Schwab F, Lafage V, Boyce R, Skalli W, Farcy JP.
Gravity line analysis in adult volunteers: age-related correlation with spinal parameters, pelvic parameters, and foot position.
Spine (Phila Pa 1976). 2006 Dec 1;31(25):E959-67. doi: 10.1097/01.brs.0000248126.96737.0f.
Abstract/Text
STUDY DESIGN: Prospective radiographic and forceplate analysis in adult volunteers.
OBJECTIVE: Assess gravity line (GL) location and foot position regarding anatomic spinal structures to evaluate key correlations and age-related changes in balance.
SUMMARY OF BACKGROUND DATA: Global spinal balance is commonly assessed by the C7 plumbline. This radiographic parameter does not offer information on foot position or forces transmitted, and poor correlation with the true GL has been demonstrated.
METHODS: A total of 75 asymptomatic adult volunteers were equally distributed into three age groups. Full length, free-standing spine radiographs were obtained with simultaneous acquisition of GL and feet location (forceplate). GL and heels were projected on each radiograph to compute their distance from anatomic entities and to investigate correlations with radiologic parameters and age-related changes.
RESULTS: In this study group, advancing age led to a significant increase in thoracic kyphosis. The plumbline from C7 shifted anteriorly with age. In the sagittal plane, the GL was anterior to the vertebral column for all groups. With age, the GL location regarding the heels remained constant, while the pelvis moved posteriorly toward the heels and underwent a small retroversion (increasing pelvic tilt). The acetabulum was the most reliable radiographic marker of the GL location.
CONCLUSIONS: This quantitative study in volunteers reveals clear age-related changes in the spino-pelvic association and offers quantitative support to the "cone of economy" concept proposed by Dubousset. The pelvis can be seen as a regulator to help maintain a rather fixed GL-heel association with age-related changes in the spinal column. Further study in patients suffering from deformity can confirm the importance of radiographic-gravity line correlations and enhance our understanding of optimal balance.
Glassman SD, Bridwell K, Dimar JR, Horton W, Berven S, Schwab F.
The impact of positive sagittal balance in adult spinal deformity.
Spine (Phila Pa 1976). 2005 Sep 15;30(18):2024-9. doi: 10.1097/01.brs.0000179086.30449.96.
Abstract/Text
STUDY DESIGN: This study is a retrospective review of 752 patients with adult spinal deformity enrolled in a multicenter prospective database in 2002 and 2003. Patients with positive sagittal balance (N = 352) were further evaluated regarding radiographic parameters and health status measures, including the Scoliosis Research Society patient questionnaire, MOS short form-12, and Oswestry Disability Index.
OBJECTIVES: To examine patients with adult deformity with positive sagittal balance to define parameters within that group that might differentially predict clinical impact.
SUMMARY OF BACKGROUND DATA: In a multicenter study of 298 adults with spinal deformity, positive sagittal balance was identified as the radiographic parameter most highly correlated with adverse health status outcomes.
METHODS: Radiographic evaluation was performed according to a standardized protocol for 36-inch standing radiographs. Magnitude of positive sagittal balance and regional sagittal Cobb angle measures were recorded. Statistical correlation between radiographic parameters and health status measures were performed. Potentially confounding variables were assessed.
RESULTS: Positive sagittal balance was identified in 352 patients. The C7 plumb line deviation ranged from 1 to 271 mm. All measures of health status showed significantly poorer scores as C7 plumb line deviation increased. Patients with relative kyphosis in the lumbar region had significantly more disability than patients with normal or lordotic lumbar sagittal Cobb measures.
CONCLUSIONS: This study shows that although even mildly positive sagittal balance is somewhat detrimental, severity of symptoms increases in a linear fashion with progressive sagittal imbalance. The results also show that kyphosis is more favorable in the upper thoracic region but very poorly tolerated in the lumbar spine.
Schwab F, Patel A, Ungar B, Farcy JP, Lafage V.
Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery.
Spine (Phila Pa 1976). 2010 Dec 1;35(25):2224-31. doi: 10.1097/BRS.0b013e3181ee6bd4.
Abstract/Text
STUDY DESIGN: Current concepts review.
OBJECTIVE: Outline the basic principles in the evaluation and treatment of adult spinal deformity patients with a focus on goals to achieve during surgical realignment surgery.
SUMMARY OF BACKGROUND DATA: Proper global alignment of the spine is critical in maintaining standing posture and balance in an efficient and pain-free manner. Outcomes data demonstrate the clinical effect of spinopelvic malalignment and form a basis for realignment strategies.
METHODS: Correlation between certain radiographic parameters and patient self-reported pain and disability has been established. Using normative values for several important spinopelvic parameters (including sagittal vertical axis, pelvic tilt, and lumbar lordosis), spinopelvic radiographic realignment objectives were identified as a tool for clinical application. Because of the complex relationship between the spine and the pelvis in maintaining posture and the wide range of "normal" values for the associated parameters, a focus on global alignment, with proportionality of individual parameters to each other, was pursued to provide clinical relevance to planning realignment for deformity across a range of clinical cases.
CONCLUSION: Good clinical outcome requires achieving proper spinopelvic alignment in the treatment of adult spinal deformity. Although variations in pelvic morphology exist, a framework has been established to determine ideal values for regional and global parameter in an individualized patient approach. When planning realignment surgery for adult spinal deformity, restoring low sagittal vertical axis and pelvic tilt values are critical goals, and should be combined with proportional lumbar lordosis to pelvic incidence.
Roussouly P, Pinheiro-Franco JL.
Biomechanical analysis of the spino-pelvic organization and adaptation in pathology.
Eur Spine J. 2011 Sep;20 Suppl 5(Suppl 5):609-18. doi: 10.1007/s00586-011-1928-x. Epub 2011 Aug 2.
Abstract/Text
INTRODUCTION: Standing in an erect position is a human property. The pelvis anatomy and position, defined by the pelvis incidence, interact with the spinal organization in shape and position to regulate the sagittal balance between both the spine and pelvis. Sagittal balance of the human body may be defined by a setting of different parameters such as (a) pelvic parameters: pelvic incidence (PI), pelvic tilt (PT) and sacral slope (SS); (b) C7 positioning: spino-pelvic angle (SSA) and C7 plumb line; (c) shape of the spine: lumbar lordosis.
BIOMECHANICAL ADAPTATION OF THE SPINE IN PATHOLOGY: In case of pathological kyphosis, different mechanical compensations may be activated. When the spine remains flexible, the hyperextension of the spine below or above compensates the kyphosis. When the spine is rigid, the only way is rotating backward the pelvis (retroversion). This mechanism is limited by the value of PI. Hip extension is a limitation factor of big retroversion when PI is high. Flexion of the knees may occur when hip extension is overpassed. The quantity of global kyphosis may be calculated by the SSA. The more SSA decreases, the more the severity of kyphosis increases. We used Roussouly's classification of lumbar lordosis into four types to define the shape of the spine. The forces acting on a spinal unit are combined in a contact force (CF). CF is the addition of gravity and muscle forces. In case of unbalance, CF is tremendously increased. Distribution of CF depends on the vertebral plate orientation. In an average tilt (45°), the two resultants, parallel to the plate (sliding force) or perpendicular (pressure), are equivalent. If the tilt increases, the sliding force is predominant. On the contrary, with a horizontal plate, the pressure increases. Importance of curvature is another factor of CF distribution. In a flat or kyphosis spine, CF acts more on the vertebral bodies and disc. In the case of important extension curvature, it is on the posterior elements that CF acts more. According to the shape of the spine, we may expect different degenerative evolution: (a) Type 1 is a long thoraco-lumbar kyphosis and a short hyperlordosis: discopathies in the TL area and arthritis of the posterior facets in the distal lumbar spine. In younger patients, L4 S1 hyperextension may induce a nutcracker L5 spondylolysis. (b) Type 2 is a flat lordosis: Stress is at its maximum on the discs with a high risk of early disc herniation than later with multilevel discopathies. (c) Type 3 has an average shape without characteristics for a specific degeneration of the spine. (d) Type 4 is a long and curved lumbar spine: this is the spine for L5 isthmic lysis by shear forces. When the patient keeps the lordosis curvature, a posterior arthritis may occur and later a degenerative L4 L5 spondylolisthesis. Older patients may lose the lordosis curvature, SSA decreases and pelvis tilt increases. A widely retroverted pelvis with a high pelvic incidence is certainly a previous Type 4 and a restoration of a big lordosis is needed in case of arthrodesis.
CONCLUSION: The genuine shape of the spine is probably one of the main mechanical factors of degenerative evolution. This shape is oriented by a shape pelvis parameter, the pelvis incidence. In case of pathology, this constant parameter is the only signature to determine the original spine shape we have to restore the balance of the patient.
During J, Goudfrooij H, Keessen W, Beeker TW, Crowe A.
Toward standards for posture. Postural characteristics of the lower back system in normal and pathologic conditions.
Spine (Phila Pa 1976). 1985 Jan-Feb;10(1):83-7.
Abstract/Text
On theoretic grounds it can be assumed that aberrations of posture may play a role in the generation of low-back pain by creating concentrations of stress. However, this assumption remains speculative because of the absence of criteria for normal posture. This study considers some of these criteria, especially as they are related to the lumbar spine and pelvis. The relations between the angle of declivity of the sacrum and radius and inclination of the lordotic curvature of the lumbar spine show good correlation. Mean values of postural parameters in the group of spondylolysis patients differ significantly from those in the group of healthy volunteers.