The biopsychosocial model is well established in chronic low back pain (CLBP) research. Nevertheless, researchers to date have overlooked the biopsychosocial aspects of Inflammatory Low Back pain (ILBP). Most health care providers are biologically oriented in their treatment of ILBP, neglecting its possible multidimensional nature. It is true that people with ILBP may present with more complex pain and physical limitations than those with chronic non-specific low back pain (CNSLBP), but it remains unexplored whether or not these limitations are affected by the same pain factors that affect CNSLBP patients. This study aims to explore and compare the biopsychosocial back pain profiles of adults with ILBP and CNSLBP.

This is a multicentre case-control study that will compare back pain in patients with ankylosing spondylitis and CNSLBP. A multidimensional pain assessment will be conducted for patients in both groups. Each patient will be assessed on one occasion by the same experienced physiotherapist.

Inclusion Criteria:

• Adult between 18 and 65 years of age
• Low back pain >3 months
• On stable medication
• Ability to walk independently without an assistive device
• Specific inclusion criteria for AS group: clinical diagnosis of ankylosing spondylitis by a rheumatologist
• Specific inclusion for CNSLBP group: clinical diagnosis by a physician for CLBP

Exclusion Criteria:

• Spinal surgery or compression fracture within the last 6 months
• Cauda equine and conus medullaris syndromes
• Severe musculoskeletal conditions affecting the upper and/or the lower limbs, such as severe inflammatory arthritis of the peripheral joints
• Severe osteoporosis
• Leg-length discrepancy
• Cancer
• Morbid obesity, or pregnancy
• Progressive neurological disease
• Psychiatric disease and/or cognitive limitations that could affect the ability to complete the study questionnaires
• Inability to read and/or understand the English language
• Severe cardiac, respiratory or neurological diseases
• Uncontrolled epilepsy
• Specific exclusion criteria for CNSLBP group: Spondyloarthropathy, or any structural abnormalities in the lumbar spine that result in serious neurological dysfunction, such as stage III-IV lumbar disc herniation, and grade III-IV spondylolisthesis

A convenience sample of adults with Ankylosing Spondylitis (AS) will be consecutively recruited from a pool of patients referred to AS clinic in the Rheumatology and Physiotherapy Departments of St. James's and Tallaght Hospitals in Dublin.

Adults with chronic non-specifi low back pain (CNSLBP) (control group) will be consecutively recruited from a pool of patients referred to the Physiotherapy Department of St. James's and Tallaght Hospitals in Dublin. An invitation to participate in the study and an information leaflet will be extended to the patients who potentially meet the recruitment criteria.