Purpose of the study: The long-term results after surgical treatment of idiopathic scoliosis depends not only on the correction in the coronal plane but also the restoration of good sagittal balance and thus satisfactory sagittal curvatures. Recent publications have shown moderate correction of the thoracic hypokyphosis of idiopathic scoliosis with instrumentations using hooks and pedicular screws. We report results in the coronal and sagittal play with a reduction technique by simultaneous translation on two rods (ST2R).

Material and method: The radiographic parameters were measured preoperatively, at 6 weeks, at 1 year, and at last follow-up (range 2 – 7.4 years) in a consecutive series of 72 patients treated with posterior instrumentation and reduction using the ST2R system. The same operator performed all procedures using stable anchors (pedicle screws or self-stabilizing clamps). Screws and clamps had a threaded polyaxial extension which was linked to the rod by a connector. The deformity was reduced by progressively tightening the two rods alternatively using the nuts on the threaded extensions. This manoeuvre enabled the vertebrae to migrate progressively toward the rods, producing an anteroposterior translation.

Results: In the coronal plane, the mean main curvature was reduced from 54 to 17 and was maintained (70%) without loss of angle at last follow-up. There was not difference between the 56 patients with thoracic scoliosis (Lenke 1–4) and the 16 patients with thoracolumbar or lumbar scoliosis (Lenke 5 and 6). In the sagittal plane, for the patients with preoperative hypokyphosis (32 patients < 20), the mean kyphosis was significantly improved from 9 to 30 and remained stable at last follow-up (31) with a mean gain of 21 (p< 0.001). One patient still had hypokyphosis (18) at last follow-up. For patients with normal kyphosis preoperatively (> 20), the mean gain was 7.

Conclusion: In this consecutive series of 72 adolescents with idiopathic scoliosis, reduction by simultaneous translation on two rods was a simple and effect method which restored normal thoracic kyphosis.

Background: context: In Adolescent Idiopathic Scoliosis (AIS), the correction of thoracic hypokyphosis with hooks instrumentation and also with pedicle screws system is moderate.

Purpose: To compare radiographic results between two instrumentations with thoracic screws using two different

Methods: of reduction: cantilever reduction (CR group– MOSS-MIAMI system) versus simultaneous translation on two rods (ST group – PASSMED system).

Study design: Retrospective comparative analysis of two consecutive cohorts of patients treated by the same surgeon at a single hospital.

Patient sample: Forty-two adolescent idiopathic thoracic scoliosis (Lenke type 1, 2 and 3) underwent a posterior spinal fusion and instrumentation: 20 patients in CR group and 22 patients in the ST group. The minimum follow-up was two years (Mean follow-up: 71 months and 47 months).

Outcomes measures: Thoracic sagittal kyphosis between T4 and T12 and Cobb angle measurements of major and minor curves evaluated preoperatively, postoperatively and the final visit, by an independent observer.

Methods: In CR group, we have used polyaxial pedicle screws and one or two monoaxial thoracic hooks. In ST group, we have used polyaxial pedicle screws and poly-axial claws which provide same stability than screws. Three groups of preoperative kyphosis were generated: 11 patients with severe hypokyphosis (T4–T12 < 10°) (5 in CR group and 6 in ST group); 11 patients with mild hypokyphosis (between 10 and 20°) (respectively 4° vs 7°) and 20 with normokyphosis (> 20°) (respectively 11 vs 9).

Results: At the final follow-up, for patients with a severe preoperative hypokyphosis, the mean gain was 14 degrees in the CR group (8° preop to 22° postop) and 25° in the ST group (6° preop to 31 postop) (p< 0.05). For patients xith mild hypokyphosis, te mean gains were respectively 7 degrees (16° preop to 23° postop) and 18° (16° preop to 34° postop) (p< 0.05). After surgery, 3 patients of CR group had hypokyphosis alors que all patients had normal kyphosis (> 20°) in the ST group. In the coronal plane, the mean correction of scoliosis are similar in the two groups (75% vs 69% p=NS)

Discussion and Conclusion: In posterior instrumentation for AIS, simultaneous reduction on two rods provides a better correction of the thoracic kyphosis than the cantilever reduction in patient with preoperative hypokyphosis. This surgical technique seems to restore thoracic normal kyphosis.