Introduction. Fretting crevice-corrosion (tribocorrosion) of metallic biomaterials is a major concern in orthopedic, spinal, dental and cardiovascular devices. 1. Stainless steel (i.e., 316L SS) is one alloy that sees extensive use in applications where fretting, crevices and corrosion may be present. While fretting-corrosion of this alloy has been somewhat studied, the concept of fretting-initiating crevice corrosion (FICC), where an initial fretting corrosion process leads to ongoing crevice-corrosion without continued fretting, is less understood. This study investigated the susceptibility of 316L SS to FICC and the role of applied potential on the process. The hypothesis is crevice-corrosion can be induced in 316L SS at potentials well below the pitting potential. Materials and Methods. A pin-on-disk fretting test system similar to that of Swaminathan et al. 2. was employed. Disks were ∼35 mm in diameter and the pin area was ∼500 mm. Samples were polished to 600 mm finish, cleaned with ethanol and distilled water. An Ag/AgCl wire as the reference, a carbon counter electrode and phosphate buffered saline (PBS, pH 7.4, Room T) were used for electrochemical testing. Load was controlled with a dead-weight system, monitored with a six-axis load cell (ATI Inc.). Interfacial motion was captured with a non-contact eddy current sensor (0.5 mm accuracy). Motion and load data acquisition was performed with Labview (National Instruments). Samples were loaded to ∼2 N. The potential per tests was increased from −250 to 250 mV (50 mV increments) with new locations and pins used in each repeat (n=3). Testing incorporated a 1 min rest before fretting (5 min, 1.25 Hz, 60 mm displacement saw tooth pattern). Fretting ceased and the load was held while currents were captured for another 5 min to assess ongoing crevice corrosion. Results. Testing showed that crevice corrosion can be initiated within minutes of fretting (or in a few cycles depending on potential; Fig. 1). Potentials as low as −100 mV showed evidence of corrosion, while sustained crevice corrosion was seen at −50 mV. As the potential increased above −50 mV, susceptibility to FICC increased. Fig. 2 is a typical cyclic polarization curve for 316L SS in PBS without fretting. Pitting starts at 400 mV vs Ag/AgCl, and the protection potential in this case is around potentials where FICC can be induced. Discussion. This study showed that 316L SS is prone to FICC starting at −100 mV and the severity of the crevice-corrosion damage depends on the applied potential (Fig. 3). Current after cessation of fretting takes longer to return to baseline or does not return indicating ongoing corrosion without fretting (Fig. 1). If the pin and disk are separated, the crevice-corrosion process stops immediately. The region immediately outside the fretting contact was crevice-like with a very small separation distance between the pin and disk surface which allowed crevice corrosion to develop (Fig. 3). Conclusion. 316L SS can undergo FICC at potentials close to normal physiological electrode potential conditions. Few fretting cycles are required to develop conditions for continued crevice-corrosion. Higher potentials increased the susceptibility of FICC in 316L SS

Background. Currently, stailess steel, titanium and carbon-fiber reinforced polyetheretherketone (CF-PEEK) plates are available for the treatment of distal radius fractures. Since the possibility to create a less rigid fixation may represent an advantage in case of ostheoporotic or poor quality bone, the aim of this study is to compare the biomechanical properties of these three materials in terms of bending stiffness with a single static load and after cyclical loading, simulating physiologic wrist motion. Materials and Methods. Three volar plating systems with fixed angle were tested: Zimmer stainless steel volar lateral column (Warsaw, IN); Hand Innovations titanium DVR (Miami, FL); Lima Corporate CF-PEEK DiPHOS-RM (San Daniele Del Friuli, Udine, Italy). For each type of plate tested four right synthetic composite bone radii were used. An unstable, extraarticular fracture was simulated by making an 8 mm gap with a saw starting 12 mm proximal to the articular surface of the radius on the distal radio-ulnar joint side. The osteotomies were made perpendicular to the long axis of the bone to allow for a consistent fracture gap on the dorsal and volar sides of the radius. Plates were implanted using all the distal and proximal fixation holes [Fig. 1]. Each synthetic radius model was potted in methylmethacrylate and tested in a bi-axial servo-hydraulic test frame (MTS Minibionix 858, universal testing machine) for load to failure by advancing a cobalt chrome sphere centered over the articular surface at a constant rate of displacement of 5 mm/min. The sphere was advanced until the construct failed or the dorsal edges of the fracture met. The resultant force was defined as bending stiffness pre fatigue. Three constructs for each plate were then dynamically loaded for 6000 cycles of fatigue at a frequency of 10Hz, with a load value corresponding to the 50% of the previously calculated bending strength. Finally, the constructs were loaded to failure, measuring the bending stiffness post fatigue. Results. All fracture constructs survived all phases of the cyclic loading testing. The mean bending stiffness pre fatigue was higher for the Zimmer plate (155.23±1.91 N/mm), in comparison to Hand Innovations (138.67±4.72 N/mm), and DiPHOS-RM (124.75±3.60 N/mm) [Fig. 2]. After cyclic loading, stiffness increased significantly of a mean 24% for the Zimmer plate (190.42±4.33 N/mm); 33% for the Hand Innovations (186.57±1.71 N/mm); and 18% for the DiPHOS-RM (146.28±1.52 N/mm) [Fig. 2–3]. Conclusions. CF-PEEK plate is less stiff than stainless steel and titanium plates, with an elastic modulus more similar to bone as well as the ability to withstand prolonged fatigue strain. From these preliminary data it might be assumed that the CF-PEEK plates could provide a sufficiently stable osteosynthesis, flexible enough to unload the implant-bone interface, minimising peak stresses at the bone- implant interface, making them particularly suitable for fracture fixation in osteoporotic patients. A proper patient selection (avoiding incompliant or non collaborative) should be performed using CF-PEEK plates to avoid possible implant breakage consequent to a fall or a second trauma on the injuried wrist until the complete fracture healing. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Aims

Limb-lengthening nails have largely replaced external fixation in limb-lengthening and reconstructive surgery. However, the adverse events and high prevalence of radiological changes recently noted with the STRYDE lengthening nail have raised concerns about the use of internal lengthening nails. The aim of this study was to compare the prevalence of radiological bone abnormalities between STRYDE, PRECICE, and FITBONE nails prior to nail removal.

Title. Longitudinal Intravital Imaging to Quantify the “Race for the Surface” Between Host Immune Cell and Bacteria for Orthopaedic Implants with S. aureus Colonization in a Murine Model. Aim. To assess S. aureus vs. host cell colonization of contaminated implants vis intravital multiphoton laser scanning microscopy (IV-MLSM) in a murine model. Method. All animal experiments were approved by IACUC. A flat stainless steel or titanium L-shaped pin was contaminated with 10. 5. CFU of a red fluorescent protein (RFP) expressing strain of USA300LAC, and surgically implanted through the femur of global GFP-transgenic mice. IV-MLSM was performed at 2, 4, and 6 hours post-op. Parallel cross-sectional CFU studies were performed to quantify the bacteria load on the implant at 2,4,6,12,18 and 24 hours. Results. 1) We developed a high-fidelity reproducible IV-MLSM system to quantify S. aureus and host cell colonization of a bone implant in the mouse femur. Proper placement of all implants were confirmed with in vivo X-rays, and ex vivo photos. We empirically derive the ROI during each imaging session by aggregating the imaged volume which ranges from (636.4um × 636.4um × 151um) = 0.625 +/- 0.014 mm. 3. of bone marrow in a global GFP-transgenic mouse. 2) IV-MLSM imaging acquisition of the “race for the surface”.In vitro MPLSM images of implants partially coated with USA300LAC (RFP-MRSA) were verified by SEM image. Results from IV-MLSM of RFP-MRSA and GFP. +. host cell colonization of the contaminated implants illustrated the mutually exclusive surface coating at 3hrs, which to our knowledge is the first demonstration of “the race for the surface” between bacteria and host cells via intravital microscopy. 3) Quantifying the “race for the surface” with CFU verification of S. aureus on the implant. 3D volumetric rendering of the GFP. +. voxels and RFP+ voxels within the ROI were generated in Imaris. The voxel numbers suggeste that the fight for the surface concludes ∼3hrs post-infection, and then transitions to an aggressive MRSA proliferation phase. The results of WT control demonstrate a significant increase in CFU by 12hrs post-op for both stainless steel (P<0.01) and titanium (P<0.01). Conclusions. We developed IV-MLSM to quantify the “Race for the Surface” between host cells and contaminating S. aureus in a murine femur implant model. This race is remarkably fast, as the implant surface is completely covered with 3hrs, peak bacterial growth on the implant occurs between 2 and 12 hours and is complete by 12hrs

Introduction. Stem geometry is known to influence the outcome in THA; however it is unknown whether the material properties, stiffness in particular can influence the stem stability and outcome. The aim of this study was to measure the influence of stem material properties on micromotion and migration using Roentgen Stereophotogrammetric Analysis (RSA) system. Methods. 41 patients were implanted with a collarless polished tapered (CPT) femoral stem (Zimmer, Warsaw, Indiana), which was made of either cobalt-chromium (CoCr) (n=21) or stainless steel (n=20). RSA was used to measure dynamically inducible micromotion (DIMM: difference in stem position in going from double-leg stance (DLS) to single leg stance (SLS)), prosthesis bending (difference in the head-tip distance when going from DLS to SLS), and mean migration of the head, tip and the cement restrictor. DIMM and bending were measured at 3 months, migration at 6, 12 and 24 months. All analyses were carried out using SPSS for windows (v.15.0.0, Chicago. IL, USA). Results were reported as mean ± 95% confidence interval (CI) and regarded as significant when p < 0.05. Results. Preliminary analysis showed that DIMM of head was significantly (p = 0.02) greater for CoCr (0.97mm ± 0.6mm) than stainless steel (0.27mm ± 0.6mm). The mean stem bending for CoCr was 0.08mm (± 0.06mm) and for stainless steel 0.15mm (± 0.06mm) (p =0.77). Both implants heads migrated posteriorly, medially and distally. The mean subsidence for the cobalt-chromium and stainless steel stems was 1.02mm (±0.19mm) (p < 0.001) and 1.12mm (± 0.34mm) (p=0.001) (p= 0.07) at 24 months. Conclusion. Dynamically induced micromotion was greater for the stiffer stem, however there were no differences in terms of over all migration, indicating that survival (in terms of loosening) should be the similar for both stainless steel and CoCr versions of this implant

Introduction. Circular frame fixation has become a cornerstone of non-union and deformity management since its inception in the 1950s. As a consequence of modularity and heterogenous patient and injury factors, the prediction of the mechanobiological environment within a defect is subject to wide variations in practice. Given these wide range of confounding variables, clinical and cadaveric experimentation is close to impossible and frame constructs are based upon clinician experience. The Finite Element Analysis (FEA) method provides a powerful tool to numerically analyse mechanics. This work aims to develop an FEA model of a tibial defect and predict the mechanical response within the construct. Materials and Methods. The geometry of a tibia was acquired via CT and a series of bone defects were digitally created in the tibial diaphysis. A 4-ring, 10-wire Ilizarov fixator was constructed using 180mm stainless steel rings and 1.8mm stainless steel wires tensioned to 1200N. An axial load (800N) was applied to simulate single leg stance of an 80kg patient. The magnitude of displacement was measured for defects with varying sizes (5–40mm). A numerical analysis was performed in large-strain regime using open-source FEA library (MoFEM). Results. Defect size did not effect displacement, but significantly influenced strain. Measured displacements were 5.72–5.78mm, however strain ranged from 14.5–100%. Moreover, it was found that bone material properties also have no significant impact on the results. Conclusions. Accounting for FEA assumptions, this model predicted a strain environment which was above expected favourable range for bone healing. The addition of graft within the environment is likely to change the mechanobiological environment which warrants further investigation. We plan to develop this model to answer further research questions in the limb reconstruction discipline and validate its accuracy with mechanical data. We believe the presented approach can be a useful tool for investigating the performance circular frames

Stem geometry is known to influence the outcome in THA; however it is unknown whether the material properties, stiffness in particular can influence the stem stability and outcome. The aim of this study was to measure the influence of stem material properties on micromotion and migration using Roentgen Stereophotogrammetric Analysis (RSA) system. 41 patients were implanted with a collarless polished tapered (CPT) femoral stem (Zimmer, Warsaw, Indiana), which was made of either cobalt-chromium (CoCr) (n=21) or stainless steel (n=20). RSA was used to measure dynamically inducible micromotion (DIMM: difference in stem position in going from double-leg stance (DLS) to single leg stance (SLS)), prosthesis bending (difference in the head-tip distance when going from DLS to SLS), and mean migration of the head, tip and the cement restrictor. DIMM and bending were measured at 3 months, migration at 6, 12 and 24 months. All analyses were carried out using SPSS for windows (v.15.0.0, Chicago. IL, USA). Results were reported as mean ± 95% confidence interval (CI) and regarded as significant when p < 0.05. Preliminary analysis showed that total head DIMM was significantly (p = 0.02) greater for CoCr (0.97mm ± 0.6mm) than stainless steel (0.27mm ± 0.6mm). The mean stem bending for CoCr was 0.08mm (± 0.06mm) and for stainless steel 0.15mm (± 0.06mm) (p =0.77). Both implants heads migrated posteriorly, medially and distally. The mean subsidence for the cobalt-chromium and stainless steel stems was 1.02mm (± 0.19mm) (p < 0.001) and 1.12mm (± 0.34mm) (p=0.001) (p= 0.07) at 24 months. It was interesting to note that the dynamically induced micromotion was greater for the stiffer stem, however there were no differences in terms of overall migration, indicating that survival (in terms of loosening) should be the similar for both steel and CoCr versions of this implant

We investigated whether an alternative tension band wire technique will produce greater compression and less displacement at olecranon (elbow) fracture sites compared to a standard figure of eight tension band technique. Olecranon fractures are commonly treated with tension band wiring using stainless steel wire in a figure of eight configuration. However recently published studies have raised doubts over the validity of the tension band concept proving that the standard figure of eight configuration does not provide fracture compression when the elbow is flexed. We propose an alternative tension band technique where the figure of eight is applied in a modified configuration producing greater compression across the fracture. An artificial elbow joint was simulated using artificial forearm (ulna) and arm (humerus) bones. The design simulated the action of the muscles around the elbow joint to produce flexion and extension. There were two arms to this investigation. (1) Standard tension band wire configuration with stainless steel. (2) Modified tension band wire configuration with stainless steel. The simulated elbow was put through a range of movement and sensors measured the compression at the articular and non-articluar surfaces of the fracture. Measurements were taken for compression with different weights applied to challenge both the techniques of tension band wiring. Measurements from the non articular surface of the fracture demonstrated greater compression with alternative tension band technique. However it was not statistically significant (ANOVA). Compression at the articular surface of the fracture exhibited statistically significant (p<0.05) greater compression with the alternative technique. Neither technique produced greater compression during flexion of the simulated elbow. The alternative tension band wiring technique proved superior in providing greater compression over the fracture site

Patellar fractures account for approximately 1% of all fractures. Open reduction and internal fixation is recommended to restore extensor continuity and articular congruity. However, complications such as nonunion and symptomatic hardware, still exist. Furthermore, there is a risk of re-fracturing of the healed bone during the removal of the implants. Magnesium (Mg), a biodegradable metal, has elastic moduli and compressive yield strength that are comparable to those of natural bone. Our previous study showed that released Mg ions enhanced fracture healing. However, Mg-based implants degrade rapidly after implantation and lead to insufficient mechanical strength to support the fracture. Microarc oxidation (MAO) is a metal surface coating that reduces corrosion. We hypothesized that Mg pins, with or without MAO, would enhance fracture healing radiologically, mechanically, and histologically, while MAO would decrease degradation of Mg pins. Patellar fracture was performed on forty-eight 18-week-old female New Zealand White rabbits according to established protocol. Briefly, the patella is osteotomized transversely and a tunnel (1.1mm) was drilled longitudinally through the two bone fragments. A pin (1 mm, stainless steel, Mg, or MAO-Mg) was inserted into the tunnel. The reduced construct was stabilized with a figure-of-eight band wire (⊘ 0.6 mm stainless steel wire). Cast immobilization was applied for 6 weeks. The rabbits were euthanized at week 8 and 12 post-operation. Microarchitecture and mechanical properties of the repaired patella were analyzed with microCT and tensile testing respectively. Histological sections of the repaired patella were stained. To evaluate the effect of the MAO treatment on degradation rate of Mg pin, the volume of the Mg pins in the patella was measured with microCT. At week 8, both Mg and Mg-MAO showed higher ratio of bone volume to tissue volume (BV/TV) than the control while there was no significant different between Mg and Mg-MAO. At week 12, Control, Mg, and Mg-MAO groups showed enlarged patella when compared to the normal patella. Tissue volume (TV) and bone volume (BV) of the patella in Mg and Mg-MAO were larger than those in the Control group. However, the Control had higher ratio of bone volume to tissue volume (BV/TV), TV density, and BV density than Mg and Mg-MAO. Tensile testing showed that the mechanical properties of the repaired patella (failure load, stiffness, ultimate strength, and energy-to-failure) of Mg and Mg-MAO were higher than that of the control at both week 8 and week 12. Histological analysis showed that there was significant new bone formation in the Mg and Mg-MAO group compared with the Control group at week 8 and 12. The degradation rate of the MAO-coated Mg pins was significantly slower than those without MAO at week 8 but no significant difference was detected at week 12. Mechanical, microarchitectural, and histological assessments showed that Mg pins, with or without MAO, enhanced fracture healing of the repaired patella compared to the Control. MAO treatment enhanced the corrosion resistance of the Mg pins at the early time point

INTRODUCTION. As computer navigated surgery continues to progress to the forefront of orthopedic care, the application of a navigated total shoulder arthroplasty has yet to appear. However, the accuracy of these systems is debated, as well as the dilemma of placing an accurate tool in an inaccurate hand. Often times a system's accuracy is claimed or validated based on postoperative imaging, but the true positioning is difficult to verify. In this study, a navigation system was used to preoperatively plan, guide, and implant surrogate shoulder glenoid implants and fiducials in nine cadaveric shoulders. A novel method to validate the position of these implants and accuracy of the system was performed using pre and post operative high resolution CT scans, in conjunction with barium sulfate impregnated PEEK surrogate implants. METHODS. Nine cadaveric shoulders were CT scanned with .5mm slice thickness, and the digital models were incorporated into a preoperative planning software. Five orthopedic shoulder specialists used this software to virtually place aTSA and rTSA glenoid components in two cadavers each (one cadaver was omitted due to incomplete implantation), positioning the components as they best deemed fit. Using a navigation system, each surgeon registered the native cadaveric bone to each respective CT. Each surgeon then used the navigation system to guide him or her through the total shoulder replacement, and implant the barium sulfate impregnated PEEK surrogate implants. Four cylindrical PEEK fiducials were also implanted in each scapula to help triangulate the position of the surrogate implants. Previous efforts were attempted with stainless steel alloy fiducials, but position and image accuracy were limited by CT artifact. BaSO. 4. PEEK provided the highest resolution on a postoperative CT with as little artifact as possible. All PEEK fiducials and surrogate implants were registered by probing points and planes with the navigation system to capture the digital position. A high resolution post operative CT scan of each specimen was obtained, and variance between the executed surgical plan and PEEK fiducials was calculated. RESULTS. The PEEK fiducials and surrogate implants that were used are compared with stainless steel fiducials in Figure 1. Figure 2 compares and contrasts the artifact present with BaSO. 4. PEEK fiducials vs stainless steel fiducials. Figure 3 illustrates the clarity of the reconstructed PEEK surrogate implant and fiducials in 3D space. Using the navigation system, the surgeons implanted the PEEK glenoid components 1.0±1.1mm anterior of center and 0.7±0.9mm superior of center relative to the preoperative plans. The average retroversion was 1.6±1.9° and inclination was 1.0±1.2° relative to the preoperative plans. CONCLUSION. The increased visible detail and decreased artifact from using a barium sulfate impregnated plastic proved to be a useful tool in determining 3D position of a surrogate implant. This technique could be applied in other biomedical applications beyond orthopedics. The validation technique also showed the accuracy and anticipated clinical benefit of a navigated total shoulder system, as the reported variance of glenoid version post shoulder replacement is ±11°. For figures, please contact authors directly

Many orthopaedic procedures require implants to be trialled before definitive implantation. Where this is required, the trials are provided in a set with the instrumentation. The most common scenario this is seen in during elective joint replacements. In Scotland (2007) the Scottish Executive (. http://www.sehd.scot.nhs.uk/cmo/CMO(2006)13.pdf. ) recommended and implemented individually packed orthopaedic implants for all orthopaedic sets. The premise for this was to reduce the risk of CJD contamination and fatigue of implants due to constant reprocessing from corrosion. During many trauma procedures determining the correct length of plate or size of implant can be challenging. Trials of trauma implants is no longer common place. Many implants are stored in closed and sealed boxes, preventing the surgeon looking at the implant prior to opening and contaminating the device. As a result many implants are incorrectly opened and either need reprocessed or destroyed due to infection control policy, thus implicating a cost to the NHS. With even the simplest implants costing several hundreds of pounds, this cost is a very significant waste in resources that could be deployed else where. My project was to develop a method to produce in department accurate, cheap and disposable trials for implants often used in trauma, where the original manufacturer do not offer the option of a trial off the shelf. The process had to not involve contaminating or destroying the original implant in the production of a trial. Several implants which are commonly used within Glasgow Royal Infirmary and do not have trials were identified. These implants were then CT scanned within their sealed and sterile packaging without contamination. Digital 3D surface renders of the models were created using free open source software (OsiriX, MeshLab, NetFabb). These models were then processed in to a suitable format for 3D printing using laser sintering via a cloud 3D printing bureau (. Shapeways.com. ). The implants were produced in polyamide PA220 material or in 316L stainless steel. These materials could be serialized using gamma irradiation or ethylene oxide gas. The steel models were suitable for autoclaving in the local CSSU. The implants produced were accurate facsimiles of the original implant with dimensions within 0.7mm. The implants were cost effective, an example being a rim mesh was reproduced in polyamide PA220 plastic for £3.50 and in 316L stainless steel for £15. The models were produced within 10 days of scanning. The stainless steel trials were durable and suitable for reprocessing and resterilisation. The production of durable, low cost and functional implant trials all completed in department was successful. The cost of production of each implant is so low that it would be offset if just one incorrect implant was opened during a single procedure. With some of the implants tested, the trials would have paid for themselves 100 times. This is a simple and cost saving technique that would help reduce department funding and aid patient care

Introduction. The process of wear and corrosion at the head-neck junction of a total hip replacement is initiated when the femoral head and stem are joined together during surgery. To date, the effects of the surface topography of the femoral head and metal stem on the contact mechanics during assembly and thus on tribology and fretting corrosion during service life of the implant are not well understood. Therefore, the objective of this study was to investigate the influence of the surface topography of the metal stem taper on contact mechanics and wear during assembly of the head-neck junction using Finite Element models. Materials and Methods. 2D axisymmetric Finite Element models were developed consisting of a simplified head-neck junction incorporating the surface topography of a threaded stem taper to investigate axial assembly with 1 kN. Subsequently, a base model and three modifications of the base model in terms of profile peak height and plateau width of the stem taper topography and femoral head taper angle were calculated. To account for the wear process during assembly a law based on the Archard equation was implemented. Femoral head was modeled as ceramic (linear-elastic), taper material was either modeled as titanium, stainless steel or cobalt-chromium (all elastic-plastic). Wear volume, contact area, taper subsidence, equivalent plastic strain, von Mises stress, engagement length and crevice width was analyzed. Results. Titanium tapers showed largest wear volume throughout all simulations, followed by stainless steel and cobalt-chromium. A larger head taper angle resulted in an increase of the wear volume for all taper materials while the increase of the plateau width resulted in a decrease of the wear volume. Taper subsidence, von Mises stress and equivalent plastic strain followed the same trends. Contact area was largest for the models with a large plateau width for all taper materials. Other taper parameters had little effect on contact area. A pure increase of the angular mismatch (AM) resulted in the strongest decrease of the engagement length, while a combined increase of the AM and plateau width showed only a moderate decrease. The smallest effect concerning the engagement length was found when a combined increase of the profile peak height and AM was simulated. Crevice width was largest for a pure increase of the AM and for a combined increase of the AM and profile peak height for all taper materials. Discussion. This study showed that depending on the surface topography and material of the stem taper, wear and taper mechanics during assembly could be affected. For the examined surface topographies wear is distinctively elevated by increasing the AM and the profile peak height due to the resulting higher mechanical loading. More parameter studies under in vivo loading and the study of other taper surface parameters like the peak-to-peak distance have to be conducted to get a deeper insight into taper mechanics and wear effects. However, this study demonstrates the importance of good manufacturing practice of components for hip replacement systems to guarantee reproducible taper mechanics. For any figures or tables, please contact authors directly

Aim. Multispecies biofilms are associated with difficult periprosthetic joint infections (PJI), particularly if they have different antibiotic sensitivities. We aimed to determine if we could generate and kill a multispecies biofilm consisting of a Gram negative and Gram positive pathogen in-vitro with antibiotic loaded calcium sulfate beads containing single or combination antibiotics. Methods. To establish whether we could co-culture mixed species biofilms various combinations of Pseudomonas aeruginosa (PA), Enterococcus faecalis (EF), Staphylococcus aureus (SA) and Enterobacter faecalis (EF) were grown together on 316L stainless steel coupons and agar plates. Based on this screen we focused on PA + EF and challenged them with high purity calcium sulfate beads (Stimulan Rapid Cure) loaded with vancomycin (V), alone tobramycin (T) alone or vancomycin and tobramycin in combination (V+T). Bioluminescence, light imaging, plate count, confocal microscopy and scanning electron microscopy were used to quantify growth. Results. On 316LSS the V loaded bead reduced both EF and PA by approximately 2 logs compared to unloaded control beads. A T alone loaded bead eliminated PA from the dual species biofilm and caused a 2-log reduction in EF. The V+T-beads reduced PA by 9-logs and EF by 8.3 logs. In terms of total CFUs V+T beads reduced the bioburden by 8.4 logs compared to V or T alone. which resulted in 2.1 and 2.6 log reductions respectively. (* P<0.05, *** P<0.001). On agar PA dominated the culture for the unloaded and V loaded beads. However, when challenged with a T loaded bead both species were able to coexist and a zone of killing was generated in both species in the multispecies biofilms. However, this zone was smaller and included more tolerant variants than the zone generated by V+T-loaded beads. Conclusions. There were species proportion differences between biofilms grown on agar and 316LSS demonstrating the importance of growth conditions on species interactions. Antibiotics against strains with differing sensitivities can shift species interactions. High purity calcium sulfate beads containing tobramycin a broad-spectrum Gram positive and negative antibiotic vancomycin, a Gram-positive targeted antibiotic killed a larger percentage of a multispecies in an in-vitro biofilm than either single gram-specific antibiotic alone, demonstrating the advantage of using combination antibiotics for treating multispecies biofilms

Aim. Fungal periprosthetic joint infections are difficult to treat and often associated with a limited outcome for patients. Candida species account for approximately 90% of all fungal infections. In vivo biofilm models play major role to study biofilm development, morphology, and regulatory molecules for bacteria. However, in vivo modeling of biofilm-associated fungi models are very rare. Furthermore, due to ethical restrictions, mammalian models are replaced with other alternative models in basic research. Recently, we have developed insect infection model G. mellonella larvae to study implant associated biofilm infections with bacteria. This model organism was not used for fungi biofilm infection yet. Thus, we aimed to establish G. mellonella as in vivo model to study fungal implant infections using Candida albicans as model organism and to test anti-fungal medication. Method. Titanium and Stainless steel K-wires were cut into small pieces with size of 4mm. For the infection process, implants were pre-incubated in specified fungal growth culture Candida albicans at 1×10. 7. CFU/ml for 30 min at 150 rpm shaking conditions. Later, these implants were washed with 10ml PBS and implanted in the larvae as mentioned. To analyze the susceptibility of the implant-associated fungal infections towards anti fungal compounds, the larvae were treated with amphotericin B, fluconazole and voriconazole after 24h of implantation. The effect of anti-fungal compounds was measured in terms of survival observation for 5 days and fungal load in larvae on 2. nd. day. To reveal the fungal biofilm formation on implant, the implants were removed on day 3 and processed for SEM analysis. Results. Pre-incubated K-wire caused the Candida infection and observed the death of the larvae. The treatment with antifungal compounds recovered the larvae from the implant-infection, except in case of Voriconazole. However, the recovery with treatment of anti fungal compounds was not effective as the larvae with planktonic infection, which highlights typical biofilm phenotype. Further, the treatment with anti-fungal compounds with Amphotericin B and Fluconazole reduced the fungal load in larvae tissue. The SEM analysis revealed the formation fungal biofilm with hyphae and spores associated with larvae tissue on implant surface. Conclusions. The results from survival analysis, antifungal treatment and SEM analysis are very promising to use of G. mellonella as in vivo model to study fungal infections on implanted materials. Our study highlights the use of G. mellonella larvae as alternative in vivo model to study implant-associated fungal infections that reduces the use of the higher mammals

Aim. The aim of this study was to define the role of implant material and surface topography on infection susceptibility in a preclinical in vivo model incorporating appropriate fracture biomechanics and bone healing. Method. The implants included in this experimental study were composed of: standard Electro polished Stainless Steel (EPSS), standard titanium (Ti-S), roughened stainless steel (RSS) and surface polished titanium (Ti-P). In an in vivo study, a rabbit humeral fracture model was used. Each rabbit received one of three Staphylococcus aureus inocula, aimed at determining the infection rate at a low, medium and high dose of bacteria. Outcome measures were quantification of bacteria on the implant and in the surrounding tissues, and determination of the infectious dose 50 (ID50). Results. Of the 72 rabbits eventually included in the in vivo study, 50 developed an infection. The ID50 was found to be: EPSS 3.89 × 103 colony forming units (CFU); RSS 8.23 × 103 CFU; Ti-S 5.66 × 103 CFU; Ti-P 3.41 × 103 CFU. Significantly lower bacterial counts were found on the Ti-S implants samples compared with RSS implants (p < 0.001) at the high inoculum. Similarly, lower bacterial counts were found in the bone samples of animals in the Ti-S group in comparison with both RSS and EPSS groups, again at the high inoculation dose (p < 0.005). Conclusions. In a preclinical in vivo model incorporating fracture biomechanics through an osteotomy, we could not identify any significant differences in susceptibility to infection when comparing titanium and steel implants with conventional (as currently used in the clinics) or modified topographies. The finding that Ti-S has a lower bacterial burden compared to both EPSS and RSS, but only when using a high bacterial inoculum, is interesting and indicates that the material (or its surface) may not influence the infection risk, but rather the infection severity. Furthermore, polished titanium implants with potential to reduce complications associated with tissue adherence, are not expected to affect the infection rate, or influence implant stability as shown in this fracture model

Background. Published simulator studies for metal/UHMWPE bearings couples showed that increasing the femoral head diameter by 1 mm increases wear by approximately 10% due to increased contact area. Therefore, there are concerns about increased wear with dual mobility hip bearings. Purpose of the study. The purpose of the study was to compare wear from dual mobility hip bearings to that with traditional fixed bearings. In addition, for the dual mobility bearings, the effect of femoral head material type on the liner wear was also evaluated. Methods. The bearings selected for the study are listed in Table 1. Prior to the start of the test all liners were soaked in lubricant for 48 hours. Hip testing was performed on a Shore Western Orbital Bearing machine in the anatomically oriented position. A simulated gait profile (synchronized at +/-23° biaxial rocking motion) with a minimum/maximum 200/2000N force was applied to the bearings at frequency of 1Hz. The lubricant used for the testing was 25% bovine serum with 0.2 % sodium azide, 20 mMol EDTA and distilled water. The test was interrupted at regular intervals for gravimetric assessment of wear amount. Findings of Study. Figure 1 shows total wear at 3 Mc and wear rates (determined from the slope of the linear regression) for all the groups. At 3 Mc, dual mobility bearings with stainless steel femoral head demonstrated 5% lower wear rate than those articulated against CoCrMo femoral heads. However, there was no statistically significant difference in the observed wear rate due to the femoral head material type. The results from the study also exhibited lower wear and wear rate for dual mobility bearings compared to fixed bearings. Dual mobility bearings with CoCrMo femoral head and stainless steel femoral head demonstrated 17% and 21% lower wear rate when compared to fixed bearings. Although dual mobility bearings possess greater contact area (due to the contact between head-liner and liner-shell compared to only head-liner in fixed bearings), no such increased trend in wear was observed. Conclusions. Dual mobility hip bearings are designed to reduce the risk of dislocation and allow for increased range of motion thus improving joint function and stability. The results from the study demonstrate that dual mobility bearings have comparable wear properties when compared to fixed bearings. For figure/table, please contact authors directly

A large body of the orthopaedic literature clearly indicates that the cement mantle surrounding the femoral component of a cemented total hip arthroplasty should be at least 2 mm thick. In the early 1970s, another concept was introduced and is still in use in France consisting of implanting a canal filling femoral component line-to-line associated with a thin cement mantle. This principle has been named the “French paradox”. An explanation to this phenomenon has been provided by in-vitro studies demonstrating that a thin cement mantle in conjunction with a canal filling stem was supported mainly by cortical bone and was subjected to low stresses. We carried out a study to evaluate the in-vivo migration patterns of 164 primary consecutive Charnley-Kerboull total hip replacements. All prosthesis in the current series combined an all-polyethylene socket and a 22.2 mm stainless steel femoral head. The monobloc double tapered (5.9 degrees) femoral component was made of 316L stainless steel with a highly polished surface (Ra = 0.04 μm), a quadrangular section, and a neck-stem angle of 130 degrees. The stem was available in six sizes with a stem length (shoulder to tip) ranging from 110 mm to 160 mm, and a neck length ranging from 24 mm to 56 mm. For each size, the femoral component was available in two to four different diameters to adapt the implant to the medullary canal. Hence the whole range comprised a total of 18 standard femoral components. The femoral preparation included removal of diaphyseal cancellous bone to obtain primary rotational and varus/valgus stability of the stem prior to the line-to-line cementation. We used the Ein Bild Roentgen Analyse Femoral Component (EBRA-FCA) method to assess the subsidence of the femoral component. At the minimum 15-year follow-up, 73 patients were still alive and had not been revised at a mean of 17.3 years, 8 patients had been revised, 66 patients were deceased, and 8 patients were lost to follow-up. The mean subsidence of the entire series was 0.63 ± 0.49 mm (0 – 1.94 mm). When using a 1.5 mm threshold, only four stems were considered to have subsided. With revision of either component for any reason as the endpoint, the cumulative survival rate at 17 years was 90.5 ± 3.2% (95% CI, 84.2% to 96.8%). With radiological loosening of the femoral component as the endpoint, the cumulative survival rate at 17 years was 96.8 ± 3.1% (95% CI, 93.2% to 100%). This study demonstrated that, in most cases, a highly polished double tapered stem cemented line-to-line does not subside up to 18-year follow-up

Aim. The aim of this study is to outline the steps and techniques required to create a patient specific 3D printed guide for the accurate placement of the origin of the femoral tunnel for single bundle ACL reconstruction. Introduction. Placements of the femoral tunnels for ACL reconstruction have changed over the years 1,2. Most recently there has been a trend towards placing the tunnels in a more anatomic position. There has been subsequent debate as to where this anatomic position should be 3. The problem with any attempt at consensus over the placement of an anatomic landmark is that each patient has some variation in their positioning and therefore a fixed point for all has compromise for all, as it is an average 4. Our aim was to attempt to make a cost effective and quick custom guide that could allow placement of the center of the patients’ newly created femoral tunnel in the mid position of their contralateral native ACL femoral footprint. Materials & Methods. We took a standard protocol MRI scan of a patient's knee without ACL injury transferred the DICOM files to a personal computer running OsiriX (Pixmeo, Geneva, Switzerland.) and analyzed it for a series of specific anatomical landmarks (fig1). These measurements and points were then utilized to create a 3D computer aided design (CAD) model of a custom guide. This was done using the 3D CAD program 123Design (Autodesk Ltd., Farnbourgh, Hampshire). This 3D model was then uploaded to an online 3D printing service and the physical guide was created in transparent acrylic based photopolymer, PA220 plastic (fig 2) and 316L stainless steel. The models created were then measured using vernier calipers to confirm the accuracy of the final guides. The models produced were accurate with no statistical difference in size and positioning of the center of the ACL footprint from the original computer model and to the position of the ACL from the MRI scans. The costs for the models 3D printed were £3.50 for the PA220 plastic, £15 for the transparent photopolymer and £25 for the 316L stainless steel. The time taken from MRI to delivery for the physical models was 7 days. Conclusion. This study serves as the first step and a proof of concept for the accurate creation of patient specific 3D printed guides for the anatomical placement of the femoral tunnel for ACL reconstruction. The guides were easy to create and produce taking only a week and with a cost of between £3.50 and £25

Aim. In vivo biofilm models play major role to study biofilm development, morphology, and regulatory molecules involve in biofilm. Due to ethical restrictions, the use mammalian models are replaced with other alternative models in basic research. Recently, we have developed insect infection model G. mellonella larvae to study implant associated biofilm infections. This model organism is easy to handle, cheap and ethical restriction free and could be used for the high through put screening of antimicrobial compounds to treat biofilm. To promote the use of this model in basic research we aimed to validate this based on the typical biofilm features such as less susceptible to the antibiotics, complexity of the biofilm structure and gene expression profile of biofilms. Method. G. mellonella larvae are maintained at 30oC on artificial diet in an incubator. Titanium and Stainless steel K-wires were cut into small pieces with size of 4mm. After sterilization with 100% alcohol, these K-wires were pre-incubated in S. aureus bacterial suspension (5×10. 6. CFU/ml) for 30 min, washed in PBS and implanted inside the larva after with help of scalpel. The larvae were incubated at 37. o. C for two day for the survival analysis. To analyze the less susceptibility of the biofilms towards antibiotics, the larvae were treated with gentamicin and compared survival with planktonic infection in G. mellonella. To reveal the complex structure of biofilm, the implants were removed and processed for the MALDI analysis. Whole genome-based transcriptome of biofilm was performed to explore the changes in transcriptional landscapes. Results. The results are very promising to validate the use of G. mellonella as in vivo model to study the biofilm formation on implanted materials. The gentamicin treatment could rescue the larvae from the planktonic infection, but not from the biofilm infection on the implants. Further, the MALDI analysis could reveal the complex structure and components of S. aureus biofilm formed on the implant inside the larvae. Finally, the transcriptomic analysis revealed the gene expression changes that can be compared to normal biofilm expression profile. Conclusions. Further, comparison of these results with other in vivo models such as rat and mouse as well as acute and chronic clinical samples from patients with implant-associated bone infections could validate and relevant use of this model to study S. aureus biofilm infections

Introduction. In my paediatric Orthopaedic practice I use Kirchner wires for the fixation of the TSF on bone. I noted a significant percentage of wire loosening during the post-operative period. The aim of this project was to establish the effectiveness of the wire clamping mechanism and find ways to reduce the incidence of wire loosening when using the TSF. Materials and Methods. In the first instance wire slippage was measured intra-operatively after the tensioner was removed using an intra-operative professional camera. Following this study mechanical tests were performed in the lab measuring the pull out properties of Kirchner wires using different bolts and different torque levels in order to tighten the wire on the fixator. Results. Our clinical study confirmed wire slippage intra-operatively immediately after the tensioner was removed. Wire slippage after the tensioner was removed was found to vary from 0.01 mm to 0.51 mm (mean 0.19 mm). Our mechanical tests showed that the ideal torque for tightening the wire on the frame using a bolt was around 15 N.m. A comparison between cannulated and slotted bolts suggested that cannulated bolts are more effective as a clamping mechanism. A comparison between aluminium made Taylor Spatial frame rings and stainless steel made Ilizarov rings suggested that the Taylor Spatial frame rings are more effective as part of a clamping mechanism. Conclusions. It is important that clinicians routinely measure the torque they use to clamp wires on circular external fixators. Clinicians and manufacturers are informed that the type of bolt used is important in maintaining wire tension. Manufacturers should design the ideal bolt which effectively grips the wire without the risk of fracture. The Ilizarov frame clamping mechanism can be effectively used with the Taylor Spatial frame