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Currently the surgical training of parietal bone graft techniques is performed on patients or specimens. Commercially available bone models do not deliver realistic haptic feedback. Thus customized parietal skull surrogates were developed for surgical training purposes. Two human parietal bones were used as reference. Based on the measurement of insertion forces of drilling, milling and saw procedures suitable material compositions for molding cortical and cancellous calvarial layers were found. Artificial skull caps were manufactured and tested. Additionally microtomograpy images of human and artificial parietal bones were performed to analyze outer table and diploe thicknesses. Significant differences between human and artificial skulls were not detected with the mechanical procedures tested. Highly significant differences were found for the diploe thickness values. In conclusion, an artificial bone has been created, mimicking the properties of human parietal bone thus being suitable for tabula externa graft lift training.

Objective: The development of a novel hybrid patient simulator was initiated to provide a safe training possibility for novice surgeons. Integrated artificial vertebrae should be able to realistically mimic the haptics of transpedicular vertebroplasty instrument insertion and pedicle screw placement. Therefore, new open-celled material compositions were developed, tested, and validated with reference to elderly human vertebrae. Methods: Vertebroplasty tool insertion force and pedicle screw torque measurements were performed. To validate the new bone surrogates for transpedicular tool insertion, a novel parametric model of the procedure was developed identifying three characteristic insertion parameters (weighting factors, cutting, and clamping forces). Furthermore, the slope of the insertion torque was used to validate the new materials against the human vertebrae for pedicle screw placement. Results: A relative error less than 6% confirmed the suitability of the parametric model for validation. The weighting factors ( ${\text{28.8}}\pm {\text{10.6}}$ ) and the clamping forces ( $\text{3.7}\pm \text{1.5}\;\text{N}/\text{mm}$ ) of the human reference were met by the bone surrogate with 1.25% of blowing agent ( ${\text{22.3}}\pm {\text{7.6}}$ and $\text{3.0}\pm \text{0.3 N/mm}$ , respectively). However, no material was able to reflect the instrument cutting forces. The slope obtained during pedicle screw placement in human vertebrae was ${\text{96.0}}\pm {\text{12.4}}$  N $\cdot$ m/m. The material composition with 1% blowing agent achieved similar results ( ${\text{97.6}}\pm {\text{14.3}}$  N $\cdot$ m/m). Conclusion: Two suitable materials that deliver realistic haptics during both instrument insertions were validated. The parametric model suitably modeled the transpedicular instrument insertion. Significance: These newly developed models provide a realistic haptic feedback during transpe-dicular instrument insertions with the potential of cement application during surgical skill training. [ABSTRACT FROM AUTHOR]

Aside from human bones, epoxy-based synthetic bones are regarded as the gold standard for biomechanical testing os osteosyntheses. There is a significant discrepancy in biomechanical testing between the determination of fracture stability due to implant treatment in experimental methods and their ability to predict the outcome of stability and fracture healing in a patient. One possible explanation for this disparity is the absence of population-specific variables such as age, gender, and ethnicity in artificial bone, which may influence the geometry and mechanical properties of bone. The goal of this review was to determine whether commercially available artificial bones adequately represent human anatomical variability for mechanical testing of femoral osteosyntheses. To summarize, the availability of suitable bone surrogates currently limits the validity of mechanical evaluations of implant-bone constructs. The currently available synthetic bones neither accurately reflect the local mechanical properties of human bone, nor adequately represent the necessary variability between various populations, limiting their generalized clinical relevance., (© 2024 Walter de Gruyter GmbH, Berlin/Boston.)

This manuscript summarizes presentations of a symposium on key considerations in design of biomechanical models at the 2019 Basic Science Focus Forum of the Orthopaedic Trauma Association. The first section outlines the most important characteristics of a high-quality biomechanical study. The second section considers choices associated with designing experiments using finite element modeling versus synthetic bones versus human specimens. The third section discusses appropriate selection of experimental protocols and finite element analyses. The fourth section considers the pros and cons of use of biomechanical research for implant design. Finally, the fifth section examines how results from biomechanical studies can be used when clinical evidence is lacking or contradictory. When taken together, these presentations emphasize the critical importance of biomechanical research and the need to carefully consider and optimize models when designing a biomechanical study., (Copyright © 2021 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the Orthopaedic Trauma Association.)

During vertebral surgery, misplaced pedicle screws can harm vital neural and vascular structures. Haptic distinction between cortical and cancellous bone structures is therefore essential for correct screw placement. This tactile experience during pedicle screw placement can be obtained by training on human or animal specimens even if expensive or ethically questionable. In this study, novel synthetic vertebrae were evaluated within a hybrid simulator to provide realistic haptics for the training of spine surgeries. Synthetic vertebrae were custommade of calcium powder-based composites imitating both, cancellous and cortical bone. The mechanical properties of synthetic surrogates were validated for pedicle screw placement and cement augmentation and were compared with those obtained from human vertebrae and insertion torques were analyzed. In human vertebrae pedicle screw torque measurements resulted in mean torque slopes of 82±33Nm/m. Calcium carbonate-based materials achieved lower torques than the human bone whereas calcium phosphate-based bone surrogates showed comparable results. A further differentiation of the calcium phosphate-based vertebrae revealed, that synthetic vertebrae with lower amounts of blowing agent, achieved suitable torques (83 ± 28Nm/m) in comparison to the human reference (p = 0.39). Cement application and subsequent fluoroscopy images confirmed, that the cancellous core of the synthetic vertebrae enabled cement augmentation. In conclusion, our findings suggest, that the artificial bone samples mimic the properties of human bone during pedicle screw placement and cement augmentation and are therefore suitable as synthetic vertebrae in a hybrid surgical simulator.

Vertebral compression fractures are treated surgically for approximately 25 years. In percutaneous cement augmentation techniques bone cement is applied to a fractured vertebra under fluoroscopic evidence to stabilize the bone fragments. Complications due to leakage of the low viscosity bone cement are reported in 5 to 15% of all routine cases. During the intraoperative application of bone cement surgeons rely on visiohaptic feedback and hence need to be familiar with the cement's rheology properties. Therefore, training is necessary. A hybrid simulator for cement augmentation training was developed but the usage of expensive real cement limits its purpose as a training modality. Twentythree inexpensive bone substitutes were developed and tested with the objective to mimic real bone cement. Cement application measurements were conducted and a mathematical model of the measurement setup was created. Compared with real bone cement, a cement substitute based on Technovit 3040 in combination with radical catchers and additional additives was identified as an appropriate substitute for cement augmentation training.

Puncturing the epidural space and lumbar puncture are common procedures in anesthesia. They are carried out blind, where a needle is advanced from posterior between two adjacent vertebrae. Two different approaches are common practice for this technique, the midline and the paramedian one. The learning curve characteristics of both approaches significantly depends on the number of punctures carried out by a medical novice. For the training of these blind procedures a hybrid simulator requires artificial structures imitating the tissues which are penetrated by the needle. Within this work a patient phantom for spinal needle insertion procedures was developed and validated successfully against literature as well as by a study carried out with medical experts.

Vertebral compression fractures can limit quality of life. Cement augmentation techniques show good results in attaining pain relief. Kyphoplasty enables a better restoration of vertebra height due to a dilatable balloon tamp, which is inflated in the fractured vertebra. Surgical training of vertebral cement augmentation techniques is currently performed on patients or specimens. To enable another training possibility for surgical residents, a new hybrid patient simulator was developed. Artificial vertebrae allocate a realistic haptic feedback during needle insertion. Based on these results, new polyurethane foam recipes were developed to either enable a realistic needle insertion as well as a balloon tamp dilatation. Needle insertion forces of the newly developed foams were compared against commercially available artificial trabecular bone material and balloon tamp dilatations were performed in manufactured materials. Based on the matching needle insertion forces, two suitable material compositions for needle insertion and balloon dilatation training were found. This investigation is considered as a prior study before evaluation on human specimen.

Surgical simulators provide a safe environment where novice surgeons can acquire their surgical skills. Although the number of patients with diseases of the musculoskeletal system is growing, the development of orthopedic simulators is still in it's infancy. The aim of this work was to identify simulation-based assessment parameters for a novel simulator in minimally invasive spine surgery. Apart from parameters targeting the duration and the surgeon's economy of motion during percutaneous bone access, parameters characterizing the movement smoothness were also examined with respect to their suitability. The results indicated, that the overall duration, the number of instrument movements, the number of velocity peaks and the Movement Arrest Period Ratio are the most promising predictors of expertise. Targeting performance improvement, the overall duration (p = 0.001), the number of instrument movements (p = 0.003) and the traveled instrument path length (p = 0.009) detected significant differences between subsequent trials. Using these parameters, a study can be designed targeting the validity and reliability of the simulation-based assessment.

Vertebroplasty and kyphoplasty are commonly used minimally invasive methods to treat vertebral compression fractures. Novice surgeons gather surgical skills in different ways, mainly by "learning by doing" or training on models, specimens or simulators. Currently, a new training modality, an augmented reality simulator for minimally invasive spine surgeries, is going to be developed. An important step in investigating this simulator is the accurate establishment of artificial tissues. Especially vertebrae and muscles, reproducing a comparable haptical feedback during tool insertion, are necessary. Two artificial tissues were developed to imitate natural muscle tissue. The axial insertion force was used as validation parameter. It appropriates the mechanical properties of artificial and natural muscles. Validation was performed on insertion measurement data from fifteen artificial muscle tissues compared to human muscles measurement data. Based on the resulting forces during needle insertion into human muscles, a suitable material composition for manufacturing artificial muscles was found.