OBJECT The purpose of this study was to analyze the usefulness of the BioFlex, a Nitinol spring rod dynamic stabilization system, and the Nitinol shape memory loop (KIMPF-DI Fixing System) as a posterior dynamic stabilization system in surgery for low-back pain. METHODS The 103 patients who underwent treatment with the BioFlex system were divided into two groups: Group 1, dynamic stabilization with or without posterior lumbar interbody fusion (PLIF); and Group 2, rigid fixation (PLIF + BioFlex system only). A total of 66 segments were treated with only the BioFlex system; in these the preoperative range of motion (ROM) was 10.0 +/- 4.3 degrees , which changed to 4.1 +/- 1.9 degrees after surgery. Adjacent-segment ROM changed from 8.4 +/- 3.4 degrees to 10.7 +/- 3.2 degrees in Group 1 and from 6.5 +/- 3.2 degrees to 10.5 +/- 4.6 degrees in Group 2 postoperatively. A total of 110 segments received both BioFlex and PLIF, with a fusion rate of 90.0%. The visual analog scale score for back pain improved from 7.3 +/- 3.1 to 1.4 +/- 1.8 in Group 1 and from 7.4 +/- 2.4 to 2.1 +/- 2.3 in Group 2. The Oswestry Disability Index improved from 35.2 +/- 6.4 to 12.1 +/- 4.5 in Group 1 and from 37.8 +/- 5.7 to 13.6 +/- 4.2 in Group 2. (The ROM and assessment scores expressed are the mean +/- standard deviation.) The 194 patients in whom Nitinol memory loops were implanted were analyzed based on the preoperative and 1-year postoperative ROM of each lumbar segment. The change of ROM in looped segments treated with PLIF was significantly reduced, but the change of ROM in looped segments without PLIF was not significant. The change of ROM at the segment adjacent to the loop was not significant, and the change of kyphosis reflected a slight recovery. CONCLUSIONS The Nitinol BioFlex dynamic stabilization system can achieve stabilization and simultaneously allow physiological movement, which can in turn decrease the degeneration of adjacent segments. When used with PLIF, the fusion rate can be expected to increase. The flexible Nitinol shape memory loop, a posterior dynamic stabilization device, is an adequate tension band that displays strength similar to the posterior ligamentous structures. In combination with PLIF at the main lesion, the BioFlex system or the Nitinol memory loop can provide posterior dynamic stabilization to the transitional upper or lower segments, enhance the fusion rate, reduce the adjacent segment degeneration, and provide dynamic stabilization of the spine.