Anatomical landmarks for acetabular abduction in adult hips: the teardrop vs. the inferior acetabular rim

  • Jin ParkEmail author
  • Gab Lae Kim
  • Kyu Hyun Yang
Original Article



The purpose of this study is to compare the acetabular teardrop (the structure located inferomedially in the acetabulum, just superior to the obturator foramen. The medial lip is the interior, and the lateral lip is the exterior of the acetabular wall) with the inferior acetabular rim as anatomical landmarks to measure the acetabular abduction angle (AAD) using coronal CT images from different levels.


Our retrospective study included 120 pelvic CT scans from patients with non-orthopedic pathologies or stress fractures of the proximal femur. The patients included 60 females with a mean age of 48 years (range 40–66) and 60 males with a mean age of 46 years (range 38–65). Each AAD was measured using coronal plane CT slices from five levels: AAD (+ 10) (10 mm anterior to the femoral head center), AAD (+ 5) (5 mm anterior to the femoral head center), AAD (0) (through the femoral head center), AAD (− 5) (5 mm posterior to the femoral head center), and AAD (− 10) (10 mm posterior to the femoral head center). The measurements were then divided into two groups: teardrop-based AADs [AAD (+ 10), AAD (+ 5), and AAD (0)] and rim-based AADs [AAD (− 5) and AAD (− 10)].


There were no mean significant differences in AAD within the groups, whereas the difference between the groups was significant. The mean teardrop-based AAD was quite significantly different from the mean rim-based AAD due to the use of different anatomical landmarks. Teardrop-based AADs are lower than rim-based AADs, leading to measurement differences of more than 10°.


AAD measurements considering the inferior acetabular rim can be more accurate than those considering the acetabular teardrop because the inferior rim represents the nearly hemispheric acetabulum better than does the teardrop. It is recommended to differentiate between the teardrop and the inferior acetabular rim when measuring AAD to avoid confusion regarding acetabular abduction.


Acetabular abduction Teardrop Inferior acetabular rim 


Author contributions

JP: project development, data collection, data analysis, manuscript writing. GLK: data collection, data analysis, manuscript writing. KHY: project development, data analysis.


There is no funding source.

Compliance with ethical standards

Conflicts of interest

The authors declare that they have no conflict of interest.

Research involving human participants or animals

This article does not contain any studies with human participants or animals performed by any of authors.


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Copyright information

© Springer-Verlag France SAS, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Orthopedic Surgery, College of Medicine, Kangdong Sacred Heart HospitalHallym UniversitySeoulSouth Korea
  2. 2.Department of Orthopedic Surgery, College of MedicineYonsei UniversitySeoulSouth Korea

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