Orthopaedic practice, biomechanics and design of prosthesis. I.
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Bibliographies as Topic↗
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Design and in vitro performance of a novel bileaflet mechanical heart valve prosthesis.
Design and in vitro performance of a novel bileaflet mechanical heart valve prosthesis are presented. The novel heart valve exhibits three main design characteristics: (i) The leaflets form a Venturi passage in open position. Thus, a beneficial pressure distribution is obtained and the leaflets are stabilised in opened position. (ii) The orifice inlet is nozzle-shaped. Flow is convectively accelerated and flow separation at the orifice inlet is avoided. (iii) The hinge design facilitates an additional axial movement of the leaflets and leads to a self cleaning effect and enhances washout of the hinges. The design of the leaflet hinges is of main importance for the functional reliability and durability of mechanical heart valves. After manufacturing first prototypes from titanium and polymeric materials the hydrodynamic performance was evaluated according to ISO 5840 and FDA guidelines. Hydrodynamic performance is comparable with the results of commonly available bileaflet mechanical heart valve prostheses. Initial durability tests showed suitable material couples for further long term studies.
Biocompatible Materials↗
Designing a prosthesis to simulate the elastic properties of skin.
The materials which are currently used to make maxillofacial prostheses are far from ideal and require considerable improvement with respect to their ability to mimic the properties of skin. To this aim, a novel three-layered maxillofacial prosthesis has been designed consisting of a silicone rubber base layer, an inner gel layer and an outer polymeric coating (to simulate the elastic properties of skin). The aim of the work in this study was to develop the inner silicone gel layer which displays similar properties to facial skin. Through the use of unique linear extensometry testing, in vivo measurements for the Area under the Curve (AUC), Hysteresis (viscoelastic behaviour), Fmax (maximum force), F30 and F60 (force after 30 and 60 seconds) were obtained from the facial skin of 15 volunteers. The results were used as a basis for developing silicone gel formulations for the inner layer, to closely resemble those of facial skin. Gels were made by the addition of both low and high molecular weight unreactive silicone fluids and were further tested for compression, water absorption and dehydration. Testing showed that a gel has been produced that closely simulates the elastic properties of skin when bonded to a base silicone rubber layer. Further testing will need to deduce whether these properties will be affected by the addition of the outer polymeric layer.
Biocompatible Materials↗
Biomechanical comparison of newly designed stemless prosthesis and conventional hip prosthesis--an experimental study.
Local bone loss after implantation of traditional stem-type prostheses remains an unsolved problem during the long-term application of total hip replacement. The stress shielding effect and osteolysis were thought to be the two main factors that result in local bone loss after prosthesis implantation. A newly designed stemless cervico-trochanteric (C-T) prosthesis was thus developed to reduce stress shielding and osteolysis caused by the implantation of conventional stem-type prosthesis. Eight synthetic femora were implanted with C-T and porous coated anatomic (PCA) prostheses. Under 2,000-Newton load, the surface strains of proximal femora were compared between the intact, PCA press-fit femora and the C-T implanted femora with three different fixation modes: two-screw fixation, three-screw fixation, and three-screw combined with cement fixation. The results revealed that stress shielding in the C-T implanted femora was significantly eliminated compared to that of the PCA implanted femora (p<0.01). No statistical difference in strain magnitude was found for the C-T implanted femora among the three different fixation modes (p>0.1). The C-T implanted femur has more physiological strain distribution. Moreover, from the C-T prosthetic characteristic design, the localized osteolysis would be also reduced due to the overall coverage of neck-trochanteric area. The newly designed C-T prosthesis may be a useful alternative to the traditional stem-type prosthesis in the future.
Arthroplasty↗
Neural mechanisms relevant to the design of an auditory prosthesis. Location and electrical characteristics.
A cochlear prosthesis designed to electrically stimulate eighth nerve fibers in deaf subjects was studied in acute guinea pig preparations. The prosthesis, which consisted of two pairs of platinum-iridium electrodes, was inserted into the scala tympani through the round window. The electrical impedances of different current paths and their effectiveness in evoking neural responses in the central auditory system are compared. Assuming lumped neural elements, the results indicate that the sites of neural excitation lie outside the scala tympani. Frequency-response characteristics of neural excitation are in agreement with resistive spread of current through tissue to the site of stimulation. Neural membrane characteristics similar to those previously studied in nonmammalian nerves seem to account for the response initiation.
Acoustic Impedance Tests↗
Swing-lock design considerations for obturator frameworks.
The conventional and swing-lock (S/L) obturator prostheses can be highly effective in restoring maxillary defects when careful attention is paid to the principles of framework design. Although the S/L modality has been available since the mid 1960s, its use in maxillofacial prosthetics has been limited, and little information is available in the literature to guide the practitioner. This modality offers a conservative design option that lies somewhere between the conventionally designed obturator prosthesis and the prosthesis designed to use extensive fixed reconstruction or endosseous implants. When the S/L obturator is considered, single, double, or dual labial bar designs are possible and may be required by the length and complexities of the arc of closure. Such designs provide a flexible labial bar that transmits less stress to abutment teeth. This article reviewed conventional obturator framework designs and compared them with S/L designs for similar patient categories.
Dental Abutments↗
Design rationale and biomechanics of Maverick Total Disc arthroplasty with early clinical results.
This paper reviews the design criteria, biomechanical and biological (wear and safety) testing of this chrome cobalt metal-on-metal, ball and socket design prosthesis. The surgical technique and early clinical results of the initial implantations are also reviewed. Initial results of 7 Maverick implantations showed all 7 patients attaining a 15 point Oswestry improvement within 3 months after implantation. This early result in a small sample is significantly quicker in recovery and improvement when compared to the historical control of the LT cage with Infuse IDE study. Longer term results and more careful study are needed of this interesting and optimistic finding.
Arthroplasty, Replacement↗
Long-term results of total hip arthroplasty with a cemented custom-designed swan-neck femoral component for congenital dislocation or severe dysplasia: a follow-up note.
BACKGROUND: This follow-up study updates the results in a consecutive series of nineteen cemented total hip replacements with a swan-neck femoral component in patients with congenital dislocation or severe hip dysplasia. The series was previously reported on in 1993. METHODS: The patients were petite, with an average height of 152 cm and an average weight of 50 kg, and the femoral canals could not accommodate an off-the-shelf femoral component. Sixteen of the nineteen hips were available for follow-up at an average of 13.3 years (range, eleven to twenty years). Fourteen hips had up-to-date clinical and radiographic examinations. RESULTS: At the time of the latest follow-up, thirteen hips were rated as excellent; two, as good; and one, as a failure because of loosening of both components requiring revision eleven years after the index operation. Another hip required acetabular revision because of loosening fifteen years after the index operation. The rates of femoral and acetabular component revision were 6% and 12.5%, respectively. Radiographic analysis demonstrated that no femoral component was loose. One cup was definitely loose at 19.5 years, and three cups were possibly loose at an average of fourteen years. The radiographic rate of acetabular loosening was 33%. The total rate of cup failure (radiographic loosening and revision) was 43%. CONCLUSIONS: The excellent clinical and radiographic results associated with the swan-neck femoral component, and the 94% rate of survival, at an average of 13.3 years (range, eleven to twenty years) indicate that the biomechanical objectives of this custom-designed prosthesis for patients with congenital dislocation or severe hip dysplasia were met. On the basis of this favorable long-term experience, we still use this prosthesis when the anatomic abnormality cannot be adequately addressed by use of a commercially available prosthetic component.
Adult↗
[Bipolar radial head prosthesis--own design].
The authors describe its own design--bipolar radial head prosthesis. The value of this prosthesis is analyzed. The early results in 10 patients, age 20-69 (average 36 years), 7 male and 3 female have been reported. The results are excellent and good. The authors conclude that this prosthesis should be used as an alternative for radial head resection.
Adult↗
Cementless total hip replacement in patients with developmental dysplasia of the hip.
This study was conducted to evaluate the clinical and radiographic results of 22 total hip replacements done in 17 consecutive patients for coxarthrosis due to developmental dysplasia or dislocation of the hip. All operations were done using an anterior approach without trochanteric osteotomy. Standard cementless prostheses were used in all cases. There was no custom-designed prosthesis used. The acetabular cup was placed in an anatomic position in the true acetabulum in every case. Bulk autograft was necessary to reconstruct the deficient acetabular roof in only 2 hips. The average follow-up was 63 months (range, 40 months to 95 months). The average Harris Hip Score was improved from a preoperative value of 35 (range, 24 to 46), to 96 (range, 79 to 100) at final follow-up. To date, no revision has been done. Three hips showed radiographic evidence suggestive of aseptic loosening (2 stems and 1 cup), but the clinical results remain satisfactory. There is no incidence of dislocation, sciatic nerve palsy, or infection.
Acetabulum↗
A look at the prosthesis-cartilage interface: design of a hip prosthesis containing pressure transducers.
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Cartilage, Articular↗
[A case of unilaterally designed obturator prosthesis].
PATIENT: A 50-year-old female patient with minor maxillary defect was afflicted with an ipsilateral oroantral fistula. A unilaterally designed obturator was constructed for the patient. She was satisfied with the obturator because no leakage or seepage into the antrum occurred during mastication. It was also aesthetically acceptable due in particular to the small size of the denture. In this clinical report, treatment with the unilaterally designed obturator is discussed. DISCUSSION: The use of functional impression techniques during the trial denture stage registered the optimal shape of the soft tissues while they were loaded under a variety of functional conditions. This acted to distribute the functional forces to the saddle area proportionally and prevented any leakage and seepage of food into the defect. CONCLUSION: The unilaterally designed obturator prosthesis has served to restore masticatory function as well as to obturate the maxillary defect.
Dental Prosthesis Design↗
Range of motion studies for total hip replacements. A comparative study with a new experimental apparatus.
Significant differences in ROM exist between different THR prosthesis designs: several of the prosthesis designs tested are marginal in flexion; several millimeters of socket wear will decrease the ROM. The results also emphasize the importance of proper component orientation at surgery. The surgeon has less latitude in orienting the components of a THR with limited ROM. Subluxation and dislocation due to rim contact can be minimized with most prosthetic units by instructing the patients to abduct and/or externally rotate their hips during acute flexion. Analyses suggest that impingement of prosthesis neck and socket rim may lead to increased risk of dislocation and increased rim wear. Prostheses with adequate ROM for everyday activities should provide stability, less frequent neck and socket contact with decreased rim wear, less force transmission to acrylic-bone interface, and less diminution of ROM with wear of the socket wall.
Hip Joint↗
Successful prosthetic fitting of a patient with epidermolysis bullosa dystrophica. Case report.
A patient with recessive dystrophic epidermolysis bullosa developed a squamous cell carcinoma of the right foot resulting in a below the knee amputation. Despite the multiple real and potential skin problems of the stump, she was successfully fitted with a simply designed prosthesis and rehabilitated.
Adult↗
Effects of adhesive fixed prosthesis retainer design on resultant resin luting agent thickness.
STATEMENT OF PROBLEM: Resin cement thickness may influence the success or otherwise of adhesive fixed prostheses and needs to be quantified for future stress analyses. PURPOSE: This study evaluated the effect of different complexities of retainer preparation design on resultant resin lute thickness. MATERIAL AND METHODS: Five retainer designs were evaluated for resin luting thickness (Panavia Ex) after cementation to appropriately selected natural teeth as follows: (1) flat plate retainer; mandibular canine; (2) occlusal rests, mandibular premolar; (3) occlusal rests, proximal grooves, mandibular premolar; (4) modified three-quarter crown, mandibular premolar; and (5) occlusal strut, maxillary premolar. Five samples of each design were prepared in vitro. A mesiodistal and a buccolingual section were obtained from each sample with a diamond saw. Measurements were carried out on the fluorescent cement lute with a confocal microscope. Mean resin thickness and cervical resin thickness were analyzed with analysis of variance and Tukey tests. RESULTS: Resin thickness (micron) for each of the retainer designs were as follows (mean +/- SD): design 1, 58 +/- 40; design 2, 67 +/- 42; design 3, 80 +/- 28; design 4, 87 +/- 15; and design 5, 85 +/- 29. There were no significant differences among the designs (mean global value 75.4). The three-quarter crown (design 4) had a significantly wider cervical resin thickness (P < or = .01) than designs 1, 2, and 3.
Analysis of Variance↗
Talonavicular joint surface anatomy and prototype resurfacing prostheses.
The curvature and extent of a joint surface largely determine the type and range of motion possible. The talonavicular surface anatomy of 10 human foot specimens has been determined quantitatively, and the data have been compared with the design parameters for a prototype prosthetic joint. It was found that, in general, the natural talus as compared with the navicular was slightly larger in surface area and in mean arc length, but slightly smaller in mean radius of curvature. The arc length of the joint was found to be generally slightly longer along an axis positioned from slightly medial of dorsal to slightly lateral of ventral. In contrast, no general orientation of the radius of curvature was observed. Also, it was found that the congruency between the talus and navicular surfaces, as indicated by corresponding radii of curvature, varied widely. In comparison to the human specimens, a previously designed prototype talonavicular prosthesis proved somewhat smaller in radius, arc length, and surface area. Experimental studies related to other prosthesis design parameters, besides type and range of motion, are in progress.
Female↗
Comparison of total hip arthroplasty performed with and without cement : a randomized trial.
BACKGROUND: This study was designed to compare the fixation of a Mallory-Head total hip prosthesis with and without cement. METHODS: Two hundred and fifty patients with osteoarthritis of the hip were randomized to receive a Mallory-Head total hip prosthesis designed for insertion with cement or the same prosthesis designed for insertion without cement. Neither the patient nor the outcomes assessor was aware of the type of prosthesis. Outcomes were assessed with respect to mortality, revision arthroplasty, health-related quality of life (evaluated with the Harris hip score, Merle d'Aubign and Postel hip score, McMaster-Toronto Arthritis Patient Preference Disability Questionnaire (MACTAR), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), and the time trade-off technique), and the six-minute-walk test. Patients were seen at three, six, and twelve months and yearly thereafter. RESULTS: The prosthesis was inserted with cement in 124 patients and without cement in 126 patients. The mean age of the patients was sixty-four years, 48% were female, and the mean duration of follow-up was 6.3 years. There were thirteen revisions in the group that had fixation with cement and six in the group that had fixation without cement (p = 0.11), and more femoral components were revised in the group that had fixation with cement (twelve versus one; p = 0.002). All health-related quality-of-life measures improved postoperatively in both groups. CONCLUSIONS: In this randomized trial, the group that had the cemented Mallory-Head hip prostheses required more revisions of the femoral component than did the group with the cementless Mallory-Head prostheses, which was perhaps related to the titanium-alloy femoral stem. Our findings are specific to the implants evaluated in this study.
Aged↗
[Horizontal stress of abutment. Particularly regarding difference in removable partial denture design].
Prosthesis with removable partial denture is a daily clinical procedure for compensating the morphological loss and hypofunction of teeth and various gnathostomatic system. The removable partial denture not only comprises of many elements such as denture base, abutment and clasp but accordingly has to undergo morphologically complicated operative process, thus posing many factors concerning the functional stability coping with diverse masticatory motions. However, from the fact that retention and stability of the denture at it's functioning are obtained basically from it's connection with abutment, assessments in multiple aspects have been made regarding the influence exerted on abutment by difference in the structural elements, i. e. clasps, which transmit the movement of denture directly. There were the assessments by means of the displacement, measuring system by the use of microdial gage, stereoscopic camera, eddy currents transfer, and magnetic resistant element, and deformation measuring systems such as photoelasticity method, holography, moiré method and strain gage method. However, these systems are the methods for assessing abutment as subject but not the assessing system including all the basic structural elements of denture. Therefore, the author has made observation of the influence exerted on the dynamics of abutment by the difference between clasps in 2 kinds and by cross arch stabilization by designing aker's clasp and RPI clasp for the abutment by the use of cast frame standardized.(ABSTRACT TRUNCATED AT 250 WORDS)
Dental Abutments↗