A vertebral skeletal stem cell lineage driving metastasis.

Vertebral bone is subject to a distinct set of disease processes from long bones, including a much higher rate of solid tumour metastases1-4. The basis for this distinct biology of vertebral bone has so far remained unknown. Here we identify a vertebral skeletal stem cell (vSSC) that co-expresses ZIC1 and PAX1 together with additional cell surface markers. vSSCs display formal evidence of stemness, including self-renewal, label retention and sitting at the apex of their differentiation hierarchy. vSSCs are physiologic mediators of vertebral bone formation, as genetic blockade of the ability of vSSCs to generate osteoblasts results in defects in the vertebral neural arch and body. Human counterparts of vSSCs can be identified in vertebral endplate specimens and display a conserved differentiation hierarchy and stemness features. Multiple lines of evidence indicate that vSSCs contribute to the high rates of vertebral metastatic tropism observed in breast cancer, owing in part to increased secretion of the novel metastatic trophic factor MFGE8. Together, our results indicate that vSSCs are distinct from other skeletal stem cells and mediate the unique physiology and pathology of vertebrae, including contributing to the high rate of vertebral metastasis.

Dispersion interaction between thin conducting cylinders.

The ground state and excited state resonance dipole-dipole interaction energy between two elongated conducting molecules is explored in this study. We review the current status for ground state interactions. This interaction is found to be of a much longer range than in the case when the molecules are pointlike and nonconducting. These are well known results found earlier by Davies, Ninham, and Richmond, and later, using a different formalism, by Rubio and co-workers. We show how the theory can be extended to excited state interactions. A characteristic property observed from our calculation is that the interaction energy dependence on separation (R) follows f(R)/R2 for both resonance and van der Waals cases in the long-range limit. Under some limits, f(R) has a logarithmic dependency, while under others, it has constant values. We predict an unusual slow decay rate for the energy transfer between conducting molecules.

Discovery of a periosteal stem cell mediating intramembranous bone formation.

Bone consists of separate inner endosteal and outer periosteal compartments, each with distinct contributions to bone physiology and each maintaining separate pools of cells owing to physical separation by the bone cortex. The skeletal stem cell that gives rise to endosteal osteoblasts has been extensively studied; however, the identity of periosteal stem cells remains unclear1-5. Here we identify a periosteal stem cell (PSC) that is present in the long bones and calvarium of mice, displays clonal multipotency and self-renewal, and sits at the apex of a differentiation hierarchy. Single-cell and bulk transcriptional profiling show that PSCs display transcriptional signatures that are distinct from those of other skeletal stem cells and mature mesenchymal cells. Whereas other skeletal stem cells form bone via an initial cartilage template using the endochondral pathway4, PSCs form bone via a direct intramembranous route, providing a cellular basis for the divergence between intramembranous versus endochondral developmental pathways. However, there is plasticity in this division, as PSCs acquire endochondral bone formation capacity in response to injury. Genetic blockade of the ability of PSCs to give rise to bone-forming osteoblasts results in selective impairments in cortical bone architecture and defects in fracture healing. A cell analogous to mouse PSCs is present in the human periosteum, raising the possibility that PSCs are attractive targets for drug and cellular therapy for skeletal disorders. The identification of PSCs provides evidence that bone contains multiple pools of stem cells, each with distinct physiologic functions.

The Infected Polypropylene Mesh: When Does Biofilm Form and Which Antiseptic Solution Most Effectively Removes It?

BACKGROUND: Polypropylene (PPE) mesh is commonly utilized to reconstruct catastrophic extensor mechanism disruptions in revision total knee arthroplasty. Unfortunately, these procedures are associated with a high rate of periprosthetic joint infection. The purpose of the current study was to: 1) visualize and quantify the progression of bacterial biofilm growth on PPE-mesh; and 2) determine which antiseptic solutions effectively remove viable bacteria. METHODS: Knitted PPE mesh samples were cultured with either methicillin-sensitive Staphylococcus aureus (MSSA) or Escherichia coli (E. coli) for 7 days, with regular quantification of colony forming units (CFUs) and visualization using scanning electron microscopy to identify maturity. Immature (24 hour) and mature (72 hour) biofilm was treated with one of 5 commercial antiseptics for 3 minutes. A 0.05% chlorhexidine gluconate, a surfactant-based formulation of ethanol, acetic acid, sodium acetate, benzalkonium chloride, diluted povidone-iodine (0.35%), undiluted (10%) povidone-iodine, and 1:1 combination of 10% povidone-iodine and 3% hydrogen peroxide. A 3-log reduction in CFUs compared to saline was considered clinically meaningful. RESULTS: The CFU counts plateaued, indicating maturity, at 72 hours for both MSSA and E. coli. The scanning electron microscopy confirmed confluent biofilm formation after 72 hours. The 10% povidone-iodine was clinically effective against all MSSA biofilms and immature E. coli biofilms. The 10% povidone-iodine with hydrogen peroxide was effective in all conditions. Only 10% povidone iodine formulations produced significantly (P < .0083) reduced CFU counts against mature biofilms. CONCLUSIONS: Bacteria rapidly form biofilm on PPE mesh. Mesh contamination can be catastrophic, and clinicians should consider utilizing an antiseptic solution at the conclusion of mesh implantation. Undiluted povidone-iodine with hydrogen peroxide should be considered when attempting to salvage infected PPE mesh.

A Consecutive Series of Vancouver B2 Periprosthetic Femur Fractures Treated With Contemporary Monoblock Versus Modular Revision Stems: Clinical and Radiographic Outcomes.

BACKGROUND: Tapered fluted titanium (TFT) stems are the implant design of choice for managing Vancouver B2 periprosthetic femur fractures (PFFs), producing reliable results over the past few decades. The aim of this study was to compare the radiographic and clinical outcomes of Vancouver B2 PFFs treated with contemporary monoblock versus modular TFTs. METHODS: A consecutive series of 113 patients (72 women, 64%, mean age 70 years [range, 26 to 96]) who had a B2 PFF were treated with either a monoblock (n = 42) or modular (n = 71) TFT stem between 2008 and 2021. The mean body mass index was 30 ± 7. The mean follow-up was 2.9 years. A radiographic review was performed to assess leg length and offset restoration, endosteal cortical contact length, and stem subsidence. Kaplan-Meier analyses were used to determine survivorship without revision, reoperation, or dislocation. RESULTS: There was no difference in the restoration of leg length (0.3 ± 8.0 mm) or offset (2.8 ± 8.2 mm) between the monoblock and modular cohorts (P > .05). Mean endosteal cortical contact length (47.2 ± 26.6 versus 46.7 ± 2 6.4 mm, P = .89) and stem subsidence (2.7 ± 3.5 versus 2.4 ± 3.2 mm, P = .66) did not differ. No difference in patient-reported outcome measures (Hip Disability and Osteoarthritis Outcome Score-Joint Replacement; Veterans RAND 12 Item Health Survey Physical and Mental; visual analog score; and Lower Extremity Activity Scale) between the groups was observed. Survivorship at 2 years free from reoperation, revision, and dislocation was 90.4, 90.3, and 97.6%, respectively, for the monoblock cohort; and 84.0, 86.9, and 90.0%, respectively, for the modular cohort. CONCLUSIONS: No significant differences in radiographic or clinical outcomes were observed between patients treated with monoblock or modular TFTs in this large series of B2 PFFs.

Origin of anomalously stabilizing ice layers on methane gas hydrates near rock surface.

Gas hydrates (GHs) in water close to freezing temperatures can be stabilised via the formation of ice layers. In a recent work [Boström et al., Astron. Astrophys., A54, 650, 2021], it was found that a surface region with partial gas dilution could be essential for obtaining nano- to micron-sized anomalously stabilizing ice layers. In this paper, it is demonstrated that the Casimir-Lifshitz free energy in multi-layer systems could induce thinner, but more stable, ice layers in cavities than those found for gas hydrates in a large reservoir of cold water. The thickness and stability of such ice layers in a pore filled with cold water could influence the leakage of gas molecules. Additional contributions, e.g. from salt-induced stresses, can also be of importance, and are briefly discussed.

Genetic Risk Factors for End-Stage Hip Osteoarthritis Treated With Total Hip Arthroplasty: A Genome-wide Association Study.

BACKGROUND: Although a genetic component to hip osteoarthritis (OA) has been described, focused evaluation of the genetic components of end-stage disease is limited. We present a genomewide association study for patients undergoing total hip arthroplasty (THA) to characterize the genetic risk factors associated with end-stage hip osteoarthritis (ESHO), defined as utilization of the procedure. METHODS: Patients who underwent primary THA for hip OA were identified in a national patient data repository using administrative codes. Fifteen thousand three hundred and fifty-five patients with ESHO and 374,193 control patients were identified. Whole genome regression of genotypic data for patients who underwent primary THA for hip OA corrected for age, sex, and body mass index (BMI) was performed. Multivariate logistic regression models were used to evaluate the composite genetic risk from the identified genetic variants. RESULTS: There were 13 significant genes identified. Composite genetic factors resulted in an odds ratio 1.04 for ESHO (P < .001). The effect of genetics was lower than that of age (Odds Ratio (OR): 2.38; P < .001) and BMI (1.81; P < .001). CONCLUSION: Multiple genetic variants, including 5 novel loci, were associated with end-stage hip OA treated with primary THA. Age and BMI were associated with greater odds of developing end-stage disease when compared to genetic factors.

Does Acetabular Bone Loss Severity Associate With Patient-Reported Outcome Measures and Reoperation Rate in Revision Total Hip Arthroplasty?

BACKGROUND: Acetabular bone loss is a challenging clinical problem when performing revision total hip arthroplasty (rTHA). This study aimed to evaluate how acetabular bone loss severity influences (1) clinical outcomes and (2) patient-reported outcome measures (PROMs) in rTHA patients. METHODS: Patients who underwent rTHA with acetabular component revision from January 2016 to February 2022 were included. Treating surgeons determined Paprosky acetabular bone loss classification intraoperatively. Patients were grouped based on numeric classification (PI, PII, or PIII) to categorize severity. Hip disability and Osteoarthritis Outcome Score for Joint Replacement (HOOS, JR.) and Lower Extremity Activity Scale (LEAS) score were collected preoperatively and 1 year postoperatively. There were 197 patients included. Paprosky classification was PI for 47 patients (23.9%), PII for 113 patients (57.4%), and PIII for 37 patients (18.8%). Mean clinical follow-up was 29 months (range, 1 to 69). RESULTS: Reoperation rate was 0% (0 patients), 6.2% (7 patients), and 10.8% (4 patients) for PI, PII and PIII groups respectively (P = .052). Mean preoperative HOOS, JR. and LEAS for PI, PII and PIII groups were significantly different, but 1-year postoperative HOOS, JR. and LEAS did not differ significantly. Rates of HOOS, JR. minimal clinically important difference achievement differed significantly between bone loss groups. CONCLUSION: In this study of rTHA patients, greater acetabular bone loss severity was associated with worse preoperative PROMs and trended toward higher reoperation rate. Postoperative PROMs for bone loss severity groups were statistically similar. Patients who had worse acetabular bone loss were more likely to achieve HOOS, JR. minimal clinically important difference postoperatively. LEVEL OF EVIDENCE: III.

Femoral Component Undersizing and Alignment are Risk Factors for Early Periprosthetic Femur Fracture.

BACKGROUND: Known risk factors for early periprosthetic femur fracture (PFF) following total hip arthroplasty (THA) include poor bone quality and the use of cementless implants. The association between femoral component size and alignment and the risk of early PFF is not well described. We evaluated radiographic parameters of femoral component sizing and alignment as risk factors for early PFF. METHODS: From 16,065 primary cementless THAs, we identified 66 cases (0.41%) of early PFFs (<90 days from index THA) at a single institution between 2016 and 2020. Sixty early PFFs were (1:2) matched to 120 controls based on the femoral component model, offset, surgical approach, age, body mass index (BMI), and gender. Radiographic assessment of preoperative bone morphology and postoperative femoral component orientation included stem alignment, metaphyseal fill, and implant congruence with medial cortical bone. A multivariable logistic regression was built to identify radiographic risk factors associated with early PFF. RESULTS: Markers of preoperative bone quality including canal calcar ratio (P = .003), canal flare index (P < .001), anteroposterior canal bone ratio (CBR) (P < .001), and lateral CBR (P < .001) were statistically associated with PFF. Distance between the medial cortical bone and implant was greater in cases of PFF (2.5 mm vs 1.4 mm) (P < .001). A multivariate analysis demonstrated that a larger lateral metaphyseal CBR (Odds Ratio [OR] 5), valgus implant alignment (OR 5), and medial implant-bone incongruity (OR 2) increased the risk of early PFF. CONCLUSION: A larger lateral metaphyseal CBR, valgus component alignment, and implant incongruity with medial cortical bone posed the greatest radiographic risk for early PFF following cementless THA.

The AAHKS Best Podium Presentation Research Award: Comparing the Efficacy of Irrigation Solutions on Staphylococcal Biofilm Formed on Arthroplasty Surfaces.

BACKGROUND: A diverse array of antibacterial solutions is utilized by orthopedic surgeons in an attempt to disperse bacterial biofilm. Few studies compare these agents against biofilm grown on clinically relevant orthopedic biomaterials, such as plastic, acrylic cement, and porous titanium. METHODS: MSSA biofilm was grown on plastic 48-well plates, polymethylmethacrylate cement beads and porous Ti-6Al-4V acetabular screw caps. Antibacterial solutions were tested according to manufacturer guidance and included: isotonic saline, vancomycin (1 mg/mL), polymyxin-bacitracin (500,000 U/L-50,000 U/L), povidone-iodine 0.3%, povidone-iodine 10%, a 1:1 combination of povidone-iodine 10% & 4% hydrogen peroxide, polyhexamethylene biguanide (PHMB) and betaine 0.04%, a commercial solution containing chlorhexidine gluconate (CHG) 0.05%, and a commercial solution containing benzalkonium chloride and ethanol. Twenty four and 72-hour biofilms were exposed to solutions for 3 minutes to reproduce intraoperative conditions. Solution efficacy was measured through sonication of treated surfaces followed by counting colony forming units and validated with a resazurin assay to assess cell viability. Experiments were performed in triplicate and repeated at least once. A three-fold log reduction in CFU counts versus controls was considered as a measure of solution efficacy. RESULTS: Saline, vancomycin and polymyxin-bacitracin were ineffective compared to other solutions against planktonic MSSA. Povidone-iodine 10% and a 1:1 solution of povidone-iodine 10% and 4% hydrogen peroxide were the only effective solutions against biofilm across all three surfaces and time points. CONCLUSION: Commercial antibacterial solutions vary significantly in their efficacy against MSSA biofilm. Efficacy globally decreased as biofilm maturity increased. Increased solution cost did not confer increased efficacy.

Reduction of Opioid Quantities at Discharge After TKA Did Not Increase the Risk of Manipulation Under Anesthesia: An Institutional Experience.

BACKGROUND: In response to the opioid epidemic, our arthroplasty service sequentially reduced the opioid quantities prescribed at primary total knee arthroplasty (TKA) discharge. However, its effect on postdischarge pain control and rehabilitation is unknown. We assessed if this decrease was associated with an increase in the risk of manipulation under anesthesia (MUA). METHODS: We retrospectively reviewed 8799 patients undergoing primary TKA from 2016 to 2019 at a single institution. There were two institution-wide reductions in the amount of opioids prescribed at discharge; therefore, we divided patients into 3 periods (P1, P2, and P3). The mean discharge morphine milligram equivalents (MMEs) went from 900 MMEs to ~525 MMEs to ~320 MMEs in P1, P2, and P3, respectively. We analyzed MUA rates and if lower discharge MMEs was a risk factor for MUA in a multivariate model. We also compared refill patterns (rates, number, refill MMEs, and total MMEs) between MUA and non-MUA patients. RESULTS: The rate of MUA did not increase with reduced discharged opioids (5.5% in P1, 5.8% in P2, and 4.6% in P3, P = .74). In a multivariate analysis, discharge MMEs of <450 was not a significant risk factor for MUA. However, a diagnosis of chronic pain (OR = 1.86, P < .001) and an elevated body mass index (OR = 1.02 per unit increase, P < .001) were significant risk factors. We did not find significant differences in any opioid prescription refill patterns in MUA and non-MUA patients. CONCLUSION: Serial reductions in discharge MMEs after primary TKA did not significantly affect the rate of MUA, a surrogate marker for pain control and the rehabilitative process.

Analysis of Hip and Knee Reconstruction Questions on the Orthopedic In-Training Examination.

BACKGROUND: It is vital for orthopedic residents and residency programs to have a current understanding of the materials and resources utilized on the Orthopedic In-Training Examination (OITE) to tailor resident educational curricula accordingly. This study presents an updated analysis of the hip and knee section of the OITE. METHODS: All OITE questions related to hip and knee reconstruction over six examinations between 2014 and 2019 were analyzed for topic, subtopic, taxonomy, imaging modalities, resident performance, and references. RESULTS: There were 166 hip and knee reconstruction questions of 1600 OITE questions (10.4%) over a six-year period. The most commonly tested topics include mechanical properties of total knee and hip implants (10.8%), instability after THA (10.8%), periprosthetic fracture (10.2%), and prosthetic joint infection (10.2%). A total of 362 references were cited from 68 different sources. The most common sources were JOA, JBJS, JAAOS, and CORR, which were collectively responsible for 68% of all citations. There was an average publication lag of 7.1 years, with 75% of all citations falling within 10 years of the question date. Compared with a prior analysis from 2005 and 2009, there were significantly more complex multistep questions regarding treatment and fewer one-step knowledge recall questions (P = .003). Similarly, recent tests had significantly more questions involving interpretation of radiographs (55%, P < .001) and advanced imaging (9.6%, P < .001), compared with a decade ago. CONCLUSIONS: The OITE continues to evolve over time, incorporating recent literature and topics. The current analysis identifies high-yield topics and resources that can guide resident preparation for the OITE hip and knee section.

How Does Contact Length Impact Titanium Tapered Splined Stem Stability: A Biomechanical Matched Pair Cadaveric Study.

BACKGROUND: Titanium tapered stems (TTS) achieve fixation in the femoral diaphysis and are commonly used in revision total hip arthroplasty. The initial stability of a TTS is critical, but the minimum contact length needed and impact of implant-specific taper angles on axial stability are unknown. This biomechanical study was performed to better guide operative decision-making by addressing these clinical questions. METHODS: Two TTS with varying conical taper angles (2° spline taper vs 3.5° spline taper) were implanted in 9 right and left matched fresh human femora. The proximal femur was removed, and the remaining femoral diaphysis was prepared to allow for either a 2 cm (n = 6), 3 cm (n = 6), or 4 cm (n = 6) cortical contact length with each implanted stem. Stepwise axial load was then applied to a maximum of 2600N or until the femur fractured. Failure was defined as either subsidence >5 mm or femur fracture. RESULTS: All 6 femora with 2 cm of stem-cortical contact length failed axial testing, a significantly higher failure rate (P < .02) than the 4 out of 6 femora and all 6 femora that passed testing at 3 cm and 4 cm, respectively, which were not statistically different from each other (P = .12). Taper angle did not influence success rates, as each matched pair either succeeded or failed at the tested contact length. CONCLUSION: 4 cm of cortical contact length with a TTS demonstrates reliable initial axial stability, while 2 cm is insufficient regardless of taper angle. For 3 cm of cortical contact, successful initial fixation can be achieved in most cases with both taper angle designs.

2020 international practice patterns in adult joint reconstruction surgery: a survey of members of the International Society of Orthopaedic Centers.

PURPOSE: It is important to assess global trends in the practice of adult reconstruction orthopaedic surgery to understand how new evidence is being implemented. The International Society of Orthopaedic Centers (ISOC) is a consortium of academic orthopaedic centers whose members' practices likely reflect contemporary evidence and indicate how orthopaedic surgery residents and fellows are trained. METHODS: We administered a 65 question, electronic survey of adult reconstruction surgeons across the ISOC centers in September 2020 to assess practice patterns. Results were assessed using descriptive statistics or by modeling the underlying response distribution, and the analysis was stratified by hospital region. RESULTS: 79 surgeons across 19 ISOC centers in 5 continents (Asia, Australia, Europe, North America, South America) completed the survey. Selected findings include: in total hip arthroplasty (THA), the posterolateral approach was used for 71 ± 42% of THA (mean ± standard deviation) and the direct anterior approach in 18% ± 34%. In total knee arthroplasty, posterior-stabilized (66% ± 39%) and cruciate-retaining (19 ± 33%) implants were most common. Robots were available in 56% (44 of 79) of surgeons' centers more commonly in Asia, Australia, and North America. Tranexamic acid was routinely used in arthroplasty by 99% (78 of 79) of surgeons. Eighty-six percent (68 of 79) submit data to joint or other registries. Virtual visits were used for 13% ± 16% of outpatient visits and by 82% (64 of 79) of surgeons overall. CONCLUSIONS: These findings may be of use now for surgeons to consider the practices of their peers at high-volume academic institutions, and in the future as we track temporal trends.

Joint Replacements in Individuals With Skeletal Dysplasias: One Institution's Experience and Response to Operative Complications.

BACKGROUND: Skeletal dysplasias are a heterogeneous group of >400 genetic disorders characterized by abnormal bone growth. Many individuals experience joint pain and limitation, coming to require joint replacement much earlier than the average-statured population. In addition, prosthesis survival rate is less in the dysplastic population. The purpose of this study is to identify risk factors for surgery and provide recommendations to improve surgical outcomes. METHODS: This a retrospective review of 29 individuals with a skeletal dysplasia who had 64 joint replacements between April 1985 and January 2019 at a single institution. We collected demographics, physical examination, medical history, imaging studies, surgical indication, and complications. RESULTS: Spondyloepiphyseal dysplasia was the most common skeletal dysplasia (7), followed by pseudoachondroplasia (4) and multiple epiphyseal dysplasia (4). Average age of the cohort was 40.6 years (range 14-64). Hip arthroplasty (34) was the most commonly performed surgery. The majority of arthroplasties (75%) required custom components. Complication rate was 37.3%, most commonly pulmonary embolism (3) and pneumonia (3). Most complications (81.8%) occurred in individuals with either a pre-existing cardiopulmonary comorbidity or lumbar/sacral deformity. Body mass index did not correlate with complication severity (R = -0.042, P = .752) or rate (R = 0.006, P = .963). CONCLUSION: Surgical complications are highest in patients with pre-existing cardiopulmonary conditions. Body mass index does not predict complications in this cohort. Preoperative evaluations for individuals with skeletal dysplasias should include comprehensive work-up of spine issues and extraskeletal systems that present an operative risk. Intraoperative protocol should include special consideration for placement on the table, airway maintenance, and spinal cord monitoring in select cases.

Validation of the Hip Disability and Osteoarthritis Outcome Score and Knee Injury and Osteoarthritis Outcome Score Pain and Function Subscales for Use in Total Hip Replacement and Total Knee Replacement Clinical Trials.

BACKGROUND: Total hip replacement (THR)/total knee replacement (TKR) studies do not uniformly measure patient centered domains, pain, and function. We aim to validate existing measures of pain and function within subscales of standard instruments to facilitate measurement. METHODS: We evaluated baseline and 2-year pain and function for THR and TKR using Hip disability and Osteoarthritis Outcome Score (HOOS)/Knee Injury and Osteoarthritis Outcome Score (KOOS), with primary unilateral TKR (4796) and THR (4801). Construct validity was assessed by correlating HOOS/KOOS pain and activities of daily living (ADL), function quality of life (QOL), and satisfaction using Spearman correlation coefficients. Patient relevant thresholds for change in pain and function were anchored to improvement in QOL; minimally clinically important difference (MCID) corresponded to "a little improvement" and a really important difference (RID) to a "moderate improvement." Pain and ADL function scores were compared by quartiles using Kruskal-Wallis. RESULTS: Two-year HOOS/KOOS pain and ADL function correlated with health-related QOL (KOOS pain and Short Form 12 Physical Component Scale ρ = 0.54; function ρ = 0.63). Comparing QOL by pain and function quartiles, the highest levels of pain relief and function were associated with the most improved QOL. MCID for pain was estimated at ≥20, and the RID ≥29; MCID for function ≥14, and the RID ≥23. The measures were responsive to change with large effect sizes (≥1.8). CONCLUSION: We confirm that HOOS/KOOS pain and ADL function subscales are valid measures of critical patient centered domains after THR/TKR, and achievable thresholds anchored to improved QOL. Cost-free availability and brevity makes them feasible, to be used in a core measurement set in total joint replacement trials.

Impact of effective polarisability models on the near-field interaction of dissolved greenhouse gases at ice and air interfaces.

We present a theory for Casimir-Polder forces acting on greenhouse gas molecules dissolved in a thin water film. Such a nano-sized film has been predicted to arise on the surface of melting ice as stabilized by repulsive Lifshitz forces. We show that different models for the effective polarisability of greenhouse gas molecules in water lead to different predictions for how Casimir-Polder forces influence their extractions from the melting ice surface. For instance, in the most intricate model of a finite-sized molecule inside a cavity, dispersion potentials push the methane molecules towards the ice surface whereas the oxygen typically will be attracted towards the closest interface (ice or air). Previous models for effective polarisability had suggested that O2 would also be pushed towards the ice surface. Release of greenhouse gas molecules from the surface of melting ice can potentially influence climate greenhouse effects. With this model, we show that some molecules cannot escape from water as single molecules. Due to the contradiction of the results and the escape dynamics of gases from water, we extended the models to describe bubble filled with several molecules increasing their buoyancy force.

Can We Avoid Implant-selection Errors in Total Joint Arthroplasty?

BACKGROUND: Implant selection in the operating room is a manual process. This manual process combined with complex compatibility rules and inconsistent implant labeling may lead to implant-selection errors. These might be reduced using an automated process; however, little is known about the efficacy of available automated error-reduction systems in the operating room. QUESTIONS/PURPOSES: (1) How often do implant-selection errors occur at a high-volume institution? (2) What types of implant-selection errors are most common? METHODS: We retrospectively evaluated our implant log database of 22,847 primary THAs and TKAs to identify selection errors. There were 10,689 THAs and 12,167 TKAs included during the study period from 2012 to 2017; there were no exclusions and we had no missing data in this study. The system provided an output of errors identified, and these errors were then manually confirmed by reviewing implant logs for each case found in the medical records. Only those errors that were identified by the system were manually confirmed. During this time period all errors for all procedures were captured and presented as a proportion. Errors identified by the software were manually confirmed. We then categorized each mismatch to further delineate the nature of these events. RESULTS: One hundred sixty-nine errors were identified by the software system just before implantation, representing 0.74 of the 22,847 procedures performed. In 15 procedures, the wrong side was selected. Twenty-five procedures had a femoral head selected that did not match the acetabular liner. In one procedure, the femoral head taper differed from the femoral stem taper. There were 46 procedures in which there was a size mismatch between the acetabular shell and the liner. The most common error in TKA that occurred in 46 procedures was a mismatch between the tibia polyethylene insert and the tibial tray. There were 13 procedures in which the tibial insert was not matched to the femoral component according to the manufacturer's guidelines. Selection errors were identified before implantation in all procedures. CONCLUSIONS: Despite an automated verification process, 0.74% of the arthroplasties performed had an implant-selection error that was identified by the software verification. The prevalence of incorrect/mismatched hip and knee prostheses is unknown but almost certainly underreported. Future studies should investigate the prevalence of these errors in a multicenter evaluation with varying volumes across the involved sites. Based on our results, institutions and management should consider an automated verification process rather than a manual process to help decrease implant-selection errors in the operating room. LEVEL OF EVIDENCE: Level IV, therapeutic study.

Disruption of the Gut Microbiome Increases the Risk of Periprosthetic Joint Infection in Mice.

BACKGROUND: Periprosthetic joint infection (PJI) is one of the most devastating complications of total joint arthroplasty. Given the mortality and morbidity associated with PJI and the challenges in treating it, there has been increased interest in risk factors that can be modified before surgery. In this study, we used a novel mouse model to consider the role of the gut microbiome as a risk factor for PJI. QUESTIONS/PURPOSES: (1) Does the state of the gut microbiota before surgery influence the likelihood of developing an established infection in a mouse model of PJI? (2) How does the state of the gut microbiota before surgery influence the local and systemic response to the presence of an established infection in a mouse model of PJI? METHODS: Male C57Bl/6 mice were divided into two groups: those with modified microbiome [INCREMENT]microbiome (n = 40) and untreated mice (n = 42). In [INCREMENT]microbiome mice, the gut flora were modified using oral neomycin and ampicillin from 4 weeks to 16 weeks of age. Mice received a titanium tibial implant to mimic a joint implant and a local inoculation of Staphylococcus aureus in the synovial space (10 colony forming units [CFUs]). The proportion of animals developing an established infection in each group was determined by CFU count. The local and systemic response to established infection was determined using CFU counts in surrounding joint tissues, analysis of gait, radiographs, body weight, serum markers of inflammation, and immune cell profiles and was compared with animals that received the inoculation but resisted infection. RESULTS: A greater proportion of animals with disrupted gut microbiota had infection (29 of 40 [73%]) than did untreated animals (21 of 42 [50%]; odds ratio, 2.63, 95% CI, 1.04-6.61; p = 0.035). The immune response to established infection in mice with altered microbiota was muted; serum amyloid A, a marker of systemic infection in mice, was greater than in mice with disrupted gut microbiota with infection (689 µg/dL; range, 68-2437 µg/dL, p < 0.05); infection associated increases in monocytes and neutrophils in the spleen and local lymph node in untreated mice but not were not observed in mice with disrupted gut microbiota. CONCLUSIONS: The findings from this in vivo mouse model suggest that the gut microbiota may influence susceptibility to PJI. CLINICAL RELEVANCE: These preclinical findings support the idea that the state of the gut microbiome before surgery may influence the development of PJI and justify further preclinical and clinical studies to develop appropriate microbiome-based interventions.

Survivorship and Clinical Outcomes of Custom Triflange Acetabular Components in Revision Total Hip Arthroplasty: A Systematic Review.

BACKGROUND: Several studies have evaluated the survivorship and clinical outcomes of custom triflange acetabular component (CTAC) usage in complex acetabular revision; however, there remains no consensus on the overall performance of this custom implant design. We therefore performed a systematic review of the literature in order to examine survivorship and complication rate of CTAC usage. METHODS: A systematic review of the literature according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was performed. A comprehensive search of PubMed, MEDLINE, EMBASE, and the Cochrane Database of Systematic Reviews was conducted for English articles using various combinations of the keywords "custom triflange," "custom-made triflange," "acetabular triflange," "THA," "THR," "revision," "bone loss," "bone defect," and "pelvic discontinuity." RESULTS: In all, 17 articles met our inclusion criteria. A total of 579 CTACs were implanted. The all-cause revision-free survivorship was 82.7%. The overall complication rate was 29%. Dislocation and infection were the most common complications observed with an incidence of 11% and 6.2%, respectively. Nerve injuries following CTAC placement had an incidence of 3.8%. The incidence of CTAC aseptic loosening was 1.7%. Overall, patients had improved outcomes as documented by postoperative hip scores. CONCLUSION: Based on the current data, CTACs have a high complication rate but remain an efficacious treatment option in complex acetabular reconstructions. When dealing with patients with significant acetabular bone loss for revision total hip arthroplasty, surgeons should continue to consider CTACs as a viable option but educate patients as to the increased risk of postoperative complications and reoperations.