Anterior instrumentation (dual screws single rod system) for the surgical treatment of idiopathic scoliosis in the lumbar area: a prospective study on 33 adolescents and young adults, based on a new system of classification

Abstract

The choice of anterior instrumentation in the treatment of lumbar scoliosis in adolescents and young adults is not a new topic for the authors. The first results achieved using the Dwyer surgical modality were reported by one of the authors followed by the results achieved using Zielke (VDS) instrumentation. Today, new techniques and new instrumentations have been developed that challenge the instrumentation choices. Here we describe how the new system of classification of scoliotic curves we developed has been used as a basis for treating idiopathic scoliosis in lumbar area in adolescents and young adults using an anterior approach. A prospective study was carried out between 1998 and 2010 at two hospital centers on 33 adolescents and young adult with idiopathic lumbar scoliosis involving curves of three kinds, on whom surgical treatment was performed using a single solid rod. Topography of curves: our system of classification includes curves corresponding to the following three type of scoliosis: Type K I: double thoracic and lumbar curves (lumbar predominant) scoliosis (17 cases) mean age 16 years all female patients. Mean Cobb angle of lumbar curve 41°. Mean Cobb angle of thoracic curve 28°. The lumbar curve was left hand convex in 15 cases and right hand convex in 2 cases. Horizontal tilting of L4 mean value 22°. C7 offset mean value 3 cm. Type K IV A: unbalanced thoracolumbar scoliosis (13 cases) mean age 17 years, ten female patients and three male patients. Mean Cobb angle of thoracolumbar curve 39°. The thoracolumbar curve was left hand convex 4 times and right hand convex 9 times. Horizontal tilting of L4 mean value 18°. C 7 offset mean value 2.5 cm. Type K VI A: real lumbar (three cases). Age: 17, 15 and 13 years; all female patients. Cobb angle of the lumbar curve 66°, 29° and 70° (all LH convex). Horizontal tilting of L4: 40°, 20° and 46°. C 7 offset: 7 cm, 1 cm and 4 cm. Surgical instrumentation: We used the EUROS AZUR anterior instrumentation for all the procedures. Cages have been used on five patients at the lower stages. Number of vertebrae instrumented: mean five vertebrae. The patients did not wear postoperative orthosis. Mean duration of procedure: 3 h 50 min. Mean blood loss: 350 cm(3). Type K I scoliosis (17 cases): Mean follow-up: 6 years. Correction of the lumbar curve Cobb angle: the mean angle has been corrected from 41° to 21°. Number of vertebrae instrumented: 4:6 times and 5:11 times. Correction of the upper thoracic curve Cobb angle: mean angle corrected from 28° to 19°. Correction of L4 horizontal tilting: mean residual was 7°. Correction of C 7 offset: mean 0.7 cm. Type K IV A scoliosis (13 cases): mean follow-up: 4 years. Correction of the lumbar curve Cobb angle: the mean angle has been corrected from 39° to 16°. Mean number of instrumented vertebrae: 5 (4:4 times, 5:6 times and 6:3 times.) Correction of L4 horizontal tilting: mean residual 5°. Correction of C 7 offset: mean 0.7 cm. Type K VI A scoliosis (three cases): mean follow-up: 7, 2 and 4 years; Correction of the lumbar curve Cobb angle: the angles have been corrected from 66° to 15°, from 29° to 11° and from 70° to 28°. Number of instrumented vertebrae: 5, 4 and 6. Correction of L4 horizontal tilting: residual tilting of 8°, 7° and 17°. Correction of C 7 offset: 1 cm, 0 cm and 1 cm. There has been no report early or late septic or vascular or neurological complications. Instrumentation failure: there were three cases of screw breakage, all occurred on the lowest implant. Revision surgery was undertaken in both cases, only the last plate needed to be replaced and the rod could be kept without any other modification of the construct. In both cases, fusion has been achieved without any loss of correction. The mean loss of correction of the main curve was 2.5° for the three series. Anterior instrumentation of lumbar idiopathic scoliosis gives highly satisfactory morphological and functional results, since the lumbar musculature is spared and the instrumentation placed at the apex of the curvature has selective effects. Despite our preference and that of other surgeons throughout the world for anterior instrumentation, we are still a minority in comparison with the users of posterior instrumentation. There are several reasons for this reticence, including surgeons' training and ideas about pedicular screw fixation, but the main reason has been the lack of a sufficiently exact system of classification. Previous comparative studies between the anterior and posterior approaches have been biased by the use of an excessively restrictive mode of classification (lumbar/thoracolumbar) of the curves. Real lumbar scoliosis, unbalanced thoracolumbar scoliosis and thoracic and lumbar double curve (lumbar predominant) scoliosis should be properly defined before being compared.