Recommended Radiographic Views for Knee Osteoarthritis Evaluation
For a patient with knee pain when osteoarthritis is suspected, obtain weight-bearing anteroposterior (AP) and patellofemoral (skyline) views as the mandatory initial imaging studies. 1
Essential Radiographic Protocol
The EULAR guidelines explicitly recommend that when imaging is needed for knee osteoarthritis evaluation, specific radiographic views are critical for optimal detection of OA features 1:
Required Views
Weight-bearing anteroposterior (AP) view: This must be obtained with the patient standing to assess the tibiofemoral compartment under physiologic load 1
Patellofemoral (skyline/tangential) view: Essential for detecting cartilage damage at the patellofemoral joint, which has superior sensitivity and specificity compared to standard views 1
Lateral view: Completes the standard three-view series for comprehensive knee assessment 1, 2
Weight-Bearing Technique Considerations
Semiflexion positioning (approximately 25-45 degrees) is superior to full extension for detecting joint space narrowing, particularly in the medial compartment 1, 3, 4
The Rosenberg projection (PA weight-bearing in 45 degrees flexion) demonstrates significantly better sensitivity for detecting medial compartment joint space narrowing compared to conventional AP views in full extension 3
Weight-bearing views in various degrees of flexion were consistently used across 27 studies evaluating optimal radiographic techniques for knee OA 1
Clinical Decision Algorithm
When to Image
Imaging is NOT required if the patient presents with typical OA features: usage-related pain, short-duration morning stiffness, age >40 years, and symptoms affecting one or few joints 1
Imaging IS indicated when:
Imaging Sequence
Plain radiography first: Conventional radiography must be performed before any other imaging modality 1
MRI consideration: Reserve for cases where radiographs are normal or show only effusion but pain persists after 4-6 weeks of conservative treatment 2, 5
Critical Pitfalls to Avoid
Pain-Related Measurement Error
Severe knee pain artificially reduces joint space width in extended-view radiographs by limiting full extension 6
In highly symptomatic knees, pain reduction from analgesics can increase measured joint space width by 0.20 mm on average, potentially masking true progression 6
Semiflexed views are unaffected by pain-related changes in extension, making them more reliable for longitudinal assessment 6
Technical Considerations
Equal weight distribution on both legs during weight-bearing views is essential for reproducible joint space measurements 7
Joint space width thresholds: <3 mm in the tibiofemoral joint and <5 mm in the patellofemoral joint indicate joint space narrowing 7
Internal rotation of 10 degrees improves interpretation of varus/valgus alignment compared to neutral or external rotation positioning 1
Exclude Referred Pain Sources
Before attributing all symptoms to knee pathology 2, 5, 8:
Hip evaluation: Obtain pelvis and proximal femur radiographs if groin pain, restricted hip range of motion, or clinical hip findings are present 5
Lumbar spine assessment: Order lumbar spine radiographs if low back pain, radicular symptoms, or posterior thigh pain patterns exist 5, 8
Approximately 20% of patients with chronic knee pain inappropriately receive knee MRI without recent radiographs or consideration of referred pain 2, 5
Radiographic Features to Assess
Weight-bearing radiographs confirm OA diagnosis by demonstrating 9:
- Joint space narrowing (most sensitive when measured in weight-bearing semiflexion) 1, 3
- Osteophytes (marginal bone formation) 7, 9
- Subchondral sclerosis 9
- Bone end deformities 9
The presence of marginal osteophytes correlates highly with cartilage defects on MRI, independent of joint space narrowing 7