Can innominate motion be used to identify persons with ankylosing spondylitis? A pilot study

Innominate movements during hip abduction and external rotation have recently been described in healthy individuals. In the present study the aim was to determine whether these hip movement tests could discriminate altered movement patterns in people with specific pelvic girdle pain (PGP) disorder. This pilot study is the first step in determining the usefulness of prone hip abduction and external rotation in the differential diagnosis of PGP disorders. A cross-sectional comparison between a convenient sample of 6 individuals who had been referred for exercise and advice following diagnosis of ankylosing spondylitis (AS) via a Medical/Rheumatological pathway and 18 healthy age and gender matched controls. Transverse and sagittal plane innominate motion was measured using a palpation and digitizing technique with a magnetic tracking device. Data analysis involved applying best-fit equations to the data and visual inspection of the produced graphs as well as conditional logistical regression for each test position to determine our ability to predict group association. Graphical comparisons demonstrate a distinction between the patients with AS and the healthy controls. Further, for all three hip conditions the innominate angle was a significant predictor of group association (p = 0.002 for AB, p = 0.005 for AB + ER and p = 0.007 for ER).