Gravitational forces and sagittal shape of the spine: Clinical estimation of their relations

The sagittal morphology of the pelvis determines the amount of lordosis needed for each individual. The proper harmony of the sagittal spinal curves allows a stable balance, economical in terms of mechanical effects and muscular energy. A previous barycentremetrical laboratory study allowed us to demonstrate that the axis of gravity of the upper body segment was located behind the lumbar vertebrae and the femoral heads, thus ensuring economy and stability. The determination of the anatomical connection of the individual gravity is thus of primary importance for the evaluation of sagittal balance. Data for 42 patients without spinal pathology, previously evaluated by barycentremetry, were used to establish a predictive equation for the application point of the gravity at the level of the third lumbar vertebra (L3). This equation, using anthropometric and radiographic pelvic and spinal parameters, was integrated into a software program called Similibary. It was applied to the same 42 subjects. These results were compared in order to validate the method. No significant difference was observed between the two techniques. This easy-to-use tool allows a personalised evaluation of the sagittal balance of the spine, both through the evaluation of the harmonious relationship between the spinal curves and the pelvis, and through the location of gravity supported by the vertebral structures in L3

Selective posterior thoracic fusion by means of direct vertebral derotation in adolescent idiopathic scoliosis: effects on the sagittal alignment

The objectives of this retrospective study were to evaluate the effect of direct vertebral derotation on the sagittal alignment of the spine after selective posterior thoracic fusion for Lenke Type I adolescent idiopathic scoliosis (AIS). Preservation of the sagittal alignment has become critical in the management of spinal deformity. Better coronal and rotational corrections in posterior selective thoracic fusion for AIS have been reported with direct vertebral derotation as compared with the simple rod rotation technique. A greater lordogenic effect has been anticipated with direct vertebral derotation; however, data comparing those two techniques in terms of correction in the sagittal plane are still lacking. Standing full-spine PA and standard lateral serial X-rays of a total of 30 consecutive patients with adolescent idiopathic scoliosis treated between 2002 and 2008 at a single institution were evaluated. All the patients had Lenke Type I curves and underwent selective posterior thoracic fusion with pedicle screw instrumentation. Patients who were treated with additional osteotomies and concave or convex thoracoplasty or concomitant anterior releases were excluded. Minimum follow-up period was 24 months. Preoperative and postoperative coronal and sagittal spinal alignments in both the groups were compared. In 13 patients, the correction was achieved by means of a simple rod rotation (SRR). In 17 patients, the technique of direct vertebral derotation (DVD) was used. Scoliosis correction averaged 67 and 69%, respectively, and was similar in both groups (p > 0.05). Thoracic kyphosis and lumbar lordosis remained unchanged in the SRR group (p > 0.1). In the direct vertebral derotation group, a significant decrease of both thoracic kyphosis and lumbar lordosis of 8.1° and 11.8°, respectively, was observed (p < 0.0001). Global sagittal balance remained within normal limits in all the patients at the latest follow-up. Decrease in thoracic kyphosis and lumbar lordosis should be taken into account when using direct vertebral derotation for selective posterior thoracic fusion in AIS. In order to preserve sagittal alignment in these patients, ultra hard rods or maneuvers that pull posteriorly the concave side of the spine, thus avoiding the application of additional flattening forces should be considered