The acetabular teardrop and its relevance to acetabular migration

Area of Science:

• Radiology
• Orthopedic Surgery
• Anatomy

Background:

• Acetabular migration is a critical indicator in hip joint assessment.
• The ilioischial line is a commonly used radiographic landmark, but its accuracy can be affected by imaging angles.
• A more consistent landmark is needed for precise measurement of acetabular migration.

Purpose of the Study:

• To determine the precise location and radiographic appearance of the acetabular teardrop figure.
• To compare the reliability of the acetabular teardrop versus the ilioischial line for measuring acetabular migration.

Main Methods:

• Five human pelvises were analyzed using photography, radiography, and sequential sectioning/reaming.
• The anatomical position of the acetabular teardrop was identified.
• Radiographic images were evaluated to assess the relationship between the ilioischial line, the acetabular teardrop, and parallax effects.

Main Results:

• The acetabular teardrop is consistently located inferomedially within the acetabulum, superior to the obturator foramen.
• The ilioischial line's projection over the medial acetabulum is variable and dependent on the anteroposterior (AP) roentgenogram angle.
• Parallax significantly alters the apparent relationship between the ilioischial line and the teardrop with minor changes in horizontal obliquity.

Conclusions:

• The acetabular teardrop is a well-defined and constant anatomical feature of the medial acetabular wall.
• The ilioischial line is less reliable due to its variable projection and susceptibility to parallax.
• The acetabular teardrop is recommended as a superior landmark for detecting and measuring medial and superior acetabular migration.