What Is This Condition?

A 72-year-old man is admitted to the hospital overnight following an elective inguinal hernia repair. There are no immediate postoperative complications, but he awakens the next morning with severe right knee pain. Medical history is notable for hypertension, chronic obstructive pulmonary disease, and mild aortic stenosis. The patient smokes half a pack of cigarettes daily and drinks alcohol on social occasions. His temperature is 38.1 C (100.5 F), blood pressure is 160/110 mm Hg, pulse is 80/min, and respirations are 16/min. Physical examination shows redness and swelling of the right knee with limited motion due to pain. Diagnostic arthrocentesis is performed, with results from synovial fluid analysis as follows:

• White blood cells: 30,000/mm³

• Neutrophils: 90%

• Polarized microscopy: Few rhomboid-shaped crystals

• Gram stain: No organisms seen

Which of the following is most likely associated with this patient's current condition?

Options:

A. Conjunctivitis
B. Heberden nodes
C. Meniscal calcification
D. Rheumatoid factor
E. Tophi
F. Transient bacteremia

Potential Triggers

• Aging

• Joint Trauma

• Surgery

• Metabolic Disorders (Hyperparathyroidism, Hemochromatosis, Hypothyroidism)

• Dehydration

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Triggers Crystal Release (e.g., Dehydration→ concentrate synovial fluid → crystal formation)

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Crystals deposit in joint cartilage and synovium

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Calcium Pyrophosphate Crystal Formation

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Calcium Pyrophosphate (CPP) Levels ↑ in the synovial fluid

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The meniscus, being avascular and fibrocartilaginous, is more prone to calcification over time

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Crystal Deposition in Meniscus
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Meniscal Calcification

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Joint Stiffness, Reduced Mobility, and further Joint Degeneration
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Further Damages to Joint Cartilage

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Meniscal Degeneration
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Chronic joint pain

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Inflammatory Response

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- White Blood Cell Count: 30,000/mm³ (indicating inflammation)

- Neutrophils: 90% (suggests acute inflammatory process)

- Polarized Microscopy:

- Few Rhomboid-shaped Crystals (indicative of pseudo-gout)

- Gram Stain: No organisms seen (rules out infection)

Source Images: NEJM

Why Other Answers Are Wrong

Option A: Conjunctivitis

• Cause: Seen in reactive arthritis, typically following a genitourinary or gastrointestinal infection.

• Incorrect here: The patient has no preceding infection, and pseudogout doesn't affect the eyes. The symptoms (knee pain and swelling) are joint-specific, not systemic.

Option B: Heberden Nodes

• Cause: These bony enlargements are found in osteoarthritis due to chronic wear-and-tear of joints.

• Incorrect here: Osteoarthritis causes chronic joint pain and doesn't produce the acute inflammatory presentation seen in this patient. The synovial fluid shows rhomboid-shaped crystals, not features of osteoarthritis.

Option D: Rheumatoid Factor

• Cause: Associated with rheumatoid arthritis (RA), an autoimmune disease causing chronic, symmetrical joint inflammation.

• Incorrect here: RA affects multiple joints, not one. Monoarticular acute pain with rhomboid-shaped crystals points to pseudogout, not RA. RA also presents with chronic symptoms, not sudden, acute flare-ups.

Option E: Tophi

• Cause: Tophi form in gout, which is due to monosodium urate crystals accumulating in joints and soft tissues.

• Incorrect here: Gout is associated with needle-shaped urate crystals (not rhomboid-shaped CPP crystals). This patient has pseudogout, involving calcium pyrophosphate deposition, not gout.

Option F: Transient Bacteremia

• Cause: Transient bacteremia can lead to septic arthritis, a bacterial infection of the joint.

• Incorrect here: The Gram stain is negative for bacteria, ruling out septic arthritis. The patient’s symptoms and findings (rhomboid crystals) align with pseudogout, not infection.

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