F. von Waldenfels et al., "Computer Assisted Optimization of Prosthetic Socket Design for the Lower Limb Amputees Using 3-D Scan", in Proc. of 3rd Int. Conf. on 3D Body Scanning Technologies, Lugano, Switzerland, 2012, pp. 15-20, http://dx.doi.org/10.15221/12.015.
Computer Assisted Optimization of Prosthetic Socket Design for the Lower Limb Amputees Using 3-D Scan
Fee von WALDENFELS 1, Stefan RAITH 1, Maximilian EDER 1, Alexander VOLF 1, Jalil JALALI 2, Laszlo KOVACS 1
1 Research Group CAPS (Computer Aided Plastic Surgery) - Klinik und Poliklinik für Plastische Chirurgie und Handchirurgie, Klinikum rechts der Isar, Technische Universität München, Germany;
2 Institute of Medical Engineering at the Technische Universität München (IMETUM), Garching, Germany
Introduction: Customary prosthetic socket construction and fabrication process do not take patient specific parameters into account, instead they are based on subjective estimations, competence and capabilities of the orthopedic technician. Therefore a high rate of inappropriate prosthetic supplies is caused to the disadvantage of the amputation patient who suffers from wounds due to excessive pressure. A development of objective planning systems is required, in order to gain higher quality in the prosthetic socket construction. The central aim of the presented work was to improve the currently empirical process of prosthesis design in orthopedic technology with the aid of 3-D scan of the amputation stump, modern imaging techniques (MRI) and computer technology (FEA).
Method: Regarding a 3-D scan protocol the amputation stump of 10 patients were scanned in upright position using a 3-D linear laser scanner. Furthermore magnet resonance imaging (MRI) was performed in lying supine position, which produced non-negligible deformation in the soft tissue of the stump. MRI datasets were segmented into different compartments representing fat, muscle and bone using a special software workflow. The segmented geometries were fitted in the surface geometry of the upright 3-D scan. Therefore a simplified FE model was built in consideration of stiffness of soft tissue and bone. The calculated models reproduced the inner anatomical structure of the stump. The described method has been validated on a patient where both upright and regular supine MR image data were accessible in addition to 3-D surface scans with the aid of software calculating the 3-D compare (mean standard deviation in mm) of the 3-D models. The results of the deformation calculations of the patients were validated in FEA simulations and gait analysis.
Results: Using 3-D compare of the obvious deformed MRI model in lying position in comparison to the upright MRI model the mean standard deviation (SD) was 13.5 mm. The 3-D comparison of the reversely calculated MRI model in comparison to the upright MRI model showed a mean standard deviation of 5.8mm (improvement factor 2.34). The mean standard deviation of 5.8mm did not exceed the mean edge length of the finite elements, thus the results are sufficiently accurate for the following simulations performed by FEA software.
Conclusion: Validation results show a considerable improvement from the deformed MRI model in comparison to the reversely calculated MRI model, which is important for a realistic and physically based computer assisted design of the prosthetic socket. Based on patient-specific 3-D model, 3-D visualization, quantification and simulation of the individual biomechanical tissue changes in the amputation stump during the interaction with the prosthetic socket can be evaluated using finite element analysis (FEA).
3-D scan, MRI, finite element analysis, prosthetic socket, optimization
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