By Sean Fenske, Editor-in-Chief

Surgical procedures have been changing for years in healthcare. Surgeons are seeking power tools to replace traditional manual processes to improve efficiency, eliminate repetitive tasks, and save time. While some power tools may be used for several steps during the surgery, others are developed to be more specialized to address a specific task. Regardless, their development comes with numerous design considerations.

There are several factors to consider with power tools that are used by surgeons, whether they are replacing previously non-powered versions or upgrading an earlier power model. Heat, weight, sound, ergonomics, and more are all critical to consider to ensure a successful design. Many of these factors, however, tie directly to the motor assembly selected to drive the power tool.

Knowing this, Peter van Beek, maxon Group’s Medical Business Development Manager, took time to address several questions about power tool design and the drive assembly selection. In the following Q&A, he speaks to the use of power tools in surgical procedures, the regulation of them, their functionality, and important design considerations.

Sean Fenske: Within orthopedics, is the use of power tools increasing, decreasing, or remaining the same? Has the introduction of robotic surgery had any impact on this?

Peter van Beek: In my assessment, power tools are increasing in prevalence to replace historical manual tasks that are part of any surgical procedure. In the modern medical system, a particular surgeon will specialize in a specific surgery, which in turn, creates a need for specialized tools. Surgeons are susceptible to repetitive motion injuries when a nearly identical procedure is performed many times within a day (day after day). Restrained budgets, a lack of surgeons, and a desire to reduce time for a particular surgery are leveraging robotic systems and associated power tools to achieve cost savings and treat more patients in a day. Surgical power tools are part of making this reality possible.

Fenske: Are there any changes to regulations of orthopedic power tools that are impacting drive assemblies?

van Beek: Over the past few years, regulatory bodies have increased the dielectric breakdown strength requirement for hand tools having direct patient contact. The IEC 60601-1 standard now mandates higher isolation voltages for medical devices in general. As an integral part of the circuit, the drive assembly must be capable of higher dielectric strengths on its own. The dielectric strength of a motor is determined by applying a higher voltage potential (500 V up to 1,500 V DC or AC) between the motor body/shaft and the grounded wire bundle of the motor. The voltage must be applied for a specified amount of time, and only a specific maximum amount of leakage current is acceptable. Accomplishing this in a very compact and power-dense motor is not easy. maxon works collaboratively with its customers to navigate this newfound hurdle by either changing the insulation within the motor and/or creating larger gaps within the motor, or by isolating the entire drive assembly within the power tool. There are techniques and strategies that can be employed to meet these new requirements. Validation requirements are increasing when several tools are in close proximity within the body and the complexity of the procedure increases.

Fenske: Is the functionality of surgical power tools changing and improving? Or are they becoming more specialized? How does this impact the design and/or motor selection?

van Beek: Yes, the functionality of the tools is improving, making their use a joy and a move away from basic functionality. The newest tools are intuitive, easy to use, ergonomic, and temperature monitored. In addition, they have the lowest weight, balance, and feedback features to aid the surgeon.

In general, many new surgical power tools are being designed for a particular single end use. Often, these specialized tools require higher customized drive assemblies consisting of several combined parts (e.g., a motor, custom hybrid gear, sensor, lead screw, and custom cabling). Making an elaborate mechatronic drive assembly is complicated and requires multiple months of teamwork between the drive assembly manufacturer and the tool designer. maxon excels at this collaborative design integration phase while running the quality in parallel.

Fenske: What factors must be considered to ensure the correct drive assembly is appropriately sized and will be capable of delivering the correct torque and speed for a given tool application?

van Beek: This is a very good question.

maxon’s ironless core motor designs have linear current-to-torque and voltage-to-speed relationships that allow the motor to be used as an analysis tool. Simply measure the current and voltage of the maxon motor in your tool and you define the torque and speed characteristics. It is critical early in development to define the risk class of your eventual tool as this changes the design approach and related quality requirements. Understanding your duty cycle is essential to determining the size of assembly needed and keeping it to a minimal size.

Due to costs, power tool development time must be minimized to propel the project forward. maxon has a proven and structured process to quickly establish the parameter requirements of the drive assembly. If a project starts well, it often ends well. Time is not lost getting started. As my grandfather would always say, “the hardest part of any job is getting started.”

Often, a specialized tool requires a specific customized motor and gearing ratios, etc. maxon specializes in customizing a drive assembly for what the tool dictates.

Fenske: Is a specific drive assembly type required for surgical power tools if that tool must be cleaned and sterilized after each operation?

van Beek: Power tools require a complete sterilization between uses. DC brushless motors are the go-to industry standard as they can achieve several thousand sterilization cycles before failure. Typical drive assembly diameters of these motors are 13, 16, 22, and 30 mm. Depending on the application, the combination of both sealing and the use of maxon’s autoclave motor is necessary. This is especially true if the drive assembly is exposed to a saline stream during use followed by a complete sterilization cycle.

Fenske: What other factors are important with the motor selection for an orthopedic power tool, or what consideration is often overlooked (not already covered here)?

van Beek: If you’re designing a power tool that requires a drive assembly, you will be spending countless hours with the motor manufacturer to create a specific engine for your power tool. A few things to consider prior to selecting the motor manufacturer:

• It is important to select a drive assembly supplier that not only can communicate well but can also work closely with your design team. maxon works in a highly collaborative manner with its customers to bring complex custom designs forward, holding frequent meetings and regularly communicating many quality and design details vital to product development.
• Work with a company that is responsive. This ensures the project will stay on schedule and not run over budget
• Don’t forget about quality requirements needed for submissions to a governing body, such as PPAP and IQ, OQ, and PQ validation. It is essential to run your design efforts in parallel with quality milestones
• Fully understanding the time expectations to develop a product from start to finish.
• Ensure compatibility of the drive electronics with the drive assembly.
• Lead time for customization will take longer than using combined catalog products. Utilizing faster methods for functional samples or at the onset of the project is recommended.

As a leading supplier of drive systems in the medical industry, maxon fully understands these key points and has over 65 years of experience addressing these needs for our customers.

Fenske: Are there any new product developments that would lend themselves to orthopedic surgical power tools?

van Beek: Industry is always pushing drive assembly manufacturers to produce smaller diameter and shorter assemblies that have higher torque and speed output capabilities. In addition, drive assemblies that can withstand more sterilization cycles and have a cannulated motor shaft are also in demand. maxon is answering the call of industry with its latest DC brushless motor families “SPEED” (2-pole stator design with 120,000 RPM top end speed capability) and “PRIME” (4-pole stator design provides a unique blend of both high torque and speed).

Fenske: Do you have any additional comments you’d like to share based on any of the topics we discussed or something you’d like to tell orthopedic device manufacturers?

van Beek: I often repeat this message due to its importance. Getting to the finish line with a medical power tool involves engineering and quality aspects. An afterthought is often the quality and validation requirements associated with a project. In a perfect world, the design and quality need to run in parallel to reach the finish line at the same time. Do not forget about quality or it will delay your launch to market. For a drive assembly manufacturer to be capable of producing quality complex drive assemblies, repeatedly and reliably, considerable time is required to order, receive, test, tweak, document, and validate fixtures, tooling, and assembly lines. At maxon, we have the know-how and expertise to guide our customers seamlessly through the quality and design processes, saving both time and money.

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