Less radiation exposure noted with computer-assisted scaphoid placement

Computer-assisted screw placement took less time than fluoroscopically-assisted placement.

Issue: August 2008

AAOS

Accurate percutaneous screw placement for scaphoid fractures remains technically challenging. Research now shows that using computer-assisted navigation may help surgeons with screw positioning while having fewer K-wire attempts.

Screw placement

Eric F. Walsh, MD, Scott Wolfe, MD, and colleagues at Hospital for Special Surgery in New York compared several parameters in 10 cadaveric wrists randomized to receive either fluoroscopic-assisted or computer-assisted volar percutaneous scaphoid screw placement.

They discovered significantly less radiation exposure during the overall time of the procedure, placement of the K-wire and screw placement in the computer-assisted group compared to the fluoroscopic-assisted group. They also found no significant differences between the groups regarding the overall or global procedural time, set-up time and time to place the K-wire.

Navigation screen (left) Targeting screen (right)
This navigation screen (left) displays both the planned and actual trajectories of the scaphoid screw placement, and can show up to nine images at a time. Surgeons use this targeting screen (right) to align the planned and actual trajectories.

Images: Walsh EF

Radiation exposure

In addition, they discovered a 1.64±0.5° difference between the actual screw placement in the computer-assisted group and the ideal screw trajectory projected by the navigation system.

While not statistically significant, the investigators found that the computer-assisted procedures needed half the number of K-wire attempts that were used in the fluoroscopic-assisted group.

“Computer navigation in percutaneous screw placement statistically significantly reduces radiation exposure to the patient, takes no longer than traditional methods, helps prevent malpositioned guide wires and, thus, reduces the number of attempts and is very precise,” Walsh said during his presentation at the American Academy of Orthopaedic Surgeons 75th Annual Meeting.

The investigators took 15±8.2 minutes to place the K-wire in the fluoroscopic-assisted procedures and 7.8±7 minutes to place the K-wire in the computer-assisted procedures, according to the study abstract. In addition, they took an average of 2.4±1.1 K-wire attempts in the fluoroscopic-assisted procedures and needed only one attempt in four of the five computer-assisted cases.

“There were statistical differences between the radiation exposure between the two techniques in global time of procedure, placing a K-wire and screw placement,” Walsh said. The investigators found a global time of radiation exposure of 72.2±7.2 seconds for the computer-assisted group compared to 258.2±142.7 seconds for the fluoroscopic-assisted group.

“We harvested the scaphoids after both procedures,” Walsh said. “There was one cortical violation of the scaphoid radial articulation using the traditional method. The screw position was too radial. And [there was] one cortical violation of the scaphoid radial articulation using navigation method. In this scenario, the screw was in the ideal axis, but positioned too proximally and repositioned before the end of the procedure.”

During computer-assisted navigation, surgeons only use the C-arm to take the initial images. After removing the C-arm, they can operate around the wrist using only the navigation screen for planning and screw placement.

For more information:

Eric F. Walsh, MD, can be reached at the Orthopedic Group Inc., 588 Pawtucket Ave., Pawtucket, RI 02860; 401-722-2400; e-mail: efwalshmd@yahoo.com. He and his colleagues received research funds in direct support of this study from Praxim, Inc.

Reference:

Walsh EF, Wolfe SW, Crisco J, et al. Computer-assisted navigation of volar percutaneous scaphoid screw placement. Paper #393. Presented at the American Academy of Orthopaedic Surgeons 75th Annual Meeting. March 5-9, 2008. San Francisco.