On serial radiographs of an uncemented proximally porous-coated femoral stem at 2 years, bony bridges are seen spanning from the cortex onto the porous coating at Gruen zones 2 and 6, with no radiolucent lines and no subsidence. This radiographic appearance indicates:
- A Impending failure requiring elective revision
- B Stable osseous ingrowth fixation, consistent with a high Engh fixation score ✓
- C Reactive fibrous membrane compatible only with unstable micromotion
- D Heterotopic ossification unrelated to implant stability
Correct answer: B. Stable osseous ingrowth fixation, consistent with a high Engh fixation score
Explanation
Spot welds, meaning bony bridging from cortex to porous coating, are the radiographic hallmark of biologic fixation by osseous integration and form part of the Engh scoring system for uncemented stems. Their presence at the porous interface with absence of lucent lines and subsidence predicts durable fixation. Pedestal formation and calcar rounding, by contrast, correlate with instability, which distinguishes option B from option C.
Reference: Campbell's Operative Orthopaedics, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.