When is a knee X-ray with a skyline view recommended?

When to Use Knee X-ray with Skyline View

A knee X-ray with skyline view should be obtained when evaluating suspected patellar fractures, subluxation, or dislocation, but is not routinely needed for all acute knee trauma cases. 1

Indications for Skyline View

The skyline view (also called patellofemoral view) is specifically indicated in the following situations:

• Suspected patellar fractures 1
• Suspected patellar subluxation or dislocation 1, 2
• Evaluation of patellofemoral joint abnormalities 2

Evidence-Based Approach to Knee Imaging

Initial Imaging for Acute Knee Trauma

1. Standard radiographs should be the first imaging study for evaluating knee pain and trauma 1, 3

   • Minimum of two views: anteroposterior (AP) and lateral 1
   • Additional patellofemoral (skyline) view is typically obtained only for suspected patellar fractures, subluxation, or dislocation 1

2. When to order knee radiographs (Ottawa Knee Rules) 1:

   • Age ≥55 years
   • Palpable tenderness over head of fibula
   • Isolated patellar tenderness
   • Inability to flex knee to 90°
   • Inability to bear weight immediately after injury
   • Inability to walk in the emergency room

Value of Skyline View in Specific Scenarios

• Patellar dislocation: Skyline view revealed avulsion fractures at the medial aspect of the patella in 54% of cases with history of subluxation or dislocation 2, 4
• Non-dislocation trauma: Skyline view showed damage in only 1 of 158 cases (0.6%) of direct or indirect injury not involving subluxation or dislocation 4
• Recent evidence: A 2023 study found that the sensitivity of AP and lateral views without skyline view (92.86%) was non-inferior to the standard set including skyline view (97.86%) for detecting patellar fractures 5

Clinical Implementation

When to Include Skyline View

• Include skyline view when:

  • History suggests patellar dislocation or subluxation 4
  • Physical exam reveals focal patellar tenderness 1
  • Suspected patellofemoral joint pathology 2, 6

• Skyline view may be omitted when:

  • Mechanism does not suggest subluxation or dislocation 4
  • No focal patellar tenderness 1
  • Limited resources or patient discomfort is a significant concern 4

Technical Considerations

• Standard skyline view requires knee flexion of approximately 45° 7
• When limited flexion is present (e.g., post-trauma), modified techniques can still obtain useful skyline views 2
  • Even with only 70° of flexion from full extension, skyline views can be obtained by adapting standard techniques 2

Common Pitfalls and Caveats

• Technical challenges: Skyline views are more frequently excluded due to technically unsatisfactory images compared to other views 6
• Unnecessary radiation: Routine use of skyline view in all knee trauma adds unnecessary radiation exposure, especially in children 4
• Patient discomfort: Obtaining skyline views may cause additional discomfort, particularly in acute trauma settings 4
• Alternative approach: For clinical or epidemiological studies, the lateral view may be easier to acquire with high quality than the skyline view while still providing information about the patellofemoral joint 6

By following these evidence-based guidelines, clinicians can optimize the use of skyline views in knee radiography, ensuring appropriate diagnosis while minimizing unnecessary radiation exposure and patient discomfort.