Developing 3D Printed Cutting Guides for Bone Tumor Surgery
The surgical cutting guides were fabricated with many features that helped the surgeon in positioning them correctly on top of the exposed bone during surgery. These features were designed using the anatomical landmarks extracted from the CT-scan of the bone pre-operatively.
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The following are the anatomical features used for guide positioning:
(1) The landmarks on the bone such as the top curve is featured on the upper side of the guide.
(2) Topology of the bone so that the bottom of the guide copies the surface of the bone.
(3) The boundary of the tumor effected area for defining the cutting path.
Surgical Resection using 3D-Printed Cutting Guides
We added additional features on the cutting guide to help guide the surgeon:
(1) Spikes were designed on the underside of the cutting guide such that the tips of the spikes follow the surface of the bone.
(2) A gusset added on the upper side of the guide which acts as an additional support during positioning.
(2) Optical markings used for detecting the positioning of the guide using 3D image processing.
Surgical Resection using 3D-Printed Cutting Guides
Improving Positioning of 3D-printed Surgical Guides using Image-processing Techniques
3D-printed Surgical Guides
3D-printed guides, recently introduced in orthopedic oncology, improve resection accuracy compared with traditional bone resection methods, but there are inaccuracies associated with them due to inevitable errors introduced by human factor, there is still a slight probability that surgeons position the guide with an error beyond the limits established during preoperative planning, yielding in patient risks.
In this study, we use image-processing techniques to quantify the positioning error of the cutting guide while its placement on the bone during the surgery. The mounting rotational and translational error was quantified from 2D images, and compared to CT-scanning images.
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The results indicate that the use of boundary tracing by image processing technique is as reliable as using CT scanning for measuring the positioning error and this technique could be developed into an intra-operative application to help surgeons position the cutting guide accurately in real-time
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Safety Margin for Cutting Guides
In this study, I studied the inaccuracies of using the 3D-Printed Cutting Guides. Using sawbones to quantitatively investigate the margin of error for various jig types and to determine a “safety margin” that could serve as a guide for surgeons and jig engineers in creating 3D-printed jigs that would reduce the risk of potential disastrous results such as positive margins.
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​​Various 3D-printed jigs were used to simulate wide resection of a distal femoral bone sarcoma on Sawbone specimens by 10 individuals with no specific prior expertise in cutting guides. We simulated the sawbone setup with and without simulated soft tissue to quantify how much of an effect it may have in positioning the guide on the bone during the surgery.
Experiments were conducted to determine the mean deviation from the boundary of the tumor experienced in placing cutting guides on the bones. The mean deviation for the four types of cutting guides ranged from 2.86 mm to 6.54 mm. We determined that a jig design should have a safety margin of 4.8 mm for standard guides and 8.65 mm for gusset guides to minimize the possibility of cutting into the tumor as a result of human error in guide placement. Further studies involving cadavers and patients are warranted.
Accuracy of 3D Printed Cutting Guides and their Design Safety Margin
Novel Positioning Feedback System as a Guidance in Bone Tumor Resection
Optical Feedback System
I designed an optical feedback system (OFS) (free of fluoroscopy or other bulky imaging equipment) that assists surgeons in accurate guide placement on the bone. The OFS, using image processing techniques (MATLAB), identified anatomical landmarks of the bone and optical markers on the 3D printed guide and plotted reference lines on the input image, along with the orientation error of the guide from its ideal position on the bone, providing the surgeon with appropriate feedback.
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The OFS detects the anatomical landmarks on the bone using the 2D pictures and defines a reference which is compared to the CT scans taken pre-operatively and gives an instantaneous feedback to the surgeon to adjust the positioning of the cutting guide before constraining them onto the bone.
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I carried out a feasibility study on twelve pairs (left and right) (n = 24) of cadavers using three types of guides (four pairs each). The surgeon constrained the specimen femurs rigidly on a bench vice and positioned the cutting guide on the femur. A surgical drill was used to fix the cutting guide to the bone using three 3.5 mm Steinmann pins. Photographs of this setup are taken using an iPhone camera in three mutually perpendicular planes (sagittal, coronal, and transverse) to calculate the orientation using OFS.
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