Biomedical subjects

E Steinhauser

Publications and source records attributed to E Steinhauser.

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↗

PubMed2007

[Primary stability of the capsule-labrum complex after reconstruction with the Mitek Bioknotless anchor system in human cadaver models].

BACKGROUND: This study examines the postoperative stability of the Mitek Bioknotless anchor system with biomechanical draw-out pulling in human cadaver shoulders. METHOD: With simulation of anterior shoulder dislocation a test group (n=10, Ø 45 years) was tested against a native group (n=8, Ø 47 years). All shoulders were dissected up to the passive stabilizers. In the test group an artificial Bankart lesion was created and repaired with three Mitek Bioknotless anchors. The humeri of both groups were fixed in 60 degrees glenohumeral abduction and 90 degrees external rotation and then dislocated in a ventral direction. For evaluation purposes the ultimate draw-out strength, mode of failure, translation of humeral head, capsular slope, and bone density in the test group were measured. RESULTS: In the test group the ultimate strength was a median of 937 N (min. 554 N, max. 1,294 N) with 28 bony anchor dislocations, 1 suture rupture, and 1 capsular rupture, and in the native group with 6 Bankart and 2 HAGL lesions it was 1,214 N (708 N, 1,471 N). The bone density showed a positive correlation to the draw-out strength regarding cortical density and total density. CONCLUSION: Regarding the high draw-out strength the Mitek Bioknotless anchor system provides enough stability for early functional treatment.

Cadaver↗

PubMed2006

[Reconstruction of the extensor tendons in revision total knee arthroplasty and tumor surgery].

Reconstruction of the extensor mechanism in extended revision after total knee replacement and tumor surgery remains a clinically relevant problem. Due to large tibial bone defects with resection of the extensor insertion area, the specific problem of patella ligament refixation frequently arises. Several biological approaches and augmentation techniques have been published. Most of these are associated with a high rate of revision surgery because of failed replacement of the extensor mechanism and unsatisfactory functional outcome. Surgical reconstruction of these tendon defects is complicated by the difficulty of completely neutralizing tensional force across the repair. To overcome this problem, methods have been developed to reinforce the reconstruction with overlapping flaps; in addition, artificial materials are being increasingly used for tension neutralization. These artificial strips need special fixation mechanisms on the tibial component and specific technical modifications of the prosthesis. The present study gives an overview of reconstruction modalities of the extensor mechanism and provides an improved technology for better reconstruction by using artificial strips combined with specific modifications of the tibial component.

Arthroplasty, Replacement, Knee↗

PubMed2006

[Biomechanical aspects of revision components for knee arthroplasty].

Total knee arthroplasty (TKA) is one of the most frequent orthopaedic surgical procedures. Despite continuous improvements in the endoprostheses, instruments, and operative techniques, revision TKA has a rate of about 10% of overall TKA. In addition to the restoration of the periprosthetic bone stock and a precise alignment, the choice of an adequate implant, which meets the patient's specific requirements, has high impact on the outcome. The most significant differences between implants involve the degree of reconstructed joint area (uni-, bi-, tri-compartimental) and the order of the constraining forces between the femoral and tibial component. Implants for revision TKA commonly range from un- or semiconstrained resurfacing implants to fully constrained hinged endoprostheses. In case of severe osseous, ligamentous, and/or muscular defects, special tumor endoprostheses or implants for arthrodesis might be an alternative option.

Arthroplasty, Replacement, Knee↗

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↗

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

[Evaluation of the assembling and retention forces of constraint liners for total hip replacement].

Dislocation is a severe complication after total hip replacement which may cause revision surgery in some cases. The use of constraint inserts that are coupled to the femoral head by a snapping mechanism provides an opportunity for treatment of recurrent dislocations. This study was aimed to investigate the assembling and retention forces of a specific constraint liner. Using a universal testing machine the assembling forces were determined for head sizes of 28 and 32 mm and the clinically mostly used as well as the maximum cup size. Subsequently, under variation of load direction and pull-out velocity the retention forces were investigated. For primary assembly of the head the required compressive forces were in a range from 197 N and 283 N depending on head and cup size (each size n = 3). Repeated assembly led to a decrease of these forces up to 29%. The retention forces always were slightly below the assembling forces, i. e. forces to remove the heads from the inserts were between 183 N and 230 N (each size n = 3). Repeated disconnection caused a decrease of the retention forces up to 16%. An increase of load velocity as well as an oblique load direction resulted in an enhancement of the retention forces. For all investigated implant sizes the retention force for the femoral head was approximately ten-times less than the interface strength between the insert and the metal-back. In case of correct implant handling the risk of disconnection between the tested constraint insert and the corresponding metal-back has not to be considered in clinical practice.

Acetabulum↗

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

[Refixation of the meniscus with the SD meniscal staple: a comparative biomechanical study on cadaver knees].

GOAL: The failure load of the SD meniscal staple was compared with the 2-0 Etibond meniscus suture in a dynamic test without isolating the meniscus. METHODS: In eight knee joint pairs, a standardized lesion of the posterior part of the medial meniscus was repaired by either three staples (7 mm) or three 2-0 Etibond sutures. After resection of the cruciate ligaments and 15 degrees external rotation, 45 degrees flexion, and 70 kg of axial loading, a tibial translation was exerted on the knee joint. The test was documented on a way force diagram, demonstrating the failure of the device at a sudden load of force. RESULTS: The average load before failure of the meniscus staple was 591.2 N (540-690 N), that of the sutures 850 N (600-1350 N). We did not find any statistical correlation to age,weight, or height of the specimens. The suture migrated, but never ruptured. In two cases the suture caused a radial meniscus lesion. Failure of the staple was detachment of the inferior part in all cases, but no migration. CONCLUSION: This test is based on the dynamic forces of the knee joint on the meniscus. Our measurements show lower failure loads of the staple compared to those of the sutures, but compared to other tests a stable method of meniscus repair.

Absorbable Implants↗

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↗

PubMed2003

[Biomechanical investigations for the development of a SLAP-II-lesion].

The superior labral-biceps-tendon-complex forms an anatomical and functional unit and combines static and dynamic elements of shoulder stability. At present, only theoretical hypotheses exist on the etiology of the microtraumatic SLAP-II-lesion. To gain further insight into this, an instrument was developed to simulate throwing motions such as the late-cocking/early acceleration phase as well as deceleration/follow-through. Sixteen freshly frozen shoulder specimens were tested, varying the loads on the biceps tendon (25 N, 50 N, 100 N) and the compression of the humeral head against the glenoid (25 N, 50 N, 80 N). Each shoulder had to run through a certain number of cycles during the particular phase of throwing. The tests were stopped after a SLAP-II-lesion was observed, or after a limit of 15,000 cycles. Every 1,000 cycles the results of the tests were checked arthroscopically. A SLAP-II-lesion developed in only 10% of the specimens during the acceleration/ late cocking phase whereas in the deceleration/ follow-through phase 83% developed such a lesion. According to our results, the deceleration/follow-through of the throwing motion seems to be responsible for creating microtraumatic SLAP-II-lesions. One reason is the loss of the centering function of the long head of the biceps tendon during total internal rotation, another is the increased posterosuperior translation of the humeral head in this position, which leads to a non-physiological contact, creating lesions in this area due to the large sheering forces.

Acceleration↗

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↗

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

[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↗

PubMed2001

[Mechanical study of spinal interbody implants--characteristics and limits of standardized testing].

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.

Biomechanical Phenomena↗