[The angular profile of a cage has no influence on segmental alignment after anterior cervical stand-alone interbody fusion].

PURPOSE OF THE STUDY The original aim of this prospective semi-randomised study was to determine associations between segmental sagittal alignment after Anterior Cervical Discectomy and Fusion (ACDF) and subjective and clinical results. Two types of cages, cage P with parallel end-plates and cage A with 5-degree angulations, were used in the patients treated for degenerative conditions. MATERIAL AND METHODS A total of 94 consecutive patients, 56 treated by single-level ACDF and 38 undergoing a two-level procedure, completed 8 years of follow-up. The patients in equally-sized A and P subgroups were examined at 6 weeks and 1, 2 and 8 years after surgery. The follow-up included X-ray in a neutral lateral position, a questionnaire assessing pain in neck and shoulder regions and JOA scores. The results including the cumulative incidence of surgical procedures indicated for adjacent segment diseases were statistically evaluated. RESULTS An average increase in the lordotic angle at 6 weeks after surgery was 2.32° for the implant P and 2.02° for the implant A subgroup. During 8 years of follow-up the average values decreased to 1.51° and 1.36°, respectively. The proportion of patients with no or minimal neck and shoulder pain decreased, in subgroup P, from the initial 85% at 6 weeks to 59% at 8 years after the surgery and, in subgroup A, from 89% to 40 %. The average JOA score of 16 at 6 weeks in both subgroups, at 8 years, had a value of 15.9 in subgroup P and 16.0 in subgroup A. The cumulative incidence of surgery for adjacent segment disease 8 years was 8.3% for subgroup P and 6.3% for subgroup A. No statistically significant differences between the subgroups at any follow-up period were recorded in either morphological characteristics or clinical outcomes. CONCLUSIONS The ability to lordotize a segment by stand-alone ACDF is below the angular resolution of current radiographic methods, irrespective of the sagittal profile of the implant used. Comparable morphological results haven´t been reflected by significant difference in subjective and clinical outcome and also in the incidence of surgery for adjacent segment disease. Such results were not expected and therefore post-operative sagittal alignment mechanisms in stand-alone cage assisted ACDF will require further investigation. Key words:cervical vertebrae, surgical technique, spinal fusion, sagittal alignment, clinical outcome.