differential for monoarthritis

Tiny Tips: OSTRICH as a differential for acute monoarthritis

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Acute monoarthritis is a common complaint in the emergency department. The differential for acute monoarthritis is broad. A delay in proper diagnosis and treatment of certain etiologies can result in significant morbidity.​1,2​ The evaluation of a patient with acute monoarthritis should begin with a focused history and physical exam which will guide further laboratory and radiographic studies. With a history of trauma or focal bony pain, radiography can be useful to rule out a fracture or tumour. In an acutely inflamed joint with an effusion and no history of trauma, arthrocentesis is necessary to differentiate between septic arthritis, crystal arthritis or an inflammatory effusion from intra-articular derangement.​1​ 

The OSTRICH mnemonic can be helpful in remembering the differential for monoarthritis: 


Septic arthritis

Tumor– chondrosarcoma, osteoid osteoma, tenosynovial giant cell tumor, metastatic disease​2​

Rheumatic and auto-immune disease – rheumatoid arthritis, spondyloarthritis, systemic lupus erythematosus, sarcoidosis​2​

Intra-articular pathology – meniscal tear, osteonecrosis, fracture 

Crystal arthropathy – monosodium urate, calcium pyrophosphate dihydrate 

Hemarthrosis – trauma, clotting disorders, anticoagulation 

This post has been copyedited and uploaded by Kimberly Vella.


  1. 1.
    Becker J, Daily J, Pohlgeers K. Acute Monoarthritis: Diagnosis in Adults. Am Fam Physician. 2016;94(10):810-816. https://www.ncbi.nlm.nih.gov/pubmed/27929277.
  2. 2.
    Ramirez Curtis M. Overview of Monoarthritis in Adults. UpToDate. https://www.uptodate.com/contents/overview-of- monoarthritis-in-adults  . Published 2017. Accessed May 20, 2019.

Fareen Zaver MD

Fareen Zaver is an Emergency Physician based in Calgary. She is the Co-Director for the CanadiEM Digital Scholars Fellowship and is the Lead Editor/Co-Founder of ALiEM Approved Instructional Resources - Professional (AIR-Pro) series