Percutaneous computer-assisted translaminar facet screw: an initial human cadaveric study

Abstract

Background context Translaminar facet screws are a minimally invasive technique for posterior lumbar fixation with good success rates. Computer-assisted image navigation using virtual fluoroscopy allows multiple simultaneous screens in various planes to plan and drive spinal instrumentation. Purpose This study evaluates the percutaneous placement of translaminar facet screws with the use of virtual fluoroscopy as an image guidance technique. Study design/setting A human cadaveric study was performed with a percutaneous reference frame applied to the iliac crest. Ten translaminar facet screws were placed bilaterally at five levels. Anteroposterior and lateral images were used to navigate 4.0-mm screws through a percutaneous portal under virtual fluoroscopy. Methods An axial computed tomographic scan through the instrumented levels was obtained after the screws were placed. Screws were graded on entry, course through the lamina, and terminus. A grading system was devised to grade the course through the lamina. Results All 10 screw-entry points were judged optimal at the spinous process laminar junction. There were five Grade I breeches with less than ½ the screw through the lamina, and five Grade 0 screw placements with the screw contained completely within the lamina. The termination point was acceptable in five screws. The screws that began on the right and terminated on the left were all found to have grade II breakouts. No screws placed the spinal canal or exiting nerve root at risk. Conclusions Virtual fluoroscopy provides significant assistance in percutaneous placement of translaminar facet screws and results in safe position of entry, lamina course, and terminus.