Extensive bone defects of the proximal femur e.g. due to aseptic loosening might require the implantation of megaprostheses. In the literature high loosening rates of such megaprostheses have been reported. However, different fixation methods have been developed to achieve adequate implant stability, which is reflected by differing design characteristics of the commonly used implants. Yet, a biomechanical comparison of these designs has not been reported. The aim of our study was to analyse potential differences in the biomechanical behaviour of three megaprostheses with different designs by measuring the primary rotational stability in vitro. Four different stem designs [Group A: Megasystem-C® (Link), Group B: MUTARS®(Implantcast), Group C: GMRS™ (Stryker) and Group D: Segmental System (Zimmer); see Fig. 1] were implanted into 16 Sawbones® after generating a segmental AAOS Typ 2 defect. Using an established method to analyse the rotational stability, a cyclic axial torque of ± 7.0 Nm along the longitudinal stem axis was applied. Micromotions were measured at defined levels of the bone and the implant [Fig. 2]. The calculation of relative micromotions at the bone-implant interface allowed classifying the rotational implant stability.Introduction:
Methods:
Concerning biomechanical research, human specimens are preferred to achieve conditions that are close to the clinical situation. On the other hand, synthetic femurs are used for biomechanical testing instead of fresh-frozen human femurs, to create standardized and comparable conditions. A new generation of synthetic femurs is currently available aiming to substitute the validated traditional one. Structural femoral properties of the new generation have already been validated, yet a biomechanical validation is missing. The aim of our study was to analyse potential differences in the biomechanical behaviour of two different synthetic femoral designs by measuring the primary rotational stability of a cementless femoral hip stem. The cementless SL-PLUS® standard stem (size 6, Smith&Nephew Orthopaedics AG, Rotkreuz, Swizerland) was implanted in two groups of synthetic femurs. Group A consists of three 2nd generation femurs and group B consists of three 4th generation femurs (both: size large, composite bone, Sawbones® Europe, Malmö, Sweden). Using an established method to analyse the rotational stability, a cyclic axial torque of ±7.0 Nm along the longitudinal stem axis was applied. Micromotions were measured at defined levels of the bone and the implant. The calculation of relative micromotions at the bone-implant interface allowed classifying the rotational implant stability.Introduction
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
Osteolysis and aseptic loosening in total hip replacement (THR) is often associated with polyethylene (PE) wear. This caused interest in alternative bearing surfaces. Since the mid nineties, research focused on hard-hard bearings like metal-on-metal (MOM) or ceramic-on-ceramic (COC). However, concerns remain about biological reactions to metallic wear debris or failure of the ceramic components. A new approach to reduce wear with a minimized risk of failure may be the use of a metallic cup in combination with a ceramic head, the so called ceramic-on-metal bearing (COM). The aim of this study was to estimate the wear behaviour at an early stage of this COM bearing type in comparison to COC bearings using a hip simulator. Simulator studies were carried out on a single station hip simulator (MTS 858 Mini Bionix II, Eden Prairie, USA) in accordance to ISO 14242-1. Bovine serum was used as the test medium. Four COM and four COC bearings were used, both 36mm in diameter. The heads were made of a mixed-oxid ceramic (Biolox Delta(r)) paired with a high carbon wrought CoCrMo cup in the COM group whereas both components were made of Biolox Delta(r) in the COC group. Simulation was run to a total of 2.4×106 cycles. Wear measurements were performed in intervals of 0.2x106 cycles using a gravimetric method (Sartorius Genius ME235S, measuring solution: 15 μg, Sartorius, Göttingen, Germany).Introduction
Material and Methods
