Finite element investigation of the influence of a new transpedicular vertebral implant positioning on biomechanical responses of the spine segment.

The optimal positioning of an implant into a living organ such as femurs and vertebra is still an open problem. In particular, vertebral implant position has a significant impact on the results on spine behaviour after treatment in terms of stiffness, range of motion (ROM), wear, loosening and failure. In the current work, a 3D finite element analysis was conducted to investigate the positioning parameters of a novel transpedicular implant (V-STRUT©, Hyprevention, France) in terms of placement of the implant in the treated vertebra. The implant was designed in order to strength osteoporotic vertebral body and the related spine segment under compressive load. The effects of the axial and sagittal positions of the implant in the treated vertebra was investigated in terms of stress and stiffness variations. A 3D finite element model of an osteoporotic spine segment was built based on a Computed Tomography (CT) scan of an osteoporotic female (69 yo). The model is composed of T12, L1 and L2 vertebrae and corresponding intervertebral discs and ligaments. The bone tissue was modeled as a heterogeneous material with properties assigned based on the grey scale levels. The intervertebral discs were modeled using two regions describing the annulus and the nucleus and linear beam elements with specific stiffness each were used representing each ligament. The simulations indicated that the sagittal position (distance d) plays a role on the stress distribution. The closer the implant to the interior wall the lower the stress applied to the spine segment. Nevertheless, the axial plane position (distance h) have limited effects on the stress applied to the bone with a higher stress applied to the device (subjected to a higher bending load). These results can have direct clinical implications when dealing with the optimal placement of the implant. It is also possible to select a particular position in order to assign a given (target) stiffness for a patient.

Effect of a new transpedicular vertebral device for the treatment or prevention of vertebral compression fractures: A finite element study.

BACKGROUND: A finite element study was performed to investigate the biomechanical performance of a novel transpedicular implant (V-STRUT©, Hyprevention, France) made of PEEK (polyetheretherketone) material in terms of strengthening the osteoporotic vertebra and the thoraco-lumbar spine. The objective was to assess numerically the efficacy of the implant to reduce the stress distribution within bone and absorb part of the stress by the implant thanks to its optimized material selection close to that of normal bone. METHODS: A numerical model was generated based on a scan of an osteoporotic patient. The model is composed of three consecutive vertebrae and intervertebral discs. A heterogeneous distribution of bone material properties was assigned to the bone. In order to investigate the rationale of the device material selection, three FE models were developed (i) without the device to serve a reference model, (ii) with device made in Titanium material and (iii) with device made in PEEK material. Stiffness and stress distribution within the spine segment were computed and compared in order to assess the implants' performances. FINDINGS: The results obtained by the simulations indicated that the novel transpedicular implant made of PEEK material provided support to the superior vertebral endplate, restored the thoraco-lumbar spine segment stiffness and reduced the stress applied to the vertebrae under the compressive load. INTERPRETATION: Implant geometry in combination with its material properties are very important factors to restore vertebral strength and stiffness and limiting the risk of fracture at the same vertebra or adjacent ones.

Hospital-based health technology assessment in France: A focus on medical devices.

Hospital-based health technology assessment (HTA) guides decisions as to whether new healthcare products should be made available within hospital structures. Its extension to medical devices (MDs) makes it possible to analyse several relevant aspects of these healthcare products in addition to their clinical value, and such evaluations are of interest to national health authorities, other healthcare establishments and industry. The aim of this work was to formulate several recommendations for a blueprint for hospital-based HTA for MDs in France. Five themes based on the work of the European Adopting hospital-based HTA in the EU (AdHopHTA) project were defined. Each member of the roundtable was then allocated a documentation task based on their experience of the theme concerned, and a literature review was carried out. An inventory of hospital-based HTA was performed and six recommendations aiming to strengthen and improve this approach were put forward: (1) encouragement of the spread of the hospital-based HTA culture and participation in communications and the promotion of this approach to hospital decision-makers; (2) adaptation of hospital-based HTA to the needs of decision-makers, taking into account the financial timetable and strategic objectives of the healthcare establishment; (3) harmonisation of the dossiers requested from industry between healthcare establishments, based on a common core; (4) promotion of the sharing of hospital-based HTA data under certain conditions, with data dissociable from the HTA report and the use of a validated methodology for the literature review; (5) creation of a composite indicator reflecting data production effort and the sharing of HTA activities, to be taken into account in the distribution of funds allocated for teaching, research and innovation missions considered of general interest; (6) the transmission of information directly from local to national level by pioneering centres. This work highlights the major issues at stake in hospital-based HTA and the need to valorise such activities in France.

A new approach to prevent contralateral hip fracture: Evaluation of the effectiveness of a fracture preventing implant.

BACKGROUND: Among the millions of people suffering from a hip fracture each year, 20% may sustain a contralateral hip fracture within 5 years with an associated mortality risk increase reaching 64% in the 5 following years. In this context, we performed a biomechanical study to assess the performance of a hip fracture preventing implant. METHODS: The implant consists of two interlocking peek rods unified with surgical cement. Numerical and biomechanical tests were performed to simulate single stance load or lateral fall. Seven pairs of femurs were selected from elderly subjects suffering from osteoporosis or osteopenia, and tested ex-vivo after implantation of the device on one side. FINDINGS: The best position for the implant was identified by numerical simulations. The loadings until failure showed that the insertion of the implant increased significantly (P<0.05) both fracture load (+18%) and energy to fracture (+32%) of the implanted femurs in comparison with the intraindividual controls. The instrumented femur resisted the implementation of the non-instrumented femur fracture load for 30 cycles and kept its performance at the end of the cyclic loading. INTERPRETATION: Implantation of the fracture preventing device improved both fracture load and energy to fracture when compared with intraindividual controls. This is consistent with previous biomechanical side-impact testing on pairs of femur using the same methodology. Implant insertion seems to be relevant to support multiple falls and thus, to prevent a second hip fracture in elderly patients.