Trunk Motion in Adolescents Undergoing Scoliosis Spinal Fusion

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^Department of Orthopaedics, Washington University School of Medicine,
~Human Performance Laboratory, Barnes-Jewish Hospital, St. Louis, MO, USA

INTRODUCTION: Pre- and postoperative radiographs have been the major form of outcome analysis of adolescent idiopathic Scoliosis (AIS) fusions. While the radiographs document static positions of the skeletal system, they do not document dynamic changes. Trunk range of motion (ROM) changes following spinal fusion have never been reported.

PURPOSE: To prospectively assess pre- and 2 year postop trunk ROM in AIS patients undergoing fusion. Our experimental hypotheses were that a decrease in ROM would occur over the entire spine and at fixed levels as a consequence of the surgery, and compensation would occur at unfused vertebral regions above and below the fusion.

METHODS: Thirty patients with AIS undergoing spinal fusion participated in tri-planar ROM tests preop, and at 12 and 24 months postop. Tests included: maximum forward and right and left lateral flexion, and right and left trunk rotation. Reflective markers were placed at 10 locations: right and left acromion processes, C7, T4, T7, T10, L4, S2 and right and left anterior superior iliac spines. A 6 camera video system captured the locations of the markers during the ROM tests. The fused region, unfused regions above and below the fusion, as well as a global spinal measure were used to assess changes among operative conditions.

RESULTS: Results indicated a loss of motion in the coronal and sagittal planes for the fused and unfused spinal regions, both above and below the fusion. The left lateral flexion in the fused region was 12°+9° preop and ~0°+7° for 12 and 24 months postop. Left lateral flexion in the distal unfused region was 7°+11° preop, 4°+9° 12 months postop and 2°+7° 24 months postop. There was a loss of motion in the coronal, sagittal, and transverse planes for the global spinal range of motion measurements. The global left lateral flexion was 35° +6° preop and ~22°+7° at 12 and 24 months postop. Left transverse plane rotation was 48°+12° preop, 35°+9° 12 months postop and 31°+9° 24 months postop. Results also indicated preop and continued postop right and left lateral flexion asymmetries. No significant correlations were found between the total fused levels and lowest instrumented vertebra, with changes in ROM below the fusion level and global changes in spinal range. The correlation between the total number of fused levels and change in global left lateral flexion was r=0.39. The correlation between the lowest instrumented vertebrae and change in global left lateral flexion was r=0.29. Our hypothesis indicating that there would be a decrease in ROM over the entire spine, and at fixed levels as a consequence of the surgery was supported. Our hypothesis indicating a compensation at unfused vertebral motion segments below the fusion level was not accepted.

CONCLUSIONS: While ROM was reduced in the fused spinal regions, it was also reduced in unfused regions. No correlations existed between total fused levels and lowest instrumented vertebra, and the global ROM and ROM below the fusion level. The lack of compensation at unfused vertebral regions at 2 years postop provides opportunity for improvement.