Rarely involved and high damage-burden joints in juvenile idiopathic arthritis: insights from the elbow, temporomandibular joint, cervical spine, hip, and shoulder.

UNLABELLED: The purpose of this study is to characterize clinical features, treatment patterns, and outcomes of rare and/or high damage-burden joints in juvenile idiopathic arthritis (JIA). Patients diagnosed with JIA between January 2008 and June 2025 were included in this retrospective study. Joints involved in less than 10% of the cohort were defined as "rarely involved," and joints contributing to the total JADI-A score of the cohort were defined as "high damage-burden" joints. Among 155 patients included, temporomandibular joint (TMJ) (7.7%), cervical spine (3.9%), and shoulder (1.9%) were defined as rarely involved joints. The joints contributing most to the total JADI-A score of the cohort, including TMJ (29%), elbow (29%), and hip (19.4%), were defined as high damage-burden joints. Polyarticular disease course was the most common pattern for elbow and TMJ involvement, whereas enthesitis-related arthritis was common for hip involvement. Patients with either one of these five involvements experienced more extensive involvement, more frequent articular relapses, and higher disease activity, frequent use of bDMARDs, and rarely achieved remission off medication (ROM) (p < 0.05). Polyarticular disease course and higher ESR at diagnosis were associated with higher odds of high damage-burden joint involvement (p < 0.05).

CONCLUSION: Elbow, hip, TMJ, cervical spine, and shoulder are rare and/or high damage-burden joints of JIA. These joint involvements seem to relate to higher disease activity, more extensive disease, arthritis relapses, frequent use of bDMARDs, rare achievement of ROM, and a risk for joint damage. More extensive inflammatory disease may predispose to involvement of rare and/or high damage-burden joints.

WHAT IS KNOWN: • Advances in the treatment of JIA, particularly the more widespread use of biologics, have led to significant improvements in long-term outcomes. • Suboptimal results are still encountered in JIA patients, even in the "biologic era."

WHAT IS NEW: • Temporomandibular joint (TMJ), cervical spine, and shoulder are among the least frequently involved joints in JIA, while TMJ, elbow, and hip are associated with a high damage burden. • These five joints seem to relate to higher disease activity, more extensive disease, articular relapses, frequent use of biologic agents, rare achievement of remission off medication, and a risk of joint damage.