Scoliosis Research Society (SRS)
Scoliosis Research Society (SRS)
An International Organization Dedicated to the Education, Research and Treatment of Spinal Deformity
Our Mission is to Foster Optimal Care for All Patients with Spinal Deformities


Fixed Sagittal Imbalance

Causes of Fixed Sagittal Imbalance (Flatback Syndrome)

1. Congenital Malformation of the Vertebra
If one or several bones are wedged forward at birth (or while growing), the spine may not develop the proper balancing lumbar lordosis. In children, the spine is usually flexible enough to compensate. However, over time, the adult spine may lose its ability to adapt to the malformed vertebra.

2. Developmental
A compensated lumbar kyphosis may decompensate as the discs degenerate over time. Similarly, a progressive thoracic kyphosis may overcome the lumbar spine’s ability to compensate over time (click here for and example). [Posterior osteotomy example]

3. Postsurgical
“Postsurgical” means that the body was not able to compensate to changes in the body’s sagittal alignment after surgery. Common causes are multilevel fusions with loss of proper lordosis or postoperative infections.

Postsurgical FSI:
Postsurgical FSI:
A) Progressive settling of the spine after sequential lumbar fusions caused a significant loss of lumbar lordosis.
B) Infection above a hypolordotic fusion (not enough lordosis) led to decompensation of sagittal alignment.
C) Distraction instrumentation led to “Flatback disorder”.

4. Flatback Disorder
In the early days of spinal instrumentation, a device called a “Harrington Rod” straightened the spine similar to how a car jack lifts a car. While it was effective in straightening the spine, it tended to remove normal lordosis and kyphosis leading to “Flatback Disorder”.

5. Infections

6. Transition Syndrome
When a segment of the spine is fused, the adjacent levels receive additional stress. At times the bones may fracture or discs may deteriorate at an accelerated rate.

Transition syndrome:
Transition syndrome:
A) A 65-year old woman with thoracolumbar scoliosis and mild positive sagittal imbalance (head in front of her hips) underwent a T10-sacrum fusion.
B) After surgery, her sagittal alignment was normal.
C) After a fall, she developed a fracture over the fusion and began to lean forward.
D) Over time, her fixed sagittal imbalanced progressed making it difficult to stand up straight.
Congenital Scoliosis
Early Onset Scoliosis
About Early Onset Scoliosis
Infantile Idiopathic Scoliosis
Thoracic Insufficiency Syndrome
Juvenile Idiopathic Scoliosis
Idiopathic Scoliosis