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Reduction of the porosity of bone cement by centrifugation significantly improves the fatigue life of the cement when smooth, waisted specimens are tested. However, bone cement in vivo has surface irregularities at the interdigitation of the cement with the trabecular bone. The effect of centrifugation on the fatigue life of Simplex P in specimens containing surface irregularities was investigated by examining both composite specimens of trabecular bone and bone cement and specimens containing a sharp, circumferential notch. For the specimens with the sharp notch, the bone cement that had been centrifuged lasted significantly longer in fatigue (47,039 +/- 40,277 cycles) than the uncentrifuged specimens (3103 +/- 1950 cycles). Eleven of 15 uncentrifuged specimens broke at the location of a void, rather than the notch. In contrast, when the porosity was reduced by centrifugation, 13 of the 15 specimens broke at the notch. For the specimens that were a composite of bone cement and trabecular bone, the centrifuged specimens had a significant increase in fatigue life compared to the uncentrifuged specimens when tested at both 7 MPA (641,056 +/- 444,131 cycles vs. 237,969 +/- 124,153 cycles) and 15 MPA (8800 +/- 4673 cycles vs. 1534 +/- 719 cycles). Reduction of porosity in bone cement by centrifugation significantly extends its fatigue life even in the presence of trabecular bone or sharp surface notches as used in total joint replacements. These data support the concept that reduction of porosity of bone cement by centrifugation may extend the duration of fixation of the components in cemented total joint arthroplasties.

The ingrowth kinetics of soft and hard tissues near pre-polymerized and in-situ-polymerized large pore, in-situ-polymerized small pore and solid acrylic implants were investigated. Empty cavities served as controls. Aqueous sodium carboxymethyl cellulose (CMC) gel was dispersed in bone cement to create interconnected porosity. After periods of insertion from 2 days up to 26 weeks in frontal and parietal bones in pigs, tissue blocks containing implants were embedded in JB4 and studied by light microscopy. After the disappearance of the CMC-gel, at first only cells invaded the large pore implants but necrotized when at some distance from the implant surface. Later, when blood vessels grew into the pores, accompanying vital fibrous connective tissue was observed. Finally, all pores were filled with connective tissue. Surrounding bone was first resorbed, starting at day 7, creating a soft tissue interface. A zone of bone deposition, starting deep in the remaining bone at day 2, moved towards the implant, thereby bridging the soft tissue interface. At 6 weeks bone grew into the pores, thus anchoring the implant. Continuing deposition of bone around the implant provided a so-called lamina dura effect with all implants. Qualitatively similar tissue kinetics were observed around solid and pre-polymerized large pore implants, evidently in the case of solid implants without tissue ingrowth. Into the small pore implants only superficial soft or hard tissue ingrowth was seen because of the too small interconnections.

A conglomerate of homologous bone-chips and n-butyl-cyanoacrylate fixes the fragments in the ultrasonic osteosynthesis. The sound pressure leads to the forced penetration of the monomer into preformed gaps of the bone surface (Volkmann and Haversian canals) up to maximum 300 microns during the polymerisation forced by ultrasound. A toothing effect between the conglomerate and the cortex takes place in this way, this one leads to a higher mechanical resistance and to specialities in the regenerative process. The term welding is founded scientifically by the mechanism of the connecting formation. On the other hand the application of the ultrasound is sensible in order to force the polymerisation.

The effect of methyl methacrylate monomer used for polymerization of surgical bone cement on phagocytosis, blood cells, tissue cells in culture, and bacteria was investigated. A concentration of 0.5% monomer reduced the ability of macrophages in vitro to phagocytize cultures of Staphylococcus epidermidis effectively. In vivo, 0.03 ml injected into mice also reduced the capacity of peritoneal macrophages to phagocytize bacteria. Extent of cellular damage to blood cells varied with concentration of monomer used and time of contact but, in general 0.5% was sufficient to alter morphology and viability of blood cells and tissue cells in culture. Polymorphonuclear neutrophils sustained more damage than other types of blood cells. Only minor alterations were detected from cooled, polymerized cement. These studies support the concept that the monomer, as well as mechanical and thermal factors, may be responsible for some of the tissue changes seen at the site of implant of bone cement following total joint arthroplastic surgery.

With the combined osteosynthesis of pathological fractures in association with tumors and/or metastases in mind, E. Merck (Darmstadt, FRG) developed a bone cement containing a cytostatic agent, methotrexate-Palacos flow y (MTX-Pf). The animal-experimental study presented here investigates the tolerability of MTX-Pf in the femurs of rabbits with lateral comparison. In these investigations we used both the concentration of 0.63% MTX, as is currently used in standard clinical surgery, as well as a much higher concentration of 2.5% MTX. The histological sections were investigated using microradiographic methods and provided no indication of any significant differences between the femora with the MTX-Pf implantation and those into which standard Palacos flow y had been implanted.

The chemical effect of polymerizing CMW and Simplex-P bone cements was recorded by intravital microscopy in the hamster's cheek pouch. Thermal effects and pressure on the tissue were eliminated. Where a direct cement-tissue contact was present, severe, apparently irreversible, microcirculatory disturbances were recorded. Both cements caused equally extensive microvascular damage. Intact epithelium and connective tissue appeared to protect the underlying vascular bed from the effect of the monomer. No differences in tissue reaction were recorded when the cement past was applied after normal and prolonged kneading.

The cardiovascular responses to forcing acrylic bone cement, Plasticine, or soft paraffin wax into the medullary cavity of the femur have been studied in rabbits and cats. An acute fall in blood pressure, occurring within a few seconds of insertion, was demonstrated with each substance. In a few of the animals the blood pressure response had a second more protracted component and it is suggested that more than one mechanism is involved. The cardiovascular effects that have been observed in man when acrylic cement is used in prosthetic hip surgery also may be due to more than one mechanism.