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PubMedDate not supplied

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↗
PubMed1995

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↗
PubMed1998

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↗
PubMed1975

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↗
PubMed1981

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↗
PubMed1989

[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↗
PubMed1996

Outcome of total hip arthroplasties with cement. Results after implantation of the Harris Design 2 prosthesis, 1983-1985.

Most reports of excellent long-term results of cemented total hip arthroplasty originate from studies of Charnley prostheses. A radiographic and clinical study was performed on 126 patients who underwent a cemented total hip arthroplasty from 1983 to 1985 with the Harris Design 2 prosthesis (Howmedica, Rutherford, NJ). The femoral component was cobalt-chromium and it had a broad, rounded medial border and a collar. The head diameter was 26 mm. A cemented all-polyethylene socket was used in all cases. At the last follow-up examination, 71% of the patients were completely free of pain and no patient had severe pain or pain at rest. Kaplan-Meier survival analysis estimated the revision rate at 10 years after operation to be 5 +/- 2% (mean +/- SEM) (including planned revisions). The rate of complete acetabular demarcation was 20% at 10 years, and femoral demarcation involving more than 50% of the bone-implant surface or endosteal cavitation was noted in only three cases. These results are as good as the best reported after total hip arthroplasty with the Charnley prosthesis.

Adult↗