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At least 199 records · Page 11Linked to original sources
PubMed2007

Auditory midbrain implant: a combined approach for vestibular schwannoma surgery and device implantation.

HYPOTHESIS: The lateral suboccipital approach is a well-established route for safe removal of vestibular schwannomas in neurofibromatosis Type 2 (NF2) patients. The goal of this study was to assess if this approach can be extended to a lateral supracerebellar infratentorial approach to enable insertion of an auditory midbrain implant (AMI) penetrating array along the tonotopic gradient of the inferior colliculus central nucleus (ICC). BACKGROUND: The AMI is a new auditory prosthesis designed for penetrating stimulation of the ICC in patients with neural deafness. The initial candidates are NF2 patients who, because of the growth and/or surgical removal of bilateral acoustic neuromas, develop neural deafness and are unable to benefit from cochlear implants. The ideal surgical approach in NF2 patients must first enable safe removal of vestibular schwannomas and then provide sufficient exposure of the midbrain for AMI implantation. METHODS: This study was performed on formalin-fixed and fresh cadaver specimens. Computed tomography scan and magnetic resonance imaging were used to study the heads of the specimens and for surgical navigation. RESULTS: The lateral suboccipital craniotomy enabled sufficient exposure of the cerebellopontine angle and internal auditory canal for tumor removal. It could then be extended to a lateral supracerebellar infratentorial approach that provided good exposure of the dorsolateral aspect of the tentorial hiatus and mesencephalon for implantation of the AMI along the tonotopic gradient of the ICC. This approach did not endanger the trochlear nerve or any major midline venous structures in the quadrigeminal cistern. CONCLUSION: This modified lateral suboccipital approach ensures safe removal of large vestibular schwannomas and provides sufficient exposure of the inferior colliculus for ideal AMI implantation.

Auditory Brain Stem Implants↗
PubMed1994

An intrapleural lung prosthesis: rationale, design, and testing.

Extracorporeal life support (ECLS or ECMO) is standard treatment for severe respiratory failure but poses many contraindications to future lung transplantation. The solution to this dilemma is the implantable gas exchange device (IGED) or artificial lung. Preliminary efforts to create such an artificial lung have been made since 1970 and include designs involving single devices, intravascular devices (i.e., IVOX), and combination heart-lung devices. Stringent requirements govern the design of such a device, the most important of which are high gas exchange efficiency, low resistance to blood flow, and size. This paper describes such a device. It incorporates large diameter inflow and outflow ports in close proximity and a low resistance wound hollow fiber core encapsulated in a compliant outer shell which conserves the work of the right ventricle. In a large animal model (adult sheep) this device was connected in line with the main pulmonary artery in series with the native lungs. This configuration has the advantages of using the lungs as an embolic filter, perfusing the lungs with fully oxygenated blood, and maintaining the integrity of the anatomy necessary for transplant. Laboratory experiments have run > 8 h. Preliminary data show that the animals have remained hemodynamically stable while the devices have supported the animals completely by supplying 100% O2 saturation with PO2 values ranging from 250-350 mm Hg. Additionally, this model makes possible the study of respiratory failure without introducing other variables such as extracorporeal circuits or pumps. The other metabolic, endocrine, and reticuloendothelial functions of normal and injured lungs can now be studied more precisely by excluding these variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Knee biomechanics and total knee replacement.

The biomechanics of the knee joint provide an important basis for the rationale in the design and selection of appropriate total knee arthroplasty. This article examines knee biomechanics in terms of patient function, prosthesis design, cruciate ligament retention, alignment, and fixation of the tibial component. While design and surgical technique for total knee replacement progress, a better understanding of the characteristics of joint loading, stress distribution, and the biologic response of bone to stress will provide the potential to improve both function and implant longevity.

Biomechanical Phenomena↗
PubMed1981

Photoelastic stress analysis of hemimandibulectomy bone reconstruction devices.

The results presented show the relative importance of muscle force and occlusal resistance locations and prosthesis/hemimandible interface length. For the prosthesis design used, the addition of muscle function on the prosthesis side has little effect upon bone stress. However, occlusal resistance on the prosthesis side produces much more stress in the bone than other resistance positions. Stress produced by the shorter prosthesis is higher at the areas of bolt/bone interface than for the long prosthesis. However, superimposed inherent stress patterns somewhat obscured the comparison with longer prostheses.

Dental Stress Analysis↗
PubMed2005

[Use of a composite prosthesis (PL-PU99) versus a biological prosthesis (Surgisis) in an experimental model of temporary abdominal closure].

INTRODUCTION: In some diseases of peritoneal origin, temporary closure of the abdominal cavity is required to avoid compartmental syndrome. This allows normal intra-abdominal pressure to be maintained and the fascial edges to be preserved for subsequent definitive closure. MATERIAL AND METHOD: Defects (7 x 4 cm) were created in the anterior abdominal wall of New Zealand white rabbits and were repaired using an oval-shaped patch of a prosthesis designed by our team (PL-PU99) or a prosthesis of biological origin (Surgisis) of similar dimensions to the defects. The biomaterials were fixed to the cut edges of the wall by 2 polypropylene running sutures interrupted only at the corners, leaving the patch in contact with the atmosphere. Fourteen days after implantation, prosthesis/anchorage tissue specimens were taken for light and scanning electron microscopy, morphometric measurements and immunohistochemical macrophage identification (using the RAM-11 antibody). RESULTS: There were no cases of mortality or implant rejection. Small areas of loose adhesions were observed on some implants (covering 0.31 +/- 0.03% of the PL-PU99 implants and 31.60 +/- 7.35% of Surgisis). The neoperitoneum induced by both implant types was homogenous and well organized, with thicknesses of 427.60 +/- 8.38 microm (PL-PU99) and 171.99 +/- 18.70 microm (Surgisis). No significant differences were observed in terms of the macrophage reaction induced (PL-PU99 19.76 +/- 1.59%; Surgisis 21.07 +/- 8.93% macrophages). CONCLUSIONS: a) The PL-PU99 prosthesis provoked fewer adhesions and generated a thicker neoperitoneum. b) Both prostheses would probably be suitable for temporary closure of the abdominal cavity.

Abdominal Wall↗
PubMed1997

Design, maintenance and biomechanical considerations in implant placement.

Successful treatment using implants involves careful consideration of fixture placement and prosthesis design if the biomechanical conditions are to be optimized. These parameters may be related to the implant/tissue interface at the individual fixture level, and thence to the relationship between the components of a prosthesis. The influence of the nature and magnitude of occlusal forces can also be significant and should be carefully assessed before placement.

Biomechanical Phenomena↗
PubMed1991

Adaptation of NASA technology for the optimum design of orthopedic knee implants.

NASA technology originally developed for designing aircraft turbine-engine blades has been adapted and applied to orthopedic knee implants. This article describes a method for tailoring an implant for optimal interaction with the environment of the tibia. The implant components are designed to control stresses in the bone for minimizing bone degradation and preventing failures. Engineers expect the tailoring system to improve knee prosthesis design and allow customized implants for individual patients.

Aerospace Medicine↗
PubMed1990

New design of hip prosthesis using carbon fibre reinforced composite.

We present a new design for a hip prosthesis using polyethylene-hydroxyapatite, a composite material with layered stiffness and good bone compatibility. In order to overcome the low stiffness of the matrix, carbon fibre reinforcement is suggested. This new collarless prosthesis was designed to give maximum stiffness at the core and lower stiffness at the bone-implant interface. For this design a 2D finite element analysis was undertaken; its results were compared with those for a titanium alloy prosthesis. The effect of the variation in the collar stiffness was also analysed.

Carbon↗
PubMed2003

Excellent results of HA coating on a grit-blasted stem: 245 patients followed for 8-12 years.

We report the outcome of a grit-blasted titanium stem designed for press-fit insertion and entirely plasma sprayed with HA. During the years 1988-1993, we performed 323 primary total hip replacements in 276 patients (189 women) with a HA-coated prosthesis. Their mean age was 48 (15-79) years. During the follow-up, 12 patients died. 19 other patients did not attend the follow-up examination, but had no major symptoms according to telephone interviews and written replies. Thus, 245 patients (291 hips) were followed for a mean of 10 (8-12) years with radiographic and clinical examinations. Only 1 stem was revised due to mechanical failure. None were revised because of infection. Osteolysis was significantly associated with wear, and wear was significantly associated with the size of the femoral head. We found a small amount of proximal bone loss (37/291) and a low incidence of distal hypertrophy of the bone (23/291). These observations indicate an essentially physiological weight distribution from the stem to the femoral bone. The changes in the bone confirmed that the femoral component was well fixed in asymptomatic patients. To conclude, we found excellent 8-12-year results with a fully HA-coated femoral prosthesis designed for press-fit insertion.

Adolescent↗
PubMedDate not supplied

Implant-supported removable overdentures in the edentulous maxilla: clinical and technical aspects.

PURPOSE: The aim of this article is to describe the indication criteria and the treatment planning for a maxillary implant-supported removable overdenture. Prostheses are designed according to the requirements of the bar system and the factors influencing the extension of the prosthesis base. MATERIALS AND METHODS: The decisive factors in determining whether a bar-retained overdenture prosthesis is indicated should be evaluated during the initial clinical examination and with the help of a reformatted computed tomographic (CT) scan that is performed with a radiologic template in place. Titanium markers represent the ideal location of the denture teeth in the diagnostic setup so that the implant position can be selected and the available space for the bar system can be assessed vertically and horizontally. RESULTS: For the overdenture prosthesis that is solely implant supported 6 to 8 implants are placed ideally at a distance of about 10 to 14 mm from center to center. A prefabricated bar system that allows the clips to be inserted between the implants can then be used. When the available bone restricts implant placement to adjacent tooth positions an individually milled bar that includes additional frictional pins and/or retentive elements needs to be planned. The prosthesis design, in particular its buccal and palatal flange extension, is determined during setup try-in, taking into account the patient's smile line, their need for facial support, and their phonetic requirements. CONCLUSION: The removable implant-supported overdenture offers flexibility in placing implants in either adjacent tooth positions or with greater distances between them depending on the available bone, as either conventional bar and clip systems or individually milled bars can be used. Adjustment of the buccal prosthesis flange and the palatal prosthesis base is made to fulfill the patient's requirements concerning esthetics, phonetics, comfort, and function.

Dental Implantation, Endosseous↗
PubMed1986

The CAD hip arthroplasty. Five to ten-year follow-up.

One hundred and fourteen total hip arthroplasties in 100 patients were performed using the CAD (computer-assisted design) prosthesis at The Hospital for Special Surgery between 1975 and 1977. Sixty-one of these patients (seventy-four hips) have been followed both clinically and radiographically for a minimum of five years (average, 7.1 years). While no hip required revision before five years, seven hips were revised between six and ten years postoperatively. Ten hips had an excellent result; forty-eight, good; eight, fair; and one, poor. Radiographic analysis revealed narrowing of the cortex of the bone medially at the region of the proximal part of the stem in the hips that were operated on as compared with the contralateral side that was not operated on. Nine hips (12 per cent) had one to two-millimeter radiolucent lines at the femoral bone-cement interface, and in five the lines were progressive. Fourteen hips (19 per cent) had radiolucent lines at the femoral bone-cement interface with a maximum width of 0.5 millimeter. Thirty-four (42 per cent) had more than three millimeters of resorption of the calcar or superomedial cyst formation. Survivorship analysis of the prosthesis predicted a 77 per cent survival rate at nine years. None of the prosthetic stems fractured despite the fact that the population was young, active, heavy, and predominantly male. The incidence of calcar resorption, however, was higher than in other studies. Thus, while the revision rate compared favorably with that of similar studies using other stem designs, compromise of the bone stock of the proximal end of the femur may be a significant disadvantage of this type of prosthesis.

Adult↗
PubMed2002

Implant complications and failures: the fixed prosthesis.

The implant-retained fixed prosthesis has been advocated as an effective restoration offering significant benefits over conventional prosthetics. The success of treatment depends on careful pre-surgical planning and prosthesis design. This paper outlines some common complications encountered during the planning, fabrication and maintenance of both large and small fixed prostheses and suggests how these complications can be minimized.

Bite Force↗
PubMed2004

A cost-effective, adjustable, femoral socket, temporary prosthesis for immediate rehabilitation of above-knee amputation.

Early ambulation after lower extremity amputation has profound benefits on the functional, psychological outcomes and enhanced prosthetic compliance among this clientele. The various potential risks of immobility--pain, oedema, muscle atrophy, phantom sensations, contractures, aerobic de-conditioning, and the like, are reduced due to early ambulation. Moreover, it assists in accelerated wound healing, preservation of postural reflexes and, above all, achievement of better psychological well-being. Though such benefits have been observed in the history of prosthetic rehabilitation, a cost-effective prosthesis for such an early management among Third World nations is still unavailable. Therefore, this article is an attempt to present an indigenously developed temporary prosthesis designed to make the above benefits possible at a lower cost. This prosthesis helps in myriad ways--immediate prosthetic fitting, early weight bearing, early ambulation--and also has the added advantage of being adjustable to anthropological variations. The ischial weight bearing, lateral opening socket reduces the pressure and shear over the stump, thus avoiding stump complications. This increases the prosthetic acceptance by the client due to early involvement in the rehabilitation. Above all, it is cost effective and comfortable, thus enhancing compliance and superior outcome in prosthetic rehabilitation, especially among the clients in Third World nations.

Amputation, Surgical↗
PubMedDate not supplied

Stability of all-porcelain, resin-bonded fixed restorations with different designs: an in vitro study.

The strength of resin-bonded, all-ceramic fixed partial dentures with different framework and prosthesis designs was evaluated. Metal dies were fabricated from a cast of a patient missing the left central incisor and the adjacent teeth were prepared to receive an all-ceramic, resin-bonded prosthesis. Framework designs were standardized and at least 10 samples were made for testing each design. Labial veneering of the pontic with Vitadur-N significantly decreased the stability compared with that of the unveneered In-Ceram framework. Circumferential veneering of the pontic and additional proximal box preparation yielded the strongest units.

Aluminum Oxide↗
PubMedDate not supplied

Implant-supported fixed partial prostheses: a retrospective study.

PURPOSE: The purpose of this retrospective study was to present treatment outcome and patient reactions to rehabilitation with implant-supported fixed partial prostheses. MATERIALS AND METHODS: Eighty-three patients were consecutively treated with implant-supported fixed partial prostheses (Brånemark system) from 1986 to 1995. Seventy-six of these 83 patients were examined (66 maxillary and 31 mandibular prostheses). The mean observation time was 53.9 months. In total, 285 implants were placed. Eleven implants were lost before loading. The first 41 prostheses were removed and the implants examined regarding the criteria for "success" and tightness of the screw joints. Only one implant had lost integration. RESULTS: The survival rate before and after loading was 96%, which included implants placed in augmented bone. All prostheses were stable at the time of examination. In prostheses with cantilevers (98 implants), 12% of the gold screws and 17% of the abutment screws showed a "not acceptable" loosening, compared to none in the prostheses without cantilevers (17 implants). The difference was not statistically significant. The mean marginal bone loss was 0.4 mm for the first year after prosthesis insertion and less than 0.1 mm per year in the following years. The most frequent prosthesis design was one pontic supported by two implants. Prostheses made in gold acrylic and titanium acrylic had more complications and showed a higher need for repair than metal-ceramic restorations. Patients reacted very positively to the esthetic results and comfort with eating, and were overall satisfied with their prostheses. CONCLUSION: Implant-supported fixed partial prostheses seem to have a very good prognosis and are well-accepted by patients.

Acrylic Resins↗
PubMed1992

Design of intramedullary prostheses to prevent bone loss: predictions based on damage-stimulated remodelling.

The adaptation of bone around intramedullary fixated prostheses, such as the femoral component of the hip joint or the radial component of the elbow joint, is well documented in follow-up studies. Bone adaptation takes the form of proximal bone atrophy accompanied, in some cases, by distal bone hypertrophy. A mechanistic model has been formulated to predict bone adaptation based on the concept that the continuous processes of damage and repair regulate bone adaptation. We apply the model to investigate the significance of two features of intramedullary prosthesis design on bone adaptation: prosthesis Young's modulus and the presence of a prosthesis collar. Results, as well, as indicating some characteristics of accumulative-damage stimulated bone adaptation, predict that a low Young's modules stem will very much reduce the extent of bone loss whereas the presence of a collar will have no significant effect. The results predict that a collarless low stiffness prosthesis is one possible approach for improving the secondary stability of intramedullary-fixated orthopaedic implants.

Adaptation, Physiological↗