François Lavaste

Clinical and radiological outcomes with the Charité artificial disc: a 10-year minimum follow-up.

This is the first report of clinical and radiologic outcomes for the CHARITÉ™ artificial disc with a minimum follow-up of 10 years. A total of 107 patients indicated for total lumbar disc replacement were implanted with the CHARITÉ™ prosthesis. Of these 107, 100 were followed for a minimum of 10 years (range 10-13.4 years). A total of 147 prostheses were implanted with 54 one-level and 45 two-level procedures and 1 three-level procedure. The prostheses were placed through a standard anterior retroperitoneal approach. Clinically, 62% had an excellent outcome, 28% had a good outcome, and 10% had a poor outcome. Of the 95 eligible to return to work, 88 (91.5%) either returned to the same job as prior to surgery or a different job. These included 63.2% (12) of those working in heavy labor employment returning to the same job. Mean flexion/extension motion was 10.3° for all levels (12.0° at L3-L4, 9.6° at L4-L5, 9.2° at L5-S1). Mean lateral motion was 5.4°. In the sagittal plane, 9 (6.1%) were anterior of geometric center, 50 (34.0%) were centered, and 88 (59.9%) were posterior of center. In the frontal plane, 110 (75%) were centered, and 37 (25%) were noted to be lateral to center. Slight subsidence was observed in two patients, but they did not require further surgery. No subluxation of the prostheses and no cases of spontaneous arthrodesis were identified. There was one case of disc height loss of 1 mm. Five patients required a secondary posterior arthrodesis. A good or excellent clinical outcome rate of 90% and a return to work rate of 91.5% compare favorably with results described in the literature for fusion for the treatment of lumbar degenerative disc disease. With a minimum follow-up of 10 years, the CHARITÉ™ artificial disc demonstrated excellent flexion/extension and lateral range of motion with no significant complications.

THREE-DIMENSIONAL GEOMETRICAL AND MECHANICAL MODELLING OF THE LUMBAR SPINE

The main objective of this study is to design a three-dimensional geometrical and mechanical finite element model of the lumbar spine. The models geometry is constructed using six parameters per vertebra. These parameters are digitized from two X-rays (anterio-posterior and lateral), thus yielding an individualized model which can be arrived at from the radiographs of a tested specimen. This procedure makes the model validation easier, as geometry is generally a factor of dispersion in experimental results. The geometrical reconstruction, in the form of a finite elements mesh, was effected for the whole lumbar spine. The global coherence of the model was verified.

A THREE-DIMENSIONAL PARAMETERIZED FINITE ELEMENT MODEL OF THE LOWER CERVICAL SPINE. STUDY OF THE INFLUENCE OF THE POSTERIOR ARTICULAR FACETS

In this study, we present a three-dimensional geometrical and mechanical finite element model of the complete lower cervical spine. The geometry of the vertebrae is parameterized which allows the model to fit different morphologies of vertebrae. The results obtained with a reduced functional unit model (without posterior arch) and with a complete functional unit model were compared with those obtained from experimental studies, when moments of flexion, extension lateral flexion and axial torque were applied. General agreement was observed. Since the model was parameterized, it was possible to study the influence of some geometrical parameters on the mechanical behavior of the cervical spine. Particularly, we focused on the influence of the posterior articular facets as their geometry is very different from those of the other spinal levels and as large inter-individual variability can be observed. The orientation of the facets with regard to the horizontal plane appeared to have a large influence on the coupled rotation to principal rotation ratio, notably in lateral flexion.

The association of sagittal spinal and pelvic parameters in asymptomatic persons and patients with isthmic spondylolisthesis.

Using a specialized orthopedic software package, the authors investigated the sagittal spinal shape and the position of the pelvis in the space in patients with isthmic spondylolisthesis and in persons with no such symptoms. Digitized lateral spinal radiographs of 30 healthy volunteers and 48 patients were evaluated. The absolute values and significant correlations between parameters were analyzed. The pelvic parameters correlated well with lordosis, which shows sagittal balance in the asymptomatic group. The hyperlordosis and the horizontally positioned sacrum in isthmic spondylolisthesis enlarge the tensile force component of gravity, which may cause the lysis. Finally, the authors developed a new balance between the pelvis and the spine after slipping of the vertebral body. The degree of slipping correlated well with the sacrofemoral anatomic constant (incidence), which is unique in each person.

The anatomic basis for the concept of lateralized femoral stems: a frontal plane radiographic study of the proximal femur.

We determined the range of sizes for a system of monoblock femoral prostheses that would provide adequate (a term defined in the text) fill in the frontal plane and restore femoral offset and leg length. We performed an anatomic study, based on measurements in 200 anteroposterior pelvic radiographs. If diaphyseal filling implants are to be used, 9 sizes are sufficient to obtain excellent canal filling and restoration of femoral offset in >80% of cases, assuming that the level of neck osteotomy can vary over a 1-cm range. When using metaphyseal filling implants, only a limited adjustment can be obtained from the level of neck osteotomy. A system limited to 8 sizes approximates the anatomy of the femoral canal with satisfactory precision in 73% of cases. If such a system is provided with only a single neck shaft angle for each stem size, it does not allow restoration of the biomechanical center of the hip in >67% of cases. A system of 8 sizes of 1 neck/shaft angle and a 22-mm modular head restores the anatomy in only 49% of cases. Approximating the frontal anatomy of 85% of femora with an implant filling the metaphysis requires at least 15 sizes distributed in 3 metaphyseal configurations, each supplied with 2 different neck shalt angles.

The importance of spinopelvic parameters in patients with lumbar disc lesions

Abstract. Using a special software program we measured spinopelvic parameters on digitised radiographs of the entire spine and the pelvis of 50 patients with lumbar disc herniation and compared these with the same measurements on 30 healthy subjects. In the disc hernia group the patients had a relatively straight spine in the sagittal plane. The sacrum was more vertical, and the value of the lumbar lordosis was lower, as was the amplitude of the spinal curvatures, when compared with those of the healthy group. This results in a higher gravitational compressive force which may, in turn, lead to progressive degeneration of the discs. The anterior shift of the line of gravity may cause spinopelvic instability, and contraction of the posterior spinal muscles in trying to balance this disturbed spatial relationship may produce back pain.Résumé. Avec un logiciel spécial nous avons mesuré des paramètres rachidiens et pelviens sur les radiographies numérisées de 50 patients avec hernie discale lombaire et de 30 sujets sains. Dans le groupe avec hernie discale les patients avaient une colonne vertébrale relativement droite dans le plan sagittal. Le sacrum était plus vertical, la lordose lombaire plus discrète et donc lamplitude des courbures vertébrales plus faible en comparaison du groupe sain. Cela peut mener à la dégénérescence progressive des disques, par suite dune plus grande force compressive gravitationnelle. La modification de la ligne de gravité antérieure peut causer linstabilité rachidienne – pelvienne. Les muscles vertébraux postérieurs peuvent avoir tendance à corriger ce déséquilibre spatial ce qui peut causer des douleurs postérieures.

A biomechanical analysis of short segment spinal fixation using a three-dimensional geometric and mechanical model.

Vertebral stabilization using spinal fixation devices is a widely used technique. A three-dimensional geometric and mechanical finite element model has been used as a simulation tool for the evaluation of the mechanical behavior of spinal devices. The geometry of lumbar vertebrae was parameterized, which allows the construction of the geometric model for a given lumbar segment from the digitization of two roentgenographs. This procedure was used to construct a finite element model for a three-vertebra segment with simulation of fractures in the middle vertebra, and with simulation of a restoration using an osteosynthesis device, implemented in a frame fashion with four screws and two rods linked by two transverse rods, and/or an anterior bone graft. Compression force and torsion moment were considered, and different cases were investigated, by varying the severity of the fracture, the geometric characteristics of the device, and the mechanical characteristics of the material joining the two intact vertebral bodies. Results were analyzed considering the mobility of the vertebral segment, which indicates the ability of the restoration system to stabilize the vertebral segment, and considering the forces and moments distribution in the device, which gives information on part of the forces that pass through the device in each situation. Results show that maximum values of forces and moments in the device are more important in compression than in torsion. Adding an anterior bone graft has an effect mainly for compression, whereas in torsion its effects is negligible. For a rigid fixation device, no significant difference was found between different fracture models, indicating that the posterior arch does not play an important role for an instrumented segment. For compression, a rigid posterior wall, or the presence of a bone graft, reduces greatly the mobility of the instrumented segment. For torsion, suppressing the two transverse rods in the device greatly increases the mobility of the instrumented segment. Using a finite element model of lumbar vertebral segment appears to be an interesting tool to analyze the behavior of an instrumented spine and to compare between different stabilization systems.

New interspinous implant evaluation using an in vitro biomechanical study combined with a finite-element analysis.

Study Design. A combined in vitro and finite-element analysis was completed to assess the biomechanical effect of a new interspinous implant on the lumbar spine. Objective. The aim was to investigate the effect of an interspinous implant on the biomechanical behavior of a vertebral segment. Methods. An in vitro study on L3–L5 segments from fresh human cadavers was conducted combined with a 3-dimensional finite-element analysis. Intact, injured, and instrumented states of L4–L5 were compared loaded in flexion-extension, lateral-bending, and torsion. The evaluated implant is an interspinous spacer fixed to the spine by 2 polyester braids looped around the proximal and distal spinous. Results. The effect of the implant appeared mainly in flexion-extension: experimental results showed reduced range of motion of the instrumented spine regarding the injured and intact one; and finite-element analysis indicated a decrease of disc stresses and increase of loads transmitted to the spinous processes. Conclusion. In this in vitro and finite-element analysis, the role of the new interspinous implant appeared to reduce motion without suppressing it and to lower stress in the disc fibers and anulus matrix. Further in vivo investigations are necessary to draw definitive conclusions.

Pelvic injuries in side impact collisions: a field accident analysis and dynamic tests on isolated pelvic bones

Firstly, a field accident analysis was carried out in order to document the lesions and the injury mechanisms encountered in lat impact. The accident database of the Laboratory of Accidentology Biomechanics (LAB) in France was used, and a sample of 219 injure occupants sustaining 381 injuries in lateral collision enables to evaluate the most frequent injuries and their location. These injuries were also analyzed with regard to car characteristics. Secondly, an experimental study of the pelvic bony structure subjected to dynamic loads was carried out in order to document i biomechanical behaviour and its lesion threshold. Twelve pelvises were tested under side loading conditions. Displacement, accelerations, applied force, and local strains of the pubic rami were obtained. The main conclusions drawn out from the two parall studies were: (1) There was a good agreement between the real lif observations and those coming from the dynamic tests; and (2) the fracture threshold was well bordered by the chosen energy level o impact, and consequently, a first corridor including the behaviou the pelvic bony structure up to the level of injury is proposed.( For the covering abstract of the conference see IRRD E201172.

Three-Dimensional Analysis of the Cervical Spine Kinematics: Effect of Age and Gender in Healthy Subjects

Study Design. A three-dimensional (3D) analysis of the cervical spine kinematics in vivo about a large asymptomatic database in order to evaluate the impact of age and gender on the necks performances. Objective. To investigate the effect of age and gender on kinematical parameters of the cervical spine, specifically quantitative parameters concerning coupled movements and proprioception, using the infra-red POLARIS measurement system. Summary of Background Data. Cervical spine kinematics has been investigated in vivo by numerous authors using various devices. However, few is known about the influence of gender and age on the 3D cervical biomechanics, specifically regarding coupled movements and proprioceptive abilities. Methods. A total of 140 asymptomatic volunteers (70 men and 70 women) aged 20 to 93 years old were enrolled. The noninvasive infrared system Polaris was used to quantify the 3D range of motion (ROM) of cervical spine and to evaluate proprioceptive abilities. For validating the protocol in terms of reproducibility, 12 volunteers were tested 3 times by 2 independent operators. Results. The standard error of measurement for the maximal ROM in the 3 space planes was 5%. Gender had no significant influence on the 3D cervical ROM, except for the “70–79 years old” group. Age had a significant influence on all main movements showing 0.55° to 0.79° magnitude decrease per decade. Age and gender had no significant influence on coupled movements. “Head-to-Target” proprioception was significantly affected by the age only in the horizontal plane. Conclusion. A data base for cervical ROM, pattern of motion, and proprioceptive capability was established in population of 140 healthy subjects of various age and gender. Significant age-related decrease in ROM and proprioceptive abilities were observed in this study. Coupled movements did not vary with gender or age; however, their role in the cervical performance increased with age since main movements were limited.