The observation was institutional review board approved (Ethics Commission, Medical University Innsbruck – Austria). All patients at the two centres who met the inclusion/exclusion criteria provided written informed consent and were included in the trial. Patient selection was based on the following inclusion and exclusion criteria. Inclusion criteria: (1) 18 to 65 years of age, (2) a single cervical disc disease between the level C3 and C7, (3) failed conservative treatment of at least 6 weeks or in case of progressive nerve root or spinal cord compression and (4) a minimum Neck Disability Index (NDI) of 15 points (30 %). Exclusion criteria: (1) cervical instability defined by translation on flexion–extension radiographs compared to the adjacent level, (2) non-mobility of the level, (3) fused adjacent levels, (4) neck pain as the solitary symptom, (5) prior surgery at target level, (6) metabolic bone disease or endocrine disorders, (7) pregnancy, (8) traumatic injury of spine, (9) HIV, metastatic cancer, presence of infection and (10) allergy to materials used in the device.
From January 2011 to December 2012, CDRs using the ROTAIO Cervical Disc Prosthesis were performed in 45 patients. All patients were successfully included, 28 patients had their last follow-up 12 months postoperatively and 17 patients were available for 24 months follow-up (mean 16.5 ± 5.8 month) . There were 27 female and 18 male patients with a mean age of 43.7 ± 7.1 years (range: 28–65 years). Seven patients were treated at C4/5, 27 patients at C5/6 and 11 patients at C6/7. All patients showed radiculopathic disorders, 4 of them in combination with mild signs of myelopathy.
The ROTAIO Cervical Disc Prosthesis (Fig. 1) is intended to be used for disc replacement in the cervical spine (C3-C7). In addition to restoring disc height, its primary function is to maintain physiological movement in the affected segment. The ROTAIO Cervical Disc Prosthesis represents a new unconstrained implant with a variable centre of rotation which should enable physiological facet-guided movement. For maximum coverage of the vertebral body end plates a total of 16 different sizes are available with various surface areas and heights. The prosthesis is pre-mounted on an insertion bracket to avoid the need for intraoperative assembly. Instruments specially developed for use with the implant system are available to ensure safe application.
The prosthesis consists of a superior and an inferior end plate (Titanium alloy to ISO 5832-3) on which the sliding elements (Cobalt-chrome alloy to ISO 5832-12) are anchored and secured by means of a fixation pin. The implant design provides an optimum fit to the anatomy of the intervertebral space. Assembly of ROTAIO is done in an axial direction. This has the effect that the slide plate is radially surrounded by the cover plate, which prevents the sliding plate from dislodgement. For optimum primary stabilization the end plates have a toothed surface. A special blasting treatment of the end plates increases surface area and thus bony integration.
A standard right-sided anterior approach was routinely performed. The surgical technique was similar to those for a routine anterior cervical decompression. Implantation of the prosthesis was performed strictly following the manufacturer’s specifications and users´ manual. The endplate preparation was - corresponding to the design of the implant - performed using a high-speed drill followed by curetting the endplates with the manufacture´s trial-implant. The posterior longitudinal ligaments were completely removed in all cases. Any remaining superior posterior osteophytes overhanging the endplate were removed. All cases were treated by neurosurgical specialists who attended manufacture´s instruction lectures.
Clinical evaluations were performed using standardized questionnaires preoperatively, postoperatively before discharge, 3 to 6, 12 and 24 months after implantation. For the clinical outcome validated self-assessment outcome measures including neck disability index (NDI), patient satisfaction index (PSI), visual analogue scale (VAS) for neck and arm pain and patients overall satisfaction were recorded. Additionally the use of non-steroidal anti-inflammatory drugs (NSAID) was assessed. The NDI ranged from 0 to 50 and VAS scores from 0 to 10. Concerning PSI patients had to answer the question, “Would you like to have the same treatment for the same ailment again?” with (1) definitely yes, (2) probably yes, (3) probably not or (4) definitely not. The use of NSAIDs was defined as: (1) never, (2) seldom; 1 to 3 times a week, (3) often; 3 to 5 times a week or (4) always; 1 or more times a day. The preoperative scores were compared with the follow-up scores. To analyse overall satisfaction, the patient had to rate their improvement in (1) excellent, (2) significantly better, (3) good, (4) mild, (5) no improvement or (6) worsening of ailment. Complications were intended to be recorded during surgery and at final follow-up.
Radiographic imaging observed the prosthesis position and function, possible signs of fusion or adjacent segment degeneration in neutral lateral and dynamic flexion and extension X-rays. To evaluate angular range of motion within the treated functional unit the Cobb-technique on dynamic lateral radiographs was used. For each measurement the mean of two observers were calculated and recorded for analysis. In four patients (index level C6/7) radiographic assessment was not possible because of prominent shoulders obscuring the images. All measurements were performed on source-digitalized images using IMPAX EE imaging software (AGFA HealthCare N.V., Belgium).
Statistical analyses were performed using IBM SPSS Statistics Version 20. The trial was designed to detect an absolute difference between pre- and postoperative data of one standard deviation with a power of 80 % at a two sided significance level (probability (p)-value) of 0.05 and a maximal dropout rate of 20 %. Comparisons were performed with the use of an unpaired t-test, or in case of nonparametric values with a Mann-Whitney-U test. Because data analysis did not show a statistically significant difference (p > 0.05) between the 12 months and the 24 months follow-up the results are presented combined under the term “last follow up”.