The Reliability and Validity of the Ankylosing Spondylitis Performance Index (ASPI) in Enthesitis-Related Arthritis

Enthesitis-related arthritis (ERA), which is considered the counterpart of adult spondyloarthropathies, is a human leukocyte antigen (HLA) B27-related subtype of juvenile idiopathic arthritis (JIA) characterized by enthesitis and arthritis, which can also affect the sacroiliac joints and axial spine. Compared to other JIA categories, ERA patients tend to have higher pain intensity, lower physical functionality, and poorer health status. Maintaining or improving physical functionality is one of the primary treatment goals for ERA patients. Physical functionality is also considered an important outcome measure for assessing disease course and effectiveness of treatment. When the literature is examined, it is seen that self-report-based questionnaires are used more frequently, and performance-based measurements are used less in the evaluation of ERA patients. The Ankylosing Spondylitis Performance Index (ASPI) is a physical performance test that consists of a combination of three reliable tests (bending, putting on socks, and standing up from the floor) developed from the Bath Ankylosing Spondylitis Functional Index (BASFI). It is reported that applying ASPI can provide more objective information about the improvement in physical functionality and a better estimate of the patients' abilities. ASPI has significant potential in this disease group, considering factors such as the fact that it was developed in adult spondyloarthropathy patients, which is the equivalent of ERA. However, its psychometric properties must be appropriate for the ASPI to be used in clinical settings and research. To our knowledge, no studies have been conducted in the current literature on the validity and reliability of the ASPI in ERA patients. Therefore, this study aimed to evaluate the test-retest reliability, construct validity, and minimal detectable change of the ASPI in assessing the physical function of patients with ERA.