Which statement most accurately describes the fixation principles for cemented versus cementless femoral stems in hip arthroplasty?

• A. Cementless uses PMMA cement for immediate fixation.
• B. Cemented uses bone cement for fixation; cementless uses screws.
• C. Cemented relies on press-fit fixation with a porous coating.
• D. Cemented uses PMMA cement for immediate fixation; cementless relies on press-fit with a porous coating for biological ingrowth; cementless requires good bone quality and stable initial fixation.

Answer: (D)

The key idea is how each femoral stem is fixed to the bone. Cemented stems rely on polymethylmethacrylate (PMMA) bone cement to fill gaps and interlock with the bone, giving immediate, stable fixation as the cement cures. This creates a cement mantle that anchors the stem right away, which can be especially advantageous in bones that are osteoporotic or when predictable early stability is desired.

Cementless stems, in contrast, depend on a tight press-fit within a roughened or porous-coated surface. The initial stability comes from the stem wedging into the canal, and over time bone grows into the porous coating to achieve biological fixation (osseointegration). For this to work well, good bone quality and a solid initial fixation are essential to minimize micromotion while healing.

So the statement aligns with the reality that cemented uses PMMA cement for immediate fixation, while cementless uses a press-fit with a porous coating to encourage biological ingrowth, with cementless requiring good bone quality and stable initial fixation. The other ideas—such as cemented relying on press-fit or cementless using screws for fixation or relying on cement-like materials—do not reflect the standard fixation principles.