Large Developed Anterior Subsidence Influences Cervical Alignment and its Avoidance in Single Level Standalone Cage Assisted Anterior Cervical Fusion

Presented at SMISS Annual Forum 2018
By Jaewon Jang MD, PhD
With Siva Reddy MBBS, DNB, Satish Kumar MBBS, DNB,

Disclosures: Jaewon Jang MD, PhD None Siva Reddy MBBS, DNB None, Satish Kumar MBBS, DNB None,

Introduction:

Recent studies have shown that cage subsidence is a major complication of anterior cervical discectomy and fusion (ACDF) using stand-alone cages regardless of the composite materials. Especially, anterior subsidence of fusion site may result in severe kyphotic deformity.

Aims/Objectives:

The purpose of this study is to evaluate the risk factors of large anterior subsidence after ACDF using a stand-alone cage and the changes of overall cervical alignment by performing a radiological analysis.

Methods:

This study included eighty patients, who underwent ACDF using stand-alone PEEK cage and DBM (demineralized bone matrix) in single level degenerative cervical disease. Radiographs were obtained before surgery, immediately after surgery, and at final follow-up for accessing the restoration of spinal column. For the radiologic parameters, anterior height (AH) and posterior height (PH) of fusion segment, segmental angle (SA), and overall C2-C7 angle (cervical sagittal angle, CSA) were assessed in plain lateral thoracolumbar radiograph. Anterior and posterior subsidence was calculated by the difference between postoperative and last follow-up AH and PH, respectively. In simple postoperative lateral radiograph, the percent of cage length to antero-posterior (AP) body length was measured. Cage height, location and species were also assessed. For patient’s pain and functional assessment, VAS, NDI, and JOA score were measured.

Results:

The average follow up period was 26.7 months. The patients were divided into two groups; group A was composed by 31 patients who anterior subsidence was more than 1mm compared to posterior subsidence and group B was composed by 49 opposite cases. Patients with large anterior subsidence had a positive correlation with posterior located cage, or lordotic cage (p < 0.05). Percent of cage length to antero-posterior body length was also associated with large anterior subsidence (p < 0.05). In sagittal alignment, SA was significantly decreased in group A at the last follow-up (p < 0.05). However, there was no significant difference of CSA between two groups at the last follow-up period. In clinical outcomes, there were no significant differences between two groups.

Conclusions:

Anterior subsidence was largely developed compared to posterior subsidence in cases with posterior located cage, lordotic cage, or low percent of cage length to AP body length. Although CSA was not significantly different between two groups, however, large developed anterior subsidence was associated with kyphotic changes of fusion segment at the last follow-up.