Long-term complications of minimally-open anterolateral interbody fusion for L5-S1.

BACKGROUND: Multiple surgical techniques and approaches exist to obtain lumbar interbody fusion. Anterolateral (oblique) is a relatively recent technique. Controversy exists for its use at the L5-S1 level. We performed this study in order to show the safety and efficacy of this technique. The aim of this study was to report the long-term complications and fusion rates of minimally-open (mini-open) anterolateral interbody fusion at the L5-S1 level. METHODS: We retrospectively analyzed all patients who underwent mini-open anterolateral interbody fusion for L5-S1 level in our department. The data collected were the following: age, sex, surgical indication, acute (less than four weeks) and long-term complications (>3 months), fusion at six months and length of follow-up. RESULTS: Seventeen patients (8M/9F) underwent mini-open anterolateral interbody fusion at L5-S1. The mean age was 64.5 years. The surgical indication was scoliosis in 10 cases, flat back in 4 cases, and spondylolisthesis in 3 cases. All patients underwent a complementary posterior procedure that included fixation. Mean blood loss was 252.9mL for the anterior procedure. Eight acute and minor complications occurred (anemia, delirium, and psoas paresis). Two acute complications required surgical intervention (cage displacement and hematoma). Long-term complications were observed in 2 cases and included proximal junction kyphosis and non-union. The fusion rate was evaluated at 88%. The mean follow-up period was 28.3 months. CONCLUSIONS: Mini-open anterolateral interbody fusion at the L5-S1 level is safe and results in fusion at the same rate as anterior interbody fusion. Most acute complications are minor and resolve spontaneously.

Management of multiple tumors in neurofibromatosis type 2 patients.

INTRODUCTION: Neurofibromatosis type 2 is characterized by the presence of bilateral vestibular schwannomas. However, other nervous system tumors may also occur. Therefore, the management of NF2 patients is complex and requires a multidisciplinary discussion in a specialized center. MATERIALS AND METHODS: All recent articles concerning tumors other than vestibular schwannoma in NF2 disease were reviewed, using PubMed databases. RESULTS: Intracranial meningiomas occur in 50% of NF2 patients, and are often multiple. Surgery remains the main treatment and should be performed in cases of growing tumors. The role of antiangiogenic therapy is currently under evaluation and the role of radiosurgery still remains to be defined in NF2 disease. Spinal tumors occur in about half of NF2 patients. Surgery should be discussed when radiological tumor progression is demonstrated, even if spinal tumors are asymptomatic, in order to preserve neurological function and good quality of life. As regards lower cranial nerve schwannomas, radiosurgery appears to be a more appropriate treatment for growing tumor with a small volume in order to avoid post-operative complications, especially swallowing disorders. Facial nerve schwannomas may appear, on MRI, like vestibular schwannomas. The diagnosis should be suspected when the facial palsy is an early symptom during cerebello-pontine tumor progression. Trigeminal schwannomas are frequent in NF2 disease and fortunately they are often asymptomatic. Among major neurofibromatosis types, peripheral nerve sheath schwannomas are only present in patients with NF2 disease and schwannomatosis. Surgical resection is required when the cutaneous schwannomas is painful or when tumor progression is observed and causes symptoms. CONCLUSION: Tumors other than vestibular schwannoma are also associated with a poor prognosis in NF2 patients. Surgery remains the main treatment in most cases. Each treatment decision in NF2 disease requires a complete evaluation of all cranial and spinal locations of the disease in order to establish surgical priorities and strategies.

[The efficacy of multimodal treatment for symptomatic vertebral hemangiomas: A report of 27 cases and a review of the literature]. / Intérêt d'une prise en charge multimodale des hémangiomes vertébraux symptomatiques : à propos de 27 cas et revue de la littérature.

INTRODUCTION: Vertebral hemangiomas (VH) represent the most common primary bone tumor of the spine and are rarely symptomatic. Currently, there is no consensus for treatment and many therapeutic options are available, alone or in combination including cementoplasty, sclerotherapy, surgery, embolization and/or radiotherapy. OBJECTIVE: To evaluate the clinical and radiological outcome of a multimodal management for symptomatic VH. METHODS: A consecutive prospective and retrospective multicenter study was conducted to review cases of symptomatic VHs between 2005 and 2015. Clinical and radiological aspects, treatment modalities and complications were evaluated preoperatively; postoperatively and at last follow-up. We also reviewed the literature of studies concerning case series of VH, published after 1990 and involving more than 10 patients. RESULTS: Twenty-seven VHs were included in our series (mean age at diagnosis: 47.9 years), out of which 26 were symptomatic. Ten presented with neurologic deficit (37%). An epidural extension was noted in 13 patients (48%). Eleven patients (41%) underwent multimodal treatments. In the multimodal group, eradication was observed in 6 patients (54%), stable residue in 5 cases (46%) with no recurrence versus 3 eradication (23%), 9 stable residue (69%) and no recurrence in the monomodal group, (P>0.05). The literature comprised 14 studies including 458 patients. Only 4 studies were focused on multimodal treatments. CONCLUSION: Based on this study, the multimodal management of symptomatic VHs appeared safe and effective. Finally, we propose an algorithm for symptomatic VHS management based on the severity of epidural extension and fracture risk.

Anterior lumbar sagittal alignment after anterior or lateral interbody fusion.

PURPOSE: Anterior or lateral interbody fusion is a treatment option for lumbar disc disease. A segmental change occurs after such surgery. This study was designed to evaluate the changes in the lumbar regional alignment after a single or two-level standalone anterior or lateral interbody fusion (ALIF or LLIF). METHODS: Data from patients referred to our institution between March 2013 and November 2015 for standalone ALIF or LLIF for low-grade isthmic spondylolisthesis or degenerative discopathy were retrospectively included in our analysis. Patients with a history of spinal fusion were excluded. Global and regional alignments were analyzed pre- and postoperatively. Pelvic tilt (PT), sacral slope (SS), sagittal vertical axis (SVA), lumbar lordosis (LL), index segmental lordosis (ISL) and L4S1 lordosis were compared. Three groups according to the pelvic incidence (PI) (low, normal and high) were separately analyzed then compared. RESULTS: Forty-one women and 27 men (mean age was 46 years; range 25-66) were included. The mean follow-up was 10.8 (range 3-34 months). The patients were globally well balanced preoperatively and remained after surgery (SVA stagnated from 16.76±28.42mm to 15.97±28.20mm, P=0.75). PT and LL did not vary. L4S1 lordosis, and ISL were significantly increased respectively from 30.56±8.59 to 34.58±7.47 (P=0.0026) and from 5.94±5.25 to 12.99±5.87 (P<0.0001) at latest follow-up. CONCLUSION: Despite effective changes in the segmental lordosis at the index levels, our findings suggest that one or two-levels standalone ALIF or LLIF had no effect on the global balance and the lumbar lordosis. The three groups behaved similarly, the regional lordosis was redistributed in a better harmony (L4S1/LL ratio went up from 55% to 61%, P=0.01). STUDY TYPE: Retrospective study. LEVEL OF EVIDENCE: 4.

Mullins effect in polyethylene and its dependency on crystal content: A network alteration model.

This contribution is focused on the Mullins effect in polyethylene. An ultra-low-density polyethylene with 0.15 crystal content, a low-density polyethylene with 0.3 crystal content and a high-density polyethylene with 0.72 crystal content are subjected to cyclic stretching over a large strain range. Experimental observations are first reported to examine how the crystal content influences the Mullins effect in polyethylene. It is found that the cyclic stretching is characterized by a stress-softening, a hysteresis and a residual strain, whose amounts depends on the crystal content and the applied strain. A unified viscohyperelastic-viscoelastic-viscoplastic constitutive model is proposed to capture the polyethylene response over a large strain range and its crystal-dependency. The macro-scale polyethylene response is decomposed into two physically distinct sources, a viscoelastic-viscoplastic intermolecular part and a viscohyperelastic network part. The local inelastic deformations of the rubbery amorphous and crystalline phases are considered by means of a micromechanical treatment using the volume fraction concept. Experimentally-based material kinetics are designed by considering the Mullins effect crystal-dependency and are introduced into the constitutive equations to capture the experimental observations. It is shown that the model is able to accurately reproduce the Mullins effect in polyethylene over a large strain range. The inherent deformation mechanisms are finally presented guided by the proposed constitutive model.

Mini-open oblique lumbar interbody fusion (OLIF) approach for multi-level discectomy and fusion involving L5-S1: Preliminary experience.

STUDY DESIGN: Technical description and single institution retrospective case series. OBJECTIVE: Evaluate technical feasibility and evaluate complications of mini-open retroperitoneal oblique lumbar interbody fusion (OLIF) at the L5-S1 level. SUMMARY OF BACKGROUND: The mini-open retroperitoneal oblique lumbar interbody fusion (OLIF) approach was first described in 2012 as a surgical approach to achieve spinal fusion while limiting invasiveness of the exposure to the anterior lumbar spine. Surgeons who use this approach, along with those who described it in cadaveric studies describe it as a feasible approach in targeting the L2 down to the L5 level and recommend alternative approaches to the L5-S1 level due to the vascular challenges and possible complications. METHODS: Technical description and single institution case series of patients treated with the OLIF between 2013 and 2015 at the L5-S1 level. The previously described surgical approach was modified by identifying and ligating the iliolumbar vein before retracting the iliac artery and vein anteriorly instead of passing between the vessels. RESULTS: Six patients (3 males, 3 females, mean age 62 years) were operated between 2013 and 2015. There were no vascular injuries or peripheral nerve trauma associated with the surgical procedure. Complications associated with the procedure included: cage displacement immediately postoperative requiring re-operation in one patient, transient psoas weakness in one patient, extended hospital stay for pain control in one patient, and transfusion was required in one patient. CONCLUSIONS: Mini-open retroperitoneal oblique lumbar interbody fusion is feasible at the L5-S1 level with limited vascular complications through a technical modification for safe mobilization of the iliac vessels by first ligating the iliolumbar vein.

Minimally invasive approach for the treatment of lumbar epidural arteriovenous fistulas with intradural venous reflux.

BACKGROUND: Vascular lesions of the spinal cord are increasingly recognized. The most common types of these lesions are dural arteriovenous fistulas (AVFs) whereas, extradural AVFs are a very rare type of spinal AVF and can be associated with either extradural or intradural venous reflux. This results in neurological deficits through congestive or compressive myeloradiculopathy. These lesions must be treated to allow stabilization or improvement of neurologic status, either by endovascular therapy or microsurgical interruption. However, because some patients are not amenable to endovascular treatment, surgery is often warranted, which usually involves hemi- or bilateral laminectomy following a midline approach with bilateral muscle stripping. The main drawback of this procedure is directly related to the morbidity of the approach. Although, minimally invasive approaches are likely to overcome this drawback, there is a lack of reported experience supporting their use for treating spinal dural AVFs. CASE PRESENTATION: Two patients, aged 62 and 79 years old, presented with rapidly progressive myelopathy characterized by paraparesis and sphincter disturbance. Spinal magnetic resonance imaging showed spinal cord oedema with perimedullary flow voids in both cases. Digital subtraction angiography revealed extradural AVFs associated with perimedullary venous reflux. Endovascular therapy was not feasible. Both patients were treated with microsurgical interruption of the intradural vein through a non-expendable retractor. Complete exclusion was confirmed on postoperative angiography, resulting in resolution of spinal cord edema and improved neurological functional status at 2-year follow-up. CONCLUSION: The minimally invasive surgical treatment of spinal AVFs with epidural venous reflux is safe and effective. This approach is a valuable alternative to endovascular therapy and the standard open microsurgical approach.

A dissecting aneurysm of a basilar perforating artery.

We report an additional case of a ruptured basilar trunk perforator aneurysm, for which an endovascular treatment was initially planned, but aborted due to the spontaneous regression of the aneurysm. Thus, a conservative management consisting on a close follow-up was decided that confirmed the favorable radiological outcome. Spontaneous regression of such aneurysm should be well-known by neurosurgeons and neuroradiologists in order to prevent the potential iatrogenic effects of the related treatment modalities.

Vertebral artery-posterior inferior cerebellar artery convergence aneurysms treated by endovascular or surgical treatment: Mid- and long-term outcome.

INTRODUCTION: Management of vertebral artery-posterior inferior cerebellar artery convergence (VA-PICA) saccular aneurysms requires a specialized neurovascular team. The objective is to preserve the functional outcome while performing a complete and reliable long-term exclusion of the aneurysm. OBJECTIVE: The aim of our study was to evaluate the outcome of patients with VA-PICA saccular aneurysms after treatment. MATERIALS AND METHODS: This was a retrospective series of 21 consecutive patients with a VA-PICA saccular aneurysm treated between 2000 and 2012 at our institution. Treatment option (endovascular or microsurgical) was decided for each patient following a multidisciplinary discussion. RESULTS: Twenty-one patients were treated for a VA-PICA saccular aneurysm including 16 for a ruptured aneurysm and 5 for an asymptomatic aneurysm. Among all patients, 11 underwent endovascular treatment and 10 had microsurgical treatment. Our results showed a major aneurysm recurrence after endovascular treatment in 3 patients that required a further endovascular treatment in 2 cases. These 3 major recurrences occurred after treatment of a ruptured aneurysm when the initial angiography demonstrated the origin of the PICA at the neck of the aneurysm. After microsurgery, angiography showed a remnant neck in 2 patients including 1 treated by further endovascular procedure. CONCLUSION: VA-PICA aneurysms are rare and require multidisciplinary management. Microsurgical treatment should be discussed when the PICA originates from the aneurysmal neck, particularly in patients with a ruptured small aneurysm, in order to obtain a reliable and long-term exclusion of the aneurysm.

Lumbar Morel-Lavallée lesion: Case report and review of the literature.

The Morel-Lavallée lesion (MLL) is a rarely reported closed degloving injury, in which shearing forces have lead to break off subcutaneous tissues from the underlying fascia. Lumbar MLL have been rarely reported to date, explaining that patients are frequently misdiagnosed. While patients could be treated conservatively or with non-invasive procedures, delayed diagnosis may require open surgery for its cure. Indeed, untreated lesions can cause pain, infection or growing subcutaneous mass that can be confused with a soft tissue tumor. We report the clinical and radiological features of a 45-year old man with voluminous lumbar MLL initially misdiagnosed. We also reviewed the relevant English literature to summarize the diagnostic tools and the main therapeutic options.

Pericallosal aneurysm: A difficult challenge for microsurgery and endovascular treatment.

INTRODUCTION: Pericallosal artery aneurysms (PAA) represent 2 to 9% of intracranial aneurysms and their management remains difficult. OBJECTIVE: We aimed to report our experience to evaluate the outcome of patients with ruptured and unruptured PAA, when the treatment modality is decided in a multidisciplinary fashion. MATERIALS AND METHODS: In this retrospective study, we included 28 patients (8 men and 20 women) treated for a PAA in our institution between 2002 and 2012, among the 2430 patients who underwent the treatment of an intracranial aneurysm in the same period. Fifteen patients harbored a ruptured aneurysm while 13 benefited from a prophylactic treatment. The mean age at diagnosis was 52 years (range 37 to 75 SD: ± 5) in patients with ruptured aneurysm and 54.2 years (range 35 to 66 SD: ± 5) in patients with unruptured aneurysm. Endovascular treatment has been performed in 9 patients while 19 patients underwent a microsurgical treatment. Clinical outcome has been assessed using the modified Rankin scale (mRS) at 3 months. Long-term imaging follow-up included a CT angiography at 36 months for clipped aneurysms and MR angiography at 6, 18 and 36 months for coiled aneurysms. RESULTS: The median follow-up was 3.4 years (range 2.8 to 4.2). The mRS was ≤ 2 in all patients with unruptured aneurysms. In patients with ruptured aneurysm, the mRS was ≤ 2 at 3 months in 13 patients (87%). Persistent cognitive disorders were noted in 8 patients with ruptured aneurysm, 2 of them were considered as possibly related to the treatment. Aneurysm recurrence has been depicted in 4 patients (at 6 months in 3 patients and 1 year in 1 patient) requiring further treatment in all cases; all of them had an aneurysm remnant on immediate conventional angiography. No recurrence was noted in patients without remnant on immediate post-treatment angiography. CONCLUSION: Both endovascular and microsurgical treatment are challenged in this location. Multidisciplinary discussion is essential to optimize the management of patients with PAA.

[Assessment of the surgeon radiation exposure during a minimally invasive TLIF: Comparison between fluoroscopy and O-arm system]. / Évaluation de l'exposition aux radiations du chirurgien lors d'un TLIF mini-invasif: comparaison entre fluoroscopie et navigation O-arm.

INTRODUCTION: Transforaminal lumbar interbody fusion with a minimally invasive approach (MIS TLIF) has become a very popular technique in the treatment of degenerative diseases of the lumbar spine, as it allows a decrease in muscle iatrogenic. However, iterative radiological controls inherent to this technique are responsible for a significant increase in exposure to ionizing radiation for the surgeon. New techniques for radiological guidance (O-arm navigation-assisted) would overcome this drawback, but this remains unproven. OBJECTIVES: To analyze the exposure of the surgeon to intraoperative X-ray during a MIS TLIF under fluoroscopy and under O-arm navigation-assisted. MATERIALS AND METHODS: This prospective study was conducted at the University Hospital of Lille from February to May 2013. Twelve patients underwent a MIS TLIF for the treatment of low-grade spondylolisthesis; six under standard fluoroscopy (group 1) and six under O-arm system (group 2). Passive dosimeters (rings and glasses) and active dosimeters for thorax were used to measure the radiation exposure of the surgeon. RESULTS: For group 1, the average time of fluoroscopy was 3.718 minutes (3.13-4.56) while no radioscopy was perform on group 2. For the first group, the average exposure dose was 12 µSv (5-20 µSv) on the thorax, 1168 µSv (510-2790 µSv) on the main hand and 179 µSv (103-486 µSv) on the lens. The exposure dose was measured zero on the second group. CONCLUSION: The maximum recommended doses can be reached, mainly for the lens. In addition to the radioprotection measures, O-arm navigation systems are safe alternatives to significantly reduce surgeon exposure.

Failed back surgery syndrome: to re-operate or not to re-operate? A retrospective review of patient selection and failures.

INTRODUCTION: Persisting pain after spine surgery remains a challenge for the patient and the pain physician. The etiology depends on age, pathology and the interval between the first and the revision surgery. In young patients who underwent initially to discectomy, the etiology of failed back surgery syndrome (FBSS) is commonly a recurrence of herniation whereas in the elderly population, who has previously undergone a spinal fusion, persisting pain might be due to secondary sagittal unbalance associated, as a consequence, to adjacent disc disease or pseudarthrosis. OBJECTIVE: To review the etiology of failed back surgery syndrome and to discuss the radiological work-up and the treatment strategies. METHODS: Retrospective analysis of 39 consecutive patients diagnosed with FBSS. For all cases, the following parameters were reviewed: original diagnosis and initial surgery, interval between the last surgery and the revision procedure, final diagnosis after revision. Treatment options were discussed. RESULTS: Twelve patients have undergone decompressive procedures and 27 had one or multilevel fusion for various back and/or leg pain. In group 1 (decompressive surgery), the mean age of patients who had a disc herniation was 42.2 years and 69 years for patients who had laminectomies for lumbar stenosis. In group 2 (fusion), the mean age was 63.3. Loss of lumbar lordosis in elderly after one or several laminectomy(ies) was found to be a cause of failure because of sagittal kyphosis and consecutive back pain. In the fused group, suboptimal correction of lumbar lordosis could generate a pseudarthrosis, proximal junctional kyphosis and persisting pain. CONCLUSION: Dealing with FBSS patients is far from simple but it corresponds to daily practice for spine surgeons. Clinical and radiological assessments should include a full diagnostic work-up focusing on sagittal balance. Surgical treatment and re-operation might be an option if a consistent source of pain is detected.

Management of cardiac migration of a distal shunt catheter: the radiological pitfalls.

Cardiac migration is a rare complication of the ventriculoperitoneal shunt. We report a case of a late migration of the distal shunt into the pulmonary arteries. The authors underline the radiological features that suggested the presence of a knot. Preoperative planning and the assistance of a vascular surgeon were required due to the presence of a knot.

Surgery in vertebral fracture: epidemiology and functional and radiological results in a prospective series of 518 patients at 1 year's follow-up.

INTRODUCTION: Recent epidemiological data for spinal trauma in France are sparse. However, increased knowledge of sagittal balance and the development of minimally invasive techniques have greatly improved surgical management. OBJECTIVES: To describe the epidemiology and management of traumatic vertebral fracture, and to analyze evolution and risk factors for poor functional outcome at 1 year's follow-up. MATERIALS AND METHODS: A prospective multicenter French cohort study was performed over a 6-month period in 2011, including all cases of vertebral fracture surgery. Data were collected by online questionnaire over the Internet. Demographic characteristics, lesion type and surgical procedures were collected. Clinical, functional and radiological assessment was carried out at 1 year. RESULTS: Five hundred and eighteen patients, with a mean age of 47 years, were included. Sixty-seven percent of fractures involved the thoracic or lumbar segment. Thirty percent of patients had multiple fractures and 28% neurological impairment. A minimally invasive technique was performed in 20% of cases and neurological decompression in 25%. Dural tear was observed in 42 patients (8%). Seventy percent of patients were followed up at 1 year. Functionally, SF-36 scores decreased on all dimensions, significantly associated with age, persistent neurological deficit and previous spine imbalance. Thirty-eight percent of working patients had returned to work. Radiologically, sagittal balance was good in 74% of cases, with fracture consolidation in 70%. DISCUSSION: Despite progress in management, spinal trauma was still a source of significant morbidity in 2011, with pronounced decrease in quality of life. Conserved sagittal balance appeared to be associated with better functional outcome.

Multidisciplinary management of intracranial aneurysms: The experience of Lille university hospital center.

BACKGROUND: In recent years, the multidisciplinary approach has become an important concern for the management of intracranial aneurysms. OBJECTIVE: This study aims to evaluate the functional outcomes of patients treated for an intracranial aneurysm (ruptured or unruptured), when the treatment modality was defined in a multidisciplinary fashion. MATERIALS AND METHODS: In this retrospective study, we included all patients (n=209) treated for an intracranial saccular aneurysm at Lille university hospital between January 2009 and December 2009. There were 70 men and 139 women with a mean age of 50.5 years (range 24 to 73 years). The clinical data were recorded before treatment including the American Society of Anesthesiology (ASA) and the World Federation of Neurosurgical Societies (WFNS) scores. Microsurgical approach was performed in 110 patients whereas 99 patients underwent an endovascular procedure. A modified Rankin Scale (mRS) was reported at 3 months after treatment. Intracranial vascular imaging was performed before and immediately after the treatment and then renewed at 3 years in all patients to detect any recurrence. RESULTS: Among the 121 patients with ruptured aneurysm, the functional outcomes were similar between patients who underwent microsurgery and patients who had an endovascular treatment. In the 88 patients with an unruptured aneurysm, functional outcomes were also similar between the two treatment modalities. Among the 99 patients treated by the endovascular approach, 4 had a significant aneurysm reopening on follow-up imaging leading to additional treatment (3 clipping, 1 coiling). No aneurysm recurrence was reported among the 110 patients who underwent microsurgical treatment. CONCLUSION: In a trained team, the multidisciplinary approach appears to be a valuable strategy in the management of intracranial aneurysms, to achieve good functional outcomes.

Minimally invasive percutaneous stabilization plus balloon kyphoplasty for the treatment of type A thoraco lumbar spine fractures: minimum 4 year's follow-up.

AIM: There is no consensus regarding the ideal treatment of type A thoraco-lumbar fractures. Many surgical techniques have been described but none has demonstrated its superiority over others. Recently, minimally invasive techniques have been widely used as they reduce the immediate morbidity related to the procedure. Percutaneous pedicle screw stabilization plus balloon kyphoplasty is a valuable technique, but there are only few data regarding clinical and radiological results in the long term. The purpose of this study was to report the long-term clinical and radiological outcome of patients undergoing minimally invasive management of thoracolumbar fracture in our institution. METHODS: This was a retrospective review of prospectively collected data. Between January 2006 and June 2008, 22 patients underwent short-segment percutaneous stabilization and balloon kyphoplasty for treatment of a type A fracture of the thoraco-lumbar spine. The study included 12 males and 10 females and the mean age was 50.5 years (25-75 years). The affected levels were T10 (N.=1), T11 (N.=1), T12 (N.=3), L1 (N.=9), L2 (N.=4), L3 (N.=3) and L4 (N.=1). RESULTS: The mean follow-up period was 60.9 months (50-75 months). The mean operative time was 77 min (range 55-135 min) and the bleeding was very low (<100 mL). VAS was significantly improved from 6.1 to 1.1 at last follow-up. Vertebral kyphosis decreased by 19° to 7.7° (ap<0.001) and local kyphosis was also significantly improved from 12.3° to 4.4° at last follow-up. We reported one screw misplacement that required early repositioning and 4 cement leakage, none of which was symptomatic. No patient worsened his neurological condition postoperatively. CONCLUSION: This treatment strategy is safe and effective. Clinical and radiological results seem to be stable over the time.

A two-phase hyperelastic-viscoplastic constitutive model for semi-crystalline polymers: application to polyethylene materials with a variable range of crystal fractions.

Polyethylene-based polymers as biomedical materials can contribute to a wide range of biomechanical applications. Therefore, it is important to identify, analyse, and predict with precision their mechanical behaviour. Polyethylene materials are semi-crystalline systems consisting of both amorphous and crystalline phases interacting in a rather complex manner. When the amorphous phase is in the rubbery state, the mechanical behaviour is strongly dependent on the crystal fraction, therefore leading to essentially thermoplastic or elastomeric responses. In this study, the finite deformation stress-strain response of polyethylene materials is modelled by considering these semi-crystalline polymers as two-phase heterogeneous media in order to provide insight into the role of crystalline and amorphous phases on the macro-behaviour and on the material deformation resistances, i.e. intermolecular and network resistances. A hyperelastic-viscoplastic model is developed in contemplation of representing the overall mechanical response of polyethylene materials under large deformation. An evolutionary optimization procedure based on a genetic algorithm is developed to identify the model parameters at different strain rates. The identification results show good agreement with experimental data, demonstrating the usefulness of the proposed approach: the constitutive model, with only one set of identified parameters, allows reproducing the stress-strain behaviour of polyethylene materials exhibiting a wide range of crystallinities, the crystal content becoming the only variable of the model.

[Epidemiology, treatment and follow-up of central nervous system hemangioblastomas in von Hippel-Lindau disease]. / Épidémiologie, traitement et suivi des hémangioblastomes du système nerveux central dans le cadre de la maladie de von Hippel-Lindau.

INTRODUCTION: Central nervous system (CNS) hemangioblastomas (HGB) are rare vascular tumors. The goal of this study was to analyze their epidemiology, treatment and prognosis in association with von Hippel-Lindau (VHL) disease. METHODS: We retrospectively reviewed a series of patients treated in our department for a CNS HGB with VHL disease between 1996 and 2008. We analyzed pre- and postoperative clinical and radiological characteristics, number of visceral lesions (fundoscopy, abdomino-pelvian CT, metanephrines), clinical course (modified Rankin Scale and McCormick scale) and late prognosis (Kaplan-Meier survival curves). RESULTS: We studied 19 cases (sex-ratio 0.9, mean age 36). The mean time to diagnosis was 61days. The main symptom was intracranial hypertension for cerebellar lesions (7/15) and a sensitive-motor deficit for medulla oblongata (2/5) or spinal lesions (5/11). Preferred locations were cerebellum (15/31), often nodulo-cystic appearance, followed by spinal cord (11/31), frequently coming with adjacent syringomyelia. Multiple locations and visceral lesions were found in two-third of the cases. Surgical removal was complete in more than three-quarter of the cases. Mean follow-up duration was 9years. Postoperative mortality rate was 16%. In cerebellar and medulla oblongata locations together, final mRS was ≤1 in 17 of the 20 cases. In spinal cord locations, final McCormick score was ≤2 in all the cases. After delayed follow-up, about two-third of patients experienced recurrence or new progressive CNS lesions. CONCLUSION: HGB are rare CNS tumors. VHL disease should be considered when an HGB is diagnosed before 30, is located at the spinal cord, comes with multiple other CNS lesions or with typical peripheral lesions. Microsurgical removal is the gold standard treatment and can offer good functional results.