Determination of Distal Fusion Level with Segmental Pedicle Screw Fixation in Single Thoracic Idiopathic Scoliosis

Inje University Sanggye Paik Hospital, Seoul, Korea

Pedicle screw fixation effectively shortens the distal fusion extent for the scoliosis by offering improved 3-D deformity correction. However in single thoracic idiopathic scoliosis the selection of distal fusion extent remains controversial.

PURPOSE: To determine the exact distal fusion level in the treatment of single thoracic idiopathic scoliosis (King 3 and 4) with segmental pedicle screw fixation.

MATERIALS AND METHODS: Forty-two single thoracic AIS patients (King 3: 32 patients, King 4: 10 patients) subjected to segmental pedicle screw fixation with minimum follow-up of 2 years (2-6 years) were retrospectively analyzed. The patients were grouped according to the distal fusion level with reference to the standing neutral vertebra (NV) for comparison of deformity correction, radiological and clinical spinal balance, using standing radiographs. Distal fusion down to NV+1 (one level longer than NV) was in 9 patients, NV in 5, NV-1 in 9, NV-2 in 12 and NV-3 in 7 patients respectively. Preoperatively lower end vertebra was 1.8 vertebra proximal to NV, and NV was 1.6 level proximal to stable vertebra. Failure to restore an adequate trunk balance, postoperative decompensation, and progression or extension of the primary curve was considered unsatisfactory.

RESULTS: Preoperative 51 ± 10° of thoracic deformity was corrected to 13 ± 5° showing 73.8% of curve correction. Preoperative 24 ± 7° of lumbar deformity was corrected to 2 ± 8° showing 93.7% of curve correction. Curve correction was not significantly affected by King type or by the distal fusion level (p › 0.05). Postoperative unsatisfactory results were detected in 14 patients; King type 3 in 9 patients (9/32, 28.1%) and King type 4 in 5 patients (5/10, 50.0%). There was no significant difference in postoperative results between the two groups (p = 0.206, Kruskal-Wallis test). Unsatisfactory results by fusion level were as follows; NV-3 in 5 (5/7, 71.4%) and NV-2 in 9 patients (9/12, 75%). All of the patients (23 patients) who were fused down to NV-1, NV or NV+1 show satisfactory result postoperatively. There was significantly higher chance of unsatisfactory results from not going to the NV-1 (p = 0.001).

CONCLUSION: In correction of single thoracic idiopathic scoliosis (King 3 and 4) with segmental pedicle screw fixation, the curve should be fused to NV-1 saving one or more motion segments when compared to the fusion to the stable vertebra.