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Biomedical subjects

M A Ritter

Publications and source records attributed to M A Ritter.

At least 19 recordsLinked to original sources
PubMed2005

Negative ultrasound findings in patients with cervical artery dissection. Negative ultrasound in CAD.

BACKGROUND: Cervical artery dissection (CAD) is a common cause of ischemic stroke in the younger age group. Modern imaging techniques allow the depiction of the mural hematoma, even in CADs with only subtle vessel alterations. The aim of this retrospective study was (1) to characterize the angiological features in CAD and (2) to determine the frequency of initially normal ultrasonography (US) findings. METHODS: 86 patients aged 44 +/- 11 years with CAD of the internal carotid (ICA), (n = 55) or the vertebral artery (VA), (n = 31), admitted to our hospital within 8 days (mean 1.6 days) of symptom onset, were included. CAD was confirmed either by CT-angiography, MRI of the neck, MR-angiography or digital substraction angiography (DSA) and was compared with the results of the initial as well as repeated US examinations of the arteries supplying the brain. RESULTS: In 75 patients (81.2 %) signs of vessel stenosis or occlusion were found while 11 patients (12.8%) with CAD of the ICA (n = 9) and the VA (n = 2) had normal US findings. The site of dissection in the US negative patients was highly variable without a predilection site. In 2 of 7 patients with repeated US examinations, complete vessel occlusion was found on follow-up, while in 5 patients again normal results were found. In four patients, there were changing findings in two alternative confirming imaging methods (MRI/DSA, CT/MRI) and in one patient conflicting findings (CT/MRI). Brain infarctions had occurred in 7 of the initially sonographically normal patients while the other 4 had suffered from transient (n = 2) or local (n = 2) symptoms only. CONCLUSION: Approximately 1 out of 8 patients with subsequently proven CAD has negative initial neurovascular US findings despite comprehensive examination. In patients with suspected CAD and negative US examination, repeated US examinations and further diagnostic imaging, especially MRI is necessary.

Adult↗
PubMed2005

Intensity-modulated radiation therapy: emerging cancer treatment technology.

The use of intensity-modulated radiation therapy (IMRT) is rapidly advancing in the field of radiation oncology. Intensity-modulated radiation therapy allows for improved dose conformality, thereby affording the potential to decrease the spectrum of normal tissue toxicities associated with IMRT. Preliminary results with IMRT are quite promising; however, the clinical data is relatively immature and overall patient numbers remain small. High-quality IMRT requires intensive physics support and detailed knowledge of three-dimensional anatomy and patterns of tumour spread. This review focuses on basic principles, and highlights the clinical implementation of IMRT in head and neck and prostate cancer.

Dose-Response Relationship, Radiation↗
PubMed2005

Role of cerebral amyloid angiopathy in intracerebral hemorrhage in hypertensive patients.

OBJECTIVE: To assess the interaction of cerebral amyloid angiopathy (CAA) and arterial hypertension as cofactors for intracerebral hemorrhage (ICH). METHODS: The authors investigated 129 postmortem brains of hypertensive patients with and without ICH. Sixty-four patients had had deep (n = 40) or lobar (n = 24) ICH. Sixty-five patients without ICH served as controls. Established risk factors for ICH (age, gender, severity of hypertension, bleeding disorders, intake of anticoagulants, and chronic alcoholism) were identified from medical records. Four specimens per brain were stained with hematoxylin-eosin and Congo red. The entire ICH cohort and subgroups were compared with controls using single-factor and multiple logistic regression analyses. RESULTS: CAA was found in 15 of 64 subjects (23%) with ICH and in five of 65 controls (8%; p = 0.026). In single-factor analysis, CAA was more prevalent in lobar ICH compared with controls (p = 0.007) but not in deep ICH. Poor control of hypertension was more prevalent in the entire ICH group (p = 0.01) and in deep ICH (p = 0.016) but not in lobar ICH. ICH was predictive of the presence of CAA (odds ratio: 5.6, 95% CI: 1.8 to 19.5, p = 0.003), and CAA was more likely to be found in lobar ICH in multivariable-adjusted analysis. After adjustment for conventional risk factors, there was a weak association between CAA and deep ICH. CONCLUSION: Cerebral amyloid angiopathy plays a major role in the pathogenesis of intracerebral hemorrhage even in patients with more evident risk factors.

Aged↗
PubMed2004

Toll-like receptor mRNA expression patterns in human dendritic cells and monocytes.

The innate immune system recognises a wide spectrum of pathogens without a need for prior exposure. The main cells responsible are monocytes, macrophages, dendritic cells (DC) and neutrophils phagocytose microbial pathogens triggering a cytokine network resulting in the development of inflammatory and specific immune responses. Findings in the Toll-like receptor (TLR) family, initially discovered in Drosophila, further elucidated these processes. Toll-like receptors induce activation of an innate immune response and at present ten TLRs have been identified, named TLRs 1-10. In addition to the ignition of the innate immune response, evidence implicates the TLR family in a spectrum of systemic disorders following bacterial infections including sepsis and multiple organ failure, and can be detrimental, leading to tissue injury. In this project, our main goal was to investigate the effects of a TLR4 ligand, lipolysaccharide (LPS) in human DC and monocytes. Our hypothesis is that different professional APCs, express different mRNA TLR transcripts. Our findings indicate that TLR expression patterns change in relation to the pathogen involved and in the case of DC, and the maturation stage the latter are upon challenging. Our results and interpretation showed significant alteration of transcript expression patterns upon LPS challenge in all cell subsets, with DC subsets expressing different TLR mRNA patterns as they go through different maturation stages.

Dendritic Cells↗
PubMed2004

Design of adaptive treatment margins for non-negligible measurement uncertainty: application to ultrasound-guided prostate radiation therapy.

Daily imaging during the course of a fractionated radiotherapy treatment has the potential for frequent intervention and therefore effective adaptation of the treatment to the individual patient. The treatment information gained from such images can be analysed and updated daily to obtain a set of patient individualized parameters. However, in many situations, the uncertainty with which these parameters are estimated cannot be neglected. In this work this methodology is applied to the adaptive estimation of setup errors, the derivation of a daily optimal pre-treatment correction strategy, and the daily update of the treatment margins after application of these corrections. For this purpose a dataset of 19 prostate cancer patients was analysed retrospectively. The position of the prostate was measured daily with an optically guided 3D ultrasound localization system. The measurement uncertainty of this system is approximately 2 mm. The algorithm finds the most likely position of the target maximizing an a posteriori probability given the set of measurements. These estimates are used for the optimal corrections applied to the target volume. The results show that the application of the optimal correction strategy allows a reduction in the treatment margins in a systematic way with increasing progression of the treatment. This is not the case using corrections based only on the measured values that do not take the measurement uncertainty into account.

Algorithms↗
PubMed2004

Long-term deterioration of joint evaluation scores.

We investigated the long-term changes in the Harris Hip and Knee Society scores (HSS and KSS) to determine whether they result from overall functional decline rather than actual changes in the condition of the prosthesis. The HHS for 106 total hip arthroplasties with a minimum follow-up of ten years, no medical complications after operation and no evidence of radiological loosening, and the KSS for 264 total knee arthroplasties with a minimum follow-up of 12 years and no medical complications after operation or signs of radiographical loosening were evaluated. There were statistically significant drops in the functional scoring components of the joint evaluation systems despite no loosening of the prostheses or other significant medical complications. The HHS declined at an average of 0.67 points per year from between three and ten years after operation (p < 0.0001). Contributing to this were deterioration in gait and limp (p < 0.0004), the use of support aids (p < 0.0001), the distance walked (p < 0.0001) and the ability to climb stairs (p < 0.0455). The functional component of the KSS declined significantly at an average 0.88 points per year betwen the third and 12th years (p < 0.0001). There were significant declines in every component of the functional score including the distance walked (p < 0.0001), the ability to climb stairs (p < 0.0001) and the use of support aids (p < 0.0001). The knee score component of the KSS did not decline significantly (p < 0.9750). The combination of functional and pain scores within the HHS system leads to an inaccurate decline in the entire score. The decline of HHS and Knee Society functional scores in total joint arthroplasties, in the absence of implant-related problems, suggests that deterioration in the functional capacity of ageing patients is an important factor in longitudinal studies using these scoring systems.

Activities of Daily Living↗
PubMed2004

Intra-operative findings in varus osteoarthritis of the knee. An analysis of pre-operative alignment in potential candidates for unicompartmental arthroplasty.

Interest in unicompartmental knee arthroplasty (UKA) for the treatment of medial compartment osteoarthritis has increased in recent years with apparent improvement in the long-term results. This is a result of improved surgical technique, patient selection, and implant design. In an effort further to improve patient selection we analysed the relationship between the pre-operative alignment of the knee and the anatomical findings at the time of surgery. We compared these findings with the indications for UKA. From 4021 total knee arthroplasties we compared intra-operative observations with the pre-operative clinical data in order to identify knees with isolated, medial, compartment changes, which would have been ideal candidates for UKA. We found that only 247 of the knees (6.1%) met anatomical qualifications for isolated, medial, unicompartmental osteoarthritis, and of these, only 168 (4.3%) met clinical standards ideal for UKA. Preoperative alignment showed a significant relationship with patterns of disease. Logistic regression revealed a relationship between pre-operative alignment and intraoperative findings resembling a Gaussian distribution. Patients with a pre-operative varus alignment of 7 degrees were slightly more likely to be selected for UKA. But the further the anatomical alignment in either direction varies from 7 degrees of varus, the more unlikely it is for the knee to exhibit a disease pattern of isolated, medial, unicompartmental osteoarthritis.

Adult↗
PubMed2003

Arterial hypertension and ischaemic stroke.

OBJECTIVES: Arterial hypertension is, besides age, the number one risk factor for ischaemic stroke. Patients with arterial hypertension frequently present with additional coexisting vascular risk factors interacting in a complex way. MATERIAL AND METHODS: This paper reviews the benefit of antihypertensive treatment, as well as different treatment options of arterial hypertension and their side-effects. RESULTS: Patients with definite arterial hypertension, but also patients with so-called normal or high-normal blood pressure are at increased risk to develop stroke and other cardiovascular complications. Vascular remodelling of small and large vessels provoked by arterial hypertension is the initial step in the development of atherosclerosis and lipohyalinosis. Vascular remodelling can be improved or even normalized by antihypertensive treatment with angiotensin-converting-enzyme inhibitors and angiotensin-I-receptor antagonists showing the most convincing effects. Angiotensin-converting-enzyme inhibitors and angiotensin-I-receptor antagonists have the lowest rate of side-effects, however, economic restraints hinder their general application. Statins are needed to treat dyslipidaemia. They also lower blood pressure and have a synergistic effect with the above two antihypertensive components in lowering blood pressure. In hypertensive patients, risk of stroke and other cardiovascular complications is determined by the blood pressure level and the presence or absence of target organ damage and the interaction with other risk factors, such as cigarette smoking, dyslipidaemia, and diabetes. These high-risk patients should be treated even more aggressively than usual. CONCLUSIONS: In the vast majority of patients and healthy individuals, target blood pressure should be as high as or below 120/80 mmHg to minimize the occurrence of stroke and other cardiovascular complications.

Angiotensin Receptor Antagonists↗
PubMed2001

Does the preoperative radiographic degree of osteoarthritis correlate to results in primary total knee arthroplasty?

The preoperative radiographs of 1,888 patients undergoing 2,759 consecutive total knee arthroplasties (TKAs) performed for osteoarthritis (OA) were retrospectively reviewed to test the hypothesis that patients with less severe OA changes experience less pain relief and lower function scores after TKA. Age at surgery averaged 70.6 years, and follow-up averaged 2.5 years. Preoperatively, pain was independent of an arthritis grade, and this likewise was noted at > or =3 years after surgery. Patients with severe and mild radiographic changes of OA eventually experienced the same degree of function and pain relief after TKA.

Adult↗
PubMed2001

The clinical significance of vacuum mixing bone cement.

This controlled study compared the strength and porosity of 48 polymethylmethacrylate cement-implant constructs prepared with open bowl versus vacuum mix technique. Forty-eight blast finished stainless steel rods of 13 mm diameter were implanted with centralizers into 17-mm inner diameter tubes that had been retrograde filled with polymethylmethacrylate cement. The eight cement preparations used were open bowl and vacuum mixed Simplex, Osteobond, Zimmer Dough Type, or Palacos R. Six replications of each condition were performed. The tubes were maintained at 37 degrees C. Each tube was cut transversely into five segments. The center three segments were used for data analysis: pushout strength, cycles to failure, and interface porosity analysis. Rod pushout data showed there was no significant difference between open bowl and vacuum mixed samples when all cement brands were combined. Mean sheer force for Palacos R vacuum mixed samples was greater than open bowl (634+/-47 versus 423+/-171), whereas the force for the Zimmer Dough Type cement open bowl was greater than that of the vacuum mixed samples (901+/-71 versus 705 +/-82). Cycles to failure data did not show significant differences when open bowl and vacuum mixed samples were compared when cements were analyzed individually or combined. Image analysis of cement-implant interfaces showed that vacuum mixing reduced void area significantly compared with open bowl mixing in the Palacos R and Osteobond preparations. Vacuum mixing does not appear to reduce cement prosthesis interface porosity or improve its mechanical properties in all cements.

Analysis of Variance↗
PubMed2001

A clinical comparison of the anterolateral and posterolateral approaches to the hip.

Patients who had anterolateral and posterolateral approaches in total hip replacement surgery were compared clinically for limp, dislocation, hospital stay, and discharge disposition. The only statistical difference was that the posterior approach had a statistically higher dislocation rate. Although the number of patients with limp was higher in the anterolateral group, the difference was not statistically different.

Adult↗
PubMed2001

Long-term followup of anatomic graduated components posterior cruciate-retaining total knee replacement.

The purpose of the current study was to evaluate the authors' 15-year experience with the Anatomic Graduated Components total knee replacement. This is a report of the survivorship of 4583 Anatomic Graduated Component total knee arthroplasties. Kaplan-Meier survival analyses were performed with the end point defined as radiographic loosening, revision, or both. This end point was subdivided into the best case scenario in which it was assumed that all the patients lost to followup were doing well throughout the study and a worst case scenario in which it was assumed that all patients lost to followup had failed results at their last clinic visit. There were six (0.18%) femoral, 21 (0.46%) tibial, and 180 (4.2%) all-polyethylene patellar component failures secondary to aseptic loosening. All femoral components and 90% of the tibial components were revised; however, only 15 patellar components were revised. The clinical survival rate with revision of one or more of the components was 98.86% at 15 years. Despite having nearly flat-on-flat geometry and retaining the posterior cruciate ligament, which should increase the stresses in the polyethylene and at the bone-cement interface, this total knee replacement has proved to have minimal wear and excellent longevity with time. The authors think this is a result of the direct compression molded polyethylene articulation and the nonmodular configuration that incorporates metal backing on the tibial component and eliminates back-sided tibial component polyethylene wear.

Adolescent↗
PubMed2001

The failure of all-polyethylene patellar components in total knee replacement.

The patellar component of total knee replacement is the most frequent source of nonseptic complications after total knee arthroplasty. The purpose of the current study was to review the radiographic factors associated with loosening of all-polyethylene patellar components. Four thousand five hundred eighty-three cases of Anatomic Graduated Components total knee replacements were performed at the authors' institution during the past 15 years. Radiographs were reviewed and loosening was defined as global radiolucency or component migration. Four thousand two hundred eighty-seven allpolyethylene patellar components were implanted. There were 180 (4.2%) loose all-polyethylene patellar components. The mean time to loosening was 2.6 years (+/- 1.75 years). Fifteen (0.3%) patellar components required revision. Five radiographic features were associated with failure. The incidence and mean time of appearance were recorded: (number; incidence; time) (1) Bone-cement radiolucency, n = 174, 96.7%, 1.4 years; (2) increased density, n = 118, 65.6%, 1.8 years; (3) trabecular collapse of the bone, n = 160, 88.9%, 2.3 years; (4) patella fracture and fragmentation, n = 133, 73.9%, 2.5 years; and (5) lateral subluxation of the residual patella bone, n = 146, 81.1%, 2.9 years. Lateral retinacular release was associated with an increased rate of patellar loosening. Loosening of the allpolyethylene patella component is an avascular process strongly associated with lateral retinacular release and for which the patient infrequently requires revision surgery.

Adolescent↗
PubMed2001

Total knee arthroplasty with 4.4 mm of tibial polyethylene: 10-year followup.

A consecutive series of 387, one-piece, 8-mm tibial components were implanted in 313 patients. All tibial prostheses were manufactured with 4.4 mm of polyethylene directly molded to a 3.6 mm cobalt chrome metal baseplate. The average age of the patients at surgery was 70.6 years. From this group, a subset of 116 patients underwent bilateral total knee arthroplasties with an 8-mm tibial component on one side and at least a 10-mm thick tibial component (at least 6.4 mm of polyethylene) on the other side. The followup averaged 10.7 years. Postoperative knee and pain scores average 81.4 points and 47.2 points, respectively. No radiographic polyethylene wear or osteolytic lesions were identified. Tibial radiolucencies were observed in four knees. There were nine failures (2.3%). Three knees were revised for infection. Five knees were revised for metallosis secondary to failure of metal-backed patellas. No loose tibial components were identified. Defining failure as revision for any reason or loosening of any component, Kaplan-Meier survival rates at 5, 10, and 15 years were 98.7%, 95.4%, and 94.3%, respectively. There was no significant difference in clinical scores or survival rates between the knee components with thicker (at least 6.4 mm) or thinner (4.4 mm) polyethylene.

Adult↗
PubMed2001

Direct compression molded polyethylene for total hip and knee replacements.

Direct compression molded polyethylene is a process of creating a net-shaped component with finished articular surfaces from ultrahigh molecular weight polyethylene by applying heat and pressure to the raw resin (usually Hi-fax 1900) with the use of fixed geometry metallic tools. The final product has no machining or finishing. Sterilization was by gamma radiation in air. Between 1974 and 1978, there were 378 cemented T-28 stems (321 patients) and 171 cemented TR-28 stems (158 patients) articulating with a cemented direct compression molded acetabular component. Radiographically, linear wear was 0.06 mm per year for the T-28 stem and 0.05 mm for the TR-28 stems. The revision rates for the acetabulum were 9.5% and 7.9%, respectively with only two acetabula having osteolysis. On the femoral side, the revision rates were 11.1% and 12.8%, with 11 cases and one case of osteolysis, respectively. Between 1983 and 1996, 4583 AGC cemented total knee replacements were done with direct compression molded nonmodular tibial components. There was no osteolysis seen in these nonmodular compression molded total knee replacements even with 0.1% failure of the femoral components and 0.4% failure of the tibial components. Failure of all of the hip and knee implants was because of poor cement technique, instability, or both. Wear and osteolysis were minimal. Direct compression molded polyethylene has stood the test of time and is a good choice among the currently available polyethylenes.

Adult↗
PubMed2001

Total knee replacement in patients with genu recurvatum.

Between June 1987 and March 1997, 57 total knee replacements were done in 53 patients with at least 5 degrees hyperextension deformity as measured on physical examination. The average recurvatum measured 11 degrees (range, 5 degrees-20 degrees). No cases of major ligamentous instability, neuromuscular disease, or inflammatory arthropathy were identified before surgery. Before surgery, Knee Society knee, function, and pain scores averaged 41 points, 41 points, and 13 points, respectively. A posterior cruciate-retaining prosthesis was implanted in all patients. The followup averaged 4.5 years (range, 3-10 years). Knee, function, and pain scores improved to 81 points, 78 points, and 43 points, respectively. Postoperative extension averaged 0 degrees (neutral) (range, 10 degrees hyperextension-10 degrees contracture). Only two (3.5%) knees had a hyperextension deformity after surgery. Both deformities measured 10 degrees and were in patients with a preoperative diagnosis of osteoarthritis. At final followup, no knee replacement was revised for any reason. In addition, only one case of a progressive radiolucent line greater than 1 mm (tibial Zone 7) was observed. Although the etiology of a hyperextension deformity should be elucidated before surgery, its presence does not preclude a well-functioning total knee replacement.

Aged↗
PubMed2001

Antibodies to human thymic epithelium form part of the murine autoreactive repertoire.

Monoclonal antibody (mAb) MR6 recognises a 200 kDa glycoprotein, gp200-MR6, which is expressed at high levels on the surface of human thymic cortical epithelium. In order to produce further mAbs against the gp200-MR6 molecule, mice were immunised with purified human gp200-MR6, hybridomas produced and supernatants screened for MR6-like reactivity on human thymic sections. Surprisingly this conventional hybridoma technique failed to produce stable hybridoma cells producing MR6-like antibodies. However, antibodies with specificities other than MR6-like were obtained. Three such antibodies (1B2, 3A3 and 4B3) were analysed further. Expression of 1B2-antigen, 3A3-antigen and 4B3-antigen was analysed on skin, tonsil and thymic sections, on cultured thymic epithelial cells (TEC), thymocytes and peripheral blood mononuclear cells (PBMC), and found to be expressed by both lymphocytes and epithelial cell populations. Furthermore, the antigens were also expressed on mouse thymic epithelial cells. The regulation of expression of these antigens was analysed following mitogen or cytokine stimulation of PBMC and cultured TEC, respectively. Expression on T cells was clearly affected by mitogens that mimic activation through the T cell receptor and expression on cultured TEC was affected by T cell-derived cytokines. Thus, the shared epithelial-lymphocyte molecules identified in this study may play a role in the cross-talk between the developing thymocytes and their epithelial microenvironment. The production of mAbs with specificities other than that of purified gp200-MR6 indicates that a wide range of B cells with specificity for components of the human thymic microenvironment exist in the normal mouse. These may detect epitopes that are shared with common pathogens to which the animals are exposed. Alternatively, they may be autoreactive B cells that are normally silent in the absence of T cell help. This help may be provided by T cells specific for human gp200-MR6, or nonspecifically by polyclonal activation induced by the adjuvant.

Animals↗