What to Look for on Knee X-ray in a 70-Year-Old Obese Male with Knee Pain
For a 70-year-old obese male with knee pain, obtain weight-bearing knee radiographs and specifically evaluate for joint space narrowing, osteophytes, subchondral sclerosis, and bone end deformities—the cardinal radiographic features of osteoarthritis. 1, 2
Initial Imaging Approach
X-ray is the initial and most appropriate imaging modality for evaluating chronic knee pain in this demographic. 1 The ACR Appropriateness Criteria rates plain radiography as a 9 out of 9 (usually appropriate) for chronic knee pain evaluation. 1
Critical Technical Detail
- Weight-bearing radiographs are essential to accurately assess joint space narrowing, as non-weight-bearing films may underestimate the severity of osteoarthritis. 2
Specific Radiographic Features to Evaluate
Primary Osteoarthritis Findings
Look for these four cardinal features on the X-ray: 2
- Joint space narrowing (most important indicator of cartilage loss)
- Osteophytes (bone spurs at joint margins)
- Subchondral sclerosis (increased bone density beneath cartilage)
- Bone end deformities (flattening or irregularity of bone surfaces)
Alignment Assessment
- Evaluate for varus or valgus deformity, which develops with progressive osteoarthritis and is particularly relevant in obese patients due to increased mechanical stress. 2
- Assess overall limb alignment, as this influences treatment planning and prognosis. 1
Additional Findings to Document
- Loose bodies (free-floating bone or cartilage fragments) 1
- Osteochondritis dissecans (if present) 1
- Chondrocalcinosis (calcium deposits suggesting pseudogout) 1
- Joint effusion (though better assessed clinically or with ultrasound) 1
Grading Severity
Use the Kellgren-Lawrence grading scale to standardize severity assessment, as this is commonly used in clinical practice and research. 2 This helps guide treatment decisions and provides a baseline for monitoring progression.
When X-ray Findings Don't Match Clinical Presentation
A critical pitfall: In patients >70 years of age, there is poor correlation between radiographic findings and pain severity. 1 Bilateral structural abnormalities on X-ray are common even with unilateral symptoms, limiting the ability to discriminate painful from non-painful knees. 1
When to Consider Advanced Imaging
MRI is not usually indicated if radiographs are diagnostic of osteoarthritis, unless: 1
- Symptoms are not explained by radiographic findings (e.g., suspected stress fracture, occult fracture)
- There is concern for alternative diagnoses (osteonecrosis, infection, inflammatory arthritis)
- Mechanical symptoms suggest meniscal tear or loose bodies requiring surgical planning
Clinical Context Integration
Obesity as a Risk Factor
Obesity is a modifiable risk factor that significantly impacts both disease progression and treatment outcomes. 1 Weight loss should be addressed as part of the core management plan regardless of radiographic findings. 1
Biopsychosocial Assessment
Screen for depression and psychological factors, as chronic knee pain is associated with increased risk of depression, anxiety, and reduced quality of life. 3 The ACR recommends evaluating mood as part of the initial assessment using a biopsychosocial approach. 3
Common Pitfalls to Avoid
Don't over-rely on radiographic severity to guide treatment decisions. Clinical symptoms and functional impact should drive management, not X-ray appearance alone. 1, 4
Don't order X-rays of the contralateral hip routinely unless there are specific clinical indicators of hip pathology, as this is usually not indicated. 1
Avoid ordering MRI reflexively when X-rays confirm osteoarthritis, as this rarely changes initial management and increases costs without improving outcomes. 1
Don't diagnose osteoarthritis based solely on imaging without clinical correlation, as radiographic changes are common in asymptomatic older adults. 4, 5