Sagittal balance in adolescent idiopathic scoliosis: radiographic study of spino-pelvic compensation after surgery.

STUDY DESIGN: Radiographic retrospective study of a consecutive series of 76 patients with adolescent idiopathic scoliosis (AIS) undergoing posterior only surgical correction and fusion. OBJECTIVE: To evaluate the sagittal profile changes in a population of adolescent idiopathic scoliosis after posterior only surgical correction. Although the relationship between pelvic indexes and sagittal profile is well known, little has been published about the sagittal profile changes after posterior surgery in adolescent idiopathic scoliosis. METHODS: Radiological data of 76 AIS patients were analyzed by an independent observer to compare pelvic indexes and spino-pelvic parameters before and at the last follow-up after surgical posterior correction. All patients underwent a posterior only surgical correction by using different anchor techniques (all screws or hybrid construct), but the same derotation correction maneuver (C-D technique). The collected data were analyzed, on AP and LL radiographic views of the entire spine in the upright position, from the same independent observer and using the same Impax software analysis. We collected for each patient on latero-lateral X-rays the following data: pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), thoracic kyphosis (TK), C7 plumb line (C7PL) and spino-sacral angle (SSA). All data were analyzed using a D'Agostino-Pearson normality test and the comparison between the groups was performed with a student's t test. RESULTS: The mean pelvic incidence (PI) of the cohort was 48.89° (± 11.24), with a mean Cobb angle for the main curve of 60.13° (± 13.6). The mean value of residual scoliosis after surgery was 28.18° (± 13.22) with an average improvement of the curve in the frontal plane of 53.2 %. The amount of curve correction of the primary scoliosis curve was statistically significant (p < 0.0001). In the evaluation of the whole group after surgery, we observed an increasing amount of PT (average delta value 2.38°) with a statistical significance (p = 0.0034). If we compare the mean ideal PT value (11.09°) with the pre- and post-operative mean true PT values, we found statistical significance only for the post-operative difference (p = 0.0014). In the general assessment, C7PL seems to remain stable after surgery, and in particular it remains negative. In Lenke 1 group, there was a mean PI value of 50.54° (± 11.45) which is higher than the one reported in the global assessment. Also in this subgroup, we observed a reduction in the mean SS values, with consequent increase in the PT values, as in the general assessment. The C7PL tends to move posteriorly after surgery and this difference is statistically significant. In Lenke 1 group we found a strong statistical significance between pre- and post-surgery data for the Cobb primary curve and for the C7PL, which continues to remain negative. The C7PL remains relatively stable only in the normokyphotic group, while it tends to move behind in the other three groups (Lenke 3, hyperkyphosis and hypokyphosis). CONCLUSIONS: In our series of 76 adolescent affected by AIS, we reported mean PI values of 48.9° with a mean pre-operative PT of 11.51°. After surgery we observed an increase in the PT mean value, about three degrees higher than the ideal value, meaning that there was some compensatory mechanism. Patients affected by AIS showed a slight posterior imbalance and the intervention of scoliosis correction seems to cause a slight further posterior imbalance, especially in Lenke 1 type curves and in patients with hypokyphosis. The clinical significance of this slight imbalance must be carefully evaluated. Further studies are necessary to better establish which could be the best surgical strategy to obtain an optimal spinal sagittal balance.

Cement leakage: safety of minimally invasive surgical techniques in the treatment of multiple myeloma vertebral lesions.

PURPOSE: To evaluate and address the safety of vertebroplasty (VP) and kyphoplasty (KP) in terms of rate and type of cement leakage in the treatment of Multiple Myeloma (MM) vertebral fractures. METHODS: A total number of 37 treated vertebrae were evaluated post-operatively by using standard X-rays and CT scan looking for a cement leakage. VP was done using a monoportal approach in all cases (18 treated levels, group A), while KP was done using a monopedicular approach in 9 levels (group B1) and using a bipedicular approach in the remaining 10 levels (group B2). A computed tomography was used to establish the presence of any cement leakage and to determine its localization. RESULTS: Vertebral augmentation through VP and KP provides immediate pain relief and an improvement of the quality of life of patients affected by MM but it is gravated by high risk of cement leakage. Cement extravasation occurred in 27.7% of total VP procedures and in 21.05% of total KP procedures, but considering the whole number of treated levels, it was more common in multi-level VP and in bipedicular KP, in which a higher quantity of cement was employed. CONCLUSIONS: KP procedure in these patients is slightly less risky but we suggest doing it with a monopedicular approach. It's mandatory to use an high viscosity cement and we suggest not to use an amount of PMMA over 2 cc and a previous treatment with bone marrow transplant is related to a lower risk of cement leakage.

Porcine models in spinal research: calibration and comparative finite element analysis of various configurations during flexion-extension.

This study was conducted to develop and calibrate a detailed 3-dimensional finite element model of the porcine lumbar spine and to compare this model with various configurations in flexion and extension. Computed tomography scans obtained from the L4-L5 lumbar segment of a Landrace x Large White pig were used to generate a solid volume. The various passive components were characterized by using a step-by-step calibration procedure in which the material properties of the anatomic structures were modified to match the corresponding in vitro data set-points retrieved from the literature. The range of motion of the totally assembled intact model was assessed under a 10-Nm flexion-extension moment and compared with data from a bilateral complete and hemifacetectomy configuration. In addition, the results from our porcine model were compared with published data regarding range of motion in a human finite element model in order to predict the configuration of the porcine model that most closely represented the human spine. Both the intact and hemifacetectomy configurations of the porcine model were comparable to the human spine. However, qualitative analysis of the instantaneous axis of rotation revealed a dissimilarity between the intact porcine model and human spine behavior, indicating the hemifacetectomy configuration of the porcine model as the most appropriate for spinal instrumentation studies. The present 3-dimensional finite element porcine model offers an additional tool to improve understanding of the biomechanics of the porcine spine and to decrease the expense of spinal research.

Monosegmental vs bisegmental pedicle fixation for the treatment of thoracolumbar spine fractures.

INTRODUCTION: The anatomy and biomechanics of the thoracolumbar spine place these segments at high risk of trauma injuries. Treatment options are either conservative or surgical, and there is a lack of consensus about the right indications. International scientific publications agree only on basic surgical principles: vertebral stability, deformity correction, protection of neurological structures and fast functional recovery. The most commonly used approach is the posterior approach, which allows the best management of most vertebral fracture patterns. The aim of this study was to compare clinical and radiological outcomes of monosegmental stabilisation with those of bisegmental stabilisation and fusion in the treatment of traumatic thoracolumbar spine fractures. MATERIALS AND METHODS: This retrospective clinical and radiological study evaluated 48 consecutive patients treated with monosegmental (Group M; n=14) or bisegmental (Group B; n=34) posterior pedicular instrumentation for thoracolumbar fractures. Fractures were classified by the new AO Spine TLIC system. Average follow-up was 30 months. Clinical outcomes in both groups were statistically compared. Radiological outcomes were evaluated in terms of vertebral anterior body height restoration and correction of the kyphotic deformity. RESULTS: Radiographical results showed no statistically significant difference between the two groups in vertebral body height restoration and correction of the kyphotic deformity. The mean postoperative somatic vertebral anterior body height in Group M was 25.8±4.52mm and in Group B it was 24.43±4.27mm. In Group M the mean postoperative kyphotic deformity was 11.10±5.71°, in Group B it was 9.09±4.93°. CONCLUSIONS: The results of this study confirm the validity of short and very short instrumentation for the treatment of well-selected type A and B vertebral fractures. In C type fractures correct surgical indication must be evaluated on an individual basis.