Development of an experimental model of burst fracture with damage characterization of the vertebral bodies under dynamic conditions.

BACKGROUND: Burst fractures represent a significant proportion of fractures of the thoracolumbar junction. The recent advent of minimally invasive techniques has revolutionized the surgical treatment of this type of fracture. However mechanical behaviour and primary stability offered by these solutions have to be proved from experimental validation tests on cadaveric specimens. Therefore, the aim of this study was to develop an original and reproducible model of burst fracture under dynamic impact. METHODS: Experimental tests were performed on 24 cadaveric spine segments (T11-L3). A system of dynamic loading was developed using a modified Charpy pendulum. The mechanical response of the segments (strain measurement on vertebrae and discs) was obtained during the impact by using an optical method with a high-speed camera. The production of burst fracture was validated by an analysis of the segments by X-ray tomography. FINDINGS: Burst fracture was systematically produced on L1 for each specimen. Strain analysis during impact highlighted the large deformation of L1 due to the fracture and small strains in adjacent vertebrae. The mean reduction of the vertebral body of L1 assessed for all the specimens was around 15%. No damage was observed in adjacent discs or vertebrae. INTERPRETATION: With this new, reliable and replicable procedure for production and biomechanical analysis of burst fractures, comparison of different types of stabilization systems can be envisaged. The loading system was designed so as to be able to produce loads leading to other types of fractures and to provide data to validate finite element modelling.

A novel approach for biomechanical spine analysis: Mechanical response of vertebral bone augmentation by kyphoplasty to stabilise thoracolumbar burst fractures.

Kyphoplasty has been shown as a well-established technique for spinal injuries. This technique allows a vertebral bone augmentation with a reduction of morbidity and does not involve any adjacent segment immobilisation. There is a lack of biomechanical information resulting in major gaps of knowledge such as: the evaluation of the "quality" of stabilisation provided by kyphoplasty as a standalone procedure in case of unstable fracture. Our objective is to analyse biomechanical response of spine segments stabilised by Kyphoplasty and PMMA cement after experiencing burst fractures. Six fresh-frozen cadaveric spine specimens constituted by five vertebra (T11-L3) and four disks were tested. A specific loading setup has been developed to impose pure moments corresponding to loadings of flexion-extension, lateral bending and axial rotation. Tests were performed on each specimen in an intact state and post kyphoplasty following a burst fracture. Strain measurements and motion variations of spinal unit are measured by a 3D optical method. Strain measurements on vertebral bodies after kyphoplasty shows a great primary stabilisation. Comparisons of mobility and angles variations between the intact and post kyphoplasty states do not highlight significant difference. Percutaneous kyphoplasty offers a good primary stability in case of burst fracture. Kinematics analysis during physiological movements shows that this stabilisation solution preserve disk mobility in each adjacent spinal unit.

Radiologic study of disc behavior following compression fracture of the thoracolumbar hinge managed by kyphoplasty: A 52-case series.

INTRODUCTION: Kyphoplasty has proved effective for durable correction of traumatic vertebral deformity following Magerl A fracture, but subsequent behavior of the adjacent discs is unclear. The objective of the present study was to analyze evolution according to severity of initial kyphosis and quality of fracture reduction. MATERIAL AND METHOD: A single-center prospective study included cases of single compression fracture of the thoracolumbar hinge managed by Kyphon Balloon Kyphoplasty with polymethylmethacrylate bone cement. Radiology focused on traumatic vertebral kyphosis (VK), disc angulation (DA) and disc height index (DHI) in the adjacent discs. Linear regression assessed the correlation between superior disc height index (SupDHI) and postoperative VK on the one hand and correction gain on the other, using the Student t test for matched pairs and Pearson correlation coefficient. RESULTS: Fifty-two young patients were included, with mean follow-up of 18.6 months. VK fell from 13.9° preoperatively to 8.2° at last follow-up. DHI found significant superior disc subsidence (P=0.0001) and non-significant inferior disc subsidence (P=0.116). DA showed significantly reduced superior disc lordosis (P=4*10(-5)). SupDHI correlated with VK correction (r=0.32). Preoperative VK did not correlate with radiologic degeneration of the adjacent discs. CONCLUSION: Correction of traumatic vertebral deformity avoids subsidence and loss of mechanical function in the superior adjacent disc. The underlying disc compensates for residual deformity. Balloon kyphoplasty is useful in compression fracture, providing significant reduction of traumatic vertebral deformity while conserving free and healthy adjacent discs. LEVEL OF EVIDENCE: IV.

Kyphopasty and vertebroplasty.

Vertebroplasty and balloon kyphoplasty are percutaneous techniques performed under radioscopic control. They were initially developed for tumoral and osteoporotic lesions; indications were later extended to traumatology for the treatment of pure compression fracture. They are an interesting alternative to conventional procedures, which are often very demanding. The benefit of these minimally invasive techniques has been demonstrated in terms of alleviation of pain, functional improvement and reduction in both morbidity and costs for society. The principle of kyphoplasty is to restore vertebral body anatomy gently and progressively by inflating balloons and then reinforcing the anterior column of the vertebra with cement. In vertebroplasty, cement is introduced directly under pressure, without prior balloon inflation. Both techniques can be associated to minimally invasive osteosynthesis in certain indications. In our own practice, we preferably use acrylic cement, for its biomechanical properties and resistance to compression stress. We use calcium phosphate cement in young patients, but only associated to percutaneous osteosynthesis due to the risk of secondary correction loss. The evolution of these techniques depends on improving personnel radioprotection and developing new systems of vertebral expansion.

Evaluation of percutaneous surgery in the treatment of thoracolumbar fractures. Preliminary results of a prospective study on 65 patients.

INTRODUCTION: We conducted a prospective, single-center, continuous study of patients operated for fractures urelated to osteoporosis at the thoracolumbar junction level using percutaneous techniques. The aim of this study was to investigate the clinical and radiological outcomes of percutaneous techniques for these indications. PATIENTS AND METHODS: This study included patients who underwent standalone balloon kyphoplasty surgery or combined with percutaneous posterior osteosynthesis in cases of associated distraction. The fractures were classified according to the Magerl classification. The patients were evaluated clinically (visual analog scale [VAS], the Oswestry Disability Index, and autonomy) and radiologically (vertebral kyphosis and height variations of the vertebral body) for 12 months. RESULTS: Sixty-five patients were included. The mean age at the time of the surgery was 45.4 years (range, 19-72 years). The main indications were A.1 fractures of L1. We noted 22% cement leakages, none having a clinical impact. In the overall series, the VAS at the lesional level improved from 5.5 (range, 3-8) preoperatively to 0.6 (range, 1-3) at 12 months. In all, 95% of the workers resumed their occupation. Traumatic kyphosis improved from 13.3° (range, 5-23°) before the surgery to 8.3° (range, 1-20°). DISCUSSION: The complication rate was low. The radiological results are comparable to those reported in the literature for other series with percutaneous surgery. Only the loss of the correction observed in the group undergoing standalone kyphoplasty with calcium phosphate cement led us to propose another type of treatment for these indications. This study must be continued over the long term to detect the appearance of discopathy related to cement leakage and to answer questions as to how cement evolves. LEVEL OF EVIDENCE: III, prospective study with low statistical power.