Ward MM- Researchers investigated 52,568 cases with ankylosing spondylitis (AS) and 4,617,179 subjects without AS from the year 1999 to 2013 to ascertain the risks of primary total hip arthroplasty (THA) and total knee arthroplasty (TKA) in older candidates (< 75 yrs old) with AS. They noted a double rate of incidence of THA in subjects with AS from 4.5 per 1000 patient-years (PY) to 9.6 per 1000 PY. They also observed the higher rates of primary TKA among candidates with AS and THA than among those without THA as the standardized incidence of primary TKA in AS was 12.3 per 1000 PY vs 5.7 per 1000 PY in the parallel group. They indicated that increased risk of TKA in AS might be an outcome of collapse from knee inflammation or alterations in lower limb biomechanics due to hip arthritis.