Flatback Syndrome

What causes flatback syndrome?

Flatback was first recognized in patients treated with Harrington rods. These straight distraction rods were standard for scoliosis from the 1950s through the 1970s. They straightened the spine side to side but often flattened the lower back. In one long-term study, 52% of Harrington-treated patients had a flat or reversed lower-back curve.

Flatback is still seen today. It can follow modern lumbar fusions that do not restore enough lordosis. Other causes include disc degeneration, a fusion that did not heal, and collapse above an earlier fusion. In a 2024 study by Dr. Diebo and colleagues, nearly half (45%) of adult deformity operations were revisions. Among patients with prior short lumbar fusions, 92.5% had less lordosis at the fused levels than their anatomy called for.

What are the symptoms?

• Leaning forward, especially as the day goes on
• Inability to stand fully upright (reported by 95% of patients in a classic series)
• Low back pain (89% in the same series)
• Neck and upper-back pain from straining to look ahead
• Tired legs, knee pain, or needing a cart or cane to walk

Why do my knees and hips hurt?

When the lower back loses its curve, the body compensates in a predictable order. First the upper back flattens and the pelvis rotates backward. When that is no longer enough, the knees bend. Dr. Diebo's research showed that older patients have less ability to tilt the pelvis and rely more on the knees. That shift costs energy and causes fatigue.

How is flatback diagnosed?

Diagnosis requires standing, full-length X-rays from the side, ideally including the hips and knees. Key measurements are:

• How much lordosis you have compared with your pelvic shape (PI–LL mismatch)
• How far forward your trunk sits over your pelvis (SVA)
• How much your pelvis is tilted back (pelvic tilt)

Dr. Diebo's group developed the global sagittal axis, a whole-body measurement that reflects both the deformity and how much a patient is compensating. See Pelvic incidence and Scoliosis X-rays.

Can flatback be treated without surgery?

Physical therapy that focuses on back-extensor and hip strength can ease symptoms. It cannot restore lordosis in segments that are already fused. Non-surgical care is still the first step for most adult deformity.

What surgery is used for flatback?

The most common correction is a pedicle subtraction osteotomy (PSO). In this procedure, a wedge of bone is removed from a vertebra and closed to restore the inward curve. A 2024 review of 595 patients reported these average results:

• Forward lean (SVA) improved from 12.4 cm to 3.9 cm
• Lumbar lordosis improved from 13° to 43°
• Disability scores were roughly cut in half

PSO is a major operation. It averaged about seven hours and about two liters of blood loss. Complications included non-healing (8%), nerve problems (8%), and failure above the fusion (6%).

Flatback that follows an earlier fusion is harder to fix than a first-time deformity. In one series, 46% of these patients needed another operation. Extra (supplemental) rods across the osteotomy greatly lower the risk of rod fracture.

Can flatback be prevented?

Often, yes. Dr. Diebo's 2024 research shows how the amount and location of lordosis needed vary with each person's pelvic shape. Planning a first lumbar fusion with that in mind may prevent flatback later.

When to see a specialist. If you lean forward, can't stand straight, or have new pain after a prior fusion, request an appointment.

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