Sagittal Plane Analysis Following Posterior Segmental Spinal Instrumentation

Purpose: To analyze the various sagittal parameters in adolescent idiopathic scoliosis (AIS) following 3 different segmental posterior spinal instrumentation and fusion after 2 years postoperative.

Methods: Radiographic measurements of 469 AIS patients (average age 14.7 years) who underwent posterior segmental spinal instrumentation (PSSI) and fusion at a single institution with a 2 year postoperative follow up were analyzed. Sagittal Cobb angle at the proximal junction (2 supradjacent disc angle change above upper instrumented vertebra), T5-T12, T12-S1, distal junction (1 infradjacent disc angle change above lowest instrumented vertebra), and C7 plumb to posterior upper end plate of S1 on preoperative, early postoperative and 2 year postoperative follow up with standing long cassette radiographs were included.

Results: Three different PSSI techniques were performed: Hook only instrumentation n=249; hybrid (hooks above and screws below) instrumentation n=116; pedicle screw (PS) instrumentation n=106. The average age at operation and Risser signs were similar among three groups (p=0.31 and 0.90 respectively). The sagittal thoracic kyphosis angle (T5-T12) at 2 years postoperation demonstrated significant decrease in PS instrumentation (10+13.6º decrease, 1+11.8º at 2 year postoperation in hooks only, and 0+11.0º at 2 year postoperation in hybrid instrumentation (p <0 .0001). The lumbar lordosis angle (T12-S1) at 2 year postoperation demonstrated a slight decrease in PS instrumentation (3+10.3º decrease, 1+14.9º increase hooks only, and 3+10.1 hybrid instrumentation; p="0.002)." Average proximal junctional changes higher (8+7.8º) compared to only group (5+8.5º) (p="0.007)."

Conclusion: Pedicle screw instrumentation, compared to hooks only and hybrid instrumentation, decreases thoracickyphosis between T5 and T12. This decrease was compensated by an slight increase in proximal junctional measurement and small decrease in lumbar lordosis. Global sagittal balance was not significantly affected at 2 year postoperation.among the 3 groups.