4. Alarm criteria for cervical, thoracic and lumbar pedicle crews

Pedicle screw fixation has become the most common surgical procedure for decompression and fusion in both common and complex spinal pathology. However, the insertion of implants into the spine has a certain risk of producing nervous tissue or vascular damage, like when a screw is misplaced. The breakage of the pedicle wall can be just a minor problem, but in certain cervical and high thoracic vertebrae, it could lead to serious complications. The use of free running EMG (f-EMG) and triggered EMG (t-EMG) as intraoperative neuromonitoring techniques is based on detecting “injury” potentials when a procedure is being performed, or by electrically stimulating a tool or a screw to obtain the muscle action potential of myotomes innervated by the roots near the stimulated site. Though its diagnostic value is still debated, it has been shown that it can be a helpful tool, but only if a proper procedure is followed. Recent meta analysis and systematic review studies using t-EMG, CAT scanning measurements for misplaced pedicle screws have helped establish that the nerve threshold is the one technique with the highest specificity of pedicle wall breach. It is not a perfect test, as underlying pathology (previous radiculopathy, polyneuropathy) can increase threshold levels. Particular comments will be delivered regarding the differences in cervical, thoracic and lumbar pedicle screw placement.