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Matthias Setzer, Mohamed Eleraky, Wesley M. Johnson, Kamran Aghayev, Nam D. Tran and Frank D. Vrionis

Object

The objective of this study was to compare the stiffness and range of motion (ROM) of 4 cervical spine constructs and the intact condition. The 4 constructs consisted of 3-level anterior cervical discectomy with anterior plating, 1-level discectomy and 1-level corpectomy with anterior plating, 2-level corpectomy with anterior plating, and 2-level corpectomy with anterior plating and posterior fixation.

Methods

Eight human cadaveric fresh-frozen cervical spines from C2–T2 were used. Three-dimensional motion analysis with an optical tracking device was used to determine motion following various reconstruction methods. The specimens were tested in the following conditions: 1) intact; 2) segmental construct with discectomies at C4–5, C5–6, and C6–7, with polyetheretherketone (PEEK) interbody cage and anterior plate; 3) segmental construct with discectomy at C6–7 and corpectomy of C-5, with PEEK interbody graft at the discectomy level and a titanium cage at the corpectomy level; 4) corpectomy at C-5 and C-6, with titanium cage and an anterior cervical plate; and 5) corpectomy at C-5 and C-6, with titanium cage and an anterior cervical plate, and posterior lateral mass screw-rod system from C-4 to C-7. All specimens underwent a pure moment application of 2 Nm with regards to flexion-extension, lateral bending, and axial rotation.

Results

In all tested motions the statistical comparison was significant between the intact condition and the 2-level corpectomy with anterior plating and posterior fixation construct. All other statistical comparisons between the instrumented constructs were not statistically significant except between the 3-level discectomy with anterior plating and the 2-level corpectomy with anterior plating in axial rotation. There were no statistically significant differences between the 1-level discectomy and 1-level corpectomy with anterior plating and the 2-level corpectomy with anterior plating in any tested motion. There was also no statistical significance between the 3-level discectomy with anterior plating and the 2-level corpectomy with anterior plating and posterior fixation.

Conclusions

This study demonstrates that segmental plate fixation (3-level discectomy) affords the same stiffness and ROM as circumferential fusion in 2-level cervical spine corpectomy in the immediate postoperative setting. This obviates the need for staged circumferential procedures for multilevel cervical spondylotic myelopathy. Given that the posterior segmental instrumentation confers significant stability to a multilevel cervical corpectomy, the surgeon should strongly consider the placement of segmental posterior instrumentation to significantly improve the overall stability of the fusion construct after a 2-level cervical corpectomy.

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Mohammed Eleraky, Ioannis Papanastassiou, Matthias Setzer, Ali A. Baaj, Nam D. Tran and Frank D. Vrionis

Object

Balloon kyphoplasty has recently been shown to be effective in providing rapid pain relief and enhancing health-related quality of life in patients with metastatic spinal tumors. When performed to treat lesions of the upper thoracic spine, kyphoplasty poses certain technical challenges because of the smaller size of the pedicle and vertebral bodies. Fluoroscopic visualization is also difficult due to interference of the shoulder. The authors' objective in the present study was to evaluate their approach and the results of balloon kyphoplasty in the upper thoracic spine in patients with metastatic spinal disease.

Methods

Fourteen patients underwent kyphoplasty via an extrapedicular approach to treat metastatic tumors in the upper (T1–5) thoracic spine. Electrodiagnostic monitoring (somatosensory and motor evoked potentials) was used in 5 cases. Three levels were treated in 7 cases, 2 levels in 2 cases, and 1 level in 5 cases. In 3 cases access was bilateral, whereas in 11 cases access was unilateral. The procedure took an average of 25 minutes per treated level, and the mean amount of cement applied was 3 ml per level. Four patients were discharged from the hospital on the day of the procedure, and 10 patients went home after 24 hours.

Results

All patients exhibited marked improvement in mean visual analog scale scores (preoperative score 79 vs postoperative score 30, respectively) and Oswestry Disability Index scores (83 vs 33, respectively). The mean kyphotic angle was 25.03° preoperatively, whereas the mean postoperative angle was 22.65° (p > 0.3). At latest follow-up, the mean kyphotic angle did not differ significantly from the postoperative kyphotic angle (26.3°, p > 0.1).

No neurological deficits or lung-related complications (pneumothorax or hemothorax) were encountered in any of the patients. Polymethylmethacrylate cement extravasations were observed in 3 (10%) of 30 treated vertebral bodies without any sequelae. By a mean follow-up of 16 months, no patients had experienced an adjacent-level fracture.

Conclusions

Balloon kyphoplasty of the upper thoracic spine via an extrapedicular approach is an efficient and safe minimally invasive procedure that may provide immediate and long-term pain relief and improvement in functional ability. It is technically challenging and has the potential for serious complications. With a fundamental knowledge of anatomy, as well as an ability to interpret fluoroscopy images, one can feasibly and safely perform balloon kyphoplasty in the upper thoracic spine.

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Nam D. Tran, Stefan Kim, Heather K. Vincent, Anthony Rodriguez, David R. Hinton, M. Ross Bullock and Harold F. Young

Object

Dysregulation of water homeostasis induces cerebral edema. Edema is a major cause of morbidity and mortality following traumatic brain injury (TBI). Aquaporin-1 (AQP-1), a water channel found in the brain, can function as a transporter for CO2 across the cellular membrane. Additionally, AQP-1's promoter contains a glucocorticoid response element. Thus, AQP-1 may be involved with edema-related brain injury and might be modulated by external conditions such as the pH and the presence of steroids. In this study, the authors investigated the hypotheses that: 1) AQP-1 participates in brain water homeostasis following TBI; 2) secondary injury (for example, acidosis) alters the expression of AQP-1 and exacerbates cerebral edema; and 3) corticosteroids augment brain AQP-1 expression and differentially affect cerebral edema under nonacidotic and acidotic conditions.

Methods

Anesthetized Sprague-Dawley rats were subjected to moderate to severe TBI (2.5–3.5 atm) or surgery without injury, and they were randomized to receive a 3-mg/kg bolus of intravenous dexamethasone within 10 minutes after injury or surgery, a 3-mg/kg bolus of dexamethasone followed by 1-mg/kg maintenance doses every 8 hours for 24 hours, or saline boluses at similar time intervals. A second group of animals was subjected to respiratory acidosis with target arterial blood pH 6.8–7.2 for 1 hour following the surgery or injury. To evaluate selective blockage of AQP-1, some animals received a single intraperitoneal dose of HgCl2 (0.3–30.0 mmol/L) within 30 minutes of injury or surgery. At 4 or 24 hours postinjury, animals were killed and their brains were harvested for mRNA, protein, or water content analyses.

Results

The authors demonstrated elevated cerebral edema levels at 4 and 24 hours following TBI. Dexamethasone administration within 1 hour of TBI attenuated the cerebral edema under nonacidotic conditions but worsened it under acidotic conditions. Selective blockage of AQP-1 channels with HgCl2 attenuated the edematous effects of corticosteroids and acidosis. Reverse transcriptase polymerase chain reaction and immunohistochemical analyses demonstrated a paucity of AQP-1 in the cerebral cortices of the uninjured animals. In contrast, AQP-1 mRNA and protein levels were higher in the cerebral cortices of animals that sustained a TBI.

Conclusions

These findings implicate an important, modifiable role for AQP-1 in water homeostasis within the CNS following TBI.