Analysis of the kinetics and yields of OH radical production from the CH3OCH2 + O2 reaction in the temperature range 195-650 K: an experimental and computational study.

The methoxymethyl radical, CH3OCH2, is an important intermediate in the low temperature combustion of dimethyl ether. The kinetics and yields of OH from the reaction of the methoxymethyl radical with O2 have been measured over the temperature and pressure ranges of 195-650 K and 5-500 Torr by detecting the hydroxyl radical using laser-induced fluorescence following the excimer laser photolysis (248 nm) of CH3OCH2Br. The reaction proceeds via the formation of an energized CH3OCH2O2 adduct, which either dissociates to OH + 2 H2CO or is collisionally stabilized by the buffer gas. At temperatures above 550 K, a secondary source of OH was observed consistent with thermal decomposition of stabilized CH3OCH2O2 radicals. In order to quantify OH production from the CH3OCH2 + O2 reaction, extensive relative and absolute OH yield measurements were performed over the same (T, P) conditions as the kinetic experiments. The reaction was studied at sufficiently low radical concentrations (∼10(11) cm(-3)) that secondary (radical + radical) reactions were unimportant and the rate coefficients could be extracted from simple bi- or triexponential analysis. Ab initio (CBS-GB3)/master equation calculations (using the program MESMER) of the CH3OCH2 + O2 system were also performed to better understand this combustion-related reaction as well as be able to extrapolate experimental results to higher temperatures and pressures. To obtain agreement with experimental results (both kinetics and yield data), energies of the key transition states were substantially reduced (by 20-40 kJ mol(-1)) from their ab initio values and the effect of hindered rotations in the CH3OCH2 and CH3OCH2OO intermediates were taken into account. The optimized master equation model was used to generate a set of pressure and temperature dependent rate coefficients for the component nine phenomenological reactions that describe the CH3OCH2 + O2 system, including four well-skipping reactions. The rate coefficients were fitted to Chebyshev polynomials over the temperature and density ranges 200 to 1000 K and 1 × 10(17) to 1 × 10(23) molecules cm(-3) respectively for both N2 and He bath gases. Comparisons with an existing autoignition mechanism show that the well-skipping reactions are important at a pressure of 1 bar but are not significant at 10 bar. The main differences derive from the calculated rate coefficient for the CH3OCH2OO → CH2OCH2OOH reaction, which leads to a faster rate of formation of O2CH2OCH2OOH.

Experimental and theoretical study of the kinetics and mechanism of the reaction of OH radicals with dimethyl ether.

The reaction of OH with dimethyl ether (CH3OCH3) has been studied from 195 to 850 K using laser flash photolysis coupled to laser induced fluorescence detection of OH radicals. The rate coefficient from this work can be parametrized by the modified Arrhenius expression k = (1.23 ± 0.46) × 10(-12) (T/298)(2.05±0.23) exp((257 ± 107)/T) cm(3) molecule(-1) s(-1). Including other recent literature data (923-1423 K) gives a modified Arrhenius expression of k1 = (1.54 ± 0.48) × 10(-12) (T/298 K)(1.89±0.16) exp((184 ± 112)/T) cm(3) molecule(-1) s(-1) over the range 195-1423 K. Various isotopomeric combinations of the reaction have also been investigated with deuteration of dimethyl ether leading to a normal isotope effect. Deuteration of the hydroxyl group leads to a small inverse isotope effect. To gain insight into the reaction mechanisms and to support the experimental work, theoretical studies have also been undertaken calculating the energies and structures of the transition states and complexes using high level ab initio methods. The calculations also identify pre- and post-reaction complexes. The calculations show that the pre-reaction complex has a binding energy of ~22 kJ mol(-1). Stabilization into the complex could influence the kinetics of the reaction, especially at low temperatures (<300 K), but there is no direct evidence of this occurring under the experimental conditions of this study. The experimental data have been modeled using the recently developed MESMER (master equation solver for multi energy well reactions) code; the calculated rate coefficients lie within 16% of the experimental values over the temperature range 200-1400 K with a model based on a single transition state. This model also qualitatively reproduces the observed isotope effects, agreeing closely above ~600 K but overestimating them at low temperatures. The low temperature differences may derive from an inadequate treatment of tunnelling and/or from an enhanced role of an outer transition state leading to the pre-reaction complex.

Aggressive granulomatous lesions associated with hip arthroplasty. Immunopathological studies.

The local immunopathological response was analyzed in six patients who had a revision of a total hip prosthesis because of an aggressive granulomatous lesion and in six patients who had a revision because of common loosening of the prosthetic stem. All twelve patients had had a total replacement arthroplasty for primary osteoarthrosis. All of the prostheses had been cemented. The aggressive granulomas consisted of well organized connective tissue containing histiocytic-monocytic and fibroblastic reactive zones. The granulomas were highly vascularized, and villous structures were observed at many sites. In contrast, the areas around the loose cemented stems were characterized by dense connective tissue. Immunohistological evaluation revealed that most of the cells in the aggressive granulomatous tissue were multinucleated giant cells and C3bi-receptor and nonspecific esterase-positive monocyte-macrophages. This cytological finding suggests a foreign-body-type reaction, compatible with the rapidly progressive lytic nature of the lesion that was shown radiographically. There was a clear-cut difference between aggressive granulomatosis and the more common lesion accompanying prosthetic loosening--namely, the relative lack of activated fibroblasts in granulomatosis. We suggest that granulomatosis involves an uncoupling of the normal sequence of monocyte-macrophage-mediated clearance of foreign material and tissue debris that is normally followed by fibroblast-mediated synthesis and remodeling of the extracellular matrix. We also suggest that aggressive granulomatosis in association with a cemented hip prosthesis is a distinct entity, not only clinically and radiographically, but also histopathologically.

The results of operative resection of the lateral end of the clavicle.

Seventy-three patients had operative resection of the lateral end of the clavicle for the treatment of a painful condition of the acromioclavicular joint. Thirty-two of the patients had had a traumatic separation of the acromioclavicular joint, eight had had a fracture of the lateral end of the clavicle, and thirty-three had primary acromioclavicular osteoarthrosis. An average of sixteen millimeters (range, fine to thirty-three had primary acromioclavicular osteoarthrosis. An average of sixteen millimeters (range, five to thirty-seven millimeters) was resected; the amount was similar in each of the three groups. The patients were evaluated an average of nine years (range, four to sixteen years) after the operation. The result was considered good in twenty-one patients, satisfactory in twenty-nine, and poor in twenty-three. A poor result was more common in the patients who had had a fracture of the lateral end of the clavicle (p<0.01). Forty-six patients reported pain with exertion, and thirteen noted pain at rest. Eighteen patients had a decrease in the strength of the involved upper extremity, and sixteen had some limitation of the mobility of the shoulder. Elevation of the lateral end of the remaining part of the clavicle as compared with the scapula was noted in eighteen patients and was more likely to be associated with pain (p<0.05). The extent of the resection was significantly associated with pain; patients who had had a smaller amount of resection (ten millimeters or less) had less pain than those who had had a larger amount (p<0.03). A good result was more common in the patients in whom less than ten millimeters had been resected and who had had a previous traumatic separation of the acromioclavicular joint or had primary acromioclavicular osteoarthrosis. We recommend that resection of the lateral end of the clavicle be considered with caution for patients who have severe post-traumatic or degenerative osteoarthrosis of the acromioclavicular joint. If resection is performed, it should not exceed ten millimeters.

Operation for old sternoclavicular dislocation. Results in 12 cases.

Twelve patients were operated upon after unsuccessful conservative treatment for complete dislocation of the sternoclavicular joint. Three methods were used; stabilisation using fascial loops, reconstruction with a tendon graft, and resection of the sternal end of the clavicle. The results were good in only four patients, three treated with a tendon graft and one by fascial loops. Another four patients had fair results, but all four treated by resection of the medial end of the clavicle had poor results, with pain and weakness of the upper extremity. In our opinion resection of the sternal end of the clavicle should not be used in old traumatic dislocation.

Immunopathological response to loose cementless acetabular components.

The membranes surrounding seven loose cementless acetabular implants were shown to contain polyethylene particles, birefringent in polarised light. Three of these implants were made of titanium alloy and the membranes around these contained titanium particles as well. There was no metallosis around the four implants made of chromium-cobalt-steel alloy. Both titanium and polyethylene particles caused migration, adherence and phagocytosis of CD11b-positive, peroxidase-negative macrophages. There were no histological signs of activation of the specific immune response; neither interleukin-2 receptor-positive activated T cells nor PCA-1 plasmablasts/plasma cells were present in the tissues. In cases of simple loosening, resident mesenchymal fibroblast-like cells were active. In aggressive granulomatosis, there were many macrophages and multinucleated giant cells but little fibroblast reaction. The clinical relevance of the findings is that the use of cementless prostheses is not a guarantee against adverse tissue reactions.

Arthroplasty for old tuberculosis of the knee.

We have reviewed six patients with old tuberculosis of the knee treated by total replacement an average of 35 years after the primary infection. Three patients had no antituberculous prophylaxis and three had drugs for two to three weeks before and three weeks after the operation. One patient with a missed primary diagnosis had a relapse of the tuberculous arthritis 18 months after his arthroplasty and was successfully treated with antituberculous drugs for one year. At an average follow-up of 6.3 years all the patients were markedly improved. Old tuberculosis of the knee can be treated successfully with arthroplasty but there is a risk of reactivation of disease and prophylactic drugs are recommended.

Cementless total replacement for old tuberculosis of the hip.

We report the results of cementless total joint replacement in 18 patients with old tuberculosis of the hip, performed, on average, 34 years after the onset of infection. Mean follow-up was 3.5 years. Only seven of the patients had antituberculous drugs during or after the operation. Using the Mayo hip score, 15 patients had excellent or good results and two had a fair rating. One patient had the prosthesis removed more than one year postoperatively for late haematogenous staphylococcal infection and had a poor rating. All the patients had relief of hip-related pain. Despite the absence of any reactivation of tuberculosis in our series, we recommend the use of specific prophylaxis.

Aggressive granulomatous lesions in cementless total hip arthroplasty.

We describe six patients with aggressive granulomatous lesions around cementless total hip prostheses. Two patients previously had a cemented prosthesis in the same hip. The Lord prosthesis was used in five patients, the PCA in one. Both prostheses were made of chrome-cobalt alloy. Pain on weight-bearing occurred on average 3.2 years after the cementless arthroplasty, and at that time radiography revealed aggressive granulomatosis around the proximal femoral stem and the acetabular component in five of the patients; one had a large solitary granuloma in the proximal femur. Revision was performed on average 4.8 years after the cementless arthroplasty. At that time all granulomas had grown large in size; while waiting for revision operation, two femoral stem components fractured. All the granulomas showed a uniform histopathology, which included histiocytosis; the cause for these lesions was thought to be plastic debris from the acetabular socket.

Cementless revision of aggressive granulomatous lesions in hip replacements.

In 16 patients we used uncemented Lord prostheses at revision operations for aggressive granulomatosis after cemented hip arthroplasties; in 12 bone grafts also were used. In 13 hips the granulomatous lesions were multifocal, and in one the acetabular component was involved. There was no evidence of infection in any case: all the patients had normal ESR and CRP levels. The revision operation was performed on average 9.4 years after the primary replacement; the mean age at revision was 64 years. On radiographs, the bone around the prosthesis had consolidated by an average of 16 months. At follow-up, two to six years later (mean 3.5 years) there had been no recurrences, nine patients had an excellent Mayo hip score, five were good and two fair.

Aggressive granulomatous lesions after hip arthroplasty.

We reviewed 19 patients who presented with aggressive granulomatosis around the femoral stem after hip replacement. All had experienced stress pain and had required revision arthroplasty on average 8.8 years after the primary operation. Fifteen patients were men and four were women; none had rheumatoid arthritis. One patient had an uncemented Moore hemiprosthesis; the others all had cemented total hip replacements. When first detected, the granulomatous lesions were multifocal in 13 patients. The first granuloma was in the region of the lesser trochanter in 10, and near the tip of the stem in only two. Speed of growth varied but on average there was doubling of the area on anteroposterior films in 2.2 years (range 6 months to 4.6 years). Aggressive granulomatous lesions in replaced hips are a distinct condition, different from simple loosening or infection; the lesions may grow rapidly, so revision surgery is indicated soon after diagnosis.

Consumption of sweet foods among adolescents in Finland.

The importance of sugar in the etiology and dental caries is well known but only a few representative studies at population level have been carried out to analyze nutritional factors related to dentistry. As the main exposure to caries the frequency of the use of sugar-products should be known more exactly than we do. The purpose of this study was to analyze the frequency of consumption of sugar-containing products among Finnish adolescents. A representative sample of 3209 Finnish adolescents between the ages of 13 and 19 was drawn. The data were obtained by mail questionnaire in February and September 1977, and in February and September 1979. The separate sample was drawn in February 1978 to analyze the changes with time during 1977-79. The response rate to all the mailed questionnaires was close to 90%. The sugar-containing foods included in the study were sugar in coffee or tea, hot chocolate, pastries and cookies, soft drinks, chewing gums, sweets and pastries. In addition, the data on the consumption of artificial sweeteners were collected. According to current health behavior dogma, girls behaved better than boys. A clear relationship was observed between a householder's educational and occupational status and the children's sugar consumption. Children from homes of low social status consumed more sugar than others. The percentage of children frequently consuming sugary products decreased with improved school success. It can be concluded that the use of sugar-containing products is especially frequent among young age groups, particularly among boys from low social background and children with poor school success. Health education should be especially directed towards them.

Four-year outcome of operative treatment of acute acromioclavicular dislocation.

Seventy of 100 consecutive randomly allocated patients who had been treated for acute total acromioclavicular dislocation with either transfixation with two smooth Kirschner wires (29 cases), two threaded Kirschner wires (20), or one ASIF cortical screw (21) were followed for an average of 4 years. The coracoclavicular ligaments were not sutured. Results were good in 67 of the 70 patients. Using stress radiographs, no redislocation was found in 56 cases. Two complete dislocations were found in patients who had been treated with screw fixation. Osteolysis of the lateral head of the clavicle was found in 13 patients, eight of whom had been treated with screw fixation (p less than 0.01). Our results speak for the use of threaded Kirschner wire fixation for the operative treatment of acute total acromioclavicular dislocation.

Inclination of the acetabular cup in erect posture radiographs.

Inclination of the acetabular component was measured in a series of 100 patients who underwent total hip replacement. The radiographs were taken with the patients in erect posture. Two different reference lines were used in the measurements: the ischial reference line, and the true horizontal line perpendicular to a plumb-line used as a vertical reference line. The values measured using these two reference lines correlated well with each other, though there were important differences caused by pelvic tilt. Often an inclination that was within the normal range when measured, using the ischial tuberosity line as a reference, shifted excessively to horizontal or vertical when control measurements were performed using the true horizontal line as the reference. We conclude that inclination of the acetabular cup should be measured in erect posture radiographs, because pelvic tilt increases the degree of inclination on the side of pelvic adduction.

Sternoclavicular dislocation. A plea for open treatment.

I report 12 cases of dislocation of the sternoclavicular joint. Eight cases were treated by closed reduction and redislocation occurred in five. The result was good in five out of these eight cases. Two cases with a redislocation and poor result were operated on: in one the sternoclavicular joint was successfully reconstructed with a palmaris longus tendon, and in the other the result was poor after medial resection of the clavicle. In four dislocations good results were obtained after primary open reduction, fixation with two Kirschner wires, and suture of the ruptured ligaments. Primary open reduction should probably be preferred in acute cases of sternoclavicular dislocation.

External fixation of the pelvic girdle as a test for assessing instability of the sacro-iliac joint.

External fixation of the pelvic girdle was used in a consecutive series of ten female patients suffering from suspected chronic instability of the sacro-iliac joint. The condition was attributed to pelvic relaxation after pregnancy in seven patients and to trauma in three. External fixation of the pelvis with a trapezoid frame reduced the average radiographic displacement of the symphysis from 5.0 to 2.4 mm in eight patients, relieved the dorsal pain in seven, and markedly improved walking ability in five. Seven of the ten patients were subsequently subjected to an anterior sacro-iliac joint arthrodesis in which square compression plates and autogenous bone grafts were used. At follow-up examination five of these patients were improved, and two unchanged. The results suggest that external fixation of the pelvis is useful in assessing painful sacro-iliac joint instability and should precede surgical intervention.

Results of elbow synovectomy in rheumatoid arthritis.

Synovectomy of the elbow was performed on 54 patients (70 elbows) with rheumatoid arthritis. The mean follow-up time was 7.5 years (range 1.5-22 years). Clinical evaluation showed marked relief of pain in 28 elbows (40%). In 27 cases (38.5%) the pain was moderate but still less than preoperatively. Severe pain was recorded in 15 cases (21.5%) at the time of check up. As to postoperative range of movement, the mean flexion are was 114.5 degrees and the mean rotation are 134.5 degrees. Latitudinal instability was recorded up to 5 degrees in 33 (47%) elbows, up to 10 degrees in 20 (28.5%), up to 15 degrees in 6 (8.5%), and more than 15 degrees in 11 (16%). The mean carrying angle was 10 degrees in valgus. Measurement of strength in flexion and extension showed a reduction of approximately 50% compared to age-matched healthy controls. Reoperations were performed in 10 elbows (14%); the interval between the primary synovectomy and second operation in these cases averaged 8 years.

Flurbiprofen inhibits heterotopic bone formation in total hip arthroplasty.

A double-blind prospective parallel group study comparing slow-release flurbiprofen with placebo in the control of ectopic bone formation was carried out in 68 patients undergoing total hip arthroplasty. Eight weeks after surgery there was evidence, significant at the 1% level, that the incidence and extent of periarticular calcification was lower in the flurbiprofen group. At an early phase, serum calcium level decreased and after 8 weeks serum alkaline phosphatase level increased more in the placebo group than in the flurbiprofen group, indicating an effect of flurbiprofen on bone mineral metabolism. Six patients were withdrawn in each treatment group, four due to side effects in the flurbiprofen group and three due to side effects in the placebo group. Overall, five patients in each group reported side effects, the nature and severity of the side effects being very similar in each group. We conclude that flurbiprofen is an efficient and safe drug in limiting ectopic bone formation following total hip arthroplasty. Heterotopic bone formation is a frequent complication after total hip replacement. Heterotopic bone reduces the extent of hip motion, reduction being more evident in cases with extensive ectopic bone formation around the hip joint. Various treatment regimens have been proposed for discouraging heterotopic bone formation. Anti-inflammatory agents such as indomethacin and ibuprofen have turned out effective. Local irradiation also prevents ectopic bone formation, but diphosphonates seem not be effective in this respect. The aim of the present study was to assess the efficacy of flurbiprofen, a new anti-inflammatory agent, in limiting heterotopic bone formation, and to note the frequency and severity of any side effects of the treatment.