PHASE-LAG OF THE INTERSEGMENTAL MOTION IN FLEXION-EXTENSION OF THE LUMBAR AND LUMBOSACRAL SPINE - AN IN-VIVO STUDY

Study Design. The lumbar and lumbosacral segmental motions were analyz ed in vivo using cineradiographic method. Objectives. To reveal the in vivo motion behavior of the lumbar and lumbosacral segments and their contribution to the whole lumbar motion. Summary of Background Data. Relation between the lumbar motion and hip joint motion has been well investigated. The lumbar motion preceded the hip flexion in forward be nding and delayed from extension of the hip joints in backward bending . However, it remains unclear how the lumbar and lumbosacral segmental motion contributed to the whole lumbar motion in vivo. Methods. Eight healthy male subjects participated in this study. The lower lumbar an d lumbosacral motion (L3-S1) was recorded using cineradiography during flexion and extension. Each trunk motion was carried out from the neu tral position to the maximum position. Segmental rotation and translat ion were measured sequentially at the L3-L4, L4-L5, and L5-S1 motion s egments. Results. Intersegmental motion lags were observed between the lumbar and lumbosacral motion segments during flexion. The lower lumb ar and lumbosacral motion (L3-S1) was initiated at the L3-L4 motion se gment. The L4-L5 segmental motion delayed from the L3-L4 motion by an average of 6 degrees and preceded the L5-S1 motion by an average of 8 degrees. In extension, motions in the L3-L4 and L4-L5 segments were sm all, and the L5-S1 segmental motion only contributed to the total lowe r lumbar motion. Conclusions. The lumbar and lumbosacral segmental mot ions occurred not simultaneously but stepwise from the upper level wit h intersegmental motion lags during flexion. These intersegmental moti on lags were much larger than the neutral zone in vitro, which implied the neutral zone in vivo should be different from the neutral zone in vitro.