Citation, DOI, disclosures and article data
Citation:
Chmiel-Nowak M, Knipe H, Baba Y, et al. Acetabular index. Reference article, Radiopaedia.org (Accessed on 19 Apr 2024) https://doi.org/10.53347/rID-74583
Disclosures:
At the time the article was last revised Henry Knipe had the following disclosures:
- Integral Diagnostics, Shareholder (ongoing)
- Micro-X Ltd, Shareholder (ongoing)
These were assessed during peer review and were determined to
not be relevant to the changes that were made.
View Henry Knipe's current disclosures
The acetabular index, also known as the acetabular roof angle or Tönnis angle, is a radiographic measurement of acetabular 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:
- decreased acetabular inclination: <0° 5 or <3°
- normal range: 0-10° 5 or 3-13° 2
- increased acetabular inclination: >10° 5 or >13° 4
- when the medial edge of the sourcil is blurred it makes this measurement difficult or impossible 4
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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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