What are the best X-ray (X-ray) views for assessing osteoarthritis (OA) of the knee?

Best X-ray Views for Assessing Knee Osteoarthritis

The optimal radiographic evaluation for knee osteoarthritis should include weight-bearing anteroposterior (AP), lateral, and patellofemoral views (either skyline/axial or Merchant view), as this combination provides the most comprehensive assessment of all three knee compartments. 1

Standard Radiographic Protocol for Knee OA

Essential Views

• Weight-bearing anteroposterior (AP) view

  • Should be obtained in standing position to accurately assess joint space narrowing
  • Preferably in slight flexion (PA flexion view with Synaflexer) to better visualize tibiofemoral joint space 1
  • Detects medial and lateral tibiofemoral compartment changes

• Lateral view

  • Evaluates posterior knee compartment
  • Assesses posterior osteophytes often missed on AP views 1
  • Shows tibial slope and patella position

• Patellofemoral view

  • Either skyline/axial view or Merchant view
  • Essential for evaluating the patellofemoral compartment 1, 2
  • Detects patellofemoral joint space narrowing and osteophytes

Additional Specialized Views

• Tunnel/PA flexion view

  • Weight-bearing posteroanterior view with knee in 30-45° flexion
  • Significantly increases detection of joint space narrowing in both medial (p=0.006) and lateral (p<0.001) compartments compared to AP view alone 3
  • Better visualizes intercondylar notch and tibial spine osteophytes 3

• Full-length standing alignment view (hip-to-ankle)

  • Useful for assessing overall limb alignment (varus/valgus)
  • Provides information on weight-bearing mechanical axis 1
  • May be obtained as baseline and followed with targeted knee views 1

Clinical Importance of Proper View Selection

Combining multiple views significantly improves diagnostic accuracy:

• Using only AP views misses many cases of OA, particularly in the patellofemoral compartment 2
• Adding either lateral or skyline view to AP increases sensitivity to 94-97% for detecting radiographic OA 2
• The combination of AP and tunnel view significantly improves detection of:
  • Medial subchondral cysts (p=0.022)
  • Lateral tibial plateau sclerosis (p=0.041)
  • Moderate-to-large osteophytes in multiple locations 3

Key Technical Considerations

• Weight-bearing is critical - non-weight-bearing views may not demonstrate malalignments that become apparent when standing 1
• Standardized positioning - minor differences in positioning can greatly alter the appearance of joint spaces 1
• AP view with 10° internal rotation improves interpretation of varus and valgus alignment compared to neutral AP views 1
• Quality matters - lateral views may be easier to acquire with high quality than skyline views in some settings 2

Common Pitfalls to Avoid

• Missing patellofemoral disease by omitting patellofemoral views
• Underestimating disease severity with non-weight-bearing views
• Failing to detect posterior osteophytes when only using AP views
• Misinterpreting alignment due to improper positioning
• Overlooking lateral compartment involvement - MR often shows lateral compartment cartilage loss when radiographs appear normal 4

Weight-bearing radiographs are essential as they reveal dynamic abnormalities like joint malalignment and subluxation that may not be apparent on non-weight-bearing images 1. When evaluating for knee OA, always prioritize obtaining high-quality images of all three compartments to avoid missing significant pathology.