Avascular Necrosis Femoral Head MCQ — NEET PG Practice Question | NEETPGAI
Avascular Necrosis Femoral Head
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bone Orthopedics
A 42-year-old man presents with a 6-month history of progressive left groin pain and restricted internal rotation of the hip. He has been on high-dose prednisolone (25 mg daily) for 3 months for systemic lupus erythematosus. MRI of the left hip is performed. The structure marked **A** in the diagram shows a pathognomonic finding on T2-weighted imaging. What is this radiological sign, and what does it indicate about the underlying pathophysiology of this patient's condition?
A. Double-line sign indicating the interface between viable and necrotic bone, reflecting disruption of subchondral blood supply leading to osteonecrosis
B. High-signal intensity on T2-weighted images indicating joint effusion secondary to osteoarthritis
C. Band-like low-signal intensity on T1-weighted images indicating granulation tissue at the margin of necrotic bone
D. Crescent sign indicating subchondral fracture with early mechanical collapse of the femoral head
Explanation
Why option 1 is correct
The double-line sign on T2-weighted MRI is the pathognomonic finding in avascular necrosis of the femoral head. It consists of a peripheral low-signal serpiginous line (representing reactive sclerosis at the interface between viable and necrotic bone) surrounding an inner high-signal line (representing granulation tissue). This sign directly reflects the disruption of subchondral blood supply, predominantly from the medial femoral circumflex artery, leading to bone death. In this patient, high-dose corticosteroids (prednisolone 25 mg daily for SLE) are a well-established risk factor for AVN, accounting for 20–30% of cases. The double-line sign is highly specific for AVN and appears on MRI before radiographic changes become evident, making MRI the gold standard for diagnosis (sensitivity and specificity both 99%). [Campbell's Operative Orthopaedics 14e — Osteonecrosis of the Hip]
Why each distractor is wrong
Option 2 (Crescent sign): The crescent sign represents a subchondral lucency (fracture line) seen on plain radiographs and indicates stage III disease (pre-collapse or early collapse). It is a radiographic finding, not an MRI finding, and appears later in the disease course than the double-line sign. The crescent sign does not represent the interface between viable and necrotic bone as specifically as the double-line sign does.
Option 3 (Band-like low-signal on T1): While a band-like low-signal line on T1-weighted images does outline the necrotic segment and is indeed an MRI finding in AVN, the question specifically asks about the structure marked A on T2-weighted imaging. The double-line sign is the characteristic T2 finding, not the T1 band. This option confuses T1 and T2 sequences.
Option 4 (High-signal on T2 indicating effusion): Joint effusion is a secondary finding that may occur in AVN but is not pathognomonic and is more commonly associated with osteoarthritis. Effusion does not indicate the specific interface between viable and necrotic bone. The high-signal inner line of the double-line sign represents granulation tissue, not simple effusion.
High-YieldNEET PG
The double-line sign on T2-weighted MRI is the gold-standard pathognomonic finding for AVN of the femoral head, appearing before any radiographic changes; it reflects the viable–necrotic bone interface and indicates disruption of subchondral blood supply.
[Campbell's Operative Orthopaedics 14e — Osteonecrosis of the Hip]
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