Methods for determining the accuracy of radiostereometric analysis (RSA)

Area of Science:

• Medical imaging
• Orthopedic biomechanics
• Radiographic analysis

Background:

• Accurate measurement of micromotion is crucial for orthopedic implants and fracture healing.
• Radiostereometric analysis (RSA) offers high precision for detecting minute movements.
• Assessing RSA accuracy in suboptimal clinical conditions, like spinal fusions, is essential.

Purpose of the Study:

• To determine the accuracy of RSA in a clinical series of spinal fusions.
• To evaluate the influence of rigid-body configuration on RSA precision.
• To correlate RSA accuracy with the condition number for marker configurations.

Main Methods:

• Test-retest methodology on a phantom under clinical spinal fusion conditions.
• Analysis of 3-D motion vectors (rotation and translation).
• Correlation of accuracy with the condition number, a marker configuration metric.
• Mathematical simulation of individual dimension accuracy using in-house software.

Main Results:

• RSA accuracy can be overestimated in individual clinical cases.
• Significant variations in accuracy were observed based on rigid-body configuration.
• The condition number explained up to 92% of the variation in overall rotation accuracy.
• Simulated accuracy (95% confidence) for rotation about the transverse axis varied from 0.4 to 4.6 degrees.

Conclusions:

• The condition number is a valuable predictor of overall RSA rotational accuracy.
• The condition number cannot solely assess accuracy for individual degrees of freedom.
• RSA accuracy in clinical spinal fusions is highly dependent on marker configuration and requires careful case-by-case evaluation.