Introduction
Materials and methods
Overall animal study design
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Two sheep were utilized for a pilot evaluation ensuring procedure safety and effectiveness. These were euthanized after 12 weeks and formed part of the histology cohort.
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An additional 8 sheep were designated as part of the 12-week survival period (histology) cohort.
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The remaining 14 sheep formed the biomechanical cohort, with a post-surgery survival period of 24 weeks.
Cohort | No. sheep | Survival period | Relevant interventions |
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Histology | 10 | 12 weeks | Pre-op CT, surgery, 8 week CT, 12 week post-euthanasia CT |
Biomechanical | 10 | 24 weeks | Pre-op CT, surgery, 12 week CT, 24 week post-euthanasia CT |
Biomechanical (t0) | 4 | 0 weeks | Pre-op CT, surgery, immediate post-surgery CT |
Surgical planning and implant design
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Pre-operative CT was imported into the planning software and the right femur manually segmented.
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The segmented bone was registered to the reference plan by manual alignment followed by iterative closest point (ICP) matching. The computed transformation was applied to the image data, aligning it with the reference plan.
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Robotic cutting paths and velocities were generated based on the reference cut geometry, aligned bone geometry and bone density extracted from aligned CT data.
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Four registration initialization points were defined at the medial and lateral condyles, patellar groove and proximally on the femur shaft.
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The bone geometry, robot path and registration points were exported as a custom surgical plan file.
Robotic system for bone tumour excision
Surgical approach
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Cutting depth of 2 mm per pass,
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Tool rotational speed of 13′000 RPM,
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Variable feedforward based on tissue density information extracted from CT:
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5 mm/sec when moving through low-density areas (air, marrow or trabecular bone),
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1 mm/sec through dense cortical bone,
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0.5 mm/sec at locations of significant density change (cortical interfaces).
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Accuracy analysis approach
Operative time analysis
Results
Average time (minutes) | ||||||
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Pinning | Positioning | Registration | Repositioning | Cutting | Repositioning/cleaning | Hole drilling/fixation |
5.25 ± 1.21 | 8.35 ± 4.1 | 4.7 ± 1.95 | 11.3 ± 3.26 | 14.3 ± 11.82 | 16.9 ± 8.19 | 28.5 ± 15.62 |
43.9 ± 15.31 | 45.4 ± 19.97 | |||||
89.3 ± 25.25 |
Translation (mm) | Rotation (°) | |||||||
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X | Y | Z | Total | X | Y | Z | Total | |
Overall | − 0.06 ± 0.4 | 0.27 ± 0.56 | − 0.05 ± 0.93 | 1.05 ± 0.53 | 1.13 ± 0.87 | 0.46 ± 0.78 | 1.05 ± 1.67 | 2.38 ± 0.98 |
Absolute | 0.33 ± 0.23 | 0.49 ± 0.37 | 0.7 ± 0.6 | 1.23 ± 0.7 | 0.64 ± 0.63 | 1.66 ± 1.04 | ||
RMS | 0.39 | 0.61 | 0.91 | 1.17 | 1.31 | 0.89 | 1.94 | 2.56 |