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 this study was to determine the prevalence of AIIS morphology in the Thai population.

Materials and Methods: The pelvic three-dimensional computerized tomography (3D CT) reconstructionsof 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, comprisinganteroposterior, 30-degree oblique, 60-degree oblique, and lateral views, were independently reviewed by two physicians. Both raters repeated the evaluationsaftera 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 morphologiesof the males and females.

Conclusion:The most common AIIS morphology in the Thai population is type II, followed by type I.

Keywords: Anterior inferior iliac spine, subspine impingement, hip impingement, hip pain, groin pain