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Biomedical subjects

R Kölbel

Publications and source records attributed to R Kölbel.

At least 19 recordsLinked to original sources
PubMed1987

Effects of stem design and material properties on stresses in hip endoprostheses.

With the aid of a three-dimensional finite element stress analysis a parameteric study of the essential aspects of the femoral component of hip endoprostheses was carried out. Various designs were investigated; these included the prosthetic stem length, the existence or non-existence of the prosthetic collar and the elastic modulus of stem and cement. Variations in the stem length have only minor effects on the stress distribution for a stem length greater than 100 mm, but the elastic modulus of the prosthetic stem has a considerable influence on the stresses. A high elastic modulus of the stem increases the stresses in the stem but it decreases stresses in the cement. The cement stresses increase with an increase in the modulus of elasticity of the cement.

Bone Cements↗
PubMed1979

[A technique for reproducible roentgenograms of the intercondylar sulcus for the study of the femoropatellar (author's transl)].

Roentgenographic documentation of certain features of FP-joint geometry and orientation may serve as guideline in deciding on the form of treatment for chondromalacia or recurrent patellar dislocation. Reproducible conditions for taking roentgen films are equally important for this purpose as well as for quantitative measurements and possible statistical work. A new positioning device for the patient's legs has been designed utilizing a parallellogram frame. The roentgenographic technique for skyline views at 30 degree, 60 degree and 90 degree inclination of the central beam relative to the femoral axis is described. The advantages over previous techniques are the ease of handling the positioning frame, the need for only vertical and horizontal adjustment of the roentgen tube, independence of the type of tube or table, reproducibility of cassette and patient positioning.

Adult↗
PubMed1978

[Spontaneous formation of angiogenic woven bone within cancellous bones. Some observations on microfractures of isolated trabecula (author's transl)].

Femoral heads removed for subcapital fracture of the femur were embedded in methacrylate. Contact roentgen films of slabs of 1--2 mm thickness were screened for aggregates of woven bone. A variety of form exceeding that seen by other methods was found, not only in association with isolated trabecula. The distribution was found to confirm earlier findings by Todd et al. (1972), Freeman et al. (1974) and Watson (1975). The aggregates were seen more frequently in porotic areas than in the trajectorial groups of trabecula in the femoral heads. Aggregates of typical shapes were also found in one hemipelvis and in a humeral head. In embedded specimens discontinuities were seen in some trabecula with aggregates and not in other elements. There was no evidence of cracks where aggregates were attached to the edges of bone plates. Some trabecula with aggregates were ground down to 100 micrometer for microradiography. Cracks of the underlying trabecula could be shown, but neither signs of resorption nor of formation or osteocyte activation could be found. Aggregates of woven bone within cancellous bone have been found in subchondral bone of experimental animals being impact loaded and in connection with discontinuities. They are found near areas bypassed by the transmission of loads, too, in osteoporosis beside the groups of pricipal trabecula, and without association with discontinuities. It is concluded, that aggregates of woven bone are the product of mesenchymal activation or some defect in the regulation of mesenchymal activity and associated with causes of bone atrophy rather than with specific mechanical conditions.

Fatigue↗
PubMed1978

[Walking with canes and forearm-crutches (author's transl)].

Partial weight bearing is frequently prescribed but cannot be controlled adequately. In a previous paper the change of forces at the hip joint as effected by a one sided cane was determined by instrumentation of the cane and a mechanical analysis of gait on a walkway. In the present study we looked at the conditions for control of partial weightbearing when two forearm crutches are used. Instrumented crutches and a forceplate were used. In walking with two forearm crutches the total of the ground reaction forces and the force pattern differ from those in free walking. The total of two crutch forces plus the force at the leg with partial weightbearing exceeds that caused by body weight alone. This is due to mass accelerations in a changed gait pattern. When the maximal leg force is reduced from 100% body weight to zero, the additional dynamic forces exceed those caused by body weight alone by 4%-19%. Only 2% of the additional dynamic forces act on the controlateral crutch while the rest is transmitted through the ipsilateral crutch. The crutch force pattern on the ipsilateral side depends more on individual gait characteristics than does that on the controlateral side. Load reduction is more pronounced in the late stages of the stand phase than in the early ones.

Adult↗
PubMed1977

[Köhler's "tear drop". Relationship between the radiologic picture and anatomic substrate].

The diagnostic value and anatomical basis of Köhler's "tear drop" has been in doubt. By means of radiographs of the right side of the pelvis taken with various degrees of rotation tilt, and by X-raying serial sections, it was possible to demonstrate how this appearance is produced. It was shown which parts of the pelvis contribute to the "tear drop". This simplifies an understanding of the radiographic appearances of the pelvis in the region of the hip joint.

Acetabulum↗
PubMed1977

[Critical observations and the loads on femoral head replacement and the femoral bone calculated for a support in 3 points (author's transl)].

In their attempts at calculation of forces acting on a femoral head implant and the forces transmitted to the bone, some authors have assumed support of the implant in a few distinct points. It can be shown, however, that forces thus calculated very much depend on the direction and point of action of the supporting forces assumed arbitrarrily. The suggestion to implant a prosthesis in a "valgus" position cannot be justified by results obtained by the method in question. The change in the resultant force at the hip joint due to positioning in "varus" or "valgus" has not been taken into account by previous authors. In the valgus position of the femoral head prosthesis the resultant hip force is up to 33% greater than that in a "varus" position.

Biomechanical Phenomena↗
PubMed1977

[Walking with canes and forearm-crutches. I. Reduction of loads at the hip and proximal end of the femur by one sided use of cane/crutch (author's transl)].

The effect of one cane or forearm-crutch on some mechanical parameters at the contralateral hip were investigated. 5 healthy individuals were photographed on a walkway while using an instrumented cane/crutch. Geometric data from an original mathematical model were taken from these fotographs and an X-ray film of the pelvis and femur. The resultant force and pressure at the hip joint, shear force in the femoral neck and, in one case, the bending moment in the trochanteric region were computed and expressed as a function of the load applied to the walking-aid. All values decreased with an increase of this load. The reduction of force and pressure at the hip joint achieved by application of a load equal to 15% of bodyweight are superior to those resulting from common operative procedures done for the samp purpose. Differences between the effects of one sided cane and forearm-crutch are negligible.

Biomechanical Phenomena↗