American Board of Surgical Assistants (ABSA) Orthopedic Practice Test

Which substance is used in bone cement to adhere to the prosthesis but not to the bone?

1. Methyl methacrylate

2. Calcium sulfate

3. Sodium phosphate

4. Polyethylene glycol

The correct answer is: Methyl methacrylate

Methyl methacrylate is known for its role as a bone cement in orthopedic procedures, particularly in the fixation of prosthetic implants. It is a type of acrylic cement that, when mixed and polymerized, forms a solid mass that binds well to the surfaces of the prosthesis. This quality makes it an excellent adhesive for securing prosthetic components in place. One of the critical features of methyl methacrylate is its tendency not to bond directly to bone tissue. Instead, it provides a mechanical interlock between the prosthesis and the surrounding bone, allowing for stability while minimizing the risk of stress shielding and bone resorption. This characteristic is vital in ensuring that while the prosthesis is secure, it does not impede future bone regrowth or healing processes. In contrast, other substances listed in the options do not serve the same purpose as methyl methacrylate in bone cement applications. For instance, calcium sulfate is often used for bone grafting and can promote bone healing but does not function as a cement for prosthetic adhesion. Sodium phosphate and polyethylene glycol have different applications in medicine and do not have the adhesive properties required for prosthetic interface in orthopedic surgery.