Citation, DOI, disclosures and article data
Citation:
Chmiel-Nowak M, Lustosa L, Thibodeau R, et al. Acetabular index. Reference article, Radiopaedia.org (Accessed on 25 Jan 2025) https://doi.org/10.53347/rID-74583
The acetabular index, also known as the acetabular roof angle or Tönnis angle, is a radiographic measurement of acetabular roof inclination. It is useful in assessing for developmental dysplasia of the hip (DDH) as well as pincer morphology in femoroacetabular impingement (FAI).
The acetabular index is measured on AP pelvic radiographs. First, a line is drawn from the medial edge of the acetabular sourcil and through to the most lateral aspect of the sourcil followed by a second line drawn in the horizontal plane of the pelvis and the angle is measured between these two lines 3,4.
Different normal ranges have been published by different authors:
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decreased acetabular inclination: <0° 5 or <3°
normal range: 0-10° 5 or 3-13° 2
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increased acetabular inclination: >10° 5 or >13° 4
History and etymology
The acetabular index has been first described by the American Orthopedic Surgeons Samuel Kleinberg and Herman Lieberman in 1936 6,7. An exact definition of the measurement has been made by the German orthopedic surgeon Dietrich Tönnis in 1984 8,9.
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1. Tannast M, Siebenrock K, Anderson S. Femoroacetabular Impingement: Radiographic Diagnosis--What the Radiologist Should Know. AJR Am J Roentgenol. 2007;188(6):1540-52. doi:10.2214/AJR.06.0921 - Pubmed
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2. Tannast M, Hanke M, Zheng G, Steppacher S, Siebenrock K. What Are the Radiographic Reference Values for Acetabular Under- and Overcoverage? Clin Orthop Relat Res. 2015;473(4):1234-46. doi:10.1007/s11999-014-4038-3 - Pubmed
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3. Welton K, Jesse M, Kraeutler M, Garabekyan T, Mei-Dan O. The Anteroposterior Pelvic Radiograph. J Bone Joint Surg. 2018;100(1):76-85. doi:10.2106/jbjs.17.00500 - Pubmed
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4. Fa L, Wang Q, Ma X. Superiority of the Modified Tönnis Angle over the Tönnis Angle in the Radiographic Diagnosis of Acetabular Dysplasia. Exp Ther Med. 2014;8(6):1934-8. doi:10.3892/etm.2014.2009 - Pubmed
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5. Clohisy J, Carlisle J, Beaulé P et al. A Systematic Approach to the Plain Radiographic Evaluation of the Young Adult Hip. J Bone Joint Surg Am. 2008;90 Suppl 4(Supplement_4):47-66. doi:10.2106/JBJS.H.00756 - Pubmed
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6.Kleinberg S. The Acetabular Index in Infants in Relation to Congenital Dislocation of the Hip. Arch Surg. 1936;32(6):1049. doi:10.1001/archsurg.1936.01180240137007
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7. Shin C, Yang E, Lim C, Yoo W, Choi I, Cho T. Which Acetabular Landmarks Are the Most Useful for Measuring the Acetabular Index and Center-Edge Angle in Developmental Dysplasia of the Hip? A Comparison of Two Methods. Clin Orthop Relat Res. 2020;478(9):2120-31. doi:10.1097/CORR.0000000000001289 - Pubmed
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8. Tönnis D. Die Angeborene Hüftdysplasie Und Hüftluxation Im Kindes- Und Erwachsenenalter. SpringerLink. 1984. doi:10.1007/978-3-662-06621-8
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9. Carlisle J, Zebala L, Shia D et al. Reliability of Various Observers in Determining Common Radiographic Parameters of Adult Hip Structural Anatomy. Iowa Orthop J. 2011;31:52-8. PMC3215114 - Pubmed
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