A study published in Spine shows that an electronic conductivity device (PediGuard, SpineGuard) significantly reduces the incidence of pedicle screw misplacement in patients with scoliosis.
In the retrospective controlled study, investigators Ovadia et al reviewed the implantation of pedicle screws in 248 paediatric patients with scoliosis of various aetiologies. Patients were split into groups: group one, which included 150 procedures that did not use the electronic conductivity device (ECD); and group two, which included 98 procedures that did use the ECD. Overall, there were 1270 pedicle screw placements analysed in group one and 1400 analysed in group two.
There were 10 procedures with neuromonitoring alarms related to pedicle screw misplacement in group one but only three procedures had these alarms in group two. This, according to Ovadia et al, meant that the use of ECD significantly reduced the incidence of clinically relevant misplaced screws. They reported: “Pedicle screw placement in deformity patients, particularly at more strategic areas, that is, the concavity and apices of spinal curvature, continue to pose a major challenge for the spine surgeon. This study has demonstrated that the use of the ECD, a simple tool with a short learning curve, significantly increased the safety of pedicle screw insertion and decreased the incidence of clinically relevant misplaced screws in scoliosis patients.”
The ECD, a free-hand drilling instrument, has an electronic conductivity sensor at its tip that can translate relative values of electronic conductivity into audible and visual signals. Ovadia et al report: “It works on the premise that cancellous bone within the pedicle possesses lower resistance than the cortical bone and soft tissues that surround it, and thus can provide the surgeon live feedback as to whether the trajectory has strayed from within normal intrapedicle spatial boundaries.”
The use of all-pedicle screw constructs in scoliosis surgery has increased in popularity in recent years, but correctly placing the screws is challenging even for experienced surgeons: Ovadia et al write that, according to some studies, pedicle screw misplacement occurs in 10-55% of cases. The consequences of misplacement include paraplegia (due to nerve root spinal cord injury or vascular injury) and severe neurologic sequelae. Therefore, there is a need to develop techniques that will improve pedicle screw placement. The free-hand technique, intraoperative fluoroscopy, triggered electromyography, intraoperative image-based navigation, and (the latest to be developed) the ECD are some of the methods used to ensure optimal placement.
Previous studies have shown the ECD to have 98% sensitivity and 99% specificity, but Ovadia et al’s study is the first to investigate the device in a large group of patients with scoliosis of diverse aetiologies. They conclude: “In our experience, the use of the ECD improved pedicle screw insertion safety. We continue to use the ECD on a routine basis in all scoliosis surgery performed at our institution.” They add that further studies were needed to see if the benefits observed with the ECD were relevant for other surgical contexts that involved pedicle screw insertion.