gms | German Medical Science

Objective: To elucidate the optimal cervical cage or prosthesis for patients suffering from cervical degeneration, a prospective randomized study in patients after single level cervical discectomy was enrolled. It consists of one arm, in which Elastic Spine Pad^TM (ESP) and Squale^TM are compared concerning the Neck Disability Index (NDI) in patients suffering from cervical stenosis (PNS) and a second arm, in which ESP is compared with Rotaio^TM in patients with cervical prolapse (PNR). ESP is a cervical prosthesis made of titanium endplates with an elastomer in between and could be interpreted as an elastic cage. Squale^TM is a ring-shaped PEEK cage and Rotaio^TM is a titanium prosthesis. To standardize the implanted device height and to reduce neck pain, the height was software assisted determined.

Methods: The software vertaplan^TM detects the worst segment of the considered spine region analyzing the movement recordings in inclination, neutral position and reclination from the plain X-rays. It repeats ROM (range of motion) analysis by using the best segment simulated in the worst to define optimal height of the device and considers current degeneration. After the segmental movement was cinematographically characterized by fluoroscopy examination of healthy volunteers, for CDS the biokinemetric triangle was inserted into the software, to be able to characterize movement of each segment, regarding the variation of the surface area of this triangle during movement, as we noticed that ROM of the adjacent levels is affected by the implanted device. ROM analysis, based on angular observations, requires complete execution of the movement to be able to make a meaningful comparison between single levels and different examinations whereas the triangle’s consideration characterizes movement behavior in a way which makes movement’s observation independent of its complete execution.

Results: In the patients enrolled in this study, significant changes (p<0.05) in movement characteristics of the adjacent levels could be shown depending on the implanted device. Segments communicate with each another, as it was observed, that the change caused by the implant propagated over several adjacent levels, until the changing finally disappeared.

Conclusion: Depending on the indication leading to surgery (stenosis in PNS or prolapse in PNR) a high-speed drill is used (PNS) or not (PNR) by a single surgeon. This individual bias requires that the implanted devices in PNS are 0.5mm higher than suggested by the software. The biokinemetric triangle significantly describes the segmental changes of motion characteristics. After completion this study, it may be shown whether the implant-specific changes in the movement characteristics of the adjacent levels lead to different courses of degeneration. Adjacent level disease would therefore be an implant-specific pattern and not the natural course.