INTRODUCTION: Transpedicular screw fixation has achieved significant popularity for scoliosis surgery. The main current existing techniques for accurate placement of pedicle screws are freehand, fluoroscopy, and surgical navigation system. However, those have advantages and limitations. Some are operator dependent, others are expensive and too bulky to be fitted in the surgical theatre. The purpose of the current study was to develop a new portable navigation system for scoliosis surgery using pedicle screws, and to evaluate its availability.
METHODS: Mechanical property of cortical and cancellous bone is much different. The new system, consisted of probe and recorder, utilizes the mechanical difference to detect the breach of the cortex by pedicle screw. The probe included load cell, which measured the load when it was tapped into the pedicle. The absolute value and change of the load were simultaneously recorded and observed. Misplacement of the pedicle screw should be evaluated measuring the change of the load and curve pattern. Load range of this system was 200 N with measurement accuracy of + 1% F.S. + 1 digit. The minimum resolution was 0.1 N. A cadaveric spine (75y.o. male, height 1.65m) was utilized for this study. Load‐displacement curve was recorded in the following three conditions: proper placement, medial and lateral breach of the pedicle walls.
RESULTS: Load‐displacement curve was smooth when there was no breach at any sites of the pedicle. The load was between 20 and 80 N, depending upon the level of the pedicle. On the contrast, large change was observed when there was medial and lateral breach of the pedicle. No any predictive curve patterns were observed when the pedicle was breached.
DISCUSSION: The new portable navigation system proved to be beneficial as an effective system for the placement of pedicle screw. However, further improvement was mandatory for clinical use, especially for the predictive value.