Role of Nuclear Medicine in Prosthetic Joint Infection
A painful hip or knee replacement asks one question: aseptic or septic loosening? The answer decides between one-stage revision and debridement with prolonged antibiotics and a second operation. Aspiration can be dry or equivocal, CRP and ESR non-specific, radiographs unhelpful. Nuclear medicine is asked precisely when the answer is not otherwise available — and it delivers only if the right study is chosen and the pattern read correctly.
When to image
- Persistent pain or a loose prosthesis when infection remains uncertain after clinical assessment, blood tests and aspiration.
- Distinguishing infection from aseptic loosening before revision surgery.
- Localising infection and assessing its extent around the prosthesis, especially when other imaging is inconclusive.
With what to image
- Three-phase bone scan screens; leucocyte + marrow decides; FDG PET/CT is the option.
- SPECT/CT throughout, to place activity at the bone–prosthesis interface or in soft tissue.
Patterns of uptake
| Study | Pattern | Interpretation |
|---|---|---|
| Three-phase bone scan | Normal | Largely excludes infection and loosening |
| Focal delayed uptake at stem tip or along the shaft | Aseptic loosening | |
| Hyperaemia on flow and blood pool with diffuse periprosthetic uptake | Suggests infection | |
| Leucocyte + marrow | Congruent — white cells match marrow | Displaced or expanded marrow; not infection |
| Incongruent — white cells without matching marrow | Infection | |
| FDG PET/CT | Bone–prosthesis interface, soft tissue or sinus tract | Favours infection |
| Synovium or head–neck junction only | Non-specific |
Infection timing follows thirds — about a third early (<3 months), a third delayed (3–12 months) from surgical seeding; late (>1 year) is usually haematogenous.
Why leucocyte + marrow decides
- Both tracers accumulate in marrow; infection recruits leucocytes while suppressing colloid uptake — hence the incongruence.
- 99mTc-HMPAO or 111In-oxine leucocytes, paired with 99mTc-sulfur colloid, read in the same planes.
- Sensitivity ≈100%, specificity ≈91%, accuracy ≈95% in failed replacements.
- Pooled by site: hip 69% / 96%, knee 80% / 93%.
- Allow time after surgery — early postoperative leucocyte uptake is physiological.
Reporting the white-cell study without its marrow scan is the commonest error in this subject.
FDG PET/CT, and its limits
- Convenient: one visit, no cell labelling, whole-body coverage.
- Pooled sensitivity and specificity both ≈86% in lower-limb prostheses.
- Head to head against leucocyte/marrow it reached only ≈71% accuracy on any criteria.
- Particle-debris reaction and aseptic loosening stay FDG-avid for years — the whole specificity problem.
- No standardised interpretation criteria, no usable SUV cut-off.
- 68Ga-citrate PET was more specific than FDG (88% vs 38%) but remains investigational.
Fuller version, with performance and pitfalls: Prosthetic joint infection.
- Bone scan excludes; leucocyte/marrow decides; FDG is the option, not the reference.
- Infection is incongruent uptake — white cells where marrow is not.
- Never report a white-cell study without its marrow scan.
- Signore A, Sconfienza LM, Borens O, et al. Consensus document for the diagnosis of prosthetic joint infections: a joint paper by the EANM, EBJIS, and ESR (with ESCMID endorsement). Eur J Nucl Med Mol Imaging. 2019;46(4):971-88.
- Signore A, Jamar F, Israel O, et al. Clinical indications, image acquisition and data interpretation for white blood cells and anti-granulocyte monoclonal antibody scintigraphy: an EANM procedural guideline. Eur J Nucl Med Mol Imaging. 2018;45(10):1816-31.
- Gheysens O, Jamar F, Glaudemans AWJM, et al. Summary: EANM/SNMMI joint guideline/procedure standard for [18F]FDG hybrid PET use in infection and inflammation in adults, version 2.0. J Nucl Med. 2025;66(3):480-1.