Which radiographic sign indicates loosening around a hip prosthesis?

• A. Progressive lucent lines at the bone-implant interface
• B. Subsidence or migration of the cup or stem
• C. Lucencies in multiple zones
• D. Changes in cup or stem position

Answer: (B)

Movement of the implant on serial radiographs is the clearest signal of loosening. When the cup or stem shows subsidence (sinking further into the bone) or migrates (shifts position over time), it means the fixation between the implant and bone has failed and micromotion is occurring at the bone–implant interface. That positional change reflects actual mechanical instability, which is the hallmark of loosening.

Lucent lines around the component or lucencies in multiple zones can accompany loosening, but they aren’t as definitive on their own because they can arise from other processes like osteolysis or cement mantle issues and may be static for some time. Noting a change in the component’s position, however, provides a direct indication that fixation has been compromised.