Transpedicular Cervical Spine Screw Placement with a Fluoroscopically-Assisted Laser Targeting System.

Joseph M. Kowalski, M.D., Richard M. Schwend, M.D., Michael K. Landi, M.D., Robert M. Lifeso, M.D., Departments of Orthopaedic Surgery and Neurosurgery, State University of New York at Buffalo

Purpose:

A simplified method of imaging and targeting the cervical spine pedicle was developed. Reproducible and accurate imaging of the pedicle allows for more precise instrumentation and significantly reduces radiation exposure to the patient and operating room personnel.

Materials and Methods:

The Dual Radiation Targeting System (DRTS™) identifies a path of x-ray radiation from the source to the image intensifier on a standard fluoroscopy machine. It positions a laser beam on that line and provides a target symbol on the monitor, after which the x-ray radiation is turned off. The point of entry and angle of approach is then guided by the laser beam. Four human cervical spines were harvested and two surgeons targeted and instrumented fifty-five pedicles from C2 to T3, with 2.7mm and 3.5mm diameter screws. Fluoroscopic guidance was used alone on one side and the DRTS™ on one side of the spine. Exposure time was recorded and the spines were stripped of soft tissue with sagittal and axial sections made to determine the amount and location of screw penetration.

Results:

Forty screws were placed with the DRTS™ and fifteen without. The mean fluoroscopy time was 3.88 seconds (range 2-10 seconds) with the DRTS, and 25.25 seconds (range 6-88 seconds) without the DRTS™ (p<0.001). Three of forty screws (7.5%) in the DRTS group, and five of fifteen screws (33%) in the group without DRTS™ assistance penetrated the pedicle cortex. Seven of these screws penetrated approximately one half the thread depth, 0.4mm to 0.55mm. One screw in the fluoroscopy alone group had penetrated approximately 13mm superomedially.

Discussion:

Screw placement in the cervical spine is a technically demanding procedure. Pedicle screw constructs in the cervical spine have biomechanical advantages over other screw constructs. Coaxial imaging of the pedicle with fluoroscopy allows the surgeon to localize and instrument more accurately. This limited cadaveric study demonstrates the advantages of using a laser targeting device in conjunction with fluoroscopy. We were able to place pedicle screws more accurately and with less radiation exposure when the DRTS™ was employed. It remains unknown whether 0.4 to 0.55 mm cortical penetration would be of significant clinical importance. These results need to be evaluated in clinical studies.

Conclusion:

The DRTS™ can assist surgeons in the accurate placement of transpedicular pedicle screws in the cervical spine. It increases accuracy and decreases radiation exposure.

(This abstract was submitted to the 33rd annual meeting of the Scoliosis Research Society, Sept 16-20, 1998.)