Anand Hasurkar, Manager of Product Engineering at Portescap, looks at the options available to surgical hand tool designers to meet the life target requirements and the cost limits.
Recent years have seen a notable trend in the design of surgical power tools away from pneumatic and corded electrical instruments and towards compact, lightweight, battery-powered tools. When looking at the selection of electric motors for these instruments, they have a number of design goals to achieve and challenges to overcome. Not only must they provide the required performance in an extremely compact package, but also offer assured reliability often over large numbers of surgeries – a challenge that is further complicated by the need to sterilise the tool after every procedure.
The most common sterilisation method used in hospitals is autoclaving, also called steam sterilisation. Here, surgical hand tools are exposed to high levels of humidity, temperature and pressure for several minutes in order to render the instrument sterile. Most autoclaves also have additional vacuum cycles to facilitate steam penetration and kill bacteria, viruses, fungi and spores that can hide inside the tool.
This repeated exposure to autoclave conditions is what gives manufacturers of powered surgical tools the most problems when it comes to electrification of the tools. And it means that the best tools, using the highest quality sterilisable motors, are expensive pieces of kit. For high volume surgery centres (often referred to as Tier-I), the high upfront cost of these premium tools is less of an issue, as the volume of patients brings down the cost per procedure to an affordable level. It is not uncommon to see these centres performing ten or more surgeries per week, with requirements for a tool life of perhaps 1,000 procedures.
Contrast that with smaller scale operations. A Tier-II centre in a typical mid-sized city might be performing just three surgeries per week, with a lifespan requirement for the tool of perhaps 500 procedures. And a Tier-II centre in smaller cities or rural areas might be performing fewer than one surgery a week, with a lifespan requirement for the tool of as little as 200 procedures. Here, the high-end motor features of the most expensive tools simply will not return value.
While the necessary lifespan of the motor in the tools used in these Tier-II or Tier-III centres is reduced, that does not mean that the centres can run the risk of the instruments failing due to the rigours of autoclave sterilisation. Inferior durability through autoclaving results in higher total cost of ownership for the customer because they must either risk cancelling surgeries while a failed tool is replaced or purchase extra tools as back-ups.
Cost-optimised sterilisable motors
The challenge for the tool designer is to select a motor that will bring down the cost of the tool without compromising its ability to withstand sterilisation over the required lifespan of the instrument.
There might be a temptation to circumvent the problem, with designers opting to use a motor not suited to survive sterilisation but adding protective sealing in the hand tool casing. This is rarely a good solution. Not only does it lead to a bulkier tool, but any cost savings from using a non-autoclavable motor are usually quickly offset by increased costs elsewhere in the tool and higher development costs.
In particular, however good the sealing might appear to be, it is very difficult to prevent pressurised steam from finding a way into the tool. Also, even a motor that might seem to offer some level of protective sealing will be susceptible to pressurised steam, with the shaft passing through the motor providing a direct path for damaging moisture.
An alternative explored by some designers is to eliminate the risk of failure due to sterilisation by placing the motor in a removable portion of the tool. The idea is that it is protected from contamination during surgery and then removed from the tool prior to sterilisation. But this is generally considered a less safe approach because contamination can still reach the motor via the coupling to the drill or saw bit.
In order, then, to match the safety standards of Tier-I centres, Tier-II and Tier-III hospitals are looking for a path to upgrade to full sterilisable hand tools using fully sterilisable motors – but at a more appropriate cost.
The solution comes through working with a motor supplier who is able to customise the motor to the specific requirements of the application. In this case, a motor manufacturer with expertise in addressing the needs of sterilisable products can offer a motor at lower cost that utilises a selective combination of autoclave resistance features. This can deliver the best outcomes and lowest cost per surgery, providing assured autoclave resistance over the shorter required lifetime of the tool.
Further, a full motion solution partner such as Portescap will have options not just for the motor, but also the gearing and controls which are also degraded by the autoclave and must be part of the life target and sterilisation protection considerations as well.
This illustrates the importance of working with a knowledgeable supplier at the earliest phases of the surgical tool design, where the most value can be created through true collaborative innovation.
Image 1: Example of a Powered Surgical Hand Tool.
Image 2: The most common sterilisation method used in hospitals is autoclaving, also called steam sterilisation.
Image 3: Benefits of Early Engagement with Motor Supplier.
Portescap offers the broadest miniature and specialty motor products in the industry, encompassing coreless brush DC, brushless DC, stepper can stack, gearheads, digital linear actuators, and disc magnet technologies. Portescap products have been serving diverse motion control needs in wide spectrum of medical and industrial applications, lifescience, instrumentation, automation, aerospace and commercial applications, for more than 70 years.
Portescap has manufacturing centers in the United States and India, and utilizes a global product development network with research and development centers in the United States, China, India and Switzerland.
For more information, visit www.portescap.com
Tel: +44 (0)1905 917477
Address: Progress House, Midland Road, Worcester, Worcestershire, WR5 1AQ, United KingdomReader Contact:
Portescap: Nicole Monaco
Tel: +1 404.877.2534