To What Extent Does Scoliosis Tethering Preserve Spinal Motion?

To what extent is spinal motion preserved when thoracic anterior vertebral body tethering is used instead of spinal fusion to treat adolescent idiopathic scoliosis? A new study has answers.

In the study, “Measurable Thoracic Motion Remains at 1 Year Following Anterior Vertebral Body Tethering, with Sagittal Motion Greater Than Coronal Motion,” the researchers evaluated spinal motion in patients with adolescent idiopathic scoliosis treated with anterior vertebral body tethering.

The findings were published in the December 2021 issue of the Journal of Bone & Joint Surgery.

“There is limited information regarding the measurable motion that is maintained over the instrumented levels following thoracic anterior vertebral body tethering surgery in humans. The purpose of the present study was to assess radiographic spinal motion 1-year vertebral body tethering,” the researchers wrote.

The 32 patients were a part of a U.S. Food and Drug Administration investigational device exemption study. At 1 year postoperatively, patients were evaluated using standing flexion-extension and side-bending radiographs in a microdose biplanar slot scanning imaging system.

The angle subtended by the screws at the upper instrumented vertebra and lower instrumented vertebra was measured to evaluate the coronal arc motion. The sagittal Cobb angle was also measured over the instrumented levels on flexion and extension radiographs.

Overall, the mean angle subtended by the screws changed from 15° ± 8° on left-bending radiographs to 8° ± 6° on right-bending radiographs. The mean coronal arc of motion on bending was 7° ± 6°, with 20 (62.5%) of 32 patients having a coronal arc of motion of greater than 5°.

The mean preoperative coronal arc of motion over the instrumented segments was 30° ± 9°. In addition, the mean kyphotic angle over the instrumented segments was 33° ± 13° in flexion and 11° ± 14° in extension, for a mean postoperative arc of motion of 21° ± 12° between flexion and extension radiographs.

“At 1 year following thoracic anterior vertebral body tethering for the treatment of adolescent idiopathic scoliosis, the thoracic spine showed a measurable range of coronal and sagittal plane motion over the instrumented levels without evidence of complete autofusion. Motion in the coronal plane decreased by 77% following anterior vertebral body tethering. These findings provide proof of concept that sagittal spinal motion is preserved after thoracic anterior vertebral body tethering, although the functional importance remains to be determined,” the study authors wrote.

Study authors included Abdul Fettah Buyuk, M.D., Todd A. Milbrandt, M.D., Smitha E. Mathew, M.B.B.S. and A. Noelle Larson, M.D., all of the Mayo Clinic in Rochester, Minnesota.