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At least 55 records · Page 3Linked to original sources
PubMed2001

[Influence of prosthesis design on intramedullary pressure formation in femur shaft implants of cemented hip endoprostheses].

The increase of intramedullary femoral pressure can lead to the intravasation of bone marrow and fat cells into the blood stream of the femoral vein and consequently into the pulmonary circulation. This effect is the same in intramedullary nailing and in the implantation of femoral stem prostheses. In a prospective study we evaluated the intraoperative, intramedullary pressure in the distal femur during the implantation of femoral stem prostheses with two different designs. In eight patients we implanted Müller straight stems and in another eight we implanted stem type Option 3000. Intramedullary pressure was recorded continuously by the implantation of a microtip pressure probe (piezoresistive principle, 50 Hz) in the distal femur. We found markedly higher pressure in Müller straight stem prostheses: range: 590-2,570 mmHg (median = 1,293, SD = 627 mmHg). Intramedullary pressure in stem prosthesis type Option 3000 was much lower: range: 59-574 mmHg (median = 289, SD = 219 mmHg). The differences were statistically significant (p = 0.0008). By changing the designs of femoral stem prostheses, the intramedullary pressure can be markedly reduced. In the case of elderly patients or those with pulmonary illness we recommend femoral stem prosthesis designs, which induce little increase in the intramedullary pressure, in order to reduce cardiopulmonary complications.

Bone Cements↗
PubMed1995

Evaluation of temporomandibular joint prostheses: review of the literature from 1946 to 1994 and implications for future prosthesis designs.

PURPOSE: This article describes the useful elements of applied temporomandibular joint (TMJ) prostheses and discusses the factors necessary to be addressed in an appropriate TMJ prostheses design. MATERIALS AND METHODS: Information about TMJ prostheses was gathered by a literature search. Only designs with the primary intention of true joint replacement were selected. The designs were divided in fossa-eminence, condylar, and total joint replacements, which are reviewed separately. RESULTS: A fossa-eminence prosthesis can be fixed by a metal plate screwed to the root of the zygomatic arch. A condylar prosthesis can be fixed by a metal plate screwed to the mandibular ramus and fitted by bending the plate or using different sizes. All reviewed designs resulted in a loss of translational movements of the mandible, especially in an anterior direction. Although the recent designs use the same materials as are used in hip and knee joint prostheses, the wear properties of the existing TMJ prostheses are still unknown. CONCLUSIONS: A future prosthesis must imitate the anterior movement of the mandible when the mouth is opened and also allow some mediolateral movement. The fitting to the skull is still a major problem, as is the combination of the required motions and low wear rates. To confirm good clinical performance of a new TMJ prosthesis, long-term follow-up studies are necessary.

Evaluation Studies as Topic↗
PubMed1981

A magnetically augmented elbow prosthesis: design and biomechanical evaluation.

Magnetically augmented joint prostheses are a relatively new concept. A prototype of an elbow prosthesis with a magnetically constrained axis was designed by the authors and subjected to various tests. It demonstrated greater stability than nonhinged devices. The magnetic bearing reduces the tensile and rotatory forces on the prosthetic fixation that occur with a constrained hinge device, thus preventing loosening and breakage.

Biomechanical Phenomena↗
PubMed2000

Kinematic analysis of total knee prosthesis designed for Asian population.

In designing a total knee replacement (TKR) prosthesis catering for the Asian population, 62 sets of femur were harvested and analyzed. The morphometrical data obtained were found to be in good agreement with dimensions typical of the Asian knee and has reaffirmed the fact that Caucasian knees are generally larger than Asian knees. Subsequently, these data when treated using a multivariate statistical technique resulted in the establishment of major design parameters for six different sizes of femoral implants. An extra-small implant size with established dimensions and geometrical shape has surfaced from the study. The differences between the Asian knees and the Caucasian knees are discussed. Employing the established femoral dimensions and motion path of the knee joint, the articulating tibia profile was generated. All the sizes of implants were modeled using a computer-aided software package. Thereupon, these models that accurately fits the local Asian knee were transported into a dynamic and kinematic analysis software package. The tibiofemoral joint was modeled successfully as a slide curve joint to study intuitively the motion of the femur when articulating on the tibia surface. An optimal tibia profile could be synthesized to mimic the natural knee path motion. Details of the analysis are presented and discussed.

Aged↗
PubMed1989

Mathematical shape optimization of hip prosthesis design.

The long-term success of artificial-joint replacement depends partly on the chances for acrylic cement failure and interface disruption. These chances can be diminished by an optimal load-transfer mechanism, whereby stress concentrations are avoided. The present paper introduces a method for numerical shape optimization, whereby the finite element method is used iteratively to determine optimal prosthetic designs, which minimize interface stresses. The method is first applied in a simplified one-dimensional model of a cemented femoral stem fixation, using acrylic cement. The results show that 30-70% cement and interface stress reductions can be obtained in principle with an optimized design. Although the actual optimal shape is susceptible to the characteristics of the joint load, the stem length, stem modulus, cement modulus and bone properties, its general geometrical characteristics are consistent, featuring proximal and distal tapers, and a belly-shaped middle region. These general characteristics are confirmed in a more realistic two-dimensional FEM model. It is concluded that this method of shape optimization can provide a meaningful basis for prosthetic design and analysis activities in general.

Bone Cements↗
PubMed1998

Hip joint prosthesis design: effect of stem introducers.

The stress levels in the femoral component of a total hip prosthesis (Corin Taper Fit, Corin Medical Ltd, Cirencester, Gloucestershire, UK) were calculated by finite element (FE) analysis. This prosthesis has two holes drilled in the shoulder to engage a stem introducer. There were no unacceptable stress levels around these holes. Instead the maximum stresses were around the periphery of the shaft of the stem, as has been observed for FE analyses of conventional designs. Three prostheses were also subjected to cyclic mechanical testing (peak load 2.3 kN) according to the appropriate British Standard. The holes were examined for cracks, before and after testing, by stereomicroscopy. All three specimens were able to withstand 5 million loading cycles with no evidence of damage. Thus it is possible to design a femoral component with holes in the shoulder, to accommodate a stem introducer, without creating unacceptable stress concentrations.

Computer Simulation↗
PubMed2005

Tubular heart valves: a new tissue prosthesis design--preclinical evaluation of the 3F aortic bioprosthesis.

BACKGROUND: It was hypothesized that native heart valves function as if they were simple tubes with sides that collapse when external pressure is applied. Because "form follows function," this hypothesis could theoretically be confirmed by implanting a simple tube into the anatomic position of any native heart valve and documenting that under the same anatomic constraints and physiologic conditions as the native valve, the tube would assume the form of that native valve. If the hypothesis were thus proved, it would follow that a tissue valve based on a tubular design would have superior flow dynamics and stress distribution and would therefore be expected to outlast currently available tissue valves. Such a tubular tissue valve, the 3F Aortic Bioprosthesis (3F Therapeutics, Inc, Lake Forest, Calif) was designed and tested in vitro against a commercially available stentless aortic bioprosthesis. METHODS: With the use of state-of-the-art testing equipment, some of which had to be developed especially to test this truly stentless bioprosthesis in vitro, transvalvular gradients, effective orifice areas, degree of transvalvular laminar flow, finite element analysis of the distribution of leaflet stress, and accelerated wear testing for long-term durability were evaluated for the new 3F Aortic Bioprosthesis in comparison with the St Jude Medical Toronto SPV aortic bioprosthesis (St Jude Medical, Inc, St Paul, Minn). RESULTS: The valve gradients were lower and the effective orifice areas were greater for the 3F Aortic Bioprosthesis at all valve sizes and under all test conditions, including cardiac outputs ranging from 2.0 to 7.0 L/min, mean perfusion pressures from 40 to 200 mm Hg, and aortic compliances of 4% and 16%. The transvalvular flow across the 3F Aortic Bioprosthesis in vitro was qualitatively smooth, with a minimum of surrounding vortices. Maximum stress occurred in the belly of the leaflets of the 3F Aortic Bioprosthesis, with minimum stress at the commissural posts. The 3F Aortic Bioprosthesis was superior to the Toronto SPV valve in accelerated wear tests. CONCLUSIONS: These in vitro studies show that a tissue aortic valve designed on the basis of the proved engineering principle that form follows function has better hemodynamics, flow dynamics, stress distribution, and durability when compared under identical in vitro conditions with an excellent commercially available tissue aortic valve.

Biomechanical Phenomena↗
PubMed1993

[Amputation and prosthesis design in severe congenital defects of the lower extremity (case reports)].

The author presents an account of three patients with severe congenital defects of the lower extremities who relied on a long-term basis on complex prosthetic appliances. In the mentioned patients the author amputated part of the malformed extremity in such a way as to preserve the "plantar" stump and it was thus possible, when solving the technical aspects of the appliance, to improve also the cosmetic covering of the defect.

Adolescent↗
PubMedDate not supplied

Artificial disc prosthesis: design concepts and criteria.

Clinical and biomechanical objectives of disc arthroplasty are reviewed in this paper. The available literature relative to these criteria for nucleus and total disc replacement where relevant is also reviewed. Clinical criteria include: pain relief, functional recovery, lower morbidity than spinal fusion, shorter recuperation, and ease of implantation and revision. Biomechanical criteria include: preservation of motion in compression-bending and compression-torsion, shock absorption, relief of abnormal stresses within and adjacent to the motion segment, stability, and alignment. A review of devices with these criteria in mind is reported.

Arthroplasty, Replacement↗
PubMed2002

The use of biomechanical orthodontic treatment concepts for removable appliances in maxillofacial prosthodontics. Part I: review of prosthesis design principles.

Maxillary cuspids are commonly included in ablative block resections in maxillectomy patients. Although the remaining incisors are poor abutments for interim or definitive obturators, they must be used if adequate retention and support is to be achieved. Orthodontic biomechanical concepts for removable appliances offer solutions for the treatment of these patients. The proper application of these concepts can improve retention, support, and force distribution to the anterior teeth and is particularly useful in younger patients when long-term maintenance of teeth is critical. The purpose of this article is to describe the rationale for this approach and its application to interim and definitive Aramany Class I and II obturators.

Biomechanical Phenomena↗
PubMed2003

The spectrum of prosthesis design for primary total knee arthroplasty.

Many types of prostheses are currently used for total knee arthroplasty. Controversy exists, however, regarding which prostheses are the most appropriate for use by individual surgeons and specific patient groups. Six types of prostheses are currently being used in the United States for primary total knee arthroplasty: posterior cruciate ligament-retaining prostheses; posterior cruciate ligament-substituting prostheses; prostheses with ceramic components; mobile-bearing prostheses; nonmodular, compression-molded polyethylene prostheses; and medial-pivot prostheses. The historical and current result of using these different types of prostheses are discussed, and the indications, contraindications, and recommendations for each type are delineated.

Anterior Cruciate Ligament↗
PubMed1994

[Cementless hip prosthesis design: a basic study and analysis of the proximal femur in normal Japanese people].

Using CT images the proximal part of 50 femora was morphologically analysed in 28 normal Japanese adults. The purpose was to determine the normal stem size and shape in order to manufacture an artificial hip joint. The results were as follows: 1) The periosteal shape and the size of the normal femur were proportional. 2) The endosteal shape and the size of the normal femur were less proportional than the periosteal shape and size. 3) The endosteal width 20 mm distal from the lesser trochanter of the normal femur was 18.2 +/- 2.7 mm. 4) The femoral head offset of the normal femur was 41.8 +/- 4.8 mm. 5) The taper angle was 4.9 degrees on average, but the tapering of the proximal medullary canal was different from the tapering of the distal medullary canal.

Adolescent↗