Capturing three-dimensional in vivo lumbar intervertebral joint kinematics using dynamic stereo-X-ray imaging

Area of Science:

• Biomechanics
• Spinal Imaging
• Orthopedics

Background:

• Accurate 3D lumbar spine kinematics are crucial for understanding spinal biomechanics.
• In vivo 3D motion capture of the lumbar spine during dynamic tasks presents significant technical challenges.
• Existing methods often lack the comprehensive 3D data needed for detailed analysis.

Purpose of the Study:

• To demonstrate a novel technique for acquiring true 3D lumbar vertebral kinematics in vivo.
• To capture these kinematics during a functional load-lifting task.
• To establish a baseline dataset for evaluating lumbar spinal function and improving biomechanical models.

Main Methods:

• Utilized a high-speed dynamic stereo-radiography (DSX) system.
• Employed a volumetric model-based bone tracking procedure with custom CT-derived 3D bone models.
• Acquired dynamic X-ray images (30 fps) of eight participants during weight-lifting tasks, with a radiation attenuator to improve image quality.

Main Results:

• Successfully derived continuous 3D intervertebral kinematics from L2 to S1.
• Observed simultaneous motion across all lumbar segments, with L5-S1 showing a reduced contribution and greater nonlinearity/variability in extension.
• Significant anterior-posterior (AP) translations (5.0 ± 0.3 mm) were noted, alongside small out-of-plane rotations and translations.

Conclusions:

• The demonstrated DSX technique effectively captures in vivo 3D lumbar kinematics during functional tasks.
• This capability addresses knowledge gaps in lumbar biomechanics and enhances the accuracy of kinematic inputs for biomechanical models.
• The technique supports the development of improved spinal implants, such as disk replacements, that better mimic natural lumbar function.