A noninvasive laser-guided preincision localizer for spine surgery

Clinical article

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The design and utilization of a novel device for noninvasive preincision localization of the target spine segment during lumbar spine surgery is presented.


The device consists of 4 low-energy laser diodes, emitting planar beams, mounted around the perimeter of a ring at right angles to each other. The beams are used to align 2 radiopaque cables hanging off the sides of the patient with the target spine segment and the radiographic source and film. The performance of the device in guiding the placement of the skin incision was prospectively evaluated in 76 consecutive patients undergoing unilateral 1-level microsurgical lumbar laminotomy. Preincision lateral radiographs obtained with the device were compared with postincision localizing radiographs in all patients.


In all patients, the location of the incision guided by the final preincision radiograph was found to precisely overlie the target segment as confirmed by a postincision radiograph, the latter obtained after exposure of the underlying laminae. In no instance was it necessary to extend the incision, modify the surgical trajectory, or repeat the postincision radiograph due to improper incision placement. The device's radiopaque cables were clearly visualized on radiography as they traversed the spine image, regardless of body mass index. The initial preincision radiograph based on the surgeon's estimate of the location of the target site localized the target segment in 58 patients (76.3%) and an adjacent segment in the remaining 18 patients (23.7%). Accuracy of the surgeon's initial estimate of the target site (but not accuracy of the device) was found to be inversely associated with body mass index (p < 0.001), thickness of the subcutaneous fat layer overlying the spine (p < 0.001), and presence of transitional lumbosacral anatomy (p = 0.03).


The localization device presented herein provides accurate noninvasive localization of the target spine segment and guides precise placement of the incision over the target segment during lumbar spine surgery.

Abbreviation used in this paper: BMI = body mass index.

Article Information

Address correspondence to: Peyman Pakzaban, M.D., 3801 Vista, Suite 440, Pasadena, Texas 77504. email: pakzaban@swbell.net.

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Schematic representation of the localizer. The device components consist of a central ring (R), 4 laser diodes (D) emitting laser beams in the sagittal (S) and axial (A) planes, 2 radiopaque cables (C), 2 weights attached to the cables (W), a clear plastic window (B) on which crosshairs are etched, and a power compartment (P) that houses the batteries and the power button.

  • View in gallery

    Schematic representation of the localizer positioned over the patient's body in prone position, demonstrated by a cross-section. Two opposite laser diodes project planar beams in the axial plane. The beams form horizontal alignment lines on the body surface (used for alignment of the cables) and vertical alignment lines on the radiographic source and film. The end result is superimposition of the radiographic images of the 2 cables on a theoretical plumb line hanging from the center of the localizer ring.

  • View in gallery

    Photographs of a homemade prototype of the localizer. A: Internal view demonstrating the 4 laser diodes (black arrows) arranged around a ring at right angles to each other. B: External view with the lasers turned on, demonstrating the 4 laser beams (arrowheads) and the 2 axial cables (white arrows).

  • View in gallery

    Artist's representation of the localizer in use. The sagittal beams are first aligned with the midline of the body. The 2 cables are then aligned with the axial beams. The radiographic film and the crosshairs on the radiographic source are then aligned with the axial beams. Reprinted with permission from Delilah Cohn (www.medillustrationstudio.com).

  • View in gallery

    Preincision lateral radiographs obtained with the localizer. A: Example of “aligned” cables traversing the target motion segment, observed in 70 patients. B: Example of “nonaligned” cables straddling the target motion segment, observed in 6 patients.

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    Scatter plot of incision size versus BMI demonstrating a strong correlation (correlation coefficient = 0.90). Fewer than 76 data points appear on this graph due to overlap of some data points.

  • View in gallery

    Schematic representation of the 3 types of misalignment. A: Misalignment of the “distal” cable by angle α. B: Misalignment of the “proximal” cable by the angle β. C: Misalignment of the radiographic source by the angle δ. The symbol ε represents the error projected on the radiographic film (F). The geometrical shapes represent the target site (black circles), radiographic image of the target site (black ovals), cables (gray circles), radiographic image of the cables (gray ovals), and the radiographic source (gray triangles).



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