Should bilateral or unilateral X-rays (X-radiation images) be ordered when suspecting arthritis in one knee?

Bilateral X-rays Should Be Ordered When Suspecting Arthritis in One Knee

Order bilateral knee X-rays when evaluating suspected arthritis, even when symptoms are unilateral, as this provides critical comparison views and detects bilateral disease that is present in the majority of cases.

Rationale for Bilateral Imaging

High Prevalence of Bilateral Disease

• Radiographic knee osteoarthritis is bilateral in 85% of patients referred to hospital, even when symptoms may initially appear unilateral 1
• Bilateral imaging allows for comparison between symptomatic and asymptomatic sides, which helps identify subtle abnormalities that might otherwise be missed 2
• The contralateral "normal" knee serves as an internal control for assessing joint space narrowing, osteophyte formation, and other degenerative changes 3

Guideline Support for Bilateral Imaging

• The International Working Group on the Diabetic Foot (IWGDF 2023) explicitly recommends that bilateral plain X-rays should ideally be performed when evaluating suspected arthropathy, even in conditions presenting with unilateral symptoms 4
• This best practice statement emphasizes the diagnostic value of comparison views for accurate assessment 4

Detection of Multicompartmental Disease

• Among affected knees, 59% show involvement of two compartments and 6% involve three compartments, making comprehensive bilateral evaluation important for treatment planning 1
• Bilateral imaging helps identify patterns associated with more severe disease, including calcium pyrophosphate crystal deposition and polyarticular involvement 1

Limitations of Evidence for Unilateral Imaging

Inconclusive Recommendations

• The American Academy of Orthopaedic Surgeons (AAOS) guidelines on osteochondritis dissecans state they are unable to recommend for or against radiographs on the contralateral asymptomatic knee, citing lack of quality evidence 4
• However, this inconclusive recommendation applies specifically to OCD lesions, not osteoarthritis, and the absence of evidence should not be interpreted as evidence against bilateral imaging 4

Standard Radiographic Views

Required Projections

• Standard knee radiographs should include anteroposterior (AP), lateral, and sunrise/Merchant views, with tunnel views added when evaluating for specific pathology 4
• Weight-bearing radiographs are preferred when possible, as they reveal dynamic abnormalities and functional joint space narrowing not apparent on non-weight-bearing films 4, 2

Optimal Technique for Arthritis Detection

• The 45-degree posteroanterior (PA) flexion weight-bearing view is superior to standard 3-foot standing AP views for detecting lateral compartment cartilage wear (83% versus 42% sensitivity) 5
• For comprehensive arthritis evaluation, combining views improves detection of osteophytes and joint space narrowing across all compartments 6

Clinical Decision-Making Algorithm

When to Order Bilateral X-rays

1. Any patient with suspected knee arthritis should receive bilateral imaging as the initial diagnostic study 4, 1
2. Patients with unilateral symptoms still warrant bilateral imaging given the 85% prevalence of bilateral radiographic disease 1
3. Comparison views are particularly valuable when subtle findings are present or when assessing disease severity 2, 3

What Bilateral Imaging Reveals

• Presence and severity of joint space narrowing in all compartments bilaterally 3, 6
• Osteophyte formation, subchondral sclerosis, and cyst formation 1, 3
• Patterns suggesting calcium pyrophosphate deposition disease or other crystal arthropathies 1
• Multicompartmental involvement that influences treatment decisions 1

Common Pitfalls to Avoid

Diagnostic Errors

• Do not assume unilateral symptoms indicate unilateral disease—this leads to incomplete assessment and missed bilateral pathology 1
• Do not rely on non-weight-bearing films alone when the patient can stand, as these miss functional joint space narrowing and malalignment 4, 2
• Do not order only AP views—lateral and additional projections significantly improve diagnostic accuracy for osteophytes and multicompartmental disease 3, 6

Cost and Radiation Considerations

• While some advocate for single-view imaging to reduce costs and radiation exposure, this approach is more appropriate for epidemiological studies than clinical diagnosis 6
• The diagnostic value of bilateral comparison views outweighs minimal additional radiation exposure in the clinical setting 4, 1
• Missing bilateral or multicompartmental disease due to inadequate initial imaging may lead to inappropriate treatment and worse outcomes 1, 3