Does Dynamic Surgical Guidance (DSG) Contribute to Safe and Accurate Pedicle Screws, A Retrospective Collection

Presented at SMISS Annual Forum 2018
By John Starr MD
With Larry Khoo MD, Karim Muradian MD, John Gaughan PhD,

Disclosures: John Starr MD B; SpineGuard. Larry Khoo MD B; SpineGuard., Karim Muradian MD None, John Gaughan PhD None,

Introduction:

The accuracy of PSP (pedicle screw placement) remains imperfect. EMG and fluoroscopy may identify a breach, but only after the pedicle breach has occurred. PSP during lumbar posterior spinal fusion (PSF) can result in medial pedicle perforations risking nerve root impingement and dural injury as well as lateral pedicle and vertebral body perforations causing possible neural or vascular injury. Intraoperative fluoroscopy has demonstrated a reduced risk of perforations but is associated with significant radiation. PSP is typically preceded by the creation of a pilot hole using some variation of the pedicle probe. With the use of an interface sensitive DSG device, the surgeon is able to detect if the tip of the pedicle probe is in cancellous bone, cortical bone, or soft tissue beyond a cortical breach. The DSG device is 100% radiation free.

Methods:

A retrospective review was carried out on 11 patients with a mean age of 55. All patients received EMG monitoring and fluoroscopic imaging. In addition, intraoperative O-arm imaging was performed following PSP in all patients. A screw was repositioned or removed immediately if imaging demonstrated a medial pedicle breach of more than 2mm, or a lateral breach greater than 4mm. An independent spinal radiologist (DP) retrospectively analysed the intraoperative scans. The positions of screws were classified as acceptable (fully contained screws or with ≤2 mm of medial wall perforation) or unacceptable (> 2 mm). The variables of pedicle screw position as defined by acceptable were examined using the Fisher (2-tailed) exact test with regard to the region (thoracolumbar or lumbar).

Results:

A total of 64 screws were inserted from T11 to S1 during 11 surgical procedures. Six surgeries were performed with the assistance of DSG and 5 surgeries employed a conventional probe. In total, 30 pedicle screws were inserted using DSG and 34 without. DSG group had no breaches and no adverse EMG readings. The control group had 2 breaches that resulted in screw re-positioning, 5.8%, 0/30 vs 2/34, p= 0.05 using difference in Poisson rates. Both breaches were medial breaches, one in Right L2 and the other in Right L4. Both screw breaches were detected by positive EMG as well as noticeable screw threads outside the medial cortex on direct inspection.

Conclusions:

The use of DSG placing thoracic and lumbar pedicle screws is both safe and useful in improving the accuracy of PSP.