- Phase II. The US Severity Score developed as described above will be tested for correlation with the Clinical Severity Score. An additional 30 subjects meeting inclusion criteria will be enrolled and assessed for arthritis by physical exam performed by a pediatric rheumatologist followed by an US exam performed by the PI. If the subject has more than 1 large or medium joint with arthritis, a single joint will be chosen by random selection. Based on the findings, the clinician will assign a clinical score, and the PI and the consulting rheumatologist will assign an US score based on the standardized US Severity Score obtained from Phase I. The PI and consulting rheumatologist will be masked to physical exam findings and the Clinical Severity Score. The US score will then be compared to the clinical score to assess how the US scoring relates with the standardized clinical measures.