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Biomedical subjects

K Ludwig

Publications and source records attributed to K Ludwig.

At least 91 records · Page 5Linked to original sources
PubMed1999

The self adapting washer for lag screw fixation of mandibular fractures: finite element analysis and preclinical evaluation.

Besides rigid fixation, lag screws have distinct advantages compared with plates in appropriate indications in mandibular fractures. However, in current lag screw systems, the relatively small area of the screw head has to transfer the tensile force which can exceed 1000 N in the symphysis, to the thin cortical bone plate. Countersinking, which is obligatory in most systems, will weaken the cortical plate. Finite element analysis (FEA) revealed that load in this situation can exceed the normal tensile strength of metal and bone. Consequently, a new washer was constructed which both increased the supporting surface and did not require countersinking. The washer is self adapting (SAW) to the cortical plate in a defined position, forming a ball and socket joint with the screw head. Using the FEA model, a ten-fold reduction in load on bone and metal was observed with the new washer. In a miniature pig mandibular symphysis fracture model, the clinical applicability and a favourable histological reaction were demonstrated, compared with conventional lag screw designs.

Alloys↗
PubMed1999

Self-adapting washer system for lag screw fixation of mandibular fractures. Part II: In vitro mechanical characterization of 2.3 and 2.7 mm lag screw prototypes and in vivo removal torque after healing.

The aim of this study was to mechanically characterize self-tapping 2.3 and 2.7 mm titanium lag screw prototypes which are part of the newly developed 'self-adapting washer' maxillofacial lag screw osteosynthesis system. In vitro in a screw testing machine the insertion torque, maximum locking torque and axial force and the ultimate torsional strength were assessed. In vivo in six miniature pigs using a mandibular symphyseal fracture model, the removal torques after 3 and 6 months of healing were measured. Additionally the bone-metal contact (BMC) of the screws was assessed histometrically. The maximum insertion torque (0.185 Nm) was far below the mechanical limits of the screws (2.3 mm = 0.96 Nm, 2.7 mm = 1.6 Nm). A tightening of the 2.7 mm screw with an axial force of 1000 N and of the 2.3 mm screw with 500-550 N leaves a safety margin of approximately one-third on the ultimate torsional strength. Clinically these values permit the use of two 2.3 mm lag screws or one 2.7 mm lag screw in mandibular symphysis fractures since 1000 N tensile axial force are required in this indication. During screw removal after 6 months healing, torque levels close to the mechanical limits of the screws were recorded and screw failures were observed. This failure rate may have been due to the BMC of 49.8% which was in the range of titanium dental implants. Accordingly the screw heads were reinforced to prevent fractures.

Animals↗
PubMed1999

Conformational intermediates and fusion activity of influenza virus hemagglutinin.

Three strains of influenza virus (H1, H2, and H3) exhibited similar characteristics in the ability of their hemagglutinin (HA) to induce membrane fusion, but the HAs differed in their susceptibility to inactivation. The extent of inactivation depended on the pH of preincubation and was lowest for A/Japan (H2 subtype), in agreement with previous studies (A. Puri, F. Booy, R. W. Doms, J. M. White, and R. Blumenthal, J. Virol. 64:3824-3832, 1990). While significant inactivation of X31 (H3 subtype) was observed at 37 degrees C at pH values corresponding to the maximum of fusion (about pH 5.0), no inactivation was seen at preincubation pH values 0.2 to 0.4 pH units higher. Surprisingly, low-pH preincubation under those conditions enhanced the fusion rates and extents of A/Japan as well as those of X31. For A/PR 8/34 (H1 subtype), neither a shift of the pH (to >5.0) nor a decrease of the temperature to 20 degrees C was sufficient to prevent inactivation. We provide evidence that the activated HA is a conformational intermediate distinct from the native structure and from the final structure associated with the conformational change of HA, which is implicated by the high-resolution structure of the soluble trimeric fragment TBHA2 (P. A. Bullough, F. M. Hughson, J. J. Skehel, and D. C. Wiley, Nature 371:37-43, 1994).

Anilino Naphthalenesulfonates↗
PubMed1999

Detection of simulated interstitial lung disease and catheters with selenium, storage phosphor, and film-based radiography.

PURPOSE: To evaluate the diagnostic performance of storage phosphor and digital selenium radiography (DSR) with asymmetric and symmetric screen-film systems at different speeds in the detection of simulated interstitial lung disease and catheters. MATERIALS AND METHODS: Patterns of simulated interstitial lung disease and catheters were superimposed over an anthropomorphic chest phantom. Hard-copy images were generated at DSR (200-, 400-, and 600-speed), storage phosphor radiography (200- and 400-speed), and asymmetric (400-speed) and symmetric (200- and 400-speed) screen-film imaging. Surface doses were measured, and receiver operating characteristic analyses were performed. RESULTS: No statistically significant differences were found between the detector systems with the same speeds for each interstitial pattern. Significantly poorer results were found at 600-speed DSR than at 200-speed DSR. Detection of catheters and nodules over high-attenuation areas was significantly worse with the symmetric screen-film system than with the other detectors. The surface dose with the DSR system, without a grid, was about 50% less than that of the other detector systems, with grids, at the same speed. CONCLUSION: No significant difference was found in the diagnostic performance at DSR, storage phosphor radiography, and film-based radiography for simulated interstitial lung disease at corresponding speeds; there was a reduction in the surface dose of about 50% with the 400-speed DSR system.

Catheterization↗
PubMed1999

Iron homeostasis in relapsing steroid-sensitive nephrotic syndrome of childhood.

AIM: Urinary transferrin loss is a typical feature in relapse of the idiopathic nephrotic syndrome, however, the impact on serum iron homeostasis and hematological parameters has not been studied systematically so far. PATIENTS AND METHODS: Therefore, we investigated serum iron (Fe), erythropoietin (EPO), ferritin (FN), transferrin (TF), total iron-binding capacity (TEBK), transferrin saturation and the soluble transferrin receptor (sTFR) combined with hematological parameters (hemoglobin, MCV, MCH) in 42 children with relapsing, steroid-sensitive nephrotic syndrome (NS) in remission (RM, n = 26) and relapse (RL, n = 16), including 13 patients who were studied in both states. Thirty-three age-matched healthy children served as controls. RESULTS: Fe, TEBK and TF were significantly reduced in RL compared to RM in cross-sectional as well as in paired studies while ferritin, hematological parameters and EPO levels remained unchanged. A significant increase, however, of the soluble transferrin-receptor could be demonstrated in cross-sectional analysis comparing RL to RM and healthy controls (3568+/-713 mg/ml vs 2625+/-576 vs 2646+/-697; p < 0.001 respectively) as well as in paired analysis of 13 patients in RL and RM (p < 0.001). CONCLUSION: We conclude that transient transferrin and iron deficiency occurs in RL of INS but this seems to be counterbalanced by upregulation of the sTFR, a mechanism that might be important in preventing the development of iron deficiency anemia during the active nephrotic state.

Adolescent↗
PubMed1999

[Sugerbaker technique in para-colostomy hernia. An analysis of personal experiences].

Paracolostomy hernias represent the most common complication after colostomy surgery occurring in approximately 30% of all patients. The need for operation, however, emerges in only 20% of the hernias becoming symptomatic with pain, difficulties in stoma care, bowel obstruction and cosmetic problems. Due to their often huge size the repair is technically difficult and frequently accompanied by complications and recurrence. The method of intraperitoneal mesh repair and lateralisation of the colon presented by Sugarbaker 1980 offers not only the advantages of sufficient strengthening of the ventral abdominal wall even in big hernias and of an aseptic technique but also the chance of simultaneous treatment of other hernias. We present 9 patients with large paracolostomy hernias operated on according to Sugarbaker. In three patients we delt with a recurrence of a paracolostomy hernia. Three patients suffered additionally from an incisional hernia, one from an umbilical hernia and another one from an inguinal hernia. The hernial orifice was usually closed with a 30 x 20 cm Gore patch. All patients (6 males, 3 females, median age 63 years) tolerated the operation well which lasted as a mean 240 min. In the follow-up we saw two recurrences one of them being small, asymptomatic and without tendency to enlargement. In conclusion we can say that a considerable improvement was achieved in 89% of our patients after surgery performed in the herein presented way. We esteem this method a good option in a situation with otherwise poor alternatives.

Aged↗
PubMed1998

[Clinical and imaging aspects of gallstone ileus. Experiences with 108 individual observations].

Cases of gallstone ileus (108) were analyzed retrospectively over 30 years. Even today, when laparoscopic cholecystectomy is done, the incidence of this rare disease remains the same. History, clinical and X-ray findings are non-specific. Aerobilia was seen in 17% of the patients. Since 1992 sonography has provided an exact diagnosis in 10 of 15 cases. In the triad of known gallstone, non-specific epigastric pain with assumed small intestinal obstruction, and impossible detection of a stone in the gallbladder, there is strong suspicion of a gallstone ileus. The evidence is given if the gallstone is seen in the bowels. Intraoperatively more than one stone was found in the intestines in 20%, and cholecystoduodenal fistulas were encountered in 83%. Other fistulas are rare. There has been no significant change in mortality for 30 years.

Aged↗
PubMed1998

[Brief preoperative radiotherapy in surgical therapy of rectal carcinoma. Long-term results of a prospective randomized study].

To ascertain whether preoperative short-term radiotherapy can improve local tumor control and the long-term survival of patients with operable rectal cancer, a prospective randomised trial was performed from 1988 to 1993. Ninety-three patients with rectal cancer were either directly treated with surgery (n = 46) or underwent preoperative radiotherapy with 5 x 3.3 Gy irradiation and operation within 48 h (n = 47). If indicated (T4, UICC stage III) patients also received postoperative irradiation. Comparison of the methods of operation (abdominoperineal amputation versus anterior resection) revealed no significant difference in 5-year survival rate (P = 0.393). Local control of R0-resected tumors was improved after preoperative irradiation (P = 0.08). The 5-year survival rate was significantly higher after preoperative short-term radiotherapy (P = 0.027). Preoperative radiotherapy is not an independent factor according to overall survival (P = 0.078) and local recurrence (P = 0.07). In agreement with the results of other authors the present study indicates improved local tumor control of rectal cancer after preoperative radiation therapy. The 5-year survival rate was significantly better after preoperative radiotherapy than after surgery alone.

Adult↗
PubMed1998

Is image selection a useful strategy to decrease the transmission time in teleradiology? A study using 100 emergency cranial CTs.

This study examines the suitability of working with a selection of images in a teleradiology consulting system in neurological or neurosurgical emergency situations. The teleradiology system was based on IBM-compatible personal computers, video digitization for data acquisition, and data transmission by Integrated System Digital Network. Forty normal and 60 abnormal emergency cranial computed tomograms were shown to a radiologist on call who presented all cases he regarded as pathologic to a neuroradiologic expert by teleradiology. To reduce transmission time, only a selection of images from the CT study was presented (up to four images per case). For each case the on-call radiologist's diagnosis (D(on-call)), the expert's diagnosis on the teleradiology screen (D(monitor)), and the expert's diagnosis on the original film (D(original)) was documented, together with an estimation of the agreement between those diagnoses. There was clinically relevant disagreement between the on-call radiologist's diagnosis and the neuroradiologist's diagnosis based on the image selection on the teleradiology monitor in 23% of cases. A clinically important discrepancy between the neuroradiologist's diagnosis based on the image selection and his diagnosis using the original films was found in 30% of cases. This was due to the presence of clinically relevant information on images not transferred by the on-call radiologist. Image quality of the transferred images was sufficient in all cases. Drastic selection of images from a complete CT study leads to a high rate of incorrect diagnoses and is not appropriate to reduce transmission time in teleradiology.

Humans↗
PubMed1998

Delayed appearance of bilateral morgagni herniae in a child with Down's syndrome.

This case report describes the delayed presentation of bilateral Morgagni herniae in a 4 1/2-year-old boy with Down's syndrome. The authors emphasize the difficulties in establishing the diagnosis, although ultrasonography appears to be valuable. A review of the literature suggests an association between Morgagni hernias and trisomy 21.

Child, Preschool↗
PubMed1998

Anastomotic leakage: impact on local recurrence and survival in surgery of colorectal cancer.

Anastomotic leakage is a serious complication in colorectal surgery, especially in the treatment of adenocarcinoma located in the left-sided colon and rectum. It is controversial whether anastomotic leakage is a prognostic factor for local recurrence and/or survival in this disease. To evaluate the impact of anastomotic dehiscence on the outcome of surgery we reviewed data on 467 consecutive patients with adenocarcinoma of the left colon and rectum treated between 1985 and 1995 in our Department. Of these, 41 (8.8%) developed anastomotic leakage. The overall-survival differed nonsignificantly (P = 0.57) between leakage and nonleakage groups. Of 331 patients with curative resection 29 showed an anastomotic leakage. There were 46 R0-resected patients who died under disease-related conditions: 7 patients in the leakage group (24.1%) and 39 in the nonleakage group (12.9%; P = 0.045). In the curatively resected group 5 of 29 patients developed local recurrence in the leakage group (17.2%) but only 26 of 302 patients in the nonleakage group (8.6%; P = 0.0357). Multivariate analysis showed only the factors of age, stage of resection, staging of lymph nodes, and tumor staging as independent prognostic factors for overall survival. For local recurrence the multivariate analysis revealed tumor staging and anastomotic leakage as independently significant. Anastomotic leakage thus appears to be a prognostic factor for local tumor recurrence of colorectal cancer. In addition, disease-related survival is considerably decreased under leakage conditions. Anastomotic leakage was not shown in this study to be an independent prognostic factor for overall survival due to the lack of statistical significance.

Adenocarcinoma↗
PubMed1998

Subtle pulmonary abnormalities: detection on monitors with varying spatial resolutions and maximum luminance levels compared with detection on storage phosphor radiographic hard copies.

PURPOSE: The purpose of this receiver operating characteristic study was to compare diagnostic efficacy with images displayed on monitors of varying spatial resolutions and maximum luminance levels to that with storage phosphor radiographic hard copies. MATERIALS AND METHODS: Seven types of simulated lesions were superimposed onto an anthropomorphic chest phantom. Images were viewed by five radiologists on a 2,560 x 2,048 pixel monitor (maximum luminance, 75 foot-lamberts), on two 1,024 x 1,024 monitors with maximum luminance levels of 25 foot-lamberts and 75 foot-lamberts, respectively, as well as on hard copies. Monitor images were viewed both without and with systematic magnification. RESULTS: Overall visualization of the lesions was best on hard copies, but visualization on the 2,560 x 2,048 monitor was not found to be substantially different. Lines, reticular opacifications, and catheters were found to be particularly poorly visualized with the 1,024 x 1,024 monitor. These results could be statistically significantly improved only with a systematic magnification; however, this involved a considerable increase in viewing time. Observer performance was markedly inferior with the 1,024 x 1,024 monitor with the lower luminance. CONCLUSION: Diagnostic performance with a 1,024 x 1,024 monitor is statistically significantly inferior to that with hard copies. A statistically significant improvement can be achieved with a high-resolution 2,560 x 2,048 monitor with a maximum luminance of 75 foot-lamberts.

Angiography, Digital Subtraction↗