Lumbar spinal stenosis is one of the degenerative diseases which have increasingly grown, as the nation is transitioning to an aging society. Even though medication is readily available as treatment for lumbar spinal stenosis, surgical treatments can be considered if symptoms are severe. The most basic operation, laminectomy and decompression, alone, can bring about improvements of symptoms by alleviating the pressure of the nerve root, however if instability is evident on the radiograph or during surgery, spinal fusion will be performed, and will yield favorable results. On the contrary, it is also common knowledge that spinal fusion can give rise to a variety of complications afterwards. New surgical procedures and apparatuses have been developed and used in clinical practices in order to overcome these complications. One of these new concepts is posterior dynamic stabilization. The purpose of posterior dynamic stabilization is to enable the spine to adjust so that, by limiting the movement to the direction which causes the pain, patients can feel at ease. Until recently, interspinous devices have been developed and applied in clinical practices in order to improve the symptoms of patients. The device is inserted after decompression of the nerve root in between the spinous processes of the lumbar part, where the symptom is present. By doing so, it not only limits the extension (without impacting flexion, axial rotation, and lateral bending) but also, alleviates the load on the facet joint by playing a role as a shock absorber. However, it is also true that the practice of this surgery has been limited due to the reports showing that; halo formed between the contact surface of the bone and the metal device might be the cause of pain; and according to a follow-up survey, fractures of the spinous process, breakaway of apparatus and post-operative complication such as kyphosis may be present. This paper will investigate the usefulness of these devices again by looking at the fundamental biomechanical effect of interspinous devices and analyzing the thesis which has been previously published.

Purpose
To compare change in biomechanical function at operated and adjacent segments and clinical results after inserting three different designs of cervical artificial arthroplasty devices.
Materials and Methods
Retrospective analysis was performed for 60 patients who had undergone single level cervical artificial arthroplasty in authors’ hospital from November 2003 to January 2010. Bryan, Prestige LP and Prodisc– C artificial discs were used in 34, 17 and 9 patients respectively. We compared preoperative and postoperative biomechanical function of operated and adjacent segments radiographically and clinical results using VAS and NDI.
Results
Biomechanical results showed as follows: range of motion(ROM) of operated and overall cervical spine was well maintained postoperatively regardless of type of devices; Prodisc – C showed statistically significant recovery of sagittal alignment at the operated segment compared to preoperative status(p=0.021); adjacent level just inferior to the operated segment showed decrease in postoperative ROM with Bryan(p=0.000); anterior intervertebral height also decreased at that segment(p=0.001); no difference showed with VAS and NDI in the three artificial disc devices.
Conclusion
Clinical results of cervical artificial arthroplasty did not show significant difference during the follow-up period, but there were statistically significant changes in biomechanical function. Therefore, adequate selection of disc device is important in cervical arthroplasty.