Sébastien Schuller

Pullout characteristics of percutaneous pedicle screws with different cement augmentation methods in elderly spines: An in vitro biomechanical study

BACKGROUND Vertebroplasty prefilling or fenestrated pedicle screw augmentation can be used to enhance pullout resistance in elderly patients. It is not clear which method offers the most reliable fixation strength if axial pullout and a bending moment is applied. The purpose of this study is to validate a new in vitro model aimed to reproduce a cut out mechanism of lumbar pedicle screws, to compare fixation strength in elderly spines with different cement augmentation techniques and to analyze factors that might influence the failure pattern. MATERIALS AND METHODS Six human specimens (82-100 years) were instrumented percutaneously at L2, L3 and L4 by non-augmented screws, vertebroplasty augmentation and fenestrated screws. Cement distribution (2 ml PMMA) was analyzed on CT. Vertebral endplates and the rod were oriented at 45° to the horizontal plane. The vertebral body was held by resin in a cylinder, linked to an unconstrained pivot, on which traction (10 N/s) was applied until rupture. Load-displacement curves were compared to simultaneous video recordings. RESULTS Median pullout forces were 488.5 N (195-500) for non-augmented screws, 643.5 N (270-1050) for vertebroplasty augmentation and 943.5 N (750-1084) for fenestrated screws. Cement augmentation through fenestrated screws led to significantly higher rupture forces compared to non-augmented screws (P=0.0039). The pullout force after vertebroplasty was variable and linked to cement distribution. A cement bolus around the distal screw tip led to pullout forces similar to non-augmented screws. A proximal cement bolus, as it was observed in fenestrated screws, led to higher pullout resistance. This cement distribution led to vertebral body fractures prior to screw pullout. CONCLUSION The experimental setup tended to reproduce a pullout mechanism observed on radiographs, combining axial pullout and a bending moment. Cement augmentation with fenestrated screws increased pullout resistance significantly, whereas the fixation strength with the vertebroplasty prefilling method was linked to the cement distribution.

Fusion Rates of Different Anterior Grafts in Thoracolumbar Fractures.

Study Design: Retrospective CT analysis of anterior fusion in thoracolumbar trauma. Objective: The aim of this study was to compare fusion rates of different bone grafts and to analyze risk factors for pseudarthrosis. Summary of Background Data: Interbody fusion is indicated in anterior column defects. Different grafts are used: autologous iliac crest, titanium mesh cages filled with cancellous bone, and autologous ribs. It is not clear which graft offers the most reliable fusion. Material and Methods: Radiologic data of 116 patients (71 men, 45 women) operated for type A2, A3, B, or C fractures were analyzed. The average age was 44.6 years (range, 16–75 y) and follow-up was 2.7 years (range, 1–9 y). All patients were treated by posterior instrumentation followed by an anterior graft: 53 cases with iliac crest, 43 cases with mesh cages, and 20 with rib grafts. Fusion was evaluated on CT and classified into complete fusion, partial fusion, unipolar pseudarthrosis, and bipolar pseudarthrosis. Results: Iliac crest fused in 66%, cages in 98%, and rib grafts in 90%. The fusion rate of cages filled with bone was significantly higher as the iliac graft fusion rate (P=0.002). The same was applied to rib grafts compared with iliac crest (P=0.041). Additional bone formation around the main graft, bridging both vertebral bodies, was observed in 31 of the 53 iliac crests grafts. Pseudarthrosis occurred more often in smokers (P=0.042). A relationship between fracture or instrumentation types, sex, age, BMI, and fusion could not be determined. Conclusions: Tricortical iliac crest grafts showed an unexpected high pseudarthrosis rate in thoracolumbar injuries. Their cortical bone is dense and their fusion surface is small. Rib grafts led to a better fusion when used in combination with the cancellous bone from the fractured vertebral body. Titanium mesh cages filled with cancellous bone led to the highest fusion rate and built a complete bony bridge between vertebral bodies. Smoking seemed to influence fusion. Level of Evidence: Case control study, Level III.

Posterior surgery in high-grade spondylolisthesis.

INTRODUCTION High-grade L5-S1 spondylolisthesis alters sagittal spinopelvic balance, which can cause low back pain and progressive neurologic disorder. The present study assessed spondylolisthesis reduction and maintenance over time with L4-S1 versus L5-S1 fusion using a lever-arm system and posterior fusion combined with lumbosacral graft. MATERIALS AND METHODS Forty patients were operated on for symptomatic high-grade spondylolisthesis, 34 of whom had full pre- and post-operative radiological analysis, with a mean follow-up of 5.4years. There were 9 L5-S1 and 25 L4-S1 instrumentations. Analysis of spinopelvic and slipping parameters and the evolution of segmental lordosis compared results between L5-S1 and L4-S1 instrumentation. RESULTS Mean Taillard spondylolisthesis index decreased from 64% to 37% (P=0.0001). Overall sagittal spinopelvic balance was not significantly changed. Overall L1-S1 and segmental L4-L5 lordosis were not affected by instrumentation. Mean L5-S1 segmental lordosis increased from 11° to 18°. There was loss of reduction from 19° to 14° with L5-S1 instrumentation, in contrast to maintained reduction with L4-S1 instrumentation (P=0.006). CONCLUSION The lever-arm system provided anterior-posterior reduction of spondylolisthesis and corrected slippage. Postoperative change in overall sagittal spinopelvic balance was slight and constant. Posterior L4-S1 fusion provided better long-term control of L5-S1 lordosis reduction than the shorter L5-S1 fusion. Retrospective study of level IV.

Vertebral column resection for thoracic hyperkyphosis in Pott's disease.

Tuberculosis (TB) is still causing a major health burden in the WHO European Region (estimation of 418,000 new patients and 60,000 deaths per year), with an increasing trend of multidrug resistance [1]. The portion of reported extrapulmonary TB cases and spondylitis (Pott’s disease) accounts for 17 % on average, but the exact magnitude of this disease is unknown and rates over 40 % are reported in some European countries [2]. Patients treated with anti-TB chemotherapy alone or with simple surgical debridement without fusion may result in disease reactivation, severe kyphosis or late instability, which in turn may lead to late onset paraplegia, back pain, sagittal imbalance and compromised pulmonary function [3]. With the destruction of the anterior column of the spine by the infection, kyphosis resulting from the progressive anterior collapse may represent one of the main criteria for surgical indication. Debridement combined with kyphosis correction by posterior instrumentation and anterior column grafting enhances the efficacy of chemotherapy at short term, and has a positive effect on sagittal balance and neurologic outcome at long term [4, 5]. The late correction of stiff and sharp angular deformities (more than 60 ) is only feasible with three-column osteotomies or VCR [6]. The VCR technique provides the greatest amount of multi-planar correction. It involves the resection of posterior elements and two vertebral bodies with adjacent discs, and the anterior column reconstruction through a posterior approach [7].

Cervical osteoblastoma resection and posterior fusion.

Osteoblastoma belongs to the category of benign skeletal tumors and represents *1 % of primary bone neoplasms [1]. Its main incidence occurs during the second and third decade of life with a 2:1 male to female ratio [2]. Cervical osteoblastoma is predominantly located in the posterior elements of the spine [3]. This osteoblastic tumor is histologically similar to osteoid osteoma, but osteoblastoma is characterized by an extent superior to 1.5 cm [4, 5]. Clinically osteoblastoma leads to unspecific neck pain, which is not relieved by aspirin, as it would typically occur in osteoid osteoma, stiffness and eventual deformities due to muscle contracture [6, 7]. Larger tumors may be recognized on conventional radiographs. The diagnosis is usually made by computed tomography (CT), where osteoblastoma appears as an inhomogeneous lytic and sclerotic mass with a radiolucent nidus surrounded by reactive sclerotic bone (stages 1 and 2 according to the Enneking staging system for benign lesions) [6, 8]. Some osteoblastomas appear more aggressive, as in the present case, and may demonstrate larger osteolytic components (stage 3 lesions). Magnetic resonance imaging (MRI) complements CT imaging and gives information on possible spinal cord, nerve root or vertebral artery compression, whereas bony lesions tend to be overestimated on MRI [5]. After diagnosis confirmation by biopsy, the appropriate treatment consists of complete marginal resection in stage 1 and 2 lesions. Stage 3 lesions require a larger resection to ensure removal of all surrounding tumor bearing tissue [8, 9].

Mini open tumor resection and percutaneous instrumentation for T11 renal cell carcinoma metastasis

Neural decompression and stabilization belong to the standards of oncologic management of metastatic vertebral lesions, which are at risk of spinal cord compression. Quality of life, tumor associated pain, pathologic fractures and the neurologic status may be improved by surgical treatment [1]. The revised Tokuhashi score [2] represents a common tool, which enables predicting prognosis on a multidisciplinary basis and to decide if conservative treatment or palliative surgery would be adequate, depending on the patient’s pathology and comorbidities. Minimally invasive surgery may enlarge the possibilities of palliative procedures. Cementoplasty has a stabilizing effect at the level of the vertebral body and reduces pain efficiently [3]. This technique can be combined with decompression of the lumbar spine, if facet joints and pedicles remain intact. Minimally invasive transpedicular tumor resection through a tubular retractor, combined with percutaneous instrumentation, has been recently described for unstable compressive lesions [4]. Additionally, metastases of well-vascularized primary tumors, such as renal cell carcinoma, present an intraoperative risk of hemorrhage and require a preoperative transarterial embolization [5, 6]. A limited open approach, focused on the tumor area, may further reduce intraoperative bleeding and operating time, which represents a theoretical advantage with regard to the patient’s morbidity.

French door laminoplasty for cervical spondylotic myelopathy

Cervical laminoplasty represents a current technique in the treatment of spondylotic myelopathy, if the stenosis is located at multiple levels [1]. Laminoplasty was originally developed in Japan because of the high prevalence of ossification of the posterior longitudinal ligament (OPLL). The principle of this technique is based on an enlargement of the canal, which decompresses the spinal cord indirectly by allowing the dural sac to drift away from the spondylotic bars. Several technical variations exist such as the Z-plasty [2] or the open door technique [3]. The technique of Kurokawa et al. [4], also named French door laminoplasty, consists of a median lamina split followed by a lateral thinning and opening of both hemilaminae. This technique seems to provide satisfying and reliable results at long-term in patients with OPLL, but also in myelopathy due to cervical spondylosis and posterior thickening of the ligamentum flavum [5]. The sagittal cervical profile has to be considered preoperatively. The role of deep extensor muscles seems crucial for the sagittal alignment, and open posterior techniques might harm the muscular balance [6]. Therefore, loss of lordosis represents a contraindication for laminoplasty because it might result in further kyphotic deformity without removing pressure on the anterior spinal cord. Furthermore, segmental instability must be diagnosed preoperatively, and supplemented with a fusion to prevent further progression.

Anterior osteotomy and percutaneous in situ contouring for correction of rigid posttraumatic T12–L1 malunion

The junctional region T12–L1 between thoracic kyphosis and lumbar lordosis has no intrinsic curvature and vertebral endplates are physiologically parallel [1]. Posttraumatic malunion and sagittal imbalance at the thoracolumbar junction may lead to accelerated disc degeneration. Surgical correction is usually indicated for severe deformities leading to chronic back pain. Closing wedge osteotomies through a single posterior approach have been advocated for lumbar and thoracolumbar levels [2]. Closing-opening wedge osteotomies have been described for thoracic deformities, thus avoiding a column shortening [3]. Double approaches allow a release and graft of the rigid anterior column, which is combined with a posterior instrumentation and correction of sagittal alignment [4, 5]. Although anterior video-assisted approaches have become increasingly minimally invasive [6], posterior correction is usually performed through a classic open procedure. Recent developments led us to combine in situ contouring, known from open posttraumatic deformity correction [7, 8], with percutaneous instrumentation and a minimal invasive anterior release. This technique avoids posterior dissection and keeps the paravertebral musculature intact, which reduces the patient’s morbidity and represents a theoretical advantage over conventional techniques.

Open versus percutaneous instrumentation in thoracolumbar fractures: magnetic resonance imaging comparison of paravertebral muscles after implant removal

OBJECTIVE Percutaneous instrumentation in thoracolumbar fractures is intended to decrease paravertebral muscle damage by avoiding dissection. The aim of this study was to compare muscles at instrumented levels in patients who were treated by open or percutaneous surgery. METHODS Twenty-seven patients underwent open instrumentation, and 65 were treated percutaneously. A standardized MRI protocol using axial T1-weighted sequences was performed at a minimum 1-year follow-up after implant removal. Two independent observers measured cross-sectional areas (CSAs, in cm2) and region of interest (ROI) signal intensity (in pixels) of paravertebral muscles by using OsiriX at the fracture level, and at cranial and caudal instrumented pedicle levels. An interobserver comparison was made using the Bland-Altman method. Reference ROI muscle was assessed in the psoas and ROI fat subcutaneously. The ratio ROI-CSA/ROI-fat was compared for patients treated with open versus percutaneous procedures by using a linear mixed model. A linear regression analyzed additional factors: age, sex, body mass index (BMI), Pfirrmann grade of adjacent discs, and duration of instrumentation in situ. RESULTS The interobserver agreement was good for all CSAs. The average CSA for the entire spine was 15.7 cm2 in the open surgery group and 18.5 cm2 in the percutaneous group (p = 0.0234). The average ROI-fat and ROI-muscle signal intensities were comparable: 497.1 versus 483.9 pixels for ROI-fat and 120.4 versus 111.7 pixels for ROI-muscle in open versus percutaneous groups. The ROI-CSA varied between 154 and 226 for open, and between 154 and 195 for percutaneous procedures, depending on instrumented levels. A significant difference of the ROI-CSA/ROI-fat ratio (0.4 vs 0.3) was present at fracture levels T12-L1 (p = 0.0329) and at adjacent cranial (p = 0.0139) and caudal (p = 0.0100) instrumented levels. Differences were not significant at thoracic levels. When adjusting based on age, BMI, and Pfirrmann grade, a significant difference between open and percutaneous procedures regarding the ROI-CSA/ROI-fat ratio was present in the lumbar spine (p < 0.01). Sex and duration of instrumentation had no significant influence. CONCLUSIONS Percutaneous instrumentation decreased muscle atrophy compared with open surgery. The MRI signal differences for T-12 and L-1 fractures indicated less fat infiltration within CSAs in patients who received percutaneous treatment. Differences were not evidenced at thoracic levels, where CSAs were smaller. Fat infiltration was not significantly different at lumbar levels with either procedure in elderly patients with associated discopathy and higher BMI. In younger patients, there was less fat infiltration of lumbar paravertebral muscles with percutaneous procedures.

Anterior corpectomy and fusion for two adjacent levels of cervical stenosis.

Multilevel anterior cervical discectomy and fusion represents a current technique in the treatment of spondylotic myelopathy and myeloradiculopathy, if the stenosis remains limited to the level of the disc and the lateral recess [1]. A partial or complete corpectomy and fusion may be preferable in situations where access to the posterior aspect of the vertebral body is needed. This is the case, if significant osteophyte formations cannot be completely removed through the intersomatic space, using a drill and a Kerrisson rongeur. Cervical corpectomy, strut graft fusion and anterior plating have been recommended for the treatment of double level stenosis [2]. This technique requires bone graft harvesting from the iliac crest. The use of a titanium mesh cage filled with autologous bone from the resected vertebra itself has been described as an alternative reconstruction technique after corpectomy [3]. Additional stabilization using an anterior cervical plate is mandatory after cage reconstruction. The implantation of expandable titanium cages has been advocated for kyphosis correction in single or multiple level corpectomies [4]. The reduction of the sagittal cervical profile seems important, in order to prevent further degeneration at adjacent segments. The role of deep extensor muscles seems crucial for the sagittal alignment, and open posterior techniques, such as laminoplasties or keyhole foraminotomies, might harm the muscular balance [5].