ABFAS Boards – Rearfoot and Forefoot Practice Test

Tc-99m bone imaging uses diphosphonate radiotracers that attach to hydroxyapatite crystals in bone. These tracers have a strong affinity for exposed hydroxyapatite surfaces, so they localize where bone remodeling and turnover are high. Areas of active osteoblastic activity—such as healing fractures, metastases, osteomyelitis, or inflammatory arthritis—accumulate more tracer and appear as hot spots on the scan. The uptake mechanism is tied to binding to hydroxyapatite, not to white blood cells, plasma proteins, or inflammatory cytokines, which is why those processes don’t explain the imaging pattern.