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Alexander G. Chartrain, Ahmed J. Awad, Jonathan J. Rasouli, Robert J. Rothrock and Brian H. Kopell

A 59-year-old woman with a 30-year history of essential tremor refractory to medical therapy underwent staged deep brain stimulation of the ventralis intermedius nucleus of the thalamus (VIM). Left-sided lead placement was performed first. Once in the operating room, microelectrode recording (MER) was performed to confirm the appropriate trajectory and identify the VIM border with the ventralis caudalis nucleus. MER was repeated after repositioning 2 mm anteriorly to reduce the likelihood of stimulation-induced paresthesias. Physical examination prior to permanent lead placement demonstrated micro-lesion effect, suggesting optimal trajectory. After implantation of the permanent lead, physical examination showed excellent results.

The video can be found here: https://youtu.be/nn3KRdmRCZ4.

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Frank J. Yuk, Jonathan J. Rasouli, Marc S. Arginteanu, Alfred A. Steinberger, Frank M. Moore, Kevin C. Yao, John M. Caridi and Yakov Gologorsky

OBJECTIVE

Rigid cervicothoracic kyphotic deformity (CTKD) remains a difficult pathology to treat, especially in the setting of prior cervical instrumentation and fusion. CTKD may result in chronic neck pain, difficulty maintaining horizontal gaze, and myelopathy. Prior studies have advocated for the use of C7 or T1 pedicle subtraction osteotomies (PSOs). However, these surgeries are fraught with danger and, most significantly, place the C7, C8, and/or T1 nerve roots at risk.

METHODS

The authors retrospectively reviewed their experience with performing T2 PSO for the correction of rigid CTKD. Demographics collected included age, sex, details of prior cervical surgery, and coexisting conditions. Perioperative variables included levels decompressed, levels instrumented, estimated blood loss, length of surgery, length of stay, complications from surgery, and length of follow-up. Radiographic measurements included C2–7 sagittal vertical axis (SVA) correction, and changes in the cervicothoracic Cobb angle, lumbar lordosis, and C2–S1 SVA.

RESULTS

Four male patients were identified (age range 55–72 years). Three patients had undergone prior posterior cervical laminectomy and instrumented fusion and developed postsurgical kyphosis. All patients underwent T2 PSO: 2 patients received instrumentation at C2–T4, and 2 patients received instrumentation at C2–T5. The median C2–7 SVA correction was 3.85 cm (range 2.9–5.3 cm). The sagittal Cobb angle correction ranged from 27.8° to 37.6°. Notably, there were no neurological complications.

CONCLUSIONS

T2 PSO is a powerful correction technique for the treatment of rigid CTKD. Compared with C7 or T1 PSO, there is decreased risk of injury to intrinsic hand muscle innervators, and there is virtually no risk of vertebral artery injury. Laminectomy may also be safer, as there is less (or no) scar tissue from prior surgeries. Correction at this distal level may allow for a greater sagittal correction. The authors are optimistic that these findings will be corroborated in larger cohorts examining this challenging clinical entity.

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Jonathan J. Rasouli, Brooke T. Kennamer, Frank M. Moore, Alfred Steinberger, Kevin C. Yao, Omar N. Syed, Marc S. Arginteanu and Yakov Gologorsky

OBJECTIVE

The C7 vertebral body is morphometrically unique; it represents the transition from the subaxial cervical spine to the upper thoracic spine. It has larger pedicles but relatively small lateral masses compared to other levels of the subaxial cervical spine. Although the biomechanical properties of C7 pedicle screws are superior to those of lateral mass screws, they are rarely placed due to increased risk of neurological injury. Although pedicle screw stimulation has been shown to be safe and effective in determining satisfactory screw placement in the thoracolumbar spine, there are few studies determining its utility in the cervical spine. Thus, the purpose of this study was to determine the feasibility, clinical reliability, and threshold characteristics of intraoperative evoked electromyographic (EMG) stimulation in determining satisfactory pedicle screw placement at C7.

METHODS

The authors retrospectively reviewed a prospectively collected data set. All adult patients who underwent posterior cervical decompression and fusion with placement of C7 pedicle screws at the authors’ institution between January 2015 and March 2019 were identified. Demographic, clinical, neurophysiological, operative, and radiographic data were gathered. All patients underwent postoperative CT scanning, and the position of C7 pedicle screws was compared to intraoperative neurophysiological data.

RESULTS

Fifty-one consecutive C7 pedicle screws were stimulated and recorded intraoperatively in 25 consecutive patients. Based on EMG findings, 1 patient underwent intraoperative repositioning of a C7 pedicle screw, and 1 underwent removal of a C7 pedicle screw. CT scans demonstrated ideal placement of the C7 pedicle screw in 40 of 43 instances in which EMG stimulation thresholds were > 15 mA. In the remaining 3 cases the trajectories were suboptimal but safe. When the screw stimulation thresholds were between 11 and 15 mA, 5 of 6 screws were suboptimal but safe, and in 1 instance was potentially dangerous. In instances in which the screw stimulated at thresholds ≤ 10 mA, all trajectories were potentially dangerous with neural compression.

CONCLUSIONS

Ideal C7 pedicle screw position strongly correlated with EMG stimulation thresholds > 15 mA. In instances, in which the screw stimulates at values between 11 and 15 mA, screw trajectory exploration is recommended. Screws with thresholds ≤ 10 mA should always be explored, and possibly repositioned or removed. In conjunction with other techniques, EMG threshold testing is a useful and safe modality in determining appropriate C7 pedicle screw placement.