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Biomedical subjects

A D Kaiser

Publications and source records attributed to A D Kaiser.

At least 19 recordsLinked to original sources
PubMed1990

An analysis of screw fixation of the femoral component in cementless hip arthroplasty.

A cementless hip stem that allows screw fixation of the collar to cortical bone in the calcar region was found to achieve enhanced rotational stability when implanted in preserved cadaveric human femora. Although the implants with screws showed less tendency for subsidence than the implants without screws, rotational micromotion was not found to be statistically different under light loading conditions. When implanted in composite bone, the addition of screws in the configuration tested was associated with significant metal-on-metal wear during combined compression and rotational cyclic loading. This finding is of concern due to potential wear particle toxicity and possible lowered fatigue life of the prosthesis. Therefore, specific design changes are recommended.

Biomechanical Phenomena↗
PubMed1990

The effect of screws and pegs on the initial fixation stability of an uncemented unicondylar knee replacement.

Two uncemented unicompartmental tibial components were examined for initial fixation stability. A conventional design that employed a single posteriorly angled peg was compared with a new design that was held in place by cancellous bone screws. The components were implanted into the medial condyles of 12 preserved human tibiae, and a cyclic load was first applied anteromedially and then posteromedially. The screwed implants failed at significantly higher loads (1634.8 +/- 121.6 N, mean +/- standard error of the mean) than the pegged implants (1103.3 +/- 152.0 N). On application of a 19.6-N preload, the screwed implants moved significantly less than the pegged implants. Although the differences in micromotion and subsidence were not always significant, there were definite trends. The screwed implants had much lower levels of temporary and permanent displacement compared with the pegged implants for all load levels from the initial load of 245.2 N up to and including the failure load. When the motion that resulted from moving the load from the anterior position to the posterior position was examined, the screwed implant's average total motion was less than 10 microns compared with almost 135 microns for the pegged implant after the 245.2-N load cycle. For the cycle before failure, the screwed implant's average motion increased to less than 29 microns, whereas the pegged implant's average total motion was almost 354 microns. From this information it appears clear that screws provide better initial fixation stability than angled pegs for uncemented unicondylar tibial components.

Biomechanical Phenomena↗
PubMed1989

Examination of rotational fixation of the femoral component in total hip arthroplasty. A mechanical study of micromovement and acoustic emission.

Rotational loosening has recently emerged as an important cause of failure of the femoral component of total hip arthroplasties. This study was designed to investigate the role played by torsional loads in loosening of cementless femoral components and to evaluate three cementing techniques involving a combination of canal irrigation, manual insertion, and vacuum mixing combined with pressure injection of the cement for their ability to improve rotational fixation. Rotational micromotion and subsidence were measured in 24 preserved human anatomic specimen femora. Acoustic emission (AE) technique was applied as a non-destructive method for evaluating material failure during loading. From the micromovement data, torque to 50 mu subsidence and torque to failure were surprisingly low with cementless fixation and with poor cement technique but were markedly improved with pulsed irrigation. Further improvement was achieved by pressure injection and vacuum mixing of the cement. However, AE was detected even in the most carefully performed cement specimens under torsional-loading conditions commonly occurring in daily activities. These signs of microfailure of the cement mantle at relatively low torsional loads suggest that the mode of failure of deeply penetrated cement is by microfracture of the cement mantle. The poor performance suggests that cementless fixation of intramedullary stems provides unsatisfactory fixation against torsional loading. There is need for major improvements in fixation mechanisms and techniques. The signs of failure of the cement mantle at normally occurring torsional loads suggest that even the best cement technique is prone to failure in torsion when exposed to normal daily use.

Acrylic Resins↗
PubMed1972

Bidirectional transcription and the regulation of Phage lambda repressor synthesis.

There are two promoters for transcription of gene cI in phage lambda, the gene that codes for phage repressor. The promoters, called pre and prm, are located on the distal (pre) and proximal (prm) sides of gene cro, which itself is adjacent to cI. Since cI and cro are transcribed in opposite directions, cI transcription initiating at pre gives rise to an antisense transcript of cro, while cI transcription initiating at prm does not. Pre, active after infection of a sensitive cell, is stimulated by products of phage genes cII and cIII, and may be located at the site defined by the mutant cY. Prm is active in an established lysogen. These conclusions are based on measurements of the rates of synthesis of antisense cro RNA, cI RNA, and repressor protein in infected and lysogenic cells. To measure antisense RNA, an assay based on the formation of nuclease-resistant, double-stranded RNA, specific to the cro region, was developed. These results raise the possibility that bidirectional transcription of cro has a regulatory function in phage lambda.

Coliphages↗
PubMed1971

Control of lambda repressor synthesis.

Direct measurements of the intracellular level of lambda repressor have been made by a DNA-filter assay and a radioimmune assay. Transcription of cI, the structural gene for repressor, appears to initiate at two different promoters, prm and pre. Promoter pre is activated during the establishment of lysogeny by the action of cII and cIII proteins at the DNA site cY. Phage mutated in cII, cIII, or cY do not make a normal burst of repressor after infection and do not efficiently lysogenize the cell. Cro product stops repressor synthesis midway in the infective cycle. Promoter prm maintains the repressor level in established lysogens. Delection mapping places it very near the right operator (Or). Prm is activated by repressor bound to the right operator. In the absence of cII or cIII protein, repressor synthesis requires active repressor and only proceeds on genomes able to bind repressor at Or.

Autoradiography↗
PubMed1971

Association of autoantibodies to different nuclear antigens with clinical patterns of rheumatic disease and responsiveness to therapy.

Using a hemagglutination test which can detect antibodies to (a) native and denatured deoxyribonucleic acid (DNA) and (b) an extractable nuclear antigen (ENA), a comparative study of patterns of autoantibody formation has been done in systemic lupus erythematosus (SLE) and related rheumatic diseases. Antibody to native DNA was present in the serum in 96% of patients with active SLE and disappeared during remissions. Antibody to ENA was found in 86% of those patients with SLE nephritis who responded to treatment but in only 8% of those who did not. The highest titers of antibody to ENA were found in patients having a mixed connective tissue disease syndrome with features of SLE, scleroderma, and myositis. The latter syndrome was notable for the absence of renal disease and for a striking responsiveness to corticosteroid therapy. Hemagglutination testing of 277 sera from normal persons and patients with a wide variety of acute diseases other than SLE revealed the presence of antibody to native DNA in only 1.4% and antibody to ENA in only 0.4%. These results yield significant correlations among the pattern of autoimmune reactivity, the clinical form of the rheumatic disease, and responsiveness to treatment. They implicate the qualitative nature of the patient's immune response as a conditioning factor in the type of disease. Together with other correlations they may allow classification of rheumatic diseases into more biologically meaningful groups and lead to more selective methods of therapy.

Adrenal Cortex Hormones↗