Ankylosing spondylitis
Factors Associated with Radiographic Spinal Involvement and Hip Involvement in Ankylosing Spondylitis

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Objectives

To determine the factors associated with radiographic spinal involvement and hip involvement in ankylosing spondylitis (AS) and assess the influence of the damage seen in the radiographs on functional outcome in patients with AS.

Methods

We included 531 consecutive patients and recorded the clinical, laboratory, and radiographic data. Based on the spinal radiographs, patients were classified into 3 categories: (1) no spinal involvement; (2) spinal involvement without fusion; and (3) spinal involvement with fusion. Hip involvement was assessed by the Bath Ankylosing Spondylitis Radiology Hip Index and defined by a score of at least 2. Logistic regression analyses were used to investigate the factors associated with the radiographic spine and hip involvements.

Results

Ninety-eight (18.5%) patients had radiographic evidence of spinal fusion and 48 (9.0%) had radiographic evidence of hip involvement. Patients who had longer disease duration, elevated C-reactive protein levels, advanced sacroiliitis, and radiographic hip involvement were significantly more likely to have spinal fusion (P < 0.05). Elevated C-reactive protein levels and advanced sacroiliitis were also significantly associated with the presence of spinal involvement without fusion (P < 0.05). Early disease onset and more radiographic severity in the spine and sacroiliac joints were the predictors of radiographic hip involvement (P < 0.05). Patients with either spine or hip involvement had significantly higher Bath Ankylosing Spondylitis Functional Index scores (P < 0.001).

Conclusion

There is a relationship between radiographic sacroiliitis, spinal fusion, and hip involvement in patients with AS. Damage to the spine and hip seen radiographically can contribute to functional impairment.

Section snippets

Patients and Clinical Assessments

We consecutively enrolled 531 patients from our rheumatology outpatient clinics. All patients had a complete set of radiographs and met the 1984 modified New York criteria for definite AS (2). For each patient, we recorded age, gender, age at disease onset, disease duration, main features, the presence of HLA-B27 antigen, and treatment. No biological agents had been used in these patients. The main features were reviewed retrospectively by clinical history and/or medical records; features

Characteristics of Patients Based on the Different Types of Radiographically Seen Damage in the Spine

Table 1 describes the disease-related characteristics of the AS patients according to the radiographic involvement in the spine. Ninety-eight (18.5%) patients had spinal involvement with fusion, 142 (26.7%) had spinal involvement without fusion, and 291 (54.8%) had no spinal involvement, using the mSASSS definition. Patients with spinal abnormalities on radiography were more frequently male and were more likely to have hip disease, an enthesitis history, and a reduced ability to exercise. No

Discussion

In this study, we investigated the factors associated with radiographic evidence of spinal fusion and hip involvement in patients with AS. Radiographic imaging is an objective measurement to assess disease severity and outcome. It was not surprising that disease duration was an important factor associated with spinal fusion. An elevated CRP level, advanced radiographic sacroiliitis, and hip involvement were the predictors for development of spinal fusion, and the former 2 were also the

Acknowledgments

The authors would like to thank the participants and staff who contributed to the study.

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  • Cited by (0)

    This study was funded by the National Science Council of Taiwan and Taipei Veterans General Hospital.

    The authors have no conflicts of interest to disclose.

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