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Biomedical subjects

M Ungethüm

Publications and source records attributed to M Ungethüm.

At least 19 recordsLinked to original sources
PubMed1988

Special problems of cementless fixation of total hip-joint endoprostheses with reference to the PM type.

The success of cement-free hip endoprosthetics is largely dependent on precise surgical techniques and primary stability of the anchorage, in which favorable biomechanical conditions as well as the quality of the stabilizing bone are of considerable importance. Information gathered from more than 1500 cementless hip-joint endoprosthesis implantations is presented with biomechanical solutions and indications regarding operating techniques, and a correlation between clinical symptoms and radiological signs of complications is discussed. In close coordination with material-specific factors, design and surface characteristics are decisive in the function and quality of anchorage of the endoprosthetic replacement. In the case of the PM total hip endoprosthesis, these widely variable values were governed strictly by biomechanical considerations, with particular reference to the resulting bone reactions. Results so far, including those relating to stable integration of the implant, must be regarded as absolutely positive and confirm the design characteristics on which this model was based. Avoiding the disadvantages of bone cement, cementless hip-joint replacement, particularly in operations for the exchange of cemented prostheses after loosening, can be regarded as a step forward in hip-joint surgery.

Biomechanical Phenomena↗
PubMed1988

[Bioactive materials. A critical review].

The bioactive materials should be divided into osteoinductive and osteostimulative materials according to their effect in bone regeneration. Already this statement requires a definition of the words used, in order to assure a real discussion. By means of the recommendations for definitions this paper is a basis for those discussions. In order to classify the bioactive materials into types of materials the potential effect onto the bone regeneration process should be considered. On the other hand the synthetic or biological origin, and the physical or biochemical structure are of great significance. Beside the classification made by the above called criteria the types of materials with their advantages and disadvantages are described. In the following discussion some problems are described like the mechanical and chemical instability, the coating of metallic substrata, the sterilization and the possibilities for the analytic characterization of hydroxylapatite.

Biocompatible Materials↗
PubMed1987

[Technology of cementless hip endoprosthetics].

The success achieved with non-cemented hip arthroplasty depends mainly on the stability of the fixation, the quality of the stabilizing bone being just as important as favourable biomechanical conditions. The results of the intensive research and development with respect to the particular features of a non-cemented hip endoprosthesis can be divided into the following basic categories: Biomechanical aspects with special reference to bone related to the design of the prosthesis; material characteristics, such as fatigue strength, tribology, corrosion resistance, and biocompatibility; and development of new materials and coatings to permit direct bonding of implant and bone. With regard to the stem of hip prostheses, the different design parameters of various types are examined to determine their typical design characteristics, such as bearing surface of the collar, geometry of cross section, anatomically adapted shaping, and surface of the implant forming the contact with the bone. The latter can be divided into macroprofiles and macro- and micro-porous coated surfaces. On the other hand, the methods of cementless fixation of acetabular cups can be primarily divided into conical and spherical screw fixation and pegged fixation with additional macroprofiles of porous surfaces. In a separate study of the biomechanical aspects of screwed sockets, the special importance of socket shape and thread geometry are presented with reference to primary stability and long-term fixation of prostheses.

Biomechanical Phenomena↗
PubMed1983

[Experimental study of improved threading of bone screws].

In order to improve the holding force between the bone and the screw, we have been carrying out experimental investigations of the stability of bone and screw connection. Especially Schanz screws with a diameter of 6 mm, used in connection with the Wagner leg lengthening device, have been taken into consideration. By use of a loading model we determined the sizes of the essential kinds of loadability of the bone-screw connection and therefrom derive directions for dimensioning. The influence of the thread parameters (e.g. flank angle, pitch, pitch angle) on the loadability of the bone-screw connection has been investigated experimentally for 17 different thread profiles. Summarizing up the results, a pitch angle of 7,5 degrees and a flank angle between 12 degrees and 15 degrees proved to enable the maximum loadability. Corresponding to the results of our trials with the loading model, the improvement of the thread was carried out on the premises of simultaneous failure of both the cortical thread and the Schanz screws by pressure or shear. The loosening behaviour of the improved thread has been tested together with the conventional thread form. The results showed a reduction of about 20% in loosening of the screws and an increase of about 30% in pressure and traction loadability.

Biomechanical Phenomena↗
PubMed1981

[The variation of the anchoring forces of knee endoprostheses due to the different conceptions and the positioning of the joints (author's transl)].

The stresses in the bone structure caused by the anchoring of a knee endoprosthesis depends on the type of the implanted prosthesis and on the positioning of the joint in respect to the directions of loading. The degree of valgus position at all has a relatively great influence on the reaction forces which have to be transmitted in the bone cement bone interface. Using simple models these characteristics can be clarified for hinged type joints as well as for condylar prostheses.

Biomechanical Phenomena↗
PubMed1980

Technological test-methods for hip prostheses.

Before the implantation of a new type of prostheses it is necessary to perform experimental tests in order to indicate obvious technical and biomechanical inconveniences before the long-time test within the human body will start. Experiments in animals can only give a rough outline of possible results. Appropriate models and simulators, however, can imitate the conditions of movement and so they are able to indicate characteristics of different types of prostheses due to material and design.

Forecasting↗
PubMed1980

[On the problem of femoral stem failure in hip replacement endoprostheses (author's transl)].

Femoral stem failure in total hip replacement is becoming an increasing problem in connection with the long time of implantation. For this reason the possible facts are described mainly responsible for the failure. By 3 cases of loss the influence of material aspects are shown on failures primary due to loosening. Only by a complete and especially careful control system in production of endoprostheses it is possible in all probability to avoid "in-vivo"-cases of technical cause only.

Aged↗
PubMed1978

[Butylcyanoacrylate--an adhesive for bonding strain gages to non-fixed biological materials (author's transl)].

Creep, hysteresis, stability, elongation capability and repeatbility of butylcyanoacrylate as a proper adhesive for bonding strain gages to non-fixed tissues have been tested with good results. Due to its excellent bonding performance butylcyanoacrylate provides the only means for bonding electrical resistance foil strain gages to biological materials for the time being. This opens new aspects for strain measurements with strain gages in the biomechanical field.

Biomechanical Phenomena↗