A 65-year-old man requires total hip replacement for osteoarthritis. For uncemented (cementless) femoral components, the PRIMARY mechanism of biological fixation is:

• A Acrylic cement polymerisation bonding to the endosteal surface
• B Press-fit cortical contact generating compressive stress at the diaphysis
• C Bone ingrowth into a porous or hydroxyapatite-coated surface ✓
• D Fibrous tissue ingrowth providing flexible anchorage

Explanation

Uncemented femoral stems achieve long-term fixation through osseointegration — direct bone ingrowth into a porous metal surface (sintered beads, fibre mesh, or 3D-printed trabecular titanium) or hydroxyapatite-coated surfaces that promote osteoblast attachment. The microstructure requires pore size of 100–400 μm for optimal ingrowth. Initial stability is by press-fit (taper-lock effect), which prevents micromotion exceeding 150 μm (the threshold beyond which fibrous tissue rather than bone forms). Cemented fixation uses PMMA acrylic cement as a grout — not adhesive — to fill the interface gap. Cementless fixation is preferred in younger patients for longer implant survivorship.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.