Abstract. OBJECTIVES. Staphylococcus aureus is one of the most common pathogens in orthopaedic biomaterial-associated infections. The transition of planktonic S. aureus to its biofilm phenotype is critical in the pathogenesis of biomaterial-associated infections and the development of antimicrobial tolerance, which leads to ineffective eradication in clinical practice. This study sought to elucidate the effect of non-lethal dispersion on antimicrobial tolerance in S. aureus biofilms. METHODS. Using a methicillin-sensitive S. aureus reference strain, the effect of non-lethal dispersion on gentamicin tolerance, cellular activity, and the intracellular metabolome of biofilm-associated bacteria were examined. Gentamicin tolerance was estimated using the dissolvable bead biofilm assay. Cellular activity was estimated using the triphenyltetrazolium chloride assay. Metabolome analysis was performed using tandem high-performance liquid chromatography and mass spectrometry. RESULTS. Non-lethal dispersion of biofilm-associated S. aureus was associated with a four-fold reduction in gentamicin tolerance and a 25% increase in cellular respiration of both dispersed and adherent cells. Metabolome analysis found non-lethal dispersion reduced intracellular levels of L-ornithine and L-proline, with increased levels of cyclic nucleotides (p<0.05) in both liberated cells and the remaining biofilm-associated bacteria. These metabolomic changes have previously been shown to be associated with inactivation of the carbon catabolite repression mechanism, which is a key regulatory gatekeeper in the cellular resuscitation of dormant S. aureus cells. CONCLUSION. The metabolomic pipeline described in this study presents a valuable tool in the elucidation of molecular mechanistic pathways in biofilm pathogenesis. Kreb's cycle reactivation, through the carbon catabolite repression regulatory mechanism, has been shown to be associated with the reversal of biofilm-associated gentamicin tolerance. Understanding of the biosynthetic changes associated with the biofilm state will assist in the discovery of novel therapeutic targets in the management of biomaterial-related infections. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Introduction:. Angular mismatch of the modular junction between the head and the trunion has been recognized as a contributing factor to fretting and corrosion of hip prostheses. Excessive angular-mismatch can lead to relative motion at the taper interface, and tribo-corrosion of the head-neck junction secondary to disruption of the passive oxide layer. Although manufacturing standards have been adopted to define acceptable tolerances for taper angles of mating components, recent investigations of failed components have suggested that stricter tolerances or changes in taper design may be necessary to avoid clinical failures secondary to excessive taper wear and corrosion. In this study we examine the effect of angular-mismatch on relative motion between the taper and bore subjected to normal gait load using finite element methods. Methods:. Computer simulations were executed using a verified finite element model (FEM), the results from which were determined to be consistent with literature. A stable, converging hexahedral mesh was defined for the trunnion (33648 elements) and a tetrahedral mesh for the femoral head (51182 elements). A friction-based sliding contact was defined at the taper-bore interface. A gait load of 1638N (2.34 × BW, BW = 700N) was applied at an angle of 30° to the trunnion axis (Figure 1) on an assembled FEM. A linear static solution was set up using Siemens NX-Nastran solver. Angular-mismatch was simulated by incrementing the conical half-angle of the bore to examine these cases: 0°, 0.005°, 0.010°, 0.015°, 0.030°, 0.050°, 0.075°, 0.100°, 0.200°and 0.300°. Results:. Relative interface micro-motion at the proximal-medial point of the taper demonstrated a lack of dependence upon angular-mismatch for tolerances up to 0.075° and a monotonic increase in micro-motion for higher tolerances (0.075–0.3 °; Figure 2). A similar trend was observed with respect to the average values of contact pressure, max von Mises stress and shear stress acting at the proximal-medial aspect of the taper (Figure 3). Non-linear correlation tests indicate a significant correlation (p < 0.0001) of mismatch angle with peak von Mises stress (r = 0.965) and relative micro-motion (r = 0.964). Discussion:. The FEA results corroborate the notion that high angular-mismatch tolerances have a deleterious effect of fretting at the trunnion-head interface. Although, stability of the implant did not appear to be compromised at relatively lower tolerances, the propensity for it is higher at higher mismatches. The simulation was, however, executed as a single-step static analysis ignoring the effect of cyclical loading often observed during gait. This abstract serves as a proof of concept to justify the further development of this FEA to study the effect of angular-mismatch tolerances on micro-motion at the trunnion-head interface. However, current results strongly indicate that tolerance for angular-mismatch can be more liberal without increasing the micro-motion and stresses at the trunnion-head interface. Significance: The effect of angular-mismatch suggests a threshold tolerance different from the industry accepted tolerance of 0.0167°. Mismatches smaller than 0.075° demonstrated only modest variation in the interface micro-motion. Additionally, the results corroborate recent clinical evidence that even with perfectly fit implants, the potential for interface micro-motion can lead to fretting-induced corrosion

Background. After surgical correction of thoracic scoliosis, an improvement in the cardio-respiratory adaptation to exercise would be expected because of the correction of the rib cage associated with the spinal deformity. This work intended to evaluate the physiologic responses to incremental exercise in patients undergoing surgical correction of adolescent idiopathic scoliosis (AIS). The hypothesis of this study was that the exercise limitations described in patients with AIS could be related with the physical deconditioning instead of being linked to the severity of the vertebral deformity. Methods. Cross-sectional study of the exercise tolerance in a series of patients with AIS type Lenke 1A, before and 2 years after surgical correction. Twenty patients with AIS and 10 healthy adolescents aged between 12 and 17 years old were evaluated. The average magnitude of the curves was 60.3±12.9 Cobb. Cardio-respiratory function was assessed before surgery and at 2-year follow-up by maximal exercise tolerance test on treadmill following a Bruce standard protocol. Maximal oxygen uptake (VO2), VCO2, expiratory volume (VE), and VE/VO2 ratio were registered. Results. Before surgery, AIS patients showed lower values than healthy controls in all cardio-respiratory parameters. The most important restrictions were the VO2max in ml/kg/min. (30.3±5.4 vs 49.9±7.5), VE (43.2±10.3 vs 82.3±10.7) and VE/CO2 ratio (25.0±3.9 vs 29.6±4.2). Contrary to expectations, two years after surgery most of these parameters decreased but differences with preoperative data were no statistically significant. Besides the great correction of the deformity (coronal plane, 71.5%; axial rotation, 49.3%), the cardio-respiratory tolerance to the exercise was not modified by surgery. Conclusions. Patients with moderate-severe AIS showed a limited tolerance to maximal exercise that does not change 2 years after surgery. This findings suggests that the reduced cardio-pulmonary function during exercise is not strictly associated to the spinal deformity, since great corrections of the spinal curves does not improve functional ventilatory parameters. In addition, the results point out a severe exercise deconditioning in AIS patients. Level of evidence. Level IV

Introduction: Existing fatigue studies of ACL fixation have two disadvantages. There is no agreed standard protocol, making comparison of various studies difficult and average results are presented, disregarding data spread. This may be over-optimistic, because approximately half the fixations will not achieve the average level. The effect of data spread can be summarised using the one-sided 80/80 lower tolerance limit (LTL). This LTL indicates the strength that at least 80% of fixations will reach, with an 80% probability. It is commonly used in engineering. We fatigue-tested a new resorbable composite screw (PLLA/tri-calcium phosphate) and a metal interference screw. We present average data and tolerance limits. Methods: Porcine BPTB grafts (Ø=9mm) were fixed inside tibial tunnels (Ø=10mm) using composite or metal screws. Each screw was tested for static pull-out strength (n=6) and cyclic loading to failure at 330N and 415N (n=5 each level). Means and standard deviations of pullout strength were compared. Log-log curves were fitted between force level and cycles to failure. LTLs were calculated. Results: During static loading, all repairs failed by graft pullout or tissue failure. During cyclic loading, all except one graft fixed with composite screws failed by pullout. Grafts fixed with metal screws failed by bone fracture in 60% of the cases. A composite screw loaded at 300N would last on average 272 cycles or at least (LTL) 7 cycles. At 200N the average and LTL were 38,218 and 966 cycles. Corresponding values for the metal screw were 263 (mean) and 12 (LTL) at 300N; and 12,454 and 564 at 200N. Discussion and Conclusions: Repairs with metal screw had higher pullout strength, but proved more prone to fatigue. Higher incidence of bone graft fracture in fatigue testing with metal screws suggests that their sharp threads act as stress risers. Fatigue testing of ACL reconstructions shows wide variation, due to several factors. Average levels are therefore over-optimistic and tolerance limits gives a better indication of screw performance. We suggest that tolerance limits should be reported in future studies

Aim. The use of piperacillin/tazobactam with vancomycin as empirical antimicrobial therapy (EAT) for prosthetic joint infection (PJI) has been associated with an increased risk of acute kidney injury (AKI), leading to propose cefepim as an alternative since 2017 in our reference center. The present study compared microbiological efficacy and tolerance of these two EAT strategies. Method. All patients with PJI empirically treated by vancomycin-cefepim (n=90) were prospectively enrolled in an observational study, and compared with vancomycin-piperacillin/tazobactam-treated historical controls (n=117), regarding: i) the proportion efficacious empirical regimen (i.e., at least one of the two molecules active against the identified organism(s) based on in vitro susceptibility testing); and ii) the incidence of empirical therapy-related adverse events (AE), classified according to the Common terminology criteria for AE (CTCAE). Results. Among the 146 (67.3%) documented infections, the EAT was considered as efficacious in 99 (99.0%) and 66 (98.5%) in the piperacillin-tazobactam and cefepim-treated patients, respectively (p=0.109). The rate of adverse events, and in particular AKI, was significantly higher in the vancomycin-piperacillin/tazobactam (n=38 [32.5%] and 32 [27.6%]) compared to the vancomycin-cefepim (n=13 [14.4%] and 5 [5.7%]) group (p=0.003 and <0.001, respectively). Of note, sex, age, and the proportion of patients receiving other nephrotoxics were similar among piperacillin/tazobactam- and cefepim-treated patients. However, in comparison with patients receiving cefepim, a higher modified Charlson's comorbitidy index (4 [IQR, 3–5] versus 2 [IQR, 2–4], p<0.001) has to be acknowledged, mainly related to a higher prevalence of baseline chronic renal injury (n=62, 53.4% versus n=34, 38.6%; p=0.035). Conclusions. The empirical use of vancomycin-cefepim in PJI was as efficient as vancomycin-piperacillin/tazobactam, and was associated with a significantly lower incidence of AKI

Purpose of the study: Because of its specific properties, linezolid (LZD) is an alternative to glycopeptides for the treatment of BJI causes by resistant Gram-positive cocci. The efficacy and tolerance of long-term (> 28d) administration remain to be determined with precision. Material and methods: This was a retrospective analysis of the files of patients who received long-term LZD for BJI with a post-treatment follow-up of at least twelve months. Results: Between January 2001 and December 2003, 68 patients (mean age 54.6 years) received LZD (600 mg/12h) intravenously then orally for a mean duration of 14.6 weeks on average (range 6–36 weeks). The orthopedic implants were infected in 31 patients (45.6%, 27 prostheses and 4 external fixators). A fistulization was diagnosed in 29 patients (42.6%). Medical and surgical treatment was undertaken in 51 patients (75%). Germs isolated from deep samples were staphylococci (n=57, 51 meti-R), and strepotococci (n=11). A polymicrobial infection was recorded in six patients (8.8%). Clinical success was achieved in 52 patients (76.5%) at the end of treatment, a result which was sustained for 48 of them to mean follow-up of 16.8 months (range 12–48). Sixty-three episodes of side effects were noted: anemia (n=29), peripheral neuropathy (n=9), nausea (n=14), headache (n=2), neutropenia (n=2), and thrombopenia (n=1), leading to discontinuation of LZD in 23 patients (33.8%) on average 11.9 weeks (range 6–36) after onset of treatment. Fifteen patients (22.1%) required transfusion. Discussion: Among the patients in this series with BJI, most caused by a multiresistant germ, the rate of success was satisfactory (48/68, 70.6%) with LZD. Treatment was associated with a high frequency of serious adverse effects leading to discontinuation in one-third of patients. Conclusion: Long-term treatment of BJI with LZD appears to be effective, including in patients with infected orthopedic material. Conversely, tolerance problems can limit is use to infections caused by mul-tiresistant Gram-positive cocci unresponsive to other compounds

Axial loading of the foot/ankle complex is an important injury mechanism in vehicular trauma, responsible for severe injuries such as calcaneus, talus and tibial pilon fractures. Axial loading may be applied to the leg externally, by the toepan and/or pedals, as well as internally by active muscle tension applied through the Achilles tendon during pre-impact bracing. In order to evaluate the effect of active muscle tension on the injury-tolerance of the foot/ankle complex, axial impact tests were performed on isolated lower legs, with and without experimentally stimulated muscle tension applied through the Achilles’ tendon. Acoustic emission was used to determine the exact time of fracture during the tests. The primary fracture mode was calcaneal fracture in both groups, but tibial pilon fractures occurred more frequently with the addition of Achilles tension. A linear regression model was developed that describes the expected axial loading injury tolerance of the foot/ankle complex in terms of specimen age, gender, mass and level of Achilles tension

Aims

The aim of this study was to compare the pain caused by the application of a tourniquet after exsanguination of the upper limb with that occurring after simple elevation.

Aims. The optimum clearance between the bearing surfaces of hip arthroplasties is unknown. Theoretically, to minimize wear, it is understood that clearances must be low enough to maintain optimal contact pressure and fluid film lubrication, while being large enough to allow lubricant recovery and reduce contact patch size. This study aimed to identify the relationship between diametrical clearance and volumetric wear, through the analysis of retrieved components. Methods. A total of 81 metal-on-metal Pinnacle hips paired with 12/14 stems were included in this study. Geometrical analysis was performed on each component, using coordinate and roundness measuring machines. The relationship between their as-manufactured diametrical clearance and volumetric wear was investigated. The Mann-Whitney U test and unpaired t-test were used, in addition to calculating the non-parametric Spearman's correlation coefficient, to statistically evaluate the acquired data. Results. The hips in this study were found to have had a median unworn diametrical clearance of 90.31 μm (interquartile range (IQR) 77.59 to 97.40); 32% (n = 26) were found to have been below the manufacturing tolerance. There was no correlation found between clearance and bearing (r. s. = -0.0004, p = 0.997) or taper (r. s. = 0.0048, p = 0.966) wear rates. The wear performance of hips manufactured within and below these specifications was not significantly different (bearing: p = 0.395; taper: p = 0.653). Pinnacles manufactured from 2007 onwards had a greater prevalence of bearing clearance below tolerance (p = 0.004). Conclusion. The diametrical clearance of Pinnacle hips did not influence their wear performance, even when below the manufacturing tolerance. The optimum clearance for minimizing hip implant wear remains unclear. Cite this article: Bone Joint Res 2020;9(8):515–523

Aims. To achieve expert clinical consensus in the delivery of hydrodilatation for the treatment of primary frozen shoulder to inform clinical practice and the design of an intervention for evaluation. Methods. We conducted a two-stage, electronic questionnaire-based, modified Delphi survey of shoulder experts in the UK NHS. Round one required positive, negative, or neutral ratings about hydrodilatation. In round two, each participant was reminded of their round one responses and the modal (or ‘group’) response from all participants. This allowed participants to modify their responses in round two. We proposed respectively mandating or encouraging elements of hydrodilatation with 100% and 90% positive consensus, and respectively disallowing or discouraging with 90% and 80% negative consensus. Other elements would be optional. Results. Between 4 August 2020 and 4 August 2021, shoulder experts from 47 hospitals in the UK completed the study. There were 106 participants (consultant upper limb orthopaedic surgeons, n = 50; consultant radiologists, n = 52; consultant physiotherapist, n = 1; extended scope physiotherapists, n = 3) who completed round one, of whom 97 (92%) completed round two. No elements of hydrodilatation were “mandated” (100% positive rating). Elements that were “encouraged” (≥ 80% positive rating) were the use of image guidance, local anaesthetic, normal saline, and steroids to deliver the injection. Injecting according to patient tolerance, physiotherapy, and home exercises were also “encouraged”. No elements were “discouraged” (≥ 80% negative rating) although using hypertonic saline was rated as being “disallowed” (≥ 90% negative rating). Conclusion. In the absence of rigorous evidence, our Delphi study allowed us to achieve expert consensus about positive, negative, and neutral ratings of hydrodilatation in the management of frozen shoulder in a hospital setting. This should inform clinical practice and the design of an intervention for evaluation. Cite this article: Bone Jt Open 2022;3(9):701–709

Local antimicrobial therapy is an integral aspect of treating orthopaedic device related infection (ODRI), which is conventionally administered via polymethylmethacrylate (PMMA) bone cement. PMMA, however, is limited by a suboptimal antibiotic release profile and a lack of biodegradability. In this study, we compare the efficacy of PMMA versus an antibioticloaded hydrogel in a single- stage revision for chronic methicillin-resistant Staphylococcus aureus (MRSA) ODRI in. sheep. Antibiofilm activity of the antibiotic combination (gentamicin and vancomycin) was determined in vitro. Swiss alpine sheep underwent a single-stage revision of a tibial intramedullary nail with MRSA infection. Local gentamicin and vancomycin therapy was delivered via hydrogel or PMMA (n = 5 per group), in conjunction with systemic antibiotic therapy. In vivo observations included: local antibiotic tissue concentration, renal and liver function tests, and quantitative microbiology on tissues and hardware post-mortem. There was a nonsignificant reduction in biofilm with an increasing antibiotic concentration in vitro (p = 0.12), confirming the antibiotic tolerance of the MRSA biofilm. In the in vivo study, four out of five sheep from each treatment group were culture negative. Antibiotic delivery via hydrogel resulted in 10–100 times greater local concentrations for the first 2–3 days compared with PMMA and were comparable thereafter. Systemic concentrations of gentamicin were minimal or undetectable in both groups, while renal and liver function tests were within normal limits. This study shows that a single-stage revision with hydrogel or PMMA is equally effective, although the hydrogel offers certain practical benefits over PMMA, which make it an attractive proposition for clinical use

Fracture related infection remains a major challenge in musculoskeletal trauma surgery. Despite best practice, treatment strategies suffer from high failure rates due to antibiotic resistance and tolerance. Bacteriophages represent a promising alternative as they retain activity against such bacteria. However, optimal phage administration protocols remain unknown, although injectable hydrogels, loaded with phage and conventional antibiotics, may support conventional therapy. In this study we tested the activity of meropenem, and two newly isolated bacteriophages (ϕ9 and ϕ3) embedded within alginate-chitosan microbeads and a hydrogel. Antibiotic and phage stability and activity were monitored in vitro, over a period of 10 days. In vivo, the same material was tested in treatment of a 5-day old Pseudomonas aeruginosa infection of a tibial plate osteotomy in mice. Treatment involved debridement and 5 days of systemic antibiotic therapy plus: i- saline, ii-phages in saline, iii-phages and antibiotics loaded into a hydrogel (n=7 mice/group). To assess the efficacy of the treatments, the infection load was monitored during revision surgery with debridement of the infected tissue after 5,10 and 13 days (euthanasia) by CFU and PFU quantification. In vitro testing confirmed that the stability of meropenem and activity of ϕ9 and ϕ3, was not affected within the alginate beads or hydrogel over 10 days. The in vivo study showed that all mice receiving phages and antibiotics loaded into a hydrogel survived the infection with a reduction of the bacterial load in the soft tissue. Active phages could be recovered from the infected site at euthanasia (10. 4. PFU/g). The hydrogel loaded with bacteriophages and meropenem showed a positive result in locally reducing the infection load indicating a synergistic effect of the selected antimicrobials. Overall, our new strategy shows encouraging results for improving the treatment of antibiotic-resistant biofilm infections that are related to medical implants

Introduction. Acquiring adaptive soft-tissue balance is one of the most important factors in total knee arthroplasty (TKA). However, there have been few reports regarding to alteration of tolerability of varus/valgus stress between before and after TKA. In particular, there is no enough data about mid-flexion stability. Based on these backgrounds, it is hypothesized that alteration of varus/valgus tolerance may influence post-operative results in TKA. The purpose of this study is an investigation of in vivo kinematic analyses of tolerability of varus/valgus stress before and after TKA, comparing to clinical results. Materials and Methods. A hundred knees of 88 consecutive patients who had knees of osteoarthritis with varus deformity were investigated in this study. All TKAs (Triathlon, Stryker) were performed using computer assisted navigation system. The kinematic parameters of the soft-tissue balance, and amount of coronal relative movement between femur and tibia were obtained by interpreting kinematics, which display graphs throughout the range of motion (ROM) in the navigation system. Femoro-tibial alignments were recorded under the stress of varus and valgus before the procedure and after implantation of all components. In each ROM (0, 30, 60, 90, 120 degrees), the data of coronal relative movement between femur and tibia (tolerability) were analyzed before and after implantation. Furthermore, correlations between tolerability of varus/valgus and clinical improvement revealed by ROM and Knee society score (KSS) were analyzed by logistic regression analysis. Results. Evaluation of soft tissue balance with navigation system revealed that the tolerance of coronal relative movement between femur and tibia (varus/valgus) after implantation was significantly decreased compared with before implantation even in mid-flexion range. There were no significant correlations between tolerability of coronal relative movement and improvement of extension range and KSS. However, mid-flexion tolerability showed negative correlation with flexion range. Discussion. One of the most important principles for ligament balancing in TKA for varus knees is involved that the medial extension gap should be within 1–3mm to avoid flexion contracture and a feeling of instability, the medial flexion gap should be equal or 1–2mm larger to the medial extension gap, and lateral extension laxity up to 5 degrees is acceptable. However, there have been few reports measuring laxity from 30 to 60 degrees. In this study, the tolerance of coronal relative movement was significantly limited even in mid-flexion. However, mid-flexion tightness was not significantly correlated with clinical results except for flexion range. This result might be suggested that high tolerability of coronal relative movement in mid-flexion range may lead to widening of flexion range of motion of the knee after TKA. For any figures or tables, please contact authors directly

Introduction. Fretting corrosion of the modular taper junction in total hip arthroplasty has been studied in several finite element (FE) studies. Manufacturing tolerances can result in a mismatch between the femoral head and stem, which can influence the taper mechanics leading to possibly more wear. Using FE models the effect of these manufacturing tolerances on the amount of volumetric wear can be studied. The removal of material in the FE model was validated against experiments simulating the clinical fretting wear process, subsequently the mismatch and assembly force were varied to study the effect on the volumetric wear. Methods. An FE model was developed in which the geometry can be updated to account for material removal due to wear. In this model the geometry was updated based on Archard's Law, using contact pressures, micromotions and a wear factor, which was determined based on accelerated fretting experiments. The linear wear was calculated using H=k*p*S. Where H is the linear wear depth in mm, k is a wear factor (mm. 3. /Nmm), p is the contact pressure (MPa) and S is the sliding distance (mm). 10 million cycles were simulated using 50 virtual steps. Using this scaling and the measured volumetric wear from the experiments a wear factor of 2.7*10. −5. was applied. Based on general manufacturing tolerances the resulting mismatch in taper angles were determined to be ± 1.26°. Using this mismatch a tip fit (figure 1a) and base fit (Figure 1b) model were created. In combination with a perfect fit, meaning no mismatch, and two different assembly forces of 4 kN and 15 kN, 6 different situations were studied. Results. No mismatch proved to result in the least amount of wear after 10 million simulated cycles (Figure 2). Assembling with 15 kN instead of 4 kN reduced the total volumetric wear and the volumetric wear rate. A base fit mismatch resulted in less volumetric wear than a tip fit mismatch. The 15 kN assembled mismatch cases showed a large initial amount of material removal after which the wear rate was lower than the 4 kN assembled cases. Discussion and conclusion. The results show that a perfect fit between the head and stem results in the least amount of wear. Furthermore a larger assembly force of 15 kN resulted in less wear than a 4 kN assembly force. The tip fit mismatch showed up to 144% more wear than the perfect fit where the base fit only had an increase in volumetric wear of 12%. The relative large tolerances in this study may overestimate actual mismatch, but give good insight into the effect that manufacturing tolerances can have on the taper mechanics and volumetric wear. Since manufacturing a perfect fit is impossible it is important to use a sufficiently high assembly force, when clinically possible, in order to reduce the amount of wear and wear rate significantly. For any figures or tables, please contact the authors directly

Staphylococcus aureus is the main cause of osteomyelitis and forms biofilm and staphylococcal abscess communities (SACs) in humans. While S. aureus has several toxins with specificity for human targets and working with human host cells would be preferred, for SACs no in vitro models, two-dimensional (2D) or three-dimensional (3D), have been described in literature to date. Advanced 3D in vitro cell culture models enable the incorporation of human cells and resemble in vivo tissue more closely than conventional 2D cell culture. Therefore, the aim of this study was to develop an in vitro model of SACs by using a 3D system. The model should allow for studies into antibiotic tolerance and S. aureus - human host cells interactions. With a clinical isolate (S. aureus JAR) or a lab strain (S. aureus ATCC 49230-GFP), SACs were grown in a collagen gel (1.78 mg/ml, Gibco) supplemented with 200 µl human plasma at 37 °C. Transmission and scanning electron microscopy was used to obtain a detailed overview of SACs, whereas immunofluorescent stainings were done to determine whether the pseudocapsule around SACs consist of fibrin. Antibiotic tolerance of SACs was assessed with 100× the minimal inhibitory concentration (MIC) of gentamicin (Roth). Bacterial clearance of non-establised SACs and established SACs with or without pseudocapsule was determined by exposure to differentiated PLB neutrophil-like cells (differentiation with 1.25% DMSO and 5% FBS for 5 days; dPLB) or primary neutrophils isolated with lymphoprep from fresh heparin blood. Degradation of the pseudocapsule was done with 7.5 µl/ml plasmin (Sigma). Colony forming unit (CFU) counts were performed as quantification method. Statistical analysis was performed with the ANOVA multiple comparison test or, when data was not normally distributed, with a Mann-Whitney U test. We have developed a 3D in vitro model of SACs which after overnight growth were on average 200 micrometers in diameter, consisted of 8 log10 CFUs and were surrounded by an inner and outer fibrin pseudocapsule. The in vitro grown SACs tolerated 100× the MIC of gentamicin for 24h and did not significantly differ from control SACs (p=0.1000). dPLB neutrophil-like cells or primary neutrophils did not clear established in vitro SACs (p=0.1102 and p=0.8767, respectively). When the fibrin pseudocapsule was degraded by the enzyme plasmin, dPLB neutrophil-like cells or primary neutrophils caused for a significant decrease in total CFU compared the SACs that did had a pseudocapsule (p=0.0333 and p=0.0272, respectively). The in vitro SACs model offers a tool for host-pathogen interaction and drug efficacy assessments and is a valuable starting point for future research

Aims. Due to their radiolucency and favourable mechanical properties, carbon fibre nails may be a preferable alternative to titanium nails for oncology patients. We aim to compare the surgical characteristics and short-term results of patients who underwent intramedullary fixation with either a titanium or carbon fibre nail for pathological long-bone fracture. Methods. This single tertiary-institutional, retrospectively matched case-control study included 72 patients who underwent prophylactic or therapeutic fixation for pathological fracture of the humerus, femur, or tibia with either a titanium (control group, n = 36) or carbon fibre (case group, n = 36) intramedullary nail between 2016 to 2020. Patients were excluded if intramedullary fixation was combined with any other surgical procedure/fixation method. Outcomes included operating time, blood loss, fluoroscopic time, and complications. Fisher’s exact test and Mann-Whitney U test were used for categorical and continuous outcomes, respectively. Results. Patients receiving carbon nails as compared to those receiving titanium nails had higher blood loss (median 150 ml (interquartile range (IQR) 100 to 250) vs 100 ml (IQR 50 to 150); p = 0.042) and longer fluoroscopic time (median 150 seconds (IQR 114 to 182) vs 94 seconds (IQR 58 to 124); p = 0.001). Implant complications occurred in seven patients (19%) in the titanium group versus one patient (3%) in the carbon fibre group (p = 0.055). There were no notable differences between groups with regard to operating time, surgical wound infection, or survival. Conclusion. This pilot study demonstrates a non-inferior surgical and short-term clinical profile supporting further consideration of carbon fibre nails for pathological fracture fixation in orthopaedic oncology patients. Given enhanced accommodation of imaging methods important for oncological surveillance and radiation therapy planning, as well as high tolerances to fatigue stress, carbon fibre implants possess important oncological advantages over titanium implants that merit further prospective investigation. Level of evidence: III, Retrospective study. Cite this article: Bone Jt Open 2022;3(8):648–655

Staphylococcus aureus is responsible for 60–70% infections of surgical implants and prostheses in Orthopaedic surgery, with cumulative treatment costs for all prosthetic joint infections estimated to be ∼ $1 billion per annum (UK and North America). Its ability to develop resistance or tolerance to a diverse range of antimicrobial compounds, threatens to halt routine elective implant surgery. One strategy to overcome this problem is to look beyond traditional antimicrobial drug therapies and investigate other treatment modalities. Biophysical modalities, such as ultrasound, are poorly explored, but preliminary work has shown potential benefit, especially when combined with existing antibiotics. Low intensity pulsed ultrasound is already licensed for clinical use in fracture management and thus could be translated quickly into a clinical treatment. Using a methicillin-sensitive S. aureus reference strain and the dissolvable bead assay, biofilms were challenged with gentamicin +/− low-intensity ultrasound (1.5MHz, 30mW/cm2, pulse duration 200µs/1KHz) for 180 minutes and 20 minutes, respectively. The primary outcome measures were colony-forming units/mL (CFU/mL) and the minimum biofilm eradication concentration (MBEC) of gentamicin. The mean number of S. aureus within control biofilms was 1.04 × 109 CFU/mL. Assessment of cellular metabolism was conducted using a liquid-chromatography-mass spectrometry, as well as a triphenyltetrazolium chloride assay coupled with spectrophotometry. There was no clinically or statistically significant (p=0.531) reduction in viable S. aureus following ultrasound therapy alone. The MBEC of gentamicin for this S. aureus strain was 256 mg/L. The MBEC of gentamicin with the addition of ultrasound was reduced to 64mg/L. Metabolic activity of biofilm-associated S. aureus was increased by 25% following ultrasound therapy (p < 0 .0001), with identification of key biosynthetic pathways activated by non-lethal dispersal. Low intensity pulsed ultrasound was associated with a four-fold reduction in the effective biofilm eradication concentration of gentamicin, bringing the MBEC of gentamicin to within clinically achievable concentrations. The mechanism of action was due to partial disruption of the extracellular matrix which led to an increase of nutrient availability and oxygen tension within the biofilm. This metabolic stimulus was responsible for the reversal of gentamicin tolerance in the biofilm-associated S. aureus

Aims. The purpose of this investigation was to determine the relationship between height, weight, and sex with implant size in total knee arthroplasty (TKA) using a multivariate linear regression model and a Bayesian model. Methods. A retrospective review of an institutional registry was performed of primary TKAs performed between January 2005 and December 2016. Patient demographics including patient age, sex, height, weight, and body mass index (BMI) were obtained from registry and medical record review. In total, 8,100 primary TKAs were included. The mean age was 67.3 years (SD 9.5) with a mean BMI of 30.4 kg/m. 2. (SD 6.3). The TKAs were randomly split into a training cohort (n = 4,022) and a testing cohort (n = 4,078). A multivariate linear regression model was created on the training cohort and then applied to the testing cohort . A Bayesian model was created based on the frequencies of implant sizes in the training cohort. The model was then applied to the testing cohort to determine the accuracy of the model at 1%, 5%, and 10% tolerance of inaccuracy. Results. Height had a relatively strong correlation with implant size (femoral component anteroposterior (AP) Pearson correlation coefficient (ρ) = 0.73, p < 0.001; tibial component mediolateral (ML) ρ = 0.77, p < 0.001). Weight had a moderately strong correlation with implant size, (femoral component AP ρ = 0.46, p < 0.001; tibial ML ρ = 0.48, p < 0.001). There was a significant linear correlation with height, weight, and sex with implant size (femoral component R. 2. = 0.607, p < 0.001; tibial R. 2. = 0.695, p < 0.001). The Bayesian model showed high accuracy in predicting the range of required implant sizes (94.4% for the femur and 96.6% for the tibia) accepting a 5% risk of inaccuracy. Conclusion. Implant size was correlated with basic demographic variables including height, weight, and sex. The linear regression and Bayesian models accurately predicted required implant sizes across multiple manufacturers based on height, weight, and sex alone. These types of predictive models may help improve operating room and implant supply chain efficiency. Level of Evidence: Level IV. Cite this article: Bone Joint J 2020;102-B(6 Supple A):85–90

INTRODUCTION. Precise determination of material loss is essential for failure analysis of retrieved hip cups. To determine wear, the measured geometry of the retrieval hast to be compared to its pristine geometry, which usually is not available. There are different approaches to generate reference geometries to approximate the pristine geometry that is commonly assumed as sphere. However, the geometry of press fit cup retrievals might not be spherical due to deformation caused by excessive press-fitting. The effect of three different reference geometries on the determined wear patterns and material loss of pristine and worn uncemented metal-on-metal hip cups was determined. METHODS. The surfaces of two cups (ASR, DePuy, Leeds; one pristine, one a worn retrieval) were digitized using a coordinate measurement machine (CRYSTA-Apex S574, Mitutoyo; 3 µm accuracy). Both cups were measured undeformed and while being deformed between a clamp. Three different methods for generating reference geometries were investigated (PolyWorks|Inspector 2018, InnovMetric). Method 1: A sphere with the nominal internal cup dimensions was generated. Method 2: A sphere was fitted to the measured data points after removing those from worn areas (deviation > 3 µm is defined as wear) to eliminate the influence of manufacturing tolerances on the nominal diameter. Method 3: Measurements, which displayed visual deformation in the computed wear pattern based on the best fit sphere, were fitted with an ellipsoid. The direction of the deformation axes and the amount of deformation were used to scale the best fit ellipsoid. Linear wear was calculated from the distance of the respective reference geometry to the measured point cloud. Finally, material loss is defined as the difference in volume of the reference geometry and the measured geometry. RESULTS. The method used for generating the reference geometry affected the determined wear greatly. Using the nominal manufacturing radius (larger than the best fit radius) for the worn cup falsely indicates deposit. This leads to approx. 39 % less wear volume compared to the best fit sphere analysis. Using an ellipsoid as reference geometry for both deformed cups improves the determination of the wear pattern and indicates areas of material loss better than a reference sphere. Additionally, the mistake in material loss determination is decreased, especially for the worn cup almost exactly to the wear volume analyzed with the best fit sphere before deformation. DISCUSSION. For correct determination of material loss best fit geometries instead of nominal sizes have to be used to compensate the differences due to manufacturing tolerances. Furthermore, deformation always has to be eliminated to generate correct wear patterns and volumes. Using an ellipsoid as reference geometry improves the outcome. For generating an even more accurate reference geometry, the exact behavior of the cup during deformation must be understood. Limitations to this method are cups that do not provide pristine areas in order to generate an appropriate best fit geometry. For any figures or tables, please contact authors directly

Aim. Bone regeneration following the treatment of Staphylococcal bone infection or osteomyelitis is challenging due to the ability of Staphylococcus aureus to invade and persist within bone cells, which could possibly lead to antimicrobial tolerance and incessant bone destruction. Here, we investigated the influence of Staphylococcal bone infection on osteoblasts metabolism and function, with the underlying goal of determining whether Staphylococcus aureus-infected osteoblasts retain their ability to produce extracellular mineralized organic matrix after antibiotic treatment. Method. Using our in vitro infection model, human osteoblasts-like Saos-2 cells were infected with high-grade Staphylococcus aureus EDCC 5055 strain, and then treated with 8 µg/ml rifampicin and osteogenic stimulators up to 21-days. Results. Immunofluorescence and transmission electron microscopic (TEM) imaging demonstrated the presence of intracellular bacteria within the infected osteoblasts as early as 2 hours post-infection. TEM micrographs revealed intact intracellular bacteria with dividing septa indicative of active replication. The infected osteoblasts showed significant amounts of intracellular bacteria colonies and alteration in metabolic activity compared to the uninfected osteoblasts (p≤0.001). Treatment of S. aureus-infected osteoblasts with a single dose of 8 µg/ml rifampicin sufficiently restored the metabolic activity comparative to the uninfected groups. Alizarin red staining and quantification of the rifampicin-treated infected osteoblasts revealed significantly lower amount of mineralized extracellular matrix after 7-days osteogenesis (p<0.05). Interestingly, prolonged osteogenic stimulation and rifampicin-treatment up to 21 days improved the extracellular matrix mineralization level comparable to the rifampicin-treated uninfected group. However, the untreated (native) osteoblasts showed significantly more quantity of mineral deposits (p≤0.001). Ultrastructural analysis of the rifampicin-treated infected osteoblasts at 21-days osteogenesis revealed active osteoblasts and newly differentiated osteocytes, with densely distributed calcium crystal deposits within the extracellular organic matrix. Moreover, residual colony of dead bacteria bodies and empty vacuoles of the fully degraded bacteria embedded within the mineralized extracellular matrix. Gene expression level of prominent bone formation markers, namely RUNX2, COL1A1, ALPL, BMP-2, SPARC, BGLAP, OPG/RANKL showed no significant difference between the infected and uninfected osteoblast at 21-days of osteogenesis. Conclusions. Staphylococcus aureus bone infection can drastically impair osteoblasts metabolism and function. However, treatment with potent intracellular penetrating antibiotics, namely rifampicin restored the metabolic and bone formation activity of surviving osteoblasts. Delay in early osteogenesis caused by the bacterial infection was significantly improved over time after successful intracellular bacteria eradication