Revision Total Hip Arthroplasties (THA) have a significantly higher failure rate than primary THA's and the most common cause is aseptic loosening of the cup. To reduce this incidence of loosening various porous metal implants with a rough surface and a porous architecture have been developed which are said to increase early osteointegration. However, for successful osteointegration a minimal micromotion between the implant and the host bone (primary stability) is beneficial. It has not been previously determined if the primary stability for the new Gription® titanium cup differs from that of the old Porocoat® titanium cup. In 10 cadaveric pelvises, divided into 20 hemipelvises, bilateral THA's were performed by an experienced surgeon (RGB) following the implant manufacturer's instructions and with the original surgical instruments provided by the company. In randomized fashion the well established Porocoat® titanium implant was implanted on one side of each each hemipelvis whereas on the corresponding opposite side the modified implant with a Gription® coating was inserted. Radiographs were taken to confirm satisfactory operative results. Subsequently, the hemipelvis and cups were placed in a biomechanical testing machine and subjected to physiological cyclic loading. Three-dimensonal loading corresponded to 30% of the load experienced in normal gait was imposed reflecting the limited weight bearing generally prescribed postoperatively. The dynamic testing took place in a multi-axial testing machine for 1000 cycles. Relative motion and micromotion were quantified using an optical measurement device (Pontos, GOM mbh, Braunschweig, Germany). Statistical evaluation was performed using the Wilcoxon signed-rank test.Introduction
Material and Methods
The frequency of revision hip arthroplasty is increasing with the increasing life expectancy and number of individuals treated with joint replacement. Newer porous implants have been introduced which may provide better treatment options for revision arthroplasty. These may require cementation to other prosthesis components and occasionally to bone, however, there is currently no information on how these porous implants interface with cement. Cylindrical bone (control group) and porous metal probes with a diameter and height of 10mm were created and subsequently cemented in a standardized setting. These were placed under tensile and torsional loading scenarios. In this experimental study, 10 human femoral heads were used to create 20 cylindrical probes with a diameter and height of 10mm. One side was tapered to 6mm for cementation and interface evaluation. A further set of 20 probes of a porous metal implant (Trabecular Metal®) was created with the same geometry. After the probes were created and lavaged, they were cemented at the tapered surface using a medium viscosity cement at a constant cementation pressure (1.2N/mm2). The setup allowed for comparison of the porous metal/cement interface (group A) with the well-studied control group interface bone/cement (group B). The maximal interface stability of groups A and B were evaluated under tensile and rotational loading scenarios and the cement penetration was measured.Introduction
Materials and Methods
As there are many reports describing avascular reactions to metal debris (ARMD) after Metal-on-Metal Hip Arthroplasty (MoMHA), the use of MoMHA, especially hip resurfacing, is decreasing worldwide. In cases of ARMD or a rise of metal ion blood levels, revision is commended even in pain free patients with a well integrated implant. The revision of a well integrated implant will cause bone loss. As most of the patients with a hip resurfacing are young and a good bone stock is desirable for further revision surgeries, the purpose of this study was to evaluate the stability of a cemented polyethylene cup in a metal hip resurfacing cup. Two different hip resurfacing systems were investigated in this study (ASR™, DePuy Orthopaedics, Leatherhead, UK; Cormet™, Corin Group, Cirencester, UK). Six different groups were formed according to the treatment and preparation of the cement-cup-interface (table 1). Before instilling cement in groups 1, 3, 5 the surface, which was contaminated with blood, was cleaned just using a gauze bandage. In groups 2, 4, 6 saline, polyhexanid and a gauze were used to clean the surface prior to the cement application. In group one and two the polyethylene cup (PE) was cemented either into Cormet™ or ASR™, just the ASR™ was further investigated in group three to six. A monoaxial load was applied while the cup was fixed with 45 degrees inclination (group 1–4) and 90 degrees inclination (group 5, 6: rotatory stability) and the failure torque was measured. In contrast to group 1 and 2, the cement penetrated the peripheral groove of the ASR™ in groups 3–6. The mean failure torque of five tests for each group was compared between the groups and the implants. The ASR™ showed mean failure torque of 0.1 Nm in group one, of 0.14 Nm in group two, of 56.9 Nm in group three, of 61.5 Nm in group four, of 2.96 Nm in group five and of 3.04 Nm in group six. The mean failure torque of the Cormet™ was 0.14 Nm both in groups one and two (table 2). In groups 1–6 there were no significant differences between the different preparations of the interface. Furthermore, in groups 1 and 2 there were no significant differences between the Cormet™ and the ASR™. The mean failure torque of group 4 was significant increased compared to group 3 (p=0.008). We saw an early failure of the cement fixation due to the smooth surface of the Cormet™ and the ASR™ components in groups 1, 2, 5, 6. In contrast to other hip resurfacing cups the ASR™ has a peripheral groove, which was not cemented except in groups 3 and 4 and therefore the lever-out failure torque was significant increased in these groups. Nevertheless, the groove did not provide stability of the cement-PE compound in case of rotatory movements. In conclusion we do not recommend the use of these methods in clinical routine. The complete removal of hip resurfacing components seems to be the most reasonable procedure.
In cases of poor bone quality intraoperative torque measurement might be an alternative to preoperative dual energy x-ray absorptiometry (DXA) to assess bone quality in Total Hip Arthroplasty (THA). 14 paired fresh frozen human femurs were included for trabecular peak torque measurement. We evaluated an existing intraoperative torque measurement method to assess bone quality and bone strength. We modified the approach to use this method in total hip arthroplasty (THA), which has not been published before. Since there are several approaches used in THA to exposure the hip joint, we decided to prefer the measurement in the femoral head which allows every surgeon to perform this measurement. Here a 6.5 × 23 mm blade was inserted into the proximal femur without harming the lateral cortical bone (figure 1). Further tests of the proximal femur evaluated the results of this new method: DXA, micro-computed tomography (μCT) and biomechanical load tests. Basic statistical analyses and multiple regressions were done. In the femoral head mean trabecular peak torque was 4.38 ± 1.86 Nm. These values showed a strong correlation with the values of the DXA, the μCT and the biomechanical load test. In comparison to the bone mineral density captured by DXA, the results of the intraoperative torque measurement showed a superior correlation with high sensitive bone quality evaluating methods (mechanical load tests and micro-computed tomography). Hence, the use of this intraoperative torque measurement seems to be more accurate in evaluating bone strength and bone quality than DXA during THA. The torque measurement provides sensitive information about the bone strength, which may affect the choice of implant in cases of poor bone stock and osteoporosis. In clinical use the surgeon may alter the prosthesis if the device indicates poor bone quality. Furthermore, we assume that the disadvantages associated with DXA scans like radiation exposure or errors caused by potential extraosteal sclerosis and interindividual soft-tissue artifacts could be excluded.
Titanium, in particular Ti6Al4V, is the standard material used in cementless joint arthroplasty. Implants are subjected to cyclic loading where fracture is the reason for re-operation in 1.5–2.4% of all revisions in total hip arthroplasty. In order to strengthen critical regions, surface treatments such as shot peening may be applied. A superficial titanium oxide layer is naturally formed on the surface as a protective film at ambient conditions. However, as its thickness is only in the range of several nanometers, it is prone to be destroyed by high loads - as present at the surface during bending - leading to an ‘oxidative wear’ in a corrosive environment [1]. The present study aims to evaluate the shot peening treatment on Ti6Al4V regarding its potential for cyclically loaded parts under a dry and a corrosive testing medium. Hour-glass shaped titanium specimens (Ti6Al4V) with a minimal diameter of 10 mm have been subjected to an annealing treatment at 620°C for 10h to remove initial residual stresses introduced during machining. Subsequently, a high-intensity shot peening treatment with cut wire followed by a low-intensity cleaning process with glass beads have been performed (Metal Improvement, Germany). Arithmetic mean roughness Ra of the treated surfaces was measured (Mahr Perthometer M2, Germany). Residual stress depth profiles prior to and after shot peening have been measured by a Fe-filtered Co-K(alpha) radiation (GE Measurement&Control, USA) and calculated using the sin2(psi) method. Fatigue strength has been determined by two servo-hydraulic hydropulsers (Bosch Rexroth, Germany) at 10 Hz and a load ratio of R=0.1 either under dry conditions (8 specimens) or surrounded by a 0.9-% saline solution (6 specimens) (BBraun, Germany) (Fig. 1). Testing has been performed until fracture occurred or the total number of 10 × 106 cycles has been reached. All fracture surfaces have been analyzed after testing using FEG-SEM (Zeiss LEO 1530 VP Gemini, Germany).Background
Materials and Methods
Failure of total knee arthroplasty (TKA) is mainly caused by biological reactions against wear particles generated at the implant. So far, wear has been mainly attributed to polyethylene (PE) and much effort has been put into understanding and optimizing the wear mechanism of PE in recent years. However, evaluation of metal wear particles and ion release in TKR has been neglected so far although the implants present large metal surface areas. In the present study we aimed to analyse the wear performance of TKA and to study the kinetics of metal ion and particle release. We hypnotized that due to abrasion and corrosion TKA will release relevant levels of Cobalt (Co), Chromium (Cr), Molybdenum (Mo) and Titanium (Ti). Implants were subjected to an in-vitro simulation applying physiological loadings and motions for 5 million walking cycles. Wear processes were determined gravimetrically and by measuring the release of Co, Cr, Mo and Ti ions using HR-ICP-MS. Surface alterations were determined through surface roughness measurements.Introduction
Methods
Polyethylene (PE) wear is known as a limiting factor for total knee replacements (TKR). Thus, preclinical wear testing is an important tool to assess the suitability of new designs and new materials. However, standardized testing (e.g. according to ISO 14243) does not cover the individual situation in the patient. Consequentially, this study investigates the following two parameters: Testing-Frequency: Patients with TKR's show a humiliated walking frequency (down to 0,5Hz) compared to standardized testing (1Hz±0.1). In the first part of this study, the influence of a decreased test frequency on the PE wear behavior is investigated Interval of lubricant replacement: For in-vitro testing bovine serum is used as a substitute for the synovial fluid. Physiologically a continuous regeneration and removement of destructed components is taking place. In contrast, for simulator testing the bovine serum is typically changed completely every 500.000 cycles/steps. Therefore the goal of the second part of this study was to test if the serum replacing interval affects the PE wear behavior. Wear tests were conducted on an AMTI force controlled knee simulator. A cruciate substituting (ultracongruent) implant design (TC Plus, Smith & Nephew, Rotkreuz, Switzerland) was used. First, a reference wear study with a test frequency of 1Hz and a lubricant replacement interval (RI) of 500.000 cycles according to ISO 14243-1:2009 was carried out. Tests were run to a total of 5 million cycles. A second wear test was run with a reduced frequency of 0.5 Hz. The reduced frequency resulted in an extended testing period for the same number of cycles. To exclude an influence of the extended time period, the lubricant was changed, in the first half of testing every 500.000 cycles corresponding to 12 days (cycle depending (CD)), and in the second part every 250.000 cycles corresponding to 6 days (time depending (TD)). Tests were run to a total of 3 million cycles. A third test was run with a frequency of 1 Hz. For this test a reduced serum RI of 150.000 cycles was choosen. This test was run to a total of 1.500.000 cycles.Background
Material and Methods
Infection following total joint arthroplasty is a major and devastating complication. After removal of the initial prosthesis, an antibiotic-impregnated cement spacer is inserted for approx. three months. Treatment is completed by a second stage revision arthroplasty. Up to now, spacers are produced from conventional bone cements that contain abrasive radio-opaque substances like zirconium dioxide or barium sulphate. As long as spacer wear products (cement particles containing these hard substances) are not fully removed during the final revision surgery they may enter the articulating surfaces of the revision implant leading to third body wear. In order to reduce the formation of reactive wear particles, a special cement (Copal(r) spacem) without abrasive zirconium dioxide or barium sulphate was developed. To date, no comparative tribological data for cement spacers have been published. Hence, we carried out a study on the wear properties of Copal(r) spacem (with and without gentamicin) in comparison to conventional bone cements (Palacos(r) R and SmartSet(r) GHV). In order to assure reproducible forms of the femoral and tibial components, silicon rubber moulds were produced and filled with the respective cement. Force-controlled simulation was carried out on an AMTI knee simulator (Figure I). The test parameters were in accordance to ISO 14243-1 with a 50% reduced axial force (partial weight bearing). Tests were carried out at 37 °C in closed chambers filled with circulating calf serum. Tests were run for 240,000 cycles (representing the average step rate during 6-8 weeks) at a frequency of 1 Hz. For wear analysis, digital photographs of the spacer were taken at the beginning and at the end of the testing period. The areas of wear scars were measured by the means of a digital image processing software.Introduction
Material and Methods
