RESTORATION OF THORACIC KYPHOSIS IN ADOLESCENT IDIOPATHIC SCOLIOSIS: COMPARATIVE ANALYSIS OF TWO METHODS OF REDUCTION – CANTILEVER REDUCTION VS TWO RODS SIMULTANEOUS TRANSLATION

Abstract

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.