Introduction: Electromyography (EMG) monitoring has been used to assess pedicle screw misplacement, its ability to reduce misplacement rates has been not well documented in pediatric spinal deformity surgery.
Objectives: To evaluate the ability of EMG monitoring to improve pedicle screw placement.
Materials and Methods: 31 patients (mean age: 14.6) who had EMG monitoring were identified and enrolled in the study. The mean preoperative Cobb angle was 60.3° (range: 50°–112°). AIS patients comprised 84%(26) of the cohort, neuromuscular 13%(4), and congenital/syndromic 3%(1). A total of 477 screws were placed and evaluated postoperatively by CT scan. Significant misplacement was considered to be >2mm medial breach or >4mm of lateral or anterior breach.
Results: Mean EMG threshold was equivalent in the misplaced and non-misplaced groups (16.0 vs. 18.7,p=0.08). However when EMG values from the same patient were ranked relative to one another, misplacement rates varied significantly with respect to percentile. Screws with EMG values in the 10th percentile had a misplacement rate of 24.4% vs. 6.8% for screws with values above the 10th percentile (p<0.001). Overall, EMG readings below the 30th percentile had a significantly higher misplacement rate (p<0.02).
Conclusion: Absolute EMG values do not correlate with misplacement rates. However, screws with EMG values in the lowest 30th percentile do have a significantly higher chance of misplacement, suggesting that these screws should be more carefully evaluated for pedicle breech at the time of surgery.
Significance: Relative EMG values from the same patient may be used to improve pedicle screw placement.