title: Anterior inferior iliac spine morphology correlates with hip range of motion: a classification system and dynamic model.
abstract: BACKGROUND
  The anterior inferior iliac spine (AIIS) contributes to hip dysfunction in patients with symptomatic impingement and resection of a prominent AIIS can reportedly improve function. However, the variability of the AIIS morphology and whether that variability correlates with risk of associated symptomatic impingement are unclear.
  
  
  OBJECTIVE
  We characterized AIIS morphology in patients with hip impingement and tested the association between specific AIIS variants and hip range of motion.
  
  
  METHODS
  We evaluated three-dimensional CT reconstructions of 53 hips (53 patients) with impingement and defined three morphological AIIS variants: Type I when there was a smooth ilium wall between the AIIS and the acetabular rim, Type II when the AIIS extended to the level of the rim, and Type III when the AIIS extended distally to the acetabular rim. A separate cohort of 78 hips (78 patients) with impingement was used to compare hip range of motion among the three AIIS types.
  
  
  RESULTS
  Mean hip flexion was limited to 120°, 107°, and 93° in hips with Type I, Type II, and Type III AIIS, respectively. Mean internal rotation was limited to 21°, 11°, and 8° in hips with Type I, Type II, and Type III AIIS, respectively.
  
  
  CONCLUSIONS
  When the AIIS is classified into three variants based on the relationship between the AIIS and the acetabular rim in patients with impingement, Type II and III variants are associated with a decrease in hip flexion and internal rotation, supporting the rationale for considering AIIS decompression for variants that extend to and below the rim.
authors: Department of Orthopedic Surgery, Meir General Hospital, Tsharnichovski Street 59, 44281, Kfar Saba, Israel. iftachhetsroni@gmail.com
authors: Iftach
authors: I
authors: Hetsroni
authors: Lazaros
authors: L
authors: Poultsides
authors: Asheesh
authors: A
authors: Bedi
authors: Christopher M
authors: CM
authors: Larson
authors: Bryan T
authors: BT
authors: Kelly
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D057925:Femoracetabular Impingement / Q000145:classification / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery; D006801:Humans; D007085:Ilium / Q000000981:diagnostic imaging*; D021621:Imaging, Three-Dimensional; D008297:Male; D011237:Predictive Value of Tests; D011857:Radiographic Image Interpretation, Computer-Assisted; D016059:Range of Motion, Articular; D012042:Registries; D014057:Tomography, X-Ray Computed; D055815:Young Adult