الفهرس 
Anatomy of spinal curvature andOnly 14 pages are availabe for public view
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Abstract
Sagittal balance reflects a shape of the spine that allows it to keep the standing position with little muscle effort .
The shape of the spine is the result of the sum of the shapes of bony elements (the vertebrae) and discs. Bone resists compression and keeps its shape under physiological compressive forces.
Normal sagittal spinal balance is a result of mutual articulation of the pelvis and the spine in the sagittal plane (spinopelvic balance ).
A normal thoracic spine should exhibit between 20 and 50 of kyphosis while the lumbar spine should be in 30 to 80 of lordosis .
The main purpose of these lordotic and kyphotic spine segments is to balance the head over the pelvis in an energy efficient position. allowing the C7 plumb line, a vertical line drawn from the center of the C7 vertebral body, to pass within a few millimeters of the posterior superior corner of S1.
By convention, positive sagittal balance occurs when the C7 plumb line falls anterior to the posterior-superior corner of the S1 endplate.
Spinal sagittal imbalance ( deformity of the spine in the sagittal plane) is nowadays a major cause of pain and disability among patient presenting to the spine clinic in daily practice.
Negative sagittal balance occurs when the C7 plumb line falls posterior to sacral plate of S1.
Sagittal balance is the most important and reliable radiographic predictor of clinical health status in the adult patient presenting with spinal deformity.
Sagittal imbalance of the spine is mainly related to any underlying pathology causing loss of lumbar lordosis (LL) such as multilevel degenerative disk disease, kyhphotic deformity, spondylolithesis , ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis, osteoporosis, tumor, trauma, or infection. Secondary causes include iatrogenic flat back syndrome being attributed to the use in the past of distraction instrumentations such asthe Harrington rods.
Change in the spine sagittal alignment can be compensated by compensatory mechanisms occurring in the spine, pelvis and lower limb areas. The main objective of these mechanisms is to allow the patient to keep an erect position.
Once sagittal imbalance has started the pelvis tilts backwards (pelvic retroversion. bringing the C7 plumb line backwards resulting in extension of the hips. This pelvic retroversion makes PT (pelvic tilt )increase putting the femoral heads forward and the sacrum and the spine backwards allowing the C7 plumb line to stay behind the femoral heads.
Pelvic incidence determines the global capacity of pelvis retroversion. the pelvis can tilt more with a high PI (pelvic incidence )than with a low PI, since there is a much wider range through which adaptation can occur.
If the full body is balanced but it is a compensated balance, which is less efficient. At the same time the posterior spine muscles act as a posterior tension band trying to restore some LL.
The adjacent segments of the kyphotic spine are hyperextended allowing for the compensation of anterior translation of the C7 plumb line. This hyperextension leads to reduction of TK(thoracic kyphosis ) in the young patients with flexible spines.
Spine hyperextension is an energy consuming process that generates increase of stresses on posterior structures resulting in risk of retrolisthesis, facet joints overstress and even sometimes isthmic lysis.. When pelvis backward rotation and spine hyperextension are not enough to keep the C7 plumb line behind the femoral heads, the only solution to keep the gravity line between the two feet is to bend the knees.
When knee flexion fails to put the C7 plumb line behind femoral heads, the full body is now in a decompensated balance, the use of external support (e.g., crutches, walker) is often the only way to keep the balance.
Thus, in the most severely imbalanced cases, the patients will present with : trunk tilted forward, retroversion of the pelvis, extension of the hips and flexion of the knees.
Symptomatic deformity is often unresponsive to nonsurgical treatment. Patients with back pain and sagittal imbalance may show little or only temporary improvement with physical therapy programs, selective nerve root blocks, facet joint injections, epidural steroid injections or bracing.
If the non surgical methods fail Surgical intervention must be done to restore sagittal balance , Either through fixation only or with osteotomy
Spinal osteotomies may be needed to restore sagittal balance according to the flexablity of the spine and the amount of correction needed
If the deformity is flexable no osteotomy is needed ,If the deformity is fixed osteotomy must be done as( SMO,PSO,VCR)