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Biomedical subjects

N C Jensen

Publications and source records attributed to N C Jensen.

16 recordsLinked to original sources
PubMed1996

Long-circulating bacteriophage as antibacterial agents.

The increased prevalence of multidrug-resistant bacterial pathogens motivated us to attempt to enhance the therapeutic efficacy of bacteriophages. The therapeutic application of phages as antibacterial agents was impeded by several factors: (i) the failure to recognize the relatively narrow host range of phages; (ii) the presence of toxins in crude phage lysates; and (iii) a lack of appreciation for the capacity of mammalian host defense systems, particularly the organs of the reticuloendothelial system, to remove phage particles from the circulatory system. In our studies involving bacteremic mice, the problem of the narrow host range of phage was dealt with by using selected bacterial strains and virulent phage specific for them. Toxin levels were diminished by purifying phage preparations. To reduce phage elimination by the host defense system, we developed a serial-passage technique in mice to select for phage mutants able to remain in the circulatory system for longer periods of time. By this approach we isolated long-circulating mutants of Escherichia coli phage lambda and of Salmonella typhimurium phage P22. We demonstrated that the long-circulating lambda mutants also have greater capability as antibacterial agents than the corresponding parental strain in animals infected with lethal doses of bacteria. Comparison of the parental and mutant lambda capsid proteins revealed that the relevant mutation altered the major phage head protein E. The use of toxin-free, bacteria-specific phage strains, combined with the serial-passage technique, may provide insights for developing phage into therapeutically effective antibacterial agents.

Animals↗
PubMed1996

The relation between trabecular bone strength and bone mineral density assessed by dual photon and dual energy X-ray absorptiometry in the proximal tibia.

The feasibility of two noninvasive methods [dual photon absorptiometry (DPA) and dual energy X-ray absorptiometry (DXA)] for prediction in vivo of local variations of trabecular bone strength within the proximal tibia was evaluated in 14 cadaveric knees. Trabecular bone strength was measured using an osteopenetrometer and from destructive compression tests performed on bone cylinders, thus measuring the penetration strength and ultimate strength in the medial, lateral, and central part of the tibial bone specimens. Linear regression analysis showed significant relations between BMD measured by DPA (r2 = 72%) or DXA (r2 = 73%) and ultimate strength. Even closer relations between BMD (DPA: r2 = 80%, DXA r2 = 81%) and penetration strength of trabecular bone were found. We conclude that DPA and DXA are suitable methods for evaluation in vivo of local variations in trabecular bone strength within the proximal tibia, and could easily be performed preoperatively before insertion of total knee arthroplasty.

Adult↗
PubMed1994

Arthroscopic repair of the ruptured meniscus: one to 6.3 years follow up.

Forty-nine patients underwent arthroscopic meniscal repair. Twenty-three had an isolated tear of the medial meniscus, four an isolated tear of the lateral meniscus, two a tear of the medial meniscus combined with a rupture of the medial collateral ligament, and 20 a tear of the anterior cruciate ligament (ACL) and a tear of one or both menisci. At the time of repair of the menisci, seven had undergone reconstruction of their ACL, whereas 13 had been treated conservatively for their ACL rupture. Seven of 10 retears were in patients with a conservatively treated ACL tear, and three were in patients with an isolated tear of a meniscus. Thirty-five patients without retears were reexamined after 5.5 years (1-6.3 years). The average Lysholm knee score before the trauma was 98 (range 75-100), and at follow-up it was 87 (range 29-100). The average Tegner's activity score before the trauma was 6 (range 3-9), and at follow-up it was 5 (range 0-9). When there is no retear, the clinical results of arthroscopic repair of the menisci are excellent. In those patients who had isolated lesions of the menisci, there were very few retears, 11% in this study. ACL deficiency of the knee greatly increases the risk of retear. In this study 46% of patients with persistent instability after an untreated ACL rupture incurred retears. There were no retears in the patients who underwent ACL reconstruction concomitant with the meniscal repair.

Adult↗
PubMed1992

Total ankle joint replacement: a clinical follow up.

The TPR total ankle joint replacement system (Smith & Nephew Richards) was implanted in 30 ankles in 25 patients. Twenty-three ankles in 18 patients were followed; 21 had rheumatoid arthritis and two had osteoarthritis. The average age at surgery was 62 years (range: 37 to 77), and the average follow up was 59 months (range: 37 to 89). The improvement was especially obvious with respect to pain and function. The average walking distance improved from 260 m preoperatively to 975 m postoperatively. Even though there was some improvement with respect to pain and function, the results of the study are disappointing in comparison to studies of ankle arthrodesis.

Adult↗
PubMed1991

Topographical distribution of trabecular bone strength in the human os calcanei.

Mechanical properties of twenty human os calcanei were determined by uniaxial compression testing of bone specimens from facies articularis talaris posterior, facies articularis cuboidea, and tuber calcanei. Specimens were taken oriented perpendicular to the planes of the facies articularis, and in tuber along the presumed loading axis throughout the gait cycle. Young's modulus and strength at facies articularis cuboidea and facies articularis talaris posterior were about three times those at the tuber calcanei. The variation of the relationship between Young's modulus and apparent density indicated differences in the orientation of the trabecula, in relation to the direction of evaluation between these locations. A more detailed analysis of the topographical variation of strength within each location was made using penetration testing of a further nineteen specimens. The results of both types of measurements indicated that the major part of the load during walking is carried by facies articularis talaris posterior and facies articularis cuboidea.

Adult↗
PubMed1990

Necrosis of the femoral heads following aorto-bifemoral vascular grafting. Case report.

A case of bilateral necrosis of the femoral head, following aorto-bifemoral vascular bypass, is reported. The necrosis of the femoral heads might be explained by a temporary obstruction of the lateral blood supply peripheral to the arteria profunda femoris, due to an increased joint pressure caused by regional oedema with joint effusion and swelling of the joint capsule.

Aged↗
PubMed1989

Correction of hallux valgus and metatarsus primus varus. Using the Cedell technique.

The Cedell procedure consists of: a proximal valgus osteotomy of the first metatarsal bone to correct the metatarsus primus varus, a soft tissue plasty at the first metatarsophalangeal joint with lateral release, and tightening of the medial capsule to correct the hallux valgus. A total of 45 operations in 31 patients (2 men and 29 women) were performed. Forty-one of these operations were followed. The average age at surgery was 24 years (range 16 to 43 years), and the average follow-up time was 23 months (range 8 to 56 months). The postoperative decrease in the intermetatarsal angle averaged 10 degrees, and the average decrease in the metatarsophalangeal angle was 26 degrees. Only a few postoperative complications were observed. At the time of follow up, 75% of the patients had no pain, 23% had only slight pain, and 2% had severe pain. Ninety-five percent were cosmetically satisfied with the operation. The Cedell operative technique has proved to be an effective procedure to correct the combined hallux valgus and metatarsus primus varus in younger patients.

Adolescent↗
PubMed1988

Screw fixation in the femoral head. Pull-out tests in cadavers.

The aim of our study was to determine whether a subchondral or a capital position of the thread of the gliding screw provided the best fixation. A pull-out test was performed on pairs of femoral neck cadaver specimens. The capital position of the thread provided the best fixation in all the pairs. A correlation was found between bone mineral content of the femoral heads and the holding power of the screws in both positions.

Aged↗
PubMed1985

Trabecular bone strength profiles at the ankle joint.

The mechanical strength of trabecular bone at the ankle joint was studied in ten amputation specimens by means of multiple penetration tests. Tibial bone was considerably weaker than talar bone (40% on average). An area of peak bone strength located posteriorly and medially to the center of the joint was found in most joints. The variation of bone strength with the depth from the surface was studied by comparing five successive 2-mm levels. At the tibia there was a statistically significant decrease of bone strength from the first to the second level. At the talus, bone strength increased at first, then decreased significantly. The absolute values of strength recorded suggest that in a substantial number of the joints studied, the resection surfaces--especially at the tibial side--might be too weak to support the loads imposed by current prosthetic designs.

Ankle Joint↗
PubMedDate not supplied

Bone strength and material properties of the glenoid.

The quality of the glenoid bone is important to a successful total shoulder replacement. Finite element models have been used to model the response of the glenoid bone to an implanted prosthesis. Because very little is known about the bone strength and the material properties at the glenoid, these models were all based on assumptions that the material properties of the glenoid were similar to those of the tibial plateau. The osteopenetrometer was used to assess the topographic strength distribution at the glenoid. Strength at the proximal subchondral level of the glenoid averaged 66.9 MPa. Higher peak values were measured posteriorly, superiorly, and anteriorly to the area of maximum concavity of the glenoid joint surface known as the bare area. One millimeter underneath the subchondral plate, average strength decreased by 25%, and at the 2 mm level strength decreased by 70%. The contribution of the cortical bone to the total glenoid strength was assessed by compression tests of pristine and cancellous-free glenoid specimens. Strength decreased by an average of 31% after the cancellous bone was removed. The material properties of the glenoid cancellous bone were determined by axial compression tests of bone specimens harvested from the central part of the glenoid subchondral area. The elastic modulus varied from approximately 100 MPa at the glenoid bare area to 400 MPa at the superior part of the glenoid. With the elastic constants used a predictor of the mechanical anisotropy, the average anisotropy ratio was 5.2, indicating strong anisotropy. The apparent density was an average 0.35 gr. cm-3, and the Poisson ratio averaged 0.263. According to our findings the anisotropy of the glenoid cancellous bone, details concerning the strength distribution, and the load-bearing function of the cortical shell should be considered in future finite element models of the glenoid.

Adult↗
PubMedDate not supplied

The quick draw approach to quality improvement.

In 1996, the North Heart Center, part of North Memorial Health Care in Robbinsdale, Minn., invested over $30,000 in a quality improvement project. Hospital administration put its support behind the effort when results began to show better outcomes, more efficiency, improved patient and provider satisfaction, and cost reduction in the system. The purpose for North Heart Center was to reduce mortality rates by 50 percent. A team of between eight and 12 people met weekly and kept to a focused and aggressive schedule. A fast-paced, action-oriented schedule helped the team maintain, its momentum throughout the process, allowing a steady stream of smaller accomplishments that moved toward the overall goal. The team found that though there was resistance, people ultimately joined when they saw the process worked. A process-flow diagram helped chart every step of any given process. The team found that people focus better on one or two variables rather than attempting to do too much at one time. Examining results to see what works and what doesn't was the next step, followed by summarizing and then redesigning the cycle to try again. Posting data in appropriate areas proved effective in eliciting support throughout the organization. The team worked hard to cultivate trust for the ideas people brought to the table. Completion of North Heart Center's initial project took several years and focuses now on reducing atrial fibrillation in cardiac surgery patients.

Cardiac Care Facilities↗