Purpose of the study: To present the results of an independent mono-centric prospective study on patients with a mobile ProDisc-C implant. This cervical artificial disc replacement (CADR), which is one of the options for avoiding cervical spine fusion, was evaluated during two-years follow-up.
Material: A total of 61 patients underwent CADR with a ProDisc-C in one or two segments at the Department of Spinal Surgery of the University Hospital in Motol, Prague, in the period from October 2004 to May 2006. Of these, 39 were included in the study and followed up for 2 years at least. Except for one patient, one segment was replaced in all patients.
Methods: The surgical procedure recommended by the manufacturer (Synthes, USA) was used throughout the study. Clinical evaluation. Each patient was examined before and immediately after surgery, and followed up at 6 and 12 weeks, and 6, 12 and 24 months. At each follow-up the patient answered the questionnaire which included the Neck Disability Index (NDI) and Visual Analoque Scale (VAS) assessment for neck and radicular pain, analgesic use and the patient's satisfaction. Radiographic examination. Radiographs were taken in antero-posterior and lateral projection, and on bending films in flexion, extension and lateral flexion on both sides. The height of the intervertebral space of the involved segment and motion of the replaced and adjacent discs in flexion and extension were measured. The radiographs were examined for potential sinking, loosening, failure or migration of the implant. Statistical evaluation. The results were statistically analysed using Student's t-test.
Results: Clinical outcome. The NDI evaluation showed that the mean value of the index improved from 44.9 pre-operatively to 26.1 and 25.9 at 1 and 2 years of follow-up, respectively, i.e. by 42.5 % in two years. The mean VAS score for neck pain changed from 5.8 pre-operatively to 3.0 and 2.7 at post-operative years 1 and 2, respectively, which is an improvement by 53.7 % in two years. The mean VAS score for radicular pain improved from 6.3 to 2.9 and 2.8 at the same intervals, which is an improvement by 53.9 % in two years. Radiographic findings. The mean height of the affected intervertebral space was 3.2 mm before and 7.4 mm after surgery and it did not change significantly thereafter. The mean range of motion at the involved segment was 4.1 degrees before and 11.1 degrees after surgery. Statistical evaluation. In assessment of both neck and radicular pain, the difference between the mean VAS score pre-operatively and that 6 weeks post-operatively was significant (t=4.4 and t=5.3, respectively; p<0.05). The difference in mean VAS scores between 6 weeks and 3 months post-operatively was not significant (t=1.69 and t=0.3, respectively; p>0.05). At the next follow-ups the mean VAS scores changed only minimally and the differences were not significant. The difference between the mean NDI before and that at 6 weeks after surgery was significant (t=11; p<0.05) and significant was also the difference between 6 weeks and 3 months after surgery (t=3.8; p<0.05). After that changes were minimal and were not significant.
Discussion: Currently, mobile implants are in the focus of interest amongst spinal specialists, their materials and shapes, primary implant stability, the centre of rotation, indications for replacement and correct operative techniques being discussed. The situation appears similar to that of 20 years ago when large joint replacement was being introduced, and it is the future that will show the right development.
Conclusions: This two-year prospective study on patients with CADR shows very good and promising outcomes. It is evident that the implant increases the range of motion at the treated segment and reduces degenerative changes in the adjacent intervertebral spaces. On the other hand, CADR is associated with complications such as artificial disc kyphosis and heterotropic ossifications. An unequivocal requirement for a correct indication and a faultless operative technique was the conclusion drawn from a detailed analysis.