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At least 1,405 records · Page 78Linked to original sources
PubMed2006

A kinematic comparison of fixed- and mobile-bearing knee replacements.

Mobile-bearing posterior-stabilised knee replacements have been developed as an alternative to the standard fixed- and mobile-bearing designs. However, little is known about the in vivo kinematics of this new group of implants. We investigated 31 patients who had undergone a total knee replacement with a similar prosthetic design but with three different options: fixed-bearing posterior cruciate ligament-retaining, fixed-bearing posterior-stabilised and mobile-bearing posterior-stabilised. To do this we used a three-dimensional to two-dimensional model registration technique. Both the fixed- and mobile-bearing posterior-stabilised configurations used the same femoral component. We found that fixed-bearing posterior stabilised and mobile-bearing posterior-stabilised knee replacements demonstrated similar kinematic patterns, with consistent femoral roll-back during flexion. Mobile-bearing posterior-stabilised knee replacements demonstrated greater and more natural internal rotation of the tibia during flexion than fixed-bearing posterior-stabilised designs. Such rotation occurred at the interface between the insert and tibial tray for mobile-bearing posterior-stabilised designs. However, for fixed-bearing posterior-stabilised designs, rotation occurred at the proximal surface of the bearing. Posterior cruciate ligament-retaining knee replacements demonstrated paradoxical sliding forward of the femur. We conclude that mobile-bearing posterior-stabilised knee replacements reproduce internal rotation of the tibia more closely during flexion than fixed-bearing posterior-stabilised designs. Furthermore, mobile-bearing posterior-stabilised knee replacements demonstrate a unidirectional movement which occurs at the upper and lower sides of the mobile insert. The femur moves in an anteroposterior direction on the upper surface of the insert, whereas the movement at the lower surface is pure rotation. Such unidirectional movement may lead to less wear when compared with the multidirectional movement seen in fixed-bearing posterior-stabilised knee replacements, and should be associated with more evenly applied cam-post stresses.

Arthroplasty, Replacement, Knee↗
PubMed2004

Use of the Dumon Y-stent in the management of malignant disease involving the carina: a retrospective review of 86 patients.

OBJECTIVE: To study the efficacy of symptom relief and the safety of the Dumon Y-stent for central airway obstruction in malignant main carinal involvement and in malignant tracheoesophageal fistulas. DESIGN: A retrospective review. SETTING: Thoracic endoscopy referral center. PATIENTS AND METHODS: The medical records of 86 patients who had undergone the placement of a Dumon Y-stent at our institution were reviewed and analyzed. RESULTS: Ninety Dumon Y-stents were placed in 86 patients to relieve symptoms of dyspnea, cough, and/or hemoptysis. Four of these patients required removal of that stent and replacement with a longer Dumon Y-stent due to tumor progression. There were only two instances of procedure-related adverse effects, which included coughing following stent placement lasting 1 week in one patient and stent migration in another patient. In the case of stent migration, the stent required immediate removal, and the patient experienced no adverse consequences. The remaining patients tolerated the stent well, and all experienced subjective symptomatic relief. There were no stent-related deaths. The average duration of a stent after placement was 133 days. The median time of survival following stent insertion was 181 days. Forty-five percent of all patients died at 3 months, and 72% died at 6 months. CONCLUSION: The Dumon Y-stent proved to be useful and was well-tolerated in the management of malignant disease involving the main carina. It also provided successful palliation in patients with malignant tracheoesophageal fistulas.

Adult↗
PubMed2002

Solving the frustrations of crown cementation.

Restoration cementation is a routine procedure, but it commonly is accomplished improperly. In this article, I have discussed several of the most frequently occurring problems with restoration cementation and have made suggestions about how to prevent them.

Cementation↗
PubMed1997

[Effect of integrated distance studs on cement thickness of implanted PE-acetabulum cups--experimental in vitro studies for improved cementing technique].

Variations in cement thickness between PE cups and acetabular bone are biomechanically unfavourable, and may contribute to prosthetic loosening. Integrated distance studs should in the first instance, prevent local thinning of the cement. In an experimental study we compared the thickness of the cement mantel of implanted PE cups without such studs. In the case of cups with studs, significantly fewer areas of thin cement (0-1 mm) were found in comparison with cups with no studs. "Bald" areas of cement (0-0.2 mm) were virtually prevented by the studs. We are of the opinion that PE cups with integrated studs on the surface ensure a uniform cement thickness around the cup, as well as decreasing the risk of "bald" areas in the cement, thus reducing loosening.

Acetabulum↗
PubMed1997

[Designing the construction of an FE model exemplified by the knee joint].

For the scientific investigation of the problems encountered in joint arthroplasty, routine use is made of clinical follow-up of patients, studies on cadaver specimens, and simulation with the aid of technical or mathematical models. An appropriate method for the stress analysis of the musculoskeletal system is the finite element method (FE method), since it is free from any restrictions in terms of the geometry of the structure to be studied. The development of a finite element model of the knee joint on the basis of computer tomography data is described. Using this method, intra-osseous stress distribution within the bones, contact stresses and the articulating surfaces between bones and implants for various boundary conditions can be calculated. For the development of such an FE model, the exterior and interior structure/geometry of the bones and implants, and the muscular forces involved, must be known. With this in mind, a method enabling the determination of surface coordinates of the knee joint from CT scans is presented. Using the special CAD-FE program I-DEASTM, plane slices and then the 3D CAD model are generated from these coordinates. After appropriate processing, the CAD model can be meshed with tetrahedral or brick elements.

Biomechanical Phenomena↗
PubMed2002

[The HEPFIEx simulator, a device for determination of friction between femur head prosthesis and cartilage].

We describe a device designed to investigate friction between various femoral head prostheses and human acetabula. It enables not only the determination of friction and the relevance of the play between the femoral head and acetabulum, but also the evaluation of the kinematic behaviour of bipolar prostheses. In the simulator, the various femoral head prostheses are placed on a special cone and tested against a human cadaveric acetabulum. The swiveling range of the device is uniaxial, and the swiveling angle is +/- 35 degrees. The maximum force produced pneumatically is 5kN. Testing of the simulator with a TEP was successful and friction-coefficients of < 0.1 were measured, as are reported in the literature.

Acetabulum↗
PubMed2002

A CMOS clock and data recovery circuit for intraocular microsystems.

This paper presents the implementation of a clock and data recovery circuit (CDR) for intraocular microsystems. The CDR was designed to minimize chip area and power consumption and to recover the clock and data signals from the incoming data stream. Since the CDR has been designed without any external components it is well suited for being integrated in an intraocular microsystem. Simulation results show that this CDR works with power dissipation of less than 2.4 mW with a single 3.3 V power supply. The simulations are based on a 0.6 micron n-well CMOS single-polysilicon, three-metal technology.

Blindness↗
PubMed2002

Bifocal ultra thin intraocular lens--optical properties and clinical results.

The therapy of the cataract with the implantation of intraocular lenses is a great success story over the last 20 years. However cataract patients cannot accommodate anymore and need additional glasses for the far and near view. In the last 10 years bifocal concepts for intraocular lenses have been investigated with little success. Our new bifocal diffractive bifocal lens showed in clinical trials with 150 Patients an excellent visual performance. Less than 10% of the patients still use additional glasses. Due to the diffractive principle the lens can be manufactured very thin. Therefore the lens can be easily implanted through very small incisions. The lens shows the potential for the replacement of multifocal glasses.

Humans↗
PubMed2002

Transpositioned flap vestibuloplasty combined with implant surgery in the severely resorbed atrophic edentulous ridge.

The use of transpositioned flap (lipswitch) vestibuloplasty combined with implant surgery in patients with severely resorbed atrophic edentulous ridges is reviewed. The cases of 17 patients with severely resorbed atrophic edentulous ridges at the mandible undergoing implant rehabilitation were reviewed. Lipswitch vestibuloplasty was followed immediately by the implant surgery. Postoperative follow-up consisted of clinical and radiographic examinations. Seventeen patients with atrophic ridges (12 class II and 5 class III) each had 2 implant fixtures placed in the mandible as abutments for a clip and bar overdenture. The average time of follow-up was 6 years. Before surgery, all patients had severely atrophic ridges with a compromised shallow vestibule of varying degrees. Satisfactory results were observed in regard to the immediate and long-term morphology of the vestibule, the health of the peri-implant tissue, the stability of implant fixtures, and the functionality of the prostheses. The lipswitch vestibuloplasty offers a safe and convenient method of surgical access for implant fixture installation, with the advantage of rebuilding the vestibule of a compromised atrophic ridge in the anterior mandible.

Atrophy↗
PubMedDate not supplied

Efficacy of shock-absorbing versus rigid pylons for impact reduction in transtibial amputees based on laboratory, field, and outcome metrics.

Prosthetic manufacturers have marketed shock-absorbing pylons (SAPs) for attenuation of injurious loads from foot-ground contact. In this study, we compared a commonly prescribed SAP with a conventional rigid pylon, using a within-subject design (n = 15 unilateral transtibial amputees), to assess effect on gait mechanics, measure transmitted accelerations in situ, and determine functional outcomes using step counts and questionnaires. No differences were found across pylons for self-selected walking speed, prosthetic-side step length, prosthetic-side loading rate and decelerative peak of the vertical ground reaction force, peak pylon acceleration, step count per week, or questionnaire results that examined pylon performance and subjects' pain and fatigue levels. The only statistically significant finding was for the prosthetic-side knee angle at initial contact, where subjects displayed an average of 2.6 degrees more flexion with the rigid pylon than the SAP while walking at a controlled speed (p = 0.004); this result indicates that transtibial amputees are able to modulate the effective stiffness of their residual limb in response to changes in prosthetic component stiffness. The results from the laboratory, field, and subjective outcome measurements suggest that the SAP in this study is as effective as a rigid pylon for unilateral transtibial amputees.

Activities of Daily Living↗