Abstract
The structural integrity of cranial implants is of great clinical importance, as they aim to provide cerebral protection after neurosurgery or trauma. With the increased use of patient-specific implants, the mechanical response of each implant cannot be characterized experimentally in a practical way. However, computational models provide an excellent possibility for efficiently predicting the mechanical response of patient-specific implants. This study developed finite element models (FEMs) of titanium-reinforced calcium phosphate (CaP–Ti) implants. The models were validated with previously obtained experimental data for two different CaP–Ti implant designs (D1 and D2), in which generically shaped implant specimens were loaded in compression at either quasi-static (1 mm/min) or impact (5 kg, 1.52 m/s) loading rates.The FEMs showed agreement with experimental data in the force–displacement response for both implant designs. The implicit FEMs predicted the peak load with an underestimation for D1 (9%) and an overestimation for D2 (11%). Furthermore, the shape of the force–displacement curves were well predicted. In the explicit FEMs, the first part of the force–displacement response showed 5% difference for D1 and 2% difference for D2, with respect to the experimentally derived peak loads. The explicit FEMs efficiently predicted the maximum displacements with 1% and 4% difference for D1 and D2, respectively. Compared to the CaP–Ti implant, an average parietal cranial bone FEM showed a stiffer response, greater energy absorption and less deformation under the same impact conditions.The framework developed for modelling the CaP–Ti implants has a potential for modelling CaP materials in other composite implants in future studies since it only used literature based input and matched boundary conditions. Furthermore, the developed FEMs make an important contribution to future evaluations of patient-specific CaP–Ti cranial implant designs in various loading scenarios.
Highlights
Cranial defects caused by trauma or neurosurgery are commonly reconstructed using autologous bone or synthetic implants
The framework developed for modelling the calcium phosphate–titanium (CaP–Ti) implants has a potential for modelling CaP materials in other composite implants in future studies since it only used literature based input and matched boundary conditions
Our study focuses on validation of computational models of the patient-specific calcium phosphate-titanium (CaP–Ti) implant, which has a somewhat more complex structure than other commonly used implants
Summary
Cranial defects caused by trauma or neurosurgery are commonly reconstructed using autologous bone or synthetic implants. The pro cedure has a high clinical complication rate (~20%), where infection is the most common complication for synthetic cranial implants (van de Vijfeijken et al, 2018) These implants have commonly been made of bioinert materials, e.g. PMMA. The outcome could potentially be improved by using osteoconductive and bioactive materials (Engstrand, 2012) One such recently introduced cranial implant, a patient-specific calcium phosphate–titanium (CaP–Ti) implant (OssDsign Cranial, OssDsign, Uppsala, Sweden), has shown promising clinical outcomes in terms of low complication rates (Engstrand et al, 2014; Kihlstrom Burenstam Linder et al, 2019; Sundblom et al, 2018). In a recent retrospective study of 50 patients, only 7.5% developed complications which lead to implant removal Since this patient cohort previously had a 64% failure rate with autologous bone or other synthetic implants (Kihlstrom Burenstam Linder et al, 2019), this outcome was considered promising. The use of computational models for assessing the mechanical behavior of cranial implants could be a solution to these challenges
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