Measuring the global mechanical properties of the human thorax: Costo-vertebral articulation.

Biomechanical simulation of the human thorax, e.g. for 3D-printed rib implant optimisation, requires an accurate knowledge of the associated articulation and tissue stiffness. The present study is focusing on determining the stiffness of the costo-vertebral articulations. Specimens of rib segments including the adjacent thoracic vertebrae and ligaments were obtained from two human post-mortem bodies at four different rib levels. The rib samples were loaded with a tensile force in the local longitudinal, sagittal and transverse direction and the resulting displacement was continuously measured. The moment-angle response of the rib articulations was also determined by applying a load at the rib end in the cranial - caudal direction and measuring the resulting displacement. The torsional load response of the costo-vertebral articulations at an applied moment between -0.1 Nm and 0.1 Nm corresponded to a median range of motion of 13.2° (6.4° to 20.9°). An almost uniform stiffness was measured in all tensile loading directions. The median displacement at the defined force of 28 N was 1.41 mm in the longitudinal, 1.55 mm in the sagittal, and 1.08 mm in the transverse direction. The measured moment-angle response of the costo-vertebral articulation is in line with the data from literature. On the contrary, larger displacements in longitudinal, sagittal and transverse directions were measured compared to the values found in literature.

Measurement of global mechanical properties of human thorax: Costal cartilage.

Surgical resection of chest wall tumours may lead to a loss of ribcage stability and requires reconstruction to allow for physical thorax functioning. When titanium implants are used especially for larger, lateral defects, they tend to break. Implant failures are mainly due to specific mechanical requirements for chest-wall reconstruction which must mimic the physiological properties and which are not yet met by available implants. In order to develop new implants, the mechanical characteristics of ribs, joints and cartilages are investigated. Rib loading is highly dependent on the global thorax kinematics, making implant development substantially challenging. Costal cartilage contributes vastly to the entire thorax load-deformation behaviour, and also to rib loading patterns. Computational models of the thoracic cage require mechanical properties on the global stiffness, to simulate rib kinematics and evaluate stresses in the ribs and costal cartilage. In this study the mechanical stiffness of human costal cartilage is assessed with bending, torsion and tensile tests. The elastic moduli for the bending in four major directions ranged from 2.2 to 60.8 MPa, shear moduli ranged from 5.7 to 24.7 MPa for torsion, and tensile elastic moduli ranging from 5.6 to 29.6 MPa. This article provides mechanical properties for costal cartilage. The results of these measurements are used for the development of a whole thorax finite element model to investigate ribcage biomechanics and subsequently to design improved rib implants.

A 3-dimensional finite-element analysis investigating the biomechanical behavior of the mandible and plate osteosynthesis in cases of fractures of the condylar process.

OBJECTIVE: The condylar region is one of the most frequent sites for mandibular fractures, with direct application of miniplates being the most commonly used open-fixation technique today. Yet, anatomic and biomechanical limitations continue to make this application technically challenging with a considerable complication rate. We sought to analyze such incongruencies with respect to the complex biomechanical behavior of the mandible. STUDY DESIGN: Individual human mandible geometry, the specific bone density distribution, and the position and orientation of the masticatory muscles were evaluated by performing computed tomography scans and a sequential dissection of the cadaver mandible. Three-dimensional finite-element analysis was performed for different fracture sites, osteosynthesis plates, and loading conditions. RESULTS: Osteosynthesis of fractures of the condylar neck with 1 or 2 miniplates of a diameter of 2.35 x 1.00 mm was found to be an insufficient fixation method. This also applies for plates (3.60 x 1.54 mm), according to Pape et al,(8) when used in singular fashion (high condylar neck fractures excepted). In cases of singular occlusal contacts in the molar region (particularly at the contralateral side of the fracture), the highest stress values inside the mandible and osteosynthetic devices could be observed. With even the static yield limit of titanium being exceeded in such cases, consecutive rapid failure of the miniplates becomes most likely when loading of the condylar region caused by bite forces cannot be prevented. CONCLUSION: We strongly recommend the use, whenever possible, of 2 plates in the manner described by Pape et al(8) for osteosynthesis of fractures of the condylar neck in combination with bicortically placed screws. The stiffness of a singular osteosynthesis plate made of titanium in a diametrical dimension of approximately 5.0 x 1.75 mm was found to be equivalent to the physiological bone stiffness in the investigated fracture sites. The actual stiffness of such a fixation plate is approximately 3 times higher than the stiffness of devices commonly in use.

Three-dimensional finite element analysis of implant stability in the atrophic posterior maxilla: a mathematical study of the sinus floor augmentation.

Sinus lifting is performed with a variety of materials and techniques without a precise knowledge of the quantity of augmentation. This study based on three-dimensional finite element analysis was designed to show which surgical procedure and which amount of peri-implant packing yields the best bony support for dental implants. Eight 3D-FE models were used. Four modeled standard situations simulated quantitatively different packing situations produced by differences in surgical approach: i. no packing; ii. thin 1 mm bony sheath; iii. oblique subcomplete packing; iv. complete bony peri-implant packing up to the implant end. A fifth model compared a standard implant with a length of 13.5 mm and a diameter of 3.75 mm with a 7-mm-long and 5-mm-thick implant. In three additional models the stress response of the bone-implant system was evaluated in the absence of a cortical layer, thus simulating an extreme degree of maxillary atrophy. In all models the modeled implants were loaded at their points of emergence with an assumed force of 100 N. The vector of the loading force was inclined 30 degrees posteriorly relative to the implant axis and 30 degrees away from the sagittal plane. The bone-implant interface was assumed to be perfect simulating full osseointegration. The final evaluation of the FE models showed complete peri-implant packing to reduce displacements of the implant tip by 32% vs. no sheathing/packing. Van Mises' equivalent stresses were used to assess the stresses in both human bone and titanium alloy implants. The highest stress levels in bone were predicted for the case without sufficient implant sheathing. In the models with adequate bony implant support, intrabony stresses were generally reduced by up to - 40%. The structural stiffness of the bone-implant system increased with the extent of sinus floor elevation. The results indicate that more extensive peri-implant packing reduces implant displacement, intrabony stresses and stresses at the bone-implant interface.