Free Hand Pedicle Screw Placement during Revision Spinal Surgery: Analysis of 552 Screws

Purpose: Placement of pedicle screws into previous fusion masses or pseudarthrosis levels of the spine is challenging because of the loss of normal anatomic landmarks. The purpose of this study is to evaluate the safety of free hand pedicle screw placement at levels with a solid posterior fusion mass as well as at levels of identified pseudarthrosis of the thoracic and lumbosacral spine without any fluoroscopic or image-guided assistance.

Methods: (See table) Thirty-seven patients underwent revision spinal surgery with posterior spinal instrumentation and fusion utilizing 552 transpedicular screws by a single surgeon from 1994 to 2003. Among 552 screws, 308 screws placed into fusion masses (208 screws) and pseudarthrosis levels (100 screws) were analyzed using radiographs, intraoperative monitoring data, and clinical outcomes. We used the quadrangulation method to find pedicle access in a prior fusion mass using any visible anatomic landmarks. Following screw placement, electrophysiologic (triggered EMG) and radiographic confirmation was performed intraoperatively.

Results: The mean age at the time of surgery was 38+6 years (range 8-75). Four screws were removed intraoperatively according to low triggered EMG criteria and three of them were repositioned (4 out of 308 total screws, 1.30%). Two patients were revised at postoperative day 3 and 6 weeks respectively for root decompression at the osteotomy site but the screw positions were correct. Two patients complained of transient weakness with foot-extension but improved spontaneously in 2 weeks (neurologic complications: 4/37 patients, 10.8%). There were no neurologic, vascular, or visceral complications with screw placement.

Conclusion: The free hand technique of thoracic and lumbosacral pedicle screw placement in revision spinal surgery is a reliable and safe method of insertion when using the quadrangulation method of gaining pedicle access through a prior fusion mass or at pseudarthrosis levels.