BONE CEMENT

Abstract: A bone cement for use in the cementing of protheses, especially protheses components for joint caps and bone marrow canals. The bone cement comprises polymethylmethacrylate, filler material in the form of particles of glass fiber or quartz having a particle size of 4 - 8 microns, and a silver ion-releasing material in the form of collodial silver (silver salt).

Description: BONE CEMENT The invention relates to bone cement especially for cementing protheses, in particular protheses components for joint caps and bone marrow canals. In 1965 a hip prothese was developed for use by elderly persons with fractures of the neck of the femur, because the conventional pins which had be*a_* used since 1938 had given such poor results. In 1970 this hip prothese was developed further into a so-called total protheses for use on patients with arthrosis, or arthritis of the hip joint owing to wear. With this type of protheses, one could reconstruct joints in which the cartilage had become worn down both in the cap o£ the joint and on the head of the joint. This- protheses, named after its inventor. Tor Christiansen f has been patented- A number of similar- protheses have gradually come on the market. To improve the stability of the protheses component in the cap of the joint and the- bone marrow canal, surgeons began to cement them in place with poiymethylmethacryiate, a cement which dentists used earlier as a filling material for tooth cavities. Sub¬ sequent examinations of patients with hip protheses cemented with this cement, however, have shown that the cement has not been strong enough and that it also may be broken down in the organism by the .enzyme catalase. Furhter ore, injuries to the surrounding bone have also been recorded, owing to the high curing temperature of the cement and to the cytotoxic liquid, the monomer, which is necessary for the curing process. The in¬ juries to the bone tissue are probably the cause of the not-infrequent infections which often occur in the bone tissue many months later. OMPI The object of the invention is to provide an improved cement which reduces or preferably eliminates the above detrimental effects. Thus r the invention relates to a bone cement which is characterized by comprising poiymethylmethacryiate, a filler material and a silver ion—releasing material. The new cement is substantially s ' tronger than the cement used previously, as may be seen from the table found below. The increased strength is obtained by the addition of filler in the form of particles of glass fiber or quartz having a particle size of • 4 — 8 microns. To reduce or eliminate the fateful complication which a post-operative infection is; a silver ion-releasing material is also added to the cement, preferably in the form of colloidal silver having an express germicidal and anti-bacterial effect. Colloidal silver solutions are combinations of insoluble forms, of silver such as iodides, chlorides, oxides, etc., with protective colloids, usually organic. The insoluble forms of silver are precipitated in the presence of the protective colloids (for example, gelatins) in such manner that the- particle size is very small and the particles do not settle but remain in suspension, and the result¬ ing Liquid has many of the advantages of an actual solution. These small particles of silver compounds act as reservoirs which release silver ions in a controlle manner and in small amounts? the actual concentration of silver ions will vary according to the nature of the silver compound present. As opposed to silver nitrate, for example, which has been used in medical applications, this colloidal silver has a so-called oligodynamic effect, in that silver ions are continuously released over a long period of time. The silver ions will pass through the membrane of the bacteria and into the DNA molecule, in this way preventing propagation of the bacteria. The ratio of the three components of the bone cement mixture can vary as may be seen from the table founl below, which shows the results of tests carried out by Det Norske Veritas. When pure poiymethylmethacryiate cement is cured at room temperature, the curing time is about 6 - 7 minutes and the curing temperature rises to about 90°C for a 10-mm thick layer. In the case of cement to which 25% glass fiber or quartz; has been added, the curing time is 12-14 minutes under similar ' conditions. For cement with 50% quartz- added, the curing- time is 20—25 minutes, and. the curing tempera¬ ture about 45°C. Since a curing time of as long as 20-25 minutes is impractical, the preferred bone cement comprises 65% poiymethylmethacryiate with an addition of 30% quartz particles and 5% colloidal silver. Qartz is preferred to glass fiber particles because the quartz particles are more irregular and thus pro¬ vide a larger surface area, than glass fiber particles. As mentioned above, the particle size for either quartz or glass fiber is between 4 and 8 microns. The larger surface area of the quartz particles may possibly help to make the cement less toxic by absorbing monomers, and one thereby also avoids the harmful high curing temperature. OMPI Bending tests were carried out at Det Norske Veritas on test rods made of poiymethylmethacryiate alone and on test rods made of the bone cement of the invention. The results were as follows; BENDING TEST Standard utilized ISO/R 178 Test Rod dimensions 4 x 10 x 80 mm Bending rate 2 mm/min Storage 16 x t Test Dimensions Bendingx Bending Bendto Sample mm module strength break N/mπT N/mm mm A 1 3.9 x 10.0 2408 58.0 4.3 A 2 4.0 x 10.0 2688 66.0 4.2 B 1 4.0 * x 10.0 5120 50.5 2.3 B 2 " 4.0 x 10.0 4941 47.7 2.2 D 1 4.0 x 10.0 4966 34.5 1.7 D 2 3.9 x 10.0 481S 35.0 1.7 Ξ 1 4.0 x 10.0 6144 28.2 1.1 E 2 4.0 x :.9.9 6723 27.8 1.0 jBending module measured as secant module with a deforma¬ tion equal to 10% of the thickness of the test sample. A » pure cement (poiymethylmethacryiate) . B = 70% by volume poiymethylmethacryiate, 25% by volume glass fiber, 5% colloidal silver D ~ * 70% by volume- poiymethylmethacryiate, 25% by volume quartz, 5% colloidal silver Ξ = 50% by volume poiymethylmethacryiate, 45% by volume quartz, 5% colloidal silver In these tests, the ' bone cement "Simplex" was used for comparison purposes; the three types of bone cement used today in hip surgery all consist of poiy¬ methylmethacr i e. The bone cement of the invention should preferably be used for the. cementing of protheses, especially protheses components in joint caps and bone marrow canals, and the results obtained up to now have been very satisfactory.

Claims: P a t e n t C a ' m s. 1. A bone cement containing poiymethylmethacryiate as a main component, characterized in that it also contains filler material in the form of particles of glass fiber or quartz having a particle size of 4 - 8 microns and a silver ion-releasing material in the form of colloidal silver (silver salt) . 2. A bone cement according to claim 1, characterized by comprising - 70 - 50% by volume poiymethylmethacryiate 25 - 45% by volume quartz- or glass fiber particles 5% by volume colloidal silver (silver salt) . 3. A bone cement according to claim 2, characterized by comprising 65%. by volume poiymethylmethacryiate 30% by volume quartz particles 5% by volume colloidal silver (silver salt) . 4. Utilization of the bone cement according to claims 1 — 3 for the cementing of protheses, especially protheses components in joint .caps and bone marrow canals. OMPI

Inventors: CHRISTIANSEN TOR
Applicants: CHRISTIANSEN KAREN S
Application year: 1981
Main classification: A61F1
IPC codes: A61K6, A61L27