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Susan Núñez-Pereira, Wolfgang Hitzl, Viola Bullmann, Oliver Meier and Heiko Koller

OBJECT

Sagittal malalignment of the cervical spine has been associated with worsened postsurgical outcomes. For better operative planning of fusion and alignment restoration, improved knowledge of ideal fusion angles and interdependences between upper and lower cervical spine alignment is needed. Because spinal and spinopelvic parameters might play a role in cervical sagittal alignment, their associations should be studied in depth.

METHODS

The authors retrospectively analyzed digital lateral standing cervical radiographs of 145 patients (34 asymptomatic, 74 symptomatic; 37 surgically treated), including full-standing radiographs obtained in 45 of these patients. Sagittal measurements were as follows: C2–7, occiput (Oc)–C2, C1–2 Cobb angles, and C-7 slope (the angle between the horizontal line and the superior endplate of C-7), as well as T4–12 and L1–S1 Cobb angles, sacral slope, pelvic incidence, and C-7 sagittal vertical axis (SVA). A correlation analysis was performed, and linear regression models were developed.

RESULTS

Statistical analyses revealed significant correlations between C2–7 and Oc–C2 (r = −0.4, p < 0.01), Oc–C2 (r = −0.3, p < 0.01), and C1–2 angle (r = −0.3, p < 0.01). C-7 slope was significantly correlated with C2–7 (r = −0.5, p < 0.01) and with Oc–C2 angle (r = 0.2, p = 0.02). Total cervical (Oc–C7) lordosis was 30.2° and did not differ significantly among asymptomatic, symptomatic, and surgically treated patients. Correlations between C2–7 and Oc–C2 alignment were stronger in asymptomatic patients (r = –0.5, p < 0.01) and surgically treated patients (r = –0.5, p < 0.01) than in symptomatic patients (r = –0.3, p = 0.01), but the between-group difference was not significant (p > 0.1). Comparing cervical and spinopelvic alignment revealed a significant correlation between sacral slope and C-7 slope (r = –0.3, p = 0.04) and C2–7 (r = 0.4, p < 0.01). The C-7 SVA correlated significantly with the C-7 slope (r = –0.4, p < 0.01). The interdependences were stronger within the occipitocervical parameters than between the cervical and remaining spinal parameters.

CONCLUSIONS

Significant correlations between the upper and lower cervical spine exist, confirming the existence of inherent compensatory mechanisms to maintain overall balance; no significant differences were found among asymptomatic, symptomatic, and surgically treated patients. The C-7 slope is a useful marker of overall sagittal alignment, acting as a link between the occipitocervical and thoracolumbar spine.

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Andre Tomasino, Karishma Parikh, Heiko Koller, Walter Zink, A. John Tsiouris, Jeremy Steinberger and Roger Härtl

Object

The purpose of this retrospective study was to quantify the anatomical relationship between the vertebral artery (VA), the cervical pedicle, and its surrounding structures, including the incidence of irregularities. Additionally, data delineating a “safe zone,” and these data's application during instrumentation with transpedicular cervical screw fixation were considered. The anatomical proximity of the VA to the cervical pedicle prevents spine surgeons from preferring cervical pedicle screws (CPSs) over lateral mass screws at levels C3–6. Accurate placement of CPSs is often difficult to determine, because this definition can vary between 1 and 4 mm of lateral “noncritical” and “critical” pedicle breaches. No previous study in a western population has investigated the VA's proximity to the cervical pedicle, its percentage of occupancy in the transverse foramen (TF), and the incidence of irregular VA pathways.

Methods

One hundred twenty-seven consecutive patients who underwent CT angiography of the neck were enrolled in this study. The measurements included the following: medial pedicle border to VA; lateral pedicle border to VA; pedicle diameter (PD); sagittal diameter of the VA; coronal diameter of the VA; sagittal diameter of the TF; and coronal diameter of the TF. The cross-sections of the VA and the TF were measured to determine the occupation ratio of the VA. In addition, a safe zone was defined based on all lateral pedicle border to VA measurements in which the VA was within the TF. The level of entry of the VA into the TF as well as irregularities of the VA and the cervical pedicles were recorded.

Results

Vertebral artery dominance on the left side was seen in 69.3% of cases. The mean PD increased from 4.9 to 6.5 mm (from C-3 to C-7, respectively). Statistically significantly bigger PDs were seen in males. The mean PD at C-2 was 5.6 mm. Entry of the VA at C-6 was seen in approximately 80% of cases. The TF occupation ratio of the VA was found to be the greatest in C-4 and C-7 (37.1 and 74.2%, respectively). The safe zone increased from C-2 to C-6 (1.1 to 1.7 mm, respectively), but was only 0.65 mm at C-7. In 23.6% of cases, an irregular pathway of the VA or irregular anatomy of a cervical pedicle was seen, with the highest incidence of irregularities found at C-2.

Conclusions

Computed tomography angiography is a valuable tool that can help determine the relationships between cervical pedicles and the VA as well as irregular VA pathways. Pedicle diameter, safe zone, and occupational ratio of the VA in the foramen determine the risk associated with instrumentation and should be assessed individually. Based on the authors' measurements, C-4 and C-7 can be considered critical levels for CPS placement. Because of this and the high incidence of irregular VA pathways and different entry points, it may be helpful to review neck CT angiography studies before considering posterior instrumentation procedures in the cervical spine.

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Heiko Koller, Michael Mayer, Juliane Zenner, Herbert Resch, Alfred Niederberger, Johann Fierlbeck, Wolfgang Hitzl and Frank L. Acosta Jr.

Object

In thoracolumbar deformity surgery, anterior-only approaches are used for reconstruction of anterior column failures. It is generally advised that vertebral body replacements (VBRs) should be preloaded by compression. However, little is known regarding the impact of different techniques for generation of preloads and which surgical principle is best for restoration of lordosis. Therefore, the authors analyzed the effect of different surgical techniques to restore spinal alignment and lordosis as well as the ability to generate axial preloads on VBRs in anterior column reconstructions.

Methods

The authors performed a laboratory study using 7 fresh-frozen specimens (from T-3 to S-1) to assess the ability for lordosis reconstruction of 5 techniques and their potential for increasing preloads on a modified distractable VBR in a 1-level thoracolumbar corpectomy. The testing protocol was as follows: 1) Radiographs of specimens were obtained. 2) A 1-level corpectomy was performed. 3) In alternating order, lordosis was applied using 1 of the 5 techniques. Then, preloads during insertion and after relaxation using the modified distractable VBR were assessed using a miniature load-cell incorporated in the modified distractable VBR. The modified distractable VBR was inserted into the corpectomy defect after lordosis was applied using 1) a lamina spreader; 2) the modified distractable VBR only; 3) the ArcoFix System (an angular stable plate system enabling in situ reduction); 4) a lordosizer (a customized instrument enabling reduction while replicating the intervertebral center of rotation [COR] according to the COR method); and 5) a lordosizer and top-loading screws ([LZ+TLS], distraction with the lordosizer applied on a 5.5-mm rod linked to 2 top-loading pedicle screws inserted laterally into the vertebra). Changes in the regional kyphosis angle were assessed radiographically using the Cobb method.

Results

The bone mineral density of specimens was 0.72 ± 22.6 g/cm2. The maximum regional kyphosis angle reconstructed among the 5 techniques averaged 9.7°−16.1°, and maximum axial preloads averaged 123.7–179.7 N. Concerning correction, in decreasing order the LZ+TLS, lordosizer, and ArcoFix System outperformed the lamina spreader and modified distractable VBR. The order of median values for insertion peak load, from highest to lowest, were lordosizer, LZ+TLS, and ArcoFix, which outperformed the lamina spreader and modified distractable VBR. In decreasing order, the axial preload was highest with the lordosizer and LZ+TLS, which both outperformed the lamina spreader and the modified distractable VBR. The technique enabling the greatest lordosis achieved the highest preloads. With the ArcoFix System and LZ+TLS, compression loads could be applied and were 247.8 and 190.6 N, respectively, which is significantly higher than the insertion peak load and axial preload (p < 0.05).

Conclusions

Including the ability for replication of the COR in instruments designed for anterior column reconstructions, the ability for lordosis restoration of the anterior column and axial preloads can increase, which in turn might foster fusion.

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Martine W. T. van Bilsen, Christopher Ullrich, Luis Ferraris, Axel Hempfing, Wolfgang Hitzl, Michael Mayer and Heiko Koller

OBJECTIVE

Computed tomography (CT) scans are accepted as the imaging standard of reference to define union after anterior cervical discectomy and fusion (ACDF). However, ideal CT criteria to diagnose union have not been identified or validated. The objective of this study was to analyze the diagnostic value of 9 CT-based criteria and identify the ideal criteria among them to assess cervical fusion after ACDF using surgical exploration as the standard of reference.

METHODS

The authors performed a retrospective radiographic study of a single surgeon’s prospective assessment of osseous fusion during cervical revision surgery by analyzing complete radiographic data in 44 patients who underwent anterior cervical revision surgery due to symptomatic suspected nonunion or adjacent level disease. All patients received standard preoperative CT scans, which were assessed by an independent radiologist to evaluate 9 diagnostic criteria for osseous union. During revision surgery, scar tissue was removed and manual segmental translation tests were performed. Nonunion was defined by visualized motion at the treated ACDF level.

RESULTS

In total, 44 patients were included in the study (30 men; patient age 54 ± 6 years, BMI 28 ± 5 kg/m2). For analysis of fusion, 75 cervical levels were explored, of which 61 levels (81%) showed intraoperative movement indicating nonunion. Statistical analysis showed that of the 9 parameters used to diagnose bone union, “bridging bone on ≥ 3 CT slices” yielded the highest sensitivity (100%) and specificity (58%). Multivariate analysis revealed that prediction accuracy was not increased if several criteria were combined to determine fusion.

CONCLUSIONS

The authors found that the best indicator of bone union was the item bridging bone on ≥ 3 CT slices. Combining the scoring of more than one criterion did not increase the diagnostic accuracy.

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Dueng-Yuan Hueng, Ming-Ying Liu and Hsin-I Ma

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Frank L. Acosta Jr., Jamal McClendon Jr., Brian A. O'Shaughnessy, Heiko Koller, Chris J. Neal, Oliver Meier, Christopher P. Ames, Tyler R. Koski and Stephen L. Ondra

Object

As the population continues to age, relatively older geriatric patients will present more frequently with complex spinal deformities that may require surgical intervention. To the authors' knowledge, no study has analyzed factors predictive of complications after major spinal deformity surgery in the very elderly (75 years and older). The authors' objective was to determine the rate of minor and major complications and predictive factors in patients 75 years of age and older who underwent major spinal deformity surgery requiring a minimum 5-level arthrodesis procedure.

Methods

Twenty-one patients who were 75 years of age or older and underwent thoracic and/or lumbar fixation and arthrodesis across 5 or more levels for spinal deformity were analyzed retrospectively. The medical and surgical records were reviewed in detail. Age, diagnosis, comorbidities, operative data, hospital data, major and minor complications, and deaths were recorded. Factors predictive of perioperative complications were identified by logistic regression analysis.

Results

The mean patient age was 77 years old (range 75–83 years). There were 14 women and 7 men. The mean follow-up was 41.2 months (range 24–81 months). Fifteen patients (71%) had at least 1 comorbidity. A mean of 10.5 levels were fused (range 5–15 levels). Thirteen patients (62%) had at least 1 perioperative complication, and 8 (38%) had at least one major complication for a total of 17 complications. There were no perioperative deaths. Increasing age was predictive of any perioperative complication (p = 0.03). However, major complications were not predicted by age or comorbidities as a whole. In a subset analysis of comorbidities, only hypertension was predictive of a major complication (OR 10, 95% CI 1.3–78; p = 0.02). Long-term postoperative complications occurred in 11 patients (52%), and revision fusion surgery was necessary in 3 (14%).

Conclusions

Patients 75 years and older undergoing major spinal deformity surgery have an overall perioperative complication rate of 62%, with older age increasing the likelihood of a complication, and a long-term postoperative complication rate of 52%. Patients in this age group with a history of hypertension are 10 times more likely to incur a major perioperative complication. However, the mortality risk for these patients is not increased.