What are the recommended X-ray views for evaluating knee pain?

Recommended X-ray Views for Knee Pain

For initial evaluation of knee pain, obtain at minimum two views—anteroposterior (AP) and lateral—with the lateral taken at 25-30 degrees of knee flexion; add a tangential patellar view to complete a standard three-view series. 1

Standard Initial Radiographic Series

Minimum Required Views

• Anteroposterior (AP) view: Essential baseline view for evaluating the tibiofemoral joint, fractures, and alignment 1, 2
• Lateral view: Must be obtained with the knee at 25-30 degrees of flexion in the lateral decubitus position, demonstrating the patella in profile 1
  • This view allows evaluation for joint effusion and, when obtained as a cross-table lateral with horizontal beam, can visualize lipohemarthrosis (indicating intra-articular fracture) 1

Recommended Third View

• Tangential patellar view (sunrise/skyline view): Should be included as part of the standard knee series to evaluate the patellofemoral joint 1
  • This is particularly important because failure to image the patellofemoral compartment results in missed cases of osteoarthritis and patellar pathology 3

Weight-Bearing Considerations

For chronic knee pain or suspected osteoarthritis, weight-bearing views significantly improve diagnostic accuracy:

• Weight-bearing AP view: Standard for chronic pain evaluation 1
• Weight-bearing PA tunnel view (Rosenberg view): The combination of weight-bearing AP and tunnel view significantly increases detection of joint space narrowing in both medial (p=0.006) and lateral (p<0.001) compartments compared to AP alone 4
  • This combination also improves identification of subchondral cysts, sclerosis, and osteophytes 4

Additional Views Based on Clinical Suspicion

For Suspected Patellar Pathology

• Patellofemoral view: Specifically indicated when patellar fracture, subluxation, or dislocation is suspected 1
• The lateral view in full extension has 98% sensitivity for detecting prior patellar dislocation, while the axial view at 30 degrees flexion has 82% specificity 5

For Trauma Cases

• Internal and external oblique views: Commonly performed as supplemental projections in acute knee trauma 1
• These are added to the standard AP and lateral views when fracture detection is critical 1

Clinical Decision Rules for When to Image

Ottawa Knee Rules (Adults and Children ≥5 years)

Radiographs are indicated if ANY of the following are present: 1, 2, 6

• Age >55 years
• Isolated tenderness of the patella (no other bone tenderness)
• Tenderness at the head of the fibula
• Inability to flex knee to 90 degrees
• Inability to bear weight both immediately after injury and in the emergency department (4 steps)

Pittsburgh Rules (Alternative criteria)

Three criteria include: 1

• Inability to bear weight
• Inability to flex the knee to 90 degrees
• Presence of bony tenderness

Critical Pitfalls to Avoid

• Never skip radiographs even when effusion is clinically obvious: Plain films are essential to rule out fractures, prosthetic complications, or chronic changes before proceeding to advanced imaging 2
• Do not order MRI without recent radiographs first: Approximately 20% of patients with chronic knee pain inappropriately receive MRI without radiographs within the prior year 1, 7
• Ensure adequate patellofemoral imaging: Using only AP and lateral views without a patellofemoral view (skyline or lateral in extension) will miss significant pathology 3
• Clinical judgment supersedes decision rules: Do not apply Ottawa or Pittsburgh rules in patients with gross deformity, palpable mass, penetrating injury, prosthetic hardware, unreliable examination due to multiple injuries, altered mental status, or neuropathy 1

Practical Algorithm

1. Acute trauma with positive Ottawa/Pittsburgh criteria: AP + lateral (25-30° flexion) + consider patellofemoral view 1, 2
2. Chronic knee pain (initial evaluation): Weight-bearing AP (or tunnel view) + lateral + tangential patellar view 1
3. Suspected patellar pathology: Standard views + dedicated patellofemoral/skyline view 1, 5
4. Suspected arthritis: Weight-bearing AP + weight-bearing tunnel view + lateral + tangential patellar 1, 4