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R Schenk

Publications and source records attributed to R Schenk.

At least 19 recordsLinked to original sources
PubMed2005

A procedure to define natural groundwater conditions of groundwater bodies in Germany.

Commissioned by Germany's Working Group of the Federal States on Water Problems (LAWA) the authors developed a procedure to define natural groundwater conditions from groundwater monitoring data. The distribution pattern of a specific groundwater parameter observed by a number of groundwater monitoring stations within a petrographically comparable groundwater typology is reproduced by two statistical distribution functions, representing the "natural" and "influenced" components. The range of natural groundwater concentrations is characterized by confidence intervals of the distribution function of the natural component. The applicability of the approach was established for four hydrochemically different groundwater typologies occurring throughout Germany. Based on groundwater monitoring data from 7920 groundwater monitoring stations, 15 different hydrochemical parameters were evaluated for each groundwater typology. For all investigated parameters the range of natural groundwater concentrations has been identified. According to the requirements of the EC Water Framework Directive (article 17) (WFD) this study is a basis for the German position to propose criteria for assessing a reference state for a "good groundwater chemical status".

Environmental Monitoring↗
PubMed2002

[Cementless socket fixation based on the "press-fit" concept in total hip joint arthroplasty].

PURPOSE OF THE STUDY: The key problem of implant fixation in THR is stress distribution, i.e. load transmission between bone and implant. The closer the load transfer is to the original physiological situation, the easier the adaptation of the periprosthetic bone to the new biomechanical conditions after implantation of the cup and the safer is its longlasting fixation. The aims of the studies were 1) to get information about the physiological load transfer in the normal hip joint, 2) to get information about the load transfer between acetabulum and acetabular sockets and vice versa, 3) to measure the periacetabular pelvic bone deformation as the stimulator of the remodelling process (third stage of osseointegration) in the normal hip joint and in hip joints fitted with different acetabular cups, 4) to study the morphological stages of osseointegration of a non-cemented press-fit cup and to compare the morphological structure of the periacetabular bone with the biomechanical data obtained by the in vitro studies and finally, 5) to compare the clinical and radiological outcome of follow-up studies of the senior author's "Press-Fit cup" with the theoretical hypotheses according to the experimental observations. MATERIAL AND METHODS: Load transfer between the acetabular bone and the femoral head on one side and press-fit cups has been determined by strain gauge measurements, finite element studies, pressure sensitive Fuji prescale films, CT-osteoabsorptiometry and telemetric measurements. Periacetabular deformation has been measured by Imetric Markers. Osseointegration of the senior author's press-fit cup and, thus, the remodelling process of the bony structures adjacent to the cup have been studied in autopsy specimens of THRs which have been in situ for several years. RESULTS: Load transfer measurements have shown that the main load in the original acetabulum as well as in the acetabulum fitted with a press-fit cup is transmitted to the periphery, especially to the acetabular cortical rim whereas the subchondral bone is exposed to lower, predominantly meridional (tension) stresses. Direct measurements of the periacetabular deformation under load revealed an increase of the peripheral press-fit with increasing stability of a (oversized) press-fit cup. Both the normal as well as the acetabulum fitted with a non-cemented cup deforms in a postero-medial direction. The histo-morphology of the periacetabular bone of autopsy specimens showed excellent bony in- and ongrowth of a porous titanium coating (SULMESH) and bone formation, especially at the periphery in zone 1 and 3 according to DeLee and Charnley. CONCLUSION: The studies have shown that the subchondral bone plate of the acetabulum has very little supportive function for non-cemented press-fit cups. For the preparation of the acetabulum it is, therefore, more important to ream the sclerotic subchondral bone until there is a well vascularized, well bleeding bone bed to facilitate osseointegration of a non-cemented acetabular socket than to preserve the subchondral bone plate as is the case in cement fixation. A non-cemented press-fit socket must transmit load predominantly to the cortical bone of the acetabular rim. Therefore, a too far medial positioning of the cup, and therefore loosing contact to the cortical rim, must be avoided under all circumstances. The clinical experience with acetabular revisions and with conversions of hip arthrodeses into a THR (where there is no subchondral bone at all) have shown the superiority of a well vascularized over a sclerotic (even mechanically stronger) bone bed. Furthermore, it has been shown that the additional use of screws for fixation of an acetabular cup is not only unnecessary but can be deleterious and causes complications including osteolysis and aseptic loosening.

Acetabulum↗
PubMed2001

Incidence and indications for reintubation during postoperative care following orthotopic liver transplantation.

STUDY OBJECTIVE: To analyze the incidence and indications for reintubation during postoperative care following orthotopic liver transplantation (OLT). DESIGN: Retrospective chart review. SETTING: Large metropolitan teaching hospital. PATIENTS: 546 adult liver transplant recipients. MEASUREMENTS AND MAIN RESULTS: The medical charts of 546 patients who underwent OLT at our institution between January 1992 and September 1996 were reviewed for the incidence and indications of reintubation throughout primary hospitalization. Eighty-one of 546 patients (14.8%) required one or more episodes of reintubation after OLT. In the majority of cases, reintubation was performed for pulmonary complications (44.6%), followed by cerebral (19.1%) and surgical (14.5%) complications. Cardiac (9.1%) and peripheral neurologic (2.7%) complications were less frequent reasons for reintubation. Overall patient survival, according to the Kaplan-Meier estimates, was 89.9%, 87.5%, 86.5%, and 82.2% after 1, 2, 3, and 5 years, respectively. In patients with one or more episodes of reintubation, overall survival decreased to 62.5% after 1, 2, and 3 years, and to 56.4% after 5 years (p < 0.001). CONCLUSIONS: The main indications for reintubation after OLT were pulmonary, cerebral, and surgical complications. These reintubation events had a considerable influence on the patient's postoperative recovery, and were associated with a significantly higher rate of mortality, than for OLT patients who did not undo reintubation.

Anti-Infective Agents↗
PubMed2001

Postoperative tracheal extubation after orthotopic liver transplantation.

BACKGROUND: The duration of postoperative mechanical ventilation and its influence on pulmonary function in liver transplant recipients is still debated controversially. METHODS: We retrospectively analyzed the incidence of immediate tracheal extubation, prolonged mechanical ventilation (>24 h following surgery), and episodes of reintubation in 546 patients who underwent orthotopic liver transplantation (OLT) at our institution. RESULTS: Immediate tracheal extubation in the operating theater was achieved in 18.7% of patients, and prolonged mechanical ventilation was required by 11.2% of patients. In these, median time of extubation was 49.5 h, whereas the remaining 70.1% of patients required ventilation support for a median 5 h after OLT. As risk factors for prolonged mechanical ventilation we identified the indications of acute liver failure and retransplantation, as well as factors such as mechanical ventilation prior to OLT, massive intraoperative bleeding, and severe reperfusion injury of the liver graft. The incidence of reintubation was 8.8% in patients who were immediately extubated following surgery, and 13.1% in patients who underwent extubation within 24 h. The incidence was significantly increased in patients requiring prolonged mechanical ventilation (36.1%). CONCLUSIONS: Immediate tracheal extubation was safe and well tolerated. The incidence of reintubation was not increased when compared to patients in whom extubation succeeded later. However, special attention should be given to transplant recipients presenting in reduced clinical condition at the time of OLT, undergoing complicated surgery, or receiving liver allografts with severe reperfusion injury because of an increased risk for prolonged mechanical ventilation.

Adolescent↗
PubMed2000

Sinus grafting with porous bone mineral (Bio-Oss) for implant placement: a 5-year study on 15 patients.

The efficacy of Bio-Oss as a graft material for sinus floor elevation was studied in 15 patients. A total of 20 sinus augmentation procedures was performed, and 6 months later 57 implants were placed into the augmented sinuses. New bone formation was confirmed in biopsies of 3 patients (new bone: 21.08% +/- 7.25% after 6 mo, 27.55% +/- 4.88% after 12 mo; Bio-Oss: 39.17% +/- 4.36% after 6 mo, 27.01% +/- 11.64% after 12 mo). After a mean loading period of 4.0 +/- 0.5 years (range 3.2 to 4.8 y), 56 implants remained in place. This study confirms Bio-Oss's good osteoconductive properties.

Adult↗
PubMed1999

Recombinant human bone morphogenetic protein-2 stimulation of bone formation around endosseous dental implants.

BACKGROUND: Successful endosseous implant placement requires that the implant be stable in alveolar bone. In certain cases, the implant can be stabilized in native bone but some part of the implant is not covered by bone tissue. This often occurs during placement of implants into extraction sites or in areas where bone resorption has occurred and the ridge width is not sufficient to completely surround the implant. In those cases, the clinician usually employs a procedure to encourage bone formation. These procedures typically include a bone graft and/or membrane therapy. Recent advances have led to the isolation, cloning, and production of recombinant human proteins that stimulate bone formation. One of these bone morphogenetic proteins (rhBMP-2) has been extensively studied in animal models and is currently being tested in human clinical trials. METHODS: In this study, rhBMP-2 was tested using a collagen sponge carrier to stimulate bone formation in defects in the canine mandible around endosseous dental implants. Six animals had a total of 48 implants placed. rhBMP-2 with the collagen carrier was implanted around 24 of these, the remainder having only the collagen carrier placed. Half the sites were covered with a nonresorbable expanded polytetrafluoroethylene membrane. Histologic analysis was performed after 4 and 12 weeks. The area of new bone formed, percentage of bone-to-implant contact in the defect area, and percentage fill of the defect was calculated. RESULTS: The addition of rhBMP-2 resulted in significantly greater amounts of new bone area and percentage of bone-to-implant contact and with more percentage fill after 4 and 12 weeks of healing. The area of new bone formed was reduced after 4 weeks when a membrane was present but after 12 weeks, there was no significant difference between membrane and non-membrane treated sites. In some specimens, new bone was found coronal to the membranes, with rhBMP-2-treated sites having greater amounts than non-rhBMP-2-treated sites. CONCLUSIONS: These data demonstrate that a bone differentiation factor significantly stimulates bone formation in peri-implant bone defects in the canine mandible. In addition, bone-to-implant contact was significantly enhanced along the rough implant surface. Membrane-treated sites had less new bone formation after 4 weeks of healing but were similar to non-membrane sites after 12 weeks. These results demonstrate that rhBMP-2 can be used to stimulate bone growth both around and onto the surface of endosseous dental implants placed in sites with extended peri-implant osseous defects.

Animals↗
PubMed1997

[HIV infection and risk behaviour among prostitutes in the Amsterdam streetwalkers' district; indications of raised prevalence of HIV among transvestites / transsexuals].

OBJECTIVE: To determine the prevalence of HIV infection and risk behaviour among various groups of streetwalkers in Amsterdam and the extent of overlap between different prostitution networks. SETTING: The family room project in the streetwalkers' district in Amsterdam, the Netherlands. METHODS: In November 1996, saliva was taken from 32 female and 25 transsexual/transvestite prostitutes and tested for antibodies against HIV. Besides, prostitutes were interviewed on risk behaviour, history of sexually transmitted diseases and mobility. RESULTS: Only one of the participants (a female prostitute) had ever injected drugs. None of the female prostitutes, but 6 of the 25 transsexuals/transvestite prostitutes (24%; 95% confidence interval: 7-41) proved seropositive. None of the HIV infected participants was aware of his serostatus. The transsexual/transvestite prostitutes frequently had receptive anal intercourse with their clients. Condom use was high, but most did not use condoms made for anal intercourse. Female prostitutes also reported a high rate of condom use with their clients. Both groups of prostitutes reported few private partners and a low rate of condom use with these partners. According to the transsexual/transvestite prostitutes many of their clients had sexual contacts with women in their private lives. Many prostitutes thought that they shared the same clients in the district. CONCLUSION: HIV infections occur quite often among transsexual/transvestite prostitutes in the streetwalkers' district in Amsterdam. The risk of further spread HIV infection to their clients (and through them to other heterosexual populations) is present. AIDS education targeted at this group is important. The use of (special) condoms when having anal intercourse in private as well as in prostitution contacts should be emphatically advised.

Female↗
PubMed1997

Rationale of a flexible press fit cup in total hip replacement. 5-year followup in 280 procedures.

A consecutive series of 280 total hip replacements in 261 patients using the Press Fit Cup with a minimum followup of 5 years is presented. The Press Fit Cup is a nonmodular acetabular component with a porous coating made of titanium fibers. It has one peg and is 1.5 mm oversized with biradial eccentricity. It has a flattened pole area, requires no screw fixation, and partially preserves elasticity. The mean age was 71 years for women, 70 years for men. Forty-seven patients (49 hips) died before the 5-year review, and five patients were unable to return for the followup because of physical infirmity. Two hundred eighteen patients (226 hips) were available for the clinical 5-year followup, and 208 patients (213 hips) were available for the radiographic followup. No intraoperative fracture of the acetabulum occurred; four hips dislocated; 94% clinically were rated as excellent or good. One hip in a patient with rheumatoid arthritis had to be revised for aseptic loosening of the cup and nine femoral stems had to be revised. No migration of the cup could be measured. There was no osteolysis seen around the cup. In six cases a radiolucent line was seen in Zone 1, and in eight hips in Zone 3. There was one hip with a continuous radiolucent line which was considered radiographically loose.

Adult↗
PubMed1996

Wear behavior and histopathology of classic cemented metal on metal hip endoprostheses.

The authors reviewed their collection of retrieved all metal hip joints (9 McKee-Farrar, 7 Müller, and 3 Huggler type prostheses) and tissues from the joint capsules and implant beds. The amount of wear was measured, and the total volume was calculated. The tissues were analyzed by atomic absorption spectral analysis or inductively coupled plasma mass spectrometry and examined by light and scanning electron microscopy. The size of particles was measured with a texture analysis system. The articulating surfaces showed many delicate scratches which represent normal wear. The calculated annual wear averaged approximately 5 mm3 per year, which is low compared with polyethylene. The cellular reaction to metal wear particles was regarded as mild. The cellular reaction to scattered and worn bone cement was always more pronounced than to metallic debris. Scanning electron microscopy confirmed the irregular shapes and mostly submicron size of the metal particles. The analytically detected metal content of the periarticular tissue was relatively low and in accordance with the wear measurements from the articulating surfaces. The excess of chromium in the tissues is discussed in the light of the elimination of cobalt as well as the relation between elements representing either corrosion products or elements still bound in wear particles.

Adult↗
PubMed1996

Hybrid external fixation in the treatment of tibial plafond fractures.

From 1992 to 1994, 37 fractures (36 patients) were treated with hybrid external fixation for tibial plafond or distal tibial fractures. The fractures were classified according to the AO classification: A1 (3), A2 (3), A3 (4), C1 (6), C2 (12), C3 (9). There were 11 open injuries, and in 27 patients (75%) the mechanism of injury was high energy trauma. Results were evaluated based on a subjective and objective rating system. Thirty-four patients were available for followup at an average of 15.2 months. All fractures in this series united with an average time to healing of 4.6 months. Anatomic or good alignment was obtained in all but 1 fracture. There were 12 excellent, 9 good, 7 fair, and 6 poor results. In the 18 C2 and C3 fractures there were 8 good to excellent, 4 fair, and 6 poor results. Degenerative changes were seen on followup radiographs in 4 of these patients. Complications occurred in 12 patients (35%) and included 1 skin slough, 5 pin tract infections, 3 deep infections, 3 nonunions, and 3 loss of reductions necessitating frame revision. This method yielded results comparable with previous studies while decreasing the number of complications resulting from treatment.

Adolescent↗
PubMed1996

Femoral nailing without a fracture table.

This retrospective trail was designed to evaluate the effectiveness and safety of femoral nailing on a radiolucent table with manual traction only. Eighty-three femoral shaft fractures treated by antegrade nailing were included in this study. Group 1 consisted of 24 femur fractures that were reduced and nailed with manual traction. Group 2 consisted of 59 femur fractures treated with the aid of a fracture table. There were 10 patients in Group 1 and 19 patients in Group 2 needing multiple procedures. In Group 1, significantly fewer redrapings and table transfers were necessary. There was no increase in operative time. There were no operative complications in Group 1 and there was 1 operative complication in Group 2--a radial nerve palsy. Postoperative malalignment was minimal in both groups. Intramedullary nailing of femoral shaft fractures on a radiolucent table using manual traction is associated with no increase in morbidity. It also facilitated quicker and more effective treatment of the patient with polytrauma. No undue risks or contraindications were identified; however, the help of an assistant was invaluable.

Femoral Fractures↗
PubMed1996

Test development and validation of a back education posttest.

Assessment of physiotherapeutic treatment efficacy is dependent on valid outcome assessment. This study examined the validity of an existing back education knowledge posttest through a series of validation tests, generated a revised test. Methods included test-item analysis, content and construct validity, expert panel review, and a series of field trials. Purposive samples and subgroups, with varying levels of knowledge of back care concepts, participated in the study. Results of the study found the existing test possessed content validity. The final version of the alternate posttest was able to detect statistically significant differences among subgroups with varying knowledge levels by one-way analysis of variance (F = 116, p < .000). This research is an initial evaluation of a new instrument, and future research is required to fully validate this instrument.

Adolescent↗
PubMed1996

[Bleeding complication in chronic stomach and duodenal ulcer--plea for resection in emergencies and in the elderly].

The bleeding complications of gastric- and duodenal ulcers have not declined in the past 20 years. This is the leading factor for the unchanged lethality of this disease. We present our results in 31 patients with gastroduodenal ulcer bleeding. The mean age was 72, 1 years and the majority of patients had an advanced stage of ulcer disease with penetration in neighbouring organs. 8 of 31 patients had to be operated under emergency conditions within 6 h. 23 patients with high risk for re-bleeding were operated early elective (12-36 h); 11 of those were in a severe shock at the beginning of the operation. After control of bleeding by intra-and extraluminar ligature all patients underwent a primary resection (B I, B II or cardiofundectomy). The lethality was 12.9% (4/31), there was no re-bleeding. With the exception of one late duodenal insufficiency none patient had to be re-operated.

Aged↗
PubMed1996

Crevice corrosion of cemented titanium alloy stems in total hip replacements.

Twenty-eight cemented Müller straight femoral stems of titanium forged alloys were mainly revised for causing pain in the patient. The pain pattern differed from aseptic loosening and pain recurred only 14.5 months on average after implantation. The character of pain was dull, permanent, and increased at rest. Some patients reported pain relief while walking. Revisions were performed on average 25.5 months after primary implantation. Data from medical records, radiographs, histology of tissues taken at revision surgery, intraoperative pH measurements, examination of retrieved stems and bone cement fragments were gathered. In the radiographs debonding was visible only in 3 cases; a spindle shaped thickening of the femora occurred 9 months on average after recurrence of pain. After a further 11 months (average), scalloping osteolyses appeared. Abraded particles like metallic titanium alloy, titanium corrosion products, polymethylmethacrylate, xray contrast medium, and polyethylene were detected. Metallic particles dominated in the joint capsule whereas more corrosion products impregnated the cement to bone interface. The distal surfaces of the stems were corroded at a higher rate, whereas the proximal regions more often were subject to abrasion. Measurements of the pH of the corroded stems revealed values of high acidity. Recurrence of pain and subperiosteal apposition of bone are due to diffusion of acid; subsequent scalloping osteolyses develop due to particle induced foreign body granulomas. The mechanism of crevice corrosion of cemented titanium based alloys does not seem applicable to cobalt and iron based implant alloys. Titanium alloys can no longer be recommended for cementation, but are as safe as ever for anchorage without cement.

Adult↗
PubMed1995

Effect of surface topology on the osseointegration of implant materials in trabecular bone.

The importance of surface topology and implant material composition on osseointegration in trabecular bone was investigated using three commericially used implant materials and surface-texturing procedures which included blasting, high temperature acid etching, and hydroxyapatite (HA) coating. Surface roughness and spacing parameters were measured for each implant group with a laser interferometric profilometer. Cylindrical implants were press-fit into trabecular bone sites in the knee of mature miniature pigs. After 12 weeks in situ, osseointegration was evaluated by (1) mechanical pushout tests to measure bone-implant interface strength and (2) quantitative morphometric measurements of the percent implant surface covered by bone. We found that HA-coated implants showed superior osseointegration in terms of both pushout failure load and surface coverage by bone measurements. An excellent correlation (r2 = .90) was found between the average roughness of the implant surface and pushout failure load. New methods for altering the local topologic and/or chemical state of the implant surface (i.e., by acid etching) may provide an important new avenue of research for improving the osseointegrative properties of orthopedic materials.

Alloys↗