The etiology of monoarthirits is vast, ranging from infections to malignancies. The infectious causes of monoarthritis are: - Gonococcus - Tuberculous - Fungal infections - Viral infections Many crystals can cause arthritis. These include: - Monosodium urate - Calcium pyrophosphate dihydrate - Oxalate - Hydroxyapatite - Lipid crystals Reactive arthritis may occur secondary to bacterial and viral infections. Trauma, malignancy, and systemic diseases can also cause monoarthrtitis. Reference: https://www.researchgate.net/publication/12794381_Assessment_investigation_and_management_of_acute_monoarthritis/figures?lo=1&utm_source=google&utm_medium=organic Image via: https://healthjade.net/monoarthritis/