Anatomic Evaluation of Two Different Techniques for the Percutaneous Insertion of Pedicle Screws in the Lumbar Spine

STUDY DESIGN: An in vitro study in which a human cadaver model was used to examine the accuracy of two different techniques of percutaneous pedicle screw insertion in the lumbar spine. OBJECTIVES: To investigate the in vitro misplacement rate of pedicle screw insertion for two different percutaneous techniques: 1) the well established Magerl technique, and 2) a new modified technique. SUMMARY OF BACKGROUND DATA: Numerous anatomic and biomechanical studies have been conducted to analyze the in vitro and in vivo characteristics of pedicle screw insertion in the lumbar spine via an open approach, whereas there is a lack of experimental data concerning the more sophisticated percutaneous procedure. METHODS: Thirty human specimens from L1 to S1 were separated into two groups (A and B). In group A, the screws were placed in accordance with the technique described by Magerl; in group B, a new modified technique developed by the authors' research group was used. After screw placement, the specimens were dissected, and pedicle violations were noted with respect to the degree and direction of the screw misplacement. RESULTS: The dissection of the specimens showed that of 360 pedicle screws, 37 were misplaced. This finding translates into an overall misplacement rate of 10%. With the Magerl technique, 23 pedicle violations (misplacement rate, 13%) were found; with the modified technique, only 14 dislocated pedicle screws (misplacement rate, 8%) were detected. This difference was not statistically significant (P = 0.118). In both groups, there were significantly more medical pedicle violations than lateral (32 medial and 5 lateral screw dislocations). The degree of the screw misplacements varied between 1.0 and 5.0 mm. The majority of pedicle violations (30 of 37) were minor, i.e., less than 3.0 mm. CONCLUSIONS: This in vitro study showed that the percutaneous technique of pedicle screw insertion in the lumbar spine is a safe and reliable procedure. Compared with the well-established Magerl technique, the new modified technique did not decrease the misplacement rate significantly, although less pedicle violations were found in the upper lumbar spine.