Procedure-specific validation of artificial vertebrae

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 (28.8}±10.6) and the clamping forces (3.7±1.5}N/mm) of the human reference were met by the bone surrogate with 1.25% of blowing agent (22.3 ± 7.6 and 3.0±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 was96.0 ± 12.4 N.m/m. The material composition with 1% blowing agent achieved similar results (97.6 ± 14.3N.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.