Early experience of placing image-guided minimally invasive pedicle screws without K-wires or bone-anchored trackers

OBJECTIVE Image guidance for spine surgery has been reported to improve the accuracy of pedicle screw placement and reduce revision rates and radiation exposure. Current navigation and robot-assisted techniques for percutaneous screws rely on bone-anchored trackers and Kirchner wires (K-wires). There is a paucity of published data regarding the placement of image-guided percutaneous screws without K-wires. A new skin-adhesive stereotactic patient tracker (SpineMask) eliminates both an invasive bone-anchored tracker and K-wires for pedicle screw placement. This study reports the authors' early experience with the use of SpineMask for "K-wireless" placement of minimally invasive pedicle screws and makes recommendations for its potential applications in lumbar fusion. METHODS Forty-five consecutive patients (involving 204 screws inserted) underwent K-wireless lumbar pedicle screw fixation with SpineMask and intraoperative neuromonitoring. Screws were inserted by percutaneous stab or Wiltse incisions. If required, decompression with or without interbody fusion was performed using mini-open midline incisions. Multimodality intraoperative neuromonitoring assessing motor and sensory responses with triggered electromyography (tEMG) was performed. Computed tomography scans were obtained 2 days postoperatively to assess screw placement and any cortical breaches. A breach was defined as any violation of a pedicle screw involving the cortical bone of the pedicle. RESULTS Fourteen screws (7%) required intraoperative revision. Screws were removed and repositioned due to a tEMG response < 13 mA, tactile feedback, and 3D fluoroscopic assessment. All screws were revised using the SpineMask with the same screw placement technique. The highest proportion of revisions occurred with Wiltse incisions (4/12, 33%) as this caused the greatest degree of SpineMask deformation, followed by a mini midline incision (3/26, 12%). Percutaneous screws via a single stab incision resulted in the fewest revisions (7/166, 4%). Postoperative CT demonstrated 7 pedicle screw breaches (3%; 5 lateral, 1 medial, 1 superior), all with percutaneous stab incisions (7/166, 4%). The radiological accuracy of the SpineMask tracker was 97% (197/204 screws). No patients suffered neural injury or required postoperative screw revision. CONCLUSIONS The noninvasive cutaneous SpineMask tracker with 3D image guidance and tEMG monitoring provided high accuracy (97%) for percutaneous pedicle screw placement via stab incisions without K-wires.