Search

This study comprised two experiments: (1) the reliability of a novel optical three-dimensional (3D) volumetric measurement system (BODYTRONIC® 600) for the assessment of lower limb circumference and volume; (2) the comparison of data obtained from BODYTRONIC® 600 with that provided by computed tomography (CT) for accuracy estimation. Reliability was assessed in 20 healthy subjects. Accuracy was determined by comparing the deviations in the surface topology of two 3D models obtained from BODYTRONIC® 600 and CT. Reliability was very high for leg circumference measures [coefficient of variations (CVs) range 0.3%-1.3%] and slightly lower for foot circumference (CVs around 2.0%). Reliability of leg volume was also found to be very high (CVs ≤ 2.5%). Differences in surface topology between BODYTRONIC® 600 and CT were primarily below 1 mm indicating high accuracy. The volumes of the foot were higher (range 0.9%-1.7%) and that of the leg, lower (range 1.0%-1.3%) compared to CT. The BODYTRONIC® 600 system provides fast, highly reliable and accurate measures of lower limb circumference and volume and can be considered as a valuable measurement tool for use in various research and clinical applications.

Evaluation of the adhesive strength of femoral components to the bone cement is a relevant parameter for predicting implant safety. In the present experimental study, three types of cemented femoral components (metallic, ceramic and silica/silane-layered ceramic) of the bicondylar Multigen Plus knee system, implanted on composite femora were analysed. A pull-off test with the femoral components was performed after different load and several cementing conditions (four groups and n=3 components of each metallic, ceramic and silica/silane-layered ceramic in each group). Pull-off forces were comparable for the metallic and the silica/silane-layered ceramic femoral components (mean 4769 N and 4298 N) under standard test condition, whereas uncoated ceramic femoral components showed reduced pull-off forces (mean 2322 N). Loading under worst-case conditions led to decreased adhesive strength by loosening of the interface implant and bone cement using uncoated metallic and ceramic femoral components, respectively. Silica/silane-coated ceramic components were stably fixed even under worst-case conditions. Loading under high flexion angles can induce interfacial tensile stress, which could promote early implant loosening. In conclusion, a silica/silane-coating layer on the femoral component increased their adhesive strength to bone cement. Thicker cement mantles (>2 mm) reduce adhesive strength of the femoral component and can increase the risk of cement break-off.

The extent of porous coating of cementless total hip stems is held responsible for radiological periprosthetic changes, the rate of thigh pain, and even its long-term success. However, there is only sparse knowledge on how the biomechanical loading conditions of the femur are influenced by the extent of porous coating in the early phase after implantation of a cementless hip stem. Aiming to evaluate the effect of surface structuring on the strain pattern of the femur, we implanted three anatomic hip stems with different extents of porous coating (full, two-thirds proximal, and penguin type) in second-generation composite femora coated with a photoelastic layer. A cortical strain mapping was conducted before and after insertion of the implants under standardized loading conditions considering relevant muscle forces. The results of the statistical analysis of three different implantation sequences proved that composite femora are suitable for repeated measurements within the applied experimental setup. Cortical strain changes including stress-shielding effects medially (-60%) and laterally (-50%) were validated with a cadaver femur. The extent of porous coating had no significant influence on the surface strain pattern for an immediate postoperative situation.

The purpose of total hip replacement (THR) is the restoration of a painless functioning hip joint with the main focus on the biomechanical properties. Advances in surgical techniques and biomaterial properties currently allow predictable surgical results in most patients. Despite the overwhelming success of this surgical procedure, the debate continues surrounding the optimal choice of implants and fixation. Femoral and acetabular implants with varying geometries and fixation methods are currently available. Problems inherent with acrylic bone cement, however, have encouraged surgeons to use alternative surfaces to allow biologic fixation. Optimal primary and secondary fixation of cementless hip stems is a precondition for long-term stability. Important criteria to achieve primary stability are good rotational and axial stability by press-fit fixation. The objective of the cementless secondary fixation is the biological integration of the implant by bony ingrowth. Nevertheless, current investigations show excellent results of cementless fixation even in older patients with reduced osseous quality. The main advantages of cementless fixation include biological integration, reduced duration of surgery, no tissue damage by cement polymerization and reduction of intraoperative embolisms. In comparison to cemented THR both, cementless sockets and stems provide good long-term results.

There is a growing need for specific revision implants to meet the increasing occurrence of failed total hip arthroplasties displaying massive deficiencies in acetabular bone stock. The developed acetabular revision cup presented in this study is aimed at individual patient solutions using a multi-axial and angular stable fixation peg as well as a modular adaptable lateral flap. To obtain an optimum implant design, a database of computed tomography scans of 69 patients' pelves was collected and computational reconstruction of the pelvic bone morphology was conducted. Based on the anatomic measurements, the direction of the fixation peg of the revision cup was evaluated using custom software and the geometry of the lateral flaps was evaluated using rapid prototyping models of the pelvis. Furthermore, we conducted preclinical examinations of the acetabular revision system with regard to the safety of the angular stable locking mechanism of the fixation pegs and the mechanical stability of the lateral flap. The dynamic tests showed no mechanical failure of the fixation peg and its angular stable connection using a cyclic maximum torque of 24.5 Nm for one million cycles. The lateral flap and its fixation showed no mechanical failure using a cyclic maximum torque of 28.4 Nm for two million cycles. In conclusion, a promising solution to satisfy the requirements for adequate anatomical fit in a wide range of acetabular defects is presented.

Background: Allogeneic bone transplantation is at risk of infection, and established disinfection methods typically compromise bone quality. High hydrostatic pressure (HHP) is well established for disinfection in food technology, and also it does protect biomechanical and biological properties of bone. This study is the first investigation of HHP regarding disinfection of bone biopsies., Materials and Methods: Bone biopsies of 34 patients with chronic infections were subjected to HHP and assessed for persisting bacterial growth. In series 1, bone biopsies were proceeded directly to HHP (10 min; maximal pressure Pmax 600 MPa). In series 2, HHP was applied after 5-day incubation in growth media (10 min or 2x30 min; Pmax 600 MPa). Furthermore, HHP-induced changes of bacterial morphology on artificially infected bone samples were evaluated by scanning electron microscopy (SEM)., Results: For series 1, 71% of the bone samples were sterilised by HHP (n=17), compared to 38% of the untreated control samples, which were obtained during the same surgery (n=8). For series 2, after prior incubation, HHP disinfected 7% of the bone specimens (n=55), all control samples showed bacterial growth (n=33). Destruction of cell wall integrity of Gram-negative strains was observed by SEM., Conclusion: The effectiveness of HHP for bone disinfection should be improved by optimising treatment parameters. Infections with barosensitive Gram-negative bacteria or yeast might represent possible clinical indications.

The femoral components of the total knee replacements are generally made of metal. In contrast, ceramic femoral components promise improved tribological and allergological properties. However, ceramic components present a risk of failure as a result of stress peaks. Stress peaks can be minimised through adequate implant design, proper material composition and optimum force transmission between bone and implant. Thus, the quality of the implant fixation is a crucial factor. The objective of the present study was to analyse the influence of the cement layer thickness on stress states in the ceramic femoral component and in the femur. Two- and three- dimensional finite element analyses of an artificial knee joint with cement layers of different thickness and with an unbalanced cement layer thickness between the ceramic femoral component and the femur were performed. Higher stress regions occurred in the area of force transmission and in the median plane. The maximum calculated stresses were below the accepted tensile strength. Stresses were found to be lower for cement layer thickness of <2.0 mm.

Aim: Reconstruction of bone defects due to malignant tumors can be realized by several methods. Up to now, two methods, irradiation and autoclaving, are available for extracorporeally devitalizing resected tumor-bearing osteochondral segments. Previous investigations have shown that human normal and tumor cells in culture were irreversibly impaired when subjected to extracorporeal high hydrostatic pressure (HHP) of 350 MPa. The aim of this study was to examine the biomechanical and immunohistochemical properties of cartilage after exposure to HHP MATERIALS AND METHODS: Osteochondral segments of bovine femoral condyles were exposed to pressure of 300 and 600 MPa (n=20 each). Biomechanical and biological properties of untreated and treated segments were evaluated by repetitive ball indention testing and immunohistochemical labelling aggrecan, link protein and collagen II. The contralateral segments served as untreated control., Results: No significant alterations concerning stiffness and relaxation of osteochondral segments even after 600 MPa were observed. Immunohistochemically, staining was positive in all cases and no differences in the labeling pattern of proteoglycanes were observed between untreated and HHP-treated specimens., Conclusion: These findings give hope that HHP eventually will be used as a new gentle way of treating resected cartilage and bone without alteration of biomechanical properties to inactivate tumor cells in order to allow autologous reimplantation.

Dislocation of the artificial joint is a serious complication of total hip replacement. Various factors with an influence on dislocation stability were determined clinically. Our goal was to develop a method for evaluating experimentally the parameters implant design, position and the load situation for their influence on joint stability. With the newly developed testing device the range of motion to impingement and to dislocation can be determined at different implant positions. In addition, the rotational moments on subluxation, i.e. the "levering out" of the femoral head, can be determined. By way of example several hip implants were examined during movements associated with dislocation, e.g. (internal-)rotation in 90 degrees flexion and 0 degrees adduction as well as with (external-)rotation in combination with 10 degrees extension and 15 degrees adduction. Irrespective of implant design and position, the following movement phases can be differentiated: undisturbed motion, impingement, subluxation and, finally, complete dislocation of the head. On the basis of the range of motion of the specific phases, the moments occurring and the direction of dislocation, different implant systems can be compared. In this study the influence of the head diameter on the dislocation stability of the hip endoprosthesis is shown. With the aid of the model presented herein, a data set showing the most favourable and/or most dislocation stable implant position can be acquired for different combinations of the implant components. Additionally, useful information for implant design can be deduced and applied to new developments and/or modifications of existing implant components.

Spinal interbody fusion has proved to be a useful procedure for the surgical stabilization of spinal segments, for which fusion cases made of metal or reinforced polymers are increasingly being used. For the mechanical testing of spinal interbody implants, a test setup has been developed on the basis of an ASTM proposal. Initially, testing of lumbar fusion cages made of CFRP (carbon fibre reinforced polymer) was carried out. The implants (UNION Cages, Medtronic Sofamor Danek), which are characterised by their radiolucency on radiography, NMR and CT scans, have a cube-shaped body with three table-tracks on the under and upper surfaces. The cages were tested at different loads. Modifications of the proposed standardized method were carried out to enable implementation of implant-oriented testing. The tested cages were shown to have adequate axial compression, shear and torsional strengths with regard to the implant body. The maximum axial compression force tolerated by the table-tracks was less than the maximal potential loading of the lumbar spine, and, with account being taken of implant design, consequences with regard to surgical technique were drawn. As dictated by the geometry of the table-tracks, parallel grooves have to be made intra-operatively in the vertebral end plates. Axial compressive loads then act on the implant body, and the table-tracks are protected from damage. To avoid in vivo failure, the tested cages should be implanted only when this specific surgical technique is employed. Using supplementary anterior or posterior instrumentation, in vivo failure of the table-tracks under physiological spinal loading is not to be expected.

Wear of the central bushing made of ultra-high molecular weight polyethylene (PE-UHMW) of the hinged knee endoprosthesis of a tumour-resection system is the leading reason for revision. The aim of the study was to optimize the wear characteristics of the endoprosthesis on the basis of the tribological properties of new materials and an additional finite element (FE) calculation taking account of the given design. In screening tests the reference combination of PE-UHMW bushing and CoCr axis--used in the clinical setting--was first tested. The PE-UHMW bushing was then replaced by one made of each of the materials reinforced high-density polyethylene (PE-HD) and carbon fibre-reinforced epoxy resin (CFRP). In addition, a new material combination with an alumina ceramic bushing and a CFRP axis was investigated. In comparison with the reference combination PE-UHMW/metal, the combination of ceramic bushing and CFRP axis showed less wear. However, with the particular design of the prosthesis studied here, high mechanical loading applied experimentally resulted in mechanical failure. FE calculations confirmed these experimental results. Improvement of the wear characteristics of this specific implant caused therefore be achieved only by optimizing the bearing design.