Ultrasound probes (L25, L50, C60; SonoSite, Bothell, WA) were chosen as models to design a needle guide. A virtual model of each probe was created using a three-dimensional laser scanner at the University of Pittsburgh School of Engineering. A virtual bracket was designed that could be attached to the ultrasound probe by a friction fit. An articulating needle guide was also designed that could be snapped on to the bracket with a friction fit (Figure 1). The guide has an articulating hinge that allows the user to guide the needle into the tissue at insonation angles between 0 degrees and 85 degrees. The bracket and articulating needle guide constitute the composite device, which I have referred to as a needle guide. The bracket is slightly flexible so that it can be attached to the probe by flexing the bracket and slipping it over the end of the probe (Figure 2). The bracket and needle guide system is designed so that a sterile sheath can be used to cover the probe and bracket while the sterile needle guide is attached outside the sterile sheath (Figure 3). An alternative is to place both the bracket and needle guide over a sterile sheath or to place the bracket and needle guide over a probe, which itself has been sterilized. For this reason, the lumen of each needle was lined with a surgical grade stainless steel insert (Figure 4). This was done to prevent the tip of the block needle from coring any of the ABS plastic from the guide and subsequently depositing it in human tissue.
Software Work Flow
Solid Works was used to design the bracket and articulating needle for each probe.
Prototypes of the needle bracket and guide were made using a three-dimensional printer in a process called stereolithography.
The bracket and needle guide were fabricated from acrylonitrile polybutadiene polystyrene (ABS plastic) at Automata (Brooklyn, NY). ABS plastic is FDA certified as contact skin compatible for up to 30 days (Government Regulation US 21 CFR FDA 181.32). ABS plastic is a mixture of acrylonitrile polybutadiene and polystyrene. Acrylonitrile butadiene is a polymer used to make latex-free gloves. Polystyrene is a clear rigid polymer used for multiple commercial processes as well as medical devices. When mixed with other polymers such as acrylonitrile polybutadiene, it can produce a wide array of deformable plastics. Polystyrene is not degraded by gamma rays.4
Ten brackets and needle guides were sent to be sterilized by IsoMedix Services, Chester, NY, using gamma rays so that they could be used with or without a sterile cover sheath.
Seven brackets sterilized by IsoMedix Services were tested for sterility by placing them on agar plates and incubating the devices in an oven at 37°C. Seven sterilized brackets were assessed for structural stability by the author after affixing them to the L50 probe.
All 7 of the brackets tested in the incubation oven showed no growth. None of these brackets tested for structural stability fractured.
The probe bracket and articulating needle guide were used by the author to administer a supraclavicular block in a 54-year-old patient with a body mass index of 56. A 90-mm, 21-gauge echogenic needle (LifeTech, Stafford, TX) was used for the block. The needle was directed to the target nerve plexus on the first insertion (Figure 5).
The author has designed and produced needle guides for 3 different probes that are made of ABS plastic using the manufacturing technique called stereolithography. This guide aligns the shaft of the needle with the beam of the ultrasound probe for in-plane ultrasound-guided nerve blocks. The guide allows the user to insert the needle at any desired angle of insonation from 0 degrees to 85 degrees relative to the plane of the skin. The guide can be fabricated to accept needles from 25 gauge to 18 gauge. The cost of the polymer for each bracket was $1.80/bracket from the manufacturer. The cost of the polymer for the needle guide is $0.10. It is designed for single use only. Using a desktop printer (Form Labs, Sommerville, MA), Automata was able to print 20 needle brackets per run and 50 needle guides per run. The cost of the printer was $4000. According to the manufacturer, it takes about 1 hour to produce 20 needle brackets and 40 minutes to produce 50 needle guides. The desktop printer functions autonomously once it is programmed and started. Amortizing the cost, the printer, and adding the labor to operate the printer, as well as the cost of packaging and sterilization, would raise the cost of the device to about $4.00 per unit in lots of 1000.
Stereolithography has allowed the author to design and manufacture inexpensive prototype needle guides, in batches of 50, for any probe of any ultrasound platform at minimal cost. A familiarity with laser scanning and three-dimensional computer-aided design is also required to complete this task.
Design of the original bracket and needle guide, for the L25 probe, took about 20 hours. Once the original design was completed, subsequent brackets for other probes required about 3 hours of computer-aided design. Each probe requires a three-dimensional laser scan of the probe or similar information from the manufacturer before the bracket can be designed.
Needle guides are not routinely used by anesthesiologists because of their cost and because the precise location of the tip of the needle for nerve block is not critical to the performance of the block. When ultrasound-guided biopsy is used for a tissue diagnosis, the user desires to know the exact location of the needle tip relative to the image of the lesion on the ultrasound scan. In this setting, the cost of the guide is less important.
Several companies make stationary (nonarticulating) needle guides. These guides do not allow the user to vary the angle of insonation to place the needle tip in proximity to the nerve (SonoSite, Bothel, WA). CIVCO (Kalona, IA) makes a needle guide via an injection-molding technique that allows the user to vary the angle of insonation from 0 degrees to 45 degrees. The cost of their reusable bracket is $400, and the cost of the disposable needle guide is $15.00. In large quantities, injection molding can be used to produce plastic parts at low cost. The cost of an injection mold, however, is about $15,000, so that 5000 parts must be manufactured to produce a part at $3.00 to pay for the fabrication cost of the injection mold.
The author has developed a disposable needle guide that costs about $4.00 to manufacture, package, and sterilize. The bracket and guide developed by the author function similar to the CIVCO bracket but allow a larger range in the angle of insonation. Moreover, the cost of the bracket is much lower. Users who would like to use this technique to produce their own guides would need to package and sterilize the guide. Peracetic acid (ReVox, Minneapolis, MN) can also be used for sterilization.
The author’s device falls under the FDA designation of a medical class 1 device. These devices are considered minimal risk. A common example is a tongue depressor. Its use in our hospital does not require registration with the FDA, investigational device exemption, or Institutional Review Board approval, because it is not for sale, and it is not being used in a study or experiment. Per FDA regulation, this report makes no claims as to the safety or efficacy of the device described. Readers may wish to review document (http://grants.nih.gov/grants/guide/rfa-files/RFA-HL--08-005.html) for more information regarding the design and use of stereolithography in the manufacture of medical devices. Interested parties may write to the author if they wish to use the CAD drawings.
The author thanks Steven Bukowski at Automata for his assistance in producing the prototypes, and the prototype fabrication shop at the University of Pittsburgh School of Engineering for creating the laser scans of the probes.
Name: Paul E. Bigeleisen, MD.
Contribution: This author designed this study, analyzed the data, and wrote the manuscript.
This manuscript was handled by: Maxime Cannesson, MD, PhD.
1. Phal PM, Brooks DM, Wolfe R. Sonographically guided biopsy of focal lesions: a comparison of freehand and probe-guided techniques using a phantom. AJR Am J Roentgenol. 2005;184:16521656.
2. Gupta RK, Lane J, Allen B, Shi Y, Schildcrout JS. Improving needle visualization by novice residents during an in-plane ultrasound nerve block simulation using an in-plane multiangle needle guide. Pain Med. 2013;14:16001607.
3. Tokumine J, Lefor AT, Yonei A, Kagaya A, Iwasaki K, Fukuda Y. Three-step method for ultrasound-guided central vein catheterization. Br J Anaesth. 2013;110:368373.
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4. Ebnesajjad S, Modjarrad K. Handbook of Polymer Applications in Medicine and Medical Devices. 2014:Cambridge, MA: Elsevier, Inc; 2153.