Segmental asymmetry and multiplanar motion of the lumbar spine: Cadaveric insights into spinal pathologies.

The lumbar spine plays a critical role in supporting multiplanar motion and distributing loads during daily activities. While global spinal symmetry is often assumed in biomechanical assessments, segmental asymmetries may exist and contribute to conditions such as low back pain (LBP). The present study investigates the multiplanar kinematic behavior and torque asymmetry of the lumbar spine using cadaveric specimens, focusing on identifying segmental asymmetries that may be masked in global motion analysis. A novel experimental setup combining a 6°-of-freedom robotic system with optical metrology was used to apply controlled flexion-extension, lateral bending, and axial rotation to human lumbar spines. The metrology system enabled precise, non-contact tracking of vertebral motion in three dimensions, ensuring accurate quantification of segmental kinematics. Symmetrical motion inputs were applied bilaterally during lateral bending and axial rotation, while torque responses were recorded. Segmental range of motion (ROM) and torque asymmetries were quantified in the coronal and axial planes. Despite symmetrical inputs, torque outputs showed asymmetries exceeding 15 % in several specimens. Segmental ROM asymmetries were observed in most vertebrae, sometimes exceeding 40 %, and could vary across planes without consistent correlation. Notably, some spines exhibited segmental asymmetry despite overall torque symmetry, highlighting the limitations of global assessments. These findings underscore the importance of segment-level analysis in spinal biomechanics. Hidden asymmetries may have clinical implications for diagnosing and treating LBP. Spinal pathologies and alignment appear to partially account for subject-specific asymmetries in lateral bending and axial rotation.