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Trigonometric Algorithm Defining the True Three-Dimensional Acetabular Cup Orientation: Correlation Between Measured

T E Snijders¹, T P C Schlösser^1,2, S M van Gaalen¹

¹Department of Orthopaedics, Clinical Orthopedic Research Center - mN, Diakonessenhuis Zeist, Zeist, the Netherlands.

JB & JS Open Access

|December 12, 2018

Summary

A new 3D trigonometric method accurately measures acetabular cup orientation in total hip arthroplasty. This reliable technique ensures consistent implant stability and surgical success, regardless of imaging method used.

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Area of Science:

Orthopedic surgery
Biomedical engineering
Medical imaging analysis

Background:

Acetabular cup orientation is critical for total hip arthroplasty (THA) success and implant stability.
Current measurement methods lack consensus due to varied imaging modalities and definitions.
A standardized 3-dimensional (3D) trigonometric approach offers unambiguous orientation definitions.

Purpose of the Study:

To validate and assess the reliability of a 3D trigonometric description for measuring acetabular cup orientation.

Main Methods:

Computed tomographic (CT) scans from 20 patients with 22 primary THA were analyzed.
Three observers independently measured coronal inclination, sagittal tilt, and transverse version on multiplanar reconstructions.
A trigonometric algorithm calculated the third plane angle from measurements in the other two planes; reliability was assessed using intraclass correlation coefficients (ICCs).

Main Results:

High ICCs were observed for measured vs. calculated angles: 0.953 (coronal inclination), 0.985 (sagittal tilt), and 0.982 (transverse version).
Excellent intraobserver and interobserver reliability were demonstrated across all measured angles (ICCs ranging from 0.978 to 0.992).

Conclusions:

The 3D trigonometric concept and algorithm provide a valid and reliable method for measuring acetabular cup orientation.
This method enables a consistent 3D definition of cup orientation, independent of imaging modality, by calculating transverse version from coronal inclination and sagittal tilt.