Prevalence of radiographic morphology of anterior inferior iliac spine in the Thai population

Background: Subspine impingement, one of the causes of hip pain, is related to an abnormal morphology of the anterior inferior iliac spine (AIIS). AIIS morphology is evaluated using Hetsroni’s classification (types I to III). Objective: The purpose of the present study was to determine the prevalence of AIIS morphology in the Thai population. Materials and Methods: The pelvic three-dimensional computerized tomography (3D CT) reconstructions of patients were evaluated retrospectively. The inclusion criterion was an age between 18 and 50 years. The exclusion criteria were hips with a joint-space width less than 3.5 mm, hips with center-edge angles less than 20 degrees, patients with primary or secondary tumors around the hips, and hips with acetabular fractures. A series of four, 3D CT images of each patient, comprising anteroposterior, 30-degree oblique, 60-degree oblique, and lateral views, were independently reviewed by two physicians. Both raters repeated the evaluations after a 2-week interval. The differences between the raters were resolved by consensus. Results: The 3D CT reconstruction images of 112 hips of 75 patients with an average age of 38.8 years were evaluated. Forty-one patients (55%) were male. The most common AIIS morphology was type II, which was found in 72 hips (64%), followed by type I (40 hips, 36%). There were no hips with type III morphology in this series. There was also no significant difference in the AIIS morphologies of the males and females. Conclusion: The most common AIIS morphology in the Thai population is type II, followed by type I.