New computer simulation system makes delicate surgery simpler.
By Andy Christensen, Medical Modeling Corp. & Kate Moore, Z Corp.
Dr. John Teichgraeber is the associate professor of surgery for the Division of Plastic and Reconstructive Surgery and the Division of Pediatric Surgery at the University of Texas Heath Science Center in Houston. With over 20 years of experience as a surgeon, he is one of the leading authorities in the area of pediatric reconstructive surgery
Recently, Dr. Teichgraeber wanted to find a way to more thoroughly prepare for surgery on his young patients. One such case was a young child, nine months old, who suffered from craniosynostosis.
The seven bones of a baby's skull are separated by soft spots called sutures. Craniosynostosis is a term that describes premature or early closure of one or more of these sutures. Many craniofacial disorders have a component of craniosynostosis that does not allow the brain to expand normally within the skull. The result, in some cases, is increased intracranial pressure. This increase in pressure around the brain can cause brain damage and vision loss in extreme cases.
The surgical procedure to correct this, called fronto-orbital advancement with cranial vault remodeling, consists of releasing the fused suture and reshaping the skull. It is generally performed by a plastic surgeon with the help of a neurosurgeon. This procedure can take from two to five hours to perform, depending on the surgeons' expertise and the severity of the case.
This type of procedure presents many challenges to the surgeon. He or she must decide where to make the new bone cuts so that the skull develops at a regular pace with normal symmetry. Without careful planning, the new cuts could expand too much or expand asymmetrically, causing the head to become misshapen. There is not a lot of time between when this problem is diagnosed and when surgical intervention must take place. Typically the surgery is performed between three and nine months of age. Dr. Teichgraeber performs many of these procedures in an average month, with a typical procedure lasting more than four hours.
Recently, Dr Teichgraeber was introduced to Z Corp's Z402 3D printing technology via Medical Modeling Corporation. Medical Modeling Corp.produces a wide range of physical models of internal biologic data derived from medical imaging modalities such as computed tomography (CT) or magnetic resonance imaging (MRI).
Andy Christensen, general manager of Medical Modeling Corp., identified a need in the medical community - a fast and relatively low-cost 3D surgical planning tool to assist surgeons in preparing for especially complex operations, particularly in craniofacial reconstruction. Medical Modeling Corp. purchased a Z402 System in January 1999 to add to their range of modeling services and to target this emerging need. Their goal was to deliver a good quality model at low cost with a one-day turnaround. "Just what the doctor ordered," so to speak.
Before the advent of 3D modeling technologies, a surgeon would rely on two-dimensional CT slices and x-rays to both diagnose and plan the surgery. Using a 2D CT scan data provided by Dr. Teichgraeber, Medical Modeling Corp. was able to import the data into the MIMICS software package provided by Materialise (Ann Arbor, MI). MIMICS has the ability to interpolate automatically between thick cross layer sections and produces files ready for rapid prototyping. This means that it can convert any data in CT or MRI format into STL format. STL is the de facto standard file format for all rapid prototyping equipment. An STL file was exported from MIMICS to the Z402. The Z402 System Software then sliced the STL file into cross-sections that can be anywhere between 0.004" and 0.010" thick. The layer thickness of the skull in this case study was 0.007 in. Data preparation takes just minutes. When the data preparation is completed, each slice or layer of data is then transferred from the software over to the Z402 3D Printer.
To begin the 3D printing process, the print assembly moves to the right and spreads a layer of powder in the same thickness as the cross section to be printed. Then, as the print assembly returns to the left, the 128 jets in the Z402 binder cartridge apply a binder solution to the powder, causing the powder particles to bind to one another in the shape of the cross-section of the layer. The feed piston comes up one layer of thickness and the build piston drops one layer of the thickness. The Z402 System then spreads a new layer of powder and repeats the process until the part is completely printed.
The model was created using a proprietary starch-based material sold by Z Corp. The model was completed in under four hours, a time savings of over twelve hours compared to high-end rapid prototyping alternatives.
The model was used by Dr. Teichgraeber in preparation for the surgery. It also was taken into the operating room non-sterile for reference during surgery. Using the model, Dr. Teichgraeber was able to perform the surgery in just three hours rather than the usual four.
"This repair was done in the least amount of time possible, while providing the patient with a great outcome, "commented Dr. Teichgraeber. "The model provided more than enough accuracy and allowed for communication before the surgery between myself and the neurosurgeon."
According to Dr. Teichgraeber, use of the Z402 System model provided three significant benefits:
- Better surgical preparation. Using the model gave Dr. Teichgraeber a three-dimensional view, which allowed him to better visualize the situation and plan more effectively.
- Reduced surgery time. Each hour of surgery can increase the risk of complications for the patient and fatigue for the surgeon.
- Reduced cost to the patient. Every hour during an operation can cost thousands of dollars. Using a conservative estimate of $2,000/hour, using this model, which cost $650, produced a return on investment of more than 300%.
With the Z402 System, Medical Modeling Corp. was able to provide a realistic 3D model for the doctor at about one third of the cost of alternative rapid prototyping methods. Using these models in the surgery planning process can reduce costs and result in a better patient experience.
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