Does vertebral body tethering cause disc and facet joint degeneration? A preliminary MRI study with minimum two years follow-up

BACKGROUND CONTEXT: Vertebral body tethering (VBT), a flexible compression-based growth modulation technique, was claimed to prevent disc degeneration due to its less rigid nature compared to other growth-friendly techniques. Yet, the consequences of VBT surgery on discs and facet joints have not been precisely acknowledged. PURPOSE: The purpose of this study was to determine the changes in the intermediate and adjacent levels at least 2 years after surgery. STUDY DESIGN/SETTING: Prospectively-followed consecutive patient cohort PATIENT SAMPLE: Adolescent idiopathic scoliosis patients who underwent thoracoscopic VBT between 2014 and 2017 were included. OUTCOME MEASURES: Degeneration of the intervertebral discs using the Pfirrmann classification; Degeneration of facet joints using a scale of 0 to 3. METHODS: Demographic, perioperative, clinical, radiographic data were collected. Skeletal maturity and height gain were assessed in every follow-up. Overcorrection, tether breakage, mechanical and pulmonary complications as well as readmission and reoperations were recorded. MRIs taken before surgery and at a minimum of 2 years follow-up were evaluated for degeneration at the intermediate and adjacent segment intervertebral discs and facet joints by a blinded senior radiologist and compared. RESULTS: Twenty-five patients with a mean of 38.6 +/- 10.6 months (24-62) of follow-up were included. The mean age at surgery was 12.2 (10-14), and the median Sanders stage was 3 (1-7). A mean of 7.7 +/- 1.1 (6-11) levels were tethered. The mean preoperative main thoracic curve magnitude of 46 degrees +/- 7.7 degrees was corrected to 23.3 degrees +/- 5.9 degrees postoperatively, which was subsequently modulated to 12 degrees +/- 11.5 degrees during the follow-up. At the time of the MRI (mean 29 +/- 9.5 (24-62) months), the median Sanders stages was 7 (5-8). A total of 217 levels of discs and bilateral facet joints were evaluated in the preoperative and follow-up MRI images. Analyses of disc and facet scores revealed no significant differences between patients. Deterioration of previously degenerated discs was noted in one patient (from grade 2 to 3), while previously healthy lower adjacent facet joints were degenerated (grade 2) in another patient. CONCLUSIONS: Intermediate discs and facet joints were preserved after growth modulation with VBT surgery at a mean of 29 months of follow-up. Studies in larger cohorts with longer follow-up are warranted to have more in-depth analyses of the effects of relative stabilization and altered biomechanical loads. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

The study followed adolescent idiopathic scoliosis patients who underwent thoracoscopic VBT for at least 2 years and found that intermediate discs and facet joints were preserved after surgery with no significant differences or further deterioration noted. In one patient, previously degenerated discs worsened, while in another patient, healthy adjacent facet joints degenerated. Further studies with larger cohorts and longer follow-up periods are needed for a more comprehensive analysis of the effects of VBT surgery.