Protective hard coatings are appealing for several technological applications and even for orthopaedic implants and prosthetic devices. For what concerns the application to prosthetic components, coating of the surface of the metallic part with low-friction and low-wear materials has been proposed [1, 2]; at the same time, concerning use of ceramic materials in joint arthroplasty, zirconia-toughned-alumina (ZTA) ceramic material has shown high strength, fracture toughness, elasticity, hardness, and wear resistance [3, 4]. The purpose of this study was to directly deposit ZTA coatings by using a novel sputter-based electron deposition technique, namely Pulsed Plasma Deposition (PPD) [5]. Preliminary characterization of realized coatings from the point of view of morphology, wettability, adhesion and friction coefficients was performed. PPD technique was used to deposit ZTA coatings; this technique is able to maintain the stoichiometry of the starting target. In this study we started from a cylindrical ZTA target (30 mm diameter × 5 mm thickness, 75% alumina / 25% zirconia) and followed the procedure described by Bianchi et al [5]. Characterization of morphology, micro-structure and chemistry of deposited coatings was performed by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) and Atomic Force Microscope (AFM). Coating-substrate interface quality were investigated by micro-scratch tests. Measurement of the contact angle between a drop of 1 ml of ultrapure water and the surface of the sample was performed to estimate the degree of wetting. A ZTA-coated stainless steel ball (AISI 420, 3 mm radius) was coupled against medical grade UHMWPE to evaluate the friction of the proposed coupling in preliminary ball-on-disk tribological tests.Introduction
Materials and methods
Total joint arthroplasty is frequently necessary when a traumatic or degenerative disease leads to develop osteoarthritis (OA). Nowadays, the main reason for long term prosthesis failure is due to osteolysys and aseptic loosening of the implant itself, that are related to UHMWPE wear debris [1–3]. Different solutions to overcome this issue have been proposed, including different couplings like metal-on-metal and ceramic-on-ceramic. Our hypothesis was that a hard ceramic thin film realized on the plastic component (i.e. UHMWPE) could improve the friction and wear performance in a prosthetic coupling. The purpose of the presented study was therefore to characterize from the point of view of structure and mechanical performance of this ceramic-coated plastic component. The thin films were specifically realized by means of the novel Pulsed Plasma Deposition (PPD) technique [4]. PPD technique was used to deposit Yttria-stabilized zirconia (YSZ at 3%) films on medical-grade UHMWPE substrates [4]. The morphology and micro-structure were characterized by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). By means of nanoindentation and scratch tests mechanical properties were investigated. Ball-on-disk tribological tests were carried out in air, deionized water and physiological solution against alumina balls (6 mm diameter, grade 200) used as counterpart; friction evaluation of the proposed approach and the corresponding worn track were analyzed by SEM-EDS.Introduction
Materials and methods
Providing proper rotational alignment of femoral component in total knee arthroplasty is mandatory to achieve correct kinematics, good ligament balance and proper patellar tracking. Recently functional references, like the function flexion axis (FFA), have been introduced to achieve this goal. Several studies reported the benefits of using the FFA but highlighted that further analyses are required to better verify the FFA applicability to the general clinical practice. Starting from the hypothesis that the FFA can thoroughly describe knee kinematics but that the joint kinematics itself can be different from flexion to extension movements, the purpose of this study was to analyse which factors could affect the FFA estimation by separately focusing on flexion and extension movements. Anatomical acquisitions and passive joint kinematics were acquired on 79 patients undergoing total knee arthroplasty using a commercial navigation system. Knee functional axis was estimated, from three flexion and extension movements separately acquired included in a range between 0° and 120°. For flexion and extension, in both pre- and post-implant conditions, internal-external (IE) rotations was analysed to track any changes in kinematic pattern, whereas differences in FFA estimation were identified by analysing the angle between the FFA itself and the transepicondylar axis (TEA) in axial and frontal plane.Introduction
Methods
Protective hard coatings are appealing for several technological applications like solar cells, organic electronics, fuel cells, cutting tools and even for orthopaedic implants and prosthetic devices. At present for what concerns the application to prosthetic components, the coating of the surface of the metallic part with low-friction and low-wear materials has been proposed [1]. Concerning the use of ceramic materials in joint arthroplasty, zirconia-toughned-alumina (ZTA) reported high strength, fracture toughness, elasticity, hardness, and wear resistance [2]. The main goal of this study was to directly deposit ZTA coating by using a novel sputter-based electron deposition technique, namely Pulsed Plasma Deposition (PPD) [3]. The realized coatings have been preliminary characterized from the point of view of morphology, wettability, adhesion and friction coefficients. ZTA coatings were deposited by PPD technique, which is able to maintain the stoichiometry of the starting target. In this case we started from a cylindrical ZTA target (30 mm diameter × 5 mm thickness, 75% alumina / 25% zirconia). The morphology, micro-structure and chemistry of deposited coatings were characterized by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectrosopy (EDS) and Atomic Force Microcscope (AFM). Coating-substrate interface quality were investigated by microscratch tests. The degree of wetting was estimated by measuring the contact angle between a drop of 1 ml of ultrapure water and the surface of the sample. Preliminary ball-on-disk tribological tests were carried out in air and deionized water coupling ZTA-coated stainless steel ball (AISI 420, 3 mm radius, grade 200) against medical grade UHMWPE to evaluate the friction of the proposed coupling.Introduction
Materials and methods
Several methods, based on both functional and anatomical references, have been studied to reach the goal of a proper knee kinematics in total knee arthroplasty (TKA). However, at present, there is still a large debate about which is the most precise and accurate method to achieve the correct rotational implant positioning. One of the main methods already used in TKA to describe the tibiofemoral flexion-extension movement, based on a kinematic technique, thus not influenced by the typical variability related to the identification of anatomical references, is called “functional flexion axis” (FFA) method. The purpose of this study was to determine the repeatability in estimating knee functional flexion axis, thus evaluating the robustness of the method for navigated total knee arthroplasty. Passive kinematic and anatomical acquisitions were performed with a commercial navigation system on 87 patients undergoing TKA with primary osteoarthritis. Knee FFA was estimated, before and after implant positioning, from three flexion-extension movements between 0° and 120° (Figure 1). The angle between Functional Flexion Axis and an arbitrary clinical reference, the transepicondylar axis (TEA), was analysed in frontal and axial view (Figure 2). Repeatability Coefficient and Intraclass Correlation Coefficient (ICC) were estimated to analyse the reliability and the agreement in identifying the axis.Introduction
Methods
Wear of the ultra-high molecular weight polyethylene (UHMWPE) insert is one of the major issue related to orthopaedic implants. In this study, the tribo-mechanical properties of zirconia-coated UHMWPE deposited by means of Pulsed Plasma Deposition (PPD) technique were analyzed. Specifically, strength to local plastic deformation, indentation work portioning and creep behavior were evaluated through nanoindentation and micro-scratch tests, whereas preliminary wear data were obtained by tribology tests. A strong reduction of plastic deformation and a drop of the creep phenomenon for the zirconia-coated UHMWPE were evidenced, whereas - in spite of similar wear data - different wear mechanism was also detected. This study supported the use of hard ceramic thin films to enhance the mechanical performance of the plastic inserts used in orthopaedics.
The use of a surgical navigation system has been demonstrated to allow to intraoperatively analyze knee kinematics during total knee arthroplasty (TKA), thus providing the surgeon with a quantitative and reproducible estimation of the knee functional behaviour. Recently severak authors used the computer assisted surgery (CAS) for kinematic evaluations during TKA, in particular to evaluate the achievement of a correct joint biomechanics after the prosthesis implantation. The major concern related to CAS is that the movements are usually passively performed, thence without a real active task performed by the subject. Starting from the hypothesis that the passive kinematics may properly describe the biomechanic behaviour of the knee, the main goal of this work was to intra-operatively compare the active kinematics of the limb, analysing a flexion movement actively performed by the patient, and the passive kinematics, manually performed by the surgeon. The anatomical and kinematic acquisitions were performed on 31 patients TKA using a commercial navigation system (BLU-IGS, Orthokey, USA). All the surgeries were performed under local anesthesia, which specifically allowed to acquire the passive and active kinematics including three flexion movements. Both in pre- and post-implant conditions, internal-external (IE) rotations and anterior-posterior (AP) translations were estimated to track any changes in the kinematic pattern.Introduction
Methods
When osteoarthritis occurs, joint replacement is the most frequent treatment. Currently, the mean survival rate for total joint arthroplasty is ∼90% after 10 years: the main reason for long-term implant failure, that generally required a revision surgery, are osteolysis and aseptic loosening of the implant, which are strongly correlated with wear debris formation from the UHMWPE insert [Ingham, 2005], as a consequence of the cyclic loading against the metallic or ceramic counterface [Dumbleton, 2002]. Wear debris bring to chronic inflammation of periprosthetic tissues causing an increase of bone reabsorption that finally provoke aseptic loosening, so implant failure[Holt, 2007]. Different solutions were proposed to reduce wear debris production but agreement has not been achieved yet. Our challenging approach prefigures the direct coating of the plastic component with a hard and well-adherent ceramic film, in order to drastically reduce wear debris formation from the plastic substrate while preserving its well-established bulk mechanical properties, especially under high local loads [Bianchi, 2013]. 3%yttria-stabilized zirconia films were deposited by PPD technique. PPD is a new vapour deposition technique based on the ablation of a target material as a consequence of the impact of a high-energy electron beam. The plasma plume of ablated material is directed toward and deposited onto the substrate. Films were characterized by SEM-EDX, X-ray diffraction, nanoindentation, adhesion and tribological tests. Moreover, capability of ZrO2–UHMWPE system of carrying local loads – i.e. an estimation of the resistance to a third-body abrasion – was investigated.Introduction
Methods
Several in vitro and in vivo studies have found correspondence between transepicondylar axis (TEA) and functional flexion axis (FFA) in healthy subjects. In addition some studies suggest that the use of FFA for rotational alignment of femoral implant may be more accurate than TEA. Ostheoarthritis (OA) may modify limb alignment and therefore flexion axis, introducing a bias at different flexion ranges during kinematic acquisition. In this study we want to understand whether OA affects somehow the FFA evaluation compared to TEA and whether the FFA could be considered a usable reference for implant positioning for osteoarthritic knees We included a group of 111 patients undergoing TKA. With a navigation system, we recorded intraoperative kinematic data in three different ranges of motion (0°-120°; 35°-80°; 35°-120°). We compared the difference in orientation of FFA (computed with the mean helical axis method) in the three ranges as also the difference with the TEA on frontal and axial planes. The correlation of preoperative limb deformity with FFA and TEA was also performed.Introduction
Methods
Patellar stability is an important component for a correct kinematic behaviour of the knee that depends on several factors such as joint geometry, muscles strength and soft tissues actions. Patellofemoral (PF) maltracking can results in many joint disorders which can cause pain and mobility alterations. The medial patellofemoral ligament (MPFL) is an important stabilizing structure for the patellofemoral joint. The aim of this study was to analyze patellofemoral kinematics with particular attention to the contribution of MPFL on patella stability. Using a navigation system PF kinematics during passive flexion/extension movements with quadriceps loaded at 60N, was recorded on 6 cadavers in three different anatomical conditions: intact knee, MPFL cut and MPFL reconstructed with graft. Test on patella was conducted without lateral force and with applied lateral force (25N). Tilt and lateral shift was evaluated in both cases at 0°. 30°, 60°and 90° of flexion.Introduction
Methods
