From the Guidelines
Ultrasound cannot be relied upon to rule out avascular necrosis (AVN) due to its limitations in visualizing bone structures and early changes of AVN. When considering the diagnosis of AVN, it is crucial to prioritize imaging modalities that offer high sensitivity and specificity for detecting early bone marrow edema, subchondral fractures, and changes in bone vascularity. According to the most recent guidelines, including the American College of Radiology (ACR) Appropriateness Criteria for osteonecrosis updated in 2022 1, MRI without IV contrast is the preferred imaging modality for diagnosing AVN due to its superior sensitivity and specificity, nearing 100% 1. The use of MRI allows for the characterization of osteonecrosis, including location, volume, and the presence of associated bone marrow edema or joint effusion, which is critical for guiding treatment decisions. While CT scans can provide valuable information on the location and extent of articular collapse, making them useful in surgical planning 1, they lack the sensitivity of MRI for early detection of AVN. Therefore, if AVN is suspected based on clinical presentation and risk factors, an MRI without IV contrast should be performed to definitively diagnose or rule out AVN, rather than relying on ultrasound or other less sensitive imaging modalities. Key points to consider in the diagnosis and management of AVN include:
- Early diagnosis is crucial for joint-preserving interventions
- MRI is the gold standard for diagnosing AVN
- Ultrasound and X-rays have limitations in detecting early AVN changes
- CT scans are useful in surgical planning but not for early detection of AVN.
From the Research
Diagnostic Methods for Avascular Necrosis
- The diagnosis of avascular necrosis (AVN) is typically made using imaging methods such as radiographs and magnetic resonance imaging (MRI) 2.
- MRI is considered the most important imaging method for early detection and staging of AVN, as well as for assessing lesion size and location before collapse of the articular surface occurs 2.
- Other imaging methods, such as scintigraphy, CT, and PET, have been used in the past, but are not currently considered the most reliable methods for diagnosing AVN 2.
Limitations of Diagnostic Methods
- While MRI is a highly sensitive and specific imaging method for diagnosing AVN, it may not always be able to detect early stages of the disease 2.
- Radiographs may not show any abnormalities in the early stages of AVN, and may only become apparent after the disease has progressed 3, 2.
- Ultrasound is not typically used as a diagnostic method for AVN, and its accuracy and reliability for this purpose are not well established 3, 4, 2, 5, 6.