An Overview of Flat Back Syndrome

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In flat back syndrome (a.k.a. fixed sagittal imbalance) the normal curve in your lumbar spine is reduced or eliminated. A primary symptom is difficulty standing for long periods of time.

Flat back syndrome can be congenital, due to degeneration or trauma, or the result of spinal surgery. Treatment often involves physical therapy, bracing, or surgery.

Woman in plank pose outside
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The spine normally has two curves, which are necessary for balance and to maintain one's center of gravity, allowing for the best biomechanics in movement.

The lumbar spine curves inward where it meets the pelvis, as does the cervical spine in the neck. These are called lordotic curves. The thoracic spine curves outward, which is called called a kyphotic curve.

The normal lordotic curves are part of the spine's natural alignment; it helps you balance your body as you meet the physical demands of your daily activities.

When these curves are lost, you can have trouble standing up straight and may stoop forward, especially by the end of the day. It may feels like you'll falling forward. You may also have to flex your hips and knees and adjust your pelvis in order to stand straight.

When you look at the body from the side, the sagittal axis (front to back) should align no more than 5 millimeters (mm) from vertical. In flat back syndrome, the center of mass is pushed forward and the axis is more than 5 mm from vertical.

Being off-center can make it hard to walk and perform other daily activities, and you may feel fatigued from the strain of trying to maintain balance.

The body compensates for flat back syndrome by carrying the head and neck forward, which can cause strain and chronic back pain in the neck, upper back, and shoulders.


Flat back syndrome can be the result a variety of processes or it can be congenital (present at birth).

Historically, Harrington-rod spinal instrumentation (sometimes used to correct scoliosis) flattened the lumbar spine and resulted in flat back syndrome, especially with age.

While modern surgical techniques have reduced this type of scoliosis correction, flat back syndrome can occur after laminectomy done to decompress spinal nerves.

Other causes include:


Diagnosis of flat back syndrome begins with a description of symptoms and medical history (especially of previous spinal deformity or spine surgery).

Your healthcare provider then performs a physical examination, including a musculoskeletal exam and a neurologic exam with you in lying and standing positions. A gait exam can also look for changes you have made to compensate for the loss of spinal curvature.

X-ray imaging of the spine can assess sagittal alignment. Your provider will consider other possible sources of the symptoms before confirming the diagnosis.


Conservative treatment for flat back syndrome includes exercises and physical therapy, which teaches stretching and strengthening exercises to improve posture.

A common strategy is using exercise to reverse the pattern of muscle imbalance that keeps the flat low back in place. Hamstring and abdominal stretches are key in this process.

The National Health Service in the United Kingdom recommends the following exercises to strengthen core, buttocks, back, neck, and rear shoulder muscles.

Using a gentle, sustained hamstring stretch held for about 30 seconds at a time (performed once or twice daily) is often the best way to restore proper alignment to your lumbar spine.

A physical therapist can assess you and recommend exercises and other forms of treatment. This can include bracing to provide better support.

In some cases, surgical correction may be necessary for restoring alignment. Various kinds of osteotomy may be considered, including:

  • Polysegmental wedge osteotomy
  • Pedical subtraction osteotomy
  • Posterior vertebral column resection
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  1. Kim D, Menger RP. Spine sagittal balance. StatPearls. Updated January 9, 2019.

  2. National Health Service. Common posture mistakes and fixes. Updated January, 2016.

  3. Roussouly P, Nnadi C. Sagittal plane deformity: an overview of interpretation and management. Eur Spine J. 2010;19(11):1824–1836. doi:10.1007/s00586-010-1476-9