Sagittal plane rotation center of lower lumbar spine during a dynamic weight-lifting activity.

This study investigated the center of rotation (COR) of the intervertebral segments of the lower lumbar spine (L4-L5 and L5-S1 segments) in sagittal plane during a weight-lifting (3.6 kg in each hand) extension activity performed with the pelvis constrained. Seven healthy subjects were studied using a dual fluoroscopic imaging technique. Using the non-weightbearing, supine position during MRI scan as a reference, the average intervertebral flexion angles of the L4-L5 and L5-S1 were 6.6° and 5.3° at flexion position of the body, respectively, and were -1.8° and -3.5° at extension position of the body, respectively. The CORs of the lower lumbar spine were found segment-dependent and changed with the body postures. The CORs of the L4-L5 segment were at the location about 75% posterior from the anterior edge of the disc at flexion positions of the body, and moved to about 92% of the posterior portion of the disc at extension positions of the body. The CORs of the L5-S1 segment were at 95% posterior portion of the disc at flexion positions of the body, and moved outside of the posterior edge of the disc by about 12% of the disc length at extension positions of the body. These results could help understand the physiological motion characters of the lower lumbar spine. The data could also provide important insights for future improvement of artificial disc designs and surgical implantation of the discs that are aimed to reproduce normal spinal functions.