A femoral stem chosen for primary cementless total hip replacement achieves 'press-fit' fixation primarily through which mechanism in the early post-operative period?
- A Osseointegration with hydroxyapatite coating
- B Mechanical interference fit between undersized canal and oversized implant generating hoop stresses ✓
- C Fibrous tissue ingrowth into porous coating
- D Bone ingrowth within 6 weeks of implantation
Correct answer: B. Mechanical interference fit between undersized canal and oversized implant generating hoop stresses
Explanation
Press-fit fixation relies on an undersized reamed canal receiving an oversized cementless stem, creating radial compressive hoop stresses at the bone–implant interface — the initial 'primary stability'. This mechanical interlock must be maintained without micromotion >150 µm to allow osseointegration (biological secondary stability) over subsequent weeks. Hydroxyapatite coating enhances later biological bonding but is not the immediate fixation mechanism.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.