 1 hour postoperatively. After 1 week, all animals displayed patency in the SR group, while only 5 of 14 and 2 of 8 surviving animals had patent vessels in the PTB + S and SR + S groups, respectively. CONCLUSIONS: This study demonstrated successful use of an intraluminal stent for acute microvascular anastomosis using the PTB technique. However, the longer-term presence of the stent at the anastomotic site led to thrombosis in multiple cases. A rapidly dissolvable stent should facilitate a light-activated microvascular anastomosis with excellent long-term patency.

Scoring the Current Risk Stratification Guidelines in Follow-up Evaluation of Patients After Metal-on-Metal Hip Arthroplasty: A Proposal for a Metal-on-Metal Risk Score Supporting Clinical Decision-Making.

BACKGROUND: In the follow-up evaluation of patients with metal-on-metal (MoM) hip replacements, current evidence suggests that orthopaedic surgeons should avoid reliance on any single investigative tool. Current risk stratification guidelines can be difficult to interpret because they do not provide guidance when there are several risk factors in different groups (high and low risk). To improve the clinical utility of risk stratification guidelines, we designed a scoring system to assess the risk of revision. METHODS: The study population consisted of 1,709 patients (1,912 hips) enrolled in a multicenter follow-up study of a recalled MoM hip replacement. Eleven scoring criteria were determined on the basis of existing follow-up algorithm recommendations and consisted of patient-related factors, symptoms, clinical status, implant type, metal ion levels, and radiographic imaging results. Forward stepwise logistic regression was conducted to determine the minimum set of predictive variables for the risk of revision and to assign variable weights. The MoM risk score for each hip was then created by averaging the weighted values of each predictive variable. RESULTS: Receiver operating characteristic curve analysis yielded good discrimination between all revised and unrevised hips, with an area under the curve of 0.82 (p < 0.001). The odds of revision for the group with a high MoM risk score were increased by 5.8-fold (95% confidence interval [CI], 3.1 to 11.0) relative to the moderate risk group and by 21.8-fold (95% CI, 9.9 to 48.0) compared with the low risk group. CONCLUSIONS: Although the use of MoM hip arthroplasty has been limited since 2010, we continue to be faced with the follow-up and risk assessment of thousands of patients who have not had a revision. As more knowledge about risk stratification is gained, the complexity of the algorithms is expected to increase. We propose the use of the MoM risk score as a tool to aid in the clinical decision-making process. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Worse health-related quality of life and hip function in female patients with elevated chromium levels.

Background and purpose - Blood metal ion levels can be an indicator for detecting implant failure in metal-on-metal (MoM) hip arthroplasties. Little is known about the effect of bilateral MoM implants on metal ion levels and patient-reported outcomes. We compared unilateral patients and bilateral patients with either an ASR hip resurfacing (HR) or an ASR XL total hip replacement (THR) and investigated whether cobalt or chromium was associated with a broad spectrum of patient outcomes. Patients and methods - From a registry of 1,328 patients enrolled in a multicenter prospective follow-up of the ASR Hip System, which was recalled in 2010, we analyzed data from 659 patients (311 HR, 348 THR) who met our inclusion criteria. Cobalt and chromium blood metal ion levels were measured and a 21-item patient-reported outcome measures (PROMs) questionnaire was used mean 6 years after index surgery. Results - Using a minimal threshold of ≥7 ppb, elevated chromium ion levels were found to be associated with worse health-related quality of life (HRQoL) (p < 0.05) and hip function (p < 0.05) in women. These associations were not observed in men. Patients with a unilateral ASR HR had lower levels of cobalt ions than bilateral ASR HR patients (p < 0.001) but similar levels of chromium ions (p = 0.09). Unilateral ASR XL THR patients had lower chromium and cobalt ion levels (p < 0.005) than bilateral ASR XL THR patients. Interpretation - Chromium ion levels of ≥7 ppb were associated with reduced functional outcomes in female MoM patients.