Beneath infection, instability and malalignment, aseptic tibial component loosening remains a major cause of failure in total knee arthroplasty (TKA) [1]. This emphasizes the need for stable primary and long-term secondary fixation of tibial baseplates. To evaluate the primary stability of cemented tibial baseplates, different pre-clinical test methods have been undergone: finite element analysis [2], static push-out [3,4] or dynamic compression-shear loading [5] until interface failure. However, these test conditions do not reflect the long-term endurance under in vivo loading modes, where the tibial baseplate is predominantly subjected to compression and shear forces in a cyclic profile [5,6]. To distinguish between design parameters the aim of our study was to develop suitable pre-clinical test methods to evaluate the endurance of the implant-cement-bone interface fixation for tibial baseplates under severe anterior (method I) and internal-external torsional (method II) shear test conditions. To create a clinically relevant cement penetration pattern a 4th generation composite bone model was customised with a cancellous core (12.5 PCF cellular rigid PU foam) to enable for high cycle endurance testing. VEGA System® PS & Columbus® CRA/PSA ZrN-multilayer coated tibial baseplates (2×12) were implanted in the customised bone model using Palacos® R HV bone cement ( An anterior compression-shear test (method II) was conducted at 2500 N for 10 million cycles and continued at 3000 N & 3500 N for each 1 million cycles (total: 12 million cycles) simulating post-cam engagement at 45° flexion. An internal-external torsional shear test (method II) was executed in an exaggeration of clinically relevant rotations [7,8] with ±17.2° for 1 million cycles at 3000 N tibio-femoral load in extension. After endurance testing either under anterior shear or internal-external torsion each tibial baseplate was mounted into a testing frame and maximum push-out strength was determined [3].Introduction
Materials & Methods
Total knee arthroplasty is a well established treatment for degenerative joint disease with good clinical results. However, complications may occur due to a biological response to polyethylene wear particles, leading to osteolysis and aseptic loosening, as well as local and systemic hypersensitivity reactions triggered by metal ions and particles such as chromium, cobalt and molybdenum. Moreover, there is an increasing demand on the performance of these implants, as this treatment is also performed in heavier, younger and middle-aged adults who have a significant physical activity and higher life expectancy. The purpose of the following study was to compare the wear characteristics and performance of a zirconium nitride (ZrN) coated knee implant, designed for patients with metal ion hypersensitivity, against the clinically established cobalt-chromium (CoCr) version under a high demanding activities wear simulation. Medium size AS Columbus® DD (Aesculap AG, Tuttlingen, Germany) femoral and tibial components with a ZrN surface were tested in comparison with the cobalt-chromium version Columbus® DD. For both groups, ultra-high-molecular weight polyethylene (UHMWPE) gliding surfaces (size T3, high 10 mm) were used. Wear simulation was performed on a load controlled 4 station knee wear simulator (EndoLab GmbH, Thansau, Germany) capable of reproducing loads and movement of daily activities measured in vivo (Bergmann et al, 2014) on 8 patients and normalized to a patient weight of 100 kg (Schwiesau et al, 2014). The load profiles were applied for 5 million cycles in a combination of 40% stairs up, 40% stairs down, 10% level walking, 8% chair raising and 2% deep squatting. Test serum was changed every 0.5 million cycles and all the components were cleaned and analyzed according to ISO 14243-2:2009(E). The gliding surfaces were evaluated for gravimetric wear and wear patterns, femur components analyzed for scratches and the test medium analyzed for metal ion concentration (cobalt, chromium, molybdenum and zirconium) using ICP-MS according to ISO 17294-2. The present study showed a wear rate reduction for the ZrN group (1.01 ± 0.29 mg/million) in comparison with the CoCr group (2.40 ± 1.18 mg/million cycles). The articulation surface of the ZrN coated femurs remained polished after the testing period, whereas the uncoated femurs showed wear scratches. Furthermore, the metal ion release from the ZrN coated implants was reduced orders of magnitude in comparison with the CoCr implants through the entire test. These results demonstrate the efficiency of ZrN coated knee implants to reduce wear as well as to prevent metal ion release in the knee joint.
Wear simulation in total knee arthroplasty (TKA) is currently based on the most frequent activity – level walking. A decade ago multi-station knee wear simulators were introduced leading to optimisations of TKA designs, component surface finish and bearing materials. One major limitation is that current wear testing is mainly focused on abrasive-adhesive wear and in vitro testing does not reflect “delamination” as an essential clinical failure mode. The objective of our study was to use a highly demanding daily activities wear simulation to evaluate the delamination risk of polyethylene materials with and without vitamin E stabilisation. A cruciate retaining fixed bearing TKA design (Columbus CR) with artificially aged polyethylene knee bearings (irradiation 30±2 kGy) blended with and without 0.1% vitamin E was used under medio-lateral load distribution and soft tissue restrain simulation. Daily patient activities with high flexion (2×40% stairs up and down, 10% level walking, 8% chair raising, 2% deep squatting) were applied for 5 million cycles. The specimens were evaluated for gravimetric wear and analysed for abrasive-adhesive and delamination wear modes.Background
Methods
Highly cross-linked polyethylene (XLPE) inserts have shown significant improvements in decreasing wear and osteolysis in total hip arthroplasty [1]. In contrast to that, XLPE has not shown to reduce wear or aseptic loosening in total knee arthroplasty [2,3,4]. One major limitation is that current wear testing in vitro is mainly focused on abrasive-adhesive wear due to level walking test conditions and does not reflect “delamination” as an essential clinical failure mode [5,6]. The objective of our study was to use a highly demanding daily activities wear simulation to evaluate the delamination risk of polyethylene materials with and without vitamin E stabilisation. A cruciate retaining fixed bearing TKA design (Columbus® CR) with artificially aged polyethylene knee bearings (irradiation 30 & 50 kGy) blended with and without 0.1% vitamin E was used under medio-lateral load distribution and soft tissue restrain simulation. Daily patient activities measured by Bergmann et al. [7] in vivo, were applied for 5 million knee wear cycles in a combination of 40% stairs up, 40 % stairs down, 10% level walking, 8% chair raising and 2% deep squatting with up to 100° flexion [8] (Fig. 1). The specimens were evaluated for gravimetric wear and analysed for abrasive-adhesive and delamination wear modes.INTRODUCTION
MATERIALS & METHODS
To evaluate carbon-fiber-reinforced PEEK as alternative biomaterial for total disc arthroplasty a closed loop between biotribology (in vitro), application of sterile particle suspensions in the epidural space of rabbits and biological response in vivo was established. To prevent adjacent level degeneration in the cervical spine, total disc arthroplasty (TDA-C) remains an interesting surgical procedure for degenerative disc disease. Short- or midterm complications are migration, impaired post-operative neurological assessment due to artefacts in x-ray and MRI diagnosis and substantial rates of heterotopic ossification. The idea was to create a TDA-C design based on a polymer-on-polymer articulation to overcome these limitations of the clinically established metal-on-polyethylene designs. The objective of our study was to characterise the biotribological behaviour of an experimental cervical disc replacement made out of carbon-fiber-reinforced (CFR) PEEK and evaluate the biological response of particulate wear debris in the epidural space in vivo.Summary Statement
Introduction
Minimally invasive implanted unicompartmental knee arthroplasty (UKA) leads to excellent functional results. Due to the reduced intraoperative visibility it is difficult to remove extruded bone cement particles, as well as bone particles generated through the sawing. These loose third body particles are frequently found in minimally invasive implanted UKA. The aim of this study was to analyse the influence of bone and cement particles on the wear rate of unicompartmental knee prostheses in vitro. Fixed- bearing unicompartmental knee prostheses (n = 3; Univation F®, Aesculap, Tuttlingen) were tested with a customized four-station servo-hydraulic knee wear simulator (EndoLab GmbH, Thansau, Germany) reproducing exactly the walking cycle as specified in ISO 14243-1:2002. After 5.0 million cycles crushed cortical bone chips were added to the test fluid for 1.5 million cycles to simulate bone particles, followed by 1.5 million cycles blended with PMMA- particles (concentration of the third-body particles: 5g/l; particle diameter: 0.5- 0.7 mm). Every 500 000 cycles the volumetric wear rate was measured (ISO 14243-2) and the knee kinematics were recorded. For the interpretation of the test results we considered four different phases: breaking in- (during the first 2.0 million cycles), the steady state- (from 2.0 million to 5 million cycles), bone particle- and cement particle phase. Finally, a statistical analysis was carried out to verify the normal distribution (Kolmogorov-Smirnov test), followed by direct comparisons to differentiate the volumetric wear amount between the gliding surfaces (paired Student's t-test, p<0.05).Introduction
Material & Methods
In TKA the generation of polyethylene wear debris is mainly affected by the factors design of the articulating bearing, contact stresses, kinematics, implant material and surface finish [McEwen et al. 2005]. The objective of our study was to evaluate the in vitro wear behaviour of fixed bearing knee designs in comprehension to the contact mechanics and resultant kinematics for different degrees of congruency.
For gravimetric wear assessment the protocol described in ISO 14243-2 has been used, followed by a kinematic analysis of the single test stations. The articulating contact and subsurface stresses have been investigated in a finite element analysis.
The wear rates between the knee design configurations differ substantially and statistically analysis demonstrates a significant difference (p<
0.01) between the test groups in correlation with congruency.
