Concurrent validity of skin-based motion capture systems in measuring dynamic lumbar intervertebral angles

Area of Science:

• Biomechanics
• Spine Motion Analysis
• Medical Imaging

Background:

• External sensors like motion capture and accelerometers are common for spine kinematics.
• Skin-based measures have limitations in capturing direct intervertebral lumbar spine motion.
• Previous research focused on static trials, lacking dynamic range analysis.

Purpose of the Study:

• To investigate the agreement between skin-based sensors (accelerometers, motion capture) and quantitative fluoroscopy (QF) for lumbar spine kinematics.
• To analyze this agreement throughout the complete dynamic range of flexion and extension.
• To assess measurement accuracy in a healthy female population.

Main Methods:

• Twenty healthy female participants underwent a standing flexion and extension protocol.
• Lumbar spine kinematics were measured concurrently using QF (L2-S1) and skin-based sensors (L2, L4, S1).
• Intervertebral angles were compared between QF and skin-based measures.

Main Results:

• Non-parametric limits of agreement were greatest at end-range flexion and extension.
• Differences between QF and skin-based measures varied between participants, with inconsistent over/underestimation.
• Skin-based systems showed good agreement with each other, suggesting interchangeability for estimation.

Conclusions:

• Skin-based sensors can estimate lumbar spine kinematics but do not directly measure intervertebral motion.
• The assumption of linear increase in measurement error is disproven; variability is participant-dependent.
• Normalizing angles and considering instrumentation posture may reduce errors in dynamic spine motion analysis.