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Acute Monoarthritis: Diagnosis in Adults

Jeremy Swisher, MD
Zachary Sitton, MD
Kimberly Burbank, MD
Chris Nelson, MD

American Family Physician. 2025;111(6):497-506.

Author disclosure: No relevant financial relationships.

This clinical content conforms to AAFP criteria for CME.

Acute monoarthritis, characterized by pain or swelling in a single joint, is a diagnostic challenge in the primary care setting. Intra-articular conditions typically manifest with reduced active and passive range of motion, whereas patients with periarticular conditions such as tendinitis or bursitis often maintain passive range of motion. When evaluating a patient with acute monoarthritis, it is essential to remember that many polyarthritic processes can initially present in a single joint. A broad differential diagnosis for monoarthritis should include septic arthritis, osteoarthritis, gout, trauma, and Lyme arthritis. Of these, septic arthritis is the most urgent and requires prompt intervention. Bacterial culture of the synovial fluid is the most accurate diagnostic test for a septic joint. However, diagnostic accuracy can be increased in the short term by evaluating additional markers such as synovial white blood cell count, synovial lactate, and serum biomarkers. These supplementary tests aid in early decision-making while awaiting bacterial culture results. Osteoarthritis is often clinically diagnosed and may be confirmed with radiography. Gout, the most prevalent crystalline arthropathy, can be diagnosed using specialized calculators, ultrasonography, and dual energy computed tomography. Gout is typically most painful at night or in the early morning. Ultrasonography is useful for identifying effusions in less-visible joints and facilitating precise joint aspiration.

Acute monoarthritis, characterized by pain and swelling in a single joint over multiple days, is a diagnostic challenge due to its diverse etiology.1,2 Effective management depends on identification of the pathology because treatment strategies vary according to the underlying cause.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation Evidence rating Comments
Active and passive range of motion should be evaluated and compared with the contralateral unaffected joint to distinguish intra-articular from periarticular etiologies.7,37 C Expert opinion and clinical guidelines
Point-of-care ultrasonography should be used to determine the presence of an effusion when clinically uncertain, especially in deeper joints such as the hip or shoulder, where effusions may be more difficult to detect on examination.40,41 C Expert opinion
In patients with suspected septic arthritis, synovial fluid should be analyzed via arthrocentesis (Gram stain, culture, white blood cell count with differential, and crystal analysis) before starting antibiotics.12,20,43 C Several randomized clinical trials and a systematic review with disease-oriented outcomes
When joint aspiration is not completed, a validated clinical decision rule, such as the American College of Rheumatology and European League Against Rheumatism Collaborative Initiative criteria, should be used with clinical and imaging data to assess and diagnose gout.3,4,46,47 C Systematic review and validated clinical decision rule
Point-of-care ultrasonography can help diagnose gout by evaluating for the presence of the double contour sign.3,5,47 C Expert opinion and observational studies

A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to https://www.aafp.org/afpsort.

JEREMY SWISHER, MD, is a sports medicine physician in the Division of Sports Medicine at the University of California, Los Angeles.

ZACHARY SITTON, MD, is a sports medicine fellow in the Department of Orthopaedic Surgery at Duke University, Durham, North Carolina.

KIMBERLY BURBANK, MD, is a family medicine resident in the Department of Family Medicine at Atrium Health Wake Forest Baptist, Winston-Salem, North Carolina.

CHRIS NELSON, MD, is an assistant professor in the Department of Family Medicine at Wake Forest University School of Medicine.

Address correspondence to Jeremy Swisher, MD, at jeremyswisher.medicine@gmail.com.

Author disclosure: No relevant financial relationships.

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