Non-invasive computer-assisted measurement of knee alignment

Area of Science:

• Orthopaedic biomechanics
• Medical imaging technology
• Clinical assessment

Background:

• Accurate knee alignment quantification is crucial in orthopaedics for disease monitoring and treatment planning.
• Current radiographic methods have limitations, necessitating improved techniques.
• Non-invasive methods are desirable for patient comfort and reduced radiation exposure.

Purpose of the Study:

• To validate an image-free navigation system for non-invasive knee alignment measurement.
• To assess the system's repeatability and agreement under various conditions (supine, standing, stress).
• To compare the system's performance against established methods or models.

Main Methods:

• An image-free navigation system was adapted using external infrared tracker mountings.
• Mechanical femoro-tibial (MFT) angle measurements were taken on a volunteer and leg model for stability assessment.
• Thirty asymptomatic volunteers underwent measurements in supine, standing, and varus-valgus stress positions.
• Intra- and inter-registration repeatability were assessed using mean difference and 95% limits of agreement.

Main Results:

• The navigation system demonstrated good intra-registration repeatability for coronal alignment (±1°).
• Sagittal alignment measurements were approximately half as repeatable as coronal measurements.
• Inter-registration agreement for supine MFT angles was ±1.6° (coronal) and ±2.3° (sagittal).
• Measurements under varus-valgus stress and standing positions showed varying degrees of agreement, with standing measurements less repeatable.

Conclusions:

• The developed navigation system provides repeatable, real-time measurements of knee alignment.
• It functions effectively under dynamic, real-time conditions, including stress maneuvers.
• This system presents a viable, non-invasive alternative to radiographic measurements in orthopaedic practice.