A 30-year-old is diagnosed with TB knee. MRI shows synovial thickening, erosion of the articular cartilage, and periarticular osteoporosis. Which radiological sign on plain X-ray is classically described in TB arthritis?
- A Whittling of bone ends
- B Chondrocalcinosis
- C Phemister's triad — juxta-articular osteoporosis, peripheral osseous erosions, and gradual narrowing of joint space ✓
- D Pencil-in-cup deformity
Correct answer: C. Phemister's triad — juxta-articular osteoporosis, peripheral osseous erosions, and gradual narrowing of joint space
Explanation
Phemister's triad is the classic radiological description of tuberculous arthritis on plain X-ray: (1) juxta-articular osteoporosis, (2) peripheral osseous erosions at the joint margins (where synovial pannus invades cartilage and bone), and (3) gradual narrowing of the joint space — this narrowing is characteristically slow because TB destroys cartilage less rapidly than pyogenic arthritis. Whittling of bone ends is seen in leprosy (leprous arthritis). Pencil-in-cup deformity is a feature of psoriatic arthritis. Chondrocalcinosis is seen in CPPD crystal deposition disease.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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