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

In this study, bone ingrowth was investigated in three-different cementless acetabular cups, titanium fiber mesh cup (non-HA), hydroxyapatite tricalcium phosphate sprayed cup (HA/TCP), alkali- and heat-treated titanium porous cup (AH). “Gap filling” was evaluated as the finding of the bone ingrowth on X-ray. The phenomenon is that slight gap between acetabulum and the cup observed after total hip arthroplasty (THA) disappear gradually. One hundred and thirty-seven consecutive primary THAs using cementless cups were evaluated for the rate of bone ingrowth. Patients were divided into three groups based on the different types of cups, 51 non-HA cups, 51 HA/TCP cups and 35 AH cups. The groups were similar with regards to age, sex, body mass index, original diagnosis, surgical technique and post operative rehabilitation. Average follow up period was35months, 33 month and 32 months respectively. Initial gap between acetabulum and the cup after operation was observed in 44 hips of non HA group, 39 hips of HA/TCP group and 33 hips of AH group. Rate of the gap filling at the last follow up was 2 hips (4.5%) in non-HA, 31 hips (79.5%) in HA/TCP and 33 hips (100%) in AH. Early gap filling that occurred for less than three months was 17.9% (7 of 39) in HA/TCP and 72.7% (24 of 33) in AH. The HA/TCP coated cup and the alkali- and heat-treated cup had the high frequency which gap filling occurred compared with the cup of only titanium fiber mesh processing. Additionally, in the AH cup more gap filling for less than three months had occurred compared with the HA/TCP cup, so AH cup is the most effective implant to obtain the bone ingrowth at an early stage and it is expected to acquire the better results

The effect of cup geometry in uncemented Total Hip Arthroplasty has not been investigated. We reviewed the radiological and clinical results of 527 primary total hip arthroplasties. We assessed the bone ingrowth potential of two geometric variations of an uncemented cup and compared hydroxyappetite and porous coated shells. Patients undergoing primary hip arthroplasty between 1997 and 2004 were prospectively entered into an arthroplasty database. Patients were reviewed at 1,2,4,5,8 and 10 years post surgery. Three acetabular shell types were used. These included hemispherical cups with porous or hydroxyapatite coating, and cups with peripheral expansion with porous coating. Radiographs with minimum 1-year follow-up were examined in 542 cases, using digital templating software. Radiographs were assessed for signs of bone in-growth, lucent lines, migration and polyethylene wear. Survivorship analysis was performed using Kaplan-Meier analysis with 95% confidence intervals. Radiological findings and cup type were analysed using Fishers exact test. Radiological evidence of bone ingrowth was seen in 82% of hemispherical cups, compared with 59% of peripherally expanded cups, which was significant (p,0.05). Bone ingrowth was not affected by the presence of HA coating. The most common diagnoses were osteoarthritis (67%) and avascular necrosis (12%). The mean age was 56 years. Survivorship with revision or impending revision for aseptic loosening was 95.6% at 7 years (95%CI 1.0134-0.8987). The 3 revisions and 1 impending revision for loosening were in patients with avascular necrosis (3) or previous acetabular and femoral osteotomies for DDH (1), with a mean age of 44 years. Hemispherical shells have improved radiographic outcome in comparison with peripherally expanded components. At 7 years, clinical results are similar for both components

Aims: Bioactive glasses are a family of silica-based synthetic biomaterials, which form chemical bonding with the surrounding bone. The limiting biologic factors of the bonding process are poorly understood. The hypothesis of the current study was that there are species-specific differences in the incorporation of bioactive glasses due to anatomic and physiologic factors. Methods: Conical porous implants made of sintered bioactive glass or titanium microspheres (Ø 250–300 μm) were surgically implanted bilaterally into the cortex of tibias or femurs in sheep, dog and rabbit. Implant incorporation was evaluated by means of push-out testing, pQCT, his-tomorphometry, BEI-SEM, and EDXA. The comparison was made at 12 weeks. A total of 176 implants were analysed. Results: Between the three species, there were significant differences in the extent of new bone ingrowth and in the mechanical strength of implant fixation. The rabbit showed the highest amount of bone ingrowth into both bioactive glass and titanium implants. Also the shear strength of the implants was superior in the rabbit compared with the dog and the sheep. Histological pattern of new bone ingrowth into bioactive glass structures was similar in the dog and in the rabbit. In contrast, the ingrowth of new bone failed into bioactive glass implants in the sheep. Conclusions: Based on these results, the sheep represents a divergent model for bone healing studies of bioactive glass. Long bones of the sheep contain yellow (fat) marrow and we assume that the poor healing response reflects the deficiency of marrow-derived osteoprogenitor cells

Aims: Early bone ingrowth is known to increase primary implant þxation and reduce the risk of early implant failure. RGD peptide (Arg-Gly-Asp) has been identi-þed as playing a key role in osteoblast attachment and proliferation on various surfaces. The aim of this study is to test whether a monolayer of RGD peptide on Ti implants will increase bone ingrowth in vivo. Methods: Controlled canine study (n=8). 6 x 10mm plasma sprayed porous coated implants (Ti6Al4V) was inserted as press-þt in the proximal tibia bilaterally. Observation period was 4 weeks. Implants was coated in a 100 μM solution of cylic (RGDfK) peptide for 24 hours (Biomet-Merck, Darmstadt, Germany). Two dogs had to be excluded due to wrong placement of the implants. Results are presented as median and range. Results: A signiþcant increase in bone/implant contact was seen for the RGD treated group (p< 0.05). Bone fraction at the interface was 0.18 (0.10–0.45) compared to 0.09 (0.05–0.14) for the control. Mechanical þxation, measured by push-out test, was increased. Shear strength was 85% higher for the RGD group; however this difference was not signiþcant. Conclusions: This study shows that implant surface treatment with RGD enhances early bone ingrowth to press-þtted implants. However, future studies will be preformed regarding coating integrity and long-term effects, as well as its performance under loaded conditions

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

Synthetic bone grafts are used in several major dental and orthopaedic procedures. Strontium, in the form of strontium ranelate, has been shown to reduce fracture risk when used to treat osteoporosis. The aim of the study was to compare bone repair in femoral condyle defects filled with either a 10% strontium substituted bioactive glass (StronBoneTM) or a TCP-CaSO4 graft. We hypothesise that strontium substituted bioactive glass increases the rate of bone ingrowth into a bone defect when compared to a TCP-CaSO4 ceramic graft. A critical size defect was created in the medial femoral condyle of 24 sheep; half were treated with a Sr-bioactive glass (StronBoneTM), and in the other animals defects were filled TCP-CaSO4. Two time points of 90 and 180 days were selected. The samples were examined with regard to: bone mineral density (BMD) from peripheral quantitative CT (pQCT), mechanical properties through indentation testing, and bony ingrowth and graft resorption through histomorphometry. The radiological density of Sr-bioactive glass in the defect is significantly higher than that of the TCP-CaSO4-filled defect at 90 and 180 days, (p=0.035 and p=0.000). At 90 days, the stiffness of the defect containing Sr-bioactive glass and is higher than that of the TCP-CaSO4 filled defect, (p=0.023). At 6 months there is no significant difference between the two materials. Histomorphometry showed no significant difference in bone ingrowth at any time point, however significantly more of the graft is retained for the StronBoneTM treatment group than the TCP-CaSO4 group at both 0 days (p=0.004) and 180 days (p=0.000). The amount of soft tissue within the defect was significantly less in the StronBoneTM group than for the TCP-CaSO4 group at 90 days (p=0.006) and 180 days (p=0.000). The data shows the mechanical stability of the defect site is regained at a faster rate with the strontium substituted bioglass than the TCP-CaSO4 alternative. Histomorphmetry shows this is not due to increased bone ingrowth but may be due to the incorporation of stiff graft particles into the trabeculae. Sr-bioactive glass produces a stronger repair of a femoral condyle defect at 3 months compared with TCP-CaSO4

Biomaterial porosity is considered one of most important proprieties required to obtain fixation of bone ingrowth and ongrowth in prostheses. Since 1998 in the USA and from in Europe a new highly porous biomaterial, Trabecular Metal Technology (TMT, ©Zimmer, USA) has been used in orthopaedic surgery. This study evaluates the short-term morphological findings of porous tantalum screws implanted in three patients with osteonecrosis of a femoral head. Tantalum trabecular metal offers several advantages over conventional materials. Its regular porosity is considered one of most important properties in bone ingrowth and ongrowth and high biocompatibility and osteoconductivity. The biomechanical properties of tantalum are sufficient to withstand physiological load. Our study disclosed a good integration. The bone penetrated the porous metal completely and many characteristics of good bio-integration were evident such as new formation of lamellae, presence of calcium and phosphorus elements, absence of fracture and signs of implant metallosis. The presence of peri-implant medullary cisternae confirmed the functional sites of new bone formation. We conclude that the porous tantalum material is an optimal osteoinductor and osteoconductor even in critical conditions

Uncemented hip implants commonly have porous coated surfaces that enhance the mechanical interlock with bone, encourage bone ingrowth and promote the formation of a stable interface between prosthesis and bone. However, the presence of tissue, either fibrous or with parts of osseous tissue, at the interface between the implant and the bone has been commonly observed after a few years in vivo. The exact mechanisms that govern the type of tissues formed at the interface are not fully understood and several theories have been proposed. This study aims to employ finite element analysis (FEA) to simulate tissue formation and differentiation around the AML (DePuy, Warsaw, USA) femoral implant by employing a tissue differentiation algorithm based on a mechanoregulatory hypothesis of fracture healing. FE models of the femur were generated using computer tomography (CT) scans. The AML prosthesis was then implanted into the bone and a granulation tissue layer of 0.75mm was created around the implant. The mechanoregulatory hypothesis of Carter et al (J.Orthop, 1988) originally developed to explain fracture healing was used with selected modifications, most notably the addition of a quantitative module to the otherwise qualitative algorithm. The tendency of ossification in the original hypothesis was modified to simulate tissue differentiation to bone, cartilage or fibrous tissue. Normal walking and stair climbing loads were used for a specified number of cycles reflecting typical patient activity post surgery. The transformation of granulation tissue to one of the three simulated tissue types was evident as the iterations progressed. The majority of the tissue type formed initially was cartilage and bone (~40% each), and occupied the mid to distal regions of the implant respectively. After tissue stabilisation, the prominent tissue type was bone (65%), occupying most of the mid-distal regions with a significant decline in cartilage tissue formed. This has been shown in clinical retrieval studies with the same implant, where maximum bone ingrowth is in the mid-distal regions of the implant, directly corresponding to the region where there is minimal micromotion. This would be the case with a diaphyseal fixation, which most AML prostheses employ for stability. Fibrous tissue formation was limited to the proximal-medial regions (~10%), with the remainder of the proximal regions filled with cartilage tissue. In addition, predicted bone formation was along the lines of the more stable cartilage tissue as opposed to directly replacing fibrous tissue. The formation of bone would require repeated periods of minimal micromotion and stress at the interface tissue; this was facilitated by the presence of cartilage tissue around the mid regions of the implant. The micromotion and interface stresses in the proximal regions of the implant were too high to encourage bone ingrowth, resulting in the presence of tissue that remained fibrous throughout the process. The FE model, employing a very simple tissue differentiation hypothesis and algorithm was able to predict the formation of different tissues at the interface. Initial bone formation was rapid, occupying the distal regions of the implant, and then gradually occupying a larger portion of the mid-regions around the implant. The proximal regions were largely occupied by a combination of fibrous and cartilage tissue. Overall, the presence of bone and cartilage tissue accounted for nearly 85% of the tissue formed which would suggest a very stable interface as predicted by the Carter’s hypothesis

Purpose: Hinged knee prostheses are mainly used for reconstruction after major tumour resection. Aseptic loosening is the main problem with these implants. One of the solutions proposed to reduce the rate of loosening is to add a hydroxyapatite collar on the shaft stems. This work was conducted to study bone ingrowth with a new hinged implant with a hydroxyapatite collar at the junction between the zone of resection and the shaft. Material and methods: Twenty-nine massive prostheses with a hydroxyapatite collar were implanted between 1998 and 2001. Nine patients were excluded from the analysis because follow-up was less than two years. This retrospective analysis thus compared twenty massive prostheses with twenty matched hinged GUEPAR prostheses without a collar. Bony ingrowth was measured on plain x-rays (two orthogonal views) at 6, 12, 24, and 36 months. Filling of the gap between the bone and the implant was also assessed. Signs of loosening were noted. Results: Mean bony ingrowth in implants with a hydroxyapatite collar was 6.58 mm at 6 months 9.84 mm at 12 months, 12.3 mm at 24 months and 13.25 mm at 36 months. Mean bony ingrowth in the implants without a hydroxyapatite collar was 1.65 mm at 6 months, 3.31 mm at 12 months, 4.8 mm at 24 months and 4.35 mm at 36 months. In the implants with a collar, gap filling was partial in five cases and total in 15. In implants without a collar, there was no gap filling in eight cases, partial filling in two cases and total filling in fifteen cases. Discussion: Prostheses with a hydroxyapatite collar enable better radiological bony ingrowth than observed in implants without a hydroxyapatite collar. Gap filling is better for prostheses with a collar. There was no case of loosening at last follow-up for implants with a hydroxyapatite collar. Conclusion: In light of these results, shaft anchorage appears to be better with implants with a hydrosyapatite collar. Confirmation of improvement in clinical outcome and lower rate of aseptic loosening will require longer follow-up

Aims. Limb salvage surgery (LSS) is the primary treatment option for primary bone malignancy. It involves the removal of bone and tissue, followed by reconstruction with endoprosthetic replacements (EPRs) to prevent amputation. Trabecular metal (TM) collars have been developed to encourage bone ingrowth (osseointegration (OI)) into EPRs. The primary aim of this study was to assess whether OI occurs when TM collars are used in EPRs for tumour. Methods. A total of 124 patients from July 2010 to August 2021 who underwent an EPR for tumour under the West of Scotland orthopaedic oncology team were identified. Overall, 81 patients (65%) met the inclusion criteria, and two consultants independently analyzed radiographs at three and 12 months, as well as the last radiograph, using a modified version of the Stanford Radiological Assessment System. Results. OI of the TM collar occurred in approximately 65% of patients at last radiograph. The percentage of patients with OI at three months (65.4%) reflected the 12-month (65%) and long-term (64.4%) follow-up. The median amount of OI across all radiographs was one at all three timepoints, with only five cases (11.1%) showing OI in all four zones at last radiograph. Radiolucency at the bone:collar junction was present in 23 cases (28.4%) at three months, but only four (6.7%) showed progression of this at 12 months. The interobserver reliability was found to be highly reliable in all parameters (p < 0.001). Conclusion. OI occurs in approximately 65% of TM collars, and is similar at three months, 12 months, and last radiograph. The extent of OI at the bone:collar junction was found to have decreased at longer-term follow-up. Furthermore, radiolucency at the bone-collar impact junction does occur in some patients but only a low number will show radiolucency progression at longer-term follow-up. Cite this article: Bone Jt Open 2024;5(12):1092–1100

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.