Quantification of continuous in vivo flexion-extension kinematics and intervertebral strains.

Purpose: Healthy subjects performed lumbar flexion and were assessed by video fluoroscopy to measure the in vivo kinematics of the lower lumbar motion segments.

Methods: Fifteen healthy subjects (8 male, 7 female, 28 ± 10 years) performed lumbar flexion and extension back to neutral while their vertebrae were imaged. The sagittal plane vertebral margins of L3-S1 were identified. Lumbar angle, segmental margin strains, axial displacements, anterior-posterior (A-P) translations, and segmental rotations over the course of flexion were measured.

Results: L4-L5 had the largest posterior margin Green strain (65%). Each segment displayed more axial displacement than A-P translation. Peak vertebral angulation occurred at approximately 75% of peak flexion during the extension phase.

Conclusion: L4-L5 exhibited the largest anterior and posterior margin strains (29 and 65%, respectively). Strains in the disc during in vivo lumbar flexion are due to both angular rotation and linear translation.