Would a lateral collateral ligament (LCL) injury to the knee show as shadowing to the lateral aspect of the knee on an X-ray?

X-ray Findings in Lateral Collateral Ligament (LCL) Injuries of the Knee

X-rays alone cannot directly visualize lateral collateral ligament injuries of the knee, as soft tissue structures like ligaments are not adequately shown on plain radiographs. 1

Limitations of X-ray in LCL Injury Diagnosis

• X-rays are primarily useful for detecting fractures and bony abnormalities, not soft tissue injuries such as ligament tears 1
• Shadowing on the lateral aspect of the knee on X-ray is not a specific finding for LCL injury 1
• X-rays serve as the initial imaging study in acute knee trauma but are limited to ruling out fractures before proceeding to advanced imaging 2

Appropriate Imaging for LCL Injuries

• MRI is the gold standard for evaluating ligamentous injuries of the knee, including LCL injuries 1
• MRI has high sensitivity (91-93%) and specificity (88-96%) for detecting ligamentous injuries of the knee 2
• MRI can detect associated findings that often accompany LCL injuries, such as:
  • Bone marrow contusions/edema 1
  • Associated injuries to other structures (as LCL injuries rarely occur in isolation) 3
  • Abnormal signal changes and course of the LCL 4

Common Pitfalls in LCL Injury Diagnosis

• Relying solely on X-rays for diagnosis of LCL injuries will lead to missed diagnoses 1, 2
• LCL injuries frequently occur with other ligamentous injuries, particularly involving the posterolateral corner structures 3
• Even when objective instability is not detected on stress radiographs, MRI may still show LCL damage 4

Clinical Correlation

• Pain around the fibular head, especially in the figure-of-four position, may indicate LCL injury even when X-rays appear normal 4
• Symptoms such as lateral knee pain, discomfort, and balance instability during activities may be present despite negative X-rays 4
• For patients with suspected LCL injury based on mechanism and clinical findings, MRI should be performed regardless of X-ray findings 2

Key Points for Clinicians

• Do not rely on X-ray "shadowing" to diagnose or exclude LCL injuries 1
• When LCL injury is clinically suspected, proceed to MRI evaluation even with normal X-rays 2
• Consider the mechanism of injury (typically forced varus stress on a slightly flexed knee) in your clinical assessment 4
• Remember that isolated LCL injuries are rare; look for associated injuries to other structures 3