Appropriate Investigation for Suspected Knee Osteoarthritis
Bilateral X-ray of knees is the most appropriate initial investigation to confirm osteoarthritis in a patient with knee pain and clicking that worsens with movement. 1
Rationale for X-ray as First-Line Investigation
The American College of Radiology (ACR) Appropriateness Criteria for chronic knee pain clearly establishes radiography as the initial imaging study of choice for evaluating suspected osteoarthritis:
- Radiographs should include at least one frontal projection of one or both knees (anteroposterior, Rosenberg, or tunnel), a tangential patellar view, and a lateral view of the affected knee 1
- Weight-bearing (standing) radiographs are ideal as they better demonstrate joint space narrowing and malalignments 1
- Bilateral views allow for comparison between affected and unaffected sides 1
Key Radiographic Findings in Osteoarthritis
X-rays can detect characteristic osteoarthritic changes including:
- Joint space narrowing
- Osteophyte formation
- Subchondral sclerosis
- Bone end deformities 2
- Calcifications of soft tissues, including deposits in degenerated meniscus, ligaments, or joint capsule 3
When to Consider Advanced Imaging
MRI is generally not indicated as an initial investigation when osteoarthritis is suspected:
- MRI without IV contrast is not usually indicated in patients for whom radiographs are diagnostic of osteoarthritis unless symptoms are not explained by the radiographic findings 1
- MRI may be considered when radiographs are normal but pain persists, or to evaluate for concomitant pathology such as meniscal tears 1
- Given the increased sensitivity of MRI for osteoarthritis, it may be indicated when more accurate or serial cartilage measurements are desired 1
Why Not Other Options?
- MRI (Option B): Unnecessary and costly as an initial test when osteoarthritis is clinically suspected; should be reserved for cases where radiographs are normal but symptoms persist 1
- Joint fluid aspiration (Option C): Primarily indicated for suspected crystal arthropathy (gout, pseudogout) or infection, not for primary diagnosis of osteoarthritis 1
- No investigation (Option D): Inadequate approach as imaging confirmation is necessary for definitive diagnosis and to exclude other pathologies 1, 3
Clinical Implications
Recent evidence suggests that radiographic diagnosis of knee osteoarthritis may influence patient beliefs about management. Patients who receive X-ray-based diagnosis and explanation of knee osteoarthritis may believe surgery is more necessary compared to those who receive only clinical explanation 4. Therefore, when discussing radiographic findings with patients, it's important to emphasize that:
- Osteoarthritis is a clinical diagnosis supported by imaging
- The severity of radiographic findings doesn't always correlate with symptom severity
- Conservative management remains first-line regardless of radiographic appearance
By following this evidence-based approach, you can accurately diagnose knee osteoarthritis while avoiding unnecessary advanced imaging, which improves cost-effectiveness and patient care.