Which fixation method for hip stems relies on bone ingrowth via a porous surface rather than bone cement?

• A. Cemented
• B. Cementless
• C. Hybrid
• D. Resurfaced

Answer: (B)

Stability of a hip stem can come from two distinct approaches: cemented fixation, which uses bone cement to glue the stem in place, and cementless fixation, which relies on bone coming to grow into a porous coating on the stem for long-term fixation.

In the cementless approach, the stem has a porous surface (often with hydroxyapatite coating). It is inserted with a snug press-fit, and over time the surrounding bone grows into the pores, creating a strong biological bond without any cement. This process of bone ingrowth (osseointegration) is what secures the implant in place as the patient heals and remodels.

Cemented fixation, by contrast, uses polymethyl methacrylate cement to fill gaps between the stem and bone for immediate anchorage, with fixation dependent on the cement mantle. The hybrid option combines both methods in different components, and resurfacing refers to a procedure that caps the femoral head rather than inserting a long stem.

So, the method that relies on bone ingrowth via a porous surface rather than bone cement is cementless fixation.