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At least 325 records · Page 18Linked to original sources
PubMed2002

Unipolar versus bipolar hemiarthroplasty: functional outcome after femoral neck fracture at a minimum of thirty-six months of follow-up.

OBJECTIVES: This investigation was undertaken to compare a series of elderly individuals who sustained a displaced femoral neck fracture treated with either a cemented bipolar prosthesis or a cemented modular unipolar prosthesis. DESIGN: A retrospective review of prospectively collected data. SETTING: Hospital-based tertiary care orthopaedic trauma practice. PATIENTS AND PARTICIPANTS: Two hundred eighty-one community dwelling elderly patients sixty-five years of age or older who sustained a displaced femoral neck fracture (Garden Types III-IV) and underwent primary prosthetic replacement. INTERVENTION: One hundred one patients received a cemented bipolar prosthesis and 180 received a cemented modular unipolar prosthesis. MAIN OUTCOME MEASUREMENTS: The study was designed to determine whether there were any significant differences in: (a) the rate of prosthetic dislocation, postoperative medical and wound complications, or need for revision surgery, and (b) the functional outcome, including the incidence of hip pain and recovery of preinjury levels of ambulatory status and activities of daily living, at a minimum of thirty-six months of follow-up. RESULTS: The two groups of patients did not differ in preinjury characteristics (age, sex, American Society of Anesthesiologist rating of operative risk, number of comorbidities, fracture type, activities of daily living, ambulatory status). There were no significant differences in the rates of postoperative medical or wound complications or dislocation. Ninety-two patients died during the period of study. Forty patients were lost to follow-up or refused to participate. Consequently, 149 patients were followed for a minimum of thirty-six months. Functional ability was compared between both groups with regard to recovery of ambulatory status and activities of daily living, as well as the incidence of hip pain at a minimum of thirty-six months of follow-up. No significant differences were found between the unipolar and bipolar groups. CONCLUSION: Based on the results of this study, there does not appear to be any advantage to the use of a bipolar endoprosthesis in the management of displaced femoral neck fractures in the elderly. Furthermore, the extra cost of bipolar endoprostheses does not seem to warrant its use.

Aged↗
PubMed1986

Biomechanics of the hip joint.

A great deal of biomechanical research remains to be done in the area of hip joint trauma so that bioengineers and other medical scientists can work with accurate bone failure data, which are essential to the design of sports equipment, vehicles, workplace situations, and prostheses. The application of biomechanical data, in addition to being essential in prosthesis design and ergonomics, also can be useful in such diverse problems as pathogenesis of degenerative joint disease, management of the postfracture patient, bracing in Perthes' disease, and in many other pathologic conditions.

Adult↗
PubMed2003

Evaluation of the effects of implant materials and designs on thermal necrosis of bone in cemented hip arthroplasty.

The exothermic polymerization of bone cement may induce thermal necrosis of bone in cemented hip arthroplasty. A finite element formulation was developed to predict the evolution of the temperature with time in the cemented hip replacement system. The developed method is capable of taking into account both the chemical reaction that generates heat during bone cement polymerization (through a kinetic model) and the physical process of heat conduction (with an energy balance equation). The possibility of thermal necrosis of bone was then evaluated based on the temperature history in the bone and an appropriate damage criterion. Specifically, we evaluate the role of implant materials and designs on the thermal response of the system. Results indicated that the peak temperature at the bone/cement interface with a metal prosthesis was lower than that with a polymer or a composite prosthesis in hip replacement systems. Necrosis of bone was predicted to occur with a polymer or a composite prosthesis while no necrosis was predicted with a metal prosthesis in the simulated conditions. When reinforcing osteoporotic hips with injected bone cement in the cancellous core of the femur, the volume of bone cement implanted is increased which may increase the risk of thermal necrosis of bone. We evaluate whether this risk can be decreased through the use of an insulator to contain the bone cement. No thermal necrosis of bone was predicted with a 3 mm thick polyurethane insulator while more damage is predicted for the use of bone cement without the insulator. This method provides a numerical tool for the quantitative simulation of the thermal behavior of bone-cement-prosthesis designs and for examining and refining new designs computationally.

Animals↗
PubMedDate not supplied

[Requirements for design of total prosthesis of the hip joint].

Analysis of the forces acting on the total endoprosthesis of the hip joint and studies carried out for 16 years of the outcomes of 546 operations have demonstrated the position at an angle of 25-40 degrees to the horizontal to be the best variant of establishing the nest of an endoprosthesis. There is a necessity of designing endoprostheses having a cervico-diaphysial angle of 145-150 degrees.

Hip Prosthesis↗
PubMed1994

The Angelchik antireflux prosthesis: long-term clinical and technical follow-up.

OBJECTIVE: To evaluate the long-term clinical outcome and compare the rupture rate of the two generations of the silicone Angelchik antireflux prosthesis. DESIGN: A cohort study. Follow-up ranged from 61 to 119 months. SETTING: A university teaching hospital. PATIENTS: Sixty-three patients: 33 patients received the first generation Angelchik device (group 1) and 30 patients received a second generation design (group 2). The two groups were comparable for sex ratio, mean age and duration of symptoms. INTERVENTIONS: Implantation of the Angelchik prosthesis. MAIN OUTCOME MEASURES: Comparison of the rupture rate and migration of the prosthesis as assessed by patient questionnaire, telephone interview and radiography of the abdomen. RESULTS: The prosthesis remained in a good position in 53% of group 1 patients and 93% of group 2 patients. The prosthesis was removed in 40% of group 1 patients, most often for rupture, and in only 7% of patients in group 2, to relieve dysphagia (p < 0.01). Grading on a Visick scale demonstrated a good result in 37% of group 1 patients and 69% of group 2 patients. Long-term dysphagia was the most prevalent adverse effect, seen in 45% of patients whose prosthesis was in a good position, and symptomatic reflux recurred in 8%. CONCLUSIONS: The second generation of the Angelchik prosthesis, resulted in a reduced rupture rate of the prosthesis. Nevertheless the high complication and the failure rates militate against continued implantation of the prosthesis.

Adult↗
PubMed2001

The implant-supported milled-bar mandibular overdenture.

Osseointegrated dental implants have been proven successful in the treatment of edentulism. The predictability of the implant-supported prosthesis has also been established. Several techniques have been described for the successful restoration of the edentulous mandible: fixed-detachable prostheses with either the original Brånemark hybrid prosthesis design or conventional implant-supported fixed partial dentures, implant-retained overdentures, and implant-supported overdentures. However, in cases of advanced ridge resorption in which facial tissue support is needed from the flanges of the prosthesis or when a removable type of prosthesis is preferred by the patient, an implant-supported prosthesis is indicated. Electric discharge machining is often used in the fabrication of the bar for an implant-supported overdenture. This procedure is very costly and technique sensitive. An alternative procedure to fabricate a milled-bar implant-supported overdenture is described. This procedure is simple and uses inexpensive equipment and materials. The milled-bar minimizes lateral and rotational displacement. The overdenture incorporates attachments that provide retention, minimizing possible movement along the path of insertion. This type of prosthesis is available to a broad patient population, especially those with advanced ridge resorption, providing an excellent result at a reduced cost. J Prosthodont 2001;10:46-51.

Aged↗
PubMed1977

Interposition arthroplasty of the carpo-metacarpal joint of the thumb.

Nine patients with osteoarthrosis of the carpo-metacarpal joint of the thumb were treated surgically with the metacarpo-trapezial silicone rubber prosthesis designed by Kessler. Patients with pantrapezoidal changes were specifically excluded. All patients at follow-up had chronic synovitis and in five the prosthesis was dislocated. In three patients who had revision operations the previously inserted prostheses were found to be badly torn.

Arthroplasty↗
PubMed1986

Patellar surface strain.

We measured longitudinal surface strains on the anterior patella at controlled simulated quadriceps loads, quadriceps angles, and knee flexion angles. We studied both the natural patella and patellas resurfaced with domed, bifaceted, and metal backed polyethylene components. Twelve matched pairs of fresh human cadaver knee specimens were tested. Midanterior longitudinal patellar strains were greatest at knee flexion angles at 45 to 60 degrees of knee flexion. Alterations in quadriceps angle medially and laterally did not decrease recorded strain values significantly. Polyethylene patellar prostheses increased patellar strains but a bifaceted component or "total contact" design minimized this effect. Metal support for the prosthetic patella decreased the recorded surface strains. This study of patellar surface strain at the three midline locations provides experimental results that may prove useful for design and validation of analytic models of the patella. The study also suggests that patellar surface strain measures may provide a method for evaluating the effects of patellar prosthesis design and resurfacing procedures.

Aged↗
PubMed2003

Use of a loudness model for hearing aid fitting. V. On-line gain control in a digital hearing aid.

Many researchers have proposed that hearing aids should process sounds so as to restore loudness perception to 'normal'. We describe how a model for predicting loudness for people with cochlear hearing loss can be implemented in a digital hearing aid so as to calculate the frequency-dependent gains that would be required to achieve that goal. It is assumed that the input signal is processed using brief segments or 'frames'. For each frame, the spectrum is calculated, usually via a fast Fourier transform (FFT). From the spectrum, an excitation pattern is calculated for a normal car and for the impaired ear of the patient. The loudness model is then used to calculate the gain required at the centre frequency of each channel in the aid, so as to match the specific loudness in the normal and impaired ears. The whole process is repeated for each successive frame, with overlap of frames and with smoothing of the gain changes across frames. We describe both an 'exact' model, which prescribes a 'curvilinear' compression characteristic at each frequency, and an approximation using 'straight' compression, which is computationally less intensive. Limitations of the present approach are described, and the approach is compared with more traditional approaches using multichannel compression, and with previous approaches using loudness models for fitting hearing aids.

Acoustic Stimulation↗
PubMed2006

[Old and new materials in the hip prosthesis].

Since the second half of the XX century a steady evolution of hip prosthesis design is taking place. Implant shape, fixation systems and materials are constantly evolving. The paper presents the materials combinations most commonly used in hip prosthesis (metal-metal, metal-polyethylene and ceramic). All the above mentioned materials have been in used for over 25 years, and thanks to minor modification and better quality are widely used all over the world. The authors basing on biochemical studies, clinical observations and personal experience present problems related to materials used in hip prosthesis.

Arthroplasty, Replacement, Hip↗
PubMed2003

Clinical and functional outcome of the Thrust Plate Prosthesis: short- and medium-term results.

OBJECTIVES: The purpose of this study was to objectively assess the functional outcome after implantation of a Thrust Plate Prosthesis. DESIGN: This retrospective study compared the gait patterns of 33 patients to a control group. BACKGROUND: Few studies have been published about this type of prosthesis describing clinical and radiographic outcome. Even though the evaluation of the functional outcome is a commonly accepted way to measure the success of an implant it has not been reported in previous studies. METHODS: Beside clinical (SF-36, and Harris Hip Score) and radiographic evaluation subjects were examined by three dimensional gait analysis and surface electromyography from seven leg and trunk muscles bilaterally. RESULTS: The average Harris Hip Score was 85.7 points, and the SF-36 only differed significantly from controls regarding physical functioning. The radiography showed considerable radiolucencies under the Thrust Plate. Kinematic parameters indicated a slight impairment of the operated limb. The analysis revealed a decreased hip (28.2%) and knee (51.2%) range of motion during gait. The joint moments on the operated side were reduced in hip (72%) and knee abduction (59%) in comparison to controls. The average electromyographic parameters indicated a significantly higher mean and peak amplitude of the tensor fasciae latae (mean 56%, peak 54%), and gluteus medius (mean 33%, peak 21%) and a lower peak activity of the gluteus maximus (19%). CONCLUSIONS: The results indicate a generally good functional outcome even though a slightly asymmetrical loading was observed. No major limitations in physical functioning and health-related quality of life was seen. The radiographic signs of loosening might indicate difficulties in achieving the proximal load transfer of this implant. RELEVANCE: The data provided in this study may serve to establish the Thrust Plate Prosthesis as an alternative procedure in total hip replacement in younger patients.

Activities of Daily Living↗
PubMed1986

The effect of the interface on the bone stresses beneath tibial components.

It was proposed that the stresses in the layer of bone immediately beneath a tibial component are an important determinant of fixation durability. Using finite element analysis, (ANSYS), the stresses were determined as a function of the amount of bone resection, the localization or completeness of implant-bone contact, and the interface material. The model was of two-dimensional sagittal slices consisting of quadrilateral elements (1 mm) with a range of seventeen material properties determined by CT scans. Typical prosthesis designs shifted the center of pressure more centrally rather than posteriorly, and thus increased anterior bone stresses. Resection up to 10 mm could actually decrease bone stresses due to an increase in bone surface area as long as complete coverage was obtained. A cement interface or direct metal on bone produced identical stresses. However a 1 mm compliant interface significantly reduced stresses in regions of high elastic modulus gradient. For rigid interfaces, the contact can be irregular, which leads to areas of over and under-stressing of bone. These conclusions have implications related to implant design.

Arthritis↗
PubMed2003

The anterior cantilever in the implant-supported screw-retained mandibular prosthesis.

STATEMENT OF PROBLEM: When implants are placed interforaminally in mandibular implant-supported screw-retained prostheses, the most anterior implant is usually positioned lingual to the incisors of the prosthesis. This creates an anterior cantilever with the entire prosthesis acting as a class I lever and possibly placing the anterior implant under alternating tension and compression during function. PURPOSE: The purpose of this study was to measure the anterior cantilever of randomly chosen patients with restored mandibular implant-supported fixed prostheses, and to establish the proportions of anterior to posterior cantilever lengths relative to the anteroposterior spread. MATERIAL AND METHODS: Thirteen edentulous patients were recruited from the University of Minnesota's dental implant program. Each patient had been restored with a maxillary complete denture and a mandibular implant-supported screw-retained prosthesis supported by 5 endosseous implants. Each patient had 1 mandibular impression made with irreversible hydrocolloid, which was poured in type III gypsum. A FaroArm precision 3D measuring stylus was used to make multiple-axis (X-Y-Z) measurements (mm) on the casts of the dental implants, of anteroposterior spread, and anterior and posterior cantilevers. Presence or absence of screw loosening was noted using a screwdriver with finger pressure. Data were analyzed using a 1-way analysis of variance to compare prostheses with loose screws to prostheses without loose screws, for each of 3 outcome measures: length of anterior cantilever, length of posterior cantilever, and anteroposterior spread (P<.05). RESULTS: Mandibular anterior cantilever lengths ranged from 5.5 to 14.4 mm with a mean of 8.78 mm. Combined posterior cantilever lengths ranged from 9.2 to 20.9 mm with a mean of 16.2 mm. Anteroposterior spread ranged from 5.2 to 12.3 mm with a mean of 7.9 mm. From a total of 65 retaining screws, 7 were found to be completely loose. No apparent correlation was found between length of mandibular anterior cantilever and screw loosening (P=.45), although the ratio of posterior cantilever to anteroposterior spread (2:4) was significantly associated with screw loosening (P=.006). CONCLUSION: Within the limitations of this study, anterior cantilevers in mandibular implant-supported screw-retained prostheses were frequent and appeared to depend on implant placement and prosthesis design. The ratio of anterior to posterior cantilever lengths was approximately 1:2.

Aged↗
PubMed1989

[Prosthodontic considerations in implant therapy].

Numerous factors affect the success or failure of the various intra-osseous implants. In particular, such considerations as the implant materials, properly selected or not, preceded by careful patient screening and thorough analysis of soft and hard tissues, implant insertion conditions, oral hygiene and the overlying prostheses determine the success of the implant therapy. Among these, the final overlying prostheses serve two major purposes of restoring lost masticatory function and esthetic improvement. In addition, due to the intimate relationship with the health and remodeling of the surrounding tissues, the prostheses must be designed with the utmost care. Analyzing this kind of osteointegrated system from the histologic standpoint of the implant/bone relationship, one can roughly classify this system into three types. One is a fibro-osseous integration yielded by enveloping with fibro connective tissue. The other is osseointegration by directly contacting with bone. Lastly, the osteoankylosis form whereby fusion of the implant and bone takes place. Irrespective of the different types and a basic physical principle applied, the function of the final prostheses should be to transmit occlusal force widely to the supporting cortical and basal bones (i.e., jaw bones) via the implant device without creating any undesirable concentrated, rotational or lateral force. Therefore, the final prostheses are not designed independently or after the implant operation. Instead, the prostheses design comes first, followed by careful analysis of the opposing occlusion, proximal dentition and other intraoral structures. Based on the determined existing intraoral environment, the particular type of implant and its form is selected to fit the individual case. Preoperative procedure requires articulator mounted study casts to evaluate the opposing occlusion and implant positioning from which the mesiodistal and buccolingual positioning is determined. Subsequently, the final prosthesis design is prewaxed and the required number of implants and their interspan distances are determined from the wax-up. Next, the Surgical Guide Plate device is employed to help determine radiographically the implant positioning and the anatomical jaw morphology. As mentioned earlier, the purpose of the final prosthesis is to restore the lost masticatory function and esthetic improvement along with presservation of the remaining teeth and harmony with the intraoral soft and hard tissues. Implants serve a critical supportive role of helping the success of the final prosthetic treatment. Intraosseous implants can be used as independent support system or can be combined with remaining natural dentition to support the overlying prosthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Dental Implants↗
PubMed1988

A modified prosthesis for the treatment of malignant esophagotracheal fistula.

Esophagotracheal fistula is usually a sequela of irradiation or laser treatment of advanced carcinoma of the esophagus or the tracheobronchial tree. Resection of the tumor in these cases is not possible, and palliative bypass surgery is highly risky. The peroral placement of a prosthesis is less invasive, but conventional prostheses often fail to occlude the fistula. The authors regularly use an endoscopic multiple-diameter bougie for dilation. After dilation, a specially designed prosthesis is pushed through the tumor stenosis to block the fistula. This procedure can be done without general anesthesia. The funnels of conventional prostheses cannot cover the fistula when there is either a wide, proximal esophagus above the fistula or a high fistula. To cope with this particular situation, a special fistula funnel was developed. It perfectly occludes the fistulas in all patients. Of 21 patients, 19 were discharged without further aspiration.

Endoscopes↗
PubMed1989

A mathematical model for the evaluation of the behaviour during flexion of condylar-type knee prostheses.

A 3D knee model was developed in order to evaluate the mechanical behaviour during flexion of condylar-type knee prosthesis. Based on the total energy minimization principle, it takes into account the articular surfaces (the tibial surface being deformable), the body weight, and the patello femoral joint. It generates the kinematics of the joint, the motion of the centre of contact, the quadriceps forces, the pressure distribution on the tibial plateau, and ligament lengths and forces between 0 and 120 degrees of flexion. The results for ten digitized knees and the commercially available prostheses are presented. They are in general agreement with experimental results published in the literature. It is concluded that this computer program may be, within its limitations, a useful tool in the preliminary evaluation of new condylar-type knee prosthesis designs.

Biomechanical Phenomena↗
PubMedDate not supplied

The outcome of implant-supported fixed prostheses from the prosthodontic perspective: proposal for a classification protocol.

PURPOSE: This article proposes a classification protocol for reporting the outcome of implant-supported fixed partial dentures. MATERIALS AND METHODS: A review of the literature revealed a contrast between the accepted criteria for assessing and presenting the outcome of osseointegrated implants and the deficient and misleading assessment and presentation of the outcome of the prostheses supported by these implants. A classification protocol comprising 6 well-defined fields with objective standards that accounts for retreatment as well as failure is proposed. This protocol has been applied where possible to reports on the outcome of fixed partial dentures in several published articles. RESULTS: In all cases there was a stark difference between the authors' claims of success and the outcome according to the 6-field protocol. It is accepted that the outcome of a given prosthesis does not necessarily correspond to the outcome of the overall prosthodontic treatment, as the latter also involves an assessment of outcome as perceived by the patient and accounts for planned revisions. CONCLUSION: If adopted, the proposed protocol would allow meaningful comparisons between prosthesis designs and between different implant systems' capacities to support such designs. It would also assist in evaluating the cost-effectiveness of implant-supported treatments.

Classification↗