Jean-Marc Mac-Thiong

Sagittal alignment of the spine and pelvis during growth.

Study Design. Prospective study of the sagittal plane alignment of the spine and pelvis in the normal pediatric population. Objectives. To document the sagittal alignment of the spine and pelvis and its change during growth in the normal pediatric population. Summary of Background Data. Pelvic morphology as well as sagittal alignment of the spine and pelvis in the pediatric population are poorly defined in the literature. Methods. Five parameters were evaluated on lateral standing radiographs of 180 normal study participants 4 to 18 years of age: thoracic kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence. Statistical analysis was performed using two-tailed Student t tests and Pearson’s coefficients (level of significance = 0.01). Results. The mean thoracic kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence values were 43.0°, 48.5°, 41.2°, 7.2° and 48.4°, respectively. There was no significant difference between males and females. Thoracic kyphosis, lumbar lordosis, pelvic tilt, and pelvic incidence were found to be weakly correlated with age, while sacral slope remained stable with growth. Conclusions. Pelvic morphology, as measured by the pelvic incidence angle, tends to increase during childhood and adolescence before stabilizing into adulthood, most likely to maintain an adequate sagittal balance in view of the physiologic and morphologic changes occurring during growth. Pelvic tilt and lumbar lordosis, two position-dependent parameters, also react by increasing with age, most likely to avoid inadequate anterior displacement of the body center of gravity. Sacral slope is achieved with the standing posture and is not further significantly influenced by age. These results are important to establish baseline values for these measurementsin the pediatric population, in view of the reported association between pelvic morphology and the development of various spinal disorders such as spondylolisthesis and scoliosis.

Sagittal plane analysis of the spine and pelvis in adolescent idiopathic scoliosis according to the coronal curve type

Study Design. A retrospective study investigated the sagittal alignment in adolescent idiopathic scoliosis (AIS). Objective. To evaluate the sagittal alignment of the spine and pelvis in adolescent idiopathic scoliosis on the basis of curve type. Summary of Background Data. The relation between the spine and pelvis highly influences the sagittal balance in adults. However, the sagittal alignment of the spine and pelvis in adolescent idiopathic scoliosis is poorly defined in the literature. Methods. Five sagittal parameters were evaluated on lateral radiographs of 160 patients with adolescent idiopathic scoliosis: thoracic kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence. The patients were classified according to their coronal curve type. Analysis of variance was used to compare the parameters between the curve types, and Pearson coefficients were used to investigate the relation between all parameters (&agr; = 0.05). Results. The thoracic kyphosis was significantly lower for King I, II, and III curves than for lumbar curves. The lumbar lordosis was higher for lumbar curves, although not significantly. No significant change between the groups was observed for the sacral slope, pelvic tilt, or pelvic incidence. The pelvic incidence was significantly correlated with the lumbar lordosis, sacral slope, and pelvic tilt for all the groups. The lumbar lordosis was strongly related to the sacral slope in all cases, but not with the thoracic kyphosis, except in the case of thoracolumbar curves. Conclusions. Thoracic kyphosis depended mostly on the spinal deformity, whereas lumbar lordosis was influenced mainly by the pelvic configuration. The scoliotic curve type was not associated with a specific pattern of sagittal pelvic morphology and balance. The pelvic incidence found in this study was significantly higher than that reported in the literature for normal adolescents. The role of the pelvic incidence in the pathogenesis of adolescent idiopathic scoliosis needs to be explored in a longitudinal study involving patients with adolescent idiopathic scoliosis and normal adolescents.

Can c7 plumbline and gravity line predict health related quality of life in adult scoliosis

Study Design. This study prospectively evaluated the health related quality of life (HRQOL) of 73 adults presenting with scoliosis at a single institution, as related to their spinal (C7 plumbline) and global (gravity line) balance. Objective. To assess the influence of sagittal and coronal balance on HRQOL in adult scoliosis. Summary of Background Data. Many surgeons believe that achieving adequate spinal balance is important in the management of adult spinal deformity, but the evidence supporting this concept remains limited. A previous study has found weak correlations between sagittal spinal balance and HRQOL in adult spinal deformity, but this finding has never been confirmed independently. In addition, although the use of the gravity line is gaining interest in the evaluation of global balance, it remains unknown if this parameter is associated with HRQOL. Methods. During a 1-year period, 73 consecutive new patients presenting with unoperated adult scoliosis and requiring full spine standing radiographs were evaluated using a force plate in order to simultaneously assess the gravity line. All patients also completed the Oswestry Disability Index (ODI) questionnaire to assess the HRQOL. Spinal balance was evaluated from the C7 plumbline and global balance from the gravity line, respectively. C7 plumbline and gravity line were both assessed with respect to the posterosuperior corner of the S1 vertebral body and central sacral vertebral line in the sagittal and coronal plane, respectively. C7 plumbline and gravity line, as well as their relative position, were correlated with the ODI, using Spearman coefficients. Results. Sagittal spinal (C7 plumbline) and global (gravity line) balance, as well as their relative position were significantly related to the ODI. A poor ODI (>34) was associated with a sagittal C7 plumbline greater than 6 cm, a sagittal gravity line greater than 6 cm, and a C7 plumbline in front of the gravity line. Correlations between coronal balance and the ODI were not statistically significant. Conclusion. Sagittal spinal and global balance was strongly related to the ODI in adults with scoliosis. The observed correlation coefficients were higher than those reported in the only previous study suggesting the detrimental association of positive sagittal balance on ODI in adult spinal deformity. Coronal spinal and global balance did not influence the ODI in the current study cohort. Thisstudy underlines the relevance of C7 plumbline and gravity line in the evaluation of spinal and global balance, and lends further support to the philosophy of achieving adequate sagittal balance in the management of adult spinal deformity, especially in patients older than 50 years old with degenerative scoliosis.

Sagittal parameters of global spinal balance: normative values from a prospective cohort of seven hundred nine Caucasian asymptomatic adults.

Study Design. Prospective study of normal sagittal global spinal balance in the Caucasian adult population. Objective. To document values for parameters of global spinal balance in 709 asymptomatic adults without spinal pathology. Summary of Background Data. Previous studies have investigated sagittal spinal balance in the normal population, but there is still a need for a large prospective database with normative values on the basis of gender and age. Methods. Spinosacral angle (SSA), spinal tilt (ST), and C7 translation ratio were evaluated in 709 asymptomatic adults (354 males and 355 females). Position of C7 plumbline relative to sacrum and hip axis (HA) was also assessed. Comparisons on the basis of gender were performed using analyses of covariance with age as covariate. Relationships between parameters and age were assessed using Spearmans coefficients. Results. Mean SSA, ST, and C7 translation ratio were respectively 130.4° ± 8.1°, 90.8° ± 3.4°, and 0.1° ± 1.9°. Mean ± 2 standard deviations were respectively 110° to 150° for SSA and 85° to 100° for ST. Mean SSA and ST were higher in females but by less than 2°. C7 plumbline was behind the HA in 86% of subjects. Correlations between global balance and age were small (−0.1 ≤ r ≤ 0.1), with only 1 correlation reaching statistical significance (SSA vs. age; r = −0.1), reflecting a slight tendency for SSA to decrease with age. There was no relationship between ST and age. Conclusion. Asymptomatic adults tend to stand with a stable global balance and it is expected that 95% of normal adults have an SSA and ST between 110° to 150° and 85° to 100°, respectively. C7 plumbline in front of the HA is not necessarily associated with a spinal pathology. Results suggest that in adults, anterior displacement of C7 plumbline with respect to sacrum cannot be attributed solely to aging and should raise a suspicion for the risk of developing spinal pathology.

Spino-pelvic sagittal balance of spondylolisthesis: a review and classification.

IntroductionIn L5-S1 spondylolisthesis, it has been clearly demonstrated over the past decade that sacro-pelvic morphology is abnormal and that it can be associated to an abnormal sacro-pelvic orientation as well as to a disturbed global sagittal balance of the spine. The purpose of this article is to review the work done within the Spinal Deformity Study Group (SDSG) over the past decade, which has led to a classification incorporating this recent knowledge.Material and methodsThe evidence presented has been derived from the analysis of the SDSG database, a multi-center radiological database of patients with L5-S1 spondylolisthesis, collected from 43 spine surgeons in North America and Europe.ResultsThe classification defines 6 types of spondylolisthesis based on features that can be assessed on sagittal radiographs of the spine and pelvis: (1) grade of slip, (2) pelvic incidence, and (3) spino-pelvic alignment. A reliability study has demonstrated substantial intra- and inter-observer reliability similar to other currently used classifications for spinal deformity. Furthermore, health-related quality of life measures were found to be significantly different between the 6 types, thus supporting the value of a classification based on spino-pelvic alignment.ConclusionsThe clinical relevance is that clinicians need to keep in mind when planning treatment that subjects with L5-S1 spondylolisthesis are a heterogeneous group with various adaptations of their posture. In the current controversy on whether high-grade deformities should or should not be reduced, it is suggested that reduction techniques should preferably be used in subjects with evidence of abnormal posture, in order to restore global spino-pelvic balance and improve the biomechanical environment for fusion.

Sagittal spino-pelvic alignment in chronic low back pain

IntroductionThe differences in sagittal spino-pelvic alignment between adults with chronic low back pain (LBP) and the normal population are still poorly understood. In particular, it is still unknown if particular patterns of sagittal spino-pelvic alignment are more prevalent in chronic LBP. The current study helps to better understand the relationship between sagittal alignment and low back pain.Materials and methodsTo compare the sagittal spino-pelvic alignment of patients with chronic LBP with a cohort of asymptomatic adults. Sagittal spino-pelvic alignment was evaluated in prospective cohorts of 198 patients with chronic LBP and 709 normal subjects. The two cohorts were compared with respect to the sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), lumbar lordosis (LL), lumbar tilt (LT), lordotic levels, thoracic kyphosis (TK), thoracic tilt (TT), kyphotic levels, and lumbosacral joint angle (LSA). Correlations between parameters were also assessed.ResultsSagittal spino-pelvic alignment is significantly different in chronic LBP with respect to SS, PI, LT, lordotic levels, TK, TT and LSA, but not PT, LL, and kyphotic levels. Correlations between parameters were similar for the two cohorts. As compared to normal adults, a greater proportion of patients with LBP presented low SS and LL associated with a small PI, while a greater proportion of normal subjects presented normal or high SS associated with normal or high PI.ConclusionSagittal spino-pelvic alignment was different between patients with chronic LBP and controls. In particular, there was a greater proportion of chronic LBP patients with low SS, low LL and small PI, suggesting the relationship between this specific pattern and the presence of chronic LBP.

Postural model of sagittal spino-pelvic alignment and its relevance for lumbosacral developmental spondylolisthesis.

Study Design. Comparative study of sagittal spino-pelvic alignment in children and adolescents with developmental lumbosacral spondylolisthesis compared with asymptomatic subjects. Objective. To develop a global postural model of sagittal spino-pelvic alignment. Summary of Background Data. The relationships between parameters of sagittal spino-pelvic alignment in developmental spondylolisthesis are still unclear. Methods. Radiographs of 120 control subjects and 131 subjects with developmental spondylolisthesis (91 low-grade, 40 high-grade) were reviewed. Subjects with high-grade spondylolisthesis were divided according to their sacro-pelvic alignment: balanced versus retroverted sacro-pelvis. Parameters of the sacro-pelvis (pelvic incidence, pelvic tilt, sacral slope), lumbosacral region (lumbosacral angle, slip percentage), lumbar spine (lumbar lordosis, lumbar tilt), thoracic spine (thoracic kyphosis, thoracic tilt), and global balance (spinal tilt, sagittal offset between C7 and femoral heads) were assessed. Parameters were compared between all groups and a correlation study was performed between all parameters. A postural model that includes the measured parameters was used to analyze the obtained correlations. Results. Significant differences in all parameters are found between all groups, except for sagittal offset. The pattern and strength of correlations is similar between normal and low-grade subjects, showing interdependence between sacro-pelvic, lumbosacral, lumbar, and thoracic regions. The pattern of relationships was altered in high-grade spondylolisthesis, especially for subjects with a retroverted sacro-pelvis for which correlations between pelvic incidence and pelvic tilt, and between the sacro-pelvic unit and lumbar spine geometry are lost. Conclusion. Children and adolescents stand with a relatively constant global sagittal spino-pelvic alignment, regardless of the local lumbosacral deformity. A normalposture is maintained in low-grade spondylolisthesis and in high-grade spondylolisthesis with a balanced sacro-pelvis. Posture is abnormal in high-grade spondylolisthesis associated with a retroverted sacro-pelvis, suggesting that surgical reduction of the local lumbosacral deformity in these patients could be attempted to restore a normal posture.

Biomechanical risk factors for proximal junctional kyphosis: a detailed numerical analysis of surgical instrumentation variables.

Study Design. Biomechanical analysis of proximal junctional kyphosis (PJK) through computer simulations and sensitivity analysis. Objective. To gain biomechanical knowledge on the risk of PJK and find surgical solutions to reduce the risks. Summary of Background Data. PJK is a pathological kyphotic deformity adjacent to the instrumentation. Clinical studies have documented its risk factors, but still little is known on how it is correlated with various individual instrumentation variables. Methods. Biomechanical spine models of 6 patients with adult scoliosis were developed, validated, and then used to perform 576 simulations, varying the proximal dissection procedure, the implant type at the upper instrumented vertebra, the sagittal rod curvature, and the proximal diameter of the proximal transition rods. Four biomechanical indices—the proximal junctional kyphotic angle, thoracic kyphosis, proximal flexion force, and proximal flexion moment—were assessed. Results. The bilateral complete facetectomy, the posterior ligaments resection, and the combination of both increased the proximal junctional kyphotic angle (respectively, by 10%, 28% and 53%) and the proximal flexion force (4%, 12%, and 22%) and moment (16%, 44%, and 83%). Compared with pedicle screws at upper instrumented vertebra, proximal transverse process hooks reduced the 3 biomechanical indices by approximately 26%. The use of proximal transition rods with reduced proximal diameter from 5.5 mm to 4 mm decreased the proximal junctional kyphotic angle (by 6%) and the proximal flexion force (4%) and moment (8%). The increase of the sagittal rod curvature from 10° to 20°, 30°, and 40° increased the proximal junctional kyphotic angle (by 6%, 13%, and 19%) and the proximal flexion force (3%, 7%, and 10%) and moment (9%, 18%, and 27%). Conclusion. Preserving more posterior proximal intervertebral elements, the use of transition rods and transverse process hooks at upper instrumented vertebra, and reducing the global sagittal rod curvature each decreased the 4 biomechanical indices that may be involved in PJK. Level of Evidence: N/A

Spinal Cord Injury in the Pediatric Population: A Systematic Review of the Literature

Spinal Cord Injury (SCI) in the pediatric population is relatively rare but carries significant psychological and physiological consequences. An interdisciplinary group of experts composed of medical and surgical specialists treating patients with SCI formulated the following questions: 1) What is the epidemiology of pediatric spinal cord injury and fractures?; 2) Are there unique features of pediatric SCI which distinguish the pediatric SCI population from adult SCI?; 3) Is there evidence to support the use of neuroprotective approaches, including hypothermia and steroids, in the treatment of pediatric SCI? A systematic review of the literature using multiple databases was undertaken to evaluate these three specific questions. A search strategy composed of specific search terms (Spinal Cord Injury, Paraplegia, Quadriplegia, tetraplegia, lapbelt injuries, seatbelt injuries, cervical spine injuries and Pediatrics) returned over 220 abstracts that were evaluated and by two observers. Relevant abstracts were then evaluated and papers were graded using the Downs and Black method. A table of evidence was then presented to a panel of experts using a modified Delphi approach and the following recommendation was then formulated using a consensus approach: Pediatric patients with traumatic SCI have different mechanisms of injury and have a better neurological recovery potential when compared to adults. Patients with SCI before their adolescent growth spurt have a high likelihood of developing scoliosis. Because of these differences, traumatic SCI should be highly suspected in the presence of abnormal neck or neurological exam, a high-risk mechanism of injury or a distracting injury even in the absence of radiological anomaly.

A proposal for a surgical classification of pediatric lumbosacral spondylolisthesis based on current literature.

The classification presented in this paper is the first specifically designed to guide surgical treatment of L5–S1 spondylolisthesis in children and adolescents. It also presents objective criteria to differentiate between low- and high-dysplastic spondylolisthesis and incorporates recent knowledge in the study of sagittal spinopelvic balance. The proposed classification is based on the following: (1) the degree of slip, (2) the degree of dysplasia, and (3) the sagittal spinopelvic balance. To classify a patient, the degree of slip is quantified first to determine if it is low-grade, high-grade, or a spondyloptosis. Then, the degree of dysplasia is evaluated based on seven criteria, in order to separate patients with low- and high-dysplastic spondylolisthesis. Finally, the sagittal spinopelvic balance is assessed from the measurement of the pelvic incidence (PI), sacral slope (SS), and pelvic tilt (PT). For low-grade spondylolisthesis, it is classified as low PI/low SS (nutcracker type) or high PI/high SS (shear type). For high-grade spondylolisthesis, it is classified as high SS/low PT (balanced pelvis) or low SS/high PT (retroverted pelvis). Such a comprehensive classification could allow to better evaluate and compare available surgical techniques, and to optimize the treatment of L5–S1 spondylolisthesis. Because the classification was designed so that groups are organized in an ascending order of severity, it becomes easier and more intuitive to develop an associated surgical algorithm because the complexity of the surgery should increase as the severity of the spondylolisthesis increases. A tentative treatment algorithm is proposed but it is not definitive because further studies are required to define the most appropriate treatment for each group.