Reinforcing the role of the conventional C-arm--a novel method for simplified distal interlocking

Abstract

Background: The common practice for insertion of distal locking screws of intramedullary nails is a freehand technique under fluoroscopic control. The process is technically demanding, time-consuming and afflicted to considerable radiation exposure of the patient and the surgical personnel. A new concept is introduced utilizing information from within conventional radiographic images to help accurately guide the surgeon to place the interlocking bolt into the interlocking hole. The newly developed technique was compared to conventional freehand in an operating room (OR) like setting on human cadaveric lower legs in terms of operating time and radiation exposure.

Methods: The proposed concept (guided freehand), generally based on the freehand gold standard, additionally guides the surgeon by means of visible landmarks projected into the C-arm image. A computer program plans the correct drilling trajectory by processing the lens-shaped hole projections of the interlocking holes from a single image. Holes can be drilled by visually aligning the drill to the planned trajectory. Besides a conventional C-arm, no additional tracking or navigation equipment is required.Ten fresh frozen human below-knee specimens were instrumented with an Expert Tibial Nail (Synthes GmbH, Switzerland). The implants were distally locked by performing the newly proposed technique as well as the conventional freehand technique on each specimen. An orthopedic resident surgeon inserted four distal screws per procedure. Operating time, number of images and radiation time were recorded and statistically compared between interlocking techniques using non-parametric tests.

Results: A 58% reduction in number of taken images per screw was found for the guided freehand technique (7.4 ± 3.4) (mean ± SD) compared to the freehand technique (17.6 ± 10.3) (p < 0.001). Total radiation time (all 4 screws) was 55% lower for the guided freehand technique compared to conventional freehand (p = 0.001). Operating time per screw (from first shot to screw tightened) was on average 22% reduced by guided freehand (p = 0.018).

Conclusions: In an experimental setting, the newly developed guided freehand technique for distal interlocking has proven to markedly reduce radiation exposure when compared to the conventional freehand technique. The method utilizes established clinical workflows and does not require cost intensive add-on devices or extensive training. The underlying principle carries potential to assist implant positioning in numerous other applications within orthopedics and trauma from screw insertions to placement of plates, nails or prostheses.

Figure 1

Guided freehand procedure. Top: A single image is taken from the distal part of the nail in arbitrary C-arm orientation. Guiding landmarks are calculated from the hole contours and projected into the image. A skin incision is performed at the incision landmark. Middle: Targeting jig and drill are inserted through the incision onto the bone surface. Under fluoroscopic control the jig is translated until the projection of the small ring coincides with the small targeting ellipse. Bottom: The jig is rotated until alignment of the projection of the large ring and the large targeting ellipse is achieved for drilling the hole

Figure 2

Screenshot of the graphical user interface of the custom-made software algorithm. A real-time window on the right displays the monitor signal of the C-arm with additional guiding landmarks. The left side of the window comprises the control elements to execute the calculation

Figure 3

Prototype of the targeting jig. Two radio-opaque rings, concentrically arranged around a drill sleeve, are used as targeting elements within a fluoroscopic projection. The small ring is inserted through a skin incision onto the cortex of the bone. Here, a rubber band was used for stabilizing the jig during handling

Figure 4

Experimental setup. Left: Cadaveric below knee specimens, instrumented with a tibia nail, were secured to an OR table. A conventional 2D C-arm could be freely positioned to visualize the distal interlocking holes. The C-arm monitor signal was processed in real-time and was routed back to the C-arm monitor. Right: A radiolucent drill was manually operated either with aid of a targeting jig or without