The Use of a Vibro-Acoustic Based Method to Determine the Composite Material Properties of a Replicate Clavicle Bone Model

Development and validation of risk of bias tool for the use of finite element analysis in dentistry (ROBFEAD)

There has been a systematic review of studies that used FEA in dental sciences, but no adequate risk of bias (RoB) analysis technique has been developed. Therefore, the development and validation process of RoB in studies using the finite element analysis in dentistry (ROBFEAD) tool is described. In the first phase of development, the scope of the tool and possible modifications were covered, and validation was done in the second phase. The developed tool comprised 6 domains and a total of 22 guiding questions in these domains. This article proposes the development and validation of ROBFEAD, a tool for measuring RoB in finite element research in dentistry.

Thin patient-specific clavicle fracture fixation plates can mechanically outperform commercial plates: An in silico approach

Current fixation plates used to operatively stabilize clavicular fractures are suboptimal, leading to reoperation rates up to 53%. Plate irritation, which can be caused by a poor geometric fit and plate thickness, has been found to be an important factor for reoperation. Moreover, muscle attachment sites (MAS) have to be detached occasionally. To improve current surgical clavicle fracture treatment with plate osteosynthesis, a change in plate design is required. The goal of this study was to design a patient-specific clavicle fracture fixation plate that includes geometrical optimization and stiffness determination. Its biomechanical performance has been compared with a commercial plate by examining the geometric fit, anatomical outline, stresses and interfragmentary motion using a finite element analysis with physiological loading and boundary conditions. Evaluation showed a better geometrical fit of the patient-specific plate as well as an improved fracture reduction. Displacements between fracture fragments were lower in case of the patient-specific plate, both when a fracture gap and no fracture gap were present. Results indicate a superior mechanical performance in terms of all investigated outcomes of the patient-specific plate compared to the commercial plate, while better aligning with the patient-specific geometry and without the need for MAS release. Due to the patient-specific geometry and reduced thickness, these fixation plates are expected to decrease the operation time, as intraoperative contouring will become irrelevant, and to decrease reoperation rates as implant irritation will be minimized.

Replacement of Destructive Pull-out Test with Modal Analysis in Primary Fixation Stability Assessment of Spinal Pedicle Screw

BACKGROUND

Pedicle screw fixation devices are the predominant stabilization systems adopted for a wide variety of spinal defects. Accordingly, both pedicle screw design and bone quality are known as the main parameters affecting the fixation strength as measured by the pull-out force and insertion torque. The pull-out test method, which is recommended by the standards of the American Society for Testing and Materials (ASTM), is destructive. A non-destructive test method was proposed to evaluate the mechanical stability of the pedicle screw using modal analysis. Natural frequency (ω_n) extracted from the modal analysis was then correlated with peak pull-out force (PPF) and peak insertion torque (PIT).

METHODS

Cylindrical pedicle screws with a conical core were inserted into two different polyurethane (PU) foams with densities of 0.16 and 0.32 g/cm3. The PIT and PPF were measured according to the well-established ASTM-F543 standard at three different insertion depths of 10, 20, and 30 mm. Modal analysis was carried out through recording time response of an accelerometer attached to the head of the screw impacted by a shock hammer. The effect of the insertion depth and foam density on the insertion torque, natural frequency, and pull-out force were quantified.

RESULTS

The maximum values of ω_n, PIT, and PPT were obtained at 2,186 Hz, 123.75 N.cm, and 981.50 N, respectively, when the screw was inserted into the high-density foam at the depth of 30 mm. The minimum values were estimated at 332 Hz, 16 N.cm, and 127 N, respectively, within the low-density PU at the depth of 10 mm. The higher value of ωn was originated from higher bone screw stability and thus more fixation strength. According to the regression analysis outcomes, the natural frequency (ω_n) was linearly dependent on the PIT (ω_n=14 PIT) and also on the PPF (ω_n=1.7 PPF). Coefficients of variation as the results of the modal analysis were significantly less than those in conventional methods (i.e. pull-out and insertion torque).

CONCLUSION

The modal analysis was found to be a reliable, repeatable, and non-destructive method, which could be considered a prospective alternative to the destructive pull-out test that is limited to the in-vitro application only. The modal analysis could be applied to assess the stability of implantable screws, such as orthopedic and spinal screws.

Proof of Concept for the Detection of Local Pressure Marks in Prosthesis Sockets Using Structural Dynamics Measurement

The wear comfort of a prosthesis is of great importance for amputee patients. The wear comfort can be affected by changes in the interface between the residual limb and prosthesis socket, which can be caused by time-dependent volume fluctuations of the tissue, leading to unwanted local pressure marks. The basis to ensure time-independent wear comfort of a prosthesis is to identify these changes. Common techniques for identifying these variations have a negative impact on the sensitive interface between the residual limb and prosthesis. The following paper contains a proof of concept for the detection of local pressure marks without affecting the described interface using structural dynamics measurements, exemplarily shown at a prosthetic socket for transfemoral amputees in a test bench scenario. The dynamical behaviour of the investigated system is analysed in the form of frequency response functions acquired for different pressure locations and preloads using an impact hammer for excitation and a triaxial acceleration sensor. The frequency response functions show major changes for the various boundary conditions with respect to their frequency-dependent compositions. The results demonstrate how the utilised method enables the identification of changes in local pressure marks regarding the variation of position and magnitude.