OBJECTIVETo investigate the biomechanical differences between the surgery and adjacent segments of intervertebral discs in the lower lumbar spine, which were implanted with Coflex into the segments of L4, and L5S1, respectively.

METHODSThree finite-element models (the model of the intact lower lumbar sacrum,the L4.5 and L5S1 segments implanted by Coflex) were developed, respectively. According to the spinal three-column loading theory, three models were forced by the physiological loads of upright standing, flexion and extension. The stress of the different areas of the disc annulus, the changes of intervertebral dorsal height and the degree of nucleus pulposus pressure were compared and analyzed.

RESULTSCoflex implanted into the L4.5 and L5S1 segments in compression and extension could both decrease the stress of the posterior area of intervertebral disc in the surgery segment, resist the changes of the intervertebral disc dorsal height and reduce the perssure of nucleus pulposus. Furthermore, the stress of the L5S1 segment decreased when Coflex fixed the L4.5 segment in extension. However, when Coflex fixed the L5S1 segment, the stress of L4.5 segment had no significant changes.

CONCLUSIONCoflex fixing the L4,5 and L5S1 segments can effectively decrease the stress of the surgery segmental discs, respectively. Furthermore, Coflex fixing L4,5 segment may play a biomechanical role in reducing the stress of L5S1 segment.