Measurable Lumbar Motion Remains 1 Year After Vertebral Body Tethering

Vertebral body tethering (VBT) is growing in popularity for skeletally immature patients with scoliosis because of presumed preservation of spinal motion. Although results have shown preserved thoracic motion, there is minimal data to support motion over the lumbar instrumented segments after VBT. The purpose of this study was to analyze the range of motion of the thoracolumbar and lumbar spine after lumbar VBT.

Retrospective review of patients treated with lumbar VBT underwent low-dose biplanar flexion-extension and lateral bending radiographs at 1 year after surgery to assess motion. Coronal motion at 1 year was compared with preoperative side-bending radiographs. The angle subtended by the screws at the upper instrumented vertebra and lower instrumented vertebra was measured on left-bending and right-bending radiographs to evaluate the coronal arc of motion and was compared with preoperative values over the same levels measured from the end plates. At 1 year postoperatively, the sagittal angle was measured over the instrumented levels on flexion and extension radiographs.

Of the 71 scoliosis patients who underwent VBT at our center eligible for 1-year follow-up, 20 had lumbar instrumentation, all of whom had lumbar bending films available at 1 year after surgery. Seven patients had both thoracic and lumbar VBT on the same day and 13 had lumbar or thoracolumbar tether only. Mean age was 13.5±1.9 years. Mean preoperative major coronal curve measured 52+8 degrees (range: 42 to 70) and mean 27 degrees (range: 13 to 40) at latest follow-up. Mean levels instrumented was 8 (range: 5 to 12), with the lowest instrumented level typically L3 (N=14). The mean preoperative coronal arc of motion over the instrumented segments was 38±13 degrees (range: 19 to 73 degrees) and decreased after surgery to a mean arc of 17±7 degrees (range: 7 to 31 degrees). However, 19 of the 20 (95%) had at least a 10-degree coronal arc of motion. Patients maintained on average 46% (range: 22% to 100%) of their preoperative coronal arc of lumbar motion over the instrumented lumbar segments. On flexion-extension lateral radiographs taken at 1 year postoperatively, there was a mean postoperative arc of motion of 30±13 degrees.

Lumbar VBT resulted in preserved flexion and extension motion at 1 year postoperatively. We also noted some preserved coronal plane motion, but this was decreased compared with preoperative values by ~50%. These findings provide proof of concept that some spinal motion is preserved after lumbar VBT in contrast to lumbar fusion where no motion is retained over the instrumented segments.