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Biomedical subjects

B Cohen

Publications and source records attributed to B Cohen.

At least 199 records · Page 11Linked to original sources
PubMed1995

Poor results of the Ribbed Hip System for cementless replacement.

We reviewed 12 patients six years after they had undergone total hip replacement with a cementless prosthesis, the Ribbed Hip System (Waldemar Link GmbH & Co, Hamburg, Germany). Aseptic loosening of one or both components had necessitated revision surgery in seven patients, in five within two years of operation. In view of our experience we question the wisdom of allowing the uncontrolled use of new prosthesis without postoperative surveillance.

Adult↗
PubMed1995

Accuracy of DEXA measurement of bone mineral density after total hip arthroplasty.

Dual-energy X-ray absorptiometry (DEXA) is increasingly used to measure changes in bone mineral density (BMD) around femoral prostheses after total hip arthroplasty. We have studied the factors which affect the accuracy of these measurements. The coefficient of variation was < 2% using a hydroxyapatite phantom, 2.7% in an anthropomorphic phantom specimen, and < 1% in repeated measurements on implanted cadaver femora. The precision did not vary with different implant materials or designs. In patients we found a mean precision error of 2.7% to 3.4%. The most significant factor affecting reproducibility was rotation of the femur. We conclude that DEXA is a precise method of measurement for small changes in BMD around femoral implants, but that correct and careful positioning of patients is essential to obtain reliable results.

Absorptiometry, Photon↗
PubMed1995

Atraumatic recurrent posterior shoulder subluxation: review of the literature and recommendations for treatment.

Isolated atraumatic recurrent posterior subluxation of the shoulder (ARPS) constitutes 1% of all shoulder subluxations; it is therefore difficult for any single clinic to gain a large experience in treating this condition. Based on a review of the literature 83 cases of ARPS out of 237 reported cases with all types of posterior subluxation of the shoulder (185 patients) were analyzed. Most cases of ARPS occur between 11 and 20 years of age; they are frequently associated with changes such as dysplasia of the glenoid labrum or an alteration in the spinoglenoid angle. More than half of all ARPS occur bilaterally. The diagnosis is based on history, physical examination including tests of instability, or on techniques of dynamic examination (ultrasonography, arthroscopy). A plan of management related to the underlying etiology has been developed. At the first occurrence, cases of subluxation should be treated conservatively by kinesitherapy and physical therapy. Operative treatment is indicated when conservative management for at least 6 months has been unsuccessful and subluxation continues to occur during everyday activities, but it should never be instituted in patients with emotional disorders. The underlying pathologic lesion should determine the technique for shoulder reconstruction in atraumatic posterior shoulder subluxation. In cases in the atraumatic voluntary subgroup, surgery is indicated if conservative treatment fails and the voluntary component has been eliminated. In this subgroup, isolated soft tissue procedures have not been shown to produce good long-term results, and supplementary bony procedures are considered necessary. Conservative treatment exclusively is recommended in voluntary cases.

Adolescent↗
PubMed1994

Cell interaction between compartments establishes the proximal-distal axis of Drosophila legs.

The appendage primordia of Drosophila are subdivided into compartments by the localized expression of transcription factors. Interaction between cells in adjacent compartments establishes organizing centres responsible for generating spatial pattern and promoting cell proliferation in the developing appendages. Localized expression of hedgehog (hh) in the posterior compartment of the leg imaginal disc directs expression of wingless (wg) in ventral-anterior cells and decapentaplegic (dpp) in dorsal-anterior cells near the anterior-posterior compartment boundary; wg then acts to specify ventral cell fate and to organize the dorsal-ventral axis of the leg. Interaction between wg-expressing ventral cells and dorsal cells near the anterior-posterior compartment boundary promotes axis formation in the leg. Here we show that the combined action of wg-expressing cells in the ventral-anterior compartment and dpp-expressing cells in the dorsal-anterior compartment activates expression of Distal-less, a gene required for proximal-distal axis formation in the limbs. These results demonstrate that sequential interaction between anterior-posterior and dorsal-ventral compartments establishes the proximal-distal axis of the limbs.

Animals↗
PubMed1994

Sp1/egr-like zinc-finger protein required for endoderm specification and germ-layer formation in Drosophila.

Much of our present knowledge of the biological processes involved in pattern formation in Drosophila is derived from segmentation analysis. Comparatively little is known about the genetic requirement and mechanisms underlying the formation and separation of germ layers by morphogenetic movements during gastrulation. Here we show that the Drosophila gene huckebein (hkb), a member of the gap-gene class of segmentation genes, is required for germ-layer formation at blastoderm. Absence of the hkb product, an Sp1/egr-like zinc-finger protein, causes the ectodermal and mesodermal primordia to expand at the expense of endoderm anlagen. Conversely, ectopic expression of hkb inhibits the formation of the major gastrulation fold which gives rise to the mesoderm and prevents normal segmentation in the ectoderm. Thus, hkb is necessary for endoderm development and its activity defines spatial limits within the blastoderm embryo in which the germ layers are established.

Amino Acid Sequence↗
PubMed1994

The human interferon alpha/beta receptor: characterization and molecular cloning.

We describe a universal ligand-binding receptor for human interferons alpha and interferon beta (type I IFNs). A soluble 40 kDa IFN-alpha/beta receptor (p40) that blocks the activity of type I IFNs was purified from urine and sequenced. Antibodies raised against p40 completely block the activity of several type I IFNs and immuno-precipitate both a cellular 102 kDa IFN-alpha/beta receptor and its cross-linked complexes with IFN-alpha 2. The receptor is a disulfide-linked dimer, consisting of 51 kDa subunits. We isolated and expressed a 1.5 kb cDNA, coding for the IFN-alpha/beta receptor. Its 331 amino acid sequence includes a leader and a transmembrane region, while its ectodomain corresponds to p40. IFN-alpha/beta receptor is physically associated with the cytoplasmic Tyr kinase JAK1, hence, in addition to ligand binding, it is directly involved in signal transduction.

3T3 Cells↗
PubMed1994

Compressive stress-relaxation behavior of bovine growth plate may be described by the nonlinear biphasic theory.

The compressive behavior of the bovine distal femoral growth plate was studied in vitro. Strain-rate controlled, compression stress-relaxation experiments were performed on cylindrical bone-growth plate-bone specimens from the interior and periphery of the growth plate. The questions addressed in this study were (a) Can the nonlinear biphasic theory, one with strain-dependent permeability, be used to represent the compressive stress-relaxation behavior of bovine growth plate? (b) How do different assumptions concerning the permeabilities of the chondro-osseous interfaces influence the inferred material properties of the growth plate? and (c) Are there any differences in these properties between the periphery and the interior of the growth plate? Intrinsic biphasic material properties--aggregate modulus (HA), Poisson's ratio (v), and nonlinear strain-dependent permeability coefficients (ko and M)--were calculated from the compression stress-relaxation data with use of a finite element model and a least squares curve-fitting procedure. To verify this constitutive model for the growth plate, an independent set of finite element analyses was performed with use of the determined intrinsic biphasic properties, and comparisons were made between these finite element predictions and two additional sets of experimental data subsequently obtained for the same specimens with use of two slower rates of compression. Excellent agreement was achieved between these finite element predictions and the latter two sets of data. The aggregate modulus was found to be insensitive to the permeability of the chondro-osseous interface. The permeability coefficients were very sensitive to, and the Poisson's ratio was only slightly sensitive to the interface permeability condition. Therefore, the periphery of the growth plate is more compliant and permeable than the interior.

Animals↗
PubMed1994

Effects of spaceflight on ocular counterrolling and the spatial orientation of the vestibular system.

We recorded the horizontal (yaw), vertical (pitch), and torsional (roll) eye movements of two rhesus monkeys with scleral search coils before and after the COSMOS Biosatellite 2229 Flight. The aim was to determine effects of adaptation to microgravity on the vestibulo-ocular reflex (VOR). The animals flew for 11 days. The first postflight tests were 22 h and 55 h after landing, and testing extended for 11 days after reentry. There were four significant effects of spaceflight on functions related to spatial orientation: (1) Compensatory ocular counterrolling (OCR) was reduced by about 70% for static and dynamic head tilts with regard to gravity. The reduction in OCR persisted in the two animals throughout postflight testing. (2) The gain of the torsional component of the angular VOR (roll VOR) was decreased by 15% and 50% in the two animals over the same period. (3) An up-down asymmetry of nystagmus, present in the two monkeys before flight was reduced after exposure to microgravity. (4) The spatial orientation of velocity storage was shifted in the one monkey that could be tested soon after flight. Before flight, the yaw axis eigenvector of optokinetic afternystagmus was close to gravity when the animal was upright or tilted. After flight, the yaw orientation vector was shifted toward the body yaw axis. By 7 days after recovery, it had reverted to a gravitational orientation. We postulate that spaceflight causes changes in the vestibular system which reflect adaptation of spatial orientation from a gravitational to a body frame of reference. These changes are likely to play a role in the postural, locomotor, and gaze instability demonstrated on reentry after spaceflight.

Animals↗
PubMed1994

Stimulation of the nodulus and uvula discharges velocity storage in the vestibulo-ocular reflex.

The nodulus and sublobule d of the uvula of rhesus and cynomolgus monkeys were electrically stimulated with short trains of pulses to study changes in horizontal slow-phase eye velocity. Nodulus and uvula stimulation produced a rapid decline in horizontal slow phase velocity, one aspect of the spatial reorientation of the axis of eye rotation that occurs when the head is tilted with regard to gravity during per- and post-rotatory nystagmus and optokinetic after-nystagmus (OKAN). Nodulus and uvula stimulation also reproduced the reduction of the horizontal time constant of post-rotatory nystagmus and OKAN that occurs during visual suppression. The brief electric stimuli (4-5 s) induced little slow-phase velocity and had no effect on the initial jump in eye velocity at the onset or the end of angular rotation. Effects of stimulation were unilateral, suggesting specificity of the output pathways. Activation of more caudal sites in the uvula produced nystagmus with a rapid rise in eye velocity, but the effects did not outlast the stimulus and did not affect VOR or OKAN time constants. Thus, stimulation of caudal parts of the uvula did not affect eye velocity produced by velocity storage. We postulate that the nodulus and sublobule d of the uvula control the time constant of the yaw axis (horizontal) component of slow-phase eye velocity produced by velocity storage.

Animals↗
PubMed1994

Orientation of human optokinetic nystagmus to gravity: a model-based approach.

Optokinetic nystagmus (OKN) was induced by having subjects watch a moving display in a binocular, head-fixed apparatus. The display was composed of 3.3 degrees stripes moving at 35 degrees/s for 45 s. It subtended 88 degrees horizontally by 72 degrees vertically of the central visual field and could be oriented to rotate about axes that were upright or tilted 45 degrees or 90 degrees. The head was held upright or was tilted 45 degrees left or right on the body during stimulation. Head-horizontal (yaw axis) and head-vertical (pitch axis) components of OKN were recorded with electro-oculography (EOG). Slow phase velocity vectors were determined and compared with the axis of stimulation and the spatial vertical (gravity axis). With the head upright, the axis of eye rotation during yaw axis OKN was coincident with the stimulus axis and the spatial vertical. With the head tilted, a significant vertical component of eye velocity appeared during yaw axis stimulation. As a result the axis of eye rotation shifted from the stimulus axis toward the spatial vertical. Vertical components developed within 1-2 s of stimulus onset and persisted until the end of stimulation. In the six subjects there was a mean shift of the axis of eye rotation during yaw axis stimulation of approximately 18 degrees with the head tilted 45 degrees on the body. Oblique optokinetic stimulation with the head upright was associated with a mean shift of the axis of eye rotation toward the spatial vertical of 9.2 degrees. When the head was tilted and the same oblique stimulation was given, the axis of eye rotation rotated to the other side of the spatial vertical by 5.4 degrees. This counterrotation of the axis of eye rotation is similar to the "Müller (E) effect," in which the perception of the upright is counterrotated to the opposite side of the spatial vertical when subjects are tilted in darkness. The data were simulated by a model of OKN with a "direct" and "indirect" pathway. It was assumed that the direct visual pathway is oriented in a body, not a spatial frame of reference. Despite the short optokinetic after-nystagmus time constants, strong horizontal to vertical cross-coupling could be produced if the horizontal and vertical time constants were in proper ratio and there were no suppression of nystagmus in directions orthogonal to the stimulus direction. The model demonstrates that the spatial orientation of OKN can be achieved by restructuring the system matrix of velocity storage. We conclude that an important function of velocity storage is to orient slow-phase velocity toward the spatial vertical during movement in a terrestrial environment.

Adult↗
PubMed1994

Posterior dislocation of the shoulder: recommendations for a classification.

Posterior dislocation of the should is rare, constituting only 2.1% of all shoulder dislocations. The mechanisms of injury may be due to direct or indirect forces, and constitutional predisposing factors also play a role. Anatomically, 97.5% of dislocations are subacromial. Three hundred articles published in the international literature concerning posterior shoulder dislocation and subluxation were reviewed and a classification determined by the underlying aetiology was developed. On this basis dislocations and subluxations may be traumatic or atraumatic, primary and recurrent; recurrent cases of voluntary dislocation are considered separately. In addition, a follow-up assessment score weighted towards stability of the shoulder after treatment is detailed.

Humans↗
PubMed1994

Results of the Souter-Strathclyde total elbow arthroplasty in patients with rheumatoid arthritis. A preliminary report.

The results of 19 consecutive Souter-Strathclyde total elbow arthroplasties (Zimmer, London) in 17 patients with a mean follow-up time of 41 months are reported. Pain relief was achieved in all cases, with 13 elbows becoming entirely pain-free. The mean range of flexion increased 24 degrees and extension improved 8 degrees, with upper limb function greatly improved. The complication rate was 32%, including three nerve palsies, of which two resolved completely, and three early postoperative dislocations. There were two cases of prosthetic loosening, one following revision surgery for a traumatic humeral fracture in the early postoperative period. The authors consider the overall functional results with the Souter-Strathclyde prosthesis to be satisfactory in this group of patients.

Adult↗
PubMed1994

p53 mutations in cervical carcinogenesis--low frequency and lack of correlation with human papillomavirus status.

p53 gene aberrations are common in human malignancies, and recent studies suggest that in cervical carcinoma p53 function is inactivated either by complex formation with human papillomavirus (HPV) E6 product or by gene mutation. Using polymerase chain reaction (PCR) followed by denaturing gradient gel electrophoresis (DGGE), we examined the mutational status of the four 'hotspot' regions of the p53 gene in 47 primary cervical carcinomas. HPV status was determined, also by PCR. In 20 of these cases, we examined for loss of heterozygosity (LOH) on chromosome 17p13. In the 47 carcinomas, and in a further 68 biopsy specimens from normal, premalignant and malignant cervix, we investigated aberrant immunocytochemical expression of p53. Immunocytochemically, abnormal p53 expression was detected in 13 of 115 cases (8/57 carcinomas). Somatic mutation in p53 was detected in 1 of 47 cervical carcinomas; 36 were positive for HPV 16, 18 or 33. A low level of allele loss (3 out of 20 cases) was detected on chromosome 17p, occurring in both HPV-positive and HPV-negative cases, and in cases with and without p53 mutations. We conclude that somatic mutation in the hotspot regions of the p53 gene occurs infrequently in cervical carcinomas; that immunocytochemically detectable levels of p53 are also infrequent; and that there is no consistent correlation between p53 mutational status, LOH on chromosome 17p or HPV status in these cancers.

Adenocarcinoma↗
PubMed1994

Study of the distribution of oral ciprofloxacin into the mucosa of the middle ear and the cortical bone of the mastoid process.

This multicentre study evaluates the distribution of ciprofloxacin into the tissue structures of the middle ear following multiple dosing of one 500 mg tablet every 12 h. The samples were taken perioperatively from adult patients due to undergo surgery for chronic otitis. Administration of ciprofloxacin was instigated 9 days prior to the operation. The samples were taken at different intervals after the last dose in order to evaluate variations in concentration with time. The average peak concentrations recorded and the time taken to reach these concentrations were as follows: middle ear mucosa (n = 16): 5.54 +/- 3.46 micrograms/g (3-4 h): cortical bone of the mastoid process (n = 21): 1.07 +/- 1.29 micrograms/g (4 h). The measurements carried out 12 h after the last dose show that concentrations of ciprofloxacin in the middle ear mucosa were still at least as high as the minimum inhibitory concentration for this antibiotic for most of the pathogens implicated in acute exacerbations of chronic otitis. These results suggest that, administered as an oral dose of 500 mg every 12 h, ciprofloxacin may be an effective agent for the treatment of chronic suppurative otitis. These results now need to be backed up by clinical trials.

Administration, Oral↗