The human body includes a large structural complement including a bone structure. This bone structure, however, may become damaged or need repair for various reasons. Generally, implants may be used to replace or repair damaged portions of the bone structure. One means of fixing these replacements to the bone structure is a bone cement or bone replacement. Moreover, the bone cement itself may be used as a prosthetic material.
In one example, a bone replacement may be used to reconstruct a portion of the bone structure. For example, in a cranio-facial application, the bone replacement may be molded to reconstruct a portion of the or anatomy that has been damaged due to disease, injury, congenital defect, or surgery. Therefore, the structure supporting the muscle and skin portions of the human anatomy can be replaced using the bone replacement material. Such bone replacement materials may also be used for more orthopedic applications where the bone replacement must support a load or be load bearing portion of the anatomy.
Most moldable bone replacement materials, often referred to as bone cement, include or are formed of an acrylic. In particular, the polymer of the bone cement includes a polymethylmethylacrylate (PMMA). Most often, finely divided portions of this PMMA is provided and mixed with a liquid monomer or polymerizable material such as acrylicesters. A polymerizing initiator is then added or released into the mixture and the mixture begins to polymerize and harden. For a short period of time, during the polymerization, the entire mixture is doughy or workable so that a physician may form the material into the shape and size desired for implantation and use.
The polymerization of the liquid is an exothermic reaction. Therefore, the bone cement increases in temperature or radiates heat during the polymerization process. Generally, the temperature of bone cement may increase to such a degree as to cause tissue necrosis. The necrosis can occur if the bone cement is implanted before the bone cement cools, or if the area is not cooled, such as by irrigation. This can decrease the efficiency of forming the bone cement in situ.
It has been proposed to produce an acrylic bone cement that has a large majority of large particles to form a highly porous final material. This porous bone cement allows for a large majority of bone in-growth into the porous structure. The porous bone cements require that the bone cement be formed in such a way to produce the porous product to allow bone in-growth.
Nevertheless, it is often desired to produce a non-porous bone cement while including reduced exothermic energy. That being, a bone cement that has a high strength due to the lack of pores, while still including a cool workable period so that it may be molded in situ to achieve those advantages.