Recent clinical data suggest improvement in the fixation of tibia trays for total knee arthroplasty when the trays are additive manufactured with highly porous bone ingrowth structures. Currently, press-fit TKA is less common than press-fit THA. This is partly because the loads on the relatively flat, porous, bony apposition area of a tibial tray are more demanding than those same porous materials surrounding a hip stem. Even the most advanced additive manufactured (AM) highly porous structures have bone ingrowth limitations clinically as aseptic loosening still remains more common in press-fit TKA vs. THA implants. Osseointegration and antibacterial properties have been shown In this At 4 weeks, a 42% increase in average pull-out shear strength between nanotube treated specimens and non-nanotube treated specimens was shown. A 21% increase in average pull-out shear strength between nanotube treated specimens and hydroxyapatite-coated specimens was shown. At 12 weeks, all specimens had statistically similar pull-out values. Bone labels demonstrated new bone formation into the porous domains on the materials as early as 2 weeks. A separate These
Biological fixation of arthroplasty devices through osseointegration via ingrowth or ongrowth can be achieved with a numerous surface treatments and technologies. Surface roughness and topography have evolved to include sintered bead, calcium phosphate coatings and more recently additive manufacturing techniques. Regardless of the technique employed, the clinical goal has always been directed at improving osseointegration and achieve rapid, stable and long-term implant fixation without compromising the mechanical properties of the device. Pre-clinical models provide insight into the in-vivo efficacy. The in vivo results of a wide range of technologies over the past 20 years have been examined by our laboratory using an adult ovine cortical and cancellous implantation model. This paper will present a twenty year experience of pre-clinical evaluation of bone ingrowth and ongrowth surfaces used for arthroplasty device fixation. The endpoints as well as understanding of the dynamic nature of the bone-implant interface continues to evolve as advanced manufacturing moves forward and the demands on the interface due to patient and surgeon expectations increase.
Modern hip replacements all have encapsulated the design concept of proximal modularity. The factors contributing to the increased wear and corrosion at the taper junction are trunnion geometry, surface characteristics, head size, impaction forces, and material coupling. This study maps the inferior and superior region of the trunnion and bore to provide a visual identification of the corrosion severity. The corrosion/wear generated inferiorly and superiorly at the bore and trunnion will be quantified to understand how corrosion is affected by mechanical stresses in relation to anatomical orientation. Three neck tapers generated from bar stock containing a threaded trunnion Ti-6Al-4V and 3× 32mm femoral heads (Co-Cr-Mo) with a +4 offset manufactured by Signature Orthopaedics were used within this study. Rectangular Rozzette strain gauges (Tokyo Sokki Kenkyujo Co., Ltd.) were adhered onto the inferior and superior sections of the neck section. The tapers were fatigued in accordance to ISO 7206 at 5Hz for 5 million cycles at 37 degrees Celsius in phosphate buffered saline. The tapers were sectioned from the center of the femoral head to split both trunnion and bore into superior and inferior components. SEM imaging of all surface areas for each component, per taper (4) was done under ×100 magnification. The images were used to quantify the corrosion present across the surface area using a MATLAB based program called Histomorph. To obtain a visual observation of the variation of corrosion across the bore and trunnion the proximal, medial, and distal regions were mapped together for both the superior and inferior sections.Introduction
Methodology
The use of polymethyl methacrylate based cement for the fixation of joint replacements although commonly applied, is still limited by interfacial weakness. This study aims to document the effects of a variety of surface treatments on implant/cement bonding and link them to their surface properties. Thirty seven femoral implant analogues of Ti6Al4V rods were given one of six different surface treatments: traditional grit blasting, wet and dry Vaquasheening, acid etching in concentrated sulphuric and hydrochloric acid, anodisation at 150V, and a combination of acid etching and anodisation, before being embedded into a commercially available poly(methyl methacrylate) bone cement. The interfacial strength, energy and stiffness were measured through pushout testing. Surface analysis included examination with scanning electron microscopy, wettability tests and roughness analysis. Results were analysed with a one-way ANOVA with post hoc tests. Overall, the coarse blasted surface created the strongest interface, followed by both etched then anodised, acid etched only, wet Vaquasheened, anodised only and finally dry vaquasheened. While anodised samples showed a weaker bond than etched samples, the combination of etching and anodisation was not different to etching alone. In addition, six different types of interface failure modes were observed, and theories as to explain their mechanism, using experimental evidence were outlined. Coarse blasted surfaces showed the strongest bonding, while other surface modifications may encourage tissue ingrowth and other biological responses, these surface treatments do not strengthen bonding for cemented fixation.
Appropriate, well characterized animal models remain essential for preclinical research. This study investigated a relevant animal model for cancellous bone defect healing. Three different defect diameters of fixed depth were compared in both skeletally immature and mature sheep. This ovine model allows for the placement of four confined cancellous defects per animal. Defects were surgically created and placed in the cancellous bone of the medial distal femoral and proximal tibial epiphyses (See Figure 1). All defects were 25 mm deep, with defect diameters of 8, 11, and 14 mm selected for comparison. Defects sites were flushed with saline to remove any residual bone particulate. The skeletally immature and mature animals corresponded to 18 month old and 5 year old sheep respectively. Animals were euthanized at 4 weeks post-operatively to assess early healing. Harvested sites were graded radiographically. The percentage of new bone volume within the total defect volume (BV/TV) was quantified through histomorphometry and μ-CT bone morphometry. Separate regions of interest were constructed within the defect to assess differences in BV/TV between periosteal and deep bone healing. Defect sites were PMMA embedded, sectioned, and stained with basic fuschin and methylene blue for histological evaluation.INTRODUCTION
METHODS
Loading of the implant/cement bond during polymerization is possible when a joint is put through passive range of motion shortly after implantation. This may adversely affect the integrity of the cement – implant interface. The aim of this study was to evaluate the effect of implant motion during cement polymerization on the mechanical properties of the cement – implant interface. Simulated titanium tibial trays (15 mm dial tray, 15 mm keel) were used in this study and implanted in cellular rigid polyurethane foam (12.5 pcf) (Sawbones Vashon, WA, USA). Surface roughness (Ra) of implants was verified as 3.60μm with a 2μm tip at 0.5 mm/s over a length of 1.6 mm (SurfAnalyzer, MAHR Federal Inc., Providence, RI, USA). Palacos cement (Heraeus Medical, Wehrheim, Germany) was mixed for 2 minutes followed by implantation and one of 3 motion regimes at two time points. Six groups were tested. Motion was applied at three minutes for three groups. This motion was 1)axial micromotion for 20 cycles at 100 microns and 0.5 Hz, 2)rotational of 20 cycles at +/− 1.5 degrees and 0.5 Hz, or 3)both motions sumultaneously. An additional three groups were tested at 6 minutes under the same conditions. Motion was applied using calibrated mechanical testing equipment (MTS systems, Eden Prarie, MN, USA). Implants were tested in tension to failure at 0.5 mm/min, 24 hrs after implantation. The peak load, stiffness and energy were determined for each sample. Data was analysed using an Analysis of Variance and a Games Howell post hoc tests where appropriate.Introduction
Methods
Gamma Irradiation is often considered the gold standard for sterilizing bone allograft. However, a dose dependant decrease in the static mechanical properties of gamma irradiated bone has been well established. Supercritical Fluid Sterilization (SCF) using carbon dioxide represents a potential alternate method to sterilize allografts. This study aimed to evaluate the effect of SCF on the static and dynamic (fatigue) properties of cortical bone in 3-point bending. Eighty paired 18-month old rabbit humeri were randomized to 4 treatments: Gamma Irradiation at 10 kGy or 25 kGy, SCF Control and SCF with Peracetic Acid (Introduction
Methods
Initial stability of the tibial component influences the success of uncemented total knee arthroplasty. In uncemented components, osseointegration provides long-term fixation which is particularly important for the tibial component. Osseointegration is facilitated by minimising bone-implant interface micromotion to within acceptable limits. To investigate initial stability, this study compares the micromotion and initial seating of two uncemented hydroxyapatite-coated tibial components, the Genesis II and Profix. This is the first stability comparison of two hydroxyapatite-coated tibial components. Six components of each type were implanted into synthetic tibias by a single orthopaedic surgeon. Good coverage was achieved. No screws or articular inserts were used. Initial seating was measured using ImageJ software at five areas on each tibia. Tibias were transected and their proximal section implanted into a molten alloy parallel to horizontal. Dynamic mechanical testing was performed using a hydraulic 858-Bionix machine. Prostheses underwent unilateral axial point-loading of 700N cyclically applied four times. The load was applied to three locations approximating femoral loading points. The loading cycle was repeated six times at each point, allowing micromotion to be recorded at three contralateral locations. Micromotion was measured by optical lasers. After dynamic testing, two tibial components of each type were removed with claw pliers while measuring the force required on the 858-Bionix machine. Implant under-surfaces were photographed for wear.Introduction
Methods
Implant contamination prior to cement application has the potential to affect the cement-implant bond. the consequences of implant contamination were investigated Fifty Titanium alloy (Ti-6Al-4V) dowels were prepared with two surface finishes comparable to existing stems. The roughness (Ra and Rq) of the dowel surface was measured before and after the pushout test. Four contaminants (Phosphate Buffered Saline (PBS), ovine marrow, ovine blood, olive oil) were prepared and heated to 37°C. Each contaminant was smeared on the dowel surface completely and uniformly approximately 4 minutes prior to implantation. Samples were separated into ten groups (n=5 per group) based on surface roughness and contaminant. Titanium alloy dowels was placed in the center of Polyvinyl chloride (PVC) tubes with bone cement, and equilibrated at 37°C in PBS for 7 days prior to mechanical testing. The push out test was performed at 1 mm per minute. The dowel surface and cement mantel were analyzed using a Scanning Electron Microscopy (SEM) to determine the distribution and composition of any debris and contaminates on the surface.Introduction
Methods
Cortical bone is a complex composite material composed of an inorganic mineral phase and organic matrix of type I collagen and various non-collagenous proteins. The hierarchical organisation of bone results in a transversely isotropic material with the mechanical properties in the long-axis (z) being superior to the radial and circumferential axes which are equivalent. This directional dependence of bone has been well reported, whilst the mechanisms/anisotropy are more difficult to study. This study examined the anistropic nature of cortical bone and the influence of different sterilisation procedures. Ninety cortical bone cubes were prepared using established techniques (Walsh and Guzelsu) and randomly allocated to three treatments; control, 15 KGy, Super Critical Fluid (SCF) (n=30 per group). The ultrasonic moduli was examined using longitudinal sound waves at 5 MHz using a pulse receive technique. Unconfined compression was performed non-destructively in longitudinal (z), circumferential (ï±) and radial orientations (r). Samples were tested to failure in the z axis. A two-way analysis of variance (treatment and time) followed by a Games Howell post hoc test and covariate analysis was performed using SPSS for Windows. Data from this study revealed some interesting and intriguing results with respect to the effects of gamma irradiation and dense gas technology on the properties of cortical bone and load transmission. A statistical decrease in the compressive stiffness and strength was noted with 15 KGy of whilst SCF treatment did not alter the properties in the r or ï orientations. Similar results were found with respect to the ultrasonic moduli (data not shown). The pilot data confirmed the adverse effects of bone in compression following gamma irradiation as we found in our recently presented ORS work. However, the study in compression demonstrated that the directional dependence that makes cortical bone a transversely isotropic material is removed following gamma irradiation with SCF did not appear to have this effect. The effects of gamma irradiation on the mechanical performance of allografts in the long bone axis may play a role in their in vivo performance. The removal of the anisotropy following gamma irradiation provides insight into the relationship(s) between the mineral and organic constituents, which requires further study.
