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Eric M. Horn, Nicholas Theodore, Neil R. Crawford, Nicholas C. Bambakidis and Volker K. H. Sonntag

Object

Lateral mass screws are traditionally used to fixate the subaxial cervical spine, while pedicle screws are used in the thoracic spine. Lateral mass fixation at C-7 is challenging due to thin facets, and placing pedicle screws is difficult due to the narrow pedicles. The authors describe their clinical experience with a novel technique for transfacet screw placement for fixation at C-7.

Methods

A retrospective chart review was undertaken in all patients who underwent transfacet screw placement at C-7. The technique of screw insertion was the same for each patient. Polyaxial screws between 8- and 10-mm-long were used in each case and placed through the facet from a perpendicular orientation. Postoperative radiography and clinical follow-up were analyzed for aberrant screw placement or construct failure.

Results

Ten patients underwent C-7 transfacet screw placement between June 2006 and March 2007. In all but 1 patient screws were placed bilaterally, and the construct lengths ranged from C-3 to T-5. One patient with a unilateral screw had a prior facet fracture that precluded bilateral screw placement. There were no intraoperative complications or screw failures in these patients. After an average of 6 months of follow-up there were no hardware failures, and all patients showed excellent alignment.

Conclusions

The authors present the first clinical demonstration of a novel technique of posterior transfacet screw placement at C-7. These results provide evidence that this technique is safe to perform and adds stability to cervicothoracic fixation.

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Mehmet Senoglu, Sam Safavi-Abbasi, Nicholas Theodore, Nicholas C. Bambakidis, Neil R. Crawford and Volker K. H. Sonntag

Object

In this study the authors investigated the anatomical, clinical, and imaging features as well as incidence of congenital defects of the C-1 arch.

Methods

The records of 1104 patients who presented with various medical problems during the time between January 2006 and December 2006 were reviewed retrospectively. The craniocervical computed tomography (CT) scans obtained in these patients were evaluated to define the incidence of congenital defects of the posterior arch of C-1. In addition, 166 dried C-1 specimens and 84 fresh human cadaveric cervical spine segments were evaluated for anomalies of the C-1 arch.

Results

Altogether, 40 anomalies (2.95%) were found in 1354 evaluated cases. Of the 1104 patients in whom CT scans were acquired, 37 (3.35%) had congenital defects of the posterior arch of the atlas. The incidence of each anomaly was as follows: Type A, 29 (2.6%); Type B, six (0.54%); and Type E, two (0.18%). There were no Type C or D defects. One patient (0.09%) had an anterior arch cleft. None of the reviewed patients had neurological deficits or required surgical intervention for their anomalies. Three cases of Type A posterior arch anomalies were present in the cadaveric specimens.

Conclusions

Most congenital anomalies of the atlantal arch are found incidentally in asymptomatic patients. Congenital defects of the posterior arch are more common than defects of the anterior arch.

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Corinna C. Zygourakis, A. Karim Ahmed, Samuel Kalb, Alex M. Zhu, Ali Bydon, Neil R. Crawford and Nicholas Theodore

The Excelsius GPS (Globus Medical, Inc.) was approved by the FDA in 2017. This novel robot allows for real-time intraoperative imaging, registration, and direct screw insertion through a rigid external arm—without the need for interspinous clamps or K-wires. The authors present one of the first operative cases utilizing the Excelsius GPS robotic system in spinal surgery. A 75-year-old man presented with severe lower back pain and left leg radiculopathy. He had previously undergone 3 decompressive surgeries from L3 to L5, with evidence of instability and loss of sagittal balance. Robotic assistance was utilized to perform a revision decompression with instrumented fusion from L3 to S1. The usage of robotic assistance in spinal surgery may be an invaluable resource in minimally invasive cases, minimizing the need for fluoroscopy, or in those with abnormal anatomical landmarks.

The video can be found here: https://youtu.be/yVI-sJWf9Iw.

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Eric M. Horn, Phillip M. Reyes, Seungwon Baek, Mehmet Senoglu, Nicholas Theodore, Volker K. H. Sonntag and Neil R. Crawford

Object

The small diameter of the pedicle can make C-7 pedicle screw insertion dangerous. Although transfacet screws have been studied biomechanically when used in pinning joints, they have not been well studied when used as part of a C7–T1 screw/rod construct. The authors therefore compared C7–T1 fixation using a C-7 transfacet screw/T-1 pedicle screw construct with a construct composed of pedicle screws at both levels.

Methods

Each rigid posterior screw/rod construct was placed in 7 human cadaveric C6–T2 specimens (14 total). Specimens were tested in normal condition, after 2-column instability, and once fixated. Nondestructive, nonconstraining pure moments (maximum 1.5 Nm) were applied to induce flexion, extension, lateral bending, and axial rotation while recording 3D motion optoelectronically. The entire construct was then loaded to failure by dorsal linear force.

Results

There was no significant difference in angular range of motion between the 2 instrumented groups during any loading mode (p > 0.11, nonpaired t-tests). Both constructs reduced motion to < 2° in any direction and allowed significantly less motion than in the normal condition. The C-7 facet screw/T-1 pedicle screw construct allowed a small but significantly greater lax zone than the pedicle screw/rod construct during lateral bending, and it failed under significantly less load than the pedicle screw/rod construct (p < 0.001).

Conclusions

When C-7 transfacet screws are connected to T-1 pedicle screws, they provide equivalent stability of constructs formed by pedicle screws at both levels. Although less resistant to failure, the transfacet screw construct should be a viable alternative in patients with healthy bone.

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Leonardo B. C. Brasiliense, Nicholas Theodore, Bruno C. R. Lazaro, Zafar A. Sayed, Fatih Ersay Deniz, Volker K. H. Sonntag and Neil R. Crawford

Object

The object of this study was to investigate the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of thoracic pedicle screws.

Methods

Forty human thoracic vertebrae (T6–11) from human cadavers were studied. Before pedicle screws were inserted, the specimens were separated into 4 groups according to the type of screw used: 1) standard pedicle screw (no cortical perforation); 2) screw with medial cortical perforation; 3) screw with lateral cortical perforation; and 4) “airball” screw (a screw that completely missed the vertebral body). Consistency among the groups for bone mineral density, pedicle diameter, and screw insertion depth was evaluated. Finally, each screw was pulled out at a constant displacement rate of 10 mm/minute while ultimate strength was recorded.

Results

Compared with well-placed pedicle screws, medially misplaced screws had 8% greater mean pullout strength (p = 0.482) and laterally misplaced screws had 21% less mean pullout strength (p = 0.059). The difference in mean pullout strength between screws with medial and lateral cortical perforations was significant (p = 0.013). Airball screws had only 66% of the mean pullout strength of well-placed screws (p = 0.009) and had 16% lower mean pullout strength than laterally misplaced screws (p = 0.395).

Conclusions

This in vitro study showed a significant difference in mean pullout strength between medial and lateral misplaced pedicle screws. Moreover, airball screws were associated with a significant loss of pullout strength.

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Ali A. Baaj, Juan S. Uribe, Tann A. Nichols, Nicholas Theodore, Neil R. Crawford, Volker K. H. Sonntag and Fernando L. Vale

Object

The objective of this work was to search a national health care database of patients diagnosed with cervical spine fractures in the US to analyze discharge, demographic, and hospital charge trends over a 10-year period.

Methods

Clinical data were derived from the Nationwide Inpatient Sample (NIS) for the years 1997 through 2006. The NIS is maintained by the Agency for Healthcare Research and Quality and represents a 20% random stratified sample of all discharges from nonfederal hospitals within the US. Patients with cervical spine fractures with and without spinal cord injury (SCI) were identified using the appropriate ICD-9-CM codes. The volume of discharges, length of stay (LOS), hospital charges, total national charges, discharge pattern, age, and sex were analyzed. National estimates were calculated using the HCUPnet tool.

Results

Approximately 200,000 hospitalizations were identified. In the non-SCI group, there was a 74% increase in hospitalizations and charges between 1997 and 2006, but LOS changed minimally. There was no appreciable change in the rate of in-hospital mortality (< 3%), but discharges home with home health care and to skilled rehabilitation or nursing facilities increased slightly. In the SCI group, hospitalizations and charges increased by 29 and 38%, respectively. There were no significant changes in LOS or discharge status in this group. Spinal cord injury was associated with increases in LOS, charges, and adverse outcomes compared with fractures without SCI. Total national charges associated with both groups combined exceeded $1.3 billion US in 2006.

Conclusions

During the studied period, increases in hospitalizations and charges were observed in both the SCI and non-SCI groups. The percentage increase was higher in the non-SCI group. Although SCI was associated with higher adverse outcomes, there were no significant improvements in immediate discharge status in either group during the 10 years analyzed.

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Sam Safavi-Abbasi, Joseph M. Zabramski, Pushpa Deshmukh, Cassius V. Reis, Nicholas C. Bambakidis, Nicholas Theodore, Neil R. Crawford, Robert F. Spetzler and Mark C. Preul

Object

The authors quantitatively assessed the effects of balloon inflation as a model of tumor compression on the brainstem, cranial nerves, and clivus by measuring the working area, angle of attack, and brain shift associated with the retrosigmoid approach.

Methods

Six silicone-injected cadaveric heads were dissected bilaterally via the retrosigmoid approach. Quantitative data were generated, including key anatomical points on the skull base and brainstem. All parameters were measured before and after inflation of a balloon catheter (inflation volume 4.8 ml, diameter 20 mm) intended to mimic tumor compression.

Results

Balloon inflation significantly shifted (p < 0.001) the brainstem and cranial nerve foramina (mean [± standard deviation] displacement of upper brainstem, 10.2 ± 3.7 mm; trigeminal nerve exit, 6.99 ± 2.38 mm; facial nerve exit, 9.52 ± 4.13 mm; and lower brainstem, 13.63 ± 8.45 mm). The area of exposure at the petroclivus was significantly greater with balloon inflation than without (change, 316.26 ± 166.75 mm2; p < 0.0001). Before and after balloon inflation, there was no significant difference in the angles of attack at the origin of the trigeminal nerve (p > 0.5).

Conclusions

This study adds an experimental component to the emerging field of quantitative neurosurgical anatomy. Balloon inflation can be used to model the effects of a mass lesion. The tumor simulation created “natural” retraction and an opening toward the upper clivus. The findings may be helpful in selecting a surgical approach to increase the working space for resection of certain extraaxial tumors.

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Rogerio Rocha, Sam Safavi-Abbasi, Cassius Reis, Nicholas Theodore, Nicholas Bambakidis, Evandro De Oliveira, Volker K. H. Sonntag and Neil R. Crawford

Object

The authors measured relevant quantitative anatomical parameters to define safety zones for the placement of C-1 posterior screws.

Methods

Nineteen linear, two angular, and four surface parameters of 20 dried atlantal specimens were evaluated. The Optotrak 3020 system was used to define the working area. Ideal angles for screw positioning were measured using digital radiographs and a free image-processing program. Six silicone-injected cadaveric heads were dissected bilaterally to study related neurovascular anatomy.

The depth (range 5.2–9.4 mm, mean 7.2 ± 1.1 mm) and width (range 5.2–8.1 mm, mean 6.5 ± 0.9 mm) of the transverse foramen varied considerably among specimens. The mean posterior working area was 43.3 mm2. All specimens accommodated 3.5-mm-diameter screws, and 93% accepted 4-mm-diameter screws. In 10 specimens (50%), partial removal of the posterior arch was necessary to accommodate a 4-mm screw. The mean maximum angle of medialization was 16.7 ± 1.3°; the mean maximum superior angulation was 21.7 ± 4.7°.

Conclusions

The anatomical configuration of the atlas and vertebral artery (VA) varied considerably among the cadaveric specimens. The heights of the C-1 pedicle, posterior arch, and posterior lamina determine the posterior working area available for screw placement. The inferior insertion of the posterior arch may have to be drilled to increase this working area, but doing so risks injury to the VA. A dense venous plexus with multiple anastomoses may cover the screw entry site, potentially obscuring the operative view and increasing the risk of hemorrhage.

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Neil R. Crawford, K. Zafer Yüksel, Şeref Doğan, Octavio Villasana-Ramos, Julio C. Soto-Barraza, Seungwon Baek, Randall W. Porter, Frederick F. Marciano and Nicholas Theodore

Object

An experiment was performed to study the limits of the ability of screws designed to center themselves in the pedicle during insertion, and to study whether straight-ahead versus inward screw insertion trajectories differ in their resistance to pullout.

Methods

Forty-nine human cadaveric lumbar vertebrae were studied. Pedicle screws were inserted in trajectories starting 0°, 10°, 20°, or 30° from the optimal trajectory, either medially or laterally misdirected. The surgeon then inserted the screw with forward thrust but without resisting the screw's tendency to reorient its own trajectory during insertion. On the opposite pedicle, a control screw was inserted with the more standard inward-angled anatomical trajectory and insertion point. Cortical wall violation during insertion was recorded. Screws were then pulled out at a constant displacement rate while ultimate strength was recorded.

Results

Lateral misdirection as small as 10° was likely to lead to cortical wall violation (3 of 7 violations). Conversely, medial misdirection usually resulted in safe screw insertion (1 of 21 violations for 10°, 20°, or 30° medial misdirection). The resistance to pullout of screws inserted in a straight-ahead trajectory did not differ significantly from that of screws inserted along an inward trajectory (p = 0.68).

Conclusions

Self-tapping, self-drilling pedicle screws can redirect themselves to a much greater extent during medial than during lateral misdirection. The cortical wall is more likely to be violated laterally than medially. The strength of straight-ahead and inward trajectories was equivalent.

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Luis Perez-Orribo, Laura A. Snyder, Samuel Kalb, Ali M. Elhadi, Forrest Hsu, Anna G. U. S. Newcomb, Devika Malhotra, Neil R. Crawford and Nicholas Theodore

OBJECTIVE

Craniovertebral junction (CVJ) injuries complicated by transverse atlantal ligament (TAL) disruption often require surgical stabilization. Measurements based on the atlantodental interval (ADI), atlas lateral diameter (ALD1), and axis lateral diameter (ALD2) may help clinicians identify TAL disruption. This study used CT scanning to evaluate the reliability of these measurements and other variants in the clinical setting.

METHODS

Patients with CVJ injuries treated at the authors' institution between 2004 and 2011 were evaluated retrospectively for demographics, mechanism and location of CVJ injury, classification of injury, treatment, and modified Japanese Orthopaedic Association score at the time of injury and follow-up. The integrity of the TAL was evaluated using MRI. The ADI, ALD1, and ALD2 were measured on CT to identify TAL disruption indirectly.

RESULTS

Among the 125 patients identified, 40 (32%) had atlas fractures, 59 (47.2%) odontoid fractures, 31 (24.8%) axis fractures, and 4 (3.2%) occipital condyle fractures. TAL disruption was documented on MRI in 11 cases (8.8%). The average ADI for TAL injury was 1.8 mm (range 0.9–3.9 mm). Nine (81.8%) of the 11 patients with TAL injury had an ADI of less than 3 mm. In 10 patients (90.9%) with TAL injury, overhang of the C-1 lateral masses on C-2 was less than 7 mm. ADI, ALD1, ALD2, ALD1 – ALD2, and ALD1/ALD2 did not correlate with the integrity of the TAL.

CONCLUSIONS

No current measurement method using CT, including the ADI, ALD1, and ALD2 or their differences or ratios, consistently indicates the integrity of the TAL. A more reliable CT-based criterion is needed to diagnose TAL disruption when MRI is unavailable.