Introduction. Long term data on the survivorship of cemented total knee arthroplasty (TKA) has demonstrated excellent outcomes; however, with younger, more active patients, surgeons have a renewed interest in improved biologic fixation obtained from highly porous, cementless implants. Early designs of cementless total knees systems were fraught with high rates of failure for aseptic loosening, particularly on the tibial component. Prior studies have assessed the bone ingrowth extent for tibial tray designs reporting near 30% extent of bone ingrowth . (1,2). While these analyses were performed on implants that demonstrated unacceptably high rates of clinical failure, a paucity of data exists on the extent on bone ingrowth in contemporary implant designs with newer methods for manufacturing the porous surfaces. We sought to evaluate the extent of attached bone on retrieved cementless tibial trays to determine if patient demographics, device factors, or radiographic results correlate to the extent of bone ingrowth in these contemporary designs. Methods. Using our IRB approved retrieval database, 17 porous tibial trays were identified and separated into groups based on manufacturer: Zimmer Natural Knee (1), Zimmer NexGen (10), Stryker Triathlon (4) and Biomet Vanguard Regenerex (2). Differences in manufacturing methods for porous material designs were recorded. Patient demographics and reason for revision are described in Table 1. Radiographs were used to measure tibiofemoral alignment and the tibial mechanical axis alignment. Components were assessed using visual light microscopy and Photoshop to map bone ingrowth extent across the porous surface. ImageJ was used to threshold and calculate values for bone, scratched metal, and available surface for bone ingrowth (Fig. 1). Percent extent was determined as the bone ingrowth compared to the surface area excluding any scratched regions from explantation. Statistics were performed among tray designs as well as between the lateral and medial pegs, if designs had pegs available for bony ingrowth. Results. Mean bone ingrowth extent was 51.4% for the tibial tray for the entire cohort. Bone ingrowth extent was statistically greater in the Zimmer NexGen design (63.8%; p=.027) compared to the other three designs (Table 2). Four sets of pegs were excluded from analysis due to lack of porous coatings or pegs having been removed at revision surgery. Across all designs, the medial peg had 45.2% ingrowth and the lateral peg had 66.1% ingrowth. The medial peg for the NexGen design had significantly less bone ingrowth compared to the lateral peg (58.7% vs. 75.4%; p=0.044). No significant differences were found in tibiofemoral alignment or tibial mechanical axis alignment between the implant groups. No significant differences were found among implants revised for aseptic loosening versus any other reason for revision (54% vs 30%; p=.18). Discussion. Our results demonstrate high rates of bone ingrowth extent in contemporary designs, further supporting porous design rationales and a role for additive manufacturing to form enhanced porosity. We plan on exploring staining techniques to confirm our visual inspection. Contemporary designs have shown successful rates for improved longevity for cementless total knee systems. For any figures or tables, please contact the authors directly

Introduction. Cementless acetabular components are commonly used in primary and revision total hip arthroplasty, and most designs have been successful despite differences in the porous coating structure. Components with 2D titanium fiber mesh coating (FM) have demonstrated high survivorships up to 97% at 20 years. 1. 3D tantalum porous coatings (TPC) have been introduced in an attempt to improve osseointegration and therefore implant fixation. Animal models showed good results with this new material one year after implantation. 2. , and clinical and radiographic studies have demonstrated satisfactory outcomes. 3. However, few retrieval studies exist evaluating in vivo bone ingrowth into TPC components in humans. We compared bone ingrowth between well-fixed FM and TPC retrieved acetabular shells using backscatter scanning electron microscopy (BSEM). Methods. 16 retrieved, well-fixed, porous coated acetabulum components, 8 FM matched to 8 TPC by gender, BMI and age, all revised for reasons other than loosening and infection, were identified from our retrieval archive (Fig. 1). The mean time in-situ was 42 months for TPC and 172 for FM components. Components were cleaned, dehydrated, and embedded in PMMA. They were then sectioned, polished, and examined using BSEM. Cross-sectional slices were analyzed for percent bone ingrowth and percent depth of bone ingrowth (Fig. 2). Analysis was done using manual segmentation and grayscale thresholding to calculate areas of bone, metal, and void space. Percent bone ingrowth was determined by assessing the area of bone compared to the void space that had potential for bone ingrowth. Results. The average bone ingrowth was 19.2% for the eight FM components and 6.9% for the eight TPC components. Bone ingrowth in the FM components was quite variable, ranging from as little as 2.3% to as much as 71.6%. Conversely, the amount of bone ingrowth seen in the TCP acetabular cups was less variable, ranging from 0.4% to 13%. By design, TPC cups were more porous; the retrieved TPC cups had ∼65–75% porosity (area void space divided by total area of void space plus metal), while the retrieved FM cups had ∼40–50% porosity. No relation was found between bone ingrowth measured in the retrievals at the length of time that they had been implanted. Discussion. The TPC retrievals were well-fixed at revision surgery, despite the small percent of the coating that had bone ingrowth. Other factors, such as high coefficient of friction, leading to effective initial fixation and sufficient bone ongrowth rather than ingrowth, may impact clinical performance. A previous study of post-mortem, well-fixed retrieved FM cups found 12 ±8% bone area ingrowth. 4. , similar to our findings. Ongoing retrieval analysis will provide further insight into possible regional trends and material ingrowth differences

Introduction. Uncemented porous coated acetabular components have gained more research emphasis in recent years compared to their cemented counterparts, largely owing to the natural biological fixation they offer. Nevertheless, sufficient peri-prosthetic bone ingrowth is essential for long-term fixation of such uncemented acetabular components. The phenomenon of bone ingrowth can be predicted based on mechanoregulatory principles of primary bone fracture healing. Literature review reveals that the surface texture of implant plays a major role in implant-bone fixation mechanism. A few insilico models based on 2-D microscale finite elements (FE) were reported in literatures to predict the influence of surface texture designs on peri-prosthetic bone ingrowth. However, most of these studies were based on FE models of dental implants. The primary objective of this study, therefore, is to mechanobiologically predict the influence of surface texture on bone- ingrowth in acetabular components considering a novel 3-D mesh-shaped surface texture on the implant. Materials/Methods. The 3-D microscale model [Fig.1] of implant-bone interface was developed using CATIA. ®. V5R20 software (DassaultSystèmes, France) and was modelled in ANSYS V15.0 FE software (Ansys Inc., PA, USA) using coupled linear elastic ten-noded tetrahedral finite elements. The model consists of cast-inbeaded mesh textured implant having finely meshed inter-bead spacing. Linear, elastic and isotropic material properties considering Young's modulus of 210 GPa and Poisson's ratio of 0.3 for stainless steel implant were employed in the model. Boundary of bone was assumed to be rich in Mesenchymal Stem Cells(MSC) with periodic boundary conditions at contralateral surfaces. The linear elastic material properties in the model were updated iteratively through a tissue differentiation algorithm that works on the principle of mechanotransduction driven by local mechanical stimuli, e.g. hydrostatic pressure and equivalent deviatoric strain. Results. Results indicate that bone ingrowth is inhibited upon increasing the inter-bead spacing and upon decreasing the bead aspect ratio. It has been observed that there is a predominant influence of bead spacing diameter on the peri-acetabular bone ingrowth. The increase in bead spacing diameter has led to increased bead height that is found to promote higher bone ingrowth with an increase in average Young's modulus of neo-tissue layer. Conclusions. The present study focussed on the development of a new texture on the implant surface and to study the influence of surface texture on bone-ingrowth in acetabular components. Since there is a promising increase in average Young's modulus of the newly formed tissue layer, it predicts the increase in stiffness of the newly formed tissue. The increase in tissue stiffness reveals that, there is not much inhibition in bone ingrowth after the employment of the acetabular implant. The numerical study based on mechanoregulatory algorithm considering the appropriate mechanical stimuli responsible for bone ingrowth, reveals that, compared to hemispherical beaded surface texture, mesh shaped surface texture provides an improved fixation of the acetabular component. For any figures or tables, please contact the authors directly

Background. Polymethylmethacrylate (PMMA) has been used for total knee arthroplasty (TKA) as a method of fixation; however, its durability has been questionable for the long-term use because of the loosening after the cement deterioration, its vulnerability toward infectious resistance, and a smaller amount of healthy bone left for the knee revision surgery. Especially, a decrease of bone density on the proximal tibia has been believed to be triggered as a result of stress shielding. When compared with a cemented TKA, a cementless TKA reduces the amount of bone loss after surgery. In 1999, the Trabecular Metal (TM), with its main composition being the porous tantalum metal, became available as a choice of the porous cementless knee joint prosthesis. The characteristics of porous tantalum metal are its great affinity to the bone as well as its similarity to cancellous bone. The porous tantalum metal starts to bond with osteoblasts, and fills up 80% of porous structure in one year; therefore, it has been characterized by its higher initial fixation strength. However, it is questionable if strong fixation strength due to bone ingrowth between the tibial tray mainly made up with the porous tantalum metal and a cancellous bone will continually be kept. Bobyn, JD, Dunbar et al. have acknowledged the existence of bone ingrowth based on the radiographic evaluation; however, their data had not been quantified in their report. In this study, the bone ingrowth density have periodically quantified using 3D bone morphometric software (TRI/3D-BON64.RATOC) after taking CT of the knee joint prosthesis. Material and Methods. From October 2011, we have reviewed 45 medial osteoarthritis knees that underwent MIS-TKA using Trabecular Metal Modular Tibia CR-type (Zimmer, Inc, Warsaw, Indiana). Ages range from 61–89 years (mean, 74.5 years), and 5 males (7 knees), and 32 females (38 knees) participated in this study. After taking CT picture with the Phantom under lower extremities, the bone ingrowth density are quantified utilizing 3D bone morphometric software (TRI/3D-BON63.RATOX). Measured areas are divided into 6 zones that are right under the pegs of TM femoral component, and the bone ingrowth density (BMC/TC) between TM and cancellous bone were periodically measured on 3, 6, 9, 12,15,18,21,24.27 months after the surgery. Also, intra-zone comparison were implemented by each period among Medial (Zone 1), Lateral (Zone 2), Medial Anterior (Zone 3), Medial Posterior (Zone 4), Lateral Anterior (Zone 5), and Lateral Posterior (Zone 6). Mann-Whitney U test and Student's t-test were used for statistical analysis. All cases of tibial component alignment was within 3 degree varus-valgus to neutral alignment. Results. Bone ingrowth and formation was increased to nine months from six months after surgery and was reduced to 12 months postoperatively. But bone resorption was aboloished 18 months after surgery without influence stress shieldings. In detail, the result was significant higher bone ingrowth and formation in medial than lateral region. I recognized that lateral lesion was affected by stress shieldings. The results was not significant difference of bone ingrowth between medial anterior and posterior region but significant difference of bone ingrowth in lateral posterior than lateral anterior

INTRODUCTION. Electron beam melting is a promising technique to produce surface structures for cementless implants. Biomimetic apatite coatings can be used to enhance bone ingrowth. The goal of this study was to evaluate bone ingrowth of an E-beam produced structure with biomimetic coating and compare this to an uncoated structure and a conventionally made implant surface. METHODS. Implants. The implants (10×4×4mm) were produced with E-beam technology. (Eurocoating). All E-beam implants had a cubic surface structure (porosity 77%). Two structures were coated (Eurocoating), one with hydroxyapatite (cubicHA) and one with brushite (cubicBR). One was left uncoated. A control specimen with a titanium plasma spray coating (TiPS) was also tested. (Figure 1). Experimental design. Surgery was performed on 12 goats. A double set of specimens was implanted in the iliac crest. 4 goats were sacrificed 3 weeks after surgery and 8 goats after 15 weeks. Push out test. The specimens were pushed out the surrounding bone by a Material Testing System (MTS) to define the mechanical strength of the bone-implant interface. Histology. Maximum bone ingrowth depth was measured with fluorescence microscopy (5 and 10 weeks) and light microscopy at HE stained slices (15 weeks). RESULTS. The mechanical strength of the bone-implant interface of the cubic structure and the cubicHA were significantly higher compared to the TiPS control at 15 weeks of implantation. (Figure 2). The maximum bone ingrowth depth of the cubicHA and cubicBR was significantly greater compared to the uncoated cubic structure at respectively 5 & 15 and 5, 10 & 15 weeks. (Figure 3). DISCUSSION & CONCLUSIONS. The results of this study are promising. The E-beam structure performed better than a clinically successful coating. Application of a biomimetic CaP based coating on this E-beam surface provided enhanced bone ingrowth. A large surface area associated with a high porosity (as seen in the cubic structure) is known to allow better bone ingrowth. However a setback of a high porosity is that it takes more time before full integration is established. Application of a biomimetic coating appeared to overcome this by providing improved fixation by bone ingrowth in the early postoperative period. ACKNOWLEDGEMENTS. This study is cosponsored by Provincia Autonoma di Trento and Eurocoating SpA, Trento, Italy

Introduction. A variety of porous coatings and substrates have been used to obtain fixation at the bone-implant interface. Clinical studies of porous tantalum, have shown radiographically well-fixed implants with limited cases of loosening. However, there has been limited retrieval analysis of porous tantalum hip implants. The purpose of this study was to investigate factors affecting bone ingrowth into porous tantalum hip implants. Methods. 126 porous tantalum acetabular shells and 7 femoral stems, were collected under an IRB-approved multicenter retrieval program. Acetabular shells that were grossly loose, cemented or complex revisions were excluded. Shells with visible bone on the surface were chosen. 20 acetabular shells (10 primary) and all femoral stems were dehydrated, embedded, sectioned, polished and bSEM imaged (Figure-1). Main shell revision reasons were infection (n=10,50%), femoral loosening (n=3,15%) and instability (n=3,15%). Analyzed implants were implanted for 2.3±1.7 years (shells) and 0.3±0.3 years (stems). Eight slices per shell and 5–7 slices per stem were analyzed. The analysis included bone area/pore area (BA/PA), BA/PA zonal depth analysis, extent of ingrowth and maximum depth of bone ingrowth. BA/PA zone depths were: Zone-1 (0–500um), Zone-2 (500–1000um) and Zone-3 (1000um-full depth). Nonparametric statistical tests investigated differences in bone measurements by location within an implant and implant type (Friedman's Variance and Kruskal-Wallis). Post-hoc Dunn tests were completed for subsequent pairwise comparisons. Spearman's rank correlation identified correlations between bone measurements and patient related variables (implantation time, age, height, weight, UCLA Activity Score). Statistical analyses were performed using PASW Statistics package. Results. BA/PA was not significantly different between acetabular shells (3.6±3.3%) and femoral stems (5.8% ± 3.9%, p=0.068). Extent of ingrowth was similar between shells (42 ± 28%) and stems (47±26%, p=0.825). Acetabular shells (76±23%) and stems (82±23%, p=0.707) had a similar maximum ingrowth depth. There were 9 shells and 2 stems (Figure-2) with full bone ingrowth into the porous tantalum substrate. When bone did not bridge the entire depth, a superficial layer of dense trabecular bone integrated with the porous layer was often observed. Localized regions of increased ingrowth were observed around screw holes. BA/PA in the superior region (4.1±2.4%) of the acetabular shells was significantly higher than in the inferior region (2.0±2.1%, p=0.047, Figure-3). Acetabular shells BA/PA in Zone-1(10.8%) was significantly higher than Zone-2 (4.9%, p=0.013) and Zone-3 (1.6%, p<0.001). BA/PA was significantly higher in Zone-1 (10.8%) than Zone-3 (2.3%, p=0.043) for femoral stems. There were no correlations between patient variables and bone measurements. Discussion. Our results demonstrate that bone ingrowth in porous tantalum hip components is concentrated in the superficial 500 um (Zone-1). This may provide the opportunity to reduce the thickness of the porous layer thus conserving more bone in future designs. Bone ingrowth in the acetabular shells was preferentially located around screw holes and superior region, similar to previous studies of other cementless designs. Only 40% of analyzed acetabular shells had implantation times greater than 2 years. Further work focused on longer term retrievals will increase understanding of the bone-implant interface. This study was supported by Zimmer and NIH (NIAMS) R01 AR47904

Introduction. Surgeons are often confronted with large amounts of bone loss during the revision of total hip prostheses. Regularly, porous metals are applied to reconstruct the missing bone. Rapid and extensive bone infiltration into the implant's pores is essential to obtain strong and durable biological fixation. Today, specialised layered manufacturing techniques provide the flexibility to produce custom-made metallic implants with a personalized external shape and a well-controlled internal network of interconnected pores. In this study, bone ingrowth in porous titanium structures that were manufactured by selective laser melting (SLM) was evaluated in an in vivo goat model. Methods. Cylindrical Ti6Al4V constructs (Ø8mm × 14mm, porosity 75%) with or without hydroxyapatite coating were implanted in six Saanen goats. Three holes were drilled in the subchondral bone of each tibia and femur. Constructs were inserted into the holes in a press-fit manner. Resonance frequency analysis was used to measure construct stability. At 3, 6 and 9 weeks after surgery, fluorochrome labels were injected. After 6 and 12 weeks, samples were explanted. Some samples were scanned with micro-CT and subsequently sectioned for histological analysis. The others were used for pull-out tests. Results. Resonance frequency analysis indicated a noticeable increase in implant stability. Evaluation of micro-CT and histological data showed bone ingrowth for all goats at 6 and 12 weeks. Most bone ingrowth occurred during the first 6 weeks, which was followed by a slight increase between week 6 and 12. Fluorochrome labeling confirmed these results. Pull-out tests showed an increased fixation at the bone-implant interface. Conclusion. Porous titanium structures manufactured by SLM have good osseointegration characteristics. As custom-made bone augments, they provide a promising approach to the reconstruction of severe bone defects

Background. Recent advances in materials and manufacturing processes for arthroplasty have allowed fabrication of intricate implant surfaces to facilitate bony attachment. However, refinement and evaluation of these new design strategies is hindered by the cost and complications of animal studies, particularly during early iterations in development process. To address this problem, we have constructed and validated an ex-vivo bone bioreactor culture system to enable empirical testing of candidate structures and materials. In this study, we investigated mineralization of a titanium wire mesh scaffold under both static and dynamic culturing using our ex vivo bioreactor system. Methods. Cancellous cylindrical bone cores were harvested from bovine metatarsals and divided into five groups under different conditions. After incubation for 4 & 7 weeks, the viability of each bone sample was evaluated using Live-Dead assay and microscopic anatomy of cells were determined using histology stain H&E. Matrix deposits on the scaffolds were examined with scanning electron microscopy (SEM) while its chemical composition was measured using energy-dispersive x–ray spectroscopy (EDX). Results. The viability of bone cores was maintained after seven weeks using our protocol and ex vivo system. From SEM images, we found more organic matrix deposition along with crystallite like structures on the metal samples pulled from the bioreactor indicating the initial stages of mineralization. EDX results further confirmed the presence of carbon and calcium phosphates in the matrix. Conclusion. A bone bioreactor can be used a tool alternate to in-vivo for bone ingrowth studies on new implant surfaces or coatings

Introduction. Titanium (Ti) alloys are used as porous bone ingrowth materials on non-cemented knee arthroplasty tibial tray implants. Nano-surface mechanism that increase the osseointegration rate between Ti alloys, and surrounding tissue has been recognized to improve the interface to ultimately allow patients to weight bear on non-cemented arthroplasty implants sooner. Bioactive TiO. 2. nanotube arrays has been shown to accelerate osseointegration. Ideally, these surfaces would both increase the adhesion of bone to the implant and help to reduction of infection to substitute for antibiotic bone cement. This study examines a combination treatment of both TiO. 2. nanotubes combined with silver nano-deposition, that simultaneously enhances osseointegration while improving infection resistance, by testing ex vivo implantation stability in an equine cadaver bone followed by in vitro and in vivo analysis to understand the biocompatibility and early stage osseointegration. Methods. 100nm diameter and 300nm length TiO. 2. nanotubes were formed on a CP titanium surface using anodization method at 20V for 45mins using 1% HF electrolyte. Silver deposition on TiO. 2. nanotubes were performed using 0.1M AgNO. 3. solution at 3V for 45s. Figure 1 shows SEM images showing (a) TiO. 2. nanotubes of 300nm length and (b) nanotubes with silver coating). Ti anodized samples with and without silver nanotubes implanted into an equine cadaver bone in an ex vivo manner to study the stability of nanotubes and the adherence of silver deposition. Silver release study was performed for a period of 14 days in a similar ex vivo manner. Dimensions for implantation samples: 2.5 mm diam. × 15 mm. For cell culture, circular disc samples 12.5mm in diameter and 3 mm in thickness were used to study the bone cell-material interactions using human fetal osteoblast (hFOB) cells. To evaluate the cell proliferation, MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) assay was used. The in vitro cell-materials interaction study was performed for a period of 4 and 7 days. In vivo study was performed using rat distal femur model for a period of 12 weeks with dense Ti samples as control (Sample dimensions: 3mm diam. × 5mm). At the end of 12 weeks, the samples were analyzed for early stage osseointegration using histological analysis and SEM imaging. Results. No significant changes in the morphology of nanotubes was observed due to the implantation process which signifies the damage resistance these nanotubes can endure during implantation and explantation. Figure 2 shows SEM images of (a) & (b) nanotubes without silver coating before and after implantation and (c) & (d) nanotubes with silver coating before and after implantation respectively. Silver nanocoatings can be observed after implantation which shows the adherence of the antimicrobial nano-coating on the surface of nanotubes. Cumulative release profiles of silver ions after 14 days showed the total release was in the effective range for antimicrobial characteristics and was well below the toxic limit specified for human cells (10 ppm) Figure 3(a) shows cumulative release profile of silver after 14 days. MTT assay and SEM images show good cell proliferation, antimicrobial effect, and increase in cell density after 7 days for samples with nanotubes and silver with no cytotoxic effects and good cell attachment on the samples as shown in Figure 3(b) MTT assay results showing cell densities after 4 and 7 days and Figure 3(c) SEM images showing cell attachment after 4 and 7 days on samples. Histological analysis and SEM images showed osteoid formation around the implant with improved bonding towards the implant and bone showing signs of early stage osseointegration. Figure 4 shows histological and SEM images showing bonding between bone and implant surface for respective samples after 12 weeks. Conclusions. Mechanically stableTiO. 2. nanotubes with strongly adhered antimicrobial silver coating were grown on the surface of titanium which were biocompatible and non-toxic. In vitro and in vivo tests indicate improved cell-materials interaction with signs of early stage osseointegration. This nano-surface treatment shows promise towards simultaneously improving early stage osseointegration and providing an infection barrier on bone ingrowth materials

Background

The optimal surgical treatment for osteonecrosis of the femoral head has yet to be elucidated. To evaluate the role of femoral fixation techniques in hip resurfacing, we present a comparison of the results for two consecutive groups: Group 1 (75 hips) received hybrid hip resurfacing implants with a cemented femoral component; Group 2 (103 hips) received uncemented femoral components. Both groups received uncemented acetabular components.

Background

Cementless short stems have the advantages of easy insertion, reduced thigh pain and being suitable for minimally-invasive surgery, therefore cementless short stem implants have been becoming more widely used. The revelation microMAX stem is a cementless short stem with a lateral flare design that allows for proximal physiological load transmission and more stable initial fixation. Images acquired with T-smart tomosynthesis using a new image reconstruction algorithm offer reduced artifacts near metal objects and clearer visualization of peri-implant trabeculae. Therefore, these images are useful for confirming implant fixation status after total hip arthroplasty (THA). We believe that T-smart tomosynthesis is useful for estimating the condition of microMAX stem fixation and will hereby report on observation of the postoperative course of microMAX stem.

Porous surfaces on orthopaedic implants have been shown to promote tissue ingrowth. This study evaluated biological fixation of novel additively manufactured porous implants with and without hydroxyapatite coatings in a canine transcortical model. Laser rapid manufacturing (LRM) Ti6Al4V cylindrical implants were built with a random interconnected architecture mimicking cancellous bone (5.2 mm diameter, 10mm length, 50–60% porous, mean pore size 450μm). Three groups were investigated in this study: as-built with no coating (LRM), as-built coated with solution precipitated hydroxyapatite (LRM-PA), and as-built coated with a plasma sprayed hydroxyapatite (LRM-PSHA). Implants were press-fit into a 5mm unicortical, perpendicular drill hole in the femoral diaphysis of the left and right femurs in 12 canines. Right femora were harvested for histology (SEM, bone ingrowth into implant within cortical region) and left femora for mechanical push-out testing (shear strength of bone-implant interface) at 4 and 12 weeks (N=6, un-paired Student's t-test, p=0.05). For mean bone ingrowth, there was no significant difference between groups at 4 weeks (LRM, LRM-PA, LRM-PSHA: 41.5+8.6%, 51+5.5% and 53.2+11%, respectively) or 12 weeks (LRM, LRM-PA, LRM-PSHA: 64.4+2.8%, 59.9+7.6%, 64.9+6.4%, respectively). LRM and LRM-PA implants had more bone ingrowth at 12 weeks than 4 weeks (p < 0 .05). Mean shear strength of all implants at 12 weeks (LRM, LRM-PA, LRM-PSHA: 39.9+3.6MPa, 33.7+4.6MPa, 36+4.1MPa respectively) were greater than at 4 weeks (LRM, LRM-PA, LRM-PSHA: 21.6+2.8MPa, 20.7+1.1MPa, 20.2+2.5MPa respectively) (p < 0 .05). No significant difference was observed between all groups at 4 or 12 weeks. Overall, this canine study confirmed the suitability of this novel additive manufacturing porous material for biological fixation by bone ingrowth. All implants exhibited high bone ingrowth and mechanical shear strength in this canine model. No difference was observed between uncoated and hydroxyapatite coated implants

Introduction. Varus alignment in total knee replacement (TKR) results in a larger portion of the joint load carried by the medial compartment. [1]. Increased burden on the medial compartment could negatively impact the implant fixation, especially for cementless TKR that requires bone ingrowth. Our aim was to quantify the effect varus alignment on the bone-implant interaction of cementless tibial baseplates. To this end, we evaluated the bone-implant micromotion and the amount of bone at risk of failure. [2,3]. Methods. Finite element models (Fig.1) were developed from pre-operative CT scans of the tibiae of 11 female patients with osteoarthritis (age: 58–77 years). We sought to compare two loading conditions from Smith et al.;. [1]. these corresponded to a mechanically aligned knee and a knee with 4° of varus. Consequently, we virtually implanted each model with a two-peg cementless baseplate following two tibial alignment strategies: mechanical alignment (i.e., perpendicular to the tibial mechanical axis) and 2° tibial varus alignment (the femoral resection accounts for additional 2° varus). The baseplate was modeled as solid titanium (E=114.3 GPa; v=0.33). The pegs and a 1.2 mm layer on the bone-contact surface were modeled as 3D-printed porous titanium (E=1.1 GPa; v=0.3). Bone material properties were non-homogeneous, determined from the CT scans using relationships specific to the proximal tibia. [2,4]. The bone-implant interface was modelled as frictional with friction coefficients for solid and porous titanium of 0.6 and 1.1, respectively. The tibia was fixed 77 mm distal to the resection. For mechanical alignment, instrumented TKR loads previously measured in vivo. [5]. were applied to the top of the baseplate throughout level gait in 2% intervals (Fig.1a). For varus alignment, the varus/valgus moment was modified to match the ratio of medial-lateral force distribution from Smith et al. [1]. (Fig.1b). Results. For both alignments and all bones, the largest micromotion and amount of bone at risk of failure occurred during mid stance, at 16% of gait (Figs.2,3). Peak micromotion, located at the antero-lateral edge of the baseplate, was 153±32 µm and 273±48 µm for mechanical and varus alignment, respectively. The area of the baseplate with micromotion above 40 µm (the threshold for bone ingrowth. [3]. ) was 28±5% and 41±4% for mechanical and varus alignment, respectively. The amount of bone at risk of failure at the bone-implant interface was 0.5±0.3% and 0.8±0.3% for the mechanical and varus alignment, respectively. Discussion. The peak micromotion and the baseplate area with micromotion above 40 µm increased with varus alignment compared to mechanical alignment. Furthermore, the amount of bone at risk of failure, although small for both alignments, was greater for varus alignment. These results suggest that varus alignment, consisting of a combination of femoral and tibial alignment, may negatively impact bone ingrowth and increase the risk of bone failure for cementless tibial baseplates of this TKR design

Long-term biological fixation and stability of uncemented acetabular implant are influenced by peri-prosthetic bone ingrowth which is known to follow the principle of mechanoregulatory tissue differentiation algorithm. A tissue differentiation is a complex set of cellular events which are largely influenced by various mechanical stimuli. Over the last decade, a number of cell-phenotype specific algorithms have been developed in order to simulate these complex cellular events during bone ingrowth. Higher bone ingrowth results in better implant fixation. It is hypothesized that these cellular events might influence the peri-prosthetic bone ingrowth and thereby implant fixation. Using a three-dimensional (3D) microscale FE model representing an implant-bone interface and a cell-phenotype specific algorithm, the objective of the study is to evaluate the influences of various cellular activities on peri-prosthetic tissue differentiation. Consequently the study aims at identifying those cellular activities that may enhance implant fixation. The 3D microscale implant-bone interface model, comprising of Porocast Bead of BHR implant, granulation tissue and bone, was developed and meshed in ANSYS (Fig. 1b). Frictional contact (µ=0.5) was simulated at all interfaces. The displacement fields were transferred and prescribed at the top and bottom boundaries of the microscale model from a previously investigated macroscale implanted pelvis model (Fig. 1a) [4]. Periodic boundary conditions were imposed on the lateral surfaces. Linear elastic, isotropic material properties were assumed for all materials. Young's modulus and Poisson's ratios of bone and implant were mapped from the macroscale implanted pelvis [4]. A cell-phenotype specific mechanoregulatory algorithm was developed where various cellular activities and tissue formation were modeled with seven coupled differential equations [1, 2]. In order to evaluate the influence of various cellular activities, a Plackett-Burman DOE scheme was adopted. In the present study each of the cellular activity was assumed to be an independent factor. A total of 20 independent two-level factors were considered in this study which resulted in altogether 24 different combinations to be investigated. All these cellular activities were in turn assumed to be regulated by local mechanical stimulus [3]. The mechano-biological simulation was run until a convergence in tissue formation was attained. The cell-phenotype specific algorithm predicted a progressive transformation of granulation tissue into bone, cartilage and fibrous tissue (Fig. 1c). Various cellular activities were found to influence the time to reach equilibrium in tissue differentiation and, thereby, attainment of sufficient implant fixation (Fig. 2, Table 1). Negative regression coefficients were predicted for the significant factors, differentiation rate of MSCs and bone matrix formation rate, indicating that these cellular activities favor peri-prosthetic bone ingrowth by facilitating rapid peri-prosthetic bone ingrowth. Osteoblast differentiation rate, on the contrary, was found to have the highest positive regression coefficient among the other cellular activities, indicating that an increase in this cellular activity delays the attainment of equilibrium in bone ingrowth prohibiting rapid implant fixation. To view tables/figures, please contact authors directly

Shoulder arthroplasty humeral stem design has evolved to accommodate patient anatomy characteristics. As a result, stems are available in numerous shapes, coatings, lengths, sizes, and vary by fixation method. This abundance of stem options creates a surgical paradox of choice. Metrics describing stem stability, including a stem's resistance to subsidence and micromotion, are important factors that should influence stem selection, but have yet to be assessed in response to the diametral (i.e., thickness) sizing of short stem humeral implants. Eight paired cadaveric humeri (age = 75±15 years) were reconstructed with surgeon selected ‘standard’ sized short-stemmed humeral implants, as well as 2mm ‘oversized’ implants. Stem sizing conditions were randomized to left and right humeral pairs. Following implantation, an anteroposterior radiograph was taken of each stem and the metaphyseal and diaphyseal fill ratios were quantified. Each humerus was then potted in polymethyl methacrylate bone cement and subjected to 2000 cycles of 90º forward flexion loading. At regular intervals during loading, stem subsidence and micromotion were assessed using a validated system of two optical markers attached to the stem and humeral pot (accuracy of <15µm). The metaphyseal fill ratio did not differ significantly between the oversized and standard stems (0.50±0.06 vs 0.50±0.10; P = 0.997, Power = 0.05); however, the diaphyseal fill ratio did (0.52±0.06 vs 0.45±0.07; P < 0.001, Power = 1.0). Neither fill ratio correlated significantly with stem subsidence or micromotion. Stem subsidence and micromotion were found to plateau following 400 cycles of loading. Oversizing stem thickness prevented implant head-back contact in all but one specimen with the least dense metaphyseal bone, while standard sizing only yielded incomplete head-back contact in the two subjects with the densest bone. Oversized stems subsided significantly less than their standard counterparts (standard: 1.4±0.6mm, oversized: 0.5±0.5mm; P = 0.018, Power = 0.748;), and resulted in slightly more micromotion (standard: 169±59µm, oversized: 187±52µm, P = 0.506, Power = 0.094,). Short stem diametral sizing (i.e., thickness) has an impact on stem subsidence and micromotion following humeral arthroplasty. In both cases, the resulting three-dimensional stem micromotion exceeded, the 150µm limit suggested for bone ingrowth, although that limit was derived from a uniaxial assessment. Though not statistically significant, the increased stem micromotion associated with stem oversizing may in-part be attributed to over-compacting the cancellous bed during broaching, which creates a denser, potentially smoother, interface, though this influence requires further assessment. The findings of the present investigation highlight the importance of proper short stem diametral sizing, as even a relatively small, 2mm, increase can negatively impact the subsidence and micromotion of the stem-bone construct. Future work should focus on developing tools and methods to support surgeons in what is currently a subjective process of stem selection

Introduction. Initial large-scale clinical studies of porous tantalum implants have been generally promising with well-fixed implants and few cases of loosening [1–3]. An initial retrieval study suggests increased bone ingrowth in a modular tibial tray design compared to the monoblock design [4]. Since micromotion at the bone-implant interface is known to influence bone ingrowth [5], the goal of this study was to determine the effect of implant design, bone quality and activity type on micromotion at the bone-implant interface, through FE modeling. Patients & Methods. Our case-specific FE model of bone was created from CT data (68 year-old female, right tibia, Fig-1). Isotropic properties of cortical and trabecular bone were derived from the calibrated CT data. Modular and monoblock porous tantalum tibial implants were virtually placed in the tibia following surgical guidelines. All models parts were 3D meshed with 4-noded tetrahedral elements (MSC.MARC-Mentat 2013, MSC Software Corporation, USA). Frictional contact was applied to the bone-tantalum interface (µ=0.88) and UHWMPE-Femoral condyle interface (µ=0.05) with all other interfaces bonded. Loading was applied to simulate walking, standing up and descending stairs. For each activity, a full load cycle [6] was applied to the femoral condyles in incremental steps. The direction and magnitude of micromotions were calculated by tracking the motions of nodes of the bone, projected onto the tibial tray. Micromotions were calculated parallel to the implant surface (shear), and perpendicularly (tensile). We report the maximum (resultant) micromotion that occurred during a cycle of each activity. The bone properties were varied to represent a range in BMD (−30%BMD, Norm, +30%BMD). We compared design type, bone quality and activity type considering micromotion below 40 µm to be favorable for bone ingrowth [5]. Results. The modular tibial tray showed lower shear micromotion than the monoblock design for shear micromotion (Fig-2). Tensile micromotion was similar between the two designs (Fig-2). Lower bone quality resulted in higher shear micromotion for the modular tibial tray design. The effect of lower bone quality on shear micromotion was less apparent for the monoblock tibial tray design. For both designs, change in the bone quality had minimal effect on the tensile micromotion. For both designs, standing up and descending stairs showed lower micromotion than walking for both the tensile and shear micromotion (Fig-3). The monoblock design showed higher micromotion for standing up and descending stairs compared to the modular design (Fig-3). Discussion. In our analysis, activity type had the highest effect on micromotion. Additionally, the modular design showed lower shear micromotion than the monoblock. Although the designs were similar for the the modular and monoblock implants, the difference in micromotion, representing the initial stability of the implant, may partially explain why retrieved modular porous tantalum tibial trays had higher bone ingrowth than the monoblock design

Introduction. Most metal-on-metal hip resurfacing implants currently being used worldwide utilize bone ingrowth fixation on the acetabular side, but cement fixation remains the standard method of fixation on the femoral side. Our hypothesis is that bone ingrowth fixation of a fully porous-coated component is superior to cement fixation of the femoral hip resurfacing component. Methods. From March 2007 to Jan 2009, 429 consecutive metal-on-metal hip resurfacing arthroplasties were performed by a single surgeon in 396 unselected patients using Biomet uncemented femoral and acetabular components. All of these were at least 5-years postop. Three patients died with causes unrelated to their hip arthroplasty. The three most common primary diagnoses were osteoarthritis in 318 (74%) cases, dysplasia in 66 (15%) hips, and osteonecrosis in 19 (4%) hips. The average size of the femoral component was 50 ± 4 cm. All pre-operative, intra-operative, and post-operative data were prospectively collected and entered into our database for review. All patients are allowed unrestricted activity including impact sports after 6 months. Results. Metal ion test results were available for 78% of patients. There were 14 (3.2%) failures identified at the time of this study. There were six (1.4%) early femoral failures (4 femoral neck fractures, 2 head collapses prior to 2 years), four loose acetabular components (one failed at 2 months postoperatively; three after 2 years), two (0.5%) adverse wear related failures (AWRF; metal ion levels ≥10 ug/L, AIA> 50. 0. , metalosis), one intertrochanteric fracture; and one failure due to subluxation. There were no cases of failure of femoral ingrowth or late femoral loosening. For the non-failed group, the average post-operative HHS score was 97±9 at their latest follow-up; the average UCLA Activity Score was 7±2. Survivorship was 96.7% at 5 years (all failures). Femoral survivorship was 98.4%. The AWRF rate was 0.5% at 5 years. No femoral failures occurred after one year postop up to 7 years. Conclusions. Bone ingrowth fixation with a fully porous femoral component in hip resurfacing remains highly durable beyond 5 years. Femoral ingrowth is more reliable than acetabular ingrowth. No cases of femoral loosening have been encountered up to 7 years post implantation. AWRF is rare (0.5% at 5 years) and is caused by acetabular component malposition

Introduction. Long-term success of the cementless acetabular component has been depends on amount of bone ingrowth around porous coated surface of the implant, which is mainly depends on primary stability, i.e. amount of micromotion at the implant-bone interface. The accurate positioning of the uncemented acetabular component and amount of interference fit (press-fit) at the rim of the acetabulum are necessary to reduce the implant-bone micromotion and that can be enhancing the bone ingrowth around the uncemented acetabular component. However, the effect of implant orientations and amount of press-fit on implant-bone micromotion around uncemented acetabular component has been relatively under investigated. The aim of the study is to identify the effect of acetabular component orientation on implant-bone relative micromotion around cementless metallic acetabular component. Materials and Method. Three-dimensional finite element (FE) model of the intact and implanted pelvises were developed using CT-scan data [1]. Five implanted pelvises model, having fixed antiversion angle (25°) and different acetabular inclination angle (30°, 35°, 40°, 45° and 50°), were generated in order to understand the effect of implant orientation on implant-bone micromotion around uncemented metallic acetabular component. The CoCrMo alloy was chosen for the implant material, having 54 mm outer diameter and 48 mm bearing diameter [1]. Heterogeneous cancellous bone material properties were assigned using CT-scan data and power law relationship [1], whereas, the cortical bone was assumed homogeneous and isotropic [1]. In the implanted pelvises models, 1 mm diametric press-fit was simulated between the rim of the implant and surrounding bone. Six nodded surface-to-surface contact elements with coefficient of friction of 0.5 were assigned at the remaining portion of the implant–bone interface [1]. Twenty-one muscle forces and hip-joint forces corresponds to peak hip-joint force of a normal walking cycle (13%) were used for the applied loading condition. Fixed constrained was prescribed at the sacroiliac joint and pubis-symphysis [1]. A submodelling technique was implemented, in order to get more accurate result around implant-bone interface [1]. Results and Discussions. The peak implant-bone sliding interfacial micromotion was observed around 75 microns around superior and supero-posterior regions of the acetabulum, whereas, micromotion was below 50 microns around other regions (area). As compared to other regions, less implant-bone micromotions were observed at the central region of the acetabulum and anterior part of the acetabulum, where micromotions were varied in the range between 5 microns to 30 microns. Although, the generated peak implant-bone sliding micromotion around the uncemented acetabulum was not vary notably due to change in inclination angle of the acetabular component, changes in patterns of implant-bone micromotions were observed and as shown [Fig.1]. Results of the present study indicated that the positioning of the uncemented acetabular component have influence on patterns of implant-bone micromotion and that might have influence on bone ingrowth and long-term success of uncemented acetabular component

Introduction. Cementless total knee arthroplasty (TKA) implants use an interference fit to achieve fixation, which depends on the difference between the inner dimensions of the implant and outer dimensions of the bone. However, the most optimal interference fit is still unclear. A higher interference fit could lead to a superior fixation, but it could also cause bone abrasion and permanent deformation during implantation. Therefore, this study aims to investigate the effect of increasing the interference fit from 350 µm to 700 µm on the primary stability of cementless tibial implants by measuring micromotions and gaps at the bone-implant interface when subjected to two loading conditions. Methods. Two cementless e.motion® tibial components (Total Knee System, B. Braun) with different interference fit and surface coating were implanted in six pairs of relatively young human cadaver tibias (47–60 years). The Orthoload peak loads of gait (1960N) and squat (1935N) were applied to the specimens with a custom made load applicator (Figure 1A). The micromotions (shear displacement) and opening/closing gaps (normal displacement) were measured with Digital Image Correlation (DIC) in 6 different regions of interest (ROIs - Figure 1B). Two General Linear Mixed Models (GLMMs) were created with micromotions and interfacial gaps as dependent variables, bone quality, loading conditions, ROIs, and interference fit implants as independent variables, and the cadaver specimens as subject variables. Results. No significant difference was found for the micromotions between the two interference fit implants (gait p=0.755, squat p=0.232), nor for interfacial gaps (gait p=0.474, squat p=0.269). In contrast, significant differences were found for the ROIs in the two dependent variables (p < 0.001). The micromotions in the anterior ROIs (AM and AL) showed fewer micromotions for the low interference fit implant (Figure 2). More closing gaps (negative values) were seen for all ROIs (Figure 3), except in AM ROI during squat, which showed opening gaps (positive values). The posterior ROIs (PM and PL) showed more closing than seen in the anterior ROIs (AM and AL) for both loading configurations. Discussion. The results presented here demonstrate that increasing the interference fit from 350 µm to 700 µm does not affect the micromotions at the implant-bone interface of tibial TKA. While micromotions values were all below the threshold for bone ingrowth (40 µm), closing gaps were quite substantial (∼−150 µm). Since cementless e.motion® TKA components with an interference fit of 350 µm had shown a survival rate of 96.2% after 8.3 years postoperatively, interfacial gaps can be expected to be within a threshold value that can guarantee good primary stability. Moreover, increasing the interference fit to 700 µm can be considered a good range for an interference fit. For any figures or tables, please contact the authors directly

Introduction. Achieving durable implant–host bone fixation is the major challenge in uncemented revision hip arthroplasty when significant bone stock deficiencies are encountered. The purpose of this study was to develop an experimental model which would simulate the clinical revision hip scenario and to determine the effects of alendronate coating on porous tantalum on gap filling and bone ingrowth in the experimental model. Methods. Thirty-six porous tantalum plugs were implanted into the distal femur, bilaterally of 18 rabbits for four weeks. There were 3 groups of plugs inserted; control groups of porous tantalum plugs (Ta) with no coating, a 2nd control group of porous tantalum plugs with micro-porous calcium phosphate coating, (Ta-CaP) and porous tantalum plugs coated with alendronate (Ta-CaP-ALN). Subcutaneous fluorochrome labelling was used to track new bone formation. Bone formation was analysed by backscattered electron microscopy and fluorescence microscopy on undecalcified histological sections. Results. The relative increase in mean volume of gap filling, bone ingrowth and total bone formation was 124%, 232% and 170% respectively in Ta-CaP-ALN compared with the uncoated porous tantalum (Ta) controls, which was statistically significant. The contact length of new bone formation on porous tantalum implants in Ta-CaP-ALN was increased by 700% (8-fold) on average compared with the uncoated porous tantalum (Ta) controls. Discussion. Alendronate coated porous tantalum significantly modulated implant bioactivity compared with controls. This study has demonstrated the significant enhancement of bone-implant gap filling and bone ingrowth, which can be achieved by coating porous tantalum with alendronate. It is proposed that, when faced with the clinical problem of revision joint replacement in the face of bone loss, the addition of alendronate as a surface coating would enhance biological fixation of the implant and promote the healing of bone defects