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Biomedical subjects

T D Brown

Publications and source records attributed to T D Brown.

At least 37 records · Page 2Linked to original sources
PubMed2000

Techniques for mechanical stimulation of cells in vitro: a review.

A wide variety of laboratory apparatuses have been devised for mechanical stimulation of cell and tissue cultures. This article reviews the functional attributes of several dozen systems developed for that purpose, including their major advantages and disadvantages. These devices can be categorized in terms of their primary loading modality: compression (hydrostatic pressure or direct platen contact), longitudinal stretch, bending, axisymmetric substrate bulge, in-plane substrate distention, fluid shear stress, or combined substrate distention and fluid shear.

Biomechanical Phenomena↗
PubMed2000

Complications with humeral head replacement.

Humeral head replacement has been shown to be an excellent surgical option for a variety of debilitating shoulder conditions. New techniques and advances in prosthetic design have furthered the success of this procedure. When performed without appropriate indications, exacting technique, and a tailored rehabilitation program, however, complications often result. Early recognition and appropriate management of these complications aid in achieving a satisfactory result.

Aged↗
PubMed2000

In-hospital resuscitation: association between ACLS training and survival to discharge.

CONTEXT: No data have been published on the relationship between advanced cardiac life support (ACLS) training of the individual who initiates resuscitation efforts and survival to discharge. OBJECTIVE: To determine whether patients whose arrests were discovered by nurses trained in ACLS had survival rates different from those discovered by nurses not trained in ACLS. DESIGN: Cohort case-comparison. SETTING: A 550-bed, tertiary care center in central Georgia. SUBJECTS: Patients whose cardiopulmonary arrest was discovered by a nurse who activated the in-hospital resuscitation mechanism. MAIN OUTCOME MEASURE: Patient survival to discharge. RESULTS: Initial rhythm was strongly related to survival to discharge and individually associated with 57% of the variability in survival. Nurse's training in advanced cardiac life support was also strongly related to survival and individually associated with 29% of the variability. Combining both the variables determined 62% of the variability in survival to discharge. Patients discovered by an ACLS-trained nurse (n=88) were about four times more likely to survive (33 survivors, 38%) than were patients, discovered by a nurse without training in ACLS (n=29, three survivors, 10%). CONCLUSION: Arrest discovery by nurses trained in ACLS is significantly and dramatically associated with higher survival-to-discharge rates.

Advanced Cardiac Life Support↗
PubMed2000

Resuscitation in the hospital: relationship of year and rhythm to outcome.

OBJECTIVE: determine the frequency of initial rhythms in in-hospital resuscitation and examine its relationship to survival. Assess changes in outcome over time. METHODS: retrospective cohort (registry) including all admissions to the Medical Center of Central Georgia in which a resuscitation was attempted between 1 January, 1987 and 31 December, 1996. RESULTS: the registry includes 3327 admissions in which 3926 resuscitations were attempted. Only the first event is reported. There were 961 hospital survivors. Survival increased from 24.2% in 1987 to 33.4% in 1996 (chi(2)=39.0, df=1, P<0.0001). Survival was affected strongly by initial rhythm (chi(2)=420.0, df=1, P<0.0001) and decreased from 63.2% for supraventricular tachycardia (SVT) to 55.3% for ventricular tachycardia (VT), 51.0% for perfusing rhythms (PER), 34.8% for ventricular fibrillation (VF), 14.3% for pulseless electrical activity (PEA) and 10.0% for asystole (ASYS). PEA was the most frequent rhythm (1180 cases) followed by perfusing (963), asystole (580), VF (459), VT (94) and SVT (38). DISCUSSION: the powerful effect of initial rhythm on survival has been reported in pre-hospital and in-hospital resuscitation. VF is considered the dominant rhythm and generally accounts for the most survivors. We report good outcome for each; however, VF represents only 13.8% of events and 16.7% of survivors. PEA accounts for more survivors (169) than does VF (160). Our improved outcome is partially explained by changes in rhythms, but other institutional variables need to be identified to fully explain the results. Further studies are needed to see if our findings can be sustained or replicated.

Adolescent↗
PubMed2000

Hinged external fixation of the elbow: optimal axis alignment to minimize motion resistance.

OBJECTIVE: To establish an optimal single hinge axis position for application of hinged external fixation to the elbow joint. DESIGN: Cadaveric biomechanical investigation. SETTING: A customized motion transducer applied passive elbow motion to six cadaveric upper extremities. The instant rotation axis of the humero-ulnar articulation was determined from three-dimensional kinematic data acquired by an electromagnetic motion tracking system. For each specimen, an optimal fixator hinge position was calculated from these motion data. INTERVENTION: A prototype articulated external fixator was applied to the elbow, first with its hinge aligned along the computed optimal position. Then the fixator was mounted in sixteen distinct off-axis positions. MAIN OUTCOME MEASURE: Additional resistance to joint motion (in terms of energy) corresponding to deliberately introduced amounts of relative malalignment between the optimal elbow axis and the actual fixator hinge axis. RESULTS: Aligning the fixator hinge along the optimized axis position resulted in a minimal amount of energy (0.15 joules) needed to rotate the elbow through a prescribed range of motion. Malpositioning the hinge by ten millimeters caused up to ten times that amount of motion resistance. CONCLUSIONS: An optimal fixator hinge position can be determined to minimize the increase in motion resistance due to fixator application. The severely increased motion resistance associated with small amounts of malalignment between the fixator hinge and the anatomic elbow axis suggests the need for highly accurate fixator hinge application.

Cadaver↗
PubMed2000

Airbag associated fatal head injury: case report and review of the literature on airbag injuries.

Airbags have been shown to significantly reduce mortality and morbidity in motor vehicle crashes. However, the airbag, like the seat belt, produces its own range of injuries. With the increasing use of airbags in the UK, airbag associated injuries will be seen more often. These are usually minor, but in certain circumstances severe and fatal injuries result. Such injuries have been described before in the medical literature, but hitherto most reports have been from North America. This is the first case report from the UK of serious injury due to airbag deployment and describes the case of a driver who was fatally injured when her airbag deployed in a moderate impact frontal collision where such severe injury would not normally have been anticipated. The range of airbag associated injuries is described and predisposing factors such as lack of seat belt usage, short stature, and proximity to airbag housing are discussed. The particular dangers airbags pose to children are also discussed.

Accidents, Traffic↗
PubMed2000

Total ankle replacement revisited.

The surgical treatment of painful, end-stage ankle arthritis includes ankle arthrodesis and total ankle replacement. In the past decade, total ankle replacement has become a viable alternative to ankle arthrodesis. Modern implant designs either involve a syndesmosis fusion and resurfacing of the medial and lateral recesses of the ankle joint or the use of a 3-component, mobile bearing implant. In limited clinical series, the early results of both these prosthetic design approaches are encouraging. In selected patients, ankle arthroplasty is an effective approach to relieving pain and improving function. The purposes of this paper are to review the clinical results from total ankle replacement and ankle arthrodesis; discuss indications, contraindications, design features, postoperative rehabilitation, and initial results for the major current total ankle designs; and present concepts for future total ankle development. In particular, this article explores the advantages and concerns with 2 prevalent but different design approaches. It also discusses future directions for total ankle replacement.

Ankle Joint↗
PubMed2000

Rotator cuff tears and associated nerve injuries.

A series of 15 patients with concomitant rotator cuff tears and infraclavicular brachial plexus injuries treated between 1980 and 1989 were reviewed. There were 6 men and 9 women with a mean age of 65 years. Seventeen nerve injuries were identified, including 12 axillary nerves, 4 suprascapular nerves, and 1 musculocutaneous nerve. One patient had an injury to all three nerves. Thirteen patients underwent operative repair of the torn rotator cuff, and 2 patients who refused surgery were treated conservatively. The average time from injury to surgery was 7.7 months. Follow-up averaged 5.5 years (range: 2-10 years). Clinical results were graded according to pain, range of motion, and strength. Postoperatively, mean active forward elevation was 137 degrees and mean active external rotation was 40 degrees. Clinically, 8 patients achieved complete nerve recovery and 7 had an incomplete recovery. Satisfactory pain relief was achieved in 87% of patients with 60% having excellent or good function. Overall, the results of rotator cuff repair with concurrent nerve injury are less favorable than those of isolated cuff repairs. Careful preoperative assessment of concomitant nerve injury should be performed to better predict outcome.

Adult↗
PubMed2000

High density polyetherurethane foam as a fragmentation and radiographic surrogate for cortical bone.

BACKGROUND: Although one of the most important factors in predicting outcome of articular fracture, the comminution of the fracture is only subjectively assessed. To facilitate development of objective, quantitative measures of comminution phenomena, there is need for a bone fragmentation surrogate. METHODS: Laboratory investigation was undertaken to develop and characterize a novel synthetic material capable of emulating the fragmentation and radiographic behavior of human cortical bone. RESULT: Screening tests performed with a drop tower apparatus identified high-density polyetherurethane foam as having suitable fragmentation properties. The material's impact behavior and its quasi-static mechanical properties are here described. Dispersal of barium sulfate (BaSO4) in the resin achieved radio-density closely resembling that of bone, without detectably altering mechanical behavior. The surrogate material's ultimate strength, elastic modulus, and quasi-static toughness are within an order of magnitude of those of mammalian cortical bone. The spectrum of comminution patterns produced by this material when impacted with varying amounts of energy is very comparable to the spectrum of bone fragment comminution seen clinically. CONCLUSIONS: A novel high-density polyetherurethane foam, when subjected to impact loading, sustains comminuted fracture in a manner strikingly similar to cortical bone. Moreover, since the material also can be doped with radio-opacifier so as to closely emulate bone's radiographic signature, it opens many new possibilities for CT-based systematic study of comminution phenomena.

Barium Sulfate↗
PubMed1999

Articulated external fixation of the ankle: minimizing motion resistance by accurate axis alignment.

This study describes how an optimal single hinge axis position can be established for the application of articulated external fixation to the ankle joint. By deliberately introducing various amounts of relative mal-alignment between the optimal talocrural joint axis and the actual fixator hinge axis, it was possible to measure the corresponding amounts of additional resistance to joint motion. In a cadaveric study of six ankle specimens, we determined the instant axis of rotation of the talocrural joint from 3-D kinematic data. acquired by an electromagnetic motion tracking system. For each specimen, an optimal fixator hinge position was calculated from these motion data. Compared to the intact natural joint, aligning the fixator along the optimized axis position caused a moderate increase in energy (0.14 J) needed to rotate the ankle through a prescribed plantar/dorsiflexion range. However, malpositioning the hinge by 10 mm caused more than five times that amount of increase in motion resistance. While articulated external fixation with limited internal fixation can establish a favorable environment for the repair of severe injuries such as tibial pilon fractures, the large additional resistance to motion accompanying a malpositioned fixator axis suggests the development of untoward intra-articular forces that could act to disturb fragment alignment.

Ankle↗
PubMed1999

Periprosthetic fractures of the acetabulum.

Periprosthetic acetabular fractures during and after total hip replacement occur infrequently. Intraoperative fractures have risen with the use of press fit cementless fixation techniques and postoperative fractures are increasing because of the long-term problems associated with osteolysis. This article outlines the classification and management of these fractures.

Acetabulum↗
PubMed1999

Activity of a purified His-tagged 3C-like proteinase from the coronavirus infectious bronchitis virus.

Previous studies in vitro of the processing of cloned polyprotein fragments from the coronavirus infectious bronchitis virus (IBV) large open reading frame (ORF1), confirmed the activity of a predicted 3C-like proteinase (3CLP) domain and suggested that the proteinase is released autocatalytically from the polyprotein in the form of a 35 kDa protein, 3CLpro, capable of further cleavages in trans. In order to identify such cleavages within the ORF1 polyprotein mediated by 3CLpro, the proteinase was expressed in bacteria, purified and used in trans cleavage assays with polyprotein fragments lacking the 3CLP domain as targets. The proteinase was expressed as a polyprotein fragment which was able to process during expression in bacterial cells, releasing mature 3CLpro. A histidine (His6) tag was introduced close to the C-terminus of the proteinase to aid purification. Processing demonstrated by the tagged proteinase was indistinguishable from that of the wild-type enzyme indicating that the site chosen for the tag was permissive. From these studies we were able to demonstrate trans cleavages consistent with the use of most of the previously predicted or identified sites within the open reading frame of gene 1. This tentatively completes the processing map for the ORF1 region with respect to 3CLpro.

Animals↗
PubMed1999

Finite element analysis of a novel design approach to resisting total hip dislocation.

OBJECTIVE: A new design concept has been developed to reduce the propensity for dislocation in total hip patients. The ability of this design to increase the stability of the hip joint is studied. DESIGN: The new design involves a convex-curved acetabular lip, extending from the hemispherical articulating surface to the outer edge of the cup. The femoral component has a matching, reverse curve. BACKGROUND: Dislocation is a continuing problem in total hip arthroplasty, a complication experienced by 2-11% of patients with primary surgeries, and much higher percentage of patients in revision series. Confounding factors and sources of variability in the clinical domain make it difficult to identify specific parameter influences. METHODS: A three-dimensional nonlinear finite element model has been developed for the purpose of studying the dislocation event. We report the first use of this finite element model to analyze the potential for improving hip stability by a new total hip component design concept. RESULTS: The results show that this new design achieves 28% more resisting moment build-up during dislocation, and has a higher range of motion from impingement to onset of subluxation. The new curved lip design also develops 50% less polyethylene von Mises stress in the impingement zone. CONCLUSIONS: This design has excellent potential for increasing the inherent stability of the total hip joint. RELEVANCE: Recurrent dislocation is the second leading cause of total hip failure next to late loosening. This study shows the potential of a new total hip design to increase the stability of the artificial hip joint.

Arthroplasty, Replacement, Hip↗
PubMed1999

Phase II trial of menogaril in non-Hodgkin's lymphomas: a Southwest Oncology Group trial.

PURPOSE: To assess the efficacy and toxicity of menogaril against non-Hodgkin's lymphoma (NHL) in a group of previously treated patients. PATIENTS AND METHODS: Sixty-two eligible patients with a histologic diagnosis of NHL were enrolled, 35 of who had intermediate or high-grade histologies and 27 of who had low-grade lymphomas. Patients with intermediate or high-grade lymphomas had received only 1 prior chemotherapy regimen, while patients with low-grade histologies had received 1 or 2 prior chemotherapy regimens. Menogaril was administered at 160 mg/m2 intravenously over 1 hour, once every 28 days. RESULTS: Among the 35 patients with intermediate or high-grade lymphomas who were evaluable for response, 6 of 35 patients achieved a partial response (PR) for a response rate of 17% (95% confidence interval: 7%-34%). Median survival in this group of patients was 13 months. For those patients with low-grade lymphoma, 5 of 26 patients achieved a PR for a response rate of 19% (95% confidence interval: 6%-38%). No complete responses were observed in either patient group. The incidence of serious (grade 3 or 4) toxicity for those with intermediate/high-grade and low-grade lymphomas was 43% and 44%, respectively. Most of these toxic effects consisted of reversible myelosuppression. Menogaril was discontinued in 2 patients due to prolonged neutropenia. Cardiotoxicity was observed in 4 patients, requiring discontinuation of the drug in 1 patient. No treatment-related deaths occurred and the overall toxicity was felt to be acceptable. CONCLUSION: The observed antitumor activity of single agent menogaril against both intermediate/high-grade and low-grade lymphomas was modest. Further exploration of this agent in patients with non-Hodgkin's lymphomas does not seem warranted.

Aged↗
PubMed1999

Avian encephalomyelitis virus is a picornavirus and is most closely related to hepatitis A virus.

The complete RNA genome of avian encephalomyelitis virus (AEV) has been molecularly cloned and sequenced. This revealed AEV to be a member of the Picornaviridae and consequently it is the first avian picornavirus for which the genome has been sequenced. Excluding the poly(A) tail the genome comprises 7032 nucleotides, which is shorter than that of any mammalian picornavirus sequenced to date. An open reading frame commencing at nucleotide 495 and terminating at position 6896 (6402 nucleotides) potentially encodes a polyprotein of 2134 amino acids. The polyprotein sequence has 39% overall amino acid identity with hepatitis A virus (HAV; genus Hepatovirus), compared to 19 to 21% for viruses from the other five picornavirus genera. Eleven cleavage products were predicted. The highest identity (49%) with HAV was in the P1 region, encoding the capsid proteins. The 5' and 3' untranslated regions (UTRs) comprise 494 and 136 nucleotides, respectively. The 5' UTR is the shortest of any picornavirus sequenced to date and, unlike HAV, it does not contain a long polypyrimidine tract.

Amino Acid Sequence↗
PubMed1999

Posterior cruciate ligament function following total knee arthroplasty: the effect of joint line elevation.

One of the most commonly cited reasons for retaining the posterior cruciate ligament (PCL) during total knee arthroplasty is to preserve femoral rollback and theoretically improve extensor mechanism efficiency (lengthening the moment arm). This study was undertaken to assess PCL function in this regard and to delineate the effects of joint line elevation that can be manipulated intraoperatively by the surgeon. The anterior movement of tibiofemoral contact following PCL resection at flexion angles 60 degrees demonstrated the beneficial effect of the PCL on extensor function. This anterior translation and the concomitant increases in quadriceps tendon load and patellofemoral contact pressures were consistently observed. This study demonstrated that small changes of the joint line position significantly influenced PCL strain and knee kinematics. In order to preserve the desired functions that would be lost with an overly lax PCL and to avoid the potential adverse effects of an overly tight PCL (posterior edge loading and increased tibiofemoral contact), the surgeon should make every effort to restore the preoperative joint line. If this is not possible, consideration should be given to posterior cruciate recession or use of a posterior cruciate substituting design.

Adult↗
PubMed1998

Mechanical behavior of human morselized cancellous bone in triaxial compression testing.

Despite its widespread use as graft material in orthopaedic surgical procedures, morselized cancellous bone has not yet been well characterized from the standpoint of its mechanical properties. To accommodate the noncohesive nature of this loose particulate form of bone, a triaxial compression test apparatus commonly used in engineering soil mechanics was adapted for the testing of fresh-frozen human morselized cancellous bone specimens. Triaxial compression tests were run to 30% axial strain at five different levels of confining pressure ranging from 0.276 to 0.552 MPa. The measured axial stress versus axial strain behavior was bimodal, characterized initially by relatively stiff linear behavior, then by a rapid transition to a much more compliant (but, again, approximately linear) domain until test cessation. The apparent axial moduli of both response regions were found to be nearly linear functions of the transverse confining pressure. As typically prepared surgically, the distribution of particle size was found to have approximately 80% of the bone graft, by weight, encompassed in particles 0.42-3.2 mm in size. Triaxial tests of samples segregated by size showed that particle size had no appreciable effect on apparent material properties. The nominal Young's modulus and Poisson's ratio of morselized cancellous bone were 100 MPa and 0.2, respectively.

Biomechanical Phenomena↗