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Difficulty: MediumOrthopedic Surgery

A 42-year-old man presents to the orthopedic clinic with a 2-month history of progressive left anterior hip and groin pain. The pain is exacerbated by climbing stairs and prolonged standing, and he frequently experiences aching at night that disrupts his sleep. His medical history is significant for severe persistent asthma, for which he has required multiple bursts of oral corticosteroids over the past 5 years. Vital signs are within normal limits. On physical examination, the patient walks with a noticeable antalgic gait. There is no erythema, warmth, or palpable effusion over the left hip. Passive internal rotation and abduction of the left hip elicit sharp pain, while straight leg raise is negative. Anteroposterior and frog-leg lateral radiographs of the left hip reveal normal joint space without evidence of fracture, subchondral sclerosis, or a crescent sign. Which of the following is the most appropriate next step in management?

  1. A
    Computed tomography of the left hip
  2. B
    Reassurance and continuation of weight bearing with oral analgesics
  3. C
    Ultrasound-guided diagnostic arthrocentesis
  4. Magnetic resonance imaging of the left hipAnswer
  5. E
    Systemic broad-spectrum antibiotic therapy

Answer

The most appropriate next step is Magnetic resonance imaging of the left hip to evaluate for early avascular necrosis.
The correct answer is magnetic resonance imaging (MRI) of the left hip. This patient's presentation of progressive groin pain exacerbated by weight-bearing, combined with a history of significant systemic corticosteroid exposure, is highly suspicious for avascular necrosis (AVN) of the femoral head. In the early stages of AVN (Ficat Stage I), plain radiographs frequently appear entirely normal. MRI is the most sensitive and specific noninvasive test for early osteonecrosis. It can detect early pathophysiologic changes such as bone marrow edema and the classic 'double-line sign' (representing a boundary of sclerosis and granulation tissue) well before any architectural collapse, subchondral cysts, or sclerosis are visible on plain films. Early diagnosis is critical because joint-preserving surgical interventions, such as core decompression, are most effective before subchondral collapse (the 'crescent sign') occurs.

Step-by-Step Solution

1
Identify the patient's major risk factors from the clinical history.
The patient has a history of chronic/recurrent oral corticosteroid use for severe asthma.
High-dose or chronic systemic corticosteroid use is one of the most common risk factors for non-traumatic avascular necrosis (osteonecrosis) of the femoral head.
2
Analyze the clinical presentation and physical examination findings.
Insidious onset of anterior hip/groin pain worsened by weight-bearing, with pain elicited on passive internal rotation and abduction.
These are the classic symptoms and focal signs of intra-articular hip pathology, specifically characteristic of early osteonecrosis.
3
Evaluate the results of the initial imaging described in the stem.
Anteroposterior and frog-leg lateral radiographs are entirely normal.
Plain films are the initial diagnostic test of choice but are notoriously insensitive for early-stage (Stage 1) avascular necrosis, often appearing completely normal before subchondral bone collapse occurs.
4
Determine the definitive next diagnostic step given the high clinical suspicion despite normal initial imaging.
Magnetic resonance imaging (MRI) of the hip.
MRI is the most sensitive and specific imaging modality for diagnosing avascular necrosis early in the disease process, allowing for joint-preserving interventions.

Key Concept

Early avascular necrosis (osteonecrosis) of the femoral head frequently presents with normal plain radiographs; MRI is the most sensitive diagnostic modality and is the definitive next step when clinical suspicion remains high.
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Orthopedic Surgery

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