Introduction

The flatback syndrome is a postural disorder of the spine described by affected patients as a feeling of leaning forwards or being "bent over" with difficulty or inability to stand erect without knees and hips flexed. The symptomatic loss of proper spinal alignment in this syndrome frequently leads to complaints of stumbling while walking, catching feet on carpets, and having particular difficulty walking on uneven ground.

Due to the strain of trying to maintain erect posture, pain and fatigue develop in cervical, thoracic and distal lumbar areas as well as in the thighs and buttocks, where muscles are under constant strain due to compensatory mechanisms.

Although flatback syndrome can result from a variety of iatrogenic etiologies, it is most commonly attributed to instrumentation, such as Harrington rods, extending into the lumbar spine (L4, L5) or the sacrum for scoliosis correction. A related syndrome of pain and sensation of imbalance with spinal sagittal malalignment resulting from lumbosacral fusions in kyphosis can be termed Kyphotic Decompensation Syndrome (KDS) or Flatbuttock.

Initial treatment for all patients with flatback and kyphotic decompensation syndromes (ex. Flatbuttock) is focused upon optimizing the compensatory mechanisms and paraspinal muscle function. When conservative management has failed, and pain and function are disabling, the spine surgeon may consider surgical treatment.

Patient Evaluation

The patient who presents for complications related to sagittal plane malalignment is most commonly in the late twenties to forties age range and has either had surgery as a teenager for scoliosis or had surgery as a young adult for 'disc' or 'instability' related pathology. Initial assessment should start with a careful history of not only the original diagnosis and surgical treatment but also an analysis of pain patterns and functional limitation. Physical examination includes a detailed neurologic evaluation and may detect abnormal reflexes, associated nerve dysfunction, weakness, and muscle contracture.

Radiographic studies should include a standing full-length standard scoliosis series. The full-length radiographs will permit calculation of frontal and sagittal plane offset of the plumbline. Should the radiographs reveal a possible non-union, a series of regional anteroposterior, lateral and oblique radiographs are obtained. With suspected junctional instability it is recommended to obtain dynamic radiographs to analyze the degree of intersegmental motion. Computed tomography, magnetic resonance imaging, and myelograms may be indicated to evaluate neurologic symptoms.

Treatment Approach

Flatback and the Kyphotic Decompensation Syndromes present in a wide spectrum of radiographic malalignment and clinical symptoms and findings. Detailed evaluation will determine if there are associated pathologies (spinal stenosis, disc herniation, instability...) which must be considered in the overall treatment of the spinal malalignment. Initial aggressive guided isometric back strengthening program is recommended in most patients. In conjunction with weight loss for overweight patients, this may provide effective treatment for mild malalignment patients. Guided exercises will also optimize the overall condition for those patients who may require surgical treatment.

In patients with flatback and fusion short of the sacrum, the evaluation of mobile segment discs is crucial. Well-hydrated discs without evidence of advanced degeneration and annular tears may be preserved when considering realignment surgery. For patients with KDS (or flatbuttock) the status of discs proximal to previous fusion must be carefully examined. Extension of fusion may be required in some cases. Once a decision has been made to realign a previous fusion, CT and MRI will assist in determining the level of corrective osteotomy. The goal of the surgical intervention is global balance, and treatment of any associated pathologies (stenosis, disc herniation, instability, pseudarthrosis).

Surgery

It should be noted that some patients suffering from flatback (or related syndromes such as flatbuttock, KDS) may benefit from simply removing prominent or painful instrumentation. The decision to proceed with such a minimal surgical approach is based upon physical exam and character of the pain. Typically, pain in these cases is attributed to instrumentation when it is localized, and reproduced by palpation over prominent components. This pain is thus different from what was felt to be pain secondary to malalignment: gluteal, quadriceps and distal lumbar back stiffness and pain which is progressive over prolonged standing or motion.

If a patient is not a candidate for simple removal of instrumentation and suffers from significant malalignment, then the surgical intervention will most likely include osteotomies (cutting through the previous spinal fusion) and revision instrumentation (removal of previous implants and replacement with a new system).

The optimal surgical strategy in a particular patient depends upon a number of factors including: levels of previous fusion, the degree of spinal imbalance, the age and general health of the patient, other associated spinal pathologies (spinal stenosis, pseudarthrosis...). In some cases the spine is best realigned through anterior and posterior approaches to the spine. This usually means an incision is made in the flank area, the spine is exposed surgically and either remaining discs are resected (if still present), or the spine is cut in the area of previous fusion to obtain the possibility of realignment during the posterior portion of the surgery.

If discs are removed than the disc space is commonly filled with fragments of the patient's own bone and sometimes a metallic cage or ring of allograft (donor) bone. The patient, after completion of the anterior surgery, is then repositioned on a special operating table in the prone position (face down) so that the second portion of the operation can be performed on the posterior portion of the spine. The posterior surgery usually involves removal of the previous instrumentation (in flatback this commonly means Harrington rods or a similar system), osteotomy of the spine (ie. Cutting through the fused spine to regain mobility), a controlled correction of the malalignment and then placement of new instrumentation to maintain the corrected position of the spine.

In some cases, the surgery of the spinal column can be performed with a technique of simultaneous anterior and posterior procedures. This approach is technically challenging, but if two teams of experienced spine surgeons are familiar with the procedure, operating time, blood loss, and risks due to instability between stages may be decreased. An additional possible advantage of a simultaneous technique is control over the anterior graft which otherwise is vulnerable to displacement during sequential procedures that involve patient repositioning.

In some patients with kyphotic decompensation (or flatbuttock) who have had previous anterior and posterior surgery, a posterior-only technique may be possible to obtain correction of the deformity. By resection of a set of pedicles (pedicle resection osteotomy) from the spine through a posterior operation, significant realignment is possible in certain cases. This technique has the advantage of offering correction through one incision (and anterior surgery may be avoided).

Complications

As with any spinal surgery, there are significant risks to revision surgery for Flatback and related syndromes. Possible complications include: deep vein thrombosis (blood clot), wound infection, radiculopathy (nerve root irritation or injury), significant blood loss, suboptimal realignment, pseudarthrosis. The complication rate for revision surgery in the setting of deformity can be up to 50%. Most of these complications can be managed without long-term concerns but revisions surgery remains a challenging area that requires significant expertise.

Discussion

The Flatback and Kyphotic Decompensation Syndromes are pathologies related to spinal fusion. Although one can recommend to never fuse the spine, it must be emphasized that fusion should be minimized, in terms of anatomic extent, and optimized in terms of rigorous patient selection and careful consideration of physiologic spinal alignment. The treatment of painful disability due to spinal malalignment must focus first on maximizing paraspinal muscular function and compensatory mechanisms. Removal of painful instrumentation can be quite successful in some cases. When these less invasive approaches are unsuccessful, realignment surgery may be indicated and excellent results are possible.

References

1. Doherty, J.H.: Complications of fusion in lumbar scoliosis. J.Bone Joint Surg. 55A:438, 1973
2. Farcy, J-P.; Schwab, F.J.: Flatback and the related Kyphotic Decompensation Syndrome. Spine 1997
3. Grobler, L.J.; Moe, J.H.; Winter, R.B.: Loss of lumbar lordosis following surgical correction of thoracolumbar deformities. Orthop Trans. 239:2, 1978
4. Kostuik, J.P.; Maurais, G.R.; Richardson, W.J.; Okajima, Y.: Combined single stage anterior and posterior osteotomy for correction of iatrogenic lumbar kyphosis. Spine 13(10):257, 1988
5. Lagrone, M.O.; Bradford, D.S.; Moe, J.H.; Lonstein, J.E.; Winter, R.B.; Ogilvie, J.W.: Treatment of symptomatic flatback after spinal fusion. J.Bone Joint Surg. 70A:569, 1988

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