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Biomedical subjects

W Plitz

Publications and source records attributed to W Plitz.

At least 19 recordsLinked to original sources
PubMed2006

Stability of anterior vertebral body screws after kyphoplasty augmentation. An experimental study to compare anterior vertebral body screw fixation in soft and cured kyphoplasty cement.

The goal of this cadaver study was to compare the stability of anterior vertebral body screws after implantation in soft or cured kyphoplasty cement. Anterior vertebral body screws were inserted in a total of 30 thoracolumbar vertebrae of ten different human specimens: ten screws were implanted in non-augmented vertebrae (group 1), ten screws were placed in soft cement (group 2), and ten screws were placed in cured cement (group 3). The screws were then tested for biomechanical axial pullout resistance. Mean axial pullout strength was 192 N (range: 10-430 N) in group 1, 364 N (range: 65-875 N) in group 2, and 271 N (range: 35-625 N) in group 3. The paired Student's t-test demonstrated a significant difference between pullout strength of groups 1 and 2 (p= 0.0475). No significant difference was seen between pullout strength of groups 1 and 3 (p= 0.2646) and between groups 2 and 3 (p= 0.3863). We achieved a 1.9 times higher pullout strength with kyphoplasty augmentation of osteoporotic vertebrae compared with the pullout strength of non-augmented vertebrae. Implantation of anterior vertebral body screws in cured cement is a satisfactory method. With this method we found a 1.4 times higher pullout strength than non-augmented vertebrae.

Bone Cements↗
PubMed2006

[Pullout resistance of conventional pedicle screw implantation in comparison to fluoroscopic computer-assisted technique].

AIM: Aim of the study was to compare pullout resistance of pedicle screws after conventional and fluoroscopic computer-assisted implantation in the cadaveric thoracic and lumbar spine. METHODS: Pedicle screws were inserted in a total of 10 vertebrae of different human specimens: 10 screws were placed using conventional technique (group 1) and 10 screws were inserted with fluoroscopic computer-assisted system contralaterally (group 2). Then pedicle screws were evaluated for biomechanical axial pullout resistance. RESULTS: Mean pullout force was 232 N (range 60-600 N) in group 1 and 353 N (range 112-625 N) in group 2. The difference was significant (p=0,0425). CONCLUSION: Fluoroscopic navigated implantation of pedicle screws increases the pullout strength in thoracic and lumbar cadaveric spines as compared with conventional methods.

Aged↗
PubMed2005

Micromotion in cemented rotating platform total knee arthroplasty: cemented tibial stem versus hybrid fixation.

INTRODUCTION: Improving the longevity and reliability of cemented total knee arthroplasty (TKA) remains a major step to achieve. It is still unclear, whether a cemented tibial stem reduces micromotion of the tibial tray and produces therefore a better initial stability or not. The higher conformity of rotating platform design and the possible rotary forces to the tibial platform may produce higher micromotion when the tibial stem remains cementless (hybrid fixation). MATERIALS AND METHODS: An in vitro study was performed using the PFC mobile bearing tibial tray (DePuy, Warswa, IN, USA) to test the hypothesis that the addition of cement surrounding the tibial stem reduces micromotion of the tibial tray in cemented TKA with mobile bearing design. Ten tibial trays with mobile design were implanted in sawbones with a 3-mm cement mantle beneath the baseplate of the tibial tray and with or without the cemented stem. Tibial trays were loaded additionally in the ventral, lateral, medial and posterior positions with 2,500 N using the Zwick Z010 instrumentation and HBM pick up Hottinger Baldwin. RESULTS: In this study, a significant increased mean maximum liftoff was found when only cementing the tibial baseplate (hybrid fixation), compared to the fully cemented tibial tray (P<0.02). CONCLUSION: In conclusion, the stem of mobile bearing tibial components should be cemented to provide increased micromotion and earlier loosening.

Arthroplasty, Replacement, Knee↗
PubMed2005

Biomechanical evaluation of a bioabsorbable expansion bolt for hamstring graft fixation in ACL reconstruction: an experimental study in calf tibial bone.

INTRODUCTION: The purpose of our study was to evaluate and compare the primary fixation strength of a novel bioabsorbable two shell expansion bolt (EB) with that of a well-established interference screw-fixation technique in hamstring reconstruction of the anterior cruciate ligament. MATERIALS AND METHODS: Thirty calf tibia plateaus (age 5-6 months) were assigned to three groups: In group I (n = 10) triple-stranded hamstring grafts were fixed with titanium interference screws (7 mm thread / 8 mm head x 25 mm). Specimens of group II (n = 10) received bioabsorbable poly-L-lactide interference screws (8 x 23 mm). In group III (n = 10), the grafts were fixed using bioabsorbable poly-D,L-lactide expansion bolts (5.8/8.5/10 mm x 35 mm). The tensile axis was placed parallel to the bone tunnel. The construction was then loaded until failure under a displacement rate of 1 mm per second. RESULTS: There were no significant differences concerning the maximum pullout force (group I: 357 N +/- 61; group II: 326 N +/- 92; group III: 343 N +/- 55). In case of the expansion bolt, we found the stiffness to be higher (61 N/mm) when compared to group I (48 N/mm), and group II (52N/mm) (P < 0.01 I vs. III). Using interference screws, we were able to demonstrate a strong correlation between torque and pullout forces (group I: r2 = 0.7; group II: r2 = 0.92). Ruptures of the suturing material occurred only in groups I and II. CONCLUSION: We conclude that hamstring graft fixation, using the presented expansion bolt, demonstrates fixation strength similar to the established screw fixation and can therefore be regarded as a reasonable alternative fixation method. Especially, since some specific disadvantages of screw fixation can be prevented by application of the bolt fixation.

Animals↗
PubMed2004

Influence of a mono-centric knee brace on the tension of the collateral ligaments in knee joints after sectioning of the anterior cruciate ligament--an in vitro study.

OBJECTIVE: To analyze the influence of knee bracing on the tension of the medial and lateral collateral ligaments in anterior cruciate ligament deficiency. DESIGN: The tension of the collateral ligaments in anterior cruciate ligament deficient knees was measured with and without knee bracing using an in vitro model. BACKGROUND: Anterior cruciate ligament deficiency increases the tension in both collateral ligaments at the knee joint. Therefore knee braces should reduce that tension increase. However, that effect has never been proven quantitatively. METHODS: After anterior cruciate ligament-transection, the forces of the medial (anterior/posterior part) and lateral collateral ligament were measured in ten fresh human cadaver knees at 0 degrees, 20 degrees, 40 degrees, 60 degrees, 80 degrees and 100 degrees of flexion, with and without application of a mono-centric knee brace. To quantify the ligament forces, strain gauges were fixed at the bony origins of the ligaments. RESULTS: Bracing led to a significant decrease of ligament forces (20-100 degrees: P < 0.0001) in the anterior part of the medial collateral ligament in all joint positions. In the posterior aspect, this effect was observed only at 40 degrees (P < 0.0001) and 80 degrees (P = 0.001) of flexion. In the lateral collateral ligament, bracing caused a strain reduction from 60 degrees to 100 degrees of flexion (P < 0.0001). Therefore a flexion angle dependent effect of knee bracing on the strain was seen in the posterior aspect of the medial and in the lateral collateral ligament in anterior cruciate ligament deficient knee joints. CONCLUSIONS: Application of a mono-centric knee brace leads to a significant position dependent reduction of collateral ligament tension after anterior cruciate ligament-rupture.

Anterior Cruciate Ligament Injuries↗
PubMed2004

Bioabsorbable expansion bolt fixation in anterior cruciate ligament reconstruction.

The current study evaluated initial fixation strength of a bioabsorbable expansion bolt compared with interference screw fixation in anterior cruciate ligament reconstruction using a bone-patellar tendon-bone graft. Thirty calf tibial plateaus with adjacent patella and extensor ligaments were used. Bioabsorbable poly-L-lactide interference screws were used for graft fixation in Group I, titanium screws in Group II, and bioabsorbable poly-DL-lactide expansion bolts were used in Group III. The mean force-to-failure (+/- standard deviation) in the three groups was 487 +/- 205 N, 713 +/- 218 N, and 594 +/- 224 N, respectively. The differences between Groups I and II were significant. No statistical differences were found regarding stiffness. Graft damage was significantly less in Group III compared with screw fixation. The fixation concept of an expansion bolt shows similar fixation strength and less graft damage compared with the established interference screw fixation. Because of the total absence of torque forces in contrast to bioabsorbable screws, the risk of implant breakage is minimized.

Absorbable Implants↗
PubMed2003

[Metal-on-metal pairs for hip prostheses].

Due to engineering deficiencies as well as problems in the basic material, the first generation of metal-on-metal hip prostheses was not up to standard.Furthermore, unsatisfying clinical results led to a decrease in the use of these prostheses.Nevertheless, there were several cases which demonstrated good results in long-term clinical outcome. After distinct improvements in manufacturing and materials, metal-on-metal prostheses have made a come back. This second generation, which are known mainly under the names METASUL and SIKOMET,have been in clinical use for up to 10 years and the good results found in biomechanical set ups seem to be confirmed in clinical trials. However, a possible disadvantage of this second generation of metal-on-metal hip prostheses might be the production of large amounts of particulate wear debris in the nanometer size range. Whether the great number of small size particles with an extended metal surface and the possible distribution of these particles in the body have biological effects on the cells and tissues (such as allergic or toxic reactions) remains unknown. Among the tribological problems, there is currently a discussion on the possible inflammatory effect of these metal particles, which might play a crucial role in longterm, systemic reactions of the body to metal particles.

Biomechanical Phenomena↗
PubMed2003

[Inflammatory responses to wear particles in vivo: a novel model in the murine knee joint].

Although it is now widely recognized that the inflammatory response to implant wear particles plays an important role in aseptic loosening of total joint replacements, the precise mechanisms of this process remain unclear. The aim of this study was to establish an animal model for the study of the adverse response to particulate wear debris and the effects on the synovial microcirculation as well as the leukocyte-endothelial cell interaction in the murine knee joint in vivo. Balb/c mice were injected with 50 microl of a 0.5-microm polystyrene particle suspension (0.1% v/v) into the knee joint. The severity of the inflammatory response was evaluated at days 1, 2, 3, 5, 7 (acute), 21 (intermediate), and 63 (chronic) after particle injection. Histological examination as well as assessment of the synovial microcirculation using intravital microscopy was performed. For the intravital microscopy measurements, the patella tendon was partially resected for visualization of the synovial tissue of the knee joint and the fluorescent markers FITC-dextran and rhodamine 6G were injected intravenously. There was a significantly enhanced leukocyte-endothelial cell interaction beginning at day 3 after particle injection with a maximum in the acute phase (days 5-7) and a subsequent decline in the intermediate (day 21) and chronic (day 63) phases. Functional capillary density was significantly increased from day 3 until day 21 after particle application. The histological examination showed an inflammatory reaction that complied widely with the temporal course of the microvascular parameters and resembled the histological appearance of the synovial-like membrane around loose joint prostheses. A novel model was established for the qualitative and quantitative investigation of the particle-induced inflammatory response in the joint environment. It was shown for the first time that there is a significantly enhanced leukocyte-endothelial cell interaction in the synovial tissue after intra-articular particle injection. This model seems to be suitable for further investigations, e.g., dealing with the biocompatibility of different particle materials.

Animals↗
PubMed2003

[Tibial malalignment of mobile-bearing prostheses--a simulator study].

Total knee replacement requires exact implantation in order to avoid long-term failure. Longitudinal in vivo studies of malaligned prostheses are problematic for ethical reasons. To assess the critical angle of tibial (varus/valgus) malalignment of knee prostheses in vitro, a simulator investigation was performed. Mobile-bearing prostheses were implanted in a simulator with 1-3 degrees valgus and varus malalignment as well as in a neutral position. More extreme malalignment caused unacceptable forces in the simulator. After each 500,000 cycles (ca. 0.5 years of walking) the replicas of the polyethylene inlay were examined and the extent of the tribocontact areas was measured until 1,500,000 total cycles. Finally the original polyethylene was examined with a scanning electron microscope. The polyethylene showed only abrasive wear without any fatigue effect. Tribocontact areas of 900-1500 mm(2) were observed under malalignment of mobile-bearing prostheses according to the manufacturer's specifications. With 1-3 degrees of malalignment, tribocontact areas were located at atypical polyethylene zones, but still showed abrasive wear only. Increasing malalignment due to a lift off of the femoral part of the prostheses with a strong torsional strength of the polyethylene made more extreme simulation impossible. Malalignment of 3 degrees could be suggested as maximum in vivo tolerability; perfect alignment with ideal implantation should be the goal. Soft tissue was given less consideration in this simulator study.

Bone Malalignment↗
PubMed2002

Tension changes in the collateral ligaments of a cruciate ligament-deficient knee joint: an experimental biomechanical study.

BACKGROUND: The biomechanical changes in the cruciate ligament-deficient knee are still widely unexplained. By producing a model of cruciate ligament insufficiency in the knee joint, we wanted to provide an experimental explanation for the great amount of secondary injuries to the knee joint after conservative treatment of an anterior cruciate ligament rupture. METHODS: The forces exerted on the medial and lateral collateral ligament were measured in ten fresh human cadaver knees. While simulating muscle force and body weight, the ligamentous loading patterns were determined before and after the anterior cruciate ligament was transected. The specimens were moved in a special apparatus from 0 degrees extension to 100 degrees flexion. Strain gauges were used to measure the ligament forces. They were fixed at the bony origins and insertions of the examined ligaments. The method allowed all ligamentous and capsular structures to be kept intact, thereby creating nearly physiological conditions by simulating muscular strength and axial force. RESULTS: During the quasistatic measurements, the relative changes of the ligament forces were determined from one angle position to the next. The variability of these relative values were very small among the ten specimens. The method yielded reproducible ligament force data. The values obtained in the intact knee joints were markedly similar to those reported in the literature. Cutting the anterior cruciate ligament led to a general increase of the ligament forces on both collateral ligaments. CONCLUSION: Our results show excess stress of the main ligamentous stabilisers after anterior cruciate ligament transection. This is an explanation for the secondary injuries often seen after conservative treatment of anterior cruciate ligament rupture as a result of impaired knee biomechanics.

Adult↗
PubMed2002

[Measuring ligament elasticity of the knee joint--elasticity measuring strip and its alternatives].

Those techniques for measuring ligament tension at the knee joint that are most commonly cited and easiest to carry out are discussed. These include four techniques based on the use of strain gauges. Apart from the Omega transducer and the buckle transducer, there is also the tendon force transducer, and the application of strain gauges to the bony ligament insertion sites. Other indirect measuring methods considered are the mercury strain transducer and the Hall effect transducer. The parameter measured with all of these methods is fluctuating current or voltage, which is then correlated with ligament tension. Three direct measurements are also discussed: the separation distances of marked fibres of the ligaments, replacement of fibres by threads, and a load cell/bone plug construction. The measured value is equated with the effective change in ligament length.

Animals↗
PubMed2001

A model for assessing the rotational stability of uncemented femoral implants.

Permanent secondary stability of the uncemented femoral stem of hip prostheses can only be achieved once primary rotational and axial stability has been ensured. Rotational stability means that the stem is resistant to the articular forces that induce rotation around the implant's longitudinal axis. The 10-year survival rates of two uncemented conical shaped stems with decisively different proximal shapes were significantly different (Schenker SK 63.9%, Zweymüller SL 97.0%). The shapes were analyzed biomechanically by testing rotational stability in a silicone model. A reduction in the mediolateral height of the metaphyseal part by one-third led to a 20% smaller angle of ascent (P < 0.01), which indicated lower resistance. The proximally broader (mediolateral) prosthesis therefore proved to have better rotational stability. The study confirms that aseptic stem loosening is attributable to the design of the proximal part of the prosthesis.

Arthroplasty, Replacement, Hip↗
PubMed2001

[A new ISO/FDIS 14242-1 compatible hip prosthesis simulator: E-SIM].

The continuing development of new, highly sophisticated materials for the articulating surfaces of total hip endoprostheses involves the need for testing, not only of biocompatibility and dynamic loadability, but also of tribological properties (friction, wear, lubrication). For decades, the wear resistance of these materials has been tested in wear simulators. In consequence of the currently often widely differing test methods, the technical committee (TC 150) of the ISO (International Organization for Standardization) has been concerned to develop an International Standard (ISO/FDIS 14242 1 and 2: Implants for Surgery--wear of total hip joint prostheses--on the basis of kinetic and kinematic data from gait analysis. This new standard will be the basis for ensuring the comparability of scientific data obtained from tribological testing of total hip endoprothesis. The new hip simulator, E-SIM, presented in this paper, complies with the currently published FDIS (Final Draft International Standard), and enables testing in accordance with these specifications.

Equipment Failure Analysis↗
PubMed2000

Biomechanical investigations on chondromalacia of the knee after meniscal flap lesion and partial meniscal resection: an experimental model.

Meniscal tears and resections may cause chondral lesions of the knee. To eliminate muscular control during investigation of this problem, we designed a biomechanical setup based on a knee-joint simulator, ensuring physiological, free-motion mobility of the joint. Fresh human knee specimens with intact cartilage were exposed to loads to 2,000 N at a frequency of 0.85 Hz during 48 hours of gait. After a preliminary test series, 18 specimens were divided into three groups: group I was tested with unchanged meniscal status, group II with arthroscopically induced mobile flap tears at the posterior horns of the menisci, and group III after partial resection of the posterior horns. Motion patterns between the groups changed after as little as a few hours due to increased translation in group III. Macroscopic and histological examination and scanning electron microscopy revealed severe chondromalacic changes after meniscal resection. We conclude that meniscal resection-however partial-may have considerable joint-damaging potential if muscle control is lacking whereas mobile flap tears maintain stability. Our findings might explain the differences in clinical reports on cartilage status after partial meniscal resection. This study underlines the importance of muscle training when active stabilisation of the knee is reduced after partial meniscal resection.

Adult↗
PubMed2000

[Autologous meniscus replacement with rib perichondrium. Experimental results].

The purpose of our study was to examine the potential of autologous perichondrial tissue to form meniscal replacements. Eighteen mature sheep were used. In 12 animals a complete meniscal resection was performed; replacement was formed using strips of autologous perichondrial tissue explanted from the lower rib; six animals with a complete meniscal resection but without any replacement served as controls. In all animals restriction from weight-bearing was achieved by means of transsection and partial achillestendon resection. Six animals each, 4 of group T and 2 of group C, were sacrificed after 3, 6 and 12 months. Perichondrial grafts and the underlying articular cartilage were removed and investigated by gross macroscopic examination, by means of light and scanning electron microscopy, polarized light examination, and biomechanical tests evaluating the failure stress and tensile modulus. In all transplanted animals a new perichondrial meniscus developed. After 3 months the transplants resembled in size and thickness normal menisci, while in the control animals only small rims of spontaneously grown tissue were detectable. Microscopically, the perichondrial menisci exhibited similarity to normal collagen fiber orientation and cellular characteristics, but, in their central region, areas of calcification disturbed the regular tissue differentiation. In contrast, spontaneously grown tissue in control animals lacked normal fiber orientation and cellularity. Scanning electron-microscopy of perichondrial menisci revealed surface characteristics similar to normal sheep menisci without fissures and lacerations, while the control specimens exhibited such defects. The femoral and tibial cartilage being in contact with the new menisci showed normal surface characteristics apart from one animal with slight surface irregularities. Control animals showed superficial lesions after 3 months, and the extent increased from 6 to 12 months postoperatively. Exemplary microangiographies of the newly grown tissue exhibited a less intense vascularisation after three months when compared to normal menisci with an improving tendency after 6 and 12 months. Biomechanically, values of the failure stress as well as of the tensile modulus of perichondrial menisci were significantly lower than those of normal contralateral menisci. But, spontaneously regenerated tissue in meniscectomized animals exhibited even smaller values also with significant differences towards original menisci. There were no significant differences in values of newly grown perichondrial menisci and spontaneously grown tissue.

Animals↗