An image-free method of elbow external fixation surgery based on computer-assisted navigation: A cadaveric study

Background

Identifying the elbow flexion-extension (FE) motion axis is crucial for the precise placement of an elbow external fixator. Traditional x-ray fluoroscopy has high radiation exposure, low accuracy, poor repeatability, and is greatly influenced by individual experience.

Purpose

This study aimed to assess the feasibility and accuracy of a novel image-free method for elbow external fixation surgery based on computer-assisted navigation.

Methods

An optical positioning system was employed to track the motion trajectory of the forearm relative to the upper arm. This system works by emitting infrared signals detected by cameras to determine the spatial positions of markers attached to the limbs. The 3D principal components analysis (PCA) was used to determine the orientation of the elbow's rotation axis by analyzing the trajectory data. The 2D circle fitting method involved fitting a circle to the projected data points on a plane perpendicular to the identified axis, ensuring precise calculation of the rotation plane and axis. A custom graphical user interface (GUI) was developed to visualize the kinematics data and guide the placement of an axis pin for the external fixator.

Results

The kinematics data of elbow FE movements showed high repeatability with RMS-radius within 1 mm, RMS-coplane less than 2 mm, Deviation-center no more than 2 mm, and deviation angle within 1.5°.

Conclusions

The proposed image-free method improves the accuracy and repeatability of elbow external fixation surgery, increasing feasibility and security.