Personalized Surgical Instruments Shayne Kondor, MESA COPT Gerald Grant, DMD, MS Peter Liacouras, Ph.D. Naval Postgraduate Dental School, Bethesda, MD MAJ James R. Schmid, DSc, PA-C US Army/Baylor University EMPA Doctoral Fellowship, Joint Base Lewis-McChord, WA LLC Michael Parsons US Army Joint Training Branch / Deployable Training Team, JCW, DD J7 Bill Macy Brian Sabert Stratasys, Eden Prairie, MN Christian Macedonia, MD Defense Advanced Research Projects Agency Arlington, VA 1 Background Additive fabrication has been called the Second Industrial Revolution . This technology allows a three-dimensional shape defined in digital space to be directly rendered into a tangible object. The transformation from virtual objects to tangible objects is fast and inexpensive compared to most traditional fabrication approaches. Thus, the revolutionary aspect of additive fabrication is not the uniform mass production of the first Industrial Revolution but the mass customization of manufactured devices . The history of surgical instruments, such as the forceps, shows an evolution of devices meant to augment the dexterity of the human hand . By the 17th Century, surgical instruments were constructed by skilled smiths and were often adorned with custom decoration . Instruments were customized to the feel and tastes of the commissioning surgeon. In the 19th Century, surgical instruments became cataloged and standardized in form. With consideration of sepsis, instruments evolved into the present stainless-steel designs in the early 20th Century . Through mass customization, General Surgery Instruments can be inexpensively tailored to the specific needs and tastes of a surgeon. Instruments can be quickly and economically printed in a biocompatible polymer using additive fabrication technology. Conceivably, a surgeon would have their hand dimensions digitized for reference, and then standard instrument designs could be digitally generated for a custom-tailored fit. Furthermore, as a surgeon gained experience or developed new procedures, the instruments could be customized to suit their individual needs. As opposed to mass-produced instruments in a medical supply catalog, a surgeon would call upon a personal catalog of unique instruments in virtual representation and produce on demand. This concept of personalized surgical instruments was investigated as a pilot demonstration of mass customization and on-demand fabrication by a team from the Naval Postgraduate Dental School (Bethesda, MD), Stratasys (Eden Prairie, MN), and the Service Chiefs Fellowship Program from the Defense Advanced Research Projects Agency (Arlington, VA). Custom spring forceps and pivot forceps devices were digitally designed, fabricated, and then evaluated using a surgical simulator. 2 Methods Digital models of spring forceps and a central pivot forceps were created in SolidWorks 2012 computer-aided design (CAD) software (Dassault Systems SolidWorks Corp., Waltham, MA), running on a Microsoft Windows 7 based workstation. The models were parameterized with key dimensions (arm lengths, finger loop positions, etc.). Custom designs were generated by simply changing the values of the key dimensions within the CAD application. Instruments were sized to fit the hands of a clinician and tailored to their expressed tastes and preferred technique. Driving dimensions were modified in the CAD model to generate a unique embodiment of an instrument. Figure 1 shows the CAD model with driving dimensions for tailoring a hemostat. Once modified to the clinician’s requests, the digital CAD model was exported and saved in the additive manufacturing standard’s file format. Figure 1. Examples of Parameterized Forceps Arm Instruments were printed in a modified ABS thermoplastic using a Fused Deposition Modeling process. The basic instrument designs were modified to replicate the mechanical performance of standard instruments (usually fabricated from stainless steel). Adaptation of the designs was necessary to accommodate the properties of presently available materials; these involved thickening of the cross-section of the forceps arms, and redesign of simple pivot hinges, to provide adequate mechanical strength and stiffness. Instruments were fabricated directly from theist digital files using a Dimension print Plus SE desktop FM printer (Stratasys, Eden Prairie, MN). Files were prepared for FM fabrication using Catalyze 4.3 (Stratasys, Eden Prairie, MN) 3D printing software running on a Microsoft Windows 7 based laptop computer. A developmental Absie-Ag material from Stratasys was used to print examples of the instruments. This material is currently under development as a potentially biocompatible and bacteriostatic material for medical applications. A customized tissue forceps and needle driver were designed to a test clinician’s personal specifications, fabricated, and tested. A subjective evaluation was performed by performing surgical procedures and suturing an incision on a Cut Suit surgical simulator (Strategic Options, San Diego, CA). 3 Results A one-piece, spring-style tissue forceps design was created in CAD. The design was tailored to fit the hand of a clinician and further tailored in stiffness to provide the desired feel during closure. A desire was expressed for an instrument that could be effectively manipulated by palm pressure. Interlocking triangular teeth were added to the tip of the instrument at the preference of the clinician. The final instrument design is depicted in Figure 2. Figure 2 Personalized Tissue Forceps Design Simple gripping and holding tests were performed to evaluate the design; feedback from the clinician drove further modifications. The stiffness of the arms, the length of the arms, and the angle of the arms at closure were modified as per the request of the clinician. Initially, the forceps were judged to be too stiff. Compliance was increased by narrowing the cross-section of the loop end. Forceps arm stiffness was increased by thickening the arms cross-section near the tip and teeth. The length of the forceps arms was customized to leave approximately 1-inch length beyond the tips of the fingers, and the angle between the arms at closure was also opened. Changing the pattern of material stand deposition affected the instrument feel in the hands of the clinician. Special FM toolpaths were developed by Stratasys to improve the durability and feel of the tissue forceps. A two-piece hinge pivot forceps design was also created in CAD. A standard pivoting arm design, common to hemostats, was modified for production in ABS plastic. A tapered “T” pivot key and tapered keyway joined the arms. Figure 3. Personalized Hemostat (left) and Needle Driver The two-piece forceps were modified into a hemostat. Driving dimensions were the arm length, arm section, jaw length, jaw section, finger loop diameter, and position. The clinician expressed a desire for an instrument that could be picked up, manipulated, and dropped from a gloved hand with minimal manual articulation. Furthermore, it was desired that the instrument allows for precise manipulation while held in the palm of the hand, as opposed to the finger loop. To meet these specifications, the forceps’ arm lengths were adjusted to place the forefinger in the pivot point with the instrument cradled in the palm of the hand. The finger loops were opened and positioned asymmetrically; a rearward-facing open loop for the thumb was placed ahead of a forward-facing open loop for the little finger. Toothed jaws were sized to perform dissection and clamping tasks. A locking rack tooth was added to the back of the arm handles for closure, the rack being actuated by palm pressure. The resulting design is depicted on the left in Figure 3. The hemostat design was digitally modified in CAD to produce other instruments. A needle driver was created by changing the jaw design, narrowing the pivot, and lengthening the forceps’ arms. Finger loops were repositioned, and the cross sectional arm area was increased to improve gripping tension. The needle driver design is shown on the right in Figure 3. A basic surgery kit was printed on the FDM device, Instruments in use During Simulated Surgery. 4 Interpretation Spring and pivot forceps instruments were designed to the specifications of a clinician based on hand dimensions, as well as personal preference for instrument feel and surgical technique. The instruments were printed on-demand using an FDM printer and used to successfully complete surgical procedures on a realistic simulator. With the development of new biocompatible materials for additive fabrication, it will be feasible to print personally customized surgical instruments on-demand. With design and fabrication cycle times of only a few hours, it will be feasible to rapidly evolve new instruments tailored to new surgical techniques and procedures.
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