What are the implications of a bone scan showing stress reactive changes after knee arthroplasty (knee replacement)?

From the Guidelines

Stress reactive changes on a bone scan after knee arthroplasty indicate a potential problem with the prosthetic joint, but the findings are not specific and may not necessarily signify infection.

Implications of Stress Reactive Changes

• The presence of stress reactive changes on a bone scan may suggest loosening of the prosthetic component, particularly if the changes are focal and localized to the area around the prosthesis 1.
• However, these changes can also be seen in asymptomatic patients, especially in the first few years after surgery, and may not necessarily indicate a problem with the prosthesis 1.
• The sensitivity and specificity of bone scans for detecting loosening or infection vary, with some studies reporting high sensitivity but low specificity 1.

Diagnostic Approach

• A normal bone scan is most helpful, as it has a high negative predictive value and suggests that loosening or infection is unlikely 1.
• If the bone scan is abnormal, further evaluation with other imaging modalities, such as CT or MRI, may be necessary to determine the cause of the abnormal findings 1.
• In some cases, a labeled leukocyte scan or a bone marrow scan may be used to differentiate between infection and aseptic loosening 1.

Clinical Correlation

• The clinical correlation of stress reactive changes on a bone scan is crucial, as the findings must be interpreted in the context of the patient's symptoms and other diagnostic tests 1.
• Patients with stress reactive changes on a bone scan should be closely monitored for signs of loosening or infection, and further evaluation and treatment should be guided by the patient's clinical presentation and diagnostic findings 1.

From the Research

Implications of Stress Reactive Changes on Bone Scan after Knee Arthroplasty

• Stress reactive changes on a bone scan after knee arthroplasty may indicate a number of potential issues, including loosening of the prosthesis, infection, or mechanical stresses on the bone 2, 3, 4, 5, 6
• These changes can be difficult to interpret, as increased uptake on a bone scan can be seen in both asymptomatic and symptomatic patients, and can persist for long periods after surgery 3, 4
• Sequential bone scans may be useful in diagnosing loosening or other complications, as they can show changes in uptake over time 3
• However, a single bone scan is not sufficient to diagnose loosening or infection, and should be used in conjunction with clinical evaluation, serological investigation, and other diagnostic imaging modalities 5, 6
• The optimal imaging strategy for evaluating complications after knee arthroplasty is still a matter of debate, and more research is needed to determine the best approach 2

Diagnostic Accuracy of Bone Scans

• The diagnostic accuracy of bone scans in detecting loosening or infection after knee arthroplasty is limited, with a positive predictive value of 2.53% and a negative predictive value of 100% in one study 5
• The sensitivity and specificity of bone scans can vary depending on the criteria used to interpret the results, and reciprocal changes in sensitivity and specificity can be seen with increasingly stringent criteria 6
• Bone scans may be useful in certain situations, such as when abnormal serology is present but joint aspirations are inconclusive, but should be used judiciously and in conjunction with other diagnostic modalities 5