The Bone scintigraphy is an imaging method that is based on the principle that radioactive markers (usually technetium-99m-labeled phosphates) are stored at sites with increased bone activity. Through this accumulation, inflammations, infections, bone remodeling processes or loosening, e.g., of hip prostheses (hip-TEP) or knee prostheses (knee-TEP) can be visualized.

Especially in the diagnosis of a prosthesis loosening bone scintigraphy can help – however there is an important temporal aspect:

1. Increased activity immediately after implantation

In the first 12 to 18 months after a prosthesis implantation, bone scintigraphy always a increased accumulation around the implant.
Why?

• After the prosthesis is implanted, the bone reacts to the trauma caused by the surgery.
• Repair processes are taking place: bone remodeling (so-called "bone remodeling") and reaction to the new mechanical stress.
• In addition, micro-movements occur between bone and prosthesis until the final healing is completed.

➡️ Result: The skeletal scintigraphy is almost always positive during this period – even if no loosening is present.

That means:
👉 An increased scintigraphy activity in the first 1 to 1.5 years is not specific for a prosthetic loosening.

2. Risk of misinterpretation (false-positive findings)

If scintigraphy were performed during this period, there would be a high risk of:

• False-positive findings: One interprets normal healing or remodeling processes mistakenly as loosening.
• Unnecessary procedures: Based on an erroneous diagnosis, unnecessary revision procedures could be performed.

Example:
A patient has 10 months after hip-TEP implantation mild pain. A scintigraphy shows an accumulation. Without consideration of the healing course a loosening could mistakenly be assumed – however the finding for this phase is completely normal.

3. Time point after 1.5 years - why this period?

After about 15–18 months:

• Has the remodeling activity largely normalized.
• The bone-implant interaction stabilizes.
• If an increased accumulation remains, this is now actually indicating pathological processes (e.g., loosening, infection).

➡️ From this point on the bone scintigraphy has a significantly higher specificity and diagnostic value for:

• Loosening (aseptic or septic)
• Implant loosening due to infection or mechanical instability
• Bone damage or osteolysis

In short:
👉 Only after about 1.5 years can a scintigraphy reliably distinguish a true loosening from normal remodeling processes.

4. Current scientific consensus

Studies and guidelines (e.g. from the German Society for Orthopaedics and Trauma Surgery, DGOU) therefore recommend:

• No skeletal scintigraphy for loosening diagnosis within the first 12-18 months after primary implantation of a hip TEP or a knee TEP.
• Instead, during this period: Clinical examination, conventional X-ray diagnostics, possibly puncture if infection is suspected.

5. Alternative diagnostics in the first 18 months

If a loosening of a hip prosthesis or knee prosthesis is suspected early (e.g. with persistent pain, fever, functional limitations), the following should be used preferentially:

• Conventional Röntgen (direct signs such as Lösen der Prothese or osteolysis)
• CT (Fine diagnostics, implant loosening test)
• Aspiration (to differentiate between septic and aseptic loosening)
• Laboratory values (CRP, white blood cell count)

Only if these methods remain unclear and the complaints persist, should scintigraphy be considered after approximately 18 months.

Conclusion: Bone scintigraphy in case of suspected prosthetic loosening is usually only useful after 1.5 years!

The skeletal scintigraphy is a valuable diagnostic tool when suspicion of a loosening of a hip or knee prosthesis exists. However, the correct timing must be considered:
In the first 12 to 18 months after implantation the findings are often distorted by normal healing and remodeling processes, making interpretation difficult and prone to error.

Only from about 1.5 years after the operation the bone scintigraphy provides reliable indications of an actual loosening or a possible infection.
Therefore, it is essential to promptly resort to conventional diagnostic methods such as clinical examination, radiographic imaging, and, if necessary, joint aspiration.

A targeted, temporally sensible scintigraphy can then contribute decisively to diagnosing a prosthesis loosening safely and setting the course for a successful therapy.

Note:
 Before 1.5 years → Scintigraphy hardly useful due to normal healing.
 After 1.5 years → Reliable tool when loosening is suspected.