Scoliosis Research Society
SRS: Scoliosis Research Society

Scoliosis Research Society

Dedicated to the optimal care of patients with spinal deformity

Other Spinal Conditions

Post-Surgical Malalignment

Patients who have undergone spinal fusions surgery (either for scoliosis or for degenerative low back conditions) are at risk for developing post-surgical malalignment. Types of post-surgical malalignment are described below; both result in an imbalance of the spine from the side (sagittal imbalance) and lead to progressive low back pain and stiffness.

  • Flat Back Syndrome: Experienced by patients who have had long fusions of the spine. The spine loses its normal inward curvature (known as lordosis); patients are unable to stand upright and are usually "pitched" forward.
  • Junctional Kyphosis: An sharp curvature that develops just above or below a previous spinal fusion. For more information on Proximal Junctional Kyphosis, click here.
  • Post-Laminectomy Curvature: Occurs, rarely, after a common procedure used to treat spinal stenosis (pinched nerves) in adults – especially if many levels are decompressed. The curvature takes on the form of scoliosis (front curve) or kyphosis (forward bend).
  • Adjacent-Level Disease: Results from a spinal fusion that places additional stress on the neighboring segments to the fused vertebrae, possibly contributing to accelerated arthritis. The body may lean to the side or forward. Significant spinal curvature typically does not occur; however, symptomatic curves can develop.
  • Post-surgical Instability: Results when a spine loses the ability to support itself after extensive low back surgery. Symptoms are similar to adjacent-level disease, but may occur within the operated levels themselves. Also, every fusion procedure has a risk that the bones will not join together.
  • Failed Fusion: Happens when the bones in a fusion procedure will not join, possibly leading to further collapse of the spine. The risk for failed fusion increases as the number of vertebra fused increases.


The spine is made up of individual vertebra linked together by a disc in the front and 2 small joints in the back of the spine—similar to the links in a watchband. The "links" or joints allow bending and twisting of the spine. These joints frequently become worn out, or arthritic, with aging or following injury, and eventually become painful. If pain is not controlled with physical therapy, exercise, and medication, a fusion may be suggested by your physician to stabilize the arthritic part(s) of the spine. Better methods of selecting patients for surgery, as well as better surgical techniques have made pseudoarthrosis a less common outcome of spinal fusion surgery.

Pseudoarthrosis is derived from a Greek term meaning "false joint". The term is used to describe the outcome of surgery that does not result in a solid fusion, which occurs more commonly in elderly patients, smokers, patients with medical problems, and patients on certain medications. Other conditions with an increased risk of pseudoarthrosis are:

  • Obesity
  • Osteoporosis
  • Chronic steroid use
  • Diabetes mellitus
  • Other chronic illnesses
  • A previous pseudoarthrosis
  • Malnutrition


A surgeon may have difficulty determining if pseudoarthrosis is present. If pseudoarthrosis has occurred, a recurrence of pain very similar in location to that before surgery will often be noted over a period of months, or the pain may gradually increase shortly after surgery.

Imaging Evaluation

  • Computerized tomography (CT) scan is the best study to identify pseudoarthrosis
  • X-rays may demonstrate loosening or breakage if instrumentation was used in surgery


If a painful pseudoarthrosis is identified, your spinal surgeon will make further recommendations for additional treatment, which may include additional surgery.

Adult / Fixed Sagittal Imbalance (flat-back syndrome)

Fixed sagittal imbalance (FSI) occurs when spinal alignment prevents patients' ability to stand up straight. Loss of sagittal balance causes patients to compensate by bending their hips and knees to try to maintain an upright posture. This puts greater strain on the muscles of the lower back and legs.

Distinguishing characteristics of sagittal imbalance are:

Posture Range Adaptability
Flexible imbalance: Patients can stand up straight if they "work at it (with their hips and knees straight)" Local: Just a few a vertebra cause significant tilt Compensated: Patients can offset imbalance by flexing knees and hips
Fixed imbalance: Patients are unable to stand up straight despite best efforts Regional: Many vertebra causing a slow forward bend Decompensated: Patients are not able to offset imbalance via adjusted posture or stance
See below.
  Mix: Many vertebra causing a slow forward bend
See below.


When lower back and leg muscles take on the burden of compensating for the sagittal imbalance, several symptoms may result:

  • Fatigue
  • Gradual loss of function
  • Decrease in the activities of daily living.

Imaging Evaluation

Imaging helps to assess segmental alignment, curvatures, instability, neurologic issues, and more:

  • X-rays with the knees and hips extended are critical to understand the extent of the imbalance.
  • CT scan helps define the bony anatomy, for example areas of neural impingement or failed fusion (pseudoarthrosis)
  • MRI is the gold-standard for demonstrating the anatomy of the nerves and discs.
  • Bone scan show areas of increased activity that may demonstrate pseudoarthrosis or otheranomalies.

These images show the importance of long-cassette x-rays with the knees and hips extended. The left picture shows the patient's compensated posture, while the right picture shows the extent of the sagittal imbalance in the same patient

Treatment Options

Nonoperative Treatment

Non-invasive, non-surgical therapies are typically the first recommendations for the treatment of sagittal imbalance:

  • Non-steroidal anti-inflammatory medications (NSAIDS)
  • Physical therapy
  • Epidural steroid injections (for diagnosing and treating lumbar pinched nerve).

Bracing is ineffective for sagittal imbalance because it weakens the posture muscles, and does not treat the underlying pathology. If the imbalance progresses and there is significant pain, surgery is usually indicated.

Operative Treatment

The decision process for surgery depends on: the type of sagittal imbalance, a history of prior surgeries, the degree and location of neural compression, the age and health of the patient, and more.

Posterior osteotomy (also called "Smith-Peterson" or "Ponte" osteotomy)

This procedure involves removing facet joints and certain ligaments. The facet joints typically limit extension of the spine so their removal (posteriorly) allows the surgeon to accentuate lordosis by tilting the bones through a mobile disc space. Over multiple levels, 5o to 15o of lordosis per level is possible.

Posterior Osteotomy:
A) A side view of the spine showing the bone and facet resection.
B) A side view after the osteotomy is closed.
C) A lateral (side) radiograph of a woman with severe, rigid, Scheurmann's kyphosis.
D) A lateral x-ray after surgery. Multi-level posterior osteotomies allowed the surgeon to reduce the kyphosis to normal levels.
Pedicle subtraction osteotomy

Surgeons use this procedure to cut through segments of the spine causing sagittal imbalance. Known as a "closing wedge osteotomy", a triangle of bone is removed so the bone can be angled backwards. (The technique similar to placing a wedge between bricks, creating a sudden backward bend in the spine.) The procedure is particularly powerful, especially in the lumbar spine where the bones are bigger, and small corrections can lead to large improvements in posture. The surgery requires the support of instrumentation above and below the osteotomy and is a major surgery with relatively high rates of complications.

Pedicle subtraction osteotomy:
A) A side view showing the area of bone resection in pink.
B) The lordotic segment after the osteotomy is closed. Note how the front of the vertebra is twice the height of the back causing lordosis.
C) The preoperative x-rays of a patient with fixed sagittal imbalance due to bone settling and infection.
D) A lateral (side) x-xrayray showing the restored lordosis after the osteotomy.
Vertebral column resection

The most powerful (and invasive) of all spinal osteotomies, the vertebral column resection is necessary when there is a sharp, severe bend in a small area. It involves essentially dislocating the spine in a controlled manner and realigning it in the proper direction.

Vertebral column resection:
A) A side view of the spine showing the additional bone removed beyond a pedicle subtraction osteotomy (added area in blue).
B) A strut graft or cage is placed between the cut vertebra.
C) & D) The front and side view of a woman with severe, rigid kyphoscoliosis.
E) & F) Postoperative front and side x-rays after the realignment procedure.
Anterior-posterior osteotomy

Like the vertebral column resection the anterior-posterior also, in essence, the anterior-posterior osteotomy (APO) dislocates the spine so that it can be repositioned properly. In an APO, he back section of the bone is removed from the back of the spine, and the front portion is removed from a separate anterior incision. The anterior-posterior osteotomy has the same effect as a vertebral column resection, but it avoids risky surgical navigating around the nerves to remove the vertebra.

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