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Biomedical subjects

W Mittelmeier

Publications and source records attributed to W Mittelmeier.

At least 19 recordsLinked to original sources
PubMed2007

Assessment of cup position from plain radiographs: impact of pelvic tilting.

The acetabular cup position after total hip arthroplasty (THA) regarding its inclination and version angles are influential parameters concerning the postoperative range of motion and dislocation stability. Standard anterior-posterior X-rays remain an important diagnostic instrument to observe the postoperative outcome and to secure quality control after THA, where an optimal positioning of the patient is recommended when taking these X-rays. The purpose of this preliminary study was to determine the effect of pelvic tilting regarding the positioning calculation of the acetabular cup from standard radiographs using a modified method according to Pettersson et al. (Acta Radiol Diagn, 23:259-263, 1982). In our model experiment, we were able to show that pelvic tilting to either side causes a considerable difference between the radiographic and calculated version angles following approximately linear functions. However, pelvic tilting to either side, leads, regarding the calculation of the inclination, to an average deviation between radiographic and calculated inclination angles less than 2 degrees .

Humans↗
PubMed2006

[Failure analysis of total knee replacement. Basics and methodological aspects of the damage analysis].

Possible causes for failure of total knee endoprostheses represent wear, malpositioning, maldimensioning and inadequate design of the implant components, manufacturing defects, material fatigue, corrosion, overloading, infection, and allergy against implant materials. There is a broad spectrum of methodical approaches for the analysis of failure cases. Substantial information for the damage analysis is provided by clinical and intraoperative findings, photo documentation, radiographic course as well as all-solid, physical and histological investigations. Principal purposes of damage analysis are the avoidance of further damage events and the gain of information for improvement of implant design and material as well as the optimisation of the biocompatibility of implants and wear products. Both a detection system of incidents and implant failures as well as a complete data collection enables early identification of system-specific, accumulated cases of implant failure.

Arthroplasty, Replacement, Knee↗
PubMed2006

[Diagnostic strategies in cases of suspected periprosthetic infection of the knee. A review of the literature and current recommendations].

Reliable confirmation of periprosthetic infection after total knee arthroplasty is a diagnostic challenge. The present work reviews published data evaluating the available diagnostic tools. Erythrocyte sedimentation rate and C-reactive protein serum levels are relatively sensitive methods with rather low specificity towards periprosthetic infection and are mainly applied to exclude infection. Studies evaluating scintigraphic methods--especially white cell scans--provide inconsistent data with varying accuracy. Consequently, white cell scans cannot be recommended as standard methods. Immunoscintigraphy with antigranulocyte antibodies and FDG-PET scans demonstrated promising results with particularly high sensitivities, but have to be validated in larger studies. Microbiological evaluation of joint aspirates proved high specificity for periprosthetic infection. However, an average of 20% of infected cases remained undetected. Nevertheless, aspiration is widely recommended for preoperative isolation of the infecting organism. Intraoperative frozen sections demonstrated excellent specificity with good sensitivity. The real accuracy of intraoperative culture and permanent histology cannot be determined due to the missing golden standard; however, a combination of both methods is recommended to define the final diagnosis. Large studies validating both methods and criteria for the final diagnosis of periprosthetic infection are necessary to optimize the diagnostic algorithm.

Arthroplasty, Replacement, Knee↗
PubMed2005

Comparing biomechanical investigations about different wiring techniques of finger joint arthrodesis.

INTRODUCTION: Multiple operative techniques are currently used for finger arthrodesis in clinical practice. The present study was designed to compare the biomechanical characteristics of typical arthrodesis techniques used in daily practice. MATERIAL AND METHODS: Osteosynthesis techniques comprising wire cerclage, thread cerclage (PDS) or intraosseous wire suture were compared in a biomechanical experiment for resistance against bending loads. The mentioned techniques were applied to artificial specimens with resected articular surfaces or by using the cup-and-cone procedure. In this process, the specimens were tested using various Kirschner-wire insertion angles as well as different arthrodesis angles (20 degrees vs 40 degrees) in a 4-point bending test with each group consisting of 6 specimens of acrylic glass. The forces prevalent in the joint space were determined by prescale pressure measurement foils. RESULTS: Wire tension banding resisted significantly higher bending moments than arthrodeses with thread tension bands (p < 0.05). All set-ups with tension banding techniques tolerated significantly higher loads than the intraosseous wire sutures without additional K-wires (p < 0.05), which showed unfavorable dislocation of contact areas resulting in instability even under relatively minor bending loads. Using the cup-and-cone technique, a geometrically larger contact area could be achieved between two unloaded fragments, but this technique showed no advantages in the opposing bending moments compared with the conventional resection method. In both techniques, a dislocation of contact surfaces towards the palmar direction could be observed with increasing bending moment. While the use of thread tension band fixation reduces the risk of plastic deformation of both osteosynthetic material and bone stock, the problem of resorption rate has to be taken into account when choosing the material for the thread. CONCLUSIONS: Considering pressure distribution and stability with and without bending loads, it is not the most rigid osteosynthesis technique which should be viewed as the ideal treatment. In contrast, it is more important to consider the various and most likely conditions to be expected in daily life after arthrodesis and therefore to chose the type of technique distributing pressure as regularly as possible.

Arthrodesis↗
PubMed2005

A novel antibacterial titania coating: metal ion toxicity and in vitro surface colonization.

Postoperative implant-associated infection is still an unresolved and serious complication in modern surgery. Antibacterial and biocompatible surfaces could both reduce infection rates and promote tissue integration. In this respect, a comparative study of the antibacterial as well as the biocompatible potential of different metal ions in vitro is presented. The assays used were growth inhibition tests with different metal salts carried out with tissue cells and bacteria under corresponding culture conditions. Additionally, in vitro tests in direct surface contact with tissue cells and bacteria onto a novel copper containing sol-gel derived titanium dioxide coating (Cu-TiO2) and a fourfold Cu-TiO2 coating were performed. The values were compared to a non-filled titanium dioxide coating and standard Ti6Al4V alloy. SEM-investigations were performed to approve the results of the in vitro tests. Among Ag+, Zn2+, Co2+, Al3+ and Hg2+, the growth inhibition tests revealed an outstanding position of copper ions as antibacterial but nevertheless bio-tolerant additive. These results were affirmed by the cell tests in direct surface contact and SEM-investigations, where best cell growth was found on the Cu-TiO2 coatings. Highest antibacterial properties with a tolerable cytocompatibility could be observed on the fourfold Cu-TiO2 coatings. Consequently, surfaces with custom-tailored antibacterial properties may be established and could be of particular interest in revision and tumor arthroplasty.

3T3 Cells↗
PubMed2004

[Stability of osteosyntheses for condylar head fractures in the clinic and biomechanical simulation].

BACKGROUND: Fractures of the condylar head are traditionally managed by closed techniques, despite a considerable rate of dysfunctional problems. PDS pin osteosynthesis (presented by Rasse 1992) via a preauricular approach failed to become established as a standard procedure due to a lack of stability. Alternatively, mini- or microplating, as performed in our patients (101 condylar head fractures between 1993 and 2000), showed high-grade limitations of translatory movements in about 30% due to scarification after loosening of osteosynthesis materials. The aim of this study was to establish an efficient procedure for achieving a functionally stable and atraumatic osteosynthesis. METHODS: For the definition of a suitable procedure, models of the mandible (standardized fractures, types A, B, and C) were osteosynthesized (six samples for each type of fracture and type of screw), each with three PDS pins, 2.0 mm resorbable, 2.0 cortical, 1.7 and 1.2 mm small fragment screws, and exposed to increasing loads in centric (0-20-35 mm opening) and eccentric (35 mm opening) condylar positions. A computerized biomechanical test stand allowed a dynamic simulation of chewing forces (16 hydraulic drives). The resulting fracture gaps were measured without contact by a motion capture system. RESULTS: Within physiological limits, only 1.7 small fragment and 2.0 mm cortical screws were able to bear occlusal loadings up to 200 N (1.2 mm small fragment screws up to 150 N, resorbable 2.0 mm screws up to 100 N, and PDS-pins up to 50 N). In a pullout experiment (condylar spongious bone of young pigs, aged 4-6 months), 1.7 mm small fragment screws showed superior retention. A consecutively developed small fragment screw-system has been applied clinically in 74 condylar head fractures (58 patients). After removal of osteosynthesis material, 41 of 49 TM joints have so far shown complete restitution. CONCLUSIONS: The newly developed osteosynthesis system using a retroauricular approach based on 1.7 mm small fragment screws makes maxillomandibular immobilization unnecessary. The extra-articular position of the screw heads prevents scar-induced articular limitations. Preexisting degenerative alterations of the TMJ soft tissues, however, will affect functional results adversely.

Absorbable Implants↗
PubMed2004

[Damage analysis illustrated by two cases of broken ceramic inserts. Recommendations for avoiding breakages caused by handling].

Due to modular design today's total hip endoprostheses provide the choice of different bearing surfaces. Particle-induced osteolysis is the major reason for implant failure. Therefore, minimization of wear rates is the essential factor for the improvement of long-term function of the implants. The bearing couple ceramic-on-ceramic offers a linear wear rate of about 0.005 mm/year. That is an essential prerequisite for successful treatment of young and active patients. Ceramic femoral heads and taper fixation became standard. After some problems in the 1970s, manufacturers achieved all kinds of improvements. Surgeons learned how to handle ceramic femoral heads correctly. Nowadays ceramic heads are reliable implants. Ceramic inserts have been used since the mid-1990s. Some acetabular systems with ceramic inserts are used in clinical studies, some are approved. Complications with ceramic inserts are rare, e.g., fracturing or chipping off. Mostly those problems are due to mishandling. In this study some clinical failures are analyzed. Recommendations how to improve the handling of ceramic inserts are proposed and discussed.

Acetabulum↗
PubMed2004

A novel test method for evaluation of the abrasive wear behaviour of total hip stems at the interface between implant surface and bone cement.

After total hip replacement, some cemented titanium stems show above-average early loosening rates. Increased release of wear particles and resulting reaction of the peri-prosthetic tissue were considered responsible. The objective was to develop a test method for analysing the abrasive wear behaviour of cemented stems and for generating wear particles at the interface with the bone cement. By means of the novel test device, cemented hip stems with different designs, surface topographies and material compositions using various bone cements could be investigated. Before testing, the cemented stems were disconnected from the cement mantle to simulate the situation of stem loosening (debonding). Subsequently, constant radial contact pressures were applied on to the stem surface by a force-controlled hydraulic cylinder. Oscillating micromotions of the stem (+/- 250 microm; 3 x 10(6)cycles; 5 Hz) were carried out at the cement interface initiating the wear process. The usability of the method was demonstrated by testing geometrically identical Ti-6A1-7Nb and Co-28Cr-6Mo hip stems (n= 12) with definite rough and smooth surfaces, combined with commercially available bone cement containing zirconium oxide particles. Under identical frictional conditions with the rough shot-blasted stems, clearly more wear particles were generated than with the smooth stems, whereas the material composition of the hip stems had less impact on the wear behaviour.

Biocompatible Materials↗
PubMed2004

[Method for the evaluation of factors influencing the dislocation stability of total hip endoprotheses].

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.

Arthroplasty, Replacement, Hip↗
PubMed2003

BISS: concept and biomechanical investigations of a new screw system for electromagnetically induced internal osteostimulation.

INTRODUCTION: The aim of an intraosseous application of electromagnetic alternating fields is to speed up both the regeneration of osteonecroses and bone regeneration. In clinical studies, the efficiency of the technique could be successfully proven by using a transducer coil. The advantage of the traditional technique was the variety of its applications in connection with various osteosynthesis systems; the disadvantage was a possible failure of the contacting leads and the resulting functional breakdown. MATERIALS AND METHODS: A newly developed BISS screw (bipolar induction screw system) with integrated coil and electrodes was compared to a standard cannulated screw used in the traditional technique. The strength of BISS screws ( n=6) and of cannulated screws ( n=6) was evaluated in comparative biomechanical tests. Examinations consisted of torsional and static and dynamic cantilever tests. All screws were made of the same material (TiAl(6)V(4)) and had identical outer dimensions. RESULTS: No significantly lower strengths could be observed when we compared BISS screws with cannulated screws. The BISS screws even showed significantly higher mechanical values due to a reinforcing effect by the attached electrode. CONCLUSION: In the modified concept of the new BISS screw, both coil and electrodes are housed in only one cannulated screw. No negative effects concerning mechanical strength and durability were associated with the new screw concept. This provides for a simpler implantation and makes removal easier, while the risk of a cable tear is avoided.

Alloys↗
PubMed2003

[Carbon fiber-reinforced plastics as implant materials].

Carbon fiber-reinforced plastics have been used clinically as an implant material for different applications for over 20 years.A review of technical basics of the composite materials (carbon fibers and matrix systems), fields of application,advantages (e.g., postoperative visualization without distortion in computed and magnetic resonance tomography), and disadvantages with use as an implant material is given. The question of the biocompatibility of carbon fiber-reinforced plastics is discussed on the basis of experimental and clinical studies. Selected implant systems made of carbon composite materials for treatments in orthopedic surgery such as joint replacement, tumor surgery, and spinal operations are presented and assessed. Present applications for carbon fiber reinforced plastics are seen in the field of spinal surgery, both as cages for interbody fusion and vertebral body replacement.

Carbon↗
PubMed2002

[Mechanical studies of lumbar interbody fusion implants].

In addition to autogenous or allogeneic bone grafts, fusion cages composed of metal or plastic are being used increasingly as spacers for interbody fusion of spinal segments. The goal of this study was the mechanical testing of carbon fiber reinforced plastic (CFRP) fusion cages used for anterior lumbar interbody fusion. With a special testing device according to American Society for Testing and Materials (ASTM) standards, the mechanical properties of the implants were determined under four different loading conditions. The implants (UNION cages, Medtronic Sofamor Danek) provide sufficient axial compression, shear, and torsional strength of the implant body. Ultimate axial compression load of the fins is less than the physiological compression loads at the lumbar spine. Therefore by means of an appropriate surgical technique parallel grooves have to be reamed into the endplates of the vertebral bodies according to the fin geometry. Thereby axial compression forces affect the implants body and the fins are protected from damaging loading. Using a supplementary anterior or posterior instrumentation, in vivo failure of the fins as a result of physiological shear and torsional spinal loads is unlikely. Due to specific complications related to autogenous or allogeneic bone grafts, fusion cages made of metal or carbon fiber reinforced plastic are an important alternative implant in interbody fusion.

Biomechanical Phenomena↗
PubMed2002

[Tissue-induced changes of the extracorporeal shockwave].

Extracorporeal shock wave therapy has been applied very frequently for more than 2 decades. Excellent results in clinical application and research led to widespread use of this noninvasive procedure. Until now the actual mode of action and biochemical pathways after extracorporeal shock wave therapy (ESWT) remain unknown. A small number of technical parameters could be determined after improved technical methods and sensor devices had been designed. It is also still unclear how these technical findings apply to the clinical setting. Therefore, we investigated the influence of musculocutaneous tissue on shock wave focus. A tissue thickness of 15 mm significantly influenced focus characteristics. We found distinct spreading and slight lateral deviation of the focus. In the same way, the peak positive pressure was significantly reduced after the shock waves had passed the musculocutaneous model. The study demonstrates that in vitro results could not be transferred directly to clinical or in vivo conditions. The clinical application of extracorporeal shock waves should be modified in intensity and number of shock waves depending on individual anatomic conditions, indication, and location.

Animals↗
PubMed2001

[Using robots in hip prosthesis implantation. Precision with the wrong concept?].

Robot-assisted milling permits more precise preparation of the proximal femur, without necessarily optimizing stem placement. Currently propagated implantation concepts involving maximized implant-cortical bone contact may result in major biomechanical disadvantages, such as unphysiological load transfer in the proximal femur and increased stiffening in this region and subsequent stress shielding. While equipment procurement and running costs are higher, evidence of longer prosthetic life over the long-term has not been forthcoming. Against this background, present efforts to propagate this system for general use in hip replacement surgery cannot be justified.

Arthroplasty, Replacement, Hip↗
PubMed2001

Biomechanical examinations of cancellous bone concerning the influence of duration and temperature of cryopreservation.

The influence of cryopreservation of cancellous bone at different temperatures and different storage periods was investigated for mechanical changes. Standardized cancellous cylinders (50 x 25 mm) were stored at -20 degrees C or -80 degrees C for 6 or 12 months, respectively, or for 2 years and then subjected to a screw pull-out test. No significant differences were found among the various storage temperatures and periods investigated. We conclude that different cryopreservation temperatures do not have any influence on the mechanical properties of cancellous bone. Also, storage duration up to 2 years has no effects on the mechanical strength of the bone.

Animals↗
PubMed2001

The Kapandji technique for fixation of distal radius fractures--a biomechanical comparison of primary stability.

The goal of this study was to compare Kapandji-K-wiring and established K-wiring techniques of the distal radius fracture for primary stability in a biomechanical model: dorsal K-wiring according to Kapandji using different angles of the K-wire, parallel and diagonal alignment of the K-wires. A new testing system which uses a synthetic material enabled us to carry out the cantilever bending test. By application of a lower load, the Kapandji procedure shows a higher reactive torque and stiffness. A higher reaction force of the other techniques, especially of the parallel wiring, are only observable under high-grade bending stress. Application of the Kapandji procedure with K-wires at a smaller angle to the axis of the radius results in the highest primary stability of the procedures investigated in the essential range of initial deformation.

Biomechanical Phenomena↗
PubMed2001

[New compounds for improving wear behavior of a tumor knee endoprosthesis].

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.

Biomechanical Phenomena↗