Patients and study design.
This was a cross-sectional study with health control. The study was performed following the Declaration of Helsinki principles and local regulations. The approval was permitted by the ethical committee of Peking University Shenzhen Hospital. All patients and healthy individuals signed informed consent.
Between December 2017 and December 2019, the study finally enrolled 104 patients with AS who fulfilled the modified New York criteria . All the patients were consecutively enrolled from the Department of Rheumatology and Immunology at Peking University Shenzhen Hospital.
The exclusion criteria included the following: a history of joint or ACW surgery; corticoid injection at the enthesis within the last six weeks; peripheral neuropathy; age <18 years; diseases other than AS; and an unwillingness to sign for consent, or did not finish all the examinations or patient-reported outcome measures (PROMs). If patients met one of the above conditions, they were excluded.
Fifty healthy persons were matched with AS patients in age, gender, and body mass index (BMI). They were selected among the hospital workers and healthy volunteers who did not have any symptoms at the entheses, without the diagnosis of spondyloarthritis or family history.
Data was collected by PROMs, laboratory data, and US assessments.
PROMs and laboratory data. All patients were examined by a qualified rheumatologist. The rheumatologist used PROMs. For each patient, the laboratory tests consisted of C reactive protein (CRP) and human leukocyte antigen B27 (HLA-B27). Disease activity was assessed by Disease Activity Score-CRP (ASDAS-CRP) and Bath Ankylosing Spondylitis Disease Activity Index (BASDAI). The interval between each examination was less than one week. The ASDAS-CRP value (VASDAS-CRP) indicated the disease activity of AS. When the value was <1.3, the disease was inactive. When the value was 1.3 ≤ VASDAS-CRP < 2.1, the disease activity was low. When the index was 2.1 ≤ VASDAS-CRP < 3.5, the disease activity was high. When the index was ≥3.5, the disease activity was very high. BASDAI was a self-assessment form to measure disease activity. It had six questions, and each question was scored from 0 to 10. When the overall score was ≥4, it indicated disease activity. Otherwise, it indicated disease inactivity. A higher score reflected a more active disease.
US assessment. Ultrasonography was performed using Toshiba Aplio 400 equipment with a linear transducer with a frequency of 7-18 MHz by an experienced sonographer who had taken part in musculoskeletal US for more than five years. All subjects were examined by grey scale and power Doppler ultrasonography. Doppler settings were standard with a pulse repetition frequency of 1000 Hz, low wall filter, and Doppler gain at a level of just below random noise. The sonographer was blinded to clinical information, and people were advised not to talk with the US examiner. US was used to evaluate 34 entheses in the upper limbs, lower limbs, trunk, and ACW. The upper limbs contained three bilateral entheses: common extensor tendon (CET), common flexor tendon (CFT), and supraspinatus tendon (SST). The lower limbs were comprised of seven bilateral entheses: quadriceps tendon (QT), proximal patella tendon (PPT), distal patella tendon (DPT), lateral collateral ligament (LCL) on the lateral femoral condyle, medial collateral ligament (MCL) on the medial femoral condyle, Achilles tendon (AT) on the calcaneus, and plantar fascia (PF). The trunk consisted of two entheses: the bilateral anterosuperior iliac spine (ASIS) and the single pubic symphysis (PS). The ACW included three entheses: bilateral sternoclavicular joint (SCJ), single manubriosternal junction (MSJ), and costochondral joint (CCJ), in which the CCJ included eight bilateral entheses from the 2nd to 5th ribs. Each site was scanned in both longitudinal and transverse planes and the images were saved. Examinations of the SST, CET, and CFT were performed in a sitting position. The QT, PPT, DPT, LCL, and MCL were assessed with the individual in the supine position with knee flexion at 30-60°. The AT and PF were examined in a prone position with the feet hanging off of the bedside. The remaining entheses were evaluated in a supine position with the elbow contacting the body. All the standardized examinations were followed by the European Society of Musculoskeletal Radiology (ESSR).
US definition. Elemental US lesions of enthesitis were as follows (Figure 1): ①hypoechogenicity with lack of the normal homogeneous fibrillar pattern; ② increased thickness measured at the insertion of 2 mm near the bone cortex, and the data followed Glasgow Ultrasound Enthesitis Scoring System (GUESS) ; ③ erosion with cortical breakage with contour defect in both longitudinal and transverse planes; ④ calcification: hyperechoic foci or bony prominence at the end of the bone contour, with or without acoustic shadow; ⑤ bursitis: the locations of bursitis consisted of suprapatellar, infrapatellar, and retrocalcaneal bursas, with the normal anteroposterior diameter less than 5 mm, 2 mm, and 3 mm, respectively ; and ⑥ Doppler signal at the insertion 2 mm near the bone surface with the tendon or ligament at a relaxation position. Enthesis US scores followed the MASEI: calcification (0-3), erosion (0 or 3), Doppler signal (0 or 3), hypoechogenicity (0-1), increased thickness (0-1), and bursitis (0-1). The US images were read by two sonographers. If there was a difference in opinion, a third sonographer would help to make a decision. A definition of enthesis US positive was at least one abnormal enthesis in one site. Acute echogenicity consisted of hypoechogenicity, increased thickness, bursitis, and Doppler signal. Chronic echogenicity included erosion and calcification.
The quantitative data were shown by mean ± standard deviation (SD), and the qualitative data were shown by percentages. A Student’s t test or Mann-Whitney U test was used for the quantitative analysis. Chi-square test (or Fisher exact test when appropriate) was used for the categorical data. According to Spearman’s correlation coefficient, correlations between disease activity and US scores were obtained. Values of p < 0.05 were significant. SPSS version 23.0 software (IBM, Armonk, NY, USA) was used for all data analyses.