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Biomedical subjects

H G Willert

Publications and source records attributed to H G Willert.

At least 55 records · Page 3Linked to original sources
PubMed1979

The morphology of polymethylmethacrylate (PMMA) bone cement: surface structures and causes of their origin.

This study deals with the correlation between the polymerizing bone cement and the surrounding tissue. The surface structures of bone cements, polymerized in air, in tissue medium (in vitro) and in human bone during implantation were investigated and compared with the contours of the tissue of the implant bed. Basing on the dimensional differences it was differentiated between contours of 1st order and 2nd order: contours of 1st order are within the macroscopic range, contours of 2nd order within the microscopic range. The surface of bone cement polymerized in living human tissue differed essentially from samples polymerized under laboratory conditions. The differences are to be seen macroscopically in the coarse relief as well as microscopically in the shape and the connection of the superficial methylmethacrylate beads. Bone cements, polymerized in air show an ideal, even and closed surface. Bone cements, polymerized in tissue medium exhibit macroscopically some wrinkles, in the microscopic range their contours are either closed (samples prepolymerized at 22 degrees C) or partly open and partly closed (samples prepolymerized at 24 degrees C). The surface of bone cement implants, retrieved from human bones are characterized macroscopically by a marked wrinkled and papillary relief, microscopically by flattened beads, and most often by an irregular, rough and open surface with isolated beads giving almost the impression of a porous surface structure. The character of the surface of the bone cement originates from external, mechanical influences, from changes in the volume of the bone cement and from effects of the surrounding tissues. The surface of the bone cement implanted in human bone conforms exactly with the contour of the adjacent tissue; the tissue contour is infact a negative of the cement surface. The incomplete connection between the superficial PMMA beads seems to be of some practical value: In areas, where the PMMA beads are largely isolated, the mechanical stressability of the "polymer composite" is relatively low. Under high load, beads and bead-clusters may break off the surface. Shattering of bone cement implants possibly may start from such an open, porous surface area where PMMA beads are extensive isolated.

Acrylic Resins↗
PubMed1979

[Temporary plugging of cystic bone tumors by bone cement (author's transl)].

Methylmethacrylate bone cement was used to refill bony defects following excisional biopsy of supposed benign or semimalign bone tumors. This procedure offers several advantages: the anatomical situation at the site of the lesion will not be altered, that means the functions of the joint and the continuity and stability of the bone will be preserved; the histological examination of the tissue is possible without a hurry; the follow up of the lesion is easily possible by X-ray-examination; further therapeutic procedures can follow without restriction, for example if the histology discovered an unsuspected malignant tumor or if the follow-up revealed a recurrency. In addition a favorable effect is the necrosis of tumor cells, eventually left behind in the bone, by the action of zytotoxic monomer and heat, originated during the polymerisation of the methylmethacrylate. In benign or semimalignant bone tumors the cement has to be removed after an adequate observation period; at this occasion the cavity again is curetted and then filled with autologous bone grafts. Since 1972 we treated 13 bone lesions by this method of "temporary bone cement plugging". The lesions were 5 giant cell tumors, 2 aneurysmal bone cysts, 2 simple bone cysts, 1 osteosarcoma, 1 malignant lymphoma, and 2 metastases of hypernephroid carcinoma. In the case of osteosarcoma an amputation was performed just after the diagnosis was made. In the other cases no local recurrances up to now were seen.

Adult↗
PubMed1977

Reactions of the articular capsule to wear products of artificial joint prostheses.

Examination of a great number of tissue samples taken from the newly formed capsules surrounding artificial joints reveals small particles of prosthetic material. Abraded from the joint by wear and tear, these particles of plastic, metal, and acrylic cement initiate a foreign-body reaction and result in the formation of granulation tissue, including macrophages and foreign-body giant cells. Typical features of tissue reactions exist for each of the materials from which prostheses are made. The consequent formation of scar tissue produces a thickening of the capsule, which, in turn, may cause a reduction in the mobility of the joint. In small amounts, the foreign-body particles are eliminated via the perivascular lymph spaces. Where this transport system is insufficient to handle the volume, however, the foreign-body response may extend to the whole environment surrounding the joint. In such cases, there may be loosening of the cemented prosthetic parts because of deterioration of contiguous bone anchors by the tissue membrane lining the bone cement.

Foreign-Body Reaction↗
PubMed1977

New prospects for a prolonged functional life-span of artificial hip joints by using the material combination polyethylene/aluminium oxide ceramin/metal.

Investigations over the years have shown that the mirror-finished Al2O3 ceramic is a much more suitable frictional counterpart to ultrahigh molecular weight (UHMW) polyethylene than metal. Despite the extremely gread hardness difference between polyethylene and Al2O3 ceramic, a considerable lower wear rate is obtained for the polyethylene socked with this new low-friction material combination. The unexpectedly favorable tribological behavior of this ceramic material in contact with polyethylene may be attributed to the following factors: better values for corrosion resistance characteristics, wettability with liquids, surfact gloss, hardness, and scratch resistance of the ceramic material in comparison with those of the hitherto used metallic implant materials (AISI-316L steel or cast Co-Cr-Mo alloy). It appears that, by using this new combination of materials for the socket and the ball, it will be possible to prolong the service life of artificial hip joints considerably without having effecy any fundamental changes in the present design and implantation principle retaining the hitherto used anchorage shaft made of wrought Co-Ni-Cr-Mo-Ti alloy Protasul-10 of extremely high corrosion fatigue strength.

Alloys↗
PubMed1976

[Treatment and prognosis of osteosarcoma in childhood (author's transl)].

126 osteosarcoma under the age of 15 years are followed up in an interclinical study. There is a steady increase of tumor incidence towards the 15th year with a slight male preponderance. The main sites of the tumor are the distal femur followed by the proximal tibia and humerus. Evidence of multiple metastases is most often present in the lungs, less often in the skeleton. Nearly always metastases became evident within 2 1/2 years after diagnosis (98%). Therefore the 2 1/2-year disease--free survival rate seems to be sufficient for prognostic evaluation. The over all 2 1/2-year survival rate was 17,5%. Though the different methods of treatment are not statistically valid, the best results can be expected after early amputation. By radiotherapy alone no cure has been achieved. Survivals were seen at any age and at any site of long bones (distal femur, proximal tibia, humerus, femur, distal radius). Prognosis of osteosarcoma in the childhood is similar to that of the adult group.

Adolescent↗