Flat Back Syndrome (Flatback Syndrome): Causes, Symptoms, and Treatment

Also called lumbar kyphosis, fixed sagittal imbalance, or straight back syndrome — flat back syndrome is the loss of natural curvature (lordosis) in the lower spine, forcing the body forward and causing back pain and fatigue that worsens throughout the day.

By Francis C. Lovecchio, MD · Attending Spine Surgeon, Hospital for Special Surgery, New York, NY

A 67-year-old woman presented with a primary complaint of back pain and an inability to stand upright. She had a prior spine fusion 5 years ago for leg pain, and did quite well for the first 3 years. Over the last two years, she noted increasing difficulty managing day-to-day tasks due to back pain. Her symptoms had progressed gradually over the prior two years, and walking more than 10 minutes was now impossible without stopping to rest.

Notably, she had little leg pain. Symptoms were concentrated in the lower back and radiated into the buttocks, but did not extend down the legs. She had no numbness, no tingling, and no shooting pain — the picture was firmly localized to the lumbar region. She described the pain as "aching" or "fatigue."

The pain resolved completely when lying down or sitting. That feature pointed toward a structural alignment problem rather than a nerve compression problem.

What is flat back syndrome?

To stand upright, most people require lordosis at the lower portion of the spine. Lordosis is a backward (inward) curvature. The lumbar spine normally has this curve, which allows the body to stand upright without continuous muscular effort. The amount and location of lordosis a person needs is dependent on the shape of their pelvis.

When patients lose that lumbar curvature, the body is forced into a forward-leaning position. The muscles of the back, pelvis, and legs must then work continuously to maintain an upright posture. The resulting fatigue accumulates throughout the day, producing pain and a pronounced sense of exhaustion.

This pattern matched the patient's presentation closely. She had no leg pain and no leg weakness — both of which would suggest nerve compression. Her symptoms were localized to the back and buttocks, with worsening fatigue as the day progressed.

Flat back syndrome can develop spontaneously as the spine degenerates and loses curvature over time. However, it can often develop due to a prior surgery in which the spine is fused "flat." That was the case with this patient: she had undergone three prior spine surgeries — one laminectomy and two fusions — and had been fused with too little lordosis. When flat back syndrome develops after a prior fusion, it is a form of failed back surgery syndrome — the umbrella term clinicians use for complications that emerge after spine surgery.

The clinical term for this condition is sagittal malalignment, also known as sagittal imbalance. When the spine loses its normal curves, the body's center of gravity shifts forward, out of the "cone of economy." Every muscle from the back down through the legs is required to compensate, and over time that compensation fails.

What are the symptoms?

Patients with flat back syndrome typically describe back pain that worsens throughout the day. In the morning they may feel relatively well, but as time spent upright accumulates — walking, standing, running errands — back pain and fatigue build. Many describe the sensation of being pushed forward, unable to remain upright regardless of effort.

The pain generally resolves when lying down or sitting. This is a telling feature: it means the muscles, which have been working all day to counter the forward pitch, are finally being relieved.

Leg pain is generally not part of the clinical picture. When a patient with flat back also has leg pain, additional pathology — such as nerve compression — is usually involved, and the symptoms must be carefully separated to determine which intervention addresses which problem.

How is flat back syndrome diagnosed?

Evaluation begins with a physical exam following a careful history of the timeline and any prior spine surgeries. In this patient's case, the exam showed that her nerves were working normally — her legs were strong, sensation was intact, and reflexes were normal. The defining finding was on standing assessment: she was visibly pitched forward.

Imaging followed. A full-body X-ray was obtained to evaluate overall alignment. A CT scan was used to assess the bone and confirm that the prior fusions had healed. An MRI was obtained to evaluate the nerves; although nerve compression was not suspected as the primary problem, it had to be ruled out before any surgery was considered.

The X-ray measurements confirmed the suspicion: she lacked appropriate curvature in the lower spine, the result of being fused too flat in prior surgeries.

Spinal alignment is measured in several ways — degrees of lordosis, gravity lines, vertebral pelvic angles — the specifics of which are beyond the scope of this article. The relevant finding, however, was clear: she did not have enough curvature at the bottom of her spine, and this was the reason she could not maintain an upright posture.

The X-ray also showed compression fractures in the upper lumbar spine, which prompted a bone density test. She was found to have osteoporosis — an essential finding that changed the pre-operative plan.

The MRI showed minor pinching of the nerve roots, but the findings did not correlate with her symptoms, which were concentrated in the back rather than the legs. This further confirmed that the underlying problem was structural. The CT scan confirmed that the prior fusions were solidly healed.

What are the treatment options?

Non-surgical treatment

The patient was offered the standard range of non-operative options: physical therapy to strengthen the supporting musculature, injections with non-operative spine providers, and oral medications.

She pursued these for several years without achieving meaningful relief. Physical therapy is appropriate in this setting — strengthening the muscles can compensate for some loss of curvature. But when the structural problem is severe enough, muscle conditioning alone cannot make up for a malaligned spine.

When surgery makes sense

The patient eventually elected to do surgery. The shape of the spine can be altered in two ways — through the discs or through the bone. Given that her discs were fused in the prior surgeries, our only option was to restore the shape of the natural spine through cutting a wedge in the bone.

What is a pedicle subtraction osteotomy?

The procedure recommended for this patient was a pedicle subtraction osteotomy, or PSO. The pedicle is the part of the vertebra that connects the front of the spine to the back. In a PSO, that section of bone is removed in a wedge-shaped fashion. Closing down the wedge induces backward curvature — restoring lordosis to a segment that has lost it.

An accessible way to describe the mechanics: it is similar to felling a tree. A wedge is cut, and the structure falls into the gap. In the spine, the wedge is cut out of the fused bone, the gap is closed, and the segment angles backward into a more natural position.

Pre-operatively, this patient had approximately six degrees of lordosis at the bottom of her spine. After the PSO, she had nearly 46 degrees — a more typical amount of lordosis for that region, sufficient to allow her to stand upright without the constant muscular compensation that had been driving her pain.

Because a PSO leads to a major change in the shape of the spine, additional rods are placed to provide extra strength. Multiple rods and screws hold the spine in its corrected position while the bone heals.

Getting your body ready for surgery

Among the most important factors in spine surgery outcomes is the patient's overall health going into the operation. The objective of pre-operative preparation is to optimize physiological reserve, so the body tolerates surgery well and recovers efficiently. For this patient (and any patient), four areas required attention before the operation could be scheduled.

Bone density. The osteoporosis identified on bone density testing had to be treated first. Any time screws and rods are placed in the spine, they require strong bone to anchor into. She was referred for medical treatment to improve her bone density before surgery was scheduled.

Muscle conditioning (prehab). She was referred to physical therapy. She had completed multiple rounds in the past — the lack of response is why surgery was being considered. The purpose of prehabilitation, however, is different: it is not to address the underlying spinal pathology, but to strengthen the supporting musculature so that post-operative recovery is more efficient.

Cardiovascular fitness. She was asked to perform approximately 20 minutes per day of cardiovascular exercise in the months before surgery. For her, a recumbent bicycle was the most practical option; this is often the case given that walking is usually painful. The goal is to give the body a measurable cardiovascular reserve heading into a long anesthetic and a multi-week recovery.

Medical optimization. Her mild diabetes, controlled with metformin, was confirmed to be well managed before scheduling. Any other medical conditions are similarly addressed before surgery is performed.

"Once we made her the best version of herself that she could possibly be, we took her for surgery."

What is recovery like?

The patient was hospitalized for approximately four days following the operation, then discharged home.

At six months post-op, her recovery has been favorable. Back pain is substantially improved, and she no longer requires a cane or walker. Side-view X-rays show the difference clearly — where she previously had almost no curvature in the lower spine, she now has 46 degrees of lordosis. That restored curvature allows her to stand in a more natural, relaxed posture.

She remains relatively early in the recovery period. Continued improvement is expected over the months and years ahead, and the result so far has been encouraging.

What are the risks?

A pedicle subtraction osteotomy is a major spine operation that carries real risks. Bone quality is critical — if osteoporosis is not addressed first, the screws may not hold reliably. Hardware failure, in which rods or screws loosen or fracture, is a possibility, particularly in patients with poor bone quality. This is part of the reason that pre-operative optimization is emphasized.

Standard risks of major spine surgery also apply: blood loss, infection, and nerve injury. The procedure is several hours long and involves substantial correction of the spine's alignment. It is not a minor operation. We are essentially "breaking" the spine in a controlled fashion. That means the body responds accordingly — so even when the surgery is performed efficiently and with low blood loss, patients can still have complications secondary to the body's inflammatory trauma response: lung, heart, or stomach problems are all possible. We are currently conducting research on methods to enhance the body's ability to respond to the trauma of surgery.

Patients who reach the point of needing a PSO have usually exhausted other treatment options, having pursued physical therapy, injections, and medications for years. For appropriately selected patients — those who are medically optimized and have a clear structural problem driving their symptoms — the surgery can produce a meaningful improvement in standing tolerance and quality of life.

Frequently asked questions

Why can't I stand up straight?

When the lumbar spine loses its natural lordosis (inward curve), the body's center of gravity shifts forward. The supporting muscles try to compensate, but cannot maintain an upright posture indefinitely. The result is a forward-pitched stance that worsens as the day progresses — a hallmark of flat back syndrome, sagittal imbalance, and related spinal deformities.

How is flat back syndrome fixed?

When the underlying problem is structural — and especially when prior fusions have healed without enough lordosis — surgery is the only reliable way to restore curvature. A pedicle subtraction osteotomy (PSO) removes a wedge of bone from a fused vertebra and closes the gap, inducing backward curvature at that level. For appropriately selected patients, this can restore upright posture and meaningfully improve quality of life.

Can flat back syndrome be reversed without surgery?

In mild cases, physical therapy and strengthening of the supporting musculature can compensate for some loss of curvature and reduce pain. When the structural malalignment is severe — particularly after prior fusion — non-surgical treatment cannot restore the lost lordosis. At that point, surgery becomes the only definitive option.

Is flat back syndrome the same as kyphosis?

They are closely related. Kyphosis is forward curvature of the spine — normal in the thoracic (mid-back) region but abnormal in the lumbar (lower) region. When the lumbar spine loses its lordosis and develops kyphosis instead, the result is flat back syndrome. The terms flat back syndrome, lumbar kyphosis, and fixed sagittal imbalance are often used interchangeably.

Considering flat back syndrome surgery in NYC?

Dr. Francis Lovecchio is an attending spine surgeon at the Hospital for Special Surgery in New York City, specializing in adult spinal deformity correction, revision spine surgery, and pedicle subtraction osteotomy. He sees patients from across the New York tri-state area — Manhattan, Brooklyn, Queens, Long Island, New Jersey, and Connecticut.

Schedule a consultation →

Key takeaways

Definitions

Lordosis. Backward curvature. This is the natural shape of the lumbar (lower) spine. This backward curvature allows the body to stand upright without the muscles having to work constantly. Loss of lumbar lordosis is the central problem in flat back syndrome.

Kyphosis. Forward curvature. This is the natural shape of the thoracic (mid-back) region. When excessive, or when the lumbar spine develops kyphosis instead of lordosis, the body pitches forward.

Sagittal malalignment. A condition where the spine's normal shape is disrupted, causing the body's center of gravity to shift forward. The body compensates by "sitting back" — bending the hips and knees — but over time this compensation fails and causes pain and fatigue.

Pedicle subtraction osteotomy (PSO). A spine surgery where a wedge of bone is cut from a vertebra — through the pedicle — and then the wedge is closed, inducing backward curvature (lordosis) into a segment of the spine. Used when the spine is fused in a flat or forward position and needs to be re-angled.

Pedicle. A part of the vertebra that connects the front of the spine (vertebral body) to the back (lamina and spinous process). The pedicle is also where surgeons place screws during spinal fusion because it provides strong fixation into the bone.

Osteoporosis. A condition where bones lose density and become more fragile. In spine surgery, osteoporosis is a concern because screws and rods need strong bone to hold on to. Treating osteoporosis before surgery improves the chances that hardware will stay in place.

Spinal fusion. A surgery that permanently connects two or more vertebrae using screws, rods, and bone graft. Once fused, those vertebrae no longer move independently. If a fusion is performed without enough lordosis, the patient may develop flat back syndrome.

Compression fracture. A fracture where a vertebra collapses, usually due to osteoporosis. Compression fractures can contribute to loss of spinal curvature and forward posture. Their presence also signals that bone quality may need to be addressed before any surgical intervention.