Childhood arthritis is a diagnosis made by clinicians based upon their clinical examination, during which patients are assessed for signs of swelling, warmth and restricted movement of the joints using the sensation of touch. Clinicians use investigations such as blood tests and scans which may be costly, associated with waiting times, can cause the patient stress or anxiety. Patients with childhood arthritis can often present with flares of their condition even when on medical treatment, which may require further investigations to determine the nature of the problem. Studies in adult Rheumatology have demonstrated that a thermal imaging camera (which detects heat given off by the body) can be useful in assessing for signs of inflammation in arthritis. The use of this camera could provide an alternative to the tests described; it does not require any contact with the patient, is quick and easy to use, and does not emit any radiation. The investigators hope that this pilot study will demonstrate that thermal imaging can be used to complement the standardised assessments of joint inflammation as done routinely in clinic and may lead to further work comparing thermal imaging with other tests such as MRI scanning and ultra-sound.

The investigators will recruit 20-50 children with arthritis affecting either knee or ankle joints. The investigators will use a highly sensitive thermal imaging camera to take pictures and short video recordings of each ankle and knee joint, recording skin temperature and colour. The investigators will compare this with the clinicians' assessment of whether the knee and ankle joints are inflamed or not. The investigators are interested in finding out whether the information recorded using the camera mirrors the assessment made by the clinician.

Inclusion Criteria:

Diagnosis of:

• Poly-articular JIA
• Oligo-articular JIA
• Psoriatic JIA
• Enthesitis-related JIA

Exclusion Criteria:

CYP below 4 years of age (pGALS is validated for school-age children and patients will be required to remain still during TI process)

Ongoing active/chronic infection requiring hospitalisation or treatment with intravenous antibiotics within 30 days of recruitment, or oral antibiotics within 14 days of recruitment

History of active tuberculosis of less than 6 months treatment or untreated latent tuberculosis

Soft tissue infection, injury or fracture of the affected joint which could confound the TI signature

Presence of any inflammatory skin condition (including, but not limited to Eczema and Psoriasis) which may be in close proximity to or overlying the joint

Presence of any other diagnosis which could cause arthritis including systemic-JIA (associated systemic inflammation may affect skin temperature independently of arthritis) or undifferentiated-JIA (excluded to ensure homogeneity of the sample investigated)

Non-English speaking patients and/or parent(s)/guardian(s)

Non-consenting CYP, or parent(s)/guardian(s)