Revision surgery for failed deformity


J.-P. FARCY (New York)



Addressing deformity in spine surgery is always a challenge. It always amounts to obtaining a fusion without setting the stage for other problems which will in time require further surgery. Deformity in adolescents is forgiving because young patients can easily tolerate oncoming problems which progress over years. In adults there is a shorter grace period before complications develop. In reviewing the cases of revision surgery that I performed over the last twenty years, eliminating the cases of infection or nerve compromise, I found that a large majority of problems were related to a malalignment which propelled the fused spine into poor balance.

In adolescents and young adults complications which can develop early after surgery are usually due to strategic errors which cause hardware failure, pseudarthrosis and early decompensation. Adolescents usually have fewer problems with fusion maturation therefore are mainly presenting with late decompensation, junctional failure  and fixed sagittal malalignment.

While late complications of adolescent surgery usually take ten to twenty years or more to become symptomatic, complications of surgery performed on adults  usually develop in the first year after surgery. Most of them are pseudarthrosis, junctional failure, instrumentation failure with associated mechanical stenosis with radiculopathy and increased deformity.

In both populations initial poor “ Spine Balance ” and malalignment are responsible for most of these complications.

“ Spine Balance ” is a complex concept which is not as obvious as it may sound. A number of radiographic parameters have been developed as guides of sagittal alignment. Values of thoracic kyphosis by Cobb measurements, and lumbar lordosis are commonly used to assess regional alignment. Global spinal alignment is commonly assessed by a plumb line method drawn onto full-length radiographs. More recently pelvic parameters have also been defined  in order to improve evaluation of sagittal plane balance. While ranges of normal values have been published, the correlation between these radiographic parameters and standing balance are poorly understood.

In an effort to understand and define spine balance we pursued research during 5 years  using spinal and pelvic offsets from a standing foot position captured through “force plate” analysis. (refer to the other hand out which is a copy of the accepted article by Spine.)

Spine balance in adults must be evaluated by considering thoracic kyphosis, thoraco-lumbar alignment, lumbar lordosis and pelvic parameters. Full length standing AP and lateral X Ray films of the spine must be obtained in a standardized position on a force plate to assess each patient’s balance. The images and the assessment of the gravity line are useful to recognize a flat thoracic spine,  thoraco-lumbar kyphosis,  loss of lumbar lordosis and retroversion of the pelvis. It is not sufficient to increase lumbar lordosis to restore Spine Balance. The overall spine must be addressed from cervical to the pelvis and corrections must be applied to achieve the best possible balance. In some cases of aging idiopathic deformity the ideal balance may necessitate correction of the fused flat thoracic spine but the technical difficulties command humility. Addressing the thoraco-lumbar alignment and the pelvic version to define how much lordosis must be increased is the best strategy to obtain a compromise sufficient for a successful outcome.

Correction is neither a question of pulling or pushing nor a matter of compression or distraction. Hardware can only provide for stable fixation of a correction obtained by osteotomies.

This reality of “ good alignment ” which is well known in orthopedic surgery does not appear to be used enough in spine surgery. Alignment is essentials in hip, knee, ankle, foot, elbow and hand surgery. It is also necessary in spine surgery although more complex to achieve. Pursuing the best alignment requires  serious planning. Planning for these cases was first made using tracing paper on which the X Ray films were reproduced. It was then possible to use trial and error by cutting through the tracing paper to approach the best final result. Today the most helpful tool is digitalized X Ray films on which we can apply successive corrections. It offers the possibility to choose the best strategy and to evaluate how such a complex and demanding strategy can be safely carried out. We have already understood that there is a specific balance for each spine there is also a specific strategy for each case and there is no preconceived possible recipe to follow. Experience and case preparation are the best guide lines. Always remember  that the ultimate goal is a successful spine arthrodesis in good balance.


Problems which require revision surgery

The crankshaft phenomenon following spine arthrodesis performed before the age of ten or on children with development delay is a deformity which requires surgical revision. It consists of a complex deformity sometimes compared to a “fixed spiral stair case” compromising alignment and balance, it requires complex osteotomy and circumferential arthrodesis  to achieve a correction which is often only acceptable.

Adolescent patients who undergo revision surgery after arthrodesis for idiopathic scoliosis present with: Hardware failure, pseudarthrosis and early decompensation. Strategy error is most often responsible for these complications which usually develop in the first 36 months after the initial surgery.

Misevaluation of slight kyphosis between two curves on a lateral X Ray film and a too short fusion usually cause junctional failure and early decompensation.

Misevaluation of a slight loss of lordosis while choosing an anterior technique with anterior instrumentation can lead a deformity to increase severely.

Misevaluation of the apex of a thoracic kyphosis and applying fixation to this apex can lead to serious increase of the kyphosis cranially.

Misevaluation and wrong choice of treatment for congenital deformity

Flatback is the most classic late complication of scoliosis surgery. The name “Flatback” was given to a clinical syndrome associated with a spine sagittal deformity called, fixed sagittal imbalance resulting from the flattening of lumbar lordosis by application of distracting forces to correct frontal deformity.

It has often been said that Harrington instrumentation was responsible for “flatback”. Harrington distraction rods used solo have caused flatback, however Harrington’s technique properly applied rarely caused flatback. In adults the application of lumbo-sacral instrumentation for fusion may also cause “fixed sagittal imbalance” associated with pelvic retroversion.

Usually called “ Flatback “ this fixed sagittal malalignment tolerated for years has created a situation in which all the compensation mechanisms were already recruited and finally exhausted leading to increasing pain. This syndrome is never acute and requires very thorough evaluation and precise planning.

Associated with fixed sagittal malalignment are junctional failure with stenosis and subluxation. In this case the still functional discs left caudally must be evaluated and salvaged as possible.

Pelvic retroversion must be assessed and corrected. The choice of osteotomy, (PSO) its level and magnitude are crucial to achieve the goal of correcting pelvic retro-version.

The upper part of the existing fusion may  fall in kyphosis cranially and extending the fusion cranially may be necessary with one or two posterior osteotomies (SPO). In this case the strategy of hardware fixation cranially must be optimized.

The older adult patients who underwent surgery for degenerative disease which caused a complication at the level of a known idiopathic scoliosis or for degenerative spine disease causing a deformity “ de novo ” . Both of these patient populations are made of patients in their fifties or older who were treated surgically for: stenosis, instability           ( subluxation) and deformity ( usually kypho-scoliosis). All  patients who were referred to my care for revision presented severe pain and postural problems. In addition more precise evaluation led to the diagnosis of pseudarthrosis, junctional failure with instability and mechanical stenosis associated with severe misalignment.

All patients were evaluated on a force plate while AP and Lat. free standing full length X ray films were obtained. A real gravity line was obtained as well as all spine and pelvis parameters. The films were scanned on a Vidar scan and correction of balance was applied  using computer simulation. When  planning was made to deal with balance the problems of stenosis and instability were evaluated with MRI scan or CT Myelogram in association with flexion/extension and bending films.

After complete evaluation of co morbidity by history and specialized consultation the decision of offering surgery was discussed with the patient and their family.

It is always a rather intrusive surgery which carries a high level of complication (20%) and requires a long recovery time for the patient (about one year) before resuming normal activity when the outcome is successful.

The complex problem of revision after adult deformity surgery. When and how?

Pain and disability are the symptoms for which adults consult for treatment of spine deformity. The deformity may result from disco-ligamentous degeneration of an aging spine affected or not by  scoliosis in the past. Magnitude of pain, disability and disfigurement are is the sole indication for surgical treatment. Pain in adult spine deformity is usually due to mechanical instability and stenosis as a result of a degenerative process. When the degenerative process does not end up in ankylosis the deformity increases and pain develops because all compensatory mechanisms used to maintain a good balance have been exhausted. There is no chance that accommodation can compensate for a failure of balance.

When a patient’s pain and disability is no longer tolerable it is only then  reasonable to go forth with a surgical intervention.  How ? While addressing adult deformity, alignment and balance which must be achieved at the time of surgery because any malalignment will set the stage for failure (failure of fusion, failure of correction and failure of stabilization). Sagittal alignment is a radiological concept while spine sagittal balance is a global concept in which other parameters enters.


Surgical technique

Most of the cases require decompression which may appear as the essential cause of pain and may justify a minimalist approach. This approach which consists of a localized decompression is acceptable if the evaluation demonstrates a stable spine with good or acceptable balance. If there is a serious imbalance with important pelvic retro-version and not 100% spine stability at all levels it is recommended to go for  complete realignment with fusion doing decompression as only a part of the procedure.

Fusion in the cases of revision are usually extended from T2 to the sacrum. With regard to bone graft we use Autologous bone graft supplemented by allograft and BMP.

Fusion in lumbar area and mainly at L5-S1 level must be circumferential.

The instrumentation is usually made by screws and rods but hooks may also be helpful to obtain fixation in thick fusion mass. I want to insist on fixation at cranial level which in my experience was best achieved with screws in T2 and T4 with a cross link rod connector at T3 level where a double sub-laminar cable is placed and tied up on the cross link connector. For the caudal fixation if screws are apparently sufficient in the sacrum I have found it to be more reliable to associate iliac fixation. The extension of fixation to the Ilium is recommended when there are L5-S1 pseudarthrosis and pelvic retro-version.

With that in mind now comes the choice of osteotomy and approaches. The choice of osteotomy comes first because only the thoraco-lumbar kyphosis and plane oblique osteotomy require an anterior approach. Posterior osteotomy PSO or SPO can be done with posterior approach. It is possible to associate a TLIF at one or two levels when it is necessary to obtain a circumferential fusion.

Osteotomy

It is a technique which is used to cut and remove a wedge of bone from the spine to reduce the length of the spine while correcting its alignment.

There are three types of osteotomy which are used to obtain a good balance.


The Posterior Sub-traction osteotomy

Well defined in the treatment of Ankylosing spondylarthritis the Pso was reviewed by Hening who described a decancellation . This decancellation is possible but dangerous when the bone does not present osteoporosis and when a previous thick fusion must be divided.

Our favorite technique is to use chisels ( Lambotte ) . All fixations must be in place and ready to apply compression between the two constructs above and below the PSO. Fixation requires a 4 to 6 rod technique with solid fixation as close as possible to the PSO. Having already decided between the 4 or 6 rod technique with all connectors installed to perform the fixation without loosing time it is then possible to proceed. A large diamond shaped laminectomy is necessary  to expose the pedicles, protect the dural matter and the nerve roots. When all nervous elements are protected and bleeding is controlled by bipolar cautery 2 smooth Steinman pins are inserted close to the pedicle from back to front converging to the anterior cortex of the vertebra. An intra-operative x ray film is obtained to reassess the angle between the pins which must be similar to the angle decided in planning the surgery. If the pins are in good position the chisels are pushed along the pins and when the cut is finished the wedge of bone can be removed by wiggling the chisels. When this maneuver is performed on one side it must be done in the same manner on the other side. To finish a reverse curette must be used to push anteriorly the part which may be  left from the mid-portion of the vertebra posterior wall.

This osteotomy may cause  serious blood loss therefore it is recommended to be ready for fixation in compression using the haemostatic tamponade which is the best way to stop bleeding.

It allows for correction in the sagittal plane of 30 to 35 degrees. It presents the advantage of offering two surfaces of bone in compression to insure proper fusion. It may give a less harmonious final aspect to the spine but it is the most efficient type of osteotomy to obtain the best balance. Done low at L4 level a PSO  allows for good correction of pelvic retro-version. Done higher in thoracic level it is a precious tool for correction of localized kyphosis. It is important when a PSO is chosen to make sure that it is applied on a spine segment already solid because if a non fused disc is left above or below the PSO it is almost a guaranty for the failure of the technique. When a disc is not fused and  PSO is the best technique to apply it is recommended to perform the necessary 360º fusion below prior to perform the PSO.


The posterior Smith Peterson osteotomy Trans isthmus osteotomy

This technique is efficient to correct kyphosis deformity and  gives an homogenous correction however it does not provide for more than five to six degrees of correction at each level and  requires a mobile anterior column. Well described and successfully used in Scheuermann kyphosis this technique in adult revision surgery is recommended to deal with junctional failure and some upper thoracic kyphosis if the anterior column was still mobile or made mobile by disc releases. Not as safe as it may appear SPOt can bleed and result in nerve damage.


The plane-oblique anterior posterior osteotomy (vertebrectomy)

This technique is the technique of choice to deal with a kyphosis in the middle of a fusion. Kyphosis may be due to a pseudarthrosis or a remodeling after hardware removal. This osteotomy requires an anterior approach to remove a wedge of one vertebra which will be matched by an asymmetrical posterior chevron osteotomy. It amounts to a vertebrectomy allowing for rotation correction of the spine in making the upper part slide and rotate on the plane surface of the osteotomy. This approach is also useful to perform anterior interbody fusion when it is necessary to extend the fusion to the lower lumbar spine.


Outcomes

The outcome is directly related to the correction obtained. When achieving the best balance for each given patient, outcomes are good to excellent. We are preparing a paper based on  data obtained from the balance evaluation to predict the outcome, given that the revision surgery was not hampered by complication.


Complications

The amount of complications are 20 to 25%. It is essential to discuss with each patient the risks taken in performing surgery. Each patient with pain and deformity following a previous surgery must understand that pain level and function impairment are the indications for revision surgery. Evaluation of pain and life style degradation of the patient is essential before discussing and planning revision surgery.

The other intra-operative complications are due to dural tear, mainly when osteotomies such as PSO are performed and while dealing with complex decompressions at the level of junctional failures. Rare nerve root injuries have occurred by the introduction of implants such as screws in a very modified anatomy with a distorted amplifier image rendition

Other complications may be related to the injury of other organs during anterior approaches however we didn’t have to deal with any of these.

Beside these complications there are other potential complications such as PE and cardio-vascular problems often developing after long surgery with heavy blood loss.

Conclusion

Our experience through trial and error of this very complex problem has shed light on the need for ‘ balance definition ”. The last five years were devoted to research on the study of “balance definition”. We have progressed to understanding that short of good balance there is no possible good outcome. We hope that future studies and more data acquisition will give us a solution towards this problem.



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