Composition
Bone cements are provided as two-component materials. Bone cements consist of a powder (i.e., pre-polymerized PMMA and or PMMA or MMA co-polymer beads and or amorphous powder, radio-opacifer, initiator) and a liquid (MMA monomer, stabilizer, inhibitor). The two components are mixed and a free radical polymerization occurs of the monomer when the initiator is mixed with the accelerator. The bone cement viscosity changes over time from a runny liquid into a dough like state that can be safely applied and then finally hardens into solid hardened material. The set time can be tailored to help the physician safely apply the bone cement into the bone bed to either anchor metal or plastic prosthetic device to bone or used alone in the spine to treat osteoporotic compression fractures.
During the exothermic free-radical polymerization process of the cement heats up. This polymerization heat reaches temperatures of around 82-86°C in the body. This temperature is superior to the critical level for the protein denaturation in the body. The cause of the low polymerization temperature in the body is the relatively thin cement coating, which should not exceed 5 mm, and the temperature dissipation via the large prosthesis surface and the flow of blood.
The individual components of the bone cement are also known in the area of dental filler materials. Acrylate-based plastics are also used in these applications. While the individual components are not always perfectly safe as pharmaceutical additives and active substances per se, as bone cement the individual substances are either converted or fully enclosed in the cement matrix during the polymerization phase from the increase in viscosity to curing. From current knowledge, cured bone cement can now be classified as safe, as originally demonstrated during the early studies on compatibility with the body conducted in the 1950s.
More recently bone cement has been use in the spine in either vertebroplasty or kyphoplasty procedures.
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