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

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

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.

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.

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.