The study will include 20 people with hand OA awaiting surgery in the fingers. Participants will undergo dual-energy CT, cone-beam CT, ultrasound, clinical examination, blood sampling and questionnaires. Images will be analysed for the presence of joint-associated crystal including monosodium urate, calcium pyrophosphate and calcium hydroxyapatite. Material obtained during surgery will be used for crystal verification and calculation of diagnostic accuracy of dual-energy CT and cone-beam CT.

Inclusion Criteria:

1. Age ≥ 18 years.

2. Informed consent obtained.

3. 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:

1. Known inflammatory rheumatic diseases (e.g. rheumatoid arthritis, gout, psoriatic arthritis, psoriasis, inflammatory bowel disease), or other joint diseases (haemochromatosis)
2. Positive anti-cyclic citrullinated peptide (>10 kU/L)
3. Known cutaneous deposition diseases (e.g. amyloidosis or porphyria).
4. Foreign material/metallic implants at the area of interest will be excluded to avoid artefacts on CBCT [68].
5. Other diseases in the area - e.g. skin disease, known previous fracture in the joint of interest.
6. Participation in experimental device or experimental drug study 3 months prior to enrolment.
7. Pregnancy or breast-feeding.
8. Previous septic arthritis at the target joint.
9. Previous surgical procedures at the target joint.
10. Injection into the target joint within 3 months prior to enrolment.
11. Inability to speak and read Danish fluently.
12. Treatment with Colchicine within the last 30 days.
13. Treatment with systemic steroids ≥7.5 mg prednisolone within the last 30 days.
14. Lack of sample obtained for reference standard, i.e. unable to obtain either synovial fluid, joint lavage fluid, joint biopsy or excite joint.
15. 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.

Patients with hand OA awaiting hand surgery of a joint with OA will be considered eligible.