Question 3 : Is there a predictive score ?

- A multi-centre prospective study would be required.

Question 4 from Denis Kaech : And what about traumatic tetraplegia following a fall in old patients ?

- Decompressive surgery is justified in case of lower signal intensity during electrophysiological exploration.

The next paper by Jean-Denis Laredo, focused on Imaging of the stenotic lumbar canal. He stated that in case of cervical stenosis, compression was very aggressive with an anterior and posterior impingement. In this situation, he pointed out the necessity of assessing the intramedullary signal.

Either this medullay signal can present with well-defined margins, which is a bad prognosis marker, or it can show indistinct margins, which is a better prognosis factor.

With regard to lumbar stenosis, MRI is very important in order to perform the following evaluations : edema of vertebral bodies (Modic ] signs are the most significant ones) ; facet joints edema; thecal sac or medullary stenosis. The surface of the canal should not be lower than 75 mm 2, which is the critical threshold, as well as an antero-posterior diameter of 8 mm. In presence of a stenosis, 1/3 is also a critical threshold. Myelography performed in a standing position or functional MRI is essential for a lumbar stenosis because 10% of patients have pathognomonic stenosis only with the

combination of static stenosis and dynamic stenosis.

Jean-Pierre Elsig then addressed the issue of Functional MRI, detailing the possibilities it offers and wondering if it will eventually replace myelography. He stated that compression was increasing when the patient was in a standing position and that functional MRI had the advantage of allowing kinetic imaging. He provided examples of correlation and of absence of correlation between classical and clinical MRI imaging. In particular, he explained that recumbent imaging modalities failed to detect dynamic stenoses, whereas functional MRI allowed to investigate the patient in all flexion, extension as well as rotation movements.

Question 1 from Aymen Ramadan to Jean-Denis Larodo : Is there a place for thin layer scanners ? - To Jean-Pierro Elsig : is it possible to do without the functional MRI ?

- Answer from Jean-Denis Laredo : Concerning thin layer scans, they are standard and routinely carried out, but it is a difficult choice to make between them and MRI.

Answer from Jean-Pierre Elsig : Good surgery can be achieved thanks to reliable MRI diagnosis, which allows to reduce failure rate.

Question 2 : What level of resolution and what kind of distinctness can be obtained with functional M R I ?

- 0.6 tesla - it is a regular MRI- 2.5 mm. Painful patient positioning results in poor resolution.

Question 3 from Gilles Perrin : Does synovial facet cyst mean instability (degenerative spondylolisthesis) ?

- Yes, if the cyst is not old, otherwise it can be stabilized.

I Question 4 : In Japan, is dynamic myelography used for assessing lumbar scolioses ?

- Yes, but FMRI is superior for axial cuts (sacco-scanner -CT with intrathecal injection- is performed with a patient in a lying position).

Patrick Corlob6 explored the subject of Electromyograms (EMG) and Evoked Potentials (S.SEP). The aim of his paper was to determine if these examinations were sufficiently relevant to identify the different vertebral levels involved. First, he explained that the lack of correlation or wrong correlation between clinical results and EMG, SEP and MEP imaging, was detrimental to the surgical outcome.

He specified EMG allowed to evaluate the location and extent of radicular lesion as well as to express a prognosis. Two techniques are currently available : needle electrode (assessing the representative muscle) and stimulo-detection focusing on H reflexes of inferior limbs. SEPs are induced by stimulation of sensitive nerve conductions for lumbar and cervical spine, but they are not appropriate for thoracic region. MEP allows to implement magnetic stimulation of the cortex.

Carlo Logroscino specified he would never consider performing surgery without electrophysiological examination, a

/ V ~ o S p l n e Nt~w/--- & J o u r n a l N~ April 2007

Q Question 1 from Robert Melcher : And what about peroperative evoked potentials ?

- Answer from Carlo Logroscino : He confirmed he used peroperative- monitoring SEP, but had trouble to perform the examination. He said the surgeon could be helped for quick surgical steps on cervical spinal cord, while the risk was lower if the surgeon performed a relatively slow surgery. He added that this method was little used in France.

- Answer from Ms Emery : she replied she used them every day, as MFPs were very predictive for myelopathy.

The last guest speaker of the diagnosis session was Carlo Logroscino who developed on Treatment Strategy, specifying what level to treat first and giving an account of his own experience about prevention of complications and patient information.

He presented laminectomy combined with fusion as a good solution for therapeutic management of tandem spine stenosis, mentioning the different types of laminoplasties : Hirabayashi, Kurokawa, etc., and C5 neurapraxia. He advocated 360 ~ decompression in case of severe stenosis. In presence of an association of cervical and lumbar stenosis, the most

symptomatic level should be treated first, identified by an accurate clinical, imaging and electrophysiological examination. He concluded that surgical intervention should be appropriate to the case, and not the reverse.

When dealing with a lumbar stenosis, do you look for an associate cervical stenosis ?

Double stenosis is systematically studied in Japan on government recommendation. Any patient suffering from lumbar stenosis can also have an associated cervical stenosis and vice versa. According to Mr Crockard, evaluations and surgical decision-making are dependent on patients' positioning. African patients are very likely to present with a double stenosis.

The Thursday afternoon session, dedicated to Decision Criteria in Cervical Stenosis opened with a paper by Evelyne Emery on treatment strategy, surgical approach and technique. She raised the issue of objective decision-making and gave an account of her critical analysis of over 120 papers, including only three prospective ones. She did not notice any difference between groups with and without surgery. Nevertheless, she has observed decreasing results over long follow up time.

In order to choose the surgical strategy and to help determining the patient's eligibility for surgery, she said she used clinical examination and MRI, CT scan...

Ms Emery has closed her presentation with a review of the techniques [posterior

approaches, mixed approaches, arthroplasty) and of their indications [segmental stenoses, extended stenoses). In her experience, the surgical strategy consisted for 80% of cases in an anterior approach.

Developing the subject of treatment strategy, Paul Cooper explained that after 50, practically everyone had arthrosis but half of patients were asymptomatic. He also stated OPPL [Ossification of Posterior Longitudinal Ligament) was frequent, and not only in Japan. According to him, the surgical decision was easy to make for medullary compression with clinical signs. However, he asked about the appropriate strategy to adopt in case of positive imaging outcome and in absence of clinical features. He said in such a situation, he preferred posterior decompression with instrumentation, although Robinson and Cloward introduced the value of an anterior approach.

In presence of contiguous osteophytes, he would opt for corporectomy and if a great number of levels were involved, he said a posterior approach was preferable.

In the clinical case he reported, he used a plate with locked screws. The result was satisfactory : patients' condition improved because they were happy with the procedure. He insisted that the outcome depended on the used score. He presented a summarized Cooper Scale ranging from 0 [intact) to -1 > 4. Professor Cooper noted greater improvement in strength than function. Motion increased but sensory loss affected hands and inferior limbs, spasticity was still present, but strength returned.

Paul Cooper, in the clinical case he presented, raised the issue of posterior decompression, which was according to him, ideal for multiple levels, especially OPPL, but should be avoided in case of pre-existing kyphosis. On the other hand, immediate laminectomy with instrumentation would allow to preserve cervical

11:3 / ~ ' ~ 0 5 p l n e N e w s & J o u r n e l N~ 5 Apri~ 2007

lordosis. He also mentioned the possibility for a secondary anterior approach.

If the spinal cord moved in the posterior direction, posterior approach would avoid the complications entailed by the anterior approach (dysphagia, etc). The presentation concluded with the assertion that combining the use of anterior and posterior approach was ideal for a multilevel lesion and kyphosis.

Paul Cooper has stopped using preoperative and peroperative electrodiagnosis because it was predictive but not preventive.

Paul Cooper uses an anterior approach if the lesion does not involve more than two levels and if lordosis is preserved. Christian Mazel says he first performs a posterior approach because it is less aggressive than an anterior approach. Jean-Pierre Elsig always starts with an anterior approach. Many attendees are of the same opinion as Christian Mazel.

Subsequently, Paul Cooper asked if laminectomy still held a place in the treatment of cervical stenosis. He also posed the question of the right moment when to add a fixation after laminectomy and/or laminoplasty. For Professor Cooper, the arguments in favour of laminoplasty were all open to criticism. Recovery rate after laminoplasty and laminectomy seemed equal according to JOA score. Nevertheless, instrumented laminectomy gave better results because it prevented harmful movements and, avoided an aggravation by kyphosis.

Kazumasa Ueyama asserted that laminectomy no longer held any place in the

treatment because it resulted in secondary kyphosis. He also referred to the post- laminectomy membrane described by LaRocca in 1974. Mr Ueyama mentioned the several techniques of laminoplasty available : Hattori, Hirabayashi, Itoh, Nakano; as well as the open door technique with spacer device in HAP. He added that skip laminectomy had little effect on myelopathy and was only effective for the removal of tumours.

In his case illustration, Kazumasa Ueyama observed only 5 occurrences of kyphosis after laminoplasty out of 59 patients, without any neurological pain. He pointed out that if the length of the spinal cord increased of more than 2 mm, it would lead to poor outcome. Shortening of the cervical spine by narrowing discs could also have an influence on the outcome. He finally specified that in presence of preoperative kyphosis, he added a fixation.

Question 1 from Alan Crockard : Have you observed nuchalgia after laminoplasty ?

- Answer from Paul Cooper : Not so much as close to the hinge.

- Answer from Kazumasa Ueyama : The duration of surgery and muscular atrophy cause pain (below C2).

- Answer from Alan Crockard : The reinsertion of muscles would be indicative of a good prognosis and he recommends as well to avoid any postoperative collar.

Paul Cooper : But according to literature, the more the patient moves, the poorer the result will be.

Question 2 from Aymen Ramadan : What to think about laminoplasty in Europe and the U.S. ? Here, in France, this technique does not seem to live up to expectations! What is the opinion of the Japanese surgeons ?

- Answer from Kazumasa Ueyama : I have e.xperience in laminectomy and I have observed limited mobility postoperatively. The arthrodesis proved useful with limited movement amplitude. We have performed laminoplasty on more than 400 patients. After the learning curve, it can be carried out within an hour without complications, with the exception of C5 (regressive), but this technique is very demanding. There is no comparative prospective study available for these two methods.

Question 3 : And what about long posterior arthrodesis ?

- Answer from Paul Cooper : C3-Thl arthrodesis does not result in degeneration above, but C2/C3 should be preserved.

The most frequently damaged level is C5-C6 (this is confirmed by the audience and on functional MRI). The cervical spine .position, which allows to best reveal a cervical dynamic foraminal stenosis is :extension in 63% of cases and rotation in 20% of cases. What is the most frequent associated pathology ? The answer is : an additional dynamic foraminal stenosis in 57% of cases on functional MRI. While according to the audience, it was thought to be a dynamic central stenosis, o

ArooSp lne N L ~ F -, & J o u r n e l N~ April 2007 !i

u Which of the two sexes most frequently suffers from stenosis ? The answer is : men.

Kazumasa Ueyama centred the next part of his presentation on spinal cord injury in cervical stenosis and dealt with the issue of the strategy to adopt in the acute period as well as in the long term. He took an example of spinal cord injury and said that 15 patients were operated among 108 cases without bony injury. Then, he commented three papers by Japanese authors. He notably advocated prophylactic decompression as a good solution to avoid tetraplegia. For him, a rapid recovery was a marker indicating a good outcome. Finally, for severe stenosis, he recommended a preventive laminoplasty.

The following speaker on Spinal Cord injury (SCI) was Evelyne Emery. She explained it could lead to various clinical expressions, mainly central cord syndrome. She reported a case where edema of white substance was the lesion detected by spinal cord sections in a patient injured and deceased five days after an accident. She said SCI in cervical stenosis occurred through a hyperextension phenomenon. After performing initial neurologic examination, she observed acute central syndrome in 17 out of 23 cases and bladder dysfunction in 20 out of 23 cases. No bone fracture was depicted on CT scans, Xrays and MRI in 90% of cases. She concluded her presentation by giving examples of preventive surgery procedures.

The Friday morning session was devoted to Thoracic Stenosis and opened with Stefano Boriani who dealt with Treatment Strategy and especially focused on the right time when to operate, the appropriate approach and technique in the treatment of arthritic stenosis, soft hernia and calcified hernia.

When canal stenosis is present in the thoracic spine, pain is very frequent but neurological signs are variable. The etiology includes the presence of masses and/or deformity.

He reported 424 cases in which tumours were present. When benign, recovery was satisfactory, but if they were malignant or if metastases were found, poorer recovery ensued. The prognosis was very variable with possible unexpected findings. He implemented oncological treatment, followed by appropriate reconstruction. He observed that infection could result in stenoses, for instance with Port's disease. He next gave the example of staphylococcus treated only with ATB. The hyperkyphosis was operated secondarily with success. The strategy applied

consisted in posterior decompression, drainage and restoration of balance.

In a different case illustration, Stefano Boriani focused on the etiology of degenerative, forms, which are less frequent (such as Scheuermann disease). In these cases, he recommended laminectomy and reconstruction. For herniated discs, the appropriate strategy was described in 1988 with anterior approach. They are frequently detected on IRM but often asymptomatic (one case out of a million is not). Pain is a good indication (14 cases over 15 years). The disc is often ossified (also in Scheuermann disease). The operation is associated with important morbidity. In many cases, the disc is adherent to the dura mater. The disc must be removed with the help of the curette or the drill with an anterior transdiscal approach. This method is effective on pain, but has less effect on sphincter disorders. If a posterior approach is necessary, it is recommended to use a transpedicular microscopic approach and treatment by thoracoscopy, but there is a learning curve for this demanding surgery.

The next presentation by Stephan Gaillard dealt with endoscopic surgery. He said that thoracic disc pathology was less infrequent than usually observed. It was often found on MRI but asymptomatic for 7% of cases. In practice, there are two possible situations : patients with clinically rich symptoms or patients with few or no symptoms. He recommended to perform MRI (CT scan) EMG, SEP, MEP or medullar angiography. He explained the decision should be made trying to find a balance between the risks related to disk herniation and those related to surgery.

In the case he reported, Stephan Gaillard insisted on the importance of assessing herniation volume and patient's age ratio and in his series, he observed large volume and young age. Posterolateral or anterior approach resulted in 11,6% morbidity. He operated 19 patients in 6 years. The mean age was 56 years. The patients

t 2 ,&rQoSplr '~, Ne~v~. & J o u r n e l N~ April 2007

were in a strict lateral decubitus. They underwent endoscopy and the operation was carried out according to the results. The surgery lasted for two hours. There were improvements in 8 cases, 10 patients returned to normal and I aggravation was observed. Mr Gaillard explained that intra- operative localization was not easy (two errors were made), especially in superior thoracic. For this reason, he recommended making a mark on the rib. In order to avoid epidural blood loss, the drilling had to be performed more anteriorly. For dural breach, he said he used glue or graft. If a choice was possible, anterior approach was preferable. Finally, he observed that performing endoscopy resulted in less morbidity.

- Answer from Stephan Gaillard : He is used to visualizing Adamkievicz artery because for him, it is important to find out the role played by this artery. The operation cannot be performed without clamping several pedicles and it is better to avoid clamping the artery.

- Answer from Stefano Boriani : There are numerous anastomoses.

Christian Mazel says that angiography is useful to inform the patient and there is a lesser risk with an anterior approach. The message is that we have to be more cautious.

- Answer from Stefano Boriani : According to him, performing angiography or not, does not make any difference.

Question 2 from Stephan Gaillard to Stefano Boriani : How to explain to the patient the medullar risk incurred when performing an angiography ?

- Answer from Stefano Boriani : The risk lies in the manipulation of the medullar cord and not in the medullar ischemia.

The majority of surgeons present would not perform an angiography.

On Friday afternoon, the Lumbar Stenosis session, tackling treatment strategy, opened with Jean-Pierre Elsig who centred his presentation on the right moment to perform additional stabilization and/or fusion after posterior decompression. First, he detailed treatment choices : according to him, to ensure primary stability, an appropriate decompression was prerequisite; primary fusion required large decompression; and in case of primary imbalance, he advocated decompression with fusion and balance reconstruction.

In conclusion, Mr Elsig said that in order to define an indication, the surgeon should take into account the patients, clinical findings and imaging; and only after a critical analysis of these elements, should he be able to make a decision.

In the following presentation by Stefano Boriani, laminectomy was described as a possible source of destabilization although giving good results for stenoses, with or without fusion (variations were reported to be small). He specified that if osteophytosis was present, stabilization was not necessary. In old patients, he said he used cemented screws. As for minimally invasive surgery of kyphotic callus, it could prove useful in some cases of hyper-lordotic stenoses.

Another high point of the symposium was the Best Thesis award, given in the name of the Argos association by Professor Christian Mazel, its president. This prize was awarded to Yoann Lafon-Jalby for his work on scoliosis correction (see page 13).

Finite e lement s imula t ion of var ious s t rategies for scol iosis surgical cor rec t ion Our work on the personalized surgery simulation provides promising prospects for the future : such a clinical tool could help surgeon in understanding the mechanisms of correction, and in performing his pre- operative surgical planning, o

A r Q o f ~ p l n e N e w s & J o u r n e l N~ April 2007 {::~qJ

a The numerical simulation for the scoliosis surgical correction could be helpful in establishing the best surgical planning for a given patient. Previous research at the Laboratoire de Biom6canique yielded a preliminary finite-element model, and demonstrated the feasibility of a patient- specific simulation. However its extreme tediousness and its lack of self-reliance made it difficult to be used in a clinical environment. The objective of our work is to take over this finite-element model, in order : first, to improve two key-parameters, i.e. automation for the assessment of patient-specific mechanical properties, and robustness (numerical stability and self- reliance) for the simulation of surgery. Second, to model various clinical cases in order to evaluate the clinical relevance of the model and to better understand mechanisms of correction. The mechanical properties identification of the spine, from in vivo data (clinical lateral bending test), was automated thanks to an optimization method driven by a priori knowledge. The precision of this tool has been estimated according to in vivo data from the clinical records of thirty scoliotic patients. A stable and user-free simulation was built for the scoliosis surgical correction for two different techniques : by the rod rotation - CotreI-Dubousset (CD)instrumentation- and by in situ bending (CIS). In particular, a specific algorithm defines and simulates the sequences of in situ bendings in agreement with the clinical expertise. The biomechanical coherence of the surgery simulation was estimated, according to the post-operative in vivo data (from the clinical records of twenty and ten scoliotic patients operated respectively by the CD and CIS surgeries), and to the clinical literature for

the per-operative surgical steps. Finally, several surgical alternatives were evaluated, and various concepts of correction were analyzed from a biomechanical point of view.

After the presentation of the Thesis Award and a brief introduction on its contents given by the author, the final part of the meeting was devoted to Neurological Postoperative Compli- cations, focusing on diagnosis, clinical presentation, investigations and treatment.

Kazumasa Ueyama dealt with cervical complications after corpectomy and laminoplasty. He reported C5 palsy in 4,6% of cases with shifting of the spinal cord. He implemented physical therapy treatments. Recovery rate for patients with severe conditions was 71% and 96% in mild ones. In severe cases, longer time was required for recovery. He observed that these lesions could not be detected by MEE Mr Ueyama, as another possible complication, mentioned axial pain after a laminoplasty. Extended surgery time plays a significant role and decrease rate of muscle area is another risk factor. He nevertheless specified that C3 laminectomy could prevent muscle area from decreasing.

The following presentation by Stephan Gaillard focused on thoracic complications. He named some of them : regressive medullar contusion, spinal cord injury, central cord syndrome and Brown- S6quard syndrome. Next, he raised the issue of the kind of investigation to perform in case of aggravation. He

resorted to MRI to look for an epidural hematoma, which is not very likely to be present. However, if it should the case, he recommended revision surgery. Spinal cord hypersignal should be treated by shockwave therapy (with little effect). LCR leak occurred due to a breach in 0% to 15% of cases. In these situations, a parietal pleural flap was fixed with bio-glue. He also recommended to avoid thoracic drainage because it entailed a risk of thoracic meningocele.

As a conclusion, he emphasized the importance of the learning curve for becoming an experienced surgeon, the preventive information given to the patient and the preoperative arteriography.

The final speaker was Carlo Logroscino who dealt with lumbar complications. The first ones he studied were intradural edema or epidural hematoma. He noted that non-myelinated sensitive nerve fibres were more resistant than motor nerve fibres.

He next stated that peroperative patient's positioning could produce vascular compressions. He also mentioned cauda equina caused by epidural hematoma with a coagulopathy and excess administration of anticoagulants contributing to its development, with a low thromboembolic risk in spine surgery. He recommended prophylactic bandage of lower limbs. According to him, if an epidural hematoma was present, the patient should be reoperated immediately. He also pointed out that insufficient decompression would lead to an acceleration of degeneration. Another complication was dural tear, which occurred in 13,2% of revision surgery versus 80/0 in primary. He explained that surgery was not always the culprit and that sometimes the breach was unavoidable. Finally, he mentioned possible complications due to the malposition of pedicle screws.

The symposium was closed with an interactive discussion and clinical case study, followed by a short version of the present synthesis, written and delivered by Professor Pierre Kehr. Ioi

FINAL TRANSLATION BY NATHALIE RICHARD WITH THE

EXCEPTION OF THE THESIS AWARD BY ANCA MITULESCU

I q / V g o . 5 1 3 1 n e N e w - - . & J o u r n a l N~ April 2007

rod rotation - CotreI-Dubousset (CD) instrumentation and by In Situ Contouring (ISC). In particular, a specific algorithm defines and simulates the sequences of in situ bendings in agreement with the clinical expertise. The biomechanical coherence of the surgery simulation was estimated, according to the post-operative in vivo data [from the clinical records of twenty

assist surgeons during the pre-operative planning to define the levels to be fused or the magnitude of the per-operative correction, by providing objective data related to mechanical implications of a given strategy.

Few authors proposed 3D numerical models to simulate scoliosis surgery techniques. Belytschko et al? ~ and Shultz et

2007 Argos thesis award Finite element simulation of various strategies for scoliosis surgical correction [r YOANN LAFON-JALBY | JEAN DUBOUSSET | JEAN-PAUL STEIB

The numerical simulation for the scoliosis surgical correction could be helpful in establishing the best

surgical planning for a given patient. Previous research at the Laboratoire

de Biom6canique yielded a preliminary finite-element model,

and demonstrated the feasibility of a patient-specific simulation. However its extreme tediousness and its lack

of self-reliance made it difficult to be used in a clinical environment.

The objective of our work is to take over this finite-element model, in order : first, to improve two key-

parameters, i.e. automation for the assessment of patient-specific

mechanical properties, and robustness (numerical stability and

self-reliance) for the simulation of surgery. Second, to model various clinical cases in order to evaluate

the clinical relevance of the model and to better understand

mechanisms of correction.

- - - h e identification of mechanical t properties of the spine, from in . . . . . vivo data [clinical lateral bending

test), was automated thanks to an optimization method driven by a priori knowledge. The precision of this tool has been estimated according to in vivo data from the clinical records of'thirty scoliotic patients. A stable and user-free simulation was built for the scoliosis surgical correction for two different techniques : by

and ten scoliotic patients who underwent CD and ISC surgeries respectively). The main per-operative surgical steps were analyzed from a biomechanical point of view, and the results were compared to clinical literature.

Our work on the personalized surgery simulation provides promising prospects for the future : such a clinical tool could help surgeon in understanding the mechanisms of correction, and in performing his pre- operative surgical planning.

Ke:y~ords = Biomechanics, scoliosis surgeG, finite- element simulation.

The surgical techniques for spinal deformity like scoliosis has evolved, from the Harrington instrumentation to the CotreI-Dubousset instrumentation [CD) and the in situ Contouring technique (ISC). Segmented surgical treatments for scoliosis perform a complex three-dimensional correction of the spine, depending on the pre- operative strategy and the per-operative maneuvers. Surgeons plan the best strategy according to the curvature type, the pre-operative flexibility tests, and general guidelines. However, in several cases, the optimal solution is difficult to assess objectively. Developing mathematical models could

al. [2] reported FE simulation of Harrington correction, without validation. Stokes and Laible r3] simulated Harrington and CD surgical corrections : Gardner-Morse and Stokes [4], as Poulin et al. [8], underlined that an identification of the patient-specific mechanical properties was necessary. Lafage et al. [6] concluded in the same way that a patient-specific geometry did not reproduce the patient-specific spine behavior during flexibility tests. So Leborgne et al. ET] proposed an inverse method to identify the disc stiffness, according to clinical standard bending test data and the corresponding FE bending test simulation : the mechanical identification was driven by a priori knowledge. Lafage et al. [~j evaluated this driven heuristic method on 10 patients, concluding to the clinical coherence of the spine stiffness distribution, despite the extreme tediousness of the procedure. Petit et al. [9] proposed an automated algorithm for mechanical identification; however, authors underlined the limit of their specific algorithm that could lead to clinically irrelevant stiffness distribution.

Lafage et al. [Sj and Dumas et al. [1~ used the Leborgne's method to personalize the 3D FE model, and performed respectively CD and ISC surgery simulations. The coherence for surgery simulation was evaluated for 10 patients and 2 patients respectively, by comparing post-operative in vivo data (from bi-planar Xray 3D reconstruction) and the virtual spine configuration [from surgery simulation). Mean differences for both 0

A n : ; i o S p l n e Ne,w,---. & J o u r n e l N~ April 2007 L.~::3.