gms | German Medical Science

Objective: Navigational guidance during the placement of pedicle screws in the lumbar spine is stated to be helpful but not a conditio sine qua non. The idea of this study was to evaluate a miniature robotic system providing passive guidance without interfering with the surgical action. Special focus was placed on the correlation of preoperative planning and postoperative accuracy of screw placement.

Methods: The SpineAssist^® (SA) is a miniature bone-mounted robot – 2.5 inch diameter, 250 gram – featuring a six-degree-of-freedom parallel design. The semi-active miniature robot is connected to a workstation, which controls its motion. It guides the surgeon to the desired implant positions according to preoperative planning, while leaving the actual surgical act in the physician’s hands. The planning is done on a 3-D model of the patient’s spine generated by the system and based on a CT scan (Figure 2). Registration is done based on fluoroscopy. The system performs automatic, per-vertebra, merge of these intra-op fluoroscopic images with the pre-op CT. The accuracy of the image registration process is visually verified by the surgeon, and the first level to be operated on is chosen. The SA device is mounted onto the clamp/frame and the system controls its motion so that it points to the exact entry point and trajectory according to the surgeon's pre-operative plan. Surgical tools are inserted by the surgeon through the arm's tip to facilitate introduction of the implant.

Results: 14 patients were entered into this study. All patients had a PLIF. A total number of 58 screws were placed using the Spineassist, 3 screws were placed without it. The majority of screws were placed in L4 or L5 (18 each), ranging from L1 to S1. The average time needed for successful registration in all patients was 15 minutes. In the postoperative CT, all screws were correctly placed within the pedicle unless planned as in-out-in screws. The average deviation between preoperative planning and postoperative results was 0.9mm axial and 1.2mm lateral. In the three screws planned with the workstation but placed without guidance, the deviation was 3.5mm

Conclusions: The SpineAssist miniature robotic system proved to be a reliable tool for exact pedicle screw placement. Planning and placement of the screws favors a lateral transmuscular approach to the pedicle, reducing traumatic mobilization of the medial muscles.