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Biomedical subjects

P Schaff

Publications and source records attributed to P Schaff.

At least 19 recordsLinked to original sources
PubMed2006

Decellularized umbilical artery treated with thin polyelectrolyte multilayer films: potential use in vascular engineering.

Decellularized allograft tissues have been identified as a potential extracellular matrix scaffold for tissue-engineered vascular substitutes. In order to improve the thromboresistance, it is necessary to pre-coat the intra-luminal vessel surface. Recently a new surface modification technique appeared, based on the alternate adsorption of positive and negative charged polyelectrolytes. Our objective was to develop an alternative vascular scaffold made of decellularized human umbilical arteries treated with a PAH/PSS polyelectrolyte multilayered film. The vessels luminal surfaces covered with the multilayer film were observed by electronic scanning microscopy. Our observations showed that the luminal surface is completely devoid of ECs following treatment with trypsin. A top view of the coated artery indicated that the multilayer uniformly covered internal surface of the vessels. The successful of the multilayer correct deposition and retention on the arterial wall were controlled by confocal microscopy using a fluorescent polyelectrolyte (rhodamine-PAH). The data suggest that decellularized cryopreserved arteries represent a potential scaffold for further vascular tissue engineering efforts. Moreover, the multilayer films can be used to coat biological surfaces and following the terminated layer (PAH or PSS), favour the cell adhesion or cell resistance.

Arteries↗
PubMed2002

Long-term results after ankle arthrodesis: clinical, radiological, gait analytical aspects.

In a retrospective study the results of operatively treated ankle joints were critically discussed. In a period from January 1, 1977 to December 31, 1994, a total of 35 arthrodeses were carried out. Seventeen patients were followed up clinically, radiologically and with a gait analysis. Not only the radiological surgical result was of interest, but also the heel-toe movement of the stiffened foot in the individually adapted orthopedic footwear compared to standard footwear. A significantly improved heel-toe movement was found in orthopedic shoes, although there is a reduction of movement in the hindfoot in the sagittal plane.

Adult↗
PubMed2001

Insulin resistance, dietary cholesterol, and cholesterol concentration in postmenopausal women.

Questions remain concerning the effect of variations in cholesterol intake on plasma cholesterol concentration, as well as on the role of factors modulating the metabolic impact of this dietary intervention. To define the impact of wide variations in dietary cholesterol intake on plasma total and low-density lipoprotein (LDL) cholesterol concentrations, as well as testing the hypothesis that resistance to insulin-mediated glucose disposal would accentuate the increase in plasma total and LDL cholesterol concentrations in response to a given increment in dietary cholesterol intake, we performed a prospective, randomized study comparing diets varying in cholesterol content in 65 healthy, postmenopausal women, 31 defined as insulin-resistant and 34 as insulin-sensitive. The changes in total and LDL cholesterol in response to increments in dietary cholesterol of up to approximately 800 mg/day were modest in magnitude, without evidence of a statistically significant diet-induced increase in cholesterol concentration, or of any difference in the responses of insulin-resistant as compared with insulin-sensitive women. These results indicate that relatively large increments in dietary cholesterol intake had little effect on total or LDL cholesterol concentrations in healthy, postmenopausal women, irrespective of whether they were insulin-resistant or insulin-sensitive.

Apolipoproteins A↗
PubMed1995

[Backward fall in Alpine skiing. Case study of the effect of the back spoiler of the ski shoe on muscle activity and kinematics].

For the investigation of the boot-induced anterior cruciate ligament injury and experimental case study with a prototype ski boot was performed. The back spoiler of this boot was designed to yield by only some degrees with a certain level of backward moment. A mechanical switch allowed to activate or to block this mechanism. Ten jumps over a prepared hill with activated and ten jumps with blocked spoiler mechanism were performed in randomised order. During the jump and landing the EMG of eight lower extremity muscles were recorded and synchronised to two S-VHS cameras suitable for 2D-analysis of the angle kinematics. The aim of these experiments was to quantify the muscular and kinematic effects caused by the new spoiler characteristics and also to establish a method for their judgement. For the quantification of the muscular effects an activity quotient was defined and for the analysis of the kinematics the time history of three body angles and their variation between the trials were found to be appropriate. The results of this case study showed an increase of the activity quotient for all observed muscles and a higher accuracy of motion with the activated spoiler mechanism. These findings an be taken as an indication for better muscular joint guiding in the knee and justify a randomised field study using the proposed methods.

Adult↗
PubMed1995

Contraction of knee flexors and extensors in skiing related to the backward fall mechanism of injury to the anterior cruciate ligament.

The purpose of this study was to examine the motion pattern and muscle activity during jumping and landing in downhill skiing to estimate the muscular involvement during the jump-landing-backward fall-anterior cruciate ligament (ACL) injury. A digitized 2-D video motion analysis and a synchronous 8-channel electromyography registration was performed over a jump on a downhill slope during 3 runs by 2 skiers and during 6 control jumps in the laboratory. The knee flexors (lateral gastrocnemius and biceps femoris) were recruited before touchdown and mean 60 ms earlier than the extensors (vastus lateralis and rectus femoris). Extensors and flexors reached peak activity simultaneously at the instant of landing. The knee flexion angle at the instant of landing was mean 36 degrees. As the landing was stabilized, the extensor activity persisted during eccentric work at increasing knee flexion as a corresponding flexor relaxation took place. The control jump in the laboratory showed a similar order of recruitment and timing of muscle contraction. The gastrocnemius was recruited mean 96 ms earlier and the biceps femoris mean 63 ms earlier than the extensors. This recruitment pattern during the landing movement suggest a learned motor program engaging the kinetic chain of the lower extremity to intercept the landing energy. The results also indicate that the knee flexor activity may protect the ACL at the instant of landing but that it is minimal shortly thereafter and probably not able to protect the ACL when a backward fall occurs. The knee was flexed substantially as the extensors became the dominating muscles. Thus, their ability to apply any anterior drawer force able to rupture the ACL is questioned.

Anterior Cruciate Ligament Injuries↗
PubMed1994

[Pattern of injuries in skiing worldwide. Can current guidelines for adjusting ski bindings reduce injuries in the future?].

World wide injuries show an overall reduction in skiing injuries. Updating the work of Hauser and Gläser (20) the average injury value declines from about 7 injuries per 1000 ski days in 1960 to 2 injuries per 1000 ski days in 1990. A stagnation can be reported for the past 5 years and no dramatic reduction is to be expected. Important, however is the trend of increasing knee injuries. As the risk for knee injuries was prevalent for female skiers (36, 15, 12) we also found a higher number of combined knee injuries especially including the medial collateral ligament (MCL). As the current binding adjustments do not focus on them, we are having a closer look about the advantages and disadvantages of each method. The final result is a suggestion for a radical change. By means of a new binding setting method and the demand for more responsibility to the skier we try to create a new skiing safety idea consisting of the setting table, a recommended binding release test and a gear binding. This is supposed to serve as the basis for a new safety approach.

Adolescent↗
PubMed1991

[Treadmill versus field trial. Movement analysis and pressure distribution in the athletic shoe].

Our current knowledge on interactions between runner and runningshoe is mainly based on treadmill measurements. In order to reveal stress load and adaptation on playing surfaces it was necessary to develop a combined measuring device out of 3-D video motion analysis and portable pressure measurement system. By means of a motor driven cart moving parallel to the subject with comparable position of cameras to the treadmill test it was possible to set up an identical trial for track and field. 12 subjects (male, age 24-32, size 9) were tested at a speed of 2.8 m/s. The varying conditions were treadmill and grass and two different constructed running shoes. 200 cycles and over 1000 steps were analyzed. The quantitative analysis of 37 parameters describing the contact phase was performed using the wilcoxon test for paired samples.-A qualitative comparison of running styles was introduced by using angle-angle-diagrams (knee and ankle by 3-D data) similar to those first described for 2-D by P.R. Cavanagh in 1973. It showed a huge interindividual variability under same conditions. Comparing the angle-angle-diagrams for the four different running conditions it was possible to classify them into three characteristic groups: non-adaptors, surface-adaptors and shoe-adaptors. Comparing track and field to treadmill measurements significant differences were found for the knee at impact: On treadmill the initial knee angle was 4.6 degrees more extended at a 13% higher angle velocity and a 30% higher angle deceleration (sig. p less than 0.05). A 7.3% higher impulse was found on grass at a 5.9% higher step length. No difference in maximum pressure was found. These results show that adaptation is performed mainly by the knee. Changing the motion pattern the knee seems to be capable of homogenizing the different stress loads to the foot. Comparing the running shoes significant differences were found in the motion of the ankle: a controversial behaviour was found to be on treadmill and grass. The pressure data revealed significant differences for the treadmill test to be in the heel area, for grass in the arch area. This points to an--up to now--unknown importance of the arch on unplain surfaces that are obviously influenced by the construction of the shoe and are not accessible by treadmill tests. The described different behaviour of shoes in treadmill and track and field tests points out the reduced validity of single treadmill tests.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1990

[Ski boots versus the knee joint. 2: What produces the forward leaning position of the ski boot?].

In contrast to the drop in the incidence of fracture of the lower leg that has been observed in recent years, the incidence of knee injuries has not decreased in skiing. There has even been a relative increase of severe knee lesions and isolated ACL ruptures, prompting us to conduct a comprehensive study of the causes of this phenomena. The goal of part 2 of the study was to comprehensively examine the forward movement in skiboots in the lab and on the slope. Studying nine beginners and eight experts, we found a 20% (sign. 0.05) lower forward-lean capability for the beginner group in the same boot. A randomized study with crossover design conducted on the slope, where we equipped 16 skiers with either soft or stiff boots for the duration of five ski days, revealed the learning behaviour and forward position on the slope depending on the boot. The pupils became definitely less adept at learning if they were required to wear stiff skiboots and showed a sign, lower forward flex angle. A skiiing style in backward lean position was adopted and supported by the fixed backward spoiler. Therefore another study was necessary and will follow (part 3) to examine the effect of a stiff backward spoiler and skiing in a backward lean position. In consideration of the facts known up to now, it is concluded that to improve safety in skiing recommendations must be given as to which boot to choose, according to the skiing level. In addition, the setting of safety bindings must consider the type of skiboot used.

Biomechanical Phenomena↗
PubMed1990

[Ski shoe versus knee joint--3: Risk for falling backward].

In contrast to the drop in the incidence of fractures of the lower leg that has been observed in recent years, the incidence of knee injuries has not decreased in skiing. There has even been a relative increase of severe knee lesions and isolated ACL ruptures, prompting us to conduct a comprehensive study of the causes of this phenomena. The goal of the study was to develop a new measuring device for alpine skiing research by combining motion analysis, pressure and force measurement, comprehensive examine the forward/backward movement in skiboots in the lab and by means of telemetry on the slope (Skiboot versus knee joint part 1/Sportverlerletzung. Sportschaden 3, 1989, pp. 149-161) and to come up with a proposal for a new safety concept to reduce the high number of knee injuries in alpine skiing in the future. The first study was devoted to the forward movement in skiboots (Skiboot versus knee joint part 2/Sportverletzung. Sportschaden 4, 1990, pp. 1-13). The results showed that a skiing style in backward lean position was adopted by skiers wearing boots with a stiff forward flexion and was supported by the fixed backward spoiler. In order to quantify the influence of the backward spoiler a special skiboot was constructed allowing the rear spoiler to give way at a variable, defined stiffness and register the angular displacement and horizontal force Fh. The results showed most clearly that even a medium rear spoiler resistance will sign, reduce the peak force values by a factor of 5.5. The acceleration at the knee joint level is significantly higher (factor 1.6, p less than 0.05) in case of a rigid spoiler. The lab tests could be confirmed on the slope (sign. reduction of max. force by factor 8). It also proved that normal skiing can be performed in such a boot without limitations. In consideration of our facts it is concluded that the principle of safety bindings must definitely apply in future in equal measure also to the ski boot. As a proposal for future safety ski boot, that allowed for the first time the rear part to give way after a certain amount of force (adjustable preload). The backward release bindings, which can often produce dangerous malfunctions if a strong force acts on them for a short period of time, could thus be complemented by a safety system in the boots. In all probability this would be a contributing factor to reducing the high incidence of knee injuries in skiing.

Adult↗
PubMed1989

[Skin boot versus knee joint--a sports medicine, orthopedic and biomechanical problem].

In contrast to the drop in the incidence of fractures of the lower leg, or tibia, that has been observed in recent years, the incidence of knee injuries has not decreased in skiing and there has been a relative increase in the frequency of severe knee lesions and of the isolated rupture of the cruciate ligament, prompting us to conduct a comprehensive study of the causes of these phenomena. It was found necessary to develop a innovative method of measurement to analyse the patterns of movement and stress to which the knee injuries were attributed. By combining and synchronizing movement analysis, measurement of pressure distribution and measurement of force it became possible to perform a detailed analysis of the forward/backward movement in the ski boot in the laboratory and also on the course by telemetry (part 1). The first two studies were devoted to the forward lean in the ski boot (part 2). Basing on movement analysis and simultaneous determination of pressure distribution along the lower leg, the influence of different ski boot models on the Vorlage, or forward lean, movement of beginners and very experienced skiers was studied. An important result of the laboratory experiment was that whereas a ski boot can be moved without difficulty into a strong forward lean position of the skier by an experienced sportsman, a beginner can only assume a forward lean with 20% less inclination (this being a significant difference). In other words: the range of the freedom of movement in such a boot is markedly limited. The assumption that in ski amateurs such a ski boot would promote skiing in backward lean position, was confirmed by studies on the course (part 3). The pupils became definitely less adept at learning if they were required to wear a stiff ski boot; analysis of movement showed that the forward lean angles were clearly smaller and that the skiers adopted a skiing style in backward lean position that exercised an undue strain on the knees. The other two studies, therefore, focussed mainly on the backward movement in the ski boot. Specifically, the fixed rear spoilers of the modern ski boots are accused of contributing to the rupture of the anterior cruciate ligament if the skier lands on the tail ends of the skis after a jump or fall in backward lean position ('big bump, flat landing' syndrome).(ABSTRACT TRUNCATED AT 400 WORDS)

Biomechanical Phenomena↗