What are the initial investigations for a specific location in the body?

Initial Investigations for Osteonecrosis

Radiography of the affected area should be the first-line imaging study for clinically suspected osteonecrosis, followed by MRI if radiographs are negative or equivocal but clinical suspicion remains high. 1

Primary Imaging Approach

Plain Radiography (First-Line)

• Obtain anteroposterior, lateral (frog-leg lateral for hip), and oblique views of the suspected area to exclude subchondral collapse in epiphyseal osteonecrosis 1
• Radiographs serve dual purposes: detecting late-stage osteonecrosis and excluding alternative diagnoses such as fracture, primary arthritis, or tumor 1
• Critical limitation: Radiographs have low sensitivity for early-stage osteonecrosis, as changes may not be visible until significant bone damage has occurred 1
• In late-stage disease, radiography will demonstrate findings of secondary osteoarthritis 1

MRI Without Contrast (Second-Line)

• MRI is the most sensitive modality for detecting early osteonecrosis and should be performed when radiographs are negative but clinical suspicion persists 1
• MRI allows quantification of the size and location of the necrotic lesion, which is essential for staging and surgical planning 1
• MRI without IV contrast is typically sufficient; contrast-enhanced MRI has limited additional value for initial diagnosis 1

Clinical Assessment Components

History and Physical Examination

• Document risk factors: corticosteroid use, alcohol consumption, trauma, coagulopathy, sickle cell disease, organ transplantation, chemotherapy, radiation exposure, and diving history 1
• Age >40 years and body mass index >24 kg/m² are associated with worse prognosis 1
• Assess for pain characteristics, particularly night pain or pain at rest that distinguishes osteonecrosis from mechanical joint problems 1
• Examine for joint range of motion limitations and focal tenderness over the affected bone 1

Laboratory Studies

• No specific laboratory tests diagnose osteonecrosis, but baseline studies help identify underlying causes and assess surgical candidacy 1
• Consider complete blood count, comprehensive metabolic panel, coagulation studies, and inflammatory markers 1
• For suspected secondary causes, obtain lipid panel (for fat embolism risk), hemoglobin electrophoresis (sickle cell disease), and thrombophilia workup if indicated 1

Imaging Modalities to Avoid Initially

Bone Scintigraphy

• Bone scans have been replaced by MRI due to poor spatial resolution, low specificity, and inability to quantify lesion size 1
• Single-photon emission CT (SPECT) showed improved accuracy in small studies of post-transplant patients but is not routinely recommended 1

CT Scanning

• CT has limited evidence supporting its use as an initial imaging study for suspected osteonecrosis 1
• CT may be useful for preoperative planning once diagnosis is established, particularly for assessing cortical bone integrity 1

PET/CT

• Early limited data for PET/CT have not demonstrated utility in diagnosing early osteonecrosis 1
• More studies are needed to determine if PET/CT may be useful for detecting multifocal osteonecrosis 1

Anatomic Coverage

The investigation approach applies to the following body regions: chest, pelvis, hip, femur, knee, tibia/fibula, ankle, foot, shoulder, humerus, elbow, forearm, wrist, and hand, including specific sites like the lunate and scaphoid 1

Critical Pitfalls to Avoid

• Do not rely solely on negative radiographs to exclude osteonecrosis in patients with persistent symptoms and risk factors; proceed to MRI 1
• Do not delay imaging in high-risk patients (those on chronic corticosteroids, post-transplant, or with known coagulopathy) even with mild symptoms 1
• Avoid ordering bone scans as they have been superseded by MRI and provide inferior diagnostic information 1
• Do not assume bilateral disease is absent; consider imaging the contralateral joint in high-risk patients as osteonecrosis is frequently bilateral 1

Staging Considerations

Once osteonecrosis is confirmed, staging systems (Ficat and Arlet, University of Pennsylvania/Steinberg, ARCO, or Japanese Orthopedic Association) guide treatment decisions, with early diagnosis critical for considering core decompression or other joint-preserving interventions before articular collapse occurs 1