Does Vertebral Body Tethering Cause Coronal Hypermobility at Adjacent Noninstrumented Levels? A Preliminary Study

Abstract

Background: Fusion into the lumbar spine with lower instrumented vertebra (LIV) of L2 and below can result in increased mobility or hypermobility of the unfused segments, potentially contributing to early disk and joint wear and subsequent degenerative arthritis. Vertebral body tethering (VBT) is a motion-preserving surgery for scoliosis, but no data is available about its effect on disk motion for the uninstrumented segments distal to the LIV. We hypothesize that VBT preserves the coronal arc of motion distal to the LIV in AIS patients without the development of hypermobility which has been observed following fusion surgery.

Methods: A single-center retrospective review was completed of adolescent idiopathic scoliosis patients who underwent VBT. Standing bending films were collected as standard of care preoperatively and at 1-year postoperatively with maximum effort on side bending according to an institutional protocol. To evaluate the coronal arc of motion, radiographic measurement of the intervertebral angles was measured at each level from the disk directly distal to LIV-S1, as described in previous literature.

Results: A total of 95 patients had clinical preoperative and postoperative bending radiographs and were included in the study. In total, there were 2086 segments measured. Sixteen patients had bilateral tether procedures and were analyzed separately. Compared with preoperative values over the same levels, paired t test showed no significant difference in the coronal arc of motion for the distal uninstrumented segments.

Conclusions: Normal segmental motion on lateral bend was preserved on the noninstrumented segments following VBT. In contrast to fusion, there was no evidence of lumbar hypermobility following VBT in scoliosis patients. This provides early evidence for preserved normal motion which could be protective against adjacent segment disease and early arthritis reported with long fusions.

Level of evidence: Level III-retrospective cohort study.

Keywords: adolescent idiopathic scoliosis; lumbar hypermobility; vertebral body tethering.