Introduction. Geometric variations of the hip joint can give rise to abnormal joint loading causing increased stress on the articular cartilage, which may ultimately lead to degenerative joint disease. In-vitro simulations of total hip replacements (THRs) have been widely reported in the literature, however, investigations exploring the tribology of two contacting cartilage surfaces, and cartilage against metal surfaces using complete hip joint models are less well reported. The aim of this study was to develop an in-vitro simulation system for investigating and comparing the tribology of complete natural hip joints and hemiarthroplasties with THR tribology. The simulation system was used to assess natural porcine hip joints and porcine hemiarthroplasty hip joints. Mean friction factor was used as the primary outcome measure to make between-group comparisons, and comparisons with previously published tribological studies. Method. In-vitro simulations were conducted on harvested porcine tissue. A method was developed enabling natural acetabula to be orientated with varying angles of version and inclination, and natural femoral heads to be potted centrally with different orientations in all three planes. Acetabula were potted with 45° of inclination and in the complete joint studies, natural femoral heads were anatomically matched and aligned (n=5). Hemiarthroplasty studies (n=5) were conducted using cobalt chrome (CoCr) heads mounted on a spigot (Figure 1), size-matched to the natural head. Natural tissue was fixed using PMMA (polymethyl methacrylate) bone cement. A pendulum friction simulator (Simulator Solutions, UK), with a dynamic loading regime of 25–800N, ± 15° flexion-extension (FE) at 1 Hertz was used. The lubricant was a 25% (v/v) bovine serum. Axial loading and motion was applied through the femoral head and frictional torque was measured using a piezoelectric transducer, from which the friction factor was calculated. Results. The correct anatomical orientation and positioning was achieved enabling in-vitro simulation testing to be conducted on hemiarthroplasty and complete hip joint samples for two-hours. Mean friction increased rapidly followed by a continued gradual increase to ≈0.03 ± 0.00 in the complete joints, with the hemiarthroplasty group plateauing at ≈0.05 ± 0.01 (Figure 2). Mean friction factor was significantly lower (t-test; p < 0.05) in the complete natural joint group. Discussion. An in-vitro simulation system for the natural hip joint with controlled orientation of the femur and acetabulum was successfully developed and used to measure friction in complete porcine hip joints and porcine hip hemiarthroplasties. A non-linear increase in friction indicative of biphasic lubrication was observed in both groups with slower exudation of fluid from the complete joints compared to the hemiarthroplasties, inferring a quicker move towards solid-phase lubrication. Higher friction in the hemiarthroplasties, which was similar to that measured in-vitro in metal-on-polyethylene THRs, was most likely due to variable clearances between the non-conforming spherical metal head and aspherical acetabulum, causing poorer congruity and distribution of the load. This could in time lead to abrasive wear and cartilage degradation. This methodology could have an important role when investigating associations between hip geometric variations, interventions for hip disease/pathology, and risk factors for cartilage degeneration

Purpose. The management of moderate to large engaging Hill-Sachs lesions is controversial and surgical options include remplissage, allograft reconstruction, and partial resurfacing arthroplasty. Few in-vitro studies have quantified their biomechanical characteristics and none have made direct comparisons. The purpose of this study was to compare joint stability and range of motion (ROM) among these procedures using an in-vitro shoulder simulator. It was hypothesized that all procedures would prevent defect engagement, but allograft and partial resurfacing would most accurately restore intact biomechanics; while remplissage would provide the greatest stabilization, possibly at the expense of motion. Method. Eight cadaveric shoulders were tested on an active in-vitro shoulder simulator. Each specimen underwent testing in 11 conditions: intact, Bankart lesion, Bankart repair, and two unrepaired Hill-Sachs lesions (30% & 45%) which were then treated with each of the three techniques. Anterior joint stability, ROM in extension and internal-external rotation, and glenohumeral engagement were assessed. Stability was quantified as resistance, in N/mm, to an anteriorly applied load of 70N. Results. Remplissage significantly increased joint stiffness compared to both defects (6.43.8 N/mm, p=0.01) and the allograft and partial resurfacing (p <= 0.04). No technique significantly surpassed the stability of the intact state (p>0.05). In adduction, the remplissage significantly reduced internal-external rotation compared to both defects (p <= 0.01), but only the 30% repair caused a significant change compared to the intact state (14.511.3 N/mm, p=0.05). In abduction, all repairs reduced rotation ROM compared to the Hill-Sachs defect (>= 8.24o, p <= 0.04), but none with respect to the intact condition (p >= 0.05). Remplissage had significantly less extension than either resurfacing procedure (>= 15.4o, p <= 0.02) and resulted in a greater reduction in extension ROM for 45% defects compared to 30% defects (11.918.91, p=0.06). All unrepaired lesions engaged during extension. None of the remplissage or allograft reconstructions engaged, however, 75% of partial resurfacing arthroplasties partially engaged. Conclusion. This study is the first biomechanical evaluation to directly compare three surgical procedures for engaging Hill-Sachs lesions. Each procedure enhanced stability; however, the enhancement provided by the resurfacing repairs more closely resembled the intact state. Remplissage of the 30% and the 45% defects improved stability and eliminated glenohumeral engagement but caused significant and progressive reductions in ROM. In comparison, both the allograft and partial resurfacing procedures re-established ranges of motion approaching those of the intact joint; however, the partial resurfacing could not fully prevent engagement. These findings indicate that the effects of each technique are not equivalent and further clinical and biomechanical studies are required

According to the Canadian Joint Replacement Registry, in 2010–2011 there were 17,303 hip replacements performed in Canada of which 10% were revisions. More than 73% of these revisions were for aseptic loosening, wear, and instability which suggests that hip biomechanics may be anomalous. The hip joint is often described as a ball-and-socket joint, which implies congruent interacting bony joint surfaces and purely rotational relative motion. This study challenges the accepted kinematic description by analysing detailed motion of the hip joint using surgical navigation technology. An in-vitro study was conducted using twelve fresh frozen cadaveric human hemi-pelvises in three soft-tissue states. Three dimensional digital models of each specimen were generated from segmentation of computed tomography images. Local coordinate reference devices, mounted on the proximal femur and anterior-superior iliac spine, were registered and tracked with an active optical localisation system. Positions and orientations were imported to custom virtual surgery software. The study used soft-tissue states as one variable and twelve combinations of flexion/extension, abduction/adduction and internal/external rotation as the other variable. The entire series of motions were repeated for (I) soft tissues intact, (II) capsule intact and (III) completely disarticulated joint. Translation of the femoral head with respect to the acetabular cup at each frame was extracted from the recorded data. An Analysis of Variance (ANOVA) was used to determine whether the means of translations in each dissection states were significantly different. Translatory motion was observed in all specimens. Significant differences were found between magnitudes of translation in distinct soft tissue states (p<0.001). Investigation of sudden changes in translational tracks of each femoral head, plotted as 2-D wave forms, showed that there were no correlations between contact zones and excursions. Interestingly, three specific maneuvers were found to be more likely to cause maximal translations: ankle on knee (where the femur is flexed and externally rotated while being abducted), ankles crossed (where the femur is flexed and externally rotated while being adducted) and the pivot (where the femur is extended and externally rotated while the pelvis is abducted). The highly accurate surgical navigation system detected subtle translatory behaviour in hip motion. The data provided evidence that the femoral head translates with respect to the acetabular cup with or without any contact between the two bones; such impingements were previously thought to be the main reason for femoral excursion. The statistical significance found between translations exhibited at different soft tissue states indirectly supports an aspherical model of the adult hip, with kinematics driven by both soft tissue and the anatomy. This work towards an improved biomechanical model of the hip could help guide both surgical intervention and implant design, leading to improved outcomes for the hundreds of thousands of hip surgeries performed globally each year

Introduction. The frequency of revision hip arthroplasty is increasing with the increasing life expectancy and number of individuals treated with joint replacement. Newer porous implants have been introduced which may provide better treatment options for revision arthroplasty. These may require cementation to other prosthesis components and occasionally to bone, however, there is currently no information on how these porous implants interface with cement. Materials and Methods. Cylindrical bone (control group) and porous metal probes with a diameter and height of 10mm were created and subsequently cemented in a standardized setting. These were placed under tensile and torsional loading scenarios. In this experimental study, 10 human femoral heads were used to create 20 cylindrical probes with a diameter and height of 10mm. One side was tapered to 6mm for cementation and interface evaluation. A further set of 20 probes of a porous metal implant (Trabecular Metal®) was created with the same geometry. After the probes were created and lavaged, they were cemented at the tapered surface using a medium viscosity cement at a constant cementation pressure (1.2N/mm2). The setup allowed for comparison of the porous metal/cement interface (group A) with the well-studied control group interface bone/cement (group B). The maximal interface stability of groups A and B were evaluated under tensile and rotational loading scenarios and the cement penetration was measured. Results. Group A showed a significantly decreased cement penetration under the same cementation pressure than group B, yet the interface showed a significantly more stable interface in the measured tests: larger maximum tensile force (effect size 2.7), superior maximum tensile strength (effect size 2.6), greater maximum torsional force (effect size 2.2), and higher rotational stiffness (effect size 1.5). Discussion and Conclusion. The porous metal/cement interface displays substantially more stability than does the bone/cement interface. Although these tests evaluate initial stability in an in-vitro setting, they appear promising with regard to their cemented stability. As a result, a multicomponent porous metal construct with cement interdigitation should not compromise the overall implant primary stability

Purpose. The coronoid process is an integral component for elbow stability. In the setting of a comminuted coronoid fracture, where repair is not possible, a prosthetic device may be beneficial in restoring elbow stability. The hypothesis of this in-vitro biomechanical study was that an anatomic coronoid prosthesis would restore stability to the coronoid deficient elbow. Method. A metal coronoid prosthesis was designed and developed based on CT-derived images adjusted for cartilage thickness. The kinematics and stability of eight fresh-frozen male cadaveric arms (mean age 77.4 years, range 69–92 years) were quantified in the intact state; after collateral ligament sectioning and repair (control state); after a simulated 40% transverse coronoid fracture; and after implantation of a coronoid prosthesis. Elbow flexion was simulated passively with the arm oriented in the varus position and the forearm in pronation. Varus-valgus angulation (VV) and internal-external rotation (IE) of the ulna relative to the humerus were quantified with an electromagnetic tracking system (Flock of Birds, Ascension Technologies, Burlington, VT, static accuracy: 1.8mm position, 0.5 orientation). Results. No significant difference was found between the intact elbow and the native coronoid control state with collateral ligament repair (mean standard deviation) (VV=0.13.1, p=0.9; IE=0.82.59, p=0.4). A significant decrease in stability was observed following the 40% coronoid fracture (VV=5.73.4, p<0.01; IE=10.93.35, p<0.001). Following coronoid hemi-arthroplasty, no significant difference in stability was found between the coronoid prosthesis and the control state (VV=0.22.7, p=1.0; IE=1.33.0, p=0.8). Conclusion. An anatomic coronoid prosthesis restores the stability of the coronoid deficient elbow similar to the intact state. Further studies are needed to determine the optimum fixation method of this device and to determine the range of sizes which would be required for the successful commercialization of this device for patient use. Clinical trials will be required to confirm the favourable findings of this in-vitro investigation

Background. Complications of metal-on-metal hip resurfacing, leading to implant failure, include femoral notching, neck fracture, and avascular necrosis. Revision arthroplasty options include femoral-only revision with a head, however mis-matching radial clearance could accelerate metal ion release. Alternatively, revision of a well-fixed acetabular component could lead to further bone loss, complicating revision surgery. We have developed a ceramic hip resurfacing system with a titanium-ceramic taper junction; taking advantage of the low frictional torque and wear rates that ceramic affords. Taking a revision scenario into account, the ceramic head has a deep female taper for the resurfacing stem, but also a superficial tapered rim. Should revision to this resurfacing be required, any femoral stem with a 12/14 taper can be implanted, onto which a dual taper adaptor is attached. The outer diameter of the taper adaptor then becomes the male taper for the superficial taper of the ceramic head; ultimately allowing retention of the acetabular component. In an in-vitro model, we have compared the fretting corrosion of this taper adaptor to existing revision taper options: a titanium-cobalt chrome (Ti-CoCr) taper junction, and a titanium-titanium sleeve-ceramic (Ti-Ti-Cer) taper junction. Methods. To simulate gait, sinusoidal cyclical loads between 300N-2300N, at a frequency of 3Hz was applied to different neck offsets generating different bending moments and torques. Bending moment and frictional torque were tested separately. An electrochemical assessment using potentiostatic tests at an applied potential of 200mV, was used to measure the fretting current (μA) and current amplitude (μA). In a short term 1000 cycle test with bending moment, four neck lengths (short to x-long) were applied. For frictional torque, four increments of increasing torque (2-4-6-8Nm) were applied. In a long-term test using the taper adaptor, the combination of worst-case scenario of bending and torque were applied, and fretting currents measured every million cycles, up to 10 million cycles. Results. Short-term test: When adjusting bending moment the taper adaptor displayed equivalent fretting currents for the short and medium neck lengths. Using the long neck the taper adaptor displayed a higher fretting current, though this was not significant (Kruskal-Wallis test). However, using the X-Long adaptor the fretting current was significantly higher than the other tapers (Fig. 1). Across the range of frictional torques, the taper adaptor displayed equivalent fretting currents to the Ti-CoCr single taper. The Ti-Ti-Cer displayed the lowest fretting currents but this was not significant when compared to the other combinations (Fig. 2). Long-term test: combining the worst case bending (X-Long) and torque (8Nm) showed consistent fretting currents and current amplitudes across 10 million cycles, with no significant variance of the median values (Fig. 3). Conclusion. Electro-chemical testing has highlighted caution if revision arthroplasty is performed using the X-Long taper adaptor. However for shorter neck lengths, fretting corrosion is comparable to existing revision tapers. The LIMA ceramic resurfacing arthroplasty is an integrated system and can be safely revised to a conventional hip system using a dual taper head, and taper adaptor

Background

Correct positioning of the femoral component in resurfacing hip arthroplasty (RHA) is an important factor in successful long-term outcomes. The purpose of computer-assisted navigation (CAS) in resurfacing is to insert the femoral neck guide wire with greater accuracy and to help size the femoral component, thus reducing the risk of notching at the head and neck junction. Several recent studies reported satisfactory precision and accuracy of CAS. However, there is little evidence that CAS is useful in the presence of anatomical deformities of the proximal femur, which is frequently observed in young patients with secondary degenerative joint disease.

Our aim was to compare the biomechanical strength modified side-to-side repair with modified pulvertaft technique keeping overlap length, anchor points, type of suture, suture throw and amount of suture similar.

In our study, we have used turkey tendons. Two investigators performed 34 repairs during one summer month. All mechanical testing was carried out using the tensile load testing machine. Variables measured were maximum load, load to first failure, modulus, load at break, mode of failure, site of failure, tensile strain, and tensile stress. The statistical comparison was carried by Levene's test and T test for means.

The mean maximum load tolerated by modified side-to-side repair was 50.3N(S.D13.7) and that by modified pulvertaft 46.96N(S.D: 16.4), overall it was 48.29 N (S.D: 14.57). The tensile stress at maximum load for modified pulvertaft and modified side-to-side repair was 4.2MPa(S.D: 3.1) and 4.7 MPa (S.D: 3.8) respectively {Overall 4.3MPa(S.D: 3.5)}. The tensile stress at yield was 4.01 MPa (S.D: 3.1) and 5.5 MPa (S.D: 3.7) respectively for modified pulvertaft and modified side-to-side repair {overall 4.44 MPa (S.D: 3.45)}. The tensile strain at maximum load respectively for side-to-side and modified pulvertaft repair was 7.87%(S.D: 33.3) and 7.84%(S.D: 34.02) respectively.

We found no statistical difference between 2 repairs in terms of strength, load to first failure, and maximum load to failure. The suture cut through was the commonest mode of failure.

Our study uniquely compares two techniques under standard conditions, and contrary to existing evidence found no difference.

Introduction

Fractures of the proximal humerus represent a major osteoporotic burden. Recent developments in CT imaging have emphasized the importance of cortical bone thickness distribution in the prevention and management of fragility fractures. We aimed to experimentally define the CT density of cortical bone in the proximal humerus for building cortical geometry maps.

Revision total hip replacements are likely to have higher complication rates than primary procedures due to the poor quality of the original bone. This may be constrained to achieve adequate fixation strength to prevent future “aseptic loosening” [1]. A thin, slightly flexible, acetabular component with a three dimensional, titanium foam in-growth surface has been developed to compensate for inferior bone quality and decreased contact area between the host bone and implant by better distributing loads across the remaining acetabulum in a revision situation. This is assumed to result in more uniform bone apposition to the implant by minimizing stress concentrations at the implant/bone contact points that may be associated with a thicker, stiffer acetabular component, resulting in improved implant performance.[2] To assemble the liner to the shell, the use of PMMA bone cement is recommended at the interface between the polyethylene insert and the acetabular shell as a locking mechanism configuration may not be ideal due to the flexibility in the shell [3].

The purpose of this study was to quantify the mechanical integrity of a thin acetabular shell with a cemented liner in a laboratory bench-top total hip revision condition. Two-point loading in an unsupported cavity was created in a polyurethane foam block to mimic the contact of the anterior and posterior columns in an acetabulum with superior and inferior defects. This simulates the deformation in an acetabular shell when loaded anatomically [4]. The application has been extended to evaluate the fatigue performance of the Titanium metal foam Revision Non-Modular Shell Sequentially Cross Linked PE All-Poly Inserts and its influence on liner fixation.

Existing techniques of posterior multi-point C1/2 stabilisation are technically demanding and can be hazardous. The coauthors have recently reported successful atlantoaxial fusion using a novel C1/2 stabilisation technique employing C1 multi-axial posterior arch screws (MA-PAS) in a clinical series of three patients where anatomical anomalies precluded established techniques.

The technically less demanding nature of this new technique, and possible wider application in patients with normal anatomy, led the authors to investigate its biomechanical stability compared to other established techniques.

Twenty-four human fresh-frozen cadaveric spines were harvested C0-C5. Motion was restricted to between C0 and C4. Each spine was non-destructively tested in flexion/extension, lateral bending and axial rotation, firstly in the intact state and then after Type 2 odontoid fracture destabilisation and insertion of Magerl-Gallie, Unicortical Harms, Bicortical Harms or MA-PAS instrumentation. ROM between C1 and C2 was monitored using two digital cameras. Results for each technique were compared statistically compared using ANOVA.

The C1-C2 joint of the intact spines demonstrated high flexibility in flexion/extension (16.5deg). After instrumentation all specimens showed significantly reduced ROM in flexion/extension (Magerl-Gallie FE = 4.2deg, Unicort Harms FE = 7.2deg, Bicort Harms FE = 4.4deg). Lateral bend ROM of instrumented specimens (Magerl-Gallie LB =3.8deg, Unicort Harms LB = 3.8deg, Bicort Harms LB =2.3 deg) was, however, similar or slightly greater than intact (2.7 deg) . MA-PAS showed similar ROM in flexion/extension (4.2 deg) as the Magerl-Gallie and Harms techniques but was slightly higher in lateral bend (5.3 deg).

The MA-PAS technique was shown to have similar biomechanical stability to the Magerl-Gallie and Harms techniques. Given the demonstrated biomechanical stability of the MA-PAS technique, it may be a suitable alternative to the existing technically demanding, and possibly more hazardous, multi-point fixation techniques in patients with normal, as well as anomalous, C1/2 segmental anatomy.

Direct arthroscopic cartilage assessment remains the gold standard. It is recommended by the International Cartilage Repair Society (ICRS) to systematically assess cartilage status during arthroscopy but this examination is highly subjective, poorly reproducible, time-consuming and lacks precision. US has shown good potential for cartilage evaluation but is limited in extra-articular conditions. It is also difficult to manually maintain a perfect perpendicularity between the ultrasound beam and the curved surface of the cartilage. Therefore, we have developed a navigated intra-articular US probe (NIAUS). The NIAUS probe could contribute to a more exhaustive and direct intra-articular evaluation of cartilage integrity. Navigation enables control of the US echo pulse perpendicularity and its localisation relative to the joint. Our objectives were (1) to evaluate automatic cartilage thickness measurement with the NIAUS probe in comparison to high definition MRI on cartilage samples, (2) to generate a real-time 3D map of the thickness parameter on samples, and (3) to demonstrate the feasibility of a full NIAUS probe cartilage scan on a specimen distal femur in arthroscopic conditions.

The NIAUS probe is a 4.5mm probe consisting of a 64 element linear array transducer with a central frequency of 13 MHz and a motorised head. The NIAUS probe is navigated. The rotating US head position is controlled by navigation in order to enable constant perpendicular acquisition of cartilage. The NIAUS probe thickness measurement (1) was evaluated on bone and cartilage samples of 9 tibial plateaus. The cartilage thickness was measured via automatic segmentation. Each sample was also scanned in a high resolution MRI (4,7 Tesla) and cartilage thickness was semi-automatically extracted for comparison. During NIAUS scan, (2) a visual 3D map was generated. Finally (3), we scanned two distal femurs with the NIAUS probe in arthroscopic navigated conditions on one specimen and a 3D map of the distal femur thickness was generated in real time.

NIAUS thickness measurement (1) absolute error compared to MRI for 9 plateaus ranged from 0.15mm to 0.32mm in median, p25=0.07 and 0.18, p75=0.28 and 0.5 respectively. 3D maps of the sample cartilage thickness (2) were generated in real time during the NIAUS scan. The cadaveric procedure (3) was conducted without incident via the two anterior portals and a 3D map of the distal femurs cartilage thickness was generated.

A precise US arthroscopic grading and scoring of cartilage during surgery could help for better standardisation, prediction of results and making “live” decisions. Our in vitro experiment shows good results compared to MRI for NAIUS cartilage thickness measurement, and our cadaveric study demonstrate the feasibility of a NIAUS scan in arthroscopic conditions. Our results are encouraging and a clinical trial is currently being designed for preliminary in vivo NIAUS evaluations of cartilage thickness compared to MRI.

Arthroscopic electrosurgical tools for ablative, desiccating or coagulative effect are delivered as monopolar or bipolar probes. Monopolar electrosurgery delivers various profiles of heat energy directly to the tissue within a non-conductive irrigant (such as water or glycine) whereas bipolar electrosurgery creates an energy source by producing an electrical arc between the bipolar electrodes on the instrument head within an electro-conductive irrigation solution (saline) - and the heat generated is then transferred to the target tissues. This study investigated the heat generation within the simulated in-vitro test model to review the level of local heat production and potential local tissue heat. In a simulated In-vitro testing environment the local heat generation using bipolar or monopolar electrosurgical probes at standard power setting in either saline or water was tested, both touching and not touching a simulated tissue target, and for variable on-times. Monopolar generated relatively little heat when used in water and not touching the tissue. By contrast the bipolar wand generated potentially damaging local tissue temperature rises when used in saline and not touching the tissue. Both probes generated high local tissue heat when touching the tissue in their recommended irrigation solution. Monopolar electrosurgery delivered high localized temperature to the simulated tissue surface, but produced relatively little heat when not touching the tissue in a water solution. Bipolar however created high local temperature within the fluid adjacent to the probe irrespective if it was touching the tissue or not. Activation of the bipolar probe away from the tissue in saline irrigation may create a potential harmful temperature within the fluid medium without delivering therapeutic thermal effect to the target tissues. Monopolar electrosurgery appears to deliver a more controlled thermal effect, and only when in contact with the target tissues – potentially creating a reduced collateral thermal footprint

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

3D printing and Bioprinting technologies are becoming increasingly popular in surgery to provide a solution for the regeneration of healthy tissues. The aim of our project is the regeneration of articular cartilage via bioprinting means, to manage isolated chondral defects. Chrondrogenic hydrogel (chondrogel: GelMa + TGF-b3 and BMP6) was prepared and sterilised in our lab following our standard protocols. Human adipose-derived mesenchymal stem cells were harvested from the infrapatellar fat pad of patients undergoing total knee joint replacements and incorporated in the hydrogel according to our published protocols. The chondrogenic properties of the chondrogel have been tested (histology, immunohistochemistry, PCR, immunofluorescence, gene analysis and 2. nd. harmonic generation microscopy) in vitro and in an ex-vivo model of human articular defect and compared with standard culture systems where the growth factors are added to the media at repeated intervals. The in-vitro analysis showed that the formation of hyaline cartilage pellet was comparable between the two strategies, with a similar metabolic activity of the cells. These results have been confirmed in the ex-vivo model: hyaline-like cartilage was observed within the chondral defect in both the chondrogel group and the control group after 28 days in culture. The use of bioprinting techniques in vivo requires the ability of stem cells to access growth factors directly in the environment they are in, as opposed to in vitro techniques where these factors are provided externally at recurrent intervals. This study showed the successful strategy of incorporating chondrogenic growth factors for the formation of hyaline-like cartilage in vitro and in an ex-vivo model of chondral loss. The incorporation of chondrogenic growth factors in a hydrogel is a possible strategy for articular cartilage regeneration

Staphylococcus aureus is the most frequently isolated organism in periprosthetic joint infections. The mechanism by which synovial fluid (SF) kills bacteria has not yet been elucidated, and a better understanding of its antibacterial characteristics is needed. We sought to analyze the antimicrobial properties of exogenous copper in human SF against S. aureus. SF samples were collected from patients undergoing total elective knee or hip arthroplasty. Different S. aureus strains previously found to be sensitive and resistant, UAMS-1 and USA300 WT, respectively, were used. We performed in-vitro growth and viability assays to determine the capability of S. aureus to survive in SF with the addition of 10µM of copper. We determined the minimum bactericidal concentration of copper (MBC-Cu) and evaluated the sensitivity to killing, comparing WT and CopAZB-deficient USA300 strains. UAMS-1 evidenced a greater sensitivity to SF when compared to USA300 WT, at 12 (p=0.001) and 24 hours (p=0.027). UAMS-1 significantly died at 24 hours (p=0.017), and USA300 WT survived at 24 hours. UAMS-1 was more susceptible to the addition of copper at 4 (p=0.001), 12 (p=0.005) and 24-hours (p=0.006). We confirmed a high sensitivity to killing with the addition of exogenous copper on both strains at 4 (p=0.011), 12 (p=0.011), and 24 hours (p=0.011). Both WT and CopAZB-deficient USA300 strains significantly died in SF, evidencing a MBC-Cu of 50µM against USA300 WT (p=0.011). SF has antimicrobial properties against S. aureus, and UAMS-1 was more sensitive than USA300 WT. The addition of 10µM of copper was highly toxic for both strains, confirming its bactericidal effect. We evidenced CopAZB-proteins involvement in copper effluxion by demonstrating the high sensitivity of the mutant strain to lower copper concentrations. Thus, we propose CopAZB-proteins as potential targets and the use of exogenous copper as possible treatment alternatives against S. aureus

Aim. The management of PJIs is slowed down by the presence of bacteria forming biofilms where they may withstand antibiotic therapy. The use of adjuvant strategies, such as hydrolytic enzymes cocktail targeting biofilm matrices and facilitating their dispersion, is a promising option to limit impact of biofilms. Our aim was to evaluate the effect of enzymes cocktail combined with antibiotic dual therapy of rifampicin and vancomycin in a relevant in-vitro model. Method. Mature methicillin-resistant Staphylococcus aureus biofilms were grown on Ti-6Al-4V coupons by adding 1mL of a 8Log10 ATCC 33591 suspension in TGN (TSB + 1% glucose + 2% NaCl) to 24-wells plates containing the coupons and incubating the plates for 24h at 37°C with a continuous 50rpm agitation. The samples were rinsed and placed in 6 wells plates containing 1ml of the enzymatic cocktail (C.D.D.) solution (tris-buffered (pH 7.0) solution of 400 U/ml of aspecific DNA/RNA endonuclease, 50 U/ml of endo-1,4-b-D-glucanase, and 0.06 U/ml of β-N-acetylhexosaminidase). 9ml of TGN or TGN containing antibiotics RIF/VAN (rifampicin 5µg/mL + vancomycin 8µg/mL) at clinically relevant concentrations found locally in bone or joints, was then added and the samples were incubated in identical conditions for 24h. The samples were then recovered and rinsed. CFU counts were obtained by recovering the bacteria with sonication, serial dilutions, and TSA plating. Biomass was determined via crystal violet staining, followed by dye solubilization in acetic acid, and absorbance measurement using a spectrophotometer. Results. Significant reductions in bacterial counts were observed in biofilms exposed to either RIF/VAN or RIF/VAN+CDD, by respectively 2,6 and 3,7Log10 when compared to samples reincubated with TGN alone (p <0.05). Additionally, CFU counts in samples exposed to RIF/VAN+CDD were reduced by 1,1Log10 when compared to those exposed to RIF/VAN (p<0,05). Significant reduction in biomass (-29,8%, p<0.05) was observed for coupons exposed to RIF/VAN+CDD when compared to C.D.D alone (figure 1). Conclusions. The concurrent utilization of enzymes with rifampicin and vancomycin, holds promise as a feasible method to address periprosthetic joint infections (PJIs). For any tables or figures, please contact the authors directly

Objective. Clinical wear depends on several factors such as implant specific factors (material, design, and sterilization), surgical factors/techniques, and patient-specific factors (weights and activities). The load magnitude for wear testing in the standard protocols (i.e., 2 kN as per ASTM F1714 or 3 kN as per ISO 14243-3) represent an average patient weight and does not address the other “what-if”’ scenarios (i.e., wear vs. patient weights, activities, duration, etc.,). The results from in-vitro testing report the data in wear (mg) or wear rate (mg/Mc) and are only applicable to the parameters (i.e., loads, bearing diameter, thickness, etc.,) used for the testing and not suitable to the variations seen in clinical scenarios. Therefore, it is essential to present the wear summary that can normalize the parameters and which is relevant in both in-vitro and in-vivo conditions. The goal of the current study is an attempt to present wear as a parameter (i.e., wear factor that combines the wear test data and established- theoretical relationship) and is thus applicable in both in-vivo and in-vitro scenarios. Methods. Wear factor was first evaluated using actual wear testing conducted on metal on cross-linked polyethylene bearings along with well-established Dowson's wall bridge equation. As per Dowson-Wallbridge, volumetric wear is V=2.376·KNWR+C or K=V/(2.376·NWR) where V is the volumetric wear in mm. 3. , K is the wear factor in mm. 3. /Nmm, N is the number of cycles, W is the load in Newtons, R is the bearing radius in mm, and C is the creep (assumed to be negligible, i.e., C=0 in this model. 28 mm simulator wear was first used to evaluate wear factor, but since simulator wear presented as a mass loss, these results were converted to volumetric wear using the equation. V. =. m. /. ρ. ,. (m is the wear in mg and r is the density of XLPE in mg/mm. 3. (=0.923). The Dowson-Wallbridge equation was then validated for predictive accuracy against actual wear testing on the predecessor THR system. The wear factor thus obtained was used to compute the theoretical-wear for other sizes (i.e., 42 and 46 mm bearings). The theoretical-wear was then compared to simulator wear for predictive accuracy. Results & Discussion. Figure1 below shows the verification of the predictive capability of the Dowson-Wallbridge equation against historical wear data. The theoretical-wear (for 42 and 46 mm bearings) evaluated using wear factor was in good agreement with the simulator wear The results show Dowson's Wallbridge equation was verified and thus can be used to assess the wear factor. The results show that the wear factor for XLPE system is 1.79 × 10. −10. mm. 3. /N-mm. Elfick et al. evaluated the clinical wear factor for 47 retrieved acetabular components with varying diameters, patients, and liner thickness ranging from 1.8 mm (thinnest) to 11.0 mm thick liners using the Dowson-Wallbridge equation and reported the mean wear factor as 1.93 × 10. −9. mm. 3. /N-m. The results of the current evaluation are also in good agreement with clinical studies

INTRODUCTION. Deformation of modular acetabular press-fit shells is a topic of much interest for surgeons and manufacturer. Such modular components utilise a titanium shell with a liner manufactured from metal, polyethylene or ceramic. Initial fixation is achieved through a press-fit between shell and acetabulum with the shell mechanically deforming upon insertion. Shell deformation may disrupt the assembly process of inserting the bearing liner into the acetabular shell for modular systems. This may adversely affect the integrity and durability of the components and the tribology of the bearing. OBJECTIVE. Most clinically relevant data to quantify and understand such shell deformation can be achieved by cadaver measurements. ATOS Triple Scan III was identified as a measurement system with the potential to perform those measurements. The study aim was to validate an ATOS Triple Scan III optical measurement system against a co-ordinate measuring machine (CMM) using in-vitro testing and to check capability/ repeatability under cadaver lab conditions. METHODS. Two sizes of custom-made acetabular shells were deformed using a uniaxial/ two-point loading frame and measured repeatedly at different loads. Roundness measurements were performed using both the ATOS Triple Scan III optical system and a co-ordinate measuring machine and then compared. The repeatability was also tested by measuring shells pre and post insertion in a cadaver lab multiple times. RESULTS. The in-vitro comparison with CMM demonstrated a maximum difference of 5 µm at the rim and 9 µm at the measurement point closest to the pole of the shell. Deviation between the two systems increased towards the pole for the in-vitro measurements. However as press fit shells are designed to be loaded at the rim, this is likely where the maximum deflection will occur as a result of the highest force. Therefore, the increased difference between the systems towards the pole is of less importance compared with accuracy at the rim. Maximum repeatability was below 1 µm for the CMM and 3 µm for the ATOS Triple Scan III optical system. Repeatability of the ATOS Triple Scan III optical system was comparable between pre insertion (below 2 µm) and post insertion (below 3 µm) measurements in the cadaver lab. In addition these values were comparable to the repeatability measured during the in-vitro validation study (below 3 µm). This proves high repeatability not only for in-vitro conditions, but also for the cadaver lab as well. CONCLUSIONS. This study supports the view that the ATOS Triple Scan III optical system fulfils the necessary requirements to accurately measure shell deformation in cadavers. As a result, the authors propose further studies using cadavers to identify the impact of other factors upon shell deformation. Other factors to be measured include bone strength, shell diameter, under reaming and wall thickness

Background:. Standardized preclinical wear testing cannot replicate the variations of wear rates and wear mechanisms seen in-vivo [1]. Therefore, a lot of studies focused on testing scenarios which replicate a wider range of patient-specific conditions such as different activities or malalignment of components. However, differences between the in-vivo and in-vitro situation regarding the environmental conditions are often neglected. Considerable differences between the in-vivo and the in-vitro situation are related to the surrounding synovial fluid and its in-vitro substitute (bovine serum). For the in-vivo knee only small volumes (1–4 ml) of synovial fluid are reported [2]. However, for in-vitro testing several hundreds of milliliters of bovine serum are typically used. Therefore, the hypothesis of this study is that fluid volume significantly influences the wear rates in simulator tests. Material and Methods:. For wear testing an established implant system (Sigma® PFC, DePuy, Warsaw, USA) has been used. Four wear tests with four different testing volumes of bovine serum were carried out: 250 ml; 150 ml; 75 ml; 45 ml. The testing volume of the original chamber (250 ml) was reduced using solids (Fig. 1). Care was taken, that the contact surfaces of the implants were completely immersed and the fluid level was kept constant in all cases (Fig. 1). The testing fluid was maintained at a temperature of 37 ± 1°. All wear tests were run displacement controlled according to ISO 14243-3: 2004 on an AMTI knee simulator. Results:. No significant differences could be detected for testing with 250 ml or 150 ml testing fluid (wear rate 9.1 mg/Mc and 8.2 mg/Mc, respectively; p = 1.000). Further volume reduction leads to a significant decrease in wear rate: Using a testing volume of 75 ml the wear rate decreases to 5.2 mg/10. 6. cycles (p = 0.010) and with a testing volume of 45 ml a wear rate of 0.9 mg/10. 6. cycles (p ≤ 0.001) could be observed. A serum degradation during simulation was observed. The amount of degradation increased with decreased serum volume, as shown through precipitation and turbidity of the serum. A small increase in wear particles size with smaller used volumes could be observed. Conclusion:. It has been shown, that the testing volume highly affects the PE wear rates. A larger testing volume caused a higher wear rate. Otherwise larger wear particles were observed when testing was carried out with a smaller testing volume. It is not known, which testing situation better replicates the in-vivo situation. The lubricant affects the wear behavior in a permanent way. Meaning, that the lubricant impacts the wear behavior of joint replacements with every activity carried out. Considering this, the role of the lubricant is underestimated and may be a highly relevant factor for the in-vivo and in-vitro wear behavior