Hip Imaging Radiograph and MRI

Courtesy: Dr T Vail, Ashok Shyam TV, Ortho

Why Hip Imaging Matters

• Imaging plays a critical role in:

  • Understanding hip biomechanics

  • Planning hip reconstruction procedures

  • Identifying intra-articular pathology

• Direct visualization (e.g., arthroscopy) highlights how challenging it can be to detect subtle pathology using imaging alone.

• Each modality (plain radiographs, MRI) has specific strengths and limitations.

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1. Imaging for Assessment of Hip Morphology

Hip morphology refers to:

• Femoral–pelvic relationship

• Leg length

• Femoral offset

• Acetabular coverage

Radiographic Evaluation Using Plain X-Rays

Several established radiographic indices guide hip analysis and preoperative templating.

Key Measurements on AP Pelvis Radiograph

• Acetabular Index (Index of Elevation)

  • Assesses acetabular inclination and coverage.

  • Measured from a horizontal reference line to the lateral acetabular edge.

• Extrusion Index

  • Ratio of uncovered femoral head to total femoral head diameter.

  • Quantifies degree of acetabular coverage.

• Center–Edge (CE) Angle

  • Evaluates superolateral femoral head coverage.

• Femoral Neck–Shaft Angle

  • Determines varus or valgus alignment.

• Femoral Neck Offset

  • Assessed best on frog-leg lateral view.

  • Important in:

    • Impingement evaluation

    • Hip resurfacing

    • Component positioning

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Reliable Radiographic Landmarks

• Teardrop Landmark

  • Most dependable reference point.

  • Compensates for pelvic rotation and tilt.

  • Used to assess:

    • Lateral subluxation

    • Superior migration

• Shenton’s Line

  • Helpful in assessing alignment, especially in developmental dysplasia of the hip.

  • Disruption suggests displacement.

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2. Imaging in Femoroacetabular Impingement (FAI)

Crossover Sign (AP Pelvis View)

• Occurs when:

  • The anterior acetabular rim crosses over the posterior rim.

• Suggests:

  • Acetabular retroversion

  • Potential anterior impingement

• Pelvic positioning and lumbar lordosis influence interpretation.

• Important for surgical planning.

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3. Imaging of Cartilage and Labral Pathology

Limitations of Plain Radiographs

• Poor sensitivity for:

  • Isolated chondral defects

  • Cartilage delamination

  • Early degenerative changes

• Detect only ~30% of loose bodies.

• Cannot reliably identify:

  • Labral tears

  • Subtle cartilage injury

Clinical implication:
Duration of symptoms often correlates with degree of degeneration, which directly impacts the success of hip-preserving procedures.

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MRI: Improved Diagnostic Accuracy

MRI offers:

• Superior visualization of:

  • Labrum

  • Articular cartilage

  • Subchondral bone

  • Soft tissues

• Better detection of:

  • Labral tears

  • Cartilage defects

  • Osteonecrosis

  • Delamination

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MR Arthrography (Gadolinium-Enhanced MRI)

• Intra-articular contrast significantly improves:

  • Sensitivity

  • Diagnostic accuracy for labral pathology

• Enhances visualization of:

  • Chondral surface irregularities

  • Intra-articular lesions

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4. Cam Lesions and Radial MRI Imaging

Newer MRI techniques, including radial imaging:

• Provide detailed assessment of:

  • Femoral head–neck junction

• Identify:

  • Cam deformities

  • Bony prominences in metaphyseal region

• Essential for diagnosing:

  • Femoroacetabular impingement

  • Associated labral tears

  • Cartilage delamination

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5. Prognostic Implications of Imaging Findings

Outcomes of hip arthroscopy and preservation surgery are influenced by:

• Degree of cartilage degeneration

• Presence of osteonecrosis

• Extent of chondral damage

Key principle:
Greater degeneration ? poorer surgical outcomes.

Therefore:

• Early and accurate imaging is critical.

• Treating labral tears alone is insufficient.

• Underlying morphological abnormalities must be addressed for optimal results.

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Clinical Takeaways

• Plain radiographs remain foundational for:

  • Morphologic assessment

  • Preoperative planning

• MRI (especially MR arthrography) is superior for:

  • Labral pathology

  • Cartilage evaluation

• Recognition of impingement patterns is essential in treatment planning.

• Imaging findings must always be interpreted in conjunction with:

  • Clinical presentation

  • Duration of symptoms

  • Surgical goals