Introduction. During revision surgery, the active electrode of an electrocautery device may get close to the implant, potentially provoking a flashover. Incidents have been reported, where in situ retained hip stems failed after isolated cup revision. Different sizes of discoloured areas, probably induced by electrocautery contact, were found at the starting point of the fracture. The effect of the flashover on the implant material is yet not fully understood. The aim of this study was to investigate the fatigue strength reduction of Ti-6Al-4V titanium alloy after electrocautery contact. Material and Methods. 16 titanium rods (Ti-6Al-4V, extra low interstitial elements, according to DIN 17851, ⊘ 5 mm, 120 mm length) were stress-relief annealed (normal atmosphere, holding temperature 622 °C, holding time 2 h) and cooled in air. An implant specific surface roughness was achieved by chemical and electrolytic polishing (Ra = 0.307, Rz = 1.910). Dry (n = 6) and wet (n = 6, 5 µl phosphate buffered saline) flashovers were applied with a hand-held electrode of a high-frequency generator (Aesculap AG, GN 640, monopolar cut mode, output power 300 W, modelled patient resistance 500 Ω). The size of the generated discoloured area on the rod's surface - representative for the heat affected zone (HAZ) - was determined using laser microscopy (VK-150x, Keyence, Japan). Rods without flashover (n = 4) served as control. The fatigue strength of the rods was determined under dynamic (10 Hz, load ratio R = 0.1), force-controlled four-point bending (FGB Steinbach GmbH, Germany) with swelling load (numerical bending stress 852 MPa with a bending moment of 17.8 Nm) until failure of the rods. The applied bending stress was estimated using a finite-element-model of a hip stem during stumbling. Metallurgical cuts were made to analyse the microstructure. Results. The control rods failed at the pushers of the setup (median: 94,550, range: 194,000 cycles). The rods with flashover failed directly at the HAZ significantly earlier than the control rods (p = 0.018). The analysis of the microstructure showed a transformation of the equiaxed α+β microstructure to a bimodal state. The size of the HAZs were equal for the dry (median: 1.51 mm. 2. , range: 5.68 mm. 2. ) and wet flashovers (median: 0.92 mm. 2. , range: 2.50 mm. 2. , p = 0.792). The cycles to failure were smaller for the dry flashover (median: 22,650 cycles, range: 5,700) than the wet flashover but not reaching statistical significance (median: 32,200, range: 57,900; p = 0.052). No correlation between the dimension of the HAZs and the cycles to failure was found (dry: r. 2. = 0.019, p = 0.8; wet: r. 2. = 0.015, p = 0.721). Discussion. Flashovers induced by an electrocautery device reduce the fatigue strength of Ti-6Al-4V. Since no correlation between the size of the HAZs and the cycles to failure was found, every contact between electrocautery devices and metal implants should be avoided. For any figures or tables, please contact authors directly

Introduction. Laser marking of implants surfaces is necessary in order to provide traceability during revisions which will help identify product problems more quickly, better execute product recalls and improve patient safety. There are several methods of marking employed within the medical field such as chemical etching, electro pencil marking, mechanical imprinting, casting of markings, marking with vibratory type contact, ink jet, hot foil and screen printing. However, these methods have various drawbacks including marking durability or addition of potentially toxic chemical compounds. As a result laser marking has become the preferred identification process for orthopedic implants. Laser marking is known for its high visual quality, good reproducibility and precision. However there are concerns about the laser marking potential to affect fatigue life of a device. There is a limited number of research papers that studied the effect of laser marking on fatigue life of implants. The objective of the current study is to investigate the effects of laser marking on the fatigue life of titanium alloy material. Material and Methods. Two groups of four point bend specimens were used to investigate the effect of laser marking on the fatigue life. The first group comprised of the specimens without laser marking while the second group comprised of specimens with laser marking currently utilized for the implant surfaces. Prior to conducting the fatigue testing, a non-destructive X-ray diffraction (XRD) residual stress analysis was conducted to determine if the laser marking had introduced any residual stresses. Imaging analysis was also conducted to examine any potential surface damage on the test sample's surface. A servo-hydraulic test machine was used for the fatigue four point bend testing regime where the inner and outer spans were 30 mm and 90 mm respectively. All testing was conducted at a frequency of 10 Hz, a stress ratio R=0.1, and sine-wave loading in air. Testing was stopped at 10 Million cycles or at failure of the specimen. Results & Discussion. Figure 1 shows that laser marking process can create a fine network of surface cracks. Table 1 shows the results of residual stress measurements. Laser making introduced high tensile stresses on the components whereas “as machined” component without laser marking exhibited compressive stresses inherent due to machining. The result from the S-N curve testing is shown in Figure 2. The current laser marking components demonstrated 41% reduction in fatigue strength compared to non-laser marked specimens. The reduction in fatigue strength is due to the residual tensile stresses generated at the laser marking location which can lead to crack propagation from small micro fractures created during the surface melting process. Conclusion. This study has shown conclusively that laser marking of implants if located at high stress regions can lead to early fatigue failure. Based on the results from the study it is advisable to locate the laser markings at the region of lowest or compressive stress areas and when possible the laser marking process should be selected as to create the minimal damage to the surface. For figures/tables, please contact authors directly.

Revision surgeries for orthopaedic infections are done in two stages – one surgery to implant an antibiotic spacer to clear the infection and another to install a permanent implant. A permanent porous implant, that can be loaded with antibiotics and allow for single-stage revision surgery, will benefit patients and save healthcare resources. Gyroid structures can be constructed with high porosity, without stress concentrations that can develop in other period porous structures [1] [2]. The purpose of this research is to compare the resulting bone and prosthesis stress distributions when porous versus solid stems are implanted into three proximal humeri with varying bone densities, using finite element models (FEM). Porous humeral stems were constructed in a gyroid structure at porosities of 60%, 70%, and 80% using computer-aided design (CAD) software. These CAD models were analyzed using FEM (Abaqus) to look at the stress distributions within the proximal humerus and the stem components with loads and boundary conditions representing the arm actively maintained at 120˚ of flexion. The stem was assumed to be made of titanium (Ti6Al4V). Three different bone densities were investigated, representing a healthy, an osteopenic, and an osteoporotic humerus, with an average bone shape created using a statistical shape and density model (SSDM) based on 75 cadaveric shoulders (57 males and 18 females, 73 12 years) [3]. The Young's moduli (E) of the cortical and trabecular bones were defined on an element-by-element basis, with a minimum allowable E of 15 MPa. The Von Mises stress distributions in the bone and the stems were compared between different stem scenarios for each bone density model. A preliminary analysis shows an increase in stress values at the proximal-lateral region of the humerus when using the porous stems compared to the solid stem, which becomes more prominent as bone density decreases. With the exception of a few mesh dependent singularities, all three porous stems show stress distributions below the fatigue strength of Ti-6Al-4V (410 MPa) for this loading scenario when employed in the osteopenic and osteoporotic humeri [4]. The 80% porosity stem had a single strut exceeding the fatigue strength when employed in the healthy bone. The results of this study indicate that the more compliant nature of the porous stem geometries may allow for better load transmission through the proximal humeral bone, better matching the stress distributions of the intact bone and possibly mitigating stress-shielding effects. Importantly, this study also indicates that these porous stems have adequate strength for long-term use, as none were predicted to have catastrophic failure under the physiologically-relevant loads. Although these results are limited to a single boney geometry, it is based on the average shape of 75 shoulders and different bone densities are considered. Future work could leverage the shape model for probabilistic models that could explore the effect of stem porosity across a broader population. The development of these models are instrumental in determining if these structures are a viable solution to combatting orthopaedic implant infections

Introduction. The fatigue strength of ultrahigh molecular weight polyethylene (UHMWPE) in total joint implants is crucial to its long term success in high demand applications, such as in the knee, and is typically determined by measuring the crack propagation resistance in razor-notched specimens under cyclic load [1]. This only tells part of the story: that is, how well the material resists crack propagation once a crack is present. A second, equally important component of fatigue strength is how well the material resists crack formation. Previous studies cyclically loaded a cantilevered post until failure [2], postulating that the post would break very quickly after crack initiation. Parran et. al. proposed a novel method to measure the crack initiation time by holding a sample in constant tension until a crack was visually observed [3]. We hypothesize that the crack initiation times of various UHMWPEs will follow similar trends as the more omnipresent crack propagation resistance tests. Materials and Methods. The following UHMWPE formulations were tested: (i) virgin, (ii) gamma sterilized in vacuum, (iii) 91 kGy gamma irradiated, and (iv) 91 kGy gamma irradiated and subsequently melted. GUR1020 and GUR1050 bar stock of varying irradiation doses were machined into compact tension specimens [4] with a notch depth of 17 mm and a blunt notch root radius of 0.25 mm, mimicking a geometry of a joint replacement component. Specimens were held in constant tension until failure; 3 to 5 different loads between 1 kN and 2.25 kN (n=3 samples per load per material) were tested. A video camera was focused on the face of the notch and took a picture every 10 seconds. The photos were reviewed to manually determine the crack initiation time (Fig 1). The time it took for the sample to completely fail – that is, shear into two separate pieces – was also recorded. Results. For all materials tested, the crack initiation time (Fig 2a,b) and the time to failure (Fig 2c,d) decreased as the applied load increased. The crack initiation time increased for the gamma sterilized materials when compared to the virgin materials while the time to failure decreased. The highly crosslinked, 91 kGy materials had crack initiation times and times to failure that were less than that of the virgin material. Post irradiation melting greatly diminished the fatigue strength of the material, yielding the lowest crack initiation time and time to failure. Discussion. The test yielded results consistent with current knowledge: that is, high-dose irradiation yields a slight drop in fatigue strength, and post-irradiation melting greatly reduces strength. This test was simple to set up and run and can be a good tool to determine the relative fatigue strengths of UHMWPE formulations for orthopaedic applications. For figures/tables, please contact authors directly.

Introduction. Porous scaffolds for bone ingrowth have numerous applications, including correcting deformities in the foot and ankle. Various materials and shapes may be selected for bridging an osteotomy in a corrective procedure. This research explores the performance of commercially pure Titanium (CPTi) and Tantalum (Ta) porous scaffold materials for use in foot and ankle applications under simplified compression loading. Methods. Finite element analysis was performed to evaluate von Mises stress in 3 porous implant designs: 1) a CPTi foot and ankle implant (Fig 1) 2) a similar Ta implant (wedge angle = 5°) and 3) a similar Ta implant with an increased wedge angle of 20°. Properties were assigned per reported material and density specifications. Clinically relevant axial compressive load of 2.5X BW (2154 N) was applied through fixtures which conform to ASTM F2077–11. Compressive yield and fatigue strength was evaluated per ASTM F2077–11 to compare CPTi performance in design 1 to the Ta performance of design 3. Results. FEA results indicate peak stresses at fixture contact locations. Similar designs (CPTi design 1 and Ta design 2) resulted in similar von Mises stresses (Fig 1). Increasing the wedge angle (Ta design 3) increased stress by 15%. The static compressive yield strength of CPTi design 1 (20,560 N) was similar to the Ta design 3 (20,902 N), with yield manifesting as barreling and crushing of the components (Fig 2a). However, the fatigue strength of CPTi (6,000 N) was 40% lower than the Ta design 3 (9,500 N) (Fig 3). In both cases fracture initiated from regions of highest stress predicted in FEA. Fracture progression was not instantaneous and was characterized by an accumulation of damage (Fig 2b–c) leading to gross component fracture and loss of implant integrity. Discussion. FEA is a useful tool to determine stress variations and can be used to identify worst case within a material: in this case, a larger implant wedge angle leads to higher stresses. Additionally, FEA accurately predicted fracture initiation location. However, material selection plays a large role in porous implant performance: although FEA predicted higher stresses in a Ta component with a greater wedge angle than a similar sized CPTi component, static compressive strengths were nearly identical, and the Ta component had 58% higher fatigue strength. When selecting a material or geometry for an implant application, both FEA and static testing allow for rapid evaluation of designs. However, caution should be used in interpreting the results: the ultimate performance of an implant in-vivo will depend on its ability to maintain integrity over a long period of time, and should be characterized by dynamic testing

BACKGROUND. This scientific work is a non-interventional, experimental and prospective comparative study of two very high-viscosity PMMA bone cements: DePuy CMW 2G and Palacos® fast R+G. Reference product: Palacos® R+G. Fast-setting PMMA bone cements are used in the endoprothetics of the patella and knee (in Australia) and are also used to cement an artificial acetabulum (in the UK). Are there any differences regarding the characteristics of the two fast-setting PMMA bone cements?. MATERIALS AND METHODS. All cements were mixed as specified by the manufacturer and analysed on the following parameters: handling properties (mixing, waiting, working and hardening phase), powder/liquid-ratio, mechanical properties (ISO 5833:2002 and DIN 53435), fatigue strength (ISO 16402) and elution profile. All tests were done in an acclimatised laboratory with temperatures set at 23.5°C ± 0.5°C and a humidity of >40%. Of two batch numbers, 11 units of each bone cement were tested. RESULTS AND DISCUSSION. The handling properties of the two tested PMMA bone cements Palacos® fast R+G and CMW 2G are highly similar (n=12). CMW 2G reaches the mixing and waiting phase approximately 20s later than Palacos® fast R+G. Palacos® fast R+G has a similar working, but a shorter hardening phase than CMW 2G. In addition, working with Palacos® fast R+G was advantageous due to its green dye. Palacos® fast R+G has a higher powder/liquid-ratio of 2.550. Due to the higher powder percentage, the cement has a shorter mixing and waiting phase than CMW 2G with a ratio of 2:1. Both analysed bone cements fulfil the quasi-static properties of ISO 5833:2002 and DIN 53435. Palacos® fast R+G was far superior in its ISO compressive strength (MPa) shown through one-way analysis of variance (ANOVA) (p<0.01) and independent two sample t-test (p<0.01) at 0.05 level of significance (n=20)(Fig. 1). CMW 2G has a higher quasi-static ISO bending strength (MPa) than Palacos® fast R+G, but the same test shows a much higher fatigue strength (ISO 16402) of Palacos® fast R+G (n=5) (Fig. 2). Palacos® R+G and Palacos® fast R+G show a similar elution profile (n=3), whereas CMW 2G shows a much lower antibiotic elution over time. CMW 2G releases approximately 1/3 of gentamicin per mould body after 24h. After day 3 and 5, CMW 2G has a significantly lower gentamicin release than Palacos® fast R+G (Fig. 3). Palacos® fast R+G has a higher gentamicin release, due to its hydrophilic polymer basis, which is identical to Palacos® R+G. CMW 2G contains pure PMMA and is therefore more hydrophobic than the other two tested cements. CONCLUSION. Handling with Palacos® fast R+G was advantageous due to its green dye. Because of the shorter handling phases of Palacos® fast R+G, it is superior as it minimises the length of surgeries. Mechanical properties according (ISO 5833:2002 and DIN 53435) were comparable. Palacos® fast R+G has a statistically significant higher ISO compressive strength (MPa). Palacos® fast R+G also showed higher fatigue strength (ISO 16402). Palacos® fast R+G was far superior in matters of gentamicin release over time

Background. Titanium, in particular Ti6Al4V, is the standard material used in cementless joint arthroplasty. Implants are subjected to cyclic loading where fracture is the reason for re-operation in 1.5–2.4% of all revisions in total hip arthroplasty. In order to strengthen critical regions, surface treatments such as shot peening may be applied. A superficial titanium oxide layer is naturally formed on the surface as a protective film at ambient conditions. However, as its thickness is only in the range of several nanometers, it is prone to be destroyed by high loads - as present at the surface during bending - leading to an ‘oxidative wear’ in a corrosive environment [1]. The present study aims to evaluate the shot peening treatment on Ti6Al4V regarding its potential for cyclically loaded parts under a dry and a corrosive testing medium. Materials and Methods. Hour-glass shaped titanium specimens (Ti6Al4V) with a minimal diameter of 10 mm have been subjected to an annealing treatment at 620°C for 10h to remove initial residual stresses introduced during machining. Subsequently, a high-intensity shot peening treatment with cut wire followed by a low-intensity cleaning process with glass beads have been performed (Metal Improvement, Germany). Arithmetic mean roughness R. a. of the treated surfaces was measured (Mahr Perthometer M2, Germany). Residual stress depth profiles prior to and after shot peening have been measured by a Fe-filtered Co-K(alpha) radiation (GE Measurement&Control, USA) and calculated using the sin. 2. (psi) method. Fatigue strength has been determined by two servo-hydraulic hydropulsers (Bosch Rexroth, Germany) at 10 Hz and a load ratio of R=0.1 either under dry conditions (8 specimens) or surrounded by a 0.9-% saline solution (6 specimens) (BBraun, Germany) (Fig. 1). Testing has been performed until fracture occurred or the total number of 10 × 10. 6. cycles has been reached. All fracture surfaces have been analyzed after testing using FEG-SEM (Zeiss LEO 1530 VP Gemini, Germany). Results. Surface roughness increased significantly (p<0.01) after shot peening treatment from R. a, annealed. = 0.24 μm (±0.09 μm) to R. a, peened. = 2.02 μm (±0.16μm). Residual stresses have been introduced during shot peening up to a depth of 200μm with a maximum of 870 MPa at the surface (Fig. 2, left). All specimens showed clear signs of fatigue fracture after failure. Regarding fatigue strength, no differences have been observed between testing in saline solution or a dry environment (Fig. 2, right). Discussion. Shot peening has shown to significantly increase fatigue strength of a Ti6Al4V alloy after testing up to 10 × 10. 6. cycles. Thus, it seems to be an appropriate treatment for highly loaded components in cementless joint arthroplasty. In this context, a corrosive environment around a cyclically loaded implant does not seem to have any influence on their long term mechanical behaviour. However, it still needs to be clarified to which extend shot peening might decrease the risk of an early implant failure due to micro-motion between assembled parts (fretting) [2]

INTRODUCTION. Since the early 2000s, highly cross-linked (HXL) UHMWPE's have become a popular option with multiple experimental and clinical studies showing that gamma or electron radiation doses between 50–100kGY reduce wear and potentially extend the bearing life of UHMWPE. However, the increased wear resistance came at a compromise to mechanical properties due to the cross-linking process. Vitamin E has been added to some HXL UHMWPE materials to offer a solution to the compromise by increasing oxidation resistance and maintaining sufficient fatigue strength. However, limited data is available on the effect of the fabrication process, especially the method of irradiation, on the properties of the Vitamin E blended HXL UHMWPE. The purpose of this study was to evaluate the effects of adding the antioxidant vitamin E to highly crosslinked UHMWPE on wear rates. METHODS. Wear testing was performed on six highly crosslinked UHMWPE acetabular liners containing vitamin E (0.1% wt. alpha tocopherol) fabricated using the Cold Irradiation Mechanically Annealed (CIMA) process, initially cross-linked with approximately 100 kGy gamma irradiation, and terminally gamma sterilized. The liners were paired with three 40mm CoCr femoral heads and 40mm three ceramic femoral heads. Testing was completed per ASTM F1714 and ISO 14242 on an orbital hip joint wear simulator (Shore Western, California) and lubricated with 90% bovine calf serum, 20mM EDTA, 0.2% wt. NaN. 3. and DI water. A 1.1Hz Paul-type loading waveform with a peak of 2kN was used for a total of 5E6 wear cycles. Three loaded soak controls were used in parallel to adjust for fluid absorption. Samples were weighed every 5E5 wear cycles. RESULTS. The wear rates for the HXL blended vitamin-E liners were calculated using the slope of the linear regression over the steady state and resulted in a wear rate of 0.49mg/Mc. This is a decrease of approximately 95% compared to the 9.54 mg/Mc 28mm ID conventional UHMWPE wear rates as well as a notable difference for the other HXL UHMWPE liner wear rates discussed in the review. DISCUSSION. HXL blended vitamin-E 40mm liners demonstrated an approximate 95% reduction in wear rates compared to a 28mm ID conventional UHMWPE. The reduced wear rate confirmed the design expectation that a higher irradiation dose in the fabrication process resulted in an increased amount of polymer crosslinking. Additionally, the wear rate of the HXL blended vitamin-E liners studied was well below 20mg/Mc, which was shown by Dowd et al. to be the threshold of osteolysis in THA. SIGNIFICANCE. The HXL vitamin E blended UHMWPE liner tested in this study demonstrated reduced wear rates by approximately 95% compared to conventional polyethylene. Osteolysis-causing wear debris is reduced while maintaining other mechanical properties. This liner material and manufacturing process is a promising alternative to conventional polyethylene, but long-term clinical results are warranted

Distal neck modularity places a modular connection at a mechanically critical location, which is also the location that confers perhaps the greatest clinical utility. The benefits of increased clinical options at that location must be weighed against the potential risks of adding an additional junction to the construct. Those risks include prosthetic neck fracture, taper corrosion, metal hypersensitivity, and adverse local tissue reaction. Further, in-vitro testing of ultimate or fatigue strength of femoral component designs has repeatedly failed to predict behavior in-vivo, raising questions about the utility of in-vitro testing that does not incorporate the effect of mechanically assisted crevice corrosion into the test design. The material properties of Ti alloy and CoCr alloy place limits on design considerations in the proximal femur. The smaller taper junctions that are necessary for primary reconstruction are particularly vulnerable to failure whereas larger taper junctions commonly used in revision modular femoral component designs have greater opportunity for success. Modular junctions of CoCr alloy on conventional Ti alloy have been shown to have a greater incidence of clinically significant mechanically assisted crevice corrosion and adverse reaction. Designs that have proven clinical strength and utility universally have larger, more robust junctions, that extend into the metaphysis of the femur. While these designs are primarily designed for revision total hip replacement (THR), they are occasionally indicated for primary THR. Overall, however, while design options at the neck-stem junction have unmatched clinical utility, no design that does not extend into the metaphysis has proven to be universally reliable. While routine use of modular neck components for primary THR does not appear to be clinically indicated based on current evidence, modular designs with proven successful proximal junctions appear to be indicated for revision THR and rare primary THR with extreme version or other anatomical circumstances

Distal neck modularity places a modular connection at a mechanically critical location which is also the location that confers perhaps the greatest clinical utility. Assessment of femoral anteversion in 342 of our total hip replacement (THR) patients by CT showed a range from −24 to 61 degrees. The use of monoblock stems in some of these deformed femurs therefore must result in a failure to appropriately reconstruct the hip and have increased risks of impingement, instability, accelerated bearing wear or fracture, and adverse local tissue reaction (ALTR). However, the risks of failing to properly reconstruct the hip without neck modularity must be weighed against the additional risks introduced by neck modularity. There are several critical design, material, and technique variables that are directly associated with higher or lower incidences of problems associated with modular neck femoral components. Unfortunately, in vitro testing of the fatigue strength of these constructs has failed to predict their behavior in vivo. Designs predicted to tolerate loads that far exceed those experienced in vivo still fail at unacceptably high rates. Titanium alloy neck components subjected to the stresses at the neck-stem junction continue to fail at an unacceptable incidence. CoCr alloy neck components, while theoretically stronger, still fracture and are further compromised by mechanically assisted crevice corrosion, metal hypersensitivity, and rarely, adverse tissue reaction. Designs that have proven clinical strength and utility universally have larger, more robust junctions that extend into the metaphysis of the femur. While these designs are primarily designed for revision THR, they are occasionally indicated for primary THR. Overall, however, while design options at the neck-stem junction have unmatched clinical utility, no design that does not extend into the metaphysis has proven to be universally reliable. While routine use for primary THR does not appear clinically indicated based on current evidence, modular designs with proven successful proximal junctions appear to be indicated for extreme version or anatomical circumstances

Introduction. Recently ventral plating implants made of carbon/PEEK composite material have been developed with apparently superior material properties in terms of implant fatigue and imaging suitability. In this study we assessed the outcome of the first clinical application of this new implant. Methods. Retrospective, single-center case series of 16 consecutive patients between 2011 and 2013 undergoing ventral stabilization surgery with a new carbon plating system (see figure 1). We collected data in terms of safety of the procedure (screw positioning, blood loss, operation time), quality and reliability of the implant (revisions, dislocations, screw loosening, fusion, adjacent segment degeneration), clinical outcome and biological tolerance (cervical pain / discomfort, dysphagia). Results. All patients were available for clinical and radiological follow up. Mean surgery time was 128 minutes, in 11 cases one in 5 cases 2 segments were treated. The clinical findings and patient's satisfaction were good in 14 and fair in two cases. All patients who completed the 6 months control had a radiographically confirmed interbody fusion; no implant loosening or failure and no infections were observed. (see figure 2). There was one implant related complication (dysphagia due to malpositioning of the plate which was removed 4 days after implant insertion) and one complication related to the approach (Horner's syndrome). Conclusion. In this retrospective study of 16 patients we found that the use of a carbon-composite plating system lead to results comparable to the “gold standard” metal plates in terms of safety / clinical outcome and reliability of the implant. There was one revision due to dysphagia. The MR imaging of the patients who have been operated with the carbon/PEEK system showed superior quality with reduced artifacts and improved diagnostical properties, especially when evaluating the neurogical structures. (see figure 3). The overall clinical outcome and patient acceptance of the implant was good. The radiologic findings on follow up of 2, 6 and 12 months have shown a high fatigue strength with no signs of implant failure in terms of dislocation, loosening or breakage. Therefore we conclude that the use of the carbon/PEEK plating system is suitable for ventral stabilization in trauma and degenerative disease

Objective. The purpose of this study was to investigate how rim poly locking scallop cutting depth could affect the rigidity of acetabular cup. Materials and Methods. (11) generic FEA models including (5) 50mm OD Ti6Al4VELI hemispherical acetabular shells with thicknesses of 3.0, 3.5, 4.0, 4.5 and 5.0mm, and (6) 4mm thick hemispherical shells with standard rim poly indexing scallops varied in cutting depths from inner diameter of the cup in 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5mm. All cups were analyzed in ANSYS® Workbench™ FEA software with a loading condition of 2000N applied to the cup rim per V15 ISO/TC 150/SC 4 N. Verification was carried out by the physical test of a same generic Ti6Al4VELI 50mmOD and 5mm thick solid hemispherical shell under 2000N rim directed load. The cup deformation was compared with FEA results. The maximum deformation of FEA scalloped cups were compared with that of solid hemispherical cups with different shell thickness. Results. The average value for physical test was 0.265(0.282/0.268) mm. The FEA result of the same 50mm OD and 5mm thick shell was 0.2464mm representing a 7% difference. (Figure 1) FEA results for solid hemisphere cups and scalloped shells are shown in Figure 2 and Figure 3 respectively. Conclusion and Discussion. Cup deformation increased in the average of 40% for every 0.5mm shell thickness decrease from 5mm to 3mm for 50mm OD solid cup. The increase of rim scallop depth from 0 to 2.5mm was equivalent to a 0.5mm shell thickness reduction for 4mm thick 50mm OD cup. The higher deformation reading in physical test was likely caused by the accumulations of the fixture deformations. Intraoperative acetabular cup deformation is a clinical issue. It increases the risk of ceramic liner fracture when the liner is inserted in the out of round cup. The increase of shell thickness is a simple and effective way to reduce the cup deformation. However it also reduces the poly thickness and that puts the adverse effects to the poly wear property and poly rim fatigue strength. The common design of the indexing scallops in the rim of cup helps the rotational locking for the poly liner. But the drawbacks including the reduction of cup stiffness must be noticed. The shallower scallop design may be warranted to maximize the cup rigidity in a given cup thickness and maximize poly thickness in a given cup rigidity

Introduction. Dual modular hip prostheses were introduced to optimize the individual and intra-surgical adaptation of the implant design to the native anatomics und biomechanics of the hip. The downside of a modular implant design with an additional modular interface is the potential susceptibility to fretting, crevice corrosion and wear [1–2]. The purpose of this study was to characterize the metal ion release of a modular hip implant system with different modular junctions and material combinations in consideration of the corrosive physiological environment. Methods. One design of a dual modular hip prosthesis (Ti6Al4V, Metha®, Aesculap AG, Germany) with a high offset neck adapter (CoCrMo, CCD-angle of 130°, neutral antetorsion) and a monobloc prosthesis (stem size 4) of the same implant type were used to characterize the metal ion release of modular and non-modular hip implants. Stems were embedded in PMMA with 10° adduction and 9° flexion according to ISO 7206-6 and assembled with ceramic (Biolox® delta) or CoCrMo femoral heads (XL-offset) by three light impacts with a hammer. All implant options were tested in four different test fluids: Ringer's solution, bovine calf serum and iron chloride solution (FeCl3-concentration: 10 g/L and 114 g/L). Cyclic axial sinusoidal compressive load (Fmax = 3800 N, peak load level of walking based on in vivo force measurements [3]) was applied for 10 million cycles using a servohydraulic testing machine (MTS MiniBionix 370). The test frequency was continuously varied between 15 Hz (9900 cycles) followed by 1 Hz (100 cycles). The metal ion concentration (cobalt, chromium and titanium) of the test fluids were analysed using ICP-OES and ICP-MS at intervals of 0, 5·105, 2·106 and 10·106 cycles (measuring sensitivity < 1 µg/L). Results. Due to the additional modular interface between stem and neck adapter the total metal ion release of the modular hip endoprosthesis system increased significantly and is comparable to the coupling of a monobloc stem and a CoCrMo femoral head (Fig. 1). The application of ceramic femoral heads reduced the total cobalt and chromium release in the stem-head taper interface of non-modular and modular stems. In comparison between the four test fluids could be observed that lower pH-values and higher FeCl3-concentrations increased the metal ion release (Fig 2). In contrast, the use of bovine calf serum decreased the metal ion release of modular junctions due to the presence of proteins and other organic components. Discussion. For testing hip implants with proximal femoral modularity according to ISO and ASTM standards, sodium chloride solutions are frequently used to determine the fatigue strength and durability of the stem-neck connection. The present study illustrate that the expansion of standard requirements of biomechanical testing and the use of alternative test fluids is necessary to simulate metal ion release by electro-chemical processes. A promising approach is the use of adapted iron-chloride solutions (10 g/L FeCl3, pH 2) to evaluate the susceptibility of modular hip junctions to fretting, crevice and contact corrosion

Prospective Randomised Control trial of 300 patients over a period of 3 years, 1 year post op follow up. Local ethic approval was attained for the study. Inclusion criteria: Age > 60, Consented to Participate in the study, Unstable Inter trochanteric fracture a) Sub trochanteric b) Medial Comminution c) Reverse Obliquity D)Severe Osteoporosis. Patients selected were randomized to Intra medullary Nail vs Hips screw. Variety of markers have been assessed: Pre OP: - Mechanism of injury, Mobility status, Pre OP ASA, Pre Op haemoglobin, living Conditions. Intra OP:- I.I Time, Time taken, Surgeon experience, Intra OP complications. Post OP:- Haemoglobin, mobility, radiographic analysis-Fracture stability and Tip Apex Distance, Thrombo embolic Complications. Follow up: - 6 weeks, 3,6,12 month follow up. There is considerable debate in literature regarding superiority of Compression Hip screw over Intra medullary nail for fixation of stable per trochanteric fractures of the femur. Biomechanical studies have shown superiority of Intra medullary device over a Compression Hip screw. Tenser et all showed an advantage over combined bending and compression failure. Mohammad et al found unstable subtrochanteric fractures with a gamma nail were stiffer. Kerush-Brinker showed that gamma nail had significantly greater fatigue strength and fatigue life. In unstable fractures Baumgartner et al found less intra op complications and less fluoroscopic time for a compression hip screw compared to a short intra medullary nail. There have been significant reports of fracture at the Tip of a short intra medullary nail. We think this complication can be avoided by using a long intra medullary device. Both in Australia and abroad the choice of which device to use depends largely on the preference of the surgeon

Ceramic-on-ceramic (COC) bearing surfaces have consistently demonstrated reliable clinical results with when coupled with appropriated designed femoral stems and acetabular shells. Ceramic bearing surfaces are highly wettable and display both boundary and hydrodynamic fluid-film lubrication modes, which lead to extremely low wear rates. Furthermore, COC bearing couples have been shown to exhibit virtually no risk of adverse biologic reaction and have not been associated with corrosion-induced adverse tissue reactions that occur with metal taper junctions, particularly head-neck taper junctions. The relative brittleness of ceramics initially was thought to be a major disadvantage; however, four decades of improvement in the manufacture of ceramics and rigorous proof testing has led an extremely low risk of fracture, perhaps lower than that for cross-linked polyethylene. More recently it has become increasing appreciated that nearly all revisions for squeaking have been restricted to specific designs and materials, including the use of a titanium elevated metal rim on the acetabular side, and more flexible femoral components made of a beta-titanium alloy (TMZF) which had thin necks and relative small tapers. Multiple clinical studies document excellent long-term survival of COC bearing couples in young patients with revision for any reason as the primary endpoint. Our own experience with 341 hips with 2 to 15 and average 9.1 year f/u demonstrates a 95% overall survivorship (revision for any reason) at 13 years in patients under 50 years of age at the time of surgery. By contrast, cross-linked polyethylene bearings have not been studied so carefully and have not been shown to be superior to ceramic-ceramic bearings in young patients. These bearing surfaces represent a very heterogeneous group of products, with varying degrees of cross-linking, post-irradiation processing methods, and additives. Cross-linked polyethylenes in general have a lower fatigue strength than conventional polyethylene and are prone to fracture, especially when thin material is subjected to high stress. Some types of cross-linked polyethylenes are prone to in vivo oxidation, leading to further mechanical compromise over time. Studies also demonstrate the absence of reduction in femoral head penetration or risk of osteolysis in heads 32mm and larger, which are commonly used today. The most recent cross-linked polyethylene products have the least clinical support for their use. The long-term biologic effects of the smaller HXLPE wear particles and newer additives, including the more recently added vitamin E compounds are unknown. Indeed, in vitro, the debris has been shown to be cytotoxic. There is a paucity of survivorship data for hips utilising HXLPE, especially in younger, more active individuals. For these reasons, we believe that the ceramic-ceramic bearings are the gold standard for THA in the young patient and that cross-linked polyethylene bearing are being continually changed and have little long term clinical outcomes data to support their use

Additive manufacturing (AM) techniques have gained attraction in orthopedic implant design with their ability to create unique shapes and structures. Depending on the application, there are different mechanical properties required. This study evaluated the mechanical properties of direct metal laser sintered (DMLS) Titanium alloy (Ti6Al4V) with and without hot isostatic pressure (HIP) treatment. Three dimensional computer modeling and the DMLS manufacturing assisted in building net or near-net samples for testing. The material testing consisted of uniaxial tension, Charpy impact, rotating beam fatigue (RBF), density, and hardness. Two sets of Ti6Al4V samples were created for testing using a DMLS process and stress relieved in a vacuum furnace prior to removal from the build platform. One set of samples were HIP treated. The two sets of samples were tested and the material properties of the non-HIP treated samples were compared to those with HIP treatment. Tension testing was conducted on fifteen (15) samples per treatment according to ASTM E8/E8M on as-built samples designed to a round specimen 3 per the standard. Fifteen (15) Charpy impact samples per treatment were built to near-net shapes. A low stress grind was performed on all surfaces and a notch was placed in the sample to comply with ASTM E23 and testing was performed in accordance with the standard. Fifteen (15) samples were built per treatment and machined for RBF per ISO 1143. RBF was performed on all samples at a frequency of 100 Hz with run out conditions of 10M cycles or failure. Density and hardness was measured on three (3) samples from each set using Archimedes' Principle and Rockwell hardness techniques respectively. The average (standard deviation) tensile strengths between the two groups were statistically different (p < 0.05). The non-HIP treated samples had an average ultimate strength of 956(10) MPa, yield strength of 896(13) MPa, and modulus of 118(2) GPa (Table 1). The HIP treated samples had an average ultimate strength of 909(4) MPa, yield strength of 832(9) MPa, and modulus of 112(3) GPa (Table 1). There was also statistical differences in the impact strength with the HIP treatment samples having a higher required force of 23.4(1.6) J compared to the non-HIP treated group of 19.8(1.8) J (Table 1). The fatigue strength of the samples HIP treated compared to the non-HIP treated group was 650 MPa and 396 MPa respectively (Table 1). This study shows that the HIP treatment of DMLS Ti6Al4V diminishes some mechanical strengths while greatly improving the fatigue life of the material. As we continue to evaluate these “new” materials for orthopedic devices, these mechanical and physical properties will help us understand the capabilities of this process and material

Distal neck modularity places a modular connection at a mechanically critical location. However, this is also the location that confers perhaps the greatest clinical utility. Assessment of femoral anteversion in 342 of our THR patients by CT showed a range from −24 to 61 degrees. The use of monoblock stems in some of these deformed femurs therefore must result in a failure to appropriately reconstruct the hip and have increased risks of impingement, instability, accelerated bearing wear or fracture, and adverse local tissue reaction (ATLR). However, the risks of failing to properly reconstruct the hip without neck modularity must be weighed against the additional risks introduced by neck modularity. There are several critical design, material, and technique variables that are directly associated with higher or lower incidences of problems associated with modular neck femoral components. These include modular neck length, design and material of both parts including the junction design, wall thickness of the receiving junction, assembly force, and bearing diameter and material. With regard to stem design and material, it has been clearly shown that the incidence of titanium neck fractures is higher in stems with a thinner wall-thickness of the receiving junction than in stems with a thicker wall-thickness. Moreover, titanium necks have been largely replaced with CoCr necks with significantly higher yield and fatigue strength. It remains to be seen if the introduction of CoCr necks will decrease or increase the risks associated with distal neck modularity. With respect to titanium necks, our experience has shown no adverse local tissue reaction, no fractures of short necks (0 of 370) and a 0.34% incidence of fractures in long necks (2/580) at 3 to 8 years following surgery. This lower incidence of neck fracture compared to other reports may relate to the relatively more rigid stem and thicker wall of the junction receiving the neck compared to other stems. With respect to CoCr modular necks, one device that mated the CoCr modular neck with a beta-titanium alloy femoral component has been shown to have a high incidence of ALTR and has been recalled. While the CoCr on Conventional Titanium Alloy modular neck experience has had a statistically significantly lower incidence of problems, we believe that we have identified two cases of ALTR. If that is the case, the CoCr neck experience may well have a higher incidence of problems that the Ti neck experience. In summary, placing a modular connection at the stem-neck junction has great clinical utility but this is a very design sensitive location. There are risks associated with the use of non-modular neck components that are incapable of properly reconstructing the spectrum of pathology that presents. This failure can lead to instability, impingement, and polyethylene fracture. Yet, the use of titanium modular necks has a small risk of component fracture while the use of cobalt-chrome modular necks may have a higher risk of adverse local tissue reaction. While the existence of a modular neck may offer great advantages at the time of primary reconstruction and of future revision, currently the risk/benefit for the use of these components is strongest in patients with more significant anatomical abnormalities or more complex revision settings

Introduction. Proper femoral stem and acetabular implant orientation is critical to the initial and long-term success of THA. Post-operative determination of cup and stem anteversion is important in cases of hip instability and planning isolated component revisions. At ISTA 2010 Dubai, we introduced a novel, simple stem modification that can be added to any stem design to help assess stem, and possibly cup anteversion with plain post-operative radiographs throughout the lifespan of the implant. [Figure 1] As the stem is rotated, the visible hole pattern changes. [Figure 2] This study was performed to further validate the accuracy and potential usefulness of this design. Methods. We prospectively reviewed 100 consecutive THA cases using the stem reference hole modification on rectangular tapered Zweymuller-type stems implanted from September 2010 to May 2012. Post-operative hip/femur CT scans were obtained to determine the true cup and stem orientation to validate and quanitify the precision of the reference holes. Intra-operative estimates of stem anteversion and combined anteversion (Ranawat Sign) were recorded. Post-operative radiograph measurement of stem anteversion (AP hip x-ray with leg in neutral rotation) was obtained and compared to the CT scan measurement referencing stem rotation relative to the knee epicondylar axis. [Figure 3] In addition, we compared the modified reference hole anteversion assessment to a control group of original unmodified stems assessed using the same methods. Results. All 100 patients had post-operative CT scans and ‘neutral’ rotation AP hip radiographs. The modified reference hole design was accurate to within 4.1 degrees compared to CT measurements. Estimates of stem anteversion in the control group (original Alloclassic or SL-Plus stems) was accurate to only 19.6 degrees with wide variablity as expected. The difference was statistically significant. Residual hip flexion contracture (2 patients) made the reference holes undetectable on radiographs. Morbid obesity did not decrease accuracy but required x-ray beam intensity modification. There was no statistical difference between standing and supine x-ray ‘neutral’ rotation radiograph measurements. The Ranawat combined stem and cup anteversion value could not predict cup anteversion reliably when subtracting the stem rotation. Two patients sustained post-operative THA dislocations that required closed reduction (occuring 2 months and 15 months after index THA). Conclusion. We conclude that hip stems with this pattern of modified anteversion reference holes provides an accurate and reliable method of determining stem component orientation post-operatively by using only simple plain radiographs. Initial finite element analysis of the modified stem hole pattern predicted that the fatigue strength was actually higher than that of the original unmodified implants indicating it is safe in the square taper design. The clinical usefulness became apparent when two hips in this series suffered dislocations. Review of the ‘neutral’ rotation xrays indicated the stem was placed in the ‘safe zone’ from 15–25 degrees and the hips would not likely need stem implant revision. We will continue to test this technology and improve the measuring techniques to accurately predict implant position post-operatively

Aims

A flexed knee gait is common in patients with bilateral spastic cerebral palsy and occurs with increased age. There is a risk for the recurrence of a flexed knee gait when treated in childhood, and the aim of this study was to investigate whether multilevel procedures might also be undertaken in adulthood.