Background: Juvenile idiopathic arthritis (JIA) is the most frequent rheumatic disease in children [1]. JIA can be responsible for progressive damage of large joints leading to functional impairment and disability. Hip involvement seems to be a predictive factor of a poor outcome in JIA patients [2].

Objectives: This study aimed to determine the frequency of hip involvement in JIA patients and to evaluate its associated factors.

Methods: We conducted a retrospective study, including children with JIA meeting the International League of Associations for Rheumatology (ILAR) 2010 criteria. For each patient, we collected the following data: age, JIA subtype, age at disease onset, disease duration, antinuclear antibodies (ANA), human leukocyte antigen B27 (HLA-B27), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels. Disease activity was assessed using the juvenile arthritis disease activity score 10 using normalized ESR (JADAS-10-ESR) for all JIA subtypes and the Juvenile Spondyloarthritis Disease Activity Index (JSpDA) for related-enthesitis arthritis (ERA) and psoriatic arthritis subtypes. Regarding hip involvement, the clinical and imaging findings (pelvic X-ray, ultrasound, and pelvic MRI) were recorded.

Results: In total, 72 children were included, with a mean age of 13.73 ± 5.06 years [2-28]. The male-to-female ratio was 1.11 (38/34). The mean age at the disease onset was 9.68 ± 4.1 years [1.5-18]. The mean disease duration of JIA was 4.44 ± 4.28 years [0.2-23].

The JIA subtypes recorded were as follows: ERA in 46% (n=33), oligoarticular in 21% (n=15), polyarticular in 11% (n=8) (negative rheumatoid factor in 5 patients), psoriatic arthritis in 11% (n=8), undifferentiated in 6% (n=4), and systemic-onset in 6% (n=4). The mean JADAS-10-ESR and JSpDA were 9.16 ± 5.44 [0-22.3] and 2.83 ± 1.68 [0-6], respectively. The mean ESR and CRP levels were 30.16 ± 26.61 [2-130] and 19.92 ± 26.16 mg/L [0.2-101], respectively. ANA and HLA-B27 were present in 16 patients (22%) and 9 patients (12%), respectively.

Hip involvement was noted in 44 patients (61%): 26 patients with ERA (59%), and 5 with oligoarticular JIA (11%). Polyarticular JIA, psoriatic arthritis, and undifferentiated JIA were each found in 4 patients with hip involvement. Hip involvement was bilateral in 25% of the cases (n=11).

In children with hip involvement, physical examination revealed hip pain in 93% (n=41), with a limited range of movement in 66% (n=29). Pelvic X-rays were performed in 82% of the patients (n=36) showing reduced joint space and/or erosions of the coxofemoral joint in 25% (n=11) and sacroiliitis in 36% (n=16). Ultrasound revealed abnormalities of the hip joint in 64% (n=28). It showed synovitis in 89% of the cases (n=25), intra-articular effusion in 25% (n=7), and enthesitis in one patient. Pelvic MRI was performed in 49 patients, revealing abnormalities of the hip joint in 63% (n=31). These abnormalities were: bone marrow edema in 42% (n=13), synovitis in 52% (n=16), articular effusion in 32% (n=10), and irregularities in 22% (n=7).

Hip involvement was significantly associated with male gender (74% vs 47%; p=0.021 ), the presence of ANA (69% vs 37%; p=0.028 ), and radiographic sacroiliitis (94% vs 45%, p=0.002 ). Furthermore, hip involvement was significantly more frequent in children with ERA ( p=0.018 ). Moreover, patients with hip involvement had higher JSpDA (3.33±1.6 vs 1.4±0.91; p=0.001 ). However, hip involvement was not correlated to the following parameters: age, disease duration, ESR, CRP, and JADAS-10-ESR. There was no association between hip involvement and the presence of HLA-B27.

Conclusion: Our study showed that hip involvement was frequent in JIA, particularly in the ERA subtype. The male gender, the presence of ANA, high disease activity, and radiographic sacroiliitis were associated factors with hip involvement in JIA.

REFERENCES: [1] Kahn P. Juvenile idiopathic arthritis: an update for the clinician. Bull NYU Hosp Jt Dis 2012; 70(3): 152-66.

[2] Naveen R, etal. Hip involvement in children with enthesitis-related arthritis (ERA) is associated with poor outcomes in adulthood. Clin Rheumatol . 2021;40(11):4619-4627.

Acknowledgements: NIL.

Disclosure of Interests: None declared.