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M Lengsfeld

Publications and source records attributed to M Lengsfeld.

At least 37 records · Page 2Linked to original sources
PubMed1994

[Automatic generation of 3-D finite element codes of the human femur].

The extremely irregular geometry of bones makes it very difficult to develop and preprocess three-dimensional finite element models (FEM). In the field of biomechanics, the finite element simulation method is a research tool of increasing importance for the prediction of stresses and the stress-compatibility testing of endoprostheses. With this in mind, a FEM preprocessor was developed with the aim of creating three dimensional models of human femurs. On the basis of postprocessed computed tomography data, this preprocessor makes possible rapid, flexible and regular cross-linking. "Brick" elements are used, which are of advantage in terms of computing time, accuracy and computer storage requirements. The software simplifies the generation of models and facilitates the investigation of individual variations, thus providing the basis for utilizing the method in the clinical setting.

Biomechanical Phenomena↗
PubMed1993

[Treatment and results of ruptures of the patellar tendon].

Ruptures of the patellar ligament are rather uncommon. In younger individuals they are due to adequate trauma, in older individuals spontaneous ruptures occur after inadequate trauma. We observed eight traumatic (mean = 26.5 years) and eleven spontaneous ruptures (mean = 57.5 years) between 1980 and 1990. There is no alternative to surgical repair of the ruptured or torn-out patellar ligament. Tendon-repair with supportive wire-looping and early functional physiotherapy produces a good functional result. The outcome of patients treated in this manner shows persisting slightly muscular atrophy of minor degree and limited knee mobility with only a little all-day handicap.

Adult↗
PubMed1993

Stresses at the meniscofemoral joint: elastostatic investigations on the applicability of interface elements.

Stress distributions at the meniscofemoral joint were analysed and the applicability of nonlinear interface elements in a finite element model (FEM) were tested. Centred and 70% off-centre load cases with a complete, a partially removed or a totally removed medial meniscus were evaluated in two dimensions. Interface width was assumed to increase linearly from almost zero to 1 mm at the inner and outer border of the femoral condyles. Maximum interface forces were found at the centre of the condyles, decreasing to zero at the peripherical and intercondylar femoral border. Simulation data concerning a removed medial meniscus or medial 70% off-centre load with complete meniscus indicated higher medial contact forces in the first case. A decrease in the elastic modulus of the articular surface tissues caused two small force transfer peaks (femoral centre and intercondylar border), which were strongly influenced by the predefined gap width.

Adult↗
PubMed1993

[Experimental determination of muscle coordination of the lower extremity].

In order to describe the lines of action of muscles acting on joints, data on the geometrical position of insertions and origins are needed. These are of fundamental relevance for the biomechanical analysis, in particular for the calculation of joint loading. A measuring device with an accuracy of 0.1 mm was designed and constructed for the collection of three-dimensional experimental data from wet anatomical specimens. The main design features of the device include a vertically adjustable stand on wheels and a rotatable scale ring with a radial pointer. After setting the reading, the apparatus permits the measurement of cylindrical coordinates The margins of the attachments of muscles acting on the hip and knee joints were measured in two specimens. Two extensive sets of morphological data are now available and can be used to create complex biomechanical computer models.

Biomechanical Phenomena↗
PubMed1992

[Morphological and numerical studies of the stress compatibility of patella implants].

Failure of total knee arthroplasty is relatively often caused by problems of the patellofemoral replacement. The purpose of this study was to analyze the distribution of stresses within an anatomical patella and the changes in stress distribution after patellar resurfacing with a Miller-Galante I patellar implant using two- and three dimensional finite element models (FEM). To assess validity, FEM results were compared with morphological findings from contact radiographs and densitographs. Internal orientation of bone trabeculae is in good agreement with the orientation of theoretically calculated principal stresses. Almost unchanged principal tensile stresses after implantation, together with the lack of extreme stress peaks within the cancellous bone ensure stress compatibility of the implant. In the case of a firmly seated implant with good bone ingrowth, increased von Mises stresses are found near the fixation peg/plate junction. Their relevance for improved bone ingrowth near this part of the interface is emphasized. At the same time, material failure at the peg/plate junction can be better understood. An analysis of the early postoperative period assuming nonlinear interface conditions failed to demonstrate an uniform distribution of normal and tangential interface forces.

Aged↗
PubMed1991

[Significance of shape differences between medial and lateral knee joint menisci for functional change of position].

The attachments of the anterior and posterior horn of the menisci to the tibial plateau are of a most important functional value. At the medial meniscus the circumference is more widely configurated, because of the greater distance between anterior and posterior horns. The areas of sagittal cuts through the menisci slightly differ regarding medial and lateral side. A higher area momentum of inertia of the medial meniscus, related to a vertical axis within the examinated sagittal plane, is found. It derives from a geometrical distribution of partial areas more distant from the axis. The medial meniscus therefore has a higher stiffness against sagittal bending stress. Experiments and theoretical stress simulation prove these results. According to them, the medial meniscus is less mobile in comparison to the lateral. These findings are discussed as a basic geometrical cause for the higher incidence of injuries of the medial meniscus.

Biomechanical Phenomena↗
PubMed1991

[Valgus osteotomy and lengthening of the femoral neck in secondary coxa vara in adolescents and adults].

Shortening of the femoral neck and proximal displacement of the greater trochanter are main problems of coxa vara after avascular necrosis of the capital epiphysis. In 24 patients an osteotomy to lengthen the femoral neck was performed to normalize the anatomic and functional situation. A clinical and radiological follow-up showed good or satisfactory results of the operation in 23 cases. Elimination or relief of pain and a negative Trendelenburg sign are important short-termed aims. Prevention or deceleration of degenerative changes in the hip joint are primary long-termed aims.

Adolescent↗
PubMed1990

Kinematics of the patellofemoral joint. Investigations on a computer model with reference to patellar fractures.

Patellofemoral kinematics were studied on a computer model. The articulating point of the patella moves from distal to proximal during flexion, until the quadriceps tendon starts to turn around the femur tendo-femoral gliding. The pattern of patellofemoral movement consists of a gliding and rolling component, the latter at its maximum at the beginning of flexion. The pathway of the instant centers of motion moves from dorsal to ventral during flexion. Stress analysis shows that the contact area is at all times the area of maximum bending stress. The distal part of the patella is the part with mechanical stress at all angles of flexion. The conclusions to be drawn for treatment are that fractures within the proximal and central part of the patella need a very high stability of internal fixation, the distal part of the patella less so. Postoperative treatment must take into account the changing contact area, because the peak stress is always at the contact area.

Biomechanical Phenomena↗
PubMed1990

[Biomechanical model calculations on the influence exerted by the sagittal sliding profile on patello-femoral load].

Patellofemoral loads are calculated by means of a mathematical model based upon an elliptical approximation of the articulating profile. Differences in the sagittal curvature of morphological and arthroplastic gliding surfaces can be approximated by a differing eccentricity of the ellipse. The joint is balanced in a static situation by two tension forces. The resultant is the vector sum of both forces and represents the entire load. Small loads in the initial flexion of the knee joint and high loads in the end of flexion are caused by a flat sagittal curve. A more eccentric shape of the articulating profile reduces the loads at the end of flexion, because the quadriceps tendon starts to turn around the femur earlier. The model also takes into account the patellar ligament turning around the proximal tibia at wide flexion angles. Besides the design of the prosthesis, patellofemoral loads depend on the height of implantation of the femoral component. It must be borne in mind that forces will vary in magnitude at different flexion angles; the patient's activities after the operation must also be considered.

Femur↗
PubMed1990

[Controlling and supporting apparatus of the deep finger flexor tendon and the long extensor tendon of the thumb. Clinico-anatomical analysis].

Full function of finger flexion requires an intact pulley system. After destruction of the pulleys, reconstruction over the metacarpal head (A1) and over the center of the proximal and middle phalanges (A2, A4) should be carried out. Calculations on a computer model suggest that the reconstructed pulley must hold the tendon close to the underlying bone. Width of the pulley and distance from the next proximal or distal joint of the inserted pulley are of minor functional importance. The amount of maximum load on the pulley, exceeding the tension of the tendon, must be considered in operation and postoperative treatment. The extensor pollicis longus tendon lies at the dorsal tubercle (tubercle of Lister) within an osseous gliding surface, where it changes direction. The deviation angle depends on the radiocarpal position and causes, in addition to the usual tension, a pressure stress to that part of the tendon. A graphical analysis of statics, based on X-rays, demonstrates maximum loads on the gliding surface. They can increase in relation to the tension force of the tendon to about 50% in the antero-posterior and to 100% in the radioulnar projection. Densitography of the distal radius shows a maximum of density where the dorsal tubercle is most prominent. Nutritional problems of that tendon are predisposed by that particular mechanical stress. Therefore spontaneous rupture of the extensor pollicis longus tendon in patients with rheumatoid arthritis or after fracture of the distal radius occurs, though infrequently. In the case of immobilization, slight ulnar abduction within the radiocarpal joint remarkably reduces the tension and pressure stresses on the tendon.

Computer Simulation↗
PubMed1989

[Stresses on the patellofemoral joint].

The patello-femoral joint is balanced by 2 tension forces of opposite direction, which are represented by the geometrical position of M. quadriceps femoris and Lig. patellae. The resultant is the vector sum of both forces and is shown by a computer simulation. Its action line runs through the center of rotation and is perpendicular to the articular point, the total torque is zero. At higher degrees of knee flexion, quadriceps tendon contacts the femur and changes direction. This effect has important influence on the amount of the resultant. The articular point of the patella moves from distal to further proximal during flexion.

Computer Simulation↗
PubMed1988

Chronic hypertension changes myosin isoenzyme pattern and decreases myosin phosphorylation in the rat heart.

We investigated systolic blood pressure (BP), ventricular myosin isoenzyme (MI) pattern, and myosin P-light chain phosphorylation (MP) of male and female normotensive (WKY) and spontaneously hypertensive rats (SHRSP). BP increased in SHRSP of both sexes during maturation. Male SHRSP reached a significantly higher BP (262 mmHg at week 64) than female SHRSP (217 mmHg at week 64). WKY remained at approximately 114 mmHg throughout the life-span investigated (5 to 64 weeks). MI pattern (expressed as %V1/%V3) shifted age-dependent to the V3 form: In female SHRSP MI pattern was 41/25 at week 18, 34/35 and 40/38 within week 22 to 32, and shifted to 18/53 until week 64. In male SHRSP MI pattern was 25/44 at week 18 and shifted gradually to 13/60 until week 53. MI patterns of WKY of both sexes were 100% V1 within week 5 to 12, shifted gradually to 51/23 and then remained constant until week 64. MP of the ventricle of female WKY and SHRSP was approximately 41% until week 52. At week 64, however, MP of female SHRSP decreased to 18% whereas female WKY remained at approximately 41%. MP of the ventricle of male WKY and SHRSP was approximately 38% until week 38. At week 44, however, MP of male SHRSP decreased to 22% whereas male WKY remained constant. Isometric tension generation of chemically skinned rat ventricular fibres increased after MP by calcium-calmodulin-dependent myosin light chain kinase. Both the shift to the V3 form and the decreased MP level might contribute to the development of cardiac failure in old SHRSP of both sexes.

Animals↗
PubMed1988

Gonadectomy and hormonal replacement changes systolic blood pressure and ventricular myosin isoenzyme pattern of spontaneously hypertensive rats.

We investigated the influence of testosterone on systolic blood pressure, heart weight, body weight, and ventricular myosin isoenzyme pattern of male spontaneously hypertensive stroke-prone rats (SHRSP). In two different study series (study 1, postpubertal; study 2, prepubertal), SHRSP were gonadectomized (HG), gonadectomized and replaced with dihydrotestosterone (HG-T), and sham-operated (H). Blood pressure was significantly higher in HG-T animals in both study series. Only prepubertal gonadectomy (study 2, HG group) led to a significantly decreased blood pressure. Heart weight and body weight were significantly diminished in the HG group when compared to the H group in study 2. Dihydrotestosterone (HG-T group) reversed this effect. In both study series gonadectomy shifted the myosin isoenzyme pattern to the V3 form while testosterone replacement led to a myosin isoenzyme pattern in favor of the V1 form. We conclude that the ventricular myosin isoenzyme pattern is under the dominant control of androgens and dissociates the expression of myosin isoenzyme from both blood pressure and cardiac hypertrophy in spontaneously hypertensive rats.

Animals↗
PubMed1988

[Functional importance of the m. extensor carpi ulnaris for distal radioulnar articulation].

Any analysis of the stability of the distal radio-ulnar joint should consider the extensor carpi ulnaris tendon. The static and kinematic function of this tendon depends on its relationship to the sigmoid notch of the radius. Morphological studies indicate the existence of a gliding surface in the sulcus of the tendon on the dorsal side of the ulnar head.

Biomechanical Phenomena↗
PubMed1988

[A ventral mantle technic with dorsolateral mediastinal saturation in the radiotherapy of Hodgkin's disease].

Between 1975 and 1981 69 patients suffering from Hodgkin's disease stage I to III were treated by radiotherapy exclusively. In contrast to the standard modalities the mantle was treated only through a ventral portal with dorsolateral boost to the posterior mediastinum. The geometrical treatment arrangement and the modalities of dose application yielded favourable dose distributions and single doses within the target volume. The analysis of failures showed no in field-failure, six marginal recurrences, and 17 distant failures, which are not related to the technique of irradiation. The described technique of mantle irradiation seems to be equivalent to the standard technique with regard to tumor control and side effects.

Cobalt Radioisotopes↗
PubMedDate not supplied

[Bone adaptation changes mechanical stress in the femur--a prospective two years follow up after Hüft-TEP implantation].

AIM: Periprosthetic adaptive bone remodeling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodeling theory with finite element analysis. Unfortunately, there is still a lack of clinical validation data. The collection of prospective volumetric bone density data with a clinical computerized tomography study after THA was previously conducted. The objective of the study presented here is an additional evaluation of femoral strain. METHOD: In a prospective clinical trial with 7 female patients after THA computerized tomography (CT) and finite element (FE) modeling was patient specifically combined immediately after surgery, as well as at three and 24 months postoperatively. Mechanical strain was expressed by strain energy density. RESULTS: Corresponding to a bone density decrease, a decrease of the femoral strain energy density was observed during the two year follow-up after surgery (approximately 20 %). The predominant change occurred within the first three months and was found to be distally stronger than proximally. CONCLUSION: As far as we are aware, this is the first combination of fully prospective 3D CT density data in vivo with patient-specific finite element modeling. The assessment of mechanical strain data during a follow-up trial should be a new approach for analyzing hip stems in clinical biomechanics. A future confirmative study based on a statistical case number calculation would increase the evidence of the results presented here.

Absorptiometry, Photon↗
PubMedDate not supplied

[Stress analysis of an anatomically-adapted femur shaft prosthesis (Lubinus SPII)].

OBJECTIVE: Very good clinical long-term results of the Lubinus SP II hip prosthesis stem were reported in the literature. We therefore asked whether there is a relationship between these findings with biomechanical data of strain gauge measurements. METHOD: 14 strain gauges were applied at a femur being measured at 10 different load cases before and after implantation of the stem. RESULTS: After stem implantation a similar patterns of principal stress distributions was observed, however, the magnitude was markedly reduced. A striking reduction of the hoop stresses at the femoral calcar was seen in the case of a missing collar contact. Even in the case of a perfect collar contact the hoop stresses were diminished after strem implantation. The S-shaped physiological stem did not correspond with a specific stress pattern measured at the femoral surface. CONCLUSION: These results suggest that the stresses at the femoral calcar may be lower than the limits of bone growth while the other parts of the femur are more physiologically stressed. However, the prosthesis may tolerate a missing collar contact during a long follow-up period. The large experimental data file presented here could be used to validate future finite element analyses which could evaluate the stress distribution within internal parts of the bone and the cement layer.

Aged↗