Evaluation of bendable surgical suction devices made of shape-memory alloy for the endonasal transsphenoid removal of pituitary tumors.
In minimally invasive surgeries, it can be difficult to reach desired anatomic areas with rigid instruments, especially when obstacles are present in the surgical corridor (e.g., during transnasal pituitary surgery). We developed a new kind of suction device constructed of the shape-memory alloy Nitinol (nickel titanium), which is adaptable to a patient's specific anatomy. Use of this device minimizes surgical risks by allowing physicians to use an endonasal transsphenoid approach. The suction device, which is equipped with a cannula made of the shape-memory alloy, was planned and manufactured with three different handpiece designs. Experienced pituitary surgeons tested the prototypes in human cadaver skulls and rated the devices on specific questionnaires. The results of their evaluation indicate that this device is a suitable tool for improving the surgical procedure. Its potential benefits include a more effective surgery and reductions in the risk of injury, the duration of surgery, and costs.
Surgeons need a high degree of skill and precision when operating in small areas during neurosurgery to remove a pituitary tumor via the endonasal transsphenoid approach. Currently, the standard surgical approach is through the nostril and nasal cavity to the pituitary gland behind the sphenoid sinus. (1-3) However, this path is a long, narrow corridor that is limited by bone and soft-tissue structures. This surgery traditionally requires the use of scissors, bone rongeurs, and coagulation instruments. Various rigid angled suction devices also are used to dissect and aspirate pituitary tumor tissue to achieve a complete excision.
Avoidance of excessive force is required to prevent complications such as injury to delicate blood vessels (ischemia or hemorrhage), the dural lining over the brain (cerebrospinal fluid leak), cranial nerves (vision loss or diplopia), and the posterior part of the pituitary gland (diabetes insipidus). Factors that contribute to such injuries include the use of instruments that are not well suited for the task and the forceful use of instruments to access an area beyond the reach of standard instruments.
The use of a limited array of rigid suction devices results in numerous exchanges of instruments, with attempts to use other angled instruments that are less effective than our new approach with a bendable suction. This results in surgical inefficiency, as well as increasing operating time and its attendant costs. Several disadvantages are recognized with the use of standard rigid suction devices:
* They are not adaptable to a patient's individual anatomy.
* The risk of surgical injury is increased with the use of inadequate instrumentation.
* The surgical field needs to be extended to allow for access.
* The limited surgical field requires the use of multiple angled suction devices.
* Limited access results in incomplete tumor resection, which increases the risk of recurrence and need for radiation therapy.
* Modification of existing suction methods by bending them is difficult, and it narrows the diameter of the cannula.
* Bent suctions are difficult to restore to their original shape, and they require more frequent replacement.
We developed a new surgical suction device that surgeons can bend into any desired shape. With this device, it should be possible to achieve better access to all areas of the surgical field and improve the safety and efficiency of surgery.
Material properties. One of the promising materials tested for the manufacture of medical devices is the shape-memory alloy (SMA). This material is already being used for stents, needles, and braces, and it is suitable for surgical instruments such as suction devices. (4)
A cannula manufactured with an SMA can be adapted to a patient s anatomy simply by bending it by hand during surgery. One particular SMA material is Nitinol (nickel titanium), which we used to develop our bendable suction device. (5)
Ergonomics. Ergonomics is important in the development of a suction handpiece. The user should be able to handle the device for a long period of time without experiencing any discomfort such as clenching of the hand or arm and fatigue and pressure marks from weight of the device. It should lie in the hand comfortably and allow for precise control in any position.
Materials and methods
In close collaboration, surgeons, product designers, and engineers, with the aid of computer-aided design (CAD) software, worked to create three different models of a new suction handpiece, designated type 2, type 3, and type 4 (figure 1). These models give the user a choice of the most comfortable fit. The design of the handpiece must take into account its connection to the suction unit. The new suction device must be usable with all common aspirators to enable worldwide application.
One suction device is the ATMOS Record 55 DDS (ATMOS Medizin Technik; Lenzkirch, Germany). Its connection adapter for the cannula has a diameter of 6 mm. The CAD software allows developers to make rapid changes in design based on improvements suggested by surgeons.
Production process. The suction handpieces are made of the titanium alloy TI6AI4V and are manufactured by a process called generative laser melting (figure 2). To ensure that the suction device can be bent by the surgeon in any desired shape according to patient-specific anatomy, an SMA was used for the suction cannula. The cannula reverts to its original shape after it is activated by heat during autoclaving. Two different inner diameters were considered: 2 and 3 mm. The handpieces are finished with a coating of black carbon to reduce light reflection during surgery (figure 3).
Autoclave test. A test was performed to confirm that a bent suction cannula would revert to it original straight shape. The cannula was heated at 120[degrees]C (248[degrees]F) for 20 minutes. The test was performed a total of 20 times.
Evaluation questionnaire. The suction devices were rated by pituitary surgeons via a questionnaire. The surgeons provided their opinions on bendability, surgical access, and ergonomics. A 5-point scale with direct and closed-ended questions was used to categorize responses. Scores ranged from -2 (not at all) to +2 (very good). Each question pertained to only a single issue, and the questions were short, simple, direct, and comprehensible.
Overall, seven questions were asked--one technical question related to the device's return to its initial straight form after heating, and six clinical questions related to its use during surgery:
* Can the suction be bent in every desired shape?
* What is the force required to bend the suction?
* Is it possible to reach the pituitary?
* Is the diameter wide enough to remove tissue?
* How is the handling/ergonomics?
* How is the handpiece design?
* Is it possible to achieve the straight shape when the suction is heated?
Additional comments were also solicited. Suggestions for improvement were considered in the design of subsequent prototypes and implemented in the 3-D CAD model of the handpiece. To provide a realistic simulation of pituitary surgery via the endonasal transsphenoid approach, fresh-frozen and fixed human cadaver skulls were used. Three surgeons from the University of Pittsburgh Medical Center (UPMC) tested the device and completed the evaluation questionnaire.
Preparation process. Current suction cannulas can be prepared in two ways: manually and mechanically. In the manual preparation process, the device is cleaned with ultrasound, a flexible brush similar to a pipe cleaner, and disinfectant solutions and water. The disinfectants must be aldehyde-free, phenol-free, and quaternary-ammonium-cation-free to avoid fixation of residuals and disturbance. The mechanical process begins with brush cleaning. This is followed by alkaline and thermal disinfection via a single-chamber disinfection device without ultrasound.
After cleaning, the devices are inspected for damage, checked for function, sterilized with steam at 134[degrees]C (273[degrees]F) for at least 5 minutes, and then packaged. (6,7) To minimize the risk of unintentional transfer of difficult-to-diagnose prions (false-folded proteins that are responsible for the fatal Creutzfeldt-Jakob disease), steam sterilization at 134[degrees]C for at least 18 minutes is recommended. (8,9)
Ethical considerations. All procedures that contributed to this work were performed in compliance with the ethical standards expressed in relevant national and institutional guidelines on human experimentation (UPMC) and in accordance with the 1975 Declaration of Helsinki as revised in 2008.
We developed three functional prototypes of this new type of suction device. In all, the bendable suction devices left a positive impression on the UPMC surgeons. After each cadaver experiment, the handpiece design was revised with the 3-D CAD program and manufactured with the laser-beam melting machine, based on the surgeons' recommendations.
We were able to straighten each bent cannula after every autoclave procedure. No changes in the coating were detected.
The surgeons rated the ability to bend the suction device in every desired form as very good, although they recommended modification of some ergonomie features, such as the position of the suction hole.
First prototype. After the round of tests with the first prototype, the surgeons noted that the handpieces were too slim, and they recommended that they be widened by about 5 mm. They also said that the first 4 cm of the suction cannula near the handpiece should be rigid to avoid undesired bending and that the connection between the cannula and handpiece must be stable. They also recommended that the balance point of the suction device be located at the air-control hole and not at the cannula connection to the suction unit.
The surgeons also commented favorably that they were able to reach all areas of the surgical field and, again, that they could bend the suction cannula in any desired shape.
Second prototype (revisedfirst prototype). For the development of the second prototype, suction devices with an inner diameter of 2 and 3 mm were manufactured. For the second round of tests, the surgeons evaluated wider suction devices: one with an inner diameter of 2 mm and the other with a 3-mm inner diameter. Both devices were equipped with a rigid proximal cannula segment of 40 mm. The 3-mm diameter device was good for drilling, but its cannula was too difficult to bend. The proximal lengthening of the cannula for 40 mm was rated as too long and needed to be shorter (20 mm for future prototypes).
The position of the air-control hole made the device unwieldy because it was set more toward the direction of the connection to the suction unit. The instrument's center of mass needs to be considered. The wider suction devices were comfortable to use except for the type 3 device, which required further widening of the supporting surface. The surgeons said the diameter of the type 3 device was too small for drilling and the proximal part of the cannula (near the handpiece) was too flexible.
Third prototype (revised second prototype). Improvements for the third prototype included the production of three wider handpieces with inner diameters of 2 and 3 mm, and the application of the surgeons' proposals. The length of the suction tube is 150 mm.
Based on the testing surgeons' proposals, we were able to design a comfortable handpiece. Their evaluations affirmed that a bendable suction device is suitable for endonasal pituitary surgery. A working length of 150 mm is adequate, and all surgical fields can be reached. The ergonomics of the type 4 handpiece were rated as very good, and this type now serves as the primary design.
The use of a bendable suction device made of an SMA reduces the need for multiple rigid suction devices and shortens surgical time, which in turn reduces costs. Moreover, the ability to bend the device means that less tissue and bone must be removed to achieve surgical access, which improves efficiency and reduces the risk of major complications secondary to unnecessary dissection.
Because surgical risk is lower, less experienced surgeons can operate more safely and effectively and achieve a more thorough tumor dissection. The bendable suction device is suitable not only for endonasal transsphenoid pituitary surgery, but it also has wide applications to other surgical procedures such as endoscopic sinus surgery and some neurosurgical procedures.
After each autoclaving procedure, the cannula can be straightened and then adapted again for the next patient.
The bendable suction cannula will be developed further. For the next phase in that development, manufacturing and testing of next-generation prototypes will continue to be based on testing by and feedback from surgeons at UPMC.
In conclusion, the SMA Nitinol allows surgeons to bend a suction cannula in any desired form to adapt it to a patient's individual anatomy. With a well-designed handpiece and the ability to choose from among different cannula diameters, surgeons can extend the application of this device to meet multiple needs. This device obviates the need to use different rigid suction devices, which results in economy of time and cost. Because the risk of life-threatening injury is reduced, less experienced surgeons can perform critical operations in a safer and more effective manner. These suction devices offer patients and surgeons the promise of optimal surgical outcomes.
From the Department of Medical Engineering, Fraunhofer Institute for Machine Tools and Forming Technology, Dresden, Germany, and the Department ofNeurosurgery, University of Leipzig Faculty of Medicine, Leipzig, Germany (Dr. Grunert); the Department of Biomedical Engineering, West Saxon University of Applied Sciences, Zwickau, Germany (Mrs. Klietz); the Department of Neurological Surgery, University of Pittsburgh Medical Center (UPMC), Pittsburgh (Dr. Gardner); and the Center for Cranial Base Surgery, UPMC Presbyterian Hospital, Pittsburgh (Dr. Fernandez-Miranda and Dr. Snyderman). The study described in this article was conducted at UPMC.
Corresponding author: Ronny Grunert, PhD, Department of Medical Engineering, Fraunhofer Institute for Machine Tools and Forming Technology, Nothnitzer Strasse 44,01187 Dresden, Germany. Email: email@example.com
Funding/support: The authors received grants from The Fraunhofer Society of Munich, Germany, for this research.
Ronny Grunert, PhD; Sandra Klietz, BEng; Paul A. Gardner, MD; Juan C. Fernandez-Miranda, MD; Carl H. Snyderman, MD, MBA
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|Title Annotation:||ORIGINAL ARTICLE|
|Author:||Grunert, Ronny; Klietz, Sandra; Gardner, Paul A.; Fernandez-Miranda, Juan C.; Snyderman, Carl H.|
|Publication:||Ear, Nose and Throat Journal|
|Date:||Dec 1, 2018|
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