Bone cement is a synthetic material used in orthopedic surgery to secure implants and stabilize bones. It provides immediate support and stable fixation, contributing to successful patient outcomes.
Understanding Bone Cement
Bone cement is primarily composed of polymethyl methacrylate (PMMA), a type of acrylic. It comes as a two-part system, consisting of a powder and a liquid mixed during surgery. The powder contains PMMA beads, an initiator for hardening, and a radio-opacifier (like barium sulfate) for X-ray visibility. The liquid component is mainly methyl methacrylate (MMA) monomer, along with an accelerator and a stabilizer to prevent premature hardening.
When the powder and liquid are combined, a chemical reaction called polymerization occurs. This transforms the mixture from a dough-like consistency into a rigid, solid material. This hardening process is exothermic, meaning it releases heat, with temperatures at the bone-cement interface potentially exceeding 70°C. Bone cement acts more as a filler or grout, creating a tight mechanical interlock between the implant and bone, rather than functioning as a glue that chemically bonds to the bone.
Primary Applications in Orthopedic Surgery
Bone cement finds widespread use in orthopedic surgery, particularly in joint replacement procedures. It is employed in total hip, knee, and shoulder replacements to securely anchor prosthetic components to the surrounding bone. This fixation provides immediate stability, allowing patients to bear weight and begin rehabilitation relatively soon after surgery.
Beyond joint replacements, bone cement is used to stabilize certain types of fractures, especially in patients with weakened bones due to conditions like osteoporosis. Procedures such as vertebroplasty and kyphoplasty involve injecting bone cement into fractured vertebrae in the spine to alleviate pain and provide stability. In some cases, bone cement also plays a role in orthopedic oncology, where it can be used to fill bone voids left after the removal of bone tumors, providing structural support to the affected area.
Considerations for Its Use
Bone cement is not a permanent material and can degrade or loosen over many years. Factors like mechanical stress and the body’s response can contribute to wear, potentially leading to the need for revision surgery to replace the implant.
During the setting process, the exothermic reaction can generate heat, with in-vivo temperatures typically ranging from 40°C to 47°C, though localized temperatures can be higher. This heat is generally dissipated into the surrounding tissue, blood, and the prosthesis. While uncommon, potential complications can include infection. Despite these considerations, bone cement remains a widely used and effective material, contributing significantly to the success of many orthopedic procedures.