Anterior Interbody Fusion of the Cervical Spine with a Zero-P Spacer. Radiographic Results with a Minimum Follow-up of One Year in a Prospective Study

PURPOSE OF THE STUDY The aim of this study was to compare the efficacy of anterior cervical microdiscectomy and fusion carried out using a newly designed interbody spacer with that of a standard cage plate construct in patients with symptomatic cervical spine spodylosis. The comparison was based on radiographic results and fusion rates. MATERIAL A total number of 113 consecutive patients were enrolled in this prospective study between October 2008 and July 2009. Mono- or bisegmental spondylosis was diagnosed in the patients in whom conservative treatment of cervicobrachial symptoms had had no effect. Patients with myelopathy were not included.. METHODS All patients underwent standard anterior microdiscectomy (at one or two levels). The novel anchored spacer Zero-P was used in 61 patients (group 1) and, in 52 patients, stabilisation was done using the interbody spacer Cornerstone and dynamic plate Premier (group 2). Lateral radiographic views of the cervical spine were obtained before surgery and at 6 weeks, and then at 3, 6 and 12 months after surgery. During follow-up, the cervical spine sagittal alignment (CobbC), segmental angle of the treated levels (CobbS), amount of segmental collapse and fusion rates were measured. RESULTS There was no significant difference in CobbC between the two groups during follow- up (p < 0.051). A significant difference in the first two values of CobbS was found (p < 0.001), but next changes in CobbS were without any difference in either group. The mean degree of interspace collapse was without any significant difference between the groups. The fusion rate was significantly higher in group 1 than group 2 nine months after surgery (p = 0.032), but was the same in both groups at 12 months after surgery (p = 1.0). CONCLUSIONS The anchored spacer Zero-P provides biomechanical stability for the cervical spine similar to the cage and dynamic plate construct. Efforts to improve the cervical stand-alone anterior fusion device and to eliminate disadvantages of plate systems should be studied in larger patient groups with longer follow-ups.