Occipital condyle screw placement and occipitocervical instrumentation using three-dimensional image-guided navigation

Safety analysis and complications of condylar screws in a single-surgeon series of 250 occipitocervical fusions

Objective

Condylar screw fixation is a rescue technique and an alternative to the conventional configuration of occipitocervical fusion. Condylar screws are utilized when previous surgical bone removal along the supraocciput has occurred which makes anchoring of a traditional barplate technically difficult or impossible. However, the challenging dissection of C0-1 necessary for condylar screw fixation and the concerns about possible complications have, thus far, prevented the acquisition of large surgical series utilizing occipital condylar screws. In the largest case series to date, this paper aims to evaluate the safety profile and complications of condylar screw fixation for occipitocervical fusion.

Methods

A retrospective safety and complication-based analysis of occipitocervical fusion via condylar screws fixation was performed.

Results

A total of 250 patients underwent occipitocervical fusions using 500 condylar screws between September 2012 and September 2018. No condylar screw pullouts, or vertebral artery impingements were observed in this series. The sacrifice of condylar veins during the dissection at C0-1 did not cause any venous stroke. Hypotrophic condyles were found in 36.4% (91 of the 250) cases and did not prevent the insertion of condylar screws. Two transient hypoglossal deficits occurred at the beginning of this surgical series and were followed by recovery a few months later. Corrective strategies were effective in preventing further hypoglossal injuries.

Conclusions

This surgical series suggests that the use of condylar screws fixation is a relatively safe and reliable option for OC fusion in both adult and pediatric patients. Methodical dissection of anatomical landmarks, intraoperative imaging, and neurophysiologic monitoring allowed the safe execution of the largest series of condylar screws reported to date. Separate contributions will follow in the future to provide details about the long-term clinical outcome of this series.

Occipital condyle screw fixation after posterior decompression for Chiari malformation: Technical report and application

BACKGROUND

Surgical techniques for stabilization of the occipital cervical junction have traditionally consisted of screw-based techniques applied in conjunction with occipital plating and rods connected to subaxial instrumentation in the form of pars, pedicle, or lateral mass screws. In patients with type 1 Chiari malformation (CM-1) and evidence of occipital cervical junction instability who have undergone posterior decompression, the occipital condyle (OC) represents a potential alternative cranial fixation point. To date, this technique has only been described in pediatric case reports and morphometric cadaver studies.

METHODS

Patients underwent posterior fossa decompression for treatment of CM. Subsequently, patients received occipital cervical stabilization using OC screws.

RESULTS

Patients were successfully treated with no post-operative morbidity. Patient 2 was found to have pseudoarthrosis and underwent revision. Both patients continue to do well at 1-year follow-up.

CONCLUSION

Placement of the OC screw offers advantages over traditional plate-based occipital fixation in that bone removal for suboccipital decompression is not compromised by the need for hardware placement, screws are hidden underneath ample soft tissue in patients with thin skin which prevents erosion, and the OC consists of primarily cortical bone which provides for robust tricortical fixation. These cases demonstrate the novel application of the OC screw fixation technique to the treatment of occipital cervical junction instability in adult patients undergoing simultaneous posterior fossa decompression.

Avoiding iatrogenic injuries to the vertebral artery: A morphometric study of the vertebral artery-free dissection area

OBJECTIVE

To determine the area of a safety window that excludes the vertebral artery for the safe access of the occipital condyle screws during occipitocervical fixation.

METHODS

This study included 138 cervical computed tomography angiograms. Six measurements per side were made in each imaging study. These measurements are from the vertebral artery to (A) the mastoid process, (B) the mastoid incisura, (C) the posterior condylar fossa, (D) the occipital condyle in its midline, and (E) the medial border of the condyle. We also measured from the tip of the mastoid process to the lower border of the occipital condyle on its lateral side (F).

RESULTS

A total of 276 areas from 138 individuals were included, of which 51.4 % were men. The mean age was 54.2 ± 18.63 years. The mean variable measurements (mm) for all the population were 21 ± 4, 16 ± 3, 6 ± 2, 3 ± 2, 2 ± 1 and 35 ± 4 for variables A-F, respectively. We found significant differences between sex when we compared measurements A (p = 0.003), C (p = 0.001), D (p = 0.000) and F (p = 0.000). The incidence rate of dominance for the vertebral artery was 18.8 % and 30.4 % for right and left respectively.

CONCLUSION

Women had significantly smaller measures than men. This could indicate a higher risk of iatrogenic injury secondary to a smaller vertebral artery-free area. Results may guide surgeons in the pre-surgical planning aiming to reduce the risk of iatrogenic injuries to the vertebral artery.

Atlanto-Occipital Transarticular Screw Fixation for the Treatment of Traumatic Occipitocervical Instability in the Pediatric Population

BACKGROUND

Atlanto-occipital transarticular screw fixation (AOTSF) has rarely been reported for fixation of the craniovertebral junction (CVJ).

METHODS

A retrospective chart review of all pediatric patients (less than 18 years of age) with an attempt of AOTSF for fixation of traumatic CVJ instability was conducted.

RESULTS

A total of 4 patients (2 boys and 2 girls; ages 2, 3, 5, and 8 years) who suffered from acute traumatic CVJ instability managed during 2007-2018 underwent an attempted AOTSF. In 2 patients, this method was technically successful. In the other 2 instances, we were not able to engage the screw into the occipital condyle. These were converted to standard occipital plate, rod, and screw fixation. All were placed in a halo subsequently for a minimum of 3 months. Three patients were fused at last follow-up (range, 17-48 months). One patient after successful AOTSF did not fuse. There were no surgical complications or revision procedures.

CONCLUSIONS

AOTSF was feasible in half of pediatric patients suffering from traumatic CVJ instability. Therefore, intraoperative salvage options and strategies should be on hand readily. In the pediatric population, where bony anatomy may pose challenges to fixation, this technique may offer a viable first-line option in selected cases, despite the overall modest success rate.

Occipital Condyle Screw Placement in Patients with Chiari Malformation: A Radiographic Feasibility Analysis and Cadaveric Demonstration

OBJECTIVE

Patients who undergo decompression surgery for Chiari malformation frequently require occipitocervical fixation. This is typically performed with occipital plates, which may cause intracranial injuries due to multiple fixation points. We undertook this study to assess the feasibility of occipital condyle (OC) screw placement as an alternative method of occipitocervical fixation in this patient population.

METHODS

Using a cadaveric model with navigational assistance, we performed the complete surgical procedure for occipitocervical fixation with OC screws. We then performed a morphometric analysis using measurements from computed tomography scans of 49 patients (32 adult, 17 pediatric) who had undergone occipitocervical fusion with instrumentation following decompression surgery for Chiari malformation. Bilateral morphometric data were analyzed for the adult and pediatric subgroups separately, as well as for the overall group.

RESULTS

The surgical procedure was successfully performed in the cadaveric model, demonstrating the feasibility of the proposed method. Ninety-eight OCs were studied in the morphometric analysis, and 80 (81.6%) met our eligibility criteria for OC screw placement. However, in 14.1% of adult OCs and 26.5% of pediatric OCs studied, placement of condylar screws would have been challenging or unsafe, according to our criteria.

CONCLUSIONS

Our findings suggest that OC screws provide a useful option for occipitocervical fixation in a substantial proportion of patients with Chiari malformation. However, rigorous preoperative analysis would be essential to identify appropriate candidates for this technique and exclude those in whom it should not be attempted. Additional study is warranted.

CT-based morphometric analysis of the occipital condyle: focus on occipital condyle screw insertion

OBJECTIVE

The segmental occipital condyle screw (OCS) is an alternative fixation technique in occipitocervical fusion. A thorough morphological study of the occipital condyle (OC) is critical for OCS placement. The authors set out to introduce a more precise CT-based method for morphometric analysis of the OC as it pertains to the placement of the segmental OCS, and they describe a novel preoperative simulation method for screw placement. Two new clinically relevant parameters, the height available for the OCS and the warning depth, are proposed.

METHODS

CT data sets from 27 fresh-frozen human cadaveric occipitocervical spines were used. All measurements were performed using a commercially available 3D reconstruction software package. The length, width, and sagittal angle of the condyle were measured in the axial plane at the base of the OC. The height of the OC and the height available for the segmental OCS were measured in the reconstructed oblique sagittal plane, fitting the ideal trajectory of the OCS recommended in the literature. The placement of a 3.5-mm-diameter screw that had the longest length of bicortical purchase was simulated into the OC in the oblique sagittal plane, with the screw path not being blocked by the occiput and not violating the hypoglossal canal cranially or the atlantooccipital joint caudally. The length of the simulated screw was recorded. The warning depth was measured as the shortest distance from the entry point of the screw to the posterior border of the hypoglossal canal.

RESULTS

The mean length and width of the OC were found to be larger in males: 22.2 ± 1.7 mm and 12.1 ± 1.0 mm, respectively, overall (p < 0.0001 for both). The mean sagittal angle was 28.0° ± 4.9°. The height available for the OCS was significantly less than the height of the OC (6.2 ± 1.3 mm vs 9.4 ± 1.5 mm, p < 0.0001). The mean screw length (19.3 ± 1.9 mm) also presented significant sex-related differences: male greater than female (p = 0.0002). The mean warning depth was 7.5 ± 1.7 mm. In 7.4% of the samples, although the height of the OC was viable, the height available for the OCS was less than 4.5 mm, thus making screw placement impractical. For these cases, a new preoperative simulation method of the OCS placement was proposed. In 92.6% of the samples that could accommodate a 3.5-mm-diameter screw, 24.0% showed that the entry point of the simulated screw was covered by a small part of the C-1 posterosuperior joint rim.

CONCLUSIONS

The placement of the segmental OCS is feasible in most cases, but a thorough preoperative radiological analysis is essential and cannot be understated. The height available for the OCS is a more clinically relevant and precise parameter than the height of the OC to enable proper screw placement. The warning depth may be helpful for the placement of the OCS.

Monitoring reduced scattering coefficient in pedicle screw insertion trajectory using near-infrared spectroscopy

Pedicle screw (PS) implantation is an ideal treatment for severe multilevel vertebra instabilities. The accuracy of fixating PS is a key factor of spinal surgery. We developed a near-infrared spectroscopy device with a needlelike optical fiber probe to monitor optical parameters (reduced scattering coefficient) of vertebra models in real time. The fresh-frozen cadaver, cats and porcine vertebras were first studied in the experiments. Moreover, the reduced scattering coefficient (μ' s) along the different trajectories of PS insertion was obtained. In the fresh-frozen cadavera experiment, μ' s values could be used to distinguish the different compositions of the thoracic vertebra. In cat vertebra experiment, μ' s values of vertebrae bones, including cortical bone (15.30 ± 0.18 cm(-1)), cancellous bone (7.84 ± 1.11 cm(-1)) and spinal cord (19.46 ± 0.21 cm(-1)), were different in vivo. In the pig vertebrae experiment, there were obvious differences between the normal and abnormal PS puncture curves based on μ' s values. Thus, μ' s values measured by using the proposed device could be used as the pattern factor in spinal fusion surgery. Our studies demonstrate that near-infrared spectroscopy method may be potentially used for assisting the PS insertion.

Correction of clivoaxial angle deformity in the setting of suboccipital craniectomy: technical note

A subset of patients with Chiari Type I malformation may develop neurological dysfunction secondary to an abnormally obtuse clivoaxial angle (CXA) and clivoaxial deformity causing deformative stress injury to the neural axis. Clivoaxial deformity can occur after initial standard suboccipital craniectomy, duraplasty, and C-1 laminectomy for brainstem compression, or severe clivoaxial deformity may be present in conjunction with a Chiari malformation. Clivoaxial deformity and abnormal CXA can be treated with an occipitocervical fusion (OCF). Performing OCF in the setting of a cranial defect can be challenging with currently available instrumentation. The authors describe their recent experience and outcomes in 3 consecutive pediatric patients using the "inside-out" technique for treating clivoaxial deformity and abnormal CXA in the setting of a craniectomy defect to restore stability to the craniocervical junction, while correcting the CXA.