Ultrasound imaging for the rheumatologist XXXVII. Sonographic assessment of the hip in ankylosing spondylitis patients

Objectives: To investigate the prevalence of ultrasound (US) detectable inflammation in hips of patients with ankylosing spondylitis (AS) and the relationship between US and measures of disease activity and severity. Methods: Consecutive patients with AS attending the rheumatology units involved in this study were enrolled. Clinical and demographical data were recorded. US examination of bilateral hips was performed at the same time, evaluating anterior longitudinal scan to search for synovial hypertrophy (SH), joint effusion (JE) or power Doppler (PD) positive synovitis. Results: A total of 56 patients were included, median age (interquartile range, IQR) 49 (39, 59.5), median disease duration 98 (72, 204) months, 80.3% were treated with TNF-α inhibitors, median BASDAI 2.65 (1.96, 3.95), 30.3% had hip tenderness. US JE was found in 26.7% of patients, US SH in 16%, no patient had detectable PD. The concordance between clinical findings and US abnormalities was moderate, with a kappa of 0.44. Patients with detectable US abnormalities had higher median visual analogue scale (VAS) pain and C-reactive protein (CRP), while there was no significant association with other measures of disease activity and disability. In the subgroup of patients with no hip tenderness, US alterations were still significantly related to higher CRP levels, while in patients with hip tenderness and no US abnormalities CRP was not higher than in the asymptomatic patients. Conclusions: US assessment of hip joint in AS patients can be considered of value, as suggested by the correlation with relevant clinical and laboratory measures. In asymptomatic patients, US examination might provide further information on subclinical involvement.