Background/Purpose: Hip involvement is the most frequent extraspinal arthritic manifestation of Ankylosing Spondylitis (AS) and a common cause of disability. It is present in 24% to 36% of AS patients, leading to total hip replacement (THR) in 5%. The purpose of this study was to examine the prevalence of hip arthritis in AS, to identify predictors of its development and possible gender differences.

Methods: 241 consecutive AS patients (162 men, age: 48.6±11years (mean±SD), disease duration: 23.6 ±11.2 years) were included in this cross-sectional study. The patients received initially: etanercept (n=117), adalimumab (n=89) infliximab (n=25), or golimumab (n=10). Anteroposterior X-rays of the pelvis, obtained before anti-TNF treatment initiation (i.e. baseline), were scored according to BASRI-hip scoring system. In parallel, the lateral x-rays of cervical and lumbar spine were scored using the mSASSS. The patients’ disease activity and functional limitation, prior entering anti-TNF treatment, were recorded by BASDAI, ASDAS-CRP/ESR, BASFI and BASMI. Mann-Whitney, two-sample t-test and logistic regression analysis were applied. The groups averages are expressed as mean±SD, or median(IQR) according to the normality of data.

Results: Hip involvement was assessed both clinically (as pain, reduced range of motion and intermalleolar distance) and radiographically, as BASRI-h score ≥ 2 at baseline anteroposterior pelvis X-rays. Definite hip involvement was detected in 85/241(35%) patients. Bilateral THR and unilateral THR underwent 10/241(4%) and 6/241(2.5%) patients respectively. No gender difference was observed (females: 25/85(30%) vs. males 54/156(35%). The patients with hip arthritis had significantly higher BASDAI-scores (6.1± 1.7 vs. 5.4± 1.9, p=0.03), ASDAS-CRP (3.9± 0.8 vs. 3.4± 0.9, p<0.0001), CRP [12.4(4.2-32) median(IQR) vs. 7(2.5-21), p=0.001], ESR [26(8-39) vs. 14(7-30), p=0.006], compared to those without. Additionally, the aforementioned patients had higher BASFI-score (6.2±1.9vs. 4.8± 2.3, p<0.0001), BASMI-score (5±2.3vs. 3.3± 1.9, p<0.0001) and reduced intermalleolar distance (88±23 vs. 104±19 cm, p<0.0001). AS patients with hip arthritis had also higher mSASSS-scores [13.5 (2- 38.5) vs. 3(0-14), p<0.0001] and increased percentage of presence of syndesmophytes [52/84 (62%) vs.58/153 (38%), p=0.001] and peripheral arthritis [48/83 (58%) vs. 66/155 (42%), p=0.001). According to multivariate logistic regression analysis, independent risk factors for hip arthritis in AS are: ASDAS-CRP (OR:1.8, CI: 1.2-2.8), presence of syndesmophytes (OR: 2.4, CI: 1.2-5) and intermalleolar distance(OR: 0.97, CI: 0.95-0.9).

Conclusion: The prevalence of hip arthritis in AS is very high (1/3) and related to high disease activity and a high mSASSscore. No gender difference in prevalence of hip arthritis was found. Considering the large impact on function, this manifestation might need more attention.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/high-prevalence-of-hip-arthritis-in-patients-with-ankylosing-spondylitis-treated-with-tnf-inhibitors/