The Cover includes a fabric sleeve and nose piece. The fabric sleeve is constructed of a double-layered medical fabric (Maxima EX; Burlington Barrier, Greensboro, NC, USA) typically used for surgical drapes and gowns. All seams are sealed using seam tape that survived testing of 100 autoclave cycles (121°C, 30 minutes per cycle; Castle steam gravity displacement sterilizer; Sybron Corp, Milwaukee, WI).
Based on the previous CURE International drill system, we selected a power screwdriver (DeWalt DCF610S2) with a maximum drilling speed of 1050 rpm. The weight of the DeWalt DCF610S2 unit is 1.0 kg, and the dimensions (with battery installed) are 19 × 15 × 6 cm. Surgeons indicated a preference for this size and weight because it closely resembles surgical drills. Qualitatively, surgeons noted that some larger hardware drills are bulky and too heavy for delicate bone drilling.
The sterile loading technique of the cover was designed with an experienced operating-room nurse (Alicia Green, RN) and requires 2 participants (see Video, Supplemental Digital Content 2, http://links.lww.com/BOT/A465; see Fig., Supplemental Digital Content 3, http://links.lww.com/BOT/A466). The first step is for a sterile staff to hold the unrolled Cover opening with their hands tucked under the rolled fabric. The second step is for a nonsterile hand to carefully place the drill into the fabric bag without touching the exterior of the Cover. The third step is for the sterile staff person to close the bag using a dry-bag–rolling technique. Once the drill is inside the bag, the Chuck Adapter easily inserts into the hexagonal drive chuck, and the custom closure mechanism can be sealed by screwing together the rotating interface on the Chuck Adapter and nose piece of the Cover.
SAFETY AND EFFICACY
First, we aimed to quantify the barrier performance of the Drill Cover system to evaluate its ability to resist transmission of blood between the sterile surgical field and nonsterile hardware drill. We designed a custom test apparatus (modeled on a standard test method, ASTM F1670-08) to determine the ability of each component of the Drill Cover system (fabric, seams, closure mechanism) to resist penetration by pressurized synthetic blood (See Figs. 4A, B, Supplemental Digital Content 4, http://links.lww.com/BOT/A467; http://links.lww.com/BOT/A468). Fabric swatches resisted a fluid penetration of up to 1.1 psi; seams resisted a penetration of up to 0.6 psi, and the closure mechanism resisted a penetration up to 0.3 psi. Current testing suggests that the Drill Cover can achieve “Level 2” liquid barrier performance, as specified by the Association for the Advancement of Medical Instrumentation (AAMI) voluntary standard AAMI/ANSI PB70:2012, pending further testing to address barrier performance after repeated use. Future work will include design refinements with the goal of achieving AAMI “Level 4” liquid barrier performance.
Second, we aimed to substantiate claims that our Drill Cover system uses a hardware drill that is safe for bone drilling. Drilling speed must be carefully considered when selecting a hardware drill for use in bone. High drilling speed can cause high temperatures that increase the risk of osteonecrosis, and necrosis prevents bone from properly healing and integrating with implants. Necrosis begins when bone reaches a temperature of 47°C for more than 1 minute.6 When drilling without irrigation, speeds above 1140 rpm have been shown to cause temperatures above 47°C.7 The Surgical Implant Generation Network recommends drilling at speeds lower than 1100 rpm, and that pushing harder (17 lbs) is better than softer (7 lbs) to control bone temperature.8 Given that the maximum unloaded speed of DeWalt DCF610S2 is 1050 rpm, it falls within the range of common orthopaedic surgical drills; this hardware drill choice does not increase the risk of drilling causing necrosis.
Third, the Drill Cover was designed for optimal ease of assembly using a sterile technique. During the design process, we assessed ease of assembly using qualitative surveys at Mulago Hospital. The first design iteration was small and form-fitting to the drill, which made the drill difficult to fit into the cover while maintaining the sterile technique. After evaluation by users at Mulago Hospital, the mode user rating for ease of the loading process was 2/5 (“difficult”) on scale from 1/5 (“very difficult”) to 5/5 (“very easy”) for the first prototype. A later, larger version was evaluated and the mode user rating was 4/5 (“easy”), which indicated that a larger bag allowed for simpler loading while maintaining the sterile technique. The current version of the fabric cover is a product of more than 90 bench-top iterations (9 of which have been user tested) and now features a bottom-load entry (see Figs. 5A, B, Supplemental Digital Content 5, http://links.lww.com/BOT/A469).
Other important design factors that we have considered, but have not addressed here, include: durability of each component after repeated use and sterilization, the effect of tool choice on drilling performance,9 sterile reprocessing considerations, material biocompatibility, and hardware drill electrical safety.
We designed a surgical drill for scale by designing specifically for end users in low-resource settings. The Drill Cover system provides surgeons a device that is durable, affordable, and safe, whereas current alternatives are inadequate for users in low-resource settings in at least one of these criteria area (new surgical drills are not affordable; donated surgical drills are not durable; manual drills or nonsterile hardware drills are not safe). The current Drill Cover has been well received by surgeons and nurses because it creates an improved sterile barrier between the operating room and drill, uses a hardware drill carefully selected for safe bone-drilling speeds, and is sized for easy loading of the drill into the bag. Each of these features represent significant improvements over previous drill cover designs.
This Drill Cover system provides a proof-of-concept for a product that can scale globally which will increase access to safe surgical drills in low- and middle-income countries (LMICs). Development of this Drill Cover system can now progress towards meeting the standards of Health Canada (our group's home country regulatory agency).
A key strength of the Drill Cover approach is that multiple covers can be provided with a single drill in a “kit”, meaning that a hardware drill can be used in back-to-back surgeries by changing drill covers, eliminating the need for immediate sterilization. A kit of 5 Drill Covers and a single drill provides capacity for an operating theater to complete 5 surgeries per day, before sterilization is needed. Furthermore, because of its low cost, hospitals with limited access to sterilization devices can stockpile Drill Covers in order to reduce dependence on same-day sterilization.
One limitation of the Drill Cover system is that it uses a drill that is not cannulated, making it difficult to use some reaming attachments, and challenging to grip Kirschner wires using a collet in the same manner as a modern surgical drill. To overcome these limitations, future Drill Cover designs will pursue compatibility with reaming attachments and an affordable cannulated drill. Another limitation is that battery-powered drills are not be as widely available as corded drills in some countries. One potential solution is to form partnerships with hardware drill suppliers so that battery-powered hardware drills (safe for bone drilling) are widely accessible in LMICs at affordable prices.
To maximize the positive impact of this Drill Cover system, the design must be optimized for safety and efficacy in order to meet medical device standards and regulations, and production growth must be sustained by product sales. Development of a sustainable model requires the use of “Integrated Innovation”10: the combination of scientific, business, and social innovation to scale using a sustainable business model and maximize impact by improving access to safe surgery for patients throughout LMICs.
If made widely available, the Drill Cover system can play a contributing role in improving surgical outcomes and efficiency in LMICs. For example, in Uganda (where we have focused our work), long bone fractures account for over 15% of hospital admissions.11 Nearly all patients should receive surgical care in a timely fashion, but in reality, a lack of resources—occasionally specific to the lack of a powered surgical drill—means that patients will long wait times or not receive surgery at all.12 Long wait times lead to extended periods of disability, reduced income, and a significant socioeconomic trickle-down effect on families and dependents.12 A widely available Drill Cover system can eventually eliminate surgical inefficiencies because of manual drill use and reduce infections because of the nonsterile hardware drill use. Next steps in the development of this Drill Cover system include a clinical study at Mulago Hospital that will track surgical site infections and surgical drilling time using both currently available tools and the Drill Cover system.
By designing for the needs of end users, we have developed a Drill Cover system that is suitable for use in low-resource settings. The Drill Cover has the potential to scale globally and improve access to safe orthopaedic trauma surgery worldwide.
The design of this Drill Cover involved significant contributions from many talented groups/individuals who are passionate about global health and surgery. We thank the members of Uganda Sustainable Trauma Orthopaedic Program, Dr Titus Beyeza and the staff at Mulago Hospital, Dr Lewis Zirkle and Joel Gillard of the Surgical Implant Generation Network, Dr Alan Giachino, the Institute for Global Orthopaedics and Trauamatology, and surgeons worldwide who contributed to the design and project feedback. We also thank UBC engineering students Justin Lam, Nicholas Slakov, Giulio Pregnolato, the UBC Engineers in Scrubs, Kwantlen Polytechnic University School of Design, the Centre for Hip Health and Mobility, Dr Robin Coope, and Florin Gheorghe of Arbutus Medical for their significant and ongoing contributions to the development of the Drill Cover system.
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surgical bone drill cover; fracture care; global orthopaedic trauma; medical device design; safe surgery
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