Sagittal spinal alignment in patients with ankylosing spondylitis by rasterstereographic back shape analysis: an observational retrospective study

BACKGROUND: Ankylosing spondylitis (AS) is a chronic-inflammatory disorder involving the sacroiliac-joints, spine, and spinal ligaments. A proper understanding of the sagittal plane alignment and posture is essential in managing deformities of the spine. AIM: The aim of this study was to evaluate the differences in sagittal plane alignment between patients with AS and healthy subjects by means of rasterstereography and to analyze the relationship between clinical assessments and postural features. DESIGN: Observational retrospective study. SETTING: This study took place from January 2012 to April 2014 at the rheumatologic out-patient clinic, Umberto I Hospital, Rome, Italy. POPULATION: Forty-six healthy subjects and twenty-five AS patients were enrolled in the study. METHODS: Spinal posture was measured by the rasterstereographic system Formetric 4D. Trunk inclination, kyphosis angle, lordosis angle, cervical and lumbar plumbline distance, and sagittal pelvic alignment were analyzed. Differences between the two groups in postural parameters were compared (primary outcomes). Multiple regression analysis was used to evaluate if postural parameters could be predicted by the Bath Ankylosing Spondylitis Metrology Index (BASMI) that is a composite index of spinal mobility, disease duration and body mass index (secondary outcomes). RESULTS: Patients with AS showed a significant increase in the kyphosis angle and the cervical plumbline distance and a significant reduction in the lordosis angle and the sagittal pelvic alignment when compared to healthy subjects. According to multiple regression analysis, BASMI influenced the kyphosis angle value with a standardized coefficient β of 1.93, the lordosis-angle value with a standardized coefficient β of -2.79 and sagittal pelvic alignment value with a standardized coefficient-β of -2.93. CONCLUSIONS: Rasterstereography has proved to be a valid tool in monitoring change in spinal structure in AS patients and has shown a strong correlation with clinimetric parameters of AS (BASMI). Future studies are needed, with a greater number of patients, in order to better characterize the evidently existing relationship between postural changes in AS patients and rasterstereography. CLINICAL REHABILITATION IMPACT: Rasterstereography has proved to be a valid tool in monitoring postural changes in AS patients and has shown a strong correlation with clinical evaluations. Therefore, the assessment of postural characteristics using the rasterstereographic system before and after a specific exercise program would be a reliable and valid advice without exposing subjects to high doses of radiations.