Positive Grid BIAS AMP 2 R2R (PC) Keygen
Latrisha Adan
In terms of osseointegration on outer surface implant porosity PC+PSHA was superior to the other three groups. Neither the acid etching nor the plasma cleaning offered any advantage in terms of implant osseointegration. There was no statistical difference in any of the biomechanical parameters among all groups in the press-fit model at 4 weeks of evaluation time.
Worldwide the need of arthroplastic surgery is considerable. Around one million hip replacements are made each year and the number of primary hip replacements is increasing [1]. Implant failure due to aseptic loosening is a very serious, painful and potentially invalidating complication and early initial fixation is essential to ensure long term survival of an implant [2, 3].
If the implant is not stable, micro motion between the implant and the surrounding bone will increase the risk of fibrous encapsulation of the implant [4, 5] which inhibits bone ingrowth and thus increases the risk of loosening of the implant.
Micro-scale topographical changes to the implant surface may affect cellular adhesion and proliferation. Surface modification may improve implant biocompatibility and thereby reduce the risk of long term implant failure.
In this study we attempt to improve early fixation/bone-implant interaction by 1) making micro-scale topographical changes by acid etching and 2) removing surface-adherent pro-inflammatory agents thereby potentially increasing biocompatibility by plasma cleaning.
Acid etching modifies the surface topography on the micro-scale leading to a greater roughness with potential to enhance implant osseointegration [6]. This treatment has been investigated in several studies, both in vitro and in vivo [7-9]. Acid etching creates a surface that enhances cell proliferation and differentiation [10, 11], as well as giving a relatively higher bone-to-implant contact, a better bone ingrowth and better osseointegration of experimental orthopedic titanium implants [12-14].
Plasma cleaning the implant surface could also improve fixation by creating a cleaner more hydrophilic surface relative to the conventional aqueous based processes. This is meant to increase surface wettability which could result in additional fixation benefit [15]. Additional to this primary effect plasma cleaning could yield a positive side effect by removing impurities such as endotoxins. This could potentially increase osseointegration, as endotoxins can induce an inflammatory response, leading to fibrous capsule formation [16]. As already mentioned this inhibits bone ingrowth, and thereby increases the probability of implant loosening [17]. Earlier studies have found promising result using plasma sterilization to increase biocompatibility and thereby osseointegration [18, 19].
The purpose of this canine study is to evaluate the effect of a specific acid etch surface treatment and plasma clean surface treatment on experimental titanium implants. We hypothesize that these surface modifications would improve biomechanical implant fixation and osseointegration.
The study was a randomized, paired animal experiment with 10 dogs. Four implants were inserted into each dog: One in each medial and one in each lateral femoral epicondyle (Fig. 1). Bone quality was assumed equal between all four implant locations. The four implants were surface treated in different ways: 1. Porous coating as a negative control (PC), 2. porous coating with Plasma Sprayed Hydroxyapatite as a positive control (PC+PSHA), 3. porous coating with Acid Etching Surface Treatment (PC+ET), and 4. porous coating with Acid Etching and Plasma Cleaning Surface Treatment (PC+ET+PLCN). After an observation period of four weeks, the dogs were terminated and the bones containing the implants were harvested and frozen. Every implant was examined mechanically by push-out-test and microscopically by histomorphometry. The study was approved and monitored by the Danish National Animal Research Inspectorate.
Custom made cylindrical Titanium alloy core implants (Ti-6A1-4V, = 6 mm, L = 10 mm) with commercially pure titanium porous coating and four different surface treatments were provided by DePuy Inc., Warsaw, IN, USA (Table 1). All Ti-6Al-4V substrates were per ASTM F-136. All Titanium beads were per ASTM F-67. All beads were attached by a sintering process in vacuum furnace. The porous coating had a mean pore diameter of 250 microns and a porosity of 40-50%. To avoid any potential pollution of the implants by hand or instruments when inserted into the bone, the implants were mounted on a threaded rod through a centrally threaded hole.
Evaluating the surface of the Acid Etched implants was done by applying the technology on a polished surface. Average surface roughness was 0.15 μm and XPS (X-ray Photoelectron Spectroscopy) confirmed that none of the chemicals were incorporated in the surface oxide layer.
Implants were passivated prior to the cleaning process by the standard validated manufacturing passivation process (ASTM A967-05) used for clinically DePuy Orthopedic implants. Plasma cleaning was done in a plasma chamber (7200 RF Plasma System; PVA TePla America, Inc.) under following conditions: Cycle time of 30 mins, O2-gas flow rate at 250 sccm, chamber pressure of 300 mTorr, and power of 500 Watts.
The outermost 0.5 mm of the implant-bone specimen was cut off and discarded. The rest of the implant with surrounding bone was divided into two sections perpendicular to the long axis of the implant with a water cooled diamond band saw (Exakt Apparatebau; Norderstedt, Germany). The outermost 3.5 mm was refrozen for use in the mechanical test. The innermost 6.0 mm was stored in 70% alcohol at 5 C for use in histological analysis. The specimens were dehydrated in graded ethanol (70-100%) containing 0.4% basic fuchsine (Merck, Darmstadt, Germany), and embedded in methyl methacrylate (MMA; Merck, Hohenbrunn, Germany). From the MMA block four vertical, uniform, random sections were cut with a hard-tissue microtome (Leiden, KDG-95; MeProTech, Heerhugowaard, The Netherlands) around the centre part of each implant. Before making the sections, the MMA block was rotated randomly around its axis to avoid biased estimates. The 50-μm-thick sections were counterstained with 2% light green (BDH Laboratory Supplies, Poole, UK) and mounted on glass. This provides red staining of non-calcified tissue and green staining of calcified tissues.
Implants were tested to failure on an axial push-out test machine (858 Mini Bionix; MTS, Eden Praire, MN, USA). The specimens were placed on a metal support jig with a 7.4 mm diameter central opening. The implant was centralized over the opening assuring a 0.7 mm distance between the implant and the support jig [20]. The direction of loading was from the cortical surface inward. The implant was pushed through the opening by a 5.0 mm diameter probe with a displacement rate of 5 mm/min on a 10 kN axial load cell. Each specimen length and diameter was measured with a micrometer and used to normalize push-out parameters [21]. Ultimate shear strength (MPa) was determined from the maximal force applied until failure of the bone-implant interface. Apparent stiffness (MPa/mm) was obtained from the slope of the linear section of the curve. Energy absorption (J/m2) was calculated from the area beneath the curve until failure. All push-out parameters were normalized by the cylindrical surface area of the transverse implant section tested.
Intercooled STATA 8.0 software (StataCorp., College Station, TX) was used. All data followed a normal distribution and fulfilled the assumptions for one-way ANOVA. Data analyzed with ANOVA was followed by Students paired t-test. Differences between means were considered statistically significant for p-values less than 0.05.
No postoperative complications were seen and all canines were fully weight bearing within three days of surgery. All animals completed the four week observation period. At the implant sites there were no clinical signs of infection.
Statistically significant more new bone was observed in zone 1 of PC+PSHA compared to the other three coatings (Fig. 4). No statistically significant differences in volume fractions were found in zone 1.
The aim of this study was to investigate a specific Acid Etch Surface Treatment and Plasma Cleaning Surface Treatment on porous coated titanium implants in a well established canine model of osseointegration [21, 23]. We could not identify positive effect of ET and ET+PLCN compared to the control PC group but PSHA-coated implants showed better osseointegration than the other three groups at outer surface implant porosity and that PSHA-coated implants showed better osseointegration than the ET and ET+PLCN groups at deep implant porosity.
This study was designed to investigate effect on early fixation, why conclusion on long term effect should be done with caution. The four weeks observation period was used since this point between healing and remodeling was ideal to measure differences between treatments that affect initial fixation [24, 25]. Previous studies using same model found statistically significant difference in both histological and mechanical parameters [23].
The experimental model used represents the part of cementless joint replacements placed in cancellous bone. We used a non-weight-bearing setup. Compared to a weight-bearing setup it lacks the more clinically relevant conditions as direct load and joint fluid pressure, but it is well standardized and has a high degree of variable control. Although load is not directly applied, the implants are susceptible to load through the biomechanical energy transmission of the bone. Canines were used, as the architecture and composition of canine bone is similar and comparable to human bone [26, 27]. Canine cancellous epiphyseal bone was chosen because the close resemblance with bone where cementless joint replacements are usually implanted. No animal model, however, gives complete information about the effect of a given alloy on human osteogenesis. The four differently treated implants were inserted in each dog, making each dog its own control and thereby preventing interspecies variation. PSHA-coated implants was used as positive control and served as validation of our model by its positive outcome [21]. Young canines were used with assumed high healing potential and in contrast to elderly canines with assumed low healing potential a statistically significant difference is harder to detect, making any difference more clinically relevant [28].
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