iPod Touch®-Assisted Instrumentation of the Spine: A Technical Report

Aim: Successful instrumentation of the spine is dependent on choosing correct starting points and insertion angles to implant screws. Although modern image guidance facilitates very precise and safe instrumentation of the spine, the necessary equipment is costly and availability is still limited. Whereas most surgeons use lateral fluoroscopy to guide instrumentation in the sagittal plane, the lateromedial angulation is often chosen by feel and experience and is checked in the anteroposterior view after implantation. To overcome the uncertainty of the lateromedial angulation, iPod touch-based applications for measuring angles can be used to assist implantation of screws.

Methods: In this study, 20 lumbar pedicle screws in 5 consecutive patients were implanted using the iPod touch. The lateromedial angulation was measured on preoperative images and reproduced in the operative field with the sterilely draped iPod touch. The instruments to implant the screws were aligned with the side of the iPod for screw insertion. Actual screw angles were remeasured on postoperative imaging.

Results: In 16 of 20 screws, the accuracy of implantation was within 3 degrees of the ideal trajectory. The four screws with an angle mismatch of 7 to 13 degrees were all implanted at the caudal end of the exposure, where maintaining the planned angulation was impeded by strong muscles pushing medially.

Conclusion: iPod touch-assisted instrumentation of the spine is a very simple technique, which, in combination with a lateral fluoroscopy, may guide placement of pedicle screws in the lumbar spine.

Acknowledgment: This study was supported by the Neurosurgery Research and Education Foundation of the American Association of Neurological Surgeons.