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Anterior Inferior Iliac Spine Morphology Correlates With Hip Range of Motion: A Classification System and Dynamic Model

  • Symposium: Advanced Hip Arthroscopy
  • Published:
Clinical Orthopaedics and Related Research®



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.


We characterized AIIS morphology in patients with hip impingement and tested the association between specific AIIS variants and hip range of motion.


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.


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.


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.

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Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

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We thank Robert M. Zbeda, BA, from the Hospital for Special Surgery, New York, NY, USA, and Gavin Duke, MD, from East River Medical Imaging, New York, NY, USA, for their part in performing interobserver assessments of anterior inferior iliac spine morphologies in this study. We thank Huong Do, MA, from the Epidemiology and Biostatistics Core, Hospital for Special Surgery, New York, NY, USA, and Joel Gagnier, PhD, from the University of Michigan, Ann Arbor, MI, USA, for their contributions in conducting data analysis in this study.

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Correspondence to Iftach Hetsroni MD.

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Each author certifies that he or she, or a member of his or her immediate family, has no funding or commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request.

Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.

This work was performed at the Hospital for Special Surgery, New York, NY, USA.

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Hetsroni, I., Poultsides, L., Bedi, A. et al. Anterior Inferior Iliac Spine Morphology Correlates With Hip Range of Motion: A Classification System and Dynamic Model. Clin Orthop Relat Res 471, 2497–2503 (2013).

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