Method for approximating the ISB pelvic coordinate system on unilateral landmarks on a hemipelvis

Area of Science:

• Biomechanics
• Orthopedics
• Medical Imaging

Background:

• Defining the International Society of Biomechanics (ISB) pelvic coordinate system is challenging with only a hemipelvis.
• Accurate pelvic coordinate systems are essential for force application, movement analysis, and literature comparison in biomechanics.

Purpose of the Study:

• To propose a method for approximating the ISB pelvic coordinate system using a hemipelvis.
• To enable biomechanical analyses when only unilateral pelvic data is available.

Main Methods:

• Utilized 66 human pelvic CT scans to establish both full pelvic ISB and hemipelvic coordinate systems (HP coordinate systems).
• Calculated inter-frame rotations to derive a generalized rotation for approximating the ISB system from HP system data.
• Validated the method using cross-validation with the Leave-one-out technique.

Main Results:

• A generalized rotation was derived, allowing approximation of the ISB coordinate system from a hemipelvis.
• The approximated ISB coordinate system showed a mean orientation difference of 5.49° ± 2.81° compared to the actual ISB system.
• Cross-validation indicated a minor increase in error angles (1.5%), demonstrating the method's reliability.

Conclusions:

• The proposed method effectively approximates the ISB pelvic coordinate system using unilateral landmarks.
• This technique offers significant benefits for in vitro and in silico biomechanical testing with hemipelvic specimens.