Electromagnetic device enables accurate placement of IM nail locking screws
Intramedullary nailing is the standard of care for most lower extremity long bone fractures. The placement of proximal locking screws is easily accomplished using jigs attached to the nail; however, placing the distal locking screws has remained challenging.
Traditionally, a fluoroscopic assistance technique of “perfect circles” is used for distal locking. This freehand technique is time-consuming and exposes the patient, surgeon and operating room personnel to additional radiation. Previous studies have reported that the use of fluoroscopy for all locking screw placement can add an additional 1.1 minutes to 6.9 minutes of fluoroscopy time, as well as an additional 12 mRem to the dominant hand of the surgeon.
We recently evaluated a virtual imaging system that uses an electromagnetic (EM) device and computer software for distal locking. Compared to fluoroscopic assistance for “perfect circles,” the EM technique is faster and requires no additional radiation exposure during distal locking.
This article explains how we use the EM system in these cases. We have found the EM device to be intuitive with a quick learning curve. The software is easy to use, and the device can be quickly assembled reducing total operative time required for distal locking of intramedullary nails.
Sensor placed and passed
The EM device (TRIGEN Sure Shot; Smith & Nephew, Memphis, Tenn.) is indicated for the placement of distal locking screws in long bone fractures treated with intramedullary nails. Currently, the device is available for use with TRIGEN antegrade and retrograde femoral, and tibial nails.
Images: Burris RB
The EM targeting device consists of a narrow sensor placed through the hollow intramedullary nail. After placement of the intramedullary nail across the fracture site, the sensor is passed through the hollow nail and connected to the monitor (Figures 1a through 1c, page 4).
An EM field-generating device is attached to the drill. This enables the distal locking holes in the nail, as well as the location and trajectory of the drill bit, to be visualized on the monitor in real-time without the use of fluoroscopy. A virtual image of the distal aspect of the nail including the locking holes is seen on the display screen.
The skin incision is localized by holding the EM device against the skin over the locking holes (Figure 2).
Next, the drill is manipulated so it is centered over the distal locking holes with the appropriate trajectory. Two circles are then seen on the monitor indicating the position and trajectory of the drill bit. The green circle displayed on the monitor indicates the location of the drill tip, while the red circle provides the surgeon with information about the trajectory of the drill (Figure 3).
Form a bull’s eye
The drill is then manipulated so that the green and red circles overlap on the monitor to form a bull’s eye, as seen the screen (Figure 4). When the bull’s eye is centered over the locking hole in the nail, the drill is passed through both cortices without the need for fluoroscopy. A standard depth gauge is used to measure screw length.
The screw is inserted using the EM device with a power screwdriver to ensure proper placement without fluoroscopy. As the screw is inserted, the bull’s eye remains centered over the locking holes ensuring the screw is passed through the nail.
Throughout the distal locking procedure, the EM device provides continuous feedback to the surgeon in real-time.
Less set-up time, no radiation
We conducted a study that compared the time required to set up and place distal locking screws in 18 femoral and 22 tibial intramedullary nails. Fifty-nine locking screws were placed using the EM device requiring an average of 228 seconds overall per screw and an average set-up time of 94 seconds. By comparison, this required significantly less time than was needed for the 41 screws placed using the “perfect circles” technique, which averaged 342 seconds per screw with an additional set-up time of 182 seconds.
All of the screws in the EM device group were placed without the need for radiation, and no misses occurred with either technique.
Placing intramedullary nail locking screws using the EM device is an easier, faster and accurate method without the hazards associated with additional radiation exposure for the surgeon.
- Chan DS, Burris B, Erdogan M, et al. The insertion of intramedullary nail locking screws without fluoroscopy: A faster and safer technique. Paper #52. Presented at the 2011 Annual Meeting of the Orthopaedic Trauma Association. Oct. 13-15. San Antonio.
- Coetzee JC, Merwe EJ van der. Exposure of surgeons-in-training to radiation during intramedullary fixation of femoral shaft fractures. S Afr Med J. 1992;8(6):312-314.
- Kempf I, Grosse A, Beck G. Closed locked intramedullary nailing: Its application to comminuted fractures of the femur. J Bone Joint Surg Am. 1985;67(5):709-702.
- Levin PE, Schoen RW, Browner BD. Radiation exposure to the surgeon during closed interlocking intramedullary nailing. J Bone Joint Surg Am. 1987; 69(5):761-766.
- Sanders RW, Koval KJ, DiPasquale T, et al. Exposure of the orthopaedic surgeon to radiation. J Bone Joint Surg Am. 1993;75(3): 326-330.
- Sugarman ID, Adam I, Bunker TD. Radiation dosage during AO locking femoral nailing. Injury. 1988;19(5):336-338.
For more information:
- R. Brandon Burris, MD, can be reached at University of South Florida, 13220 USF Laurel Dr., MDF 5th Floor, MDC 106, Tampa, FL 33612; 813-396-9639; email: email@example.com.
- Daniel S. Chan, MD, can be reached at Orthopaedic Trauma Service, Florida Orthopaedic Institute, 5 Tampa General Cir., Suite 710, Tampa, FL 33606; 813-253-2068; email: firstname.lastname@example.org.
Disclosures: Burris and Chan have no relevant financial disclosures.