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Biomedical subjects

A Rohlmann

Publications and source records attributed to A Rohlmann.

34 records · Page 2Linked to original sources
PubMed1980

[The stresses in femur. I. Intact femur without consideration of the iliotibial tract (author's transl)].

Stresses in femur under different load conditions were computed with the finite element method. The computer model was composed of 1950 spatial elements. The calculated results were confirmed using 34 strain gauge rosettes, attached on the femur surface. The load conditions were chosen as at the stance phase of walking and as standing on two legs. Additionally, the effect of joint forces under different directions were investigated. It is the main conclusion of this work that the computed quantitative results are only relevant when the geometry and the material properties of the metaphysical bone are copied exactly for the computer model.

Biomechanical Phenomena↗
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

[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

[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↗
PubMedDate not supplied

[In vivo measurement of hip joint stress. 1. Physical therapy].

The forces acting during physiotherapy in both hip joints of one patient have been measured in vivo using a telemeterized joint prosthesis. During supported exercises the loads are up to 50% of the body weight (BW). Active movement of the leg against resistance in a lying position let the forces rise up to 250% BW. During symmetric two-legged-stance the load is typically 70% BW, while during walking peak values of about 300% BW were measured. By use of one crutch a 25% reduction of the joint force can be achieved.

Biomechanical Phenomena↗
PubMedDate not supplied

[Reproducibility of surface measurements of the back using the opTRImetric method].

The early detection of scoliosis as well as the supervision of its progress without or with a minimal number of X-rays, is the aim of surface measurements by the opTRImetric method. The device, the method and the measured variables are described. The main aim of the work was the determination of the reproducibility of the measured variables. The variation of the measured variables caused by the stance and measurement method are given. It appears that the use of a balance for equal footloading results in a posture different from the "normal" one, and that the reproducibility of this posture seems even less than of the posture adopted when equiloading of the legs is subjectively attempted.

Adolescent↗
PubMedDate not supplied

[Stresses on the femur following hip joint replacement].

The stresses in femur after joint replacement have been calculated with the finite element method and the results were checked by using strain gauges glued on the surface of the femur and on the prosthetic stem. The influence of stem length and prosthetic collar on the distribution of the stresses have been investigated. The stem length has only a minor effect on the stress distribution if the stem has a texture which allows transfer of tension and shear at the interface endoprosthesis--bone cement. Merely at the tip of the stem changes of the stresses are obvious. The stresses in the bone near the resection plane are distinctly reduced if the prosthesis has a collar. These results have very limited relevance for implants with a smooth stem which does not allow the transfer of tension and shear at the interface endoprosthesis--bone cement.

Bone Cements↗