The use of pedicle screw-rod system for the posterior fixation in cervico-thoracic junction

Pedicle morphometry of the C7 and T1 vertebrae in an argentine population

Background

We evaluated how and whether the pedicular morphometry of the C7 and T1 vertebrae might impact C7/T1 spinal fusions for patients from Argentina.

Methods

Using computed tomography (CT) scans, we evaluated the pedicular morphology at the C7 and T1 levels.

Results

Among 102 male and female CT studies, we observed significant differences in the height, width, length, and morphometry of the C7 and T1 pedicles.

Conclusion

This study of C7/T1 CT scans revealed significant sex-based morphometric differences, particularly in pedicle height, width, and length at C7 and T1. Given the notable variability in vertebral characteristics observed in our study sample, we recommend preoperative planning with CT scans for C7/T1 fusion.

Modified pedicle screw fixation under guidance of stress analysis for cervicothoracic junction: Surgical technique and outcomes

BACKGROUND

In cervicothoracic junction, the use of strong fixation device such as pedicle screw placement is often needed.

OBJECTIVE

The current study aimed to evaluate the accuracy and safety of pedicle screw placement using stress conduction analysis in the clinical application.

METHODS

We retrospectively collected patients who underwent pedicle screw internal fixation in cervicothoracic junction. Patients were divided into conventional nail placement (Group A) and modified pedicle screw implantation under guidance of stress analysis (Group B) according to the methods of pedicle screw placement. The accuracy of pedicle screw placement was assessed by computed tomography (CT) examination, and the success rate was calculated.

RESULTS

A total of 80 patients who underwent pedicle screw internal fixation in cervicothoracic junction were included. There were no obvious differences in baseline characteristics between two groups. The success rate of total screw placement, cervical spine screw placement and upper thoracic spine screw placement in Group B was higher than those in Group A (P< 0.001, P= 0.005, P= 0.008). Additionally, Heary Grade I in the Group B was higher than Group A (P= 0.001).

CONCLUSION

Stress analysis-guided technique can increase the accuracy of pedicle screw placement. Importantly, it meets the requirements of internal fixation of the cervicothoracic junction.

C7 intra-laminar screws for complex cervicothoracic spine surgery-a case series

Background

C7 has relatively unique anatomy compared to the remainder of the subaxial cervical spine (C3-C6) and upper thoracic spine. The C7 laminar has been previously reported in feasibility and biomechanical studies as an adequate fixation point in contrast to the lateral mass or pedicles, with few reports of its use in clinical practice. The purpose of this study was to review the safety and efficacy of using the C7 laminar as a fixation point in constructs involving the cervical spine and cervicothoracic junction.

Methods

Between February 2013 and July 2016, 10 patients (6 males, 4 females) had 19 C7 intra-laminar screws sited (bilateral in 9 patients, unilateral in 1 patient). Six patients had trauma as an underlying etiology, 2 of which had pseudoarthrosis from prior surgery. Three patients had cervical myelopathy from degenerative disease, 2 of which required anterior and posterior instrumentation for correction of deformity and 1 which had stand-alone posterior fixation. One patient had stabilization for an underlying malignancy.

Results

One patient died 2 weeks following their high cervical injury secondary to complications of respiratory failure. None of the remaining 9 patients were noted to have construct failure at a median follow up of 1 year (range, 6 months to 4 years) and all were noted to have satisfactory positioning of the instrumentation on post-operative imaging. The patient with malignancy died 6 months later from extra-spinal disease, there was one wound breakdown requiring debridement without infection in a revision case, and one patient required laminectomy for post-traumatic syrinx formation.

Conclusions

The C7 laminar provides an alternative fixation point for constructs involving the subaxial cervical spine and cervicothoracic junction, with excellent safety and efficacy in this small series. Larger series are required to more clarify the risk profile of this technique.

Posterior Rigid Instrumentation of C7: Surgical Considerations and Biomechanics at the Cervicothoracic Junction. A Review of the Literature

BACKGROUND

The cervicothoracic junction is a challenging anatomic transition in spine surgery. It is commonly affected by different types of diseases that may significantly impair stability in this region. The seventh cervical vertebra (C7) is an atypical cervical vertebra with unique anatomic features compared to subaxial cervical spine (C3 to C6). C7 has relatively broader laminae, larger pedicles, smaller lateral masses, and a long nonbifid spinous process. These features allow a variety of surgical methods for performing posterior rigid instrumentation in the form of different types of screws, such as lateral mass screws, pedicle screws, transfacet screws, and intralaminar screws. Many biomechanical studies on cadavers have evaluated and compared different types of implants at C7.

METHODS

We reviewed PubMed/Medline by using specific combinations of keywords to summarize previously published articles that examined C7 posterior rigid instrumentation thoroughly in an experimental fashion on patients or cadavers with additional descriptive radiologic parameters for evaluation of the optimum surgical technique for each type.

RESULTS

A total of 44 articles were reported, including 22 articles that discussed anatomic considerations (entry points, sagittal and axial trajectories, and features of screws) and another 22 articles that discussed the relevant biomechanical testing at this transitional region if C7 was directly involved in terms of receiving posterior rigid implants.

CONCLUSIONS

C7 can accommodate different types of screws, which can provide additional benefits and risks based on availability of bony purchase, awareness of surgical technique, biomechanics, and anatomic considerations.

Which salvage fixation technique is best for the failed initial screw fixation at the cervicothoracic junction? A biomechanical comparison study

PURPOSE

The pedicle screw construct is the most widely used technique for instrumentation at cervicothoracic junction (CTJ) because of its high biomechanical stability. However, we may need salvage fixation options for it as there might be a situation when pedicle screw is not available or it initially fails in order to obviate the need to instrument an additional motion segment. We aimed to evaluate the ability of using salvage screw fixations at CTJ (C7, T1, T2), when the initial fixation method fails.

METHODS

Fifteen fresh-frozen cadaveric specimens (C7-T2) were tested for pull-out strength (POS, N) and insertion torque (IT, Nm) of three C7 fixation techniques (lateral mass, pedicle and laminar screw) and three upper thoracic spine instrumentation (pedicle screws with straight trajectory, anatomical trajectory pedicle screws and laminar screw). Data are shown as mean ± standard deviation (SD).

RESULTS

C7 pedicle screws generated statistically greater IT and POS than other C7 fixation techniques (P < 0.05). Similar trends were observed with pedicle fixation as a salvage procedure (P < 0.05). Laminar screws yielded significantly higher POS values than lateral mass fixation when applied as a salvage C7 fixation (mean POS: lateral mass screw-299.4 ± 173.8 N, laminar screw-629.3 ± 216.1, P = 0.013). Significant relationship was established between IT and POS for all screws using Pearson correlation coefficient analysis (r = 0.624, P < 0.01). Pedicle screw with different trajectory (anatomical vs straightforward) did not show any significant difference in terms of POS as the initial and salvage fixation of upper thoracic spine. As a salvage fixation technique, there was no significant difference between laminar screw and a pedicle screw with different trajectory (P > 0.05).

CONCLUSION

Laminar screws appear to provide stronger and more reproducible salvage fixation than lateral mass screws for C7 fixation, if pedicle screw should fail. If failure of initial pedicle screw is verified at the upper thoracic spine, both laminar screw and pedicle screw with different trajectory could be an option of salvage fixation. Our results suggest that pedicle screws and laminar screw similarly provide a strong fixation for salvage applications in the cervicothoracic junction.

Easy method to simplify "freehand" subaxial cervical pedicle screw insertion

Study Design:

Technical note.

Objectives:

The objective of this study is to check out safety and rationality of standardized and fast tricks to select trajectory of subaxial cervical pedicle screw (SCPS) insertion, based on simple angles to bony landmarks.

Materials and Methods:

Stage 1 – Computed tomography (CT)-morphometric analysis of C3–C7 vertebrae of ten patients with cervical degenerative diseases. Stage 2 – SCPS insertion in 6 cadavers, according to the developed technique (59 pedicle screws). Stage 3 – SCPS insertion in 6 patients, according to the developed technique (32 pedicle screws).

Results:

CT-morphometric analysis showed that the average length of C3–C7 pedicle channels was 32 mm, the average angle between a pedicle axis and an axis of contralateral lamina - 180°, the average angle between a pedicle axis and plane of a posterior surface of a lateral mass amounted to 90° and the coordinates of an optimal entry point – 2 mm from a lateral edge and 2 mm from an upper edge of the lateral mass posterior surface. During the cadaveric study, 39 screws had a satisfactory position (66.1%), 7 screws permissible (11.9%), and 13 screws unacceptable (22%). During the clinical study, 26 screws (81.25%) had satisfactory position, 4 (12.5%) had permissible position, and 2 (6.25%) unacceptable position.

Conclusion:

Developed and clinically approved a method for simplicity SCPS insertion is relatively safe and cheap. No doubt, it requires further investigation, but the results of primary analysis allow us to recommend it to wide practical application.

Reoperation rates for symptomatic nonunions in posterior cervicothoracic fusions with and without bone morphogenetic protein in a cohort of 450 patients

OBJECTIVE

Fusions across the cervicothoracic junction have been challenging because of the large biomechanical forces exerted resulting in frequent reoperations for nonunions. The objective of this study was to investigate a retrospective cohort using chart review of posterior cervicothoracic spine fusions with and without bone morphogenetic protein (BMP) and to determine the reoperation rates for symptomatic nonunions in both groups.

METHODS

Between January 2009 and September 2013, posterior cervicothoracic spine fusion cases were identified from a large spine registry (Kaiser Permanente). Demographics, diagnoses, operative times, lengths of stay, and reoperations were extracted from the registry. Reoperations for symptomatic nonunions were adjudicated via chart review. Logistic regression was used to estimate odds ratios and 95% confidence intervals. Kaplan-Meier curves for the non-BMP and BMP groups were generated and compared using the log-rank test.

RESULTS

In this cohort there were 450 patients (32.7% with BMP) with a median follow-up of 1.4 years (interquartile range [IQR] 0.5–2.7 years). Kaplan-Meier curves showed no significant difference in reoperation rates for nonunions using the log-rank test (p = 0.088). In a subset of patients with more than 1 year of follow-up, 260 patients were identified (43.1% with BMP) with a median follow-up duration of 2.4 years (IQR 1.6–3.3 years). There was no statistically significant difference in the symptomatic operative nonunion rates for posterior cervicothoracic fusions with and without BMP (0.0% vs 2.7%, respectively; p = 0.137) for more than 1 year of follow-up.

CONCLUSIONS

This study presents the largest series of patients using BMP in posterior cervicothoracic spine fusions. Reoperation rates for symptomatic nonunions with more than 1 year of follow-up were 0% with BMP and 2.7% without BMP. No statistically significant difference in the reoperation rates for symptomatic nonunions with or without BMP was found.

Impact of dynamic alignment, motion, and center of rotation on myelopathy grade and regional disability in cervical spondylotic myelopathy

OBJECT

Cervical stenosis is a defining feature of cervical spondylotic myelopathy (CSM). Matsunaga et al. proposed that elements of stenosis are both static and dynamic, where the dynamic elements magnify the canal deformation of the static state. For the current study, the authors hypothesized that dynamic changes may be associated with myelopathy severity and neck disability. This goal of this study was to present novel methods of dynamic motion analysis in CSM.

METHODS

A post hoc analysis was performed of a prospective, multicenter database of patients with CSM from the AOSpine North American study. One hundred ten patients (34%) met inclusion criteria, which were symptomatic CSM, age over 18 years, baseline flexion/extension radiographs, and health-related quality of life (HRQOL) questionnaires (modified Japanese Orthopaedic Association [mJOA] score, Neck Disability Index [NDI], the 36-Item Short Form Health Survey Physical Component Score [SF-36 PCS], and Nurick grade). The mean age was 56.9 ± 12 years, and 42% of patients were women (n = 46). Correlations with HRQOL measures were analyzed for regional (cervical lordosis and cervical sagittal vertical axis) and focal parameters (kyphosis and spondylolisthesis between adjacent vertebrae) in flexion and extension. Baseline dynamic parameters (flexion/extension cone relative to a fixed C-7, center of rotation [COR], and range of motion arc relative to the COR) were also analyzed for correlations with HRQOL measures.

RESULTS

At baseline, the mean HRQOL measures demonstrated disability and the mean radiographic parameters demonstrated sagittal malalignment. Among regional parameters, there was a significant correlation between decreased neck flexion (increased C2–7 angle in flexion) and worse Nurick grade (R = 0.189, p = 0.048), with no significant correlations in extension. Focal parameters, including increased C-7 sagittal translation overT-1 (slip), were significantly correlated with greater myelopathy severity (mJOA score, Flexion R = −0.377, p = 0.003; mJOA score, Extension R = −0.261, p = 0.027). Sagittal slip at C-2 and C-4 also correlated with worse HRQOL measures. Reduced flexion/extension motion cones, a more posterior COR, and smaller range of motion correlated with worse general health SF-36 PCS and Nurick grade.

CONCLUSIONS

Dynamic motion analysis may play an important role in understanding CSM. Focal parameters demonstrated a significant correlation with worse HRQOL measures, especially increased C-7 sagittal slip in flexion and extension. Novel methods of motion analysis demonstrating reduced motion cones correlated with worse myelopathy grades. More posterior COR and smaller range of motion were both correlated with worse general health scores (SF-36 PCS and Nurick grade). To our knowledge, this is the first study to demonstrate correlation of dynamic motion and listhesis with disability and myelopathy in CSM.

Construct Type and Risk Factors for Pseudarthrosis at the Cervicothoracic Junction

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

The primary goal is to compare the clinical results of 2 types of constructs commonly used at the cervicothoracic junction: small rods (3.2-mm/3.5-mm rods) or transitional constructs. The secondary goal is to perform a case-control study of risk factors for pseudarthrosis at the cervicothoracic junction.

SUMMARY OF BACKGROUND DATA

Various constructs have been used to stabilize across the cervicothoracic junction; however, no study to date has objectively compared their outcome. Our hypothesis was that both constructs would have similar fusion and complication rates.

METHODS

A retrospective review of a prospectively collected database revealed 135 patients with the aforementioned constructs and having followed up with imaging at 6 months, 12 months, and 24 months. Univariate analysis comparing the 2 different construct groups was performed. Multivariate analysis for risk factors of pseudarthrosis was also performed.

RESULTS

There were a total of 10 patients with pseudarthrosis at 2-year follow-up. There was no difference in pseudarthrosis rate between the small rods (7%) and transitional constructs (8.6%) (P = 0.99). The overall construct lengths were similar (5.8 levels in small rods, 6.7 levels in transitional construct). Blood loss was higher in transitional constructs (574 ± 69 mL) than in small rods (236 ± 53 mL) (P < 0.001). Transitional constructs also had longer operating times (249 min) than small rods (207 min) (P < 0.03). Overall complication rate was higher in the transitional constructs (P < 0.03). Tobacco use, corpectomy, lack of an anterior construct, and construct length were all risk factors for cervicothoracic junction pseudarthrosis in the multivariate analysis.

CONCLUSION

Overall pseudarthrosis rates were similar between small rods and transitional constructs. There was higher complications rate, blood loss, and operating time associated with transitional constructs. Pseudarthrosis risk factors at the cervicothoracic junction include tobacco use, corpectomy, lack of an anterior construct, and longer constructs.

LEVEL OF EVIDENCE

3.