In flat back syndrome, also called 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.
Your spine normally has two curves, which keep your balance and maintain your 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 lordotic curves. The thoracic spine curves outward, which is a kyphotic curve.
The lordotic and kyphotic curves are part of your spine's natural alignment. When these curves are diminished, you can have trouble standing up straight and may stoop forward, especially by the end of the day. It may feel like you'll falling forward. You may also have to flex your hips and knees and adjust your pelvis in order to stand straight.1
Normally, 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.1 In flat back syndrome, the center of mass is pushed forward and the axis measures 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 pain in the neck, upper back, and shoulders.
Anatomy of the Lumbar Spine
A variety of issues can cause flat back syndrome.
Some causes include:1
Congenital (present at birth)
Ankylosing spondylitis (a type of inflammatory arthritis of the spine)
Compression fractures of the vertebrae, such as due to osteoporosis
Degenerative disc disease
Flat back syndrome can occur after spine surgery, such as laminectomy. In the past, surgically implanted devices used to correct scoliosis often flattened the lumbar spine and resulted in flat back syndrome, especially with age. Updated surgical techniques have reduced this complication.
Diagnosis of flat back syndrome begins with a medical history that includes your history of spine deformities or back surgery.
Your doctor would also do a physical examination, including a musculoskeletal exam and a neurologic exam. Your gait exam is an assessment of your walking, which might have changed to compensate for your loss of spinal curvature.
X-ray imaging of the spine can visualize your sagittal alignment. Your provider will consider other possible sources of the symptoms before confirming the diagnosis.
Conservative treatment for flat back syndrome begins with exercises and physical therapy, which include stretching and strengthening exercises to improve posture.
A common strategy is using exercise to reverse the pattern of muscle imbalance that keeps the lower back flat. Hamstring and abdominal stretches are key in this process.
Exercises to strengthen core, buttocks, back, neck, and rear shoulder muscles include.2
Side-lying leg raises
Seated rows in a gym or pull-ups
A gentle, sustained hamstring stretch held for about 30 seconds at a time, repeated three to five times in a row (performed once or twice daily) is a good way to restore proper alignment to your lumbar spine.
Your physical therapist can assess you and recommend exercises and other forms of treatment. This can include bracing to provide better support.1
In some cases, surgical correction may be necessary for restoring alignment.
Surgeries that may be considered, include:
Polysegmental wedge osteotomy
Pedical subtraction osteotomy
Posterior vertebral column resection