Radiographs of a young adult with chronic monoarthritis of the knee show juxta-articular osteoporosis, marginal erosion, and relative preservation of the articular cartilage space until late in the disease. This combination is known as:

• A Phemister triad of tuberculous arthritis ✓
• B Kocher criteria for septic arthritis
• C Steinberg classification of femoral head necrosis
• D Larsen grading of rheumatoid arthritis

Explanation

The Phemister triad defines tuberculous arthritis on imaging: juxta-articular osteoporosis, peripheral marginal erosion, and gradual narrowing of the joint space that occurs late because tubercle bacilli destroy cartilage slowly compared with pyogenic infection. In pyogenic septic arthritis the joint space is lost early, which is the discriminating point. The Kocher criteria are clinical predictors, not radiographic signs.

Reference: Apley and Solomon's System of Orthopaedics and Trauma, 10th ed.

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