Phase Lag of the Intersegmental Motion in Flexion-Extension of the Lumbar and Lumbosacral Spine

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Abstract
The lumbar and lumbosacral segmental motions were analyzed in vivo using cineradiographic method. To reveal the in vivo motion behavior of the lumbar and lumbosacral segments and their contribution to the whole lumbar motion. Relation between the lumbar motion and hip joint motion has been well investigated. The lumbar motion preceded the hip flexion in forward bending 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. Eight healthy male subjects participated in this study. The lower lumbar and lumbosacral motion (L3-S1) was recorded using cineradiography during flexion and extension. Each trunk motion was carried out from the neutral position to the maximum position. Segmental rotation and translation were measured sequentially at the L3-L4, L4-L5, and L5-S1 motion segments. Intersegmental motion lags were observed between the lumbar and lumbosacral motion segments during flexion. The lower lumbar and lumbosacral motion (L3-S1) was initiated at the L3-L4 motion segment. The L4-L5 segmental motion delayed from the L3-L4 motion by an average of 6° and preceded the L5-S1 motion by an average of 8°. In extension, motions in the L3-L4 and L4-L5 segments were small, and the L5-S1 segmental motion only contributed to the total lower lumbar motion. The lumbar and lumbosacral segmental motions occurred not simultaneously but stepwise from the upper level with intersegmental motion lags during flexion. These intersegmental motion 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.