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.

[Foot equipment of diabetic arteriopathy]. / L'appareillage du pied des artéritiques diabétiques.

Surgical appliances have a place of choice in the care of the foot with trophic lesions in diabetics, after partial amputation and as a preventive measure when it is free from trophic disorders. The type of appliance will depend on the footwear and the possibility of wearing orthopedic soles, whatever the stage of the affection. For the foot free from trophic disorders the shoes should be wide fitting, in soft leather and of the seamless type. Made to measure shoes should be reserved for badly deformed feet. The soles should be molded in silicone or polyurethane to distribute weight bearing and to avoid it over zones at risk. Appliances for the foot with trophic lesions should allow the resumption of walking. If the lesions are too extensive an orthosis is performed or a specific type of slipper with molded soles is worn to avoid pressure on the wounds. After amputation of toes a silicone orthoplasty is used to fill the interdigital space to avoid deformity of the other toes. If a front of foot has been amputated a corrected silicone molded sole with false extremity is applied. For a back of foot amputation an orthoprosthesis is made, preferentially in silicone introductible in a regular high sided shoe. In order to fulfil its preventive or temporary role, the appliance should evolve with time and be followed up regularly with close collaboration between the diabetic specialist the podologist and the orthotist.