From the Guidelines
The diagnostic workup for avascular necrosis (AVN) of the hip should begin with plain radiographs, followed by MRI without IV contrast as the next imaging study, as it is the gold standard diagnostic tool with nearly 100% sensitivity. The initial evaluation should include a thorough clinical history and physical examination, focusing on risk factors such as corticosteroid use, alcohol consumption, trauma, and underlying conditions like sickle cell disease or lupus 1.
Key Components of the Diagnostic Workup
- A complete blood count, comprehensive metabolic panel, coagulation studies, and lipid profile should be ordered to evaluate for underlying causes
- Additional tests may include erythrocyte sedimentation rate and C-reactive protein to rule out inflammatory conditions, and specific tests based on suspected etiologies such as hemoglobin electrophoresis for sickle cell disease or antiphospholipid antibodies for hypercoagulable states
- Bone scans can be useful but are less sensitive than MRI
- CT scans may help assess bone architecture and collapse in advanced cases, and are superior to MRI in showing the location and extent of articular collapse 1
Importance of Early Diagnosis
Early diagnosis is crucial as treatment outcomes are significantly better when AVN is identified before femoral head collapse occurs. MRI without IV contrast can predict necrotic volume well, whereas CT without IV contrast can show the location and extent of articular collapse well 1. In rare situations where diagnosis remains unclear despite imaging, bone biopsy may be considered, though this is uncommon with modern imaging techniques.
Imaging Recommendations
- Variant 1: Radiography is usually appropriate for the initial imaging of clinically suspected osteonecrosis
- Variant 2: MRI without IV contrast is usually appropriate as the next imaging study for clinically suspected osteonecrosis following normal or suspicious radiographs
- Variant 3: In the setting of known osteonecrosis with articular collapse by radiographs, MRI without IV contrast or CT without IV contrast is usually appropriate as the next imaging study for preoperative planning 1
From the Research
Diagnostic Approach
To diagnose avascular necrosis of the hip, the following steps can be taken:
- Imaging studies such as MRI and bone scintigraphy can be used to visualize necrosis indirectly in the early stages 2
- In later stages, plain X-rays and CT scans can be used to demonstrate calcification, new bone formation, and microfractures 2
- The ARCO-classification of the Association for the Research of Osseous Circulation is essential in diagnosis, with stage 0 only being found histologically, and reversible early stage 1 showing MR signal changes 3
- Pathologic examination is necessary for confirming the diagnosis of avascular necrosis, especially among older patients without known risk factors 4
Imaging Modalities
The following imaging modalities can be used to diagnose avascular necrosis of the hip:
- MRI: best imaging method for visualizing necrosis indirectly in the early stages 2
- Bone scintigraphy: can be used to visualize necrosis indirectly in the early stages, but to a lesser extent than MRI 2
- Plain X-rays: can be used to demonstrate calcification, new bone formation, and microfractures in later stages 2
- CT scans: can be used to demonstrate calcification, new bone formation, and microfractures in later stages 2
Staging and Treatment
The staging and treatment of avascular necrosis of the hip can be summarized as follows:
- Stage 1: reversible early stage, treated with core decompression, physiotherapy, and bisphosphonates 3
- Stage 2: irreversible early stage, treated with stem cell therapy, proximal femoral osteotomies, and (non)vascularised bone transplantation 3
- Stage 3: subchondral fracture, treated with proximal femoral osteotomies and (non)vascularised bone transplantation 3
- Stage 4: secondary arthritis of the hip, treated with resurfacing or short stem hip arthroplasty, or conventional THA 3