Introduction. Metal ion and particle release, particularly cobalt, has become an important subject in total hip arthroplasty, as it has shown to induce metal hypersensitivity, adverse local tissue reactions and systemic ion related diseases. The purpose of the following study was compare the ion release barrier function of a zirconium nitride (ZrN) multilayer coated hip stem for cemented use, designed for patients with metal ion hypersensitivity, against its uncoated version in a test configuration simulating the worst case scenario of a severely debonded hip stem. The ZrN multilayer coating is applied on a CoCrMo hip stem and consists of a thin adhesive chromium layer, five alternating intermediate layers out of chromium nitride (CrN) and chromium carbonitride (CrCN) and a final zirconium nitride (ZrN) shielding layer [1]. Methods. Hip stems with a ZrN multilayer coating (CoreHip AS, Aesculap AG, Germany) were tested in comparison with a cobalt-chrome uncoated version (CoreHip, Aesculap AG, Germany). In order to create a worst case scenario, the smallest stem size with the biggest offset in combination with an XL ceramic head (offset +7 mm) was used. The stems were embedded according to the ISO 7206-6 test in a bone cement sheet. Once the bone cement was bonded, the stem was pulled out and a PMMA grain was placed inside the femoral cavity in order to uprise the hip stem above its embedding line and simulate a debonded cemented hip stem with a severe toggling condition. The dynamic test was performed under bovine serum environment with an axial force of 3.875 kN [2] at 11.6 Hz for 15 million cycles. The test was interrupted after 1, 3, 5, 10 and 15 million cycles and the surfaces of the stems were analyzed through scanning electron microscopy (SEM) with energy dispersive X-Ray (EDX). Moreover, the test medium was analyzed for metal ion concentration (cobalt, chromium and molybdenum) using ICP-MS. Results. The SEM/EDX analysis demonstrated that the ZrN multilayer coating kept its integrity, as no trace of the substrate material (CoCrMo) could be detected. Furthermore, the taper of the ZrN group showed less fretting and corrosion than the taper of the CoCrMo stem (Fig.1). Moreover, the ion concentration analysis showed a reduction of up to two orders of magnitude in the release of cobalt, chromium and molybdenum in the ZrN coated stems in comparison with the uncoated version. Discussion. The results showed that, even in a worst case scenario of high micro-motion due to a severe stem debonding within the cement mantle, the hip stems with a ZrN multilayer coating substantially reduce the release of ions from the substrate material. For any figures or tables, please contact the authors directly

A design modification to the DJO Linear hip stem was performed to facilitate use of the stem with the minimally invasive direct anterior approach. While the main design consideration was to reduce the overall stem length, it was also important to increase congruency of the implant and proximal cortical bone to ensure initial stability. An initial design attempt produced a geometry that was difficult to insert into the femur; therefore, reconstructed digital models of the femur (ADaMs by Materialise) were obtained and used to delineate the best fit implant cross section. The ADaMs models were constructed from 74 CT scans taken from northern Europeans undergoing investigations for cardio-vascular conditions. Using equivalency points, models representing the bone mean, ±1σ, and ±2σ were constructed. The ADaMs models are pictured in Figure 1. After importing the ADaMs models in the Solidworks CAD environment, the existing Linear stem was ideally positioned in the femur model and equally spaced planes parallel to the resection plane were defined as shown in Figure 2. At each plane, the shape of the cortical bone was determined and then used to define an implant cross section that was congruent to the bone, at least as large as the Linear hip stem, and symmetric about its midline. After using the base ADaMs models to drive the design's geometry, the final design fit was validated for very small patients using a hypothetical size −4σ extrapolation of the ADaMs models. The digital reconstructions improved the design process by providing accurate, tangible models of the actual femur geometry. From these models, the design team was able to visualize how implant geometry should be constructed to optimize congruency, symmetry, and favorable insertion characteristics. Additionally, the ADaMs models served to validate the design for a challenging condition and as a starting point for computer simulations that were able to predict the insertion difficulty encountered in the initial, pre ADaMs model design. The final redesign was launched in the US in 2014 as the TaperFill hip stem

Purpose of our study is to present the design rationale and the early clinical results for the Parva Stem, an innovative short hip stem. The Parva implant has been designed in order to address the bone sparing concept of a short stem able to achieve a good cervical and interthrocanteric primary fixation associated with a the reliable primary fixation the isthmus level. The stem has been designed to address the larger possible variety of anatomical variations too. The stem therefore features innovative design concepts including the latest generation Modular Neck System, coupled with a revolutionary manufacturing process and surface engineering technology. This manufacturing process (Powder manufacturing Technology) and Ingrowth Surface (Ti-Por) will be also briefly discussed in the presentation. Our early clinical results will be also presented (150 stem-one yr. maximum follow up will be presented) although they are not the main purpose of our study oriented more on the novel design and technological manufacturing advancement. The feed-back we had so far with this state of the art implant is extremely encouraging. Of course further data collection and longer follow up will be needed in order to confirm these early promising results

Introduction. Finite element (FE) models are commonly used to analyse the mechanical behaviour of the bone under different conditions. They provide detail information but they can be numerically expensive and this limits their use in cases where large or numerous simulations are required. On the other hand, 2D models show less computational cost but the precision of results depends on the approach used for the simplification. Three 2D approaches are commonly used: models without side-plate (WOSP)[1]; models with variable thickness side-plate and constant cortical thickness (SPCT)[2]; models with side-plate and variable cortical thickness (SPVT)[3]. The aim of this study is to determine which 2D approach reproduces best the FE results obtained with a 3D model involving hip stems. Methods. The 2D models were generated by the intersection of the 3D model with the stem symmetry plane. Three approaches were considered to assure 3D-2D correspondence: 1) consider variable thickness for the cortical elements so that their transversal area moment of inertia equals the cross-sectional area moment of inertia from the 3D model (model WOSP); 2) include an additional side-plate with variable thickness to match the area moment of inertia from the 3D model, and consider constant thickness for the cortical bone elements (model SPCT); 3) include the side-plate but consider variable thickness for the cortical bone elements, derived from the 3D model (model SPVT). In all cases, the cancellous bone and stem elements had variable thickness computed so that their transversal area moment of inertia was equal to the cross-sectional area moment of inertia measured in the 3D model. This was done at different levels (Fig.1), providing a thickness distribution for the 2D elements. FE analyses were carried out for the static loading condition simulating stair climbing[4]. All materials were defined as linear isotropic and homogeneous. The post-operative situation where bone ingrowth is achieved was considered, resulting in bonded contact between the bone and the implant. The comparison between the 2D and 3D models was done based on three physical quantities: the Von Mises stresses (σ. VM. ); the strain energy density (U) and the interfacial shear stress (t) along the stem-bone interface. Results. Fig.2 shows the σ. VM. , U and t distributions for the 3D model and in the three 2D models. In general, the values for the three physical quantities were under estimated in all 2D models although the differences were small. However, the maximum values of σ. VM. and U were larger in the 2D models than in the 3D model, whereas maximum t values were under estimated. Discussion. It is possible to use 2D simplifications based on the stem symmetry plane to perform FE analyses when large number of simulations is needed or when the computational cost needs to be limited. In this way, a side-plate with variable thickness should be considered to obtain close results to the 3D model, while cortical bone thickness can be kept constant and cancellous bone thickness is varied. For figures/tables, please contact authors directly.

In the United Kingdom's National Joint Registry 2018 Annual Report, the combination of a POLARSTEM hip stem and R3 acetabular component has the lowest revision rate of any total hip arthroplasty (THA) construct combination at 7 years. Although revision rates remain a crucial measure of an implant combination's performance, there is increasingly more attention being given to patient-reported outcome measures (PROMs), which often reflect the endpoints that patients’ themselves consider of paramount importance in choosing to undergo THA. Therefore, the current analysis was undertaken to better understand the PROMs-based performance of this combination. Bespoke implant reports were requested for the POLARSTEM/R3 combination with OXINIUM™ heads and highly cross-linked polyethylene (XLPE) bearing. Reports used data from the National Health Service PROMs programme, which collected the Oxford Hip Score (OHS), EQ-5D and EQ-VAS. Health gain scores, calculated as differences between preoperative and 6-month post-operative scores, were adjusted to account for any differences in patient demographics between comparative groups. The mean OHS adjusted health gain score for the construct combination was 22.8 (95% confidence interval [CI]: 22.4 – 23.1; n = 1799 patients) compared to 21.2 (95% CI: 21.2 – 21.3; n = 111,055). For EQ-5D, the scores were 0.462 (95% CI: 0.451 – 0.473; n = 1685) for the construct and 0.434 (95% CI: 0.433 – 0.436; n = 102,448) for the class average. For EQ-VAS, the construct had adjusted scores of 14.2 (95% CI: 13.4 – 14.9; n = 1605) compared to the class average of 11.4 (95% CI: 11.3 – 11.5; n = 98,610). There were also more patients who rated their satisfaction as ‘excellent’ in the specific construct group. Comparisons were statistically significant in all cases (p < 0.001). In conclusion, in addition to excellent mid-term survivorship, the POLARSTEM/R3 construct combination has demonstrated superior PROMs that may improve patient outcomes

Introduction. Stress shielding is one of the major concerns of load bearing implants (e.g. hip prostheses). Stiff implants cause stress shielding, which is thought to contribute to bone resorption1. On the contrary, low-stiffness implants generate high interfacial stresses that have been related to pain and interfacial micro-movements². Different attempts have been made to reduce these problems by optimizing either the stem design3 or using functionally graded implants (FGI) where the stem's mechanical properties are optimized4. In this way, new additive manufacturing technologies allow fabricating porous materials with well-controlled mesostructure, which allows tailoring their mechanical properties. In this work, Finite Element (FE) simulations are used to develop an optimization methodology for the shape and material properties of a FGI hip stem. The resorbed bone mass fraction and the stem head displacement are used as objective functions. Methodology. The 2D-geometry of a femur model (Sawbones®) with an implanted Profemur-TL stem (Wright Medical Technology Inc.) was used for FE simulations. The stem geometry was parameterized using a set of 8 variables (Figure 1-a). To optimize the stem's material properties, a grid was generated with equally spaced points for a total of 96 points (Figure 1-b). Purely elastic materials were used for the stem and the bone. Two bone qualities were considered: good (Ecortical=20 GPa, Etrabecular=1.5 GPa) and medium (Ecortical=15 GPa, Etrabecular=1 GPa). Poisson ratio was fixed to v=0.3. Loading corresponded to stair climbing. Hip contact force along with abductors, vastus lateralis and vastus medialis muscles were considered5 for a bodyweight of 847 N. The resorbed bone mass fraction was evaluated from the differences in strain energy densities between the intact bone and the implanted bone2. The displacement of the load point on the femoral head was computed. The optimization problem was formulated as the minimization of the resorbed bone mass fraction and the head displacement. It was solved using a genetic algorithm. Results. For the Profemur-TL design, bone resorption was around 36% and 56% for good and medium bone qualities, respectively (Fig. 2). The corresponding head displacements were 11.75 mm and 21.19 mm. Optimized solutions showed bone resorption from 15% to 26% and from 44% to 65% for good and medium bone qualities, respectively. Corresponding head displacements ranged from 11.85 mm to 12.25 mm and from 16.9 mm to 22.6 mm. Conclusion. The obtained set of solutions constitutes an improvement of the implant performance for this functionally graded implant (FGI) compared to the original implant for both bone qualities. From these simulations, the final solution for the FGI could be chosen based on manufacturing restrictions or another performance indicator

INTRODUCTION:. Good survival rates of cementless hip stems serve as motivation for further development, just like modular implant systems or short stems. New aims are worth striving for, e.g. soft tissue or bone sparing options with similar survival rates in case of short stems. Even minimal design modifications might result in complications, e.g. missing osseointegration, loosening of the implant or painful stem, as shown in the past. One of these developments is the Biomet – GTS™ stem [Fig. 1], a hybrid between conventional cementless straight stem and potentially sparing short stem. Aim of this biomechanical study was to analyze, if the biomechanical behavior of the stem is comparable to a clinically proofed design with respect to the stem fixation in the bone and to the mechanical behavior of the stem itself. That's why the primary stability of the GTS™ stem has been determined and subsequently was compared to the Zimmer – CLS® stem. MATERIAL & METHODS. Four GTS™ stems and four CLS® stems were implanted standardized in eight synthetic femurs. Micromotions of the stem and the bone were measured at different sites. A high precision measuring device was used to apply two different cyclic load situations: 1. Axial torque of +/−7 Nm around the longitudinal stem axis to determine the rotational implant stability. 2. Varus-valgus-torque of +/−3, 5 Nm to determine the bending behavior of the stem. Comparing the motions of the stem and femur at different sites allowed the calculation of relative micromotions at the bone-implant-interface. RESULTS:. Lowest relative micromotions were detected near the lesser trochanter within the proximal part of both stems. Maximum relative micromotions were measured near the proximal end of the stem for both designs, indicating a proximal fixation of both stems [Fig. 2]. Concerning varus-valgus-torque, a similar flexibility between proximal stem shoulder and distal tip of stem was shown for both stems. DISCUSSION & CONCLUSION:. The relative micromotions of both groups seem to indicate an adequate primary stability of the stems. Obviously, the shortened design might have no fundamental influence on the biomechanical rotational stability in the bone. Compared to the CLS® stem, the GTS™ seemed to act similar flexibel during varus-valgus-torque application. Both stems might follow the bending of the bone instead of ‘tilting’ within the femur. This study showed, that the CLS® stem and the GTS™ stem biomechanically behave similar. However, a clinical confirmation of these experimental results remains to be

A novel cementless tapered wedge femoral hip implant has been designed at a reduced length and with a geometry optimized to better fit a wide array of bone types (Accolade II, Stryker, Mahwah, USA). In this study, finite element analysis (FEA) is used to compare the initial stability of the new proposed hip stem to predicate tapered wedge stem designs. A fit analysis was also conducted. The novel stem was compared to a predicate standard tapered stem and a shortened version of that same predicate stem. Methods. The novel shortened tapered wedge stem geometry was designed based on a morphological study of 556 CT scans. We then selected 10 discrete femoral geometries of interest from the CT database, including champagne fluted and stove pipe femurs. The novel and the predicate stems were virtually implanted in the bones in ABAQUS CAE. A total of thirty FEA models were meshed with 4 nodes linear tetrahedral elements. Bone/implant interface properties was simulated with contact surface and a friction coefficient of 0.35. Initial stability of each stem/bone assembly was calculated using stair-climbing loading conditions. The overall initial stability of the HA coated surface was evaluated by comparing the mean rotational, vertical, gap-opening and total micromotion at the proximal bone/implant interface of the novel and predicate stem designs. To characterize the fit of the stem designs we analyzed the ratio of a distal (60 mm below lesser trochanter) and a proximal (10 mm above lesser trochanter) cross section. A constant implantation height of 20 mm above the lesser trochanter was used. The fit of the stems was classified as Type 1 (proximal and distal engagement), Type 2 (proximal engagement only) and Type 3 (distal engagement only). Results. The mean % micromotion of the HA coated surface greater than 50 mm was lowest at 40.2% (SD 11.5%) for the novel tapered wedge stem compared to the clinically successful predicate stem design (Accolade TMAZ, Stryker, Mahwah, USA) at 44.9% (SD 13.2%) and its shortened version at 48.5% (SD 9.0%) as shown in Figure 1. Improved initial stability of the new stem was also confirmed for rotational, vertical and gap-opening micromotion. However, there was no statistically significant difference. The novel tapered stem design showed a well balanced proximal to distal ratio throughout the complete size range. The novel tapered stem design showed a reduced percentage of distal engagements (2.8%) compared to the predicate standard stem (17.2%). In the 40 to 60 year old male group the distal engagement for the standard stem increases (28.2%), whereas the distal engagements for the novel stem remains unchanged (1.3%). Discussion. It appears that through optimization of the novel tapered wedge geometry, a reduced length of a tapered wedge stem can be accomplished without jeopardizing initial stability. This data also shows that simply shortening an existing tapered wedge design may reduce the initial stability, albeit not statistically significant in this model. Optimising the shape of the stem has also significantly reduced the incidence of distal only type fixation in a computer model

Introduction. Hip stem taper wear and corrosion is a multifactorial process involving mechanical, chemical and biological damage modes. For the most cases it seems likely that the mechanically driven fretting wear is accompanied by other damage modes like pitting corrosion, galvanic corrosion or metal transfer. Recent retrieval studies have reported that the taper surface topography may affect taper damage resulting from fretting and corrosion [1]. Therefore, the current study aimed to examine effects of different taper topography parameters and material combinations on taper mechanics and results regarding wear and corrosion have been investigated. Materials and Methods. Combined experimental and numerical studies were conducted using titanium, cobalt-chromium and stainless steel generic tapers (Figure1). Uniaxial tensile tests were performed to determine the mechanical properties of the materials examined. For the taper studies macro-geometry of ceramic ball heads (BIOLOX. ®. delta) and tapers were characterized using a coordinate measuring machine, and assembly experiments according to ISO7206-10 were conducted up to 4kN. Before and after loading, taper subsidence was quantified by assembly height measurements. Taper micro-geometry, taper surface deformation, and contact area were determined by profilometry. Initial numerical studies determined coefficients of friction for the three material combinations. Macro- and micro-geometries of the tapers were modelled, and taper subsidence and assembly load served as boundary conditions. Further studies used simplified models to examine effects of varying profile depths and angular gaps on surface deformation, taper subsidence, contact area, engagement length and pull-off force. Results. Largest coefficient of friction and pull-off forces were calculated for steel (µ=0.32), cobalt-chromium revealed the lowest with µ=0.18. Titanium showed largest deformations and taper subsidence throughout all calculations (Figure2, Figure3). Taper subsidence, engagement length and deformations increased with increasing profile depth while contact area decreased. Pull-off forces were almost constant for different profile depths while they increased for increasing angular gaps. Taper subsidence and deformations also increased with increasing angular gap while engagement length decreased and contact area almost remained constant. Discussion. In order to decrease wear and corrosion micromotions should be minimized. Therefore, smaller angular gaps and smaller profile depths seems to be beneficial since deformation and taper subsidence are reduced. Literature data confirmed the results for different angular gaps showing that a larger angular gap is associated with larger amounts of micromotion and wear [2, 3]. Additionally, larger angular gaps and larger profile depths result in larger plastic deformation facilitating subsurface crack initiation and propagation. A large angular gap may also facilitate particle release [4]. Larger pull-off forces can indicate larger resistance against micromotion. Therefore, steel may tend to later develop fretting-corrosion in situ. However, among the metals examined steel also showed the largest equivalent plastic strain. This study is limited to pairings involving ceramic heads. These can help mitigating fretting corrosion resulting from micromotion between ball head and cobalt-chromium or titanium alloy tapers [5]. However, future studies will include other ball head materials. In conclusion, this study showed that taper surface topography affects taper mechanics and is important in terms of wear and corrosion

Accurate detection of migration of hip arthroplasty stems without the burden of bone markers and stereo-radiographic equipment is of interest. This would facilitate the study of stem migration in an experimental setting, but more importantly, it would allow assessing stem loosening in patients with a painful hip outside a study protocol. We developed and validated a marker-free automated CT-based spatial analysis method (CTSA) to quantify stem-bone migration in successive CT scan acquisitions. First, we segmented the bone and stem within both three-dimensional images, then we pairwise registered those elements (Fig. 1). By comparing the rigid transformations of stem and bone, we calculated the migration of the stem with reference to the bone and transferred the three translation and three rotation parameters to an anatomic coordinate system. Based on the rigid transformation, we also calculated the point of the stem that presented the maximal migration (PMM). Accuracy was assessed in a stem-bone model (Fig. 2) by imposing 39 predefined stem rotations and translations, and by comparing those with values calculated with the CTSA tool. In all cases, differences were below 0.20 mm for translations and 0.19° for rotations (95% tolerance interval (95% TI) below 0.22 mm and 0.20°, largest standard deviation of the signed error (SDSE) 0.081 mm and 0.057°). Precision was defined as stem migration calculated in eight clinical relevant zero-migration scenarios. In all cases, precision was below 0.05 mm and 0.08° (95% TI below 0.06 mm and 0.08°, largest SDSE 0.012 mm and 0.020°). The largest displacement of the PMM on the stem was 0.169mm. The precision estimated in five patients was very dependent on the CT scan resolution and was below 0.48 mm and 0.37° (95% TI below 0.59 mm and 0.61°, largest SDSE 0.202 mm and 0.279°, largest displacement of the PMM 0.972 mm). In optimized conditions, the precision in patients improved largely and was below 0.040 mm and 0.111° (largest SDSE 0.202 mm and 0.279°, largest displacement of the PMM 0.156 mm). Our marker-free automated CT-based spatial analysis can detect hip stem migration with an accuracy and precision comparable to that of radiostereometric analysis (RSA), but without the burden of bone markers and the cost of stereo-radiographic equipment. As such, we believe our tool could make accurate measurement of stem migration available to departments without access to RSA and boost this type of research. Moreover, as CTSA does not rely on bone makers, it is applicable to all-comers with a painful hip arthroplasty. Indeed, in those patients with a reference CT scan after hip replacement, a new CT scan could demonstrate stem migration. If no initial CT scan is available, a reference scan could be taken during a first visit and repeated later. Additionally, a “stress test” of the hip could be performed. During such test, comparing CT images acquired during forced maximal intern and external rotation could demonstrate stem loosening

INTRODUCTION. Immediate post-operative stability of a cementless hip design is one of the key factors for osseointegration and therefore long-term success [1]. This study compared the initial stability of a novel, shortened, hip stem to a predicate standard tapered wedge stem design with good, long-term, clinical history. The novel stem is a shortened, flat tapered wedge stem design with a shape that was based on a bone morphology study of 556 CT scans to better fit a wide array of bone types [2]. METHODS. Test methods were based on a previous study [3]. Five stems of the standard tapered wedge design (Accolade, Stryker Orthopaedics, Mahwah, NJ) and the novel stem (Accolade II, Stryker Orthopaedics, Mahwah, NJ) were implanted into a homogenous set of 10 synthetic femora (Figure 1) utilizing large left fourth generation. composite femurs (Sawbones, Pacific Labs, Seattle, WA). The six degrees-of-freedom (6 DoF) motions of the implanted stems were recorded under short-cycle stair-climbing loads. Minimum head load was 0.15 kN and the maximum load varied between 3x Body Weights (BW) and 6 BW. Loading began with 100-cycles of “normal” 3 BW and was stepped up to 4 BW, 5 BW & 6 BW for 50-cycles each. Prior to each load increase, 50 cycles of 3 BW loading was applied. This strategy allowed a repeatable measure of cyclic stability after each higher load was applied. The 6 DoF micromotion data, acquired during the repeated 3 BW loading segments, were reduced to four outcome measures: two stem migrations (retroversion and subsidence at minimum load) and two cyclic motions (cyclic retroversion and cyclic subsidence). Data were analyzed using repeated measures ANOVA with a single between-subjects factor (stem type) and repeated measures defined by load-step (3 BW, 4 BW, 5 BW 6 BW). RESULTS. Both stems retroverted under increasing load (p = 0.0011, Fig 2). Retroversion of the novel stem was significantly smaller than that of the standard tapered wedge stem (p = 0.023). The rate of increase in retroversion with increasing load was significantly lower for the novel stem (p = 0.026). In addition, both stems subsided under increasing load (p = 0.0015, Fig 3). Subsidence of the novel stem was significantly smaller than that of the standard tapered wedge stem (p = 0.016). The rate of increase in subsidence with increasing load was significantly lower for the novel stem (p = 0.022). With regard to cyclic motions, both cyclic retroversion and cyclic subsidence were significantly lower for the novel stems (p = 0.0033 & p = 0.0098). In addition, the rate of increase in cyclic motion was significantly lower for the novel stems for both cyclic retroversion (p = 0.0021) and cyclic subsidence (p = 0.023). DISCUSSION. In this study, the novel tapered wedge stem demonstrated an improved stability compared to the clinically successful predicate design. It appears that through optimization of the proximal geometry, a reduction in the length of the stem can be accomplished without jeopardizing initial stability

Introduction. Cementless femoral hip stems crucially depend on the initial stability to ensure a long survival of the prosthesis. There is only a small margin between obtaining the optimal press fit and a femoral fracture. The incidence of an intraoperative fracture is reported to be as high as 30% for revision surgery. The aim of this study is to assess what information is contained in the acoustic sound produced by the insertion hammer blows and explore whether this information can be used to assess optimal seating and warn for impeding fractures. Materials and Methods. Acoustic measurements of the stem insertion hammer blows were taken intra-operatively during 7 cementless primary (Wright Profemur Primary) and 2 cementless revision surgeries (Wright Profemur R Revision). All surgeries were carried out by the same experienced surgeon. The sound was recorded using 6 microphones (PCB 130E2), mounted at a distance of approximately 1 meter from the surgical theater. The 7 primary implants were inserted without complication, 1 revision stem induced a fracture distally during the insertion process. Two surgeons were asked to listen independently to the acoustic sounds post-surgery and to label the hits in the signal they would associate with either a fully fixated implant or with a fracture sound. For 3 out of 7 primary measurements the data was labeled the same by the two surgeons, 4 were labeled differently or undecided and both indicated several hits that would be associated with fracture for the fractured revision case. The acquired time signals were processed using a number of time and frequency domain processing techniques. Results. Figure 1 shows the convergence of a set of time and frequency features (selected temporal moments, decay and 99% energy time [1]) during a primary cementless insertion for which both surgeons labeled hit 12 as the final insertion hit. However, such convergence of the feature set was not as clear for the other 6 cases. Figure 2 shows the result of a feature that tracks the relative weight of low frequency content in the signal relative to the peak power present in the total frequency range for the two revision surgeries. This feature shows several spikes above 0.4 during the case with fractures, whereas none are present for the non-fractured revision case. The spikes concurred with the hits indicated by the surgeon panel post-surgery to have a sound associated with fractures. Conclusions. Assessment of this initial stability is a challenging task for the surgeon, who mainly has to rely on auditory and sensatory feedback. Although these findings look promising for an early detection and warning for (micro-) fractures, endpoint detection based on acoustic information is more challenging. The difficulty to determine the endpoint based solely on acoustic information was also reflected by the challenge of the surgeon panel to label the acoustic signals post-surgery. Data gathering is currently in progress to extend both the primary and revision set to 15 intra-operative measurements for further validation of these preliminary results

INTRODUCTION

Wedge femoral stems used in total hip arthroplasty (THA) have evolved with modifications including shorter lengths, reduced distal geometries, and modular necks. Unlike fit and fill stems which contact most of the metaphysis, tapered wedge femoral stems are designed to achieve proximal medial/lateral fixation. These single taper, wedge stems have demonstrated positive clinical outcomes. The tapered wedge stem evaluated in this study has further reduced distal geometry to provide a wedge-fit within the metaphysis of the proximal femoral canal for all femur types (Dorr A, B, C). The objective of this study was to evaluate the early clinical outcomes, including femoral stem subsidence, of a tapered wedge femoral stem.

Introduction

Although total hip arthroplasty (THA) has been one of the most successful, reliable and common prosthetic techniques since the introduction of cemented low-friction arthroplasty by Charnley in the early 1960s, aseptic loosening due to stem-cement and cement-bone interface failures as well as cement fractures have been known to occur. To overcome this loosening, the stem should be mechanically retentive and stable for long term repetitive loading. Migration studies have shown that all stems migrate within their cement mantle, sometimes leading to the stem being debonded from the cement [1]. If we adopt the hypothesis that the stems debond from the cement mantle, the stem surface should be polished. For the polished stem, the concept of a double taper design, which is tapered in the anteroposterior (AP) and mediolateral (ML) planes, and a triple-tapered design, which has trapezoidal cross-section with the double tapered, have been popularized. Both concepts performed equally well clinically [2]. In this study, we aimed to analyze stress patterns for both models in detail using the finite element (FE) method.

Introduction

After arthroplasty, stress shielding and high shear stresses at the bone-implant interface are common problems of load bearing implants (e.g. hip prostheses). Stiff implants cause stress shielding, which is thought to contribute to bone resorption¹. High shear stresses, originated by low-stiffness implants, have been related to pain and interfacial micro-movements², prohibiting adequate implant initial fixation.

A non-homogeneous distribution of mechanical properties within the implant could reduce the stress shielding and interfacial shear stresses³. Such an implant is called “functionally graded implant” (FGI). FGI require porous materials with well-controlled micro-architecture, which can now be obtained with new additive manufacturing technologies (e.g. Electron Beam Melting).

Finite element (FE) simulations in ANSYS-v14.5 are used to develop an optimization methodology to design a hip FGI.

Introduction

Proper initial fixation of the stem in the femoral canal is important to achieve successful long-term clinical results in total hip arthroplasty (THA) and bipolar hemiarthroplasty (BHA). However, this factor fully relies on surgeon's experience and skill during the hammering process. The goal of this study is to evaluate the frequency of the stem hammering sound which enables the achievement of proper stem fixation and avoiding femoral bone fracture.

The Parva stem has been designed in order to achieve a good cervical and interthrocanteric primary fixation associated with a reliable fit at the isthmus level.

The stem has been conceived to address the larger possible variety of proximal femoral anatomic variations too.

Ability to adapt to patients anatomies being one of the major limitations of earlier neck preserving implants.

The stem therefore features innovative design concepts including the latest generation Modular Neck System, coupled with a revolutionary metal powder manufacturing process and surface engineering technology.

Our first 150 cases with minimum 1 year follow up are presented. All patients have been followed employing the Harris Hip Score and the reduced WOMAC questionnaire to judge their degree of satisfaction.

Particular care has been posed to analyze results for those patients anatomies (i.e. Very Valgus or Varus femurs) where normally neck sparing stems have problems to correctly fit in.

The feed-back we had with this very innovative implant is very encouraging.

Further data collection and longer follow up will be needed in order to confirm these early promising results.

Introduction

Although total hip replacement (THR) has been described as the operation of the century, there is still room for improvement. There is therefore continued effort for advanced implants and bearing surfaces, moreover so, for the younger patient with a longer life expectancy and increased needs.

INTRODUCTION

Total hip arthroplasty (THA) is a very successful orthopaedic treatment with 15 years implant survival reaching 95%, but decreasing age and increasing life expectancy of THA patients ask for much longer lasting solutions. Shorter and more flexible cementless stems are of high interest as these allow to maintain maximum bone stock and reduce adverse long-term bone remodeling.1 However, decreasing stem length and reducing implant stiffness might compromise the initial stability by excessively increasing interfacial stresses. In general, a good balance between implant stability and reduced stress shielding must be provided to obtain durable THA reconstruction.2

This finite element (FE) study aimed to evaluate primary stability and bone remodeling of a new design of short hip implant with solid and U-shaped cross-section.

Background

Tapered cementless femoral components have been used in total hip arthroplasty (THA) constructs for more than 20 years. The Synergy femoral component was introduced in 1996 as a second generation titanium proximally porous-coated tapered stem with dual offsets to better restore femoral offset at THA (Figure 1). The purpose of this study was to evaluate the outcome of the authors' experience using the Synergy stem at minimum 15 years of follow-up.