Longitudinal changes in segmental range of motion following cervical artificial disc replacement

Abstract

Background Cervical artificial disc replacement (ADR) has emerged as a popular new treatment because of its potential benefit of averting an adjacent segment disease following ACDF. However, ADR also has problems such as heterotopic ossification, or mechanical failure, which raises concerns that the artificial disc would lose its function at some point. Purpose To estimate the life expectancy of artificial disc, we analyzed longitudinal changes in the range of motion at the implanted segment during follow-up in a cohort of patients with healthy facet joints before surgery. Patients and methods We reviewed the charts and radiologic studies of 30 patients operated upon by ADR with Mobi-C in single level since 2006. All patients had healthy cervical facet joints (less than or equal to grade 1 according to grading systems for cervical facet joint degeneration) preoperatively. We assessed clinical outcomes with neck disability index (NDI) and visual analogue pain score (VAS) on neck and arm over follow-up and also measured the ROM at the implanted segment on dynamic radiographs during follow-up. The mean follow-up period was 42.4 ± 15.9 months. We then assessed the linearity of the changes in the ROM at the implanted segment in a linear mixed model. Results All patients showed improved clinical outcomes. On average, the NDI, VAS on neck and arm improved with representing 74%, 76% and 92% improvement. ROMs at the implanted segment were maintained at slightly increased levels until 24 months postoperatively (P=0.529). However, after 24 months, ROMs at the implanted segment decreased significantly until last follow-up (P<0.001). In addition, the decreasing pattern after 24 months showed a regular regression (P<0.001). Based on this regular regression, we estimated that ROMs at the implanted segments would be less than 2 degrees at 10.24 years postoperatively. Conclusion In the present study, we could assume that the implanted segment would lose its motion at 10.24 years after artificial disc replacement. In other words, an artificial disc may lose its function someday. Keywords: anterior cervical

discectomy

artificial disc replacement (ADR)

range of motion (ROM)

implanted

segment

longitudinal