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Biomedical subjects

R Frigg

Publications and source records attributed to R Frigg.

34 records · Page 2Linked to original sources
PubMed1997

Tracking prions: the neurografting approach.

The physical nature of the agent that causes transmissible spongiform encephalopathies (the 'prion'), is the subject of passionate controversy. Investigation of it has benefited tremendously from the use of transgenic and knockout technologies. However, prion diseases present several other enigmas, including the mechanism of brain damage and how the affinity of the agent for the central nervous system is controlled. Here we show that such questions can be effectively addressed in transgenic and knockout systems, and that pathogenesis may be clarified even before we can be certain about the nature of the infectious agent. Availability of mice overexpressing the Prnp gene (which encodes the normal prion protein) and Prnp knockout mice allows for selective reconstitution experiments aimed at expressing PrP in specific portions of the brain or in selected populations of hemato- and lymphopoietic origin. We summarize how such studies can offer insights into how prions administered to peripheral sites can gain access to central nervous tissue, and into the molecular requirements for spongiform brain damage.

Animals↗
PubMed1997

The hybrid ring tubular external fixator: a biomechanical study.

OBJECTIVE: To measure and compare the mechanical properties in bending of the four-ring, and three-ring/one-tube hybrid external fixation frames. DESIGN. IN VITRO: measurements of the mechanical behaviour of ring and ring-tubular external fixation frames. In the latter, one ring of the full circular frame was replaced by one tube and Schanz screws. BACKGROUND: The mechanical properties of the classical Ilizarov four-ring external fixation frames has been compared to those of other external fixation frames by various authors. However, in clinical practice the hybrid fixation frame is being used with increasing frequency. Therefore the mechanical properties of the latter are of immediate interest and clinical value. METHODS: On explanted sheep tibiae with single and double osteotomies, frame stiffness in the four-point bending mode was measured at different K-wire tensions, comparing the values obtained from four-ring frames, to those of three-ring-tubular hybrid frames. These measurements were made under conditions of (a) bone distraction (BD), and (b) segment transport (ST), both at the initial and final stages of this procedure. RESULTS: In circular frames, frame stiffness in bending for increasing K-wire tension showed a Gaussian distribution both in distraction and post-ST with an optimum at 1000 N. In ring tubular hybrid frames, however, frame stiffness showed a more linear relationship to K-wire tension. CONCLUSIONS: In the four-ring Ilizarov external fixation frame, the exchange of one ring with one tube and one Schanz screw both reduced frame stiffness in bending and converted to linear its relationship to K-wire tension. RELEVANCE: Under clinical conditions, the use of a similar ring tubular hybrid external fixator allows the adjustment of frame stiffness in a simple and practical way. This is not the case with the original ring fixation frame.

Journal Article↗
PubMed1994

[The AO external clamp fixator. New techniques in external stabilization of tibial fractures].

A serious disadvantage of conventional external fixators is the opening of the medullary canal. This creates a direct communication between the canal and the exterior. The new pinless external fixator does not have this disadvantage. The clamps of the new fixator system do not penetrate cortical bone, they simply rest on the cortical surface. The clinical indications of this easily managed system are fractures of the tibial shaft in cases in which primary internal fixation is precluded either by precarious local or general conditions, or even by a lack of infrastructure. In such situations the pinless external fixator is an excellent device to achieve a good fracture stabilisation rapidly, while leaving open all subsequent alteration of treatment. In case of secondary change to an intramedullary nail the pinless fixator facilitates the procedure, because this fixator can be also used as an distractor during nailing. Furthermore this fixator can be combined with any intramedullary nail to increase the stability in case of very proximal or distal as well as highly instable shaft fractures. The clamps of the pinless external fixator set are used in combination with the standard AO fixator system.

Adult↗
PubMed1994

[External fixator: surgical technique, pinless fixator, change in procedure].

External Fixation-Technique: The advantages of external over internal fixation are as follows: a) endosteal and periosteal blood supply is undisturbed, b) "low-tech" equipment may be used, c) secondary adjustments are possible and d) easy implant removal. These benefits however are outweighed by the main disadvantages of long term external fixation i.e. pin complications and delayed union of fractures. Better understanding of postoperative management and careful application of screws of improved design will lead to better results. Today's standard applications of external fixation for tibial fractures is a unilateral fixator, using Schanz screws. The pin-bone interface is the most critical site of all external fixation. By avoiding heat necrosis (low temperature drilling) and preventing micro motion at the pin-bone interface (by applying bending- or more recently radial-preload), pin complications such as infection and loosening can be reduced. Two Schanz screws are inserted into each main fragment and are connected with one short tube per fragment. The fracture is then reduced by using these tubes as handles. After reduction a third tube connects the first two by means of two tube-to-tube clamps. This type of fixation will easily allow for three dimensional secondary corrections of alignment. Approximately three weeks following the injury some motion at the fracture site will stimulate callus formation. This can be achieved by destabilisation, dynamisation or "active stimulation" of the fracture site [2]. Pinless fixator: The pinless external fixator holds the fragments firmly with pointed clamps that penetrate about one millimeter into cortical bone without entering and contaminating the medullary canal.(ABSTRACT TRUNCATED AT 250 WORDS)

Equipment Design↗
PubMed1993

Effect of flexible drive diameter and reamer design on the increase of pressure in the medullary cavity during reaming.

Reaming the medullary cavity before insertion of an intramedullary nail, results in an increase in both temperature and pressure. This may lead to aseptic necrosis of the cortex and to fat embolism, whereby the increased pressure in the medullary cavity plays a significant role. This paper aims to determine whether a reduction of the drive diameter combined with a different reamer design reduces the amount of intramedullary pressure. The pressure levels were measured in plexiglass tubes filled with a mixture of vaseline and paraffin. The viscoelastic properties of this mixture at 20 degrees C were equivalent to those of bovine medullary fat at 36 degrees C. In comparison with the conventional reamer system (9.0 mm drive + 9.5 mm AO reamer), the 7.0 mm drive+AO reamer and the 7.0 mm drive+hollow reamer, the pressure values were reduced as follows: 1. 9.0 mm drive + 9.5 mm hollow reamer: diaphyseally by 19%, metaphyseally by 21% 2. 7.0 mm drive + 9.5 mm AO reamer: diaphyseally by 48%, metaphyseally by 49% 3. 7.0 mm drive + 9.5 mm hollow reamer: diaphyseally by 61%, metaphyseally by 66%. If the gap between the flexible shaft and the wall of the plexiglass tube became large enough, only small pressure values were recorded for all three types of reamer. In summary, it can be stated that the reduction of the drive diameter causes a sustained reduction in the intramedullary pressure, but that the newly developed hollow reamer only leads to a further reduction in pressure in combination with a thin flexible drive.

Equipment Design↗
PubMed1993

A new solid unreamed tibial nail for shaft fractures with severe soft tissue injury.

In a prospective study, 51 tibial shaft fractures with severe open or closed soft tissue damage were treated with a new, thin (8 mm or 9 mm) solid locking nail, inserted without reaming. At 6 months or more after trauma, 43 cases were reviewed. Fractures were classified according to Müller with six type A, 25 type B, and 12 type C fractures. In 13 cases there was group II (n = 8) or group III (n = 5) closed soft tissue damage (Tscherne). Of 30 open fractures, 16 were group OII, six were group OIIIA and eight were group OIIIB (Gustilo). Postoperative treatment in 42 of 44 cases was possible without additional cast or brace. Full weight bearing was achieved in 26 cases within 12 weeks, and in 42 cases within 26 weeks. In 43 cases, fracture healing occurred with a mean of 21.9 weeks (range 12-40 weeks). There was one case with valgus of 6 degrees and three cases with anterecurvatum deformities of 5 degrees to 10 degrees. In four cases there was an external rotation malalignment between 10 degrees and 20 degrees. In three cases we found an internal rotation deformity of 10 degrees to 20 degrees. Shortening between 0.5 and 1.0 cm was found in five cases, and in one case shortening was 1.5 cm. None of the patients had an osteomyelitis.

Adolescent↗
PubMed1992

Biomechanical evaluation of the Pinless external fixator.

In open fractures especially in those with severe soft tissue damage, fracture stabilisation is best achieved by using external fixators. There are some intrinsic complications which occur during classical external pin fixation. To overcome the problem of pin track infection and vascular damage from drilling, the Pinless external fixator was developed. It is based on the idea of a forceps with trocar points, which only penetrate the bone cortex superficially. The function of the device was tested in two mechanical trials and two in vitro tests in which one pinless clamp was put under a controlled load of 50 N, 150 cycles/day and studied over a 5 week period in sheep. The loads and time range of the experiment were chosen to simulate a temporary fracture stabilisation in a patient not bearing weight. The main question to be answered was whether the Pinless external fixator would be able to maintain stable fixation. Furthermore, it was to determine the changes at the trocar-to-bone interface. The clamp was found to maintain 72% of the initially applied clamping force after 5 weeks of in vivo application and it was found to be tight at removal. Some decrease of clamping force was found during the first 20 days and then the force tended to level off. There was no slippage nor did the clamp penetrate the cortex. There were no obvious signs of infection around the trocar-holes and in the bacterial tests no pathological cultures were grown. Histology revealed very localised bone reactions, the indentation caused by the trocar tips being only 1.2 mm deep. The study concludes, as far as could be ascertained from these tests, that it is safe to use pinless external fixation for temporary fracture fixation.

Animals↗
PubMed1992

Depth-force patterns of periodontal probing. Attachment-gain in relation to probing force.

It was the purpose of this study to determine whether probing force had an influence on the amount of clinical attachment-gain assessed after treatment by scaling and rootplaning. A probing device was constructed which allowed simultaneous monitoring of probing force and probe penetration and which standardized the insertion pathway for repeated measurements. In 10 periodontal patients, 2 deep pockets were selected which were measured before and after periodontal treatment by scaling and root-planing. Depth-force plots were compared by superimposition. Depth values were determined at 5 different force levels (0.25, 0.50, 0.75, 1.00 and 1.25 N) on each plot and changes of clinical attachment levels were calculated. A significant relationship was seen between probing force and attachment level. The values obtained with 0.25 N were significantly different from the values obtained with higher forces (p less than 0.001). Slight, but non-significant differences were noted in the amount of attachment-gain obtained at the 5 force levels. At a probing force level of 0.25 N, there was 0.80 mm mean attachment gain. With 0.50 N, there was a gain of 0.70 mm; with 0.75 N the gain amounted to 0.67 mm in mean. At 1.00 N and at 1.25 N, a gain of 0.66 mm was recorded.

Adult↗
PubMed1991

[Unreamed tibial nail in tibial shaft fractures with severe soft tissue damage. Initial clinical experiences].

In a prospective study, since March 1989, 55 tibial shaft fractures have been treated with a new, unreamed solid tibial nail (UTN). This nail was initially designed as a temporary implant. The first 33 cases with second or third degree soft tissue damage were reviewed 6 months or more after the operation. Fractures were classified according to Müller: 6 type A (18.2%), 15 type B (45.5%), and 12 type C (36.7%). In 9 cases (27.3%), there was GII (n = 4) or GIII (n = 5) closed soft tissue damage according to Tscherne's classification. The 24 open fractures (72.7%) comprised 11 OII, 3 OIIIA and 10 OIIIB fractures (Gustilo classification). 24 patients (72.7%) were polytraumatized, the mean PTS (Hannover Polytrauma Score) was 18 points (range: 8-65 points). All fractures were stabilized without reaming. The implant diameter was 8mm (n = 14) or 9 mm (n = 19). Static locking was performed in 31 cases. Dermatofasciotomy was necessary because of compartment syndrome in 14 cases. In 1 grade IIIB open fracture soft tissue coverage was performed with a latissimus dorsi myocutaneous free flap 4 days after nailing. In 32 of the 33 cases the use of an additional cast or brace was not necessary during the follow-up treatment; 1 patient had a cast for 8 weeks for the treatment of accompanying injuries. Full weight-bearing was achieved in 5 cases within 3 weeks, in 16 cases within 12 weeks, and in 30 cases within 26 weeks. In 16 cases (48.5%) the interlocking screws were removed after 5-26 weeks (mean: 10 weeks).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Biomechanics of the interlocking nail. A study of the proximal interlock.

Conventional interlocking nails for the femur use an inclined proximal interlocking screw; the AO/ASIF universal interlocking nail utilizes a transverse interlocking screw which is anchored in cortical bone. The transverse position of the screw allows one to employ the nail for either the right or left side. The yield strength of the thinner diameter transverse screw, (thread 4.5 mm. core 3.0 mm) was compared with that of the Grosse-Kempf nail oblique screw (thread 6.3 mm, core 4.5 mm) by testing in cadaver femora to evaluate the risk of fatigue failure. The test, performed using slow loading rates (50 N/s), simulated either a diaphyseal or a subtrochanteric fracture situation. The test rig applied a load corresponding to body weight and pull at the trochanter. Taking the highest load without plastic deformation as a criterion, the mechanical strength of the two screws was evaluated for each fracture situation. The thinner but shorter transverse interlocking screw demonstrated higher strength (4500 N vs. 3000 N; P less than or equal to 0.02) than the thicker inclined screw in the diaphyseal and the subtrochanteric fracture situation (2300 N vs. 1100 N; P less than or equal to 0.06). The biomechanical test showed the transverse screw to have sufficient and superior strength.

Biomechanical Phenomena↗
PubMed1990

Reaming versus non-reaming in medullary nailing: interference with cortical circulation of the canine tibia.

Medullary nails have only been used with reluctance in the treatment of open fractures since reaming interferes with the cortical circulation. The technique of interlocking offers the interesting possibility of inserting a relatively stiff nail which does not necessarily require reaming. The effects of reaming prior to nail insertion upon the cortical circulation was investigated in the canine tibia. Intravital staining with procion red was used to trace areas of disturbed circulation. Nail insertion without reaming provided clear advantages for the bone's blood supply, while reaming disturbed perfusion in two-thirds of the cortical area and regionally extended through the entire thickness of the cortex. The disturbance without reaming was limited to the inner layer of the cortex and involved only one-third of the cortical cross-section.

Animals↗
PubMed1980

[Locking of the intramedullary nail in the medullary cavity of the tibia (author's transl)].

Whether or not an effective locking of the medullary nail in transverse direction is achieved after medullary nailing of the tibia, is a moot point in literature. Researchers agree, however, that the essential locking of the nail occurs on the longitudinal axis of the nail. The authors conducted studies with strain gauges measuring the expansion and introduced together with the nail in order to obtain information on the elastic performance of the nail in transverse and longitudinal direction. The curves plotted from the data obtained, present a typical appearance. After the tibia has been properly reamed, a medullary nail of the AO is subjected to both elastic transverse compression as well as slight longitudinal bending after nailing. In case of excessive reaming the transverse elastic effect is only slight. If, on the other hand, reaming is not effected wide enough, the bone may burst open or the nail may undergo plastic deformation.

Biomechanical Phenomena↗
PubMedDate not supplied

A crucial role for B cells in neuroinvasive scrapie.

Although prion proteins are most efficiently propagated through intracerebral inoculation, peripheral administration has caused the diseases kuru, iatrogenic Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy (BSE) and new-variant CJD. The development of neurological disease after peripheral inoculation depends on prion expansion within cells of the lymphoreticular system. Here we investigate the identity of these cells by using a panel of immune-deficient mice inoculated with prions intraperitoneally: we found that defects affecting only T lymphocytes had no apparent effect, but that all mutations that disrupted the differentiation and response of B lymphocytes prevented the development of clinical scrapie. As an absence of B cells and of antibodies correlates with severe defects in follicular dendritic cells, a lack of any of these three components may prevent the development of clinical scrapie. However, we found that scrapie developed after peripheral inoculation in mice expressing immunoglobulins that were exclusively of the M subclass and without detectable specificity for the normal form of the prion PrPC, and in mice which had differentiated B cells but no functional follicular dendritic cells. We conclude that differentiated B cells are crucial for neuroinvasion by scrapie, regardless of the specificity of their receptors.

Animals↗
PubMedDate not supplied

Intramedullary pressure increase for different commercial and experimental reaming systems: an experimental investigation.

OBJECTIVE: To measure the differences in intramedullary (IM) pressure for commercial reamer systems. DESIGN: IM pressure values for the following systems were measured: AO, Biomet, Howmedica grey reamer, Richards, and Zimmer. To investigate the influence of shaft diameter, the AO reamer head was additionally connected to a small shaft (A6/A7). The pressures were measured in plexiglass tubes filled with a mixture of petroleum jelly and paraffin oil with flow properties at 20 degrees C equivalent to those of bovine medullary fat at 36 degrees C. The reaming assemblies were inserted into the tubes using a materials testing machine at a constant speed. In addition, pressure measurements were made using five pairs of human femora to compare Biomet reamers with the AO reamer with thin, flexible drives (A6/A7). RESULTS: The following pressure distributions were obtained (millimeters of mercury; mean value +/- standard deviation): 9.5-millimeter reamer: low for Biomet (272+/-39); moderate for Richards (810+/-101); and high for Howmedica (990+/-132), AO conventional (1,000+/-97), and Zimmer (1,140+/-183); 13.0-millimeter reamer: low for Biomet (132+/-21), Howmedica (204+/-45), and Zimmer (226+/-33); moderate for AO conventional (474+/-42); and very high for Richards (1,734+/-127). The second worst system (AO conventional: 1,000+/-97) became the second best system by simple reduction of the shaft diameter (A6/A7: 378+/-33). CONCLUSION: A comparison of shaft diameters and pressure increase clearly showed that the system with the thinnest shaft produced the lowest pressure values and vice versa.

Equipment Design↗