Partial correction of Cobb angle prior to posterior spinal instrumentation

Abstract

Background: A substantial contribution to the overall surgical correction of Cobb angle has been observed to occur prior to securing the instrumentation. Knowledge specific to the amount of correction prior to instrumentation is scarce in the medical literature. If significant correction is due to the positioning and muscle stripping during exposure of the spine, questions arise about the usefulness and need for extensive rod-rotation maneuvers to further straighten the spine. This study quantifies the extent of correction achieved from standing to prone, with the spine exposed before and after instrumentation.

Materials and methods: Eleven patients with the diagnosis of adolescent idiopathic scoliosis (AIS) and a right thoracic major curve were included in the study. Intraoperative changes in Cobb angle were measured before and after instrumentation, as well as postoperatively. The patients underwent posterior spinal instrumentation by the same surgical team using the rod-rotation techniques. Radiographs were taken prior to surgery, intraoperatively before and after instrumentation and postoperatively within one week from surgery. Cobb angle measurements were performed by the same examiner.

Results: The median preoperative Cobb angle of 60 degrees +/-14 degrees (48-90 degrees ) corrected to a median of 26 degrees +/-22 degrees (10-80 degrees ) on the right bend film, to a median of 55 degrees +/-12 degrees (30-70 degrees ) intraoperatively after exposure, and to a median 30 degrees +/-10 degrees (20-46 degrees ) after rod-rotation/instrumentation and fixation. The follow-up standing radiograph median Cobb angle was 40 degrees +/-14 degrees (9-56 degrees ). A median intraoperative correction of 28 degrees was obtained, 10 degrees of which was prior to the rod rotation and instrumentation. High variability was observed in the percentage contribution of pre-instrumentation release with a median of 42%+/-25% (0-67%).

Conclusion: Approximately one-third of the total correction occurred prior to instrumentation being applied, and even though it was variable and substantial, the actual surgical rod rotation and instrumentation maneuver provided the majority of correction.