Diagnostic Accuracy of Dual-energy CT

Inclusion criteria

• Age ≥ 18 years.
• Informed consent obtained.
• Patients with hand OA as defined by the American College of Rheumatology Classification Criteria for hand OA:

• Hand pain, aching or stiffness

And 3 or 4 of the following features:

• Hard tissue enlargement of ≥2 of the 10 selected joints*.
• Hard tissue enlargement of ≥2 of the 10 DIP joints.
• Fewer than 3 swollen MCP joints.
• Deformity of at least 1 of 10 selected joints*. *The 10 selected joints are the second and third DIP, the second and third PIP, and the first carpometacarpal joints of both hands.

Exclusion criteria

• Known inflammatory rheumatic diseases (e.g. rheumatoid arthritis, gout, psoriatic arthritis, psoriasis, inflammatory bowel disease), or other joint diseases (haemochromatosis)
• Positive anti-cyclic citrullinated peptide (>10 kU/L)
• Known cutaneous deposition diseases (e.g. amyloidosis or porphyria).
• Foreign material/metallic implants at the area of interest will be excluded to avoid artefacts on CBCT [68].
• Other diseases in the area - e.g. skin disease, known previous fracture in the joint of interest.
• Participation in experimental device or experimental drug study 3 months prior to enrolment.
• Pregnancy or breast-feeding.
• Previous septic arthritis at the target joint.
• Previous surgical procedures at the target joint.
• Injection into the target joint within 3 months prior to enrolment.
• Inability to speak and read Danish fluently.
• Treatment with Colchicine within the last 30 days.
• Treatment with systemic steroids ≥7.5 mg prednisolone within the last 30 days.
• Lack of sample obtained for reference standard, i.e. unable to obtain either synovial fluid, joint lavage fluid, joint biopsy or excite joint.
• Any other condition that in the opinion of the investigator may interfere with study participation.

There will be no restriction on sex or Kellgren-Lawrence (KL) grading.