O1052: Major Cobb Angle Did Not Decrease in 92% of Patients After Vertebral Body Tethering (VBT) Surgery Following First Erect Radiograph

Background: Much enthusiasm has been generated around VBT as an alternative to fusion treatment. However, the majority of series report little difference between Cobb angles on the first erect post-operative x-ray and final follow-up (Rushton 2021, Newton 2018), suggesting VBT is not consistently modulating spine growth in a way that significantly effects Cobb Angle.

Methods: Adolescent idiopathic scoliosis (AIS) patients who underwent VBT with > 2 yrs follow up between Dec 2013- Jan 2020 in a multi-center registry were reviewed. Change in Cobb angle was calculated by subtracting the Cobb angle at final follow up from that on first erect postoperative radiographs. A change in Cobb angle < 5° was considered within normal measurement variability (consistent with prior study, Morrissy 1990).

Results: 113 patients met inclusion criteria with mean age of 12.9 yrs (SD 1.3) and a mean follow up of 3.7 yrs (2.0 to 6.8). A mean of 6.6 levels were tethered. Preoperative mean major Cobb angle was 51.1°(32° to 75°), which corrected to a mean major Cobb of 27.4° (10° to 53°) on first erect radiographs. At final follow up, mean major Cobb was 31.1°(-50° to 69°). 50.4% (57/113) of curves were stable (Cobb angles within 5° of their first erect radiograph on final follow up). A total of 41.6% (n=47) had > 5° of increase in Cobb angle following the initial erect radiograph. 8% (n=9) showed more than 5° of decrease in Cobb angle during the follow up period, and 4.4% (n=5) had greater than 10° of correction. 2 of those 5 patients that corrected more than 10° overcorrected, ending up with 30° and 50° curves in the opposite direction.

Conclusion: Although this technique holds promise and many of the curves remained stable from first erect to final follow up (50%), only 9/113 VBT patients in this series demonstrated improvement in Cobb angle over time following first erect imaging, including 2 patients that overcorrected. Further research is needed to identify the differentiating factors between those patients that progressed, didn't progress or overcorrected to determine which patients are more likely to benefit from.