Consequences of Juvenile Idiopathic Arthritis on Single Leg Squat Performance in Youth

Objective Juvenile idiopathic arthritis (JIA) affects body structure and function outcomes that may increase the risk of acute joint injury. The purpose of this study was to examine single leg squat (SLS) biomechanics for youth with JIA and their healthy peers. The study design was a matched pair cohort study. Methods Sixty‐five youth (JIA n = 30; control n = 35) participated in this ethics‐approved study. Participants performed 3 sets of 5 consecutive SLS tasks. Disease activity and functional status were assessed using the Juvenile Arthritis Disease Activity Score and Child Health Assessment Questionnaire. Indexed (most‐affected leg [JIA]; dominant leg [control]) and contralateral extremity biomechanics were obtained using a 12‐camera system. Outcomes included hip flexion/extension (FE), adduction/abduction (AA), and internal/external (IE) rotation range of motion (ROM). Data were analyzed using a multivariate random coefficient model in R (α⍺ = 0.05). Results A total of 29 matched pairs were analyzed. Youth with JIA had low disease activity and performed the SLS with a more internally rotated hip (indexed leg P = 0.023, β = –1.9°). Female participants displayed greater hip FE (indexed leg P = 0.015, β = –4.3°; contralateral leg P = 0.005, β = –4.8°) and IE ROM (indexed leg P = 0.021, β = –2.1°) than male participants. Associations were observed for body mass index and hip IE ROM (contralateral leg P = 0.001, β = –0.4°), knee flexion angle, and hip FE ROM (indexed leg P = 0.001, β = 0.4°; contralateral leg P = 0.001, β = 0.5°) and AA (indexed leg P = 0.010, β = 0.1°; contralateral leg P = 0.002, β = 0.2°). Conclusion This study identified functional alterations for an SLS in youth with JIA. These findings support the use of physical therapy as part of a multidisciplinary management approach, to restore normal hip posture and movement.