Computed Tomography-Based Occipital Condyle Morphometry in an Indian Population to Assess the Feasibility of Condylar Screws for Occipitocervical Fusion

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.

An alternative way of C1 screwing: Supralaminar C1 lateral mass screws

Study Design:

This study involves literature review, technical note, and case series.

Objectives:

The objectives were to analyze indications and contraindications, advantages, and disadvantages for C1 lateral mass screw (LMS) insertion above or partially above the arch, to descript technical features, and to give examples of the practical application of this technique and investigated its safety.

Methods:

A literature review was carried out in English and Russian in PubMed, Google Scholar, and eLibrary databases. We selected four patients, treated in our clinic, which was carried out partially supralaminar C1 LMS.

Results:

Only three descriptions of supralaminar C1 LMS were found in the literature. Four adult patients underwent posterior C1–C2 screw fixation with C1 LMS along the superior edge of the C1 arch at our clinic. Partially supralaminar C1 screws were inserted on one of the sides due to the difficulties of using classical techniques. The main reasons for supralaminar screw fixation were narrow C1 lamina, hypertrophied venous plexus, and intraoperative failures of classic techniques application (broken screw trajectory, profuse venous bleeding from the plexus). The average follow-up time for the patients was 2.7 years, no complications were noted, and all had a satisfactory spinal fusion.

Conclusions:

The proposed types of C1 LMS above or partially above the C1 arch can be useful alternative method of C1 screwing in selected patients. Indications for the use of the supralaminar C1 LMS method can be narrow C1 posterior arch and pedicle, pronounced C1-C2 venous plexus, some V3 segment anomalies at C1 level, small arthritic inferior part of lateral mass, and intraoperative failures of classic techniques application.

Feasibility of occipital condyle screw placement in patients with Chiari malformation type I: a computed tomography-based morphometric study

BACKGROUND

The occipital condyle (OC) screw is an alternative technique for occipitocervical fixation that is especially suitable for revision surgery in patients with Chiari malformation type I (CMI). This study aimed to investigate the feasibility and safety of this technique in patients with CMI.

METHODS

The CT data of 73 CMI patients and 73 healthy controls were retrospectively analyzed. The dimensions of OCs, including length, width, height, sagittal angle, and screw length, were measured in the axial, sagittal, and coronal planes using CT images. The OC available height was measured in the reconstructed oblique parasagittal plane of the trajectory.

RESULTS

The mean length, width, and height of OCs in CMI patients were 17.79 ± 2.31 mm, 11.20 ± 1.28 mm, and 5.87 ± 1.29 mm, respectively. All OC dimensions were significantly smaller in CMI patients compared with healthy controls. The mean screw length and sagittal angle were 19.13 ± 1.97 mm and 33.94° ± 5.43°, respectively. The mean OC available height was 6.36 ± 1.59 mm. According to criteria based on OC available height and width, 52.1% (76/146) of OCs in CMI patients could safely accommodate a 3.5-mm-diameter screw.

CONCLUSIONS

The OC screw is feasible in approximately half of OCs in CMI patients. Careful morphometric analyses and personalized surgical plans are necessary for the success of this operation in CMI patients.

Occipital condyle screw fixation viability according to age and gender anatomy: A computed tomography-based analysis

OBJECTIVE

To assess the Occipital condyle morphology in an all-age population of Northeastern Mexico, and determine age and gender related changes for surgical viability.

METHODS

A total of 175 consecutive HRCT scans were included and divided into 5 age groups. The condylar length, width, height, sagittal angle, anterior, posterior and medial intercondylar distances, and intercondylar angle of the OC were measured.

RESULTS

Mean condylar length, width, and height in total population were 20.58 mm, 9.42 mm, and 9.02 mm, respectively. Differences were observed in most morphometric parameters when comparing age groups. Significant intergender differences in total population were observed in most parameters, when individualizing each age group the height remained significant in all. The group with the least height measurement was aged 5-9 years, this however, could allow the OC screw (≥6.5 mm) placement.

CONCLUSION

Differences in most morphometric parameters of OC were observed between age groups and gender, particularly patients with 5-9 years. However, all groups presented a minimum height that allows the placement of a standard screw. A preoperative imaging study is always recommended due to the variability and complexity of the region.

Safe trajectory for an occipital condyle screw: A computer simulation study

OBJECTIVE

The purpose of this study was to evaluate the feasibility of posterior occipital condyle screw (OCS) placement analysis of the safe trajectory area for screw insertion.

METHODS

Computed tomographic angiography scans of patients (46 males and 27 females) with normal occipitocervical structures were obtained consecutively. Vertebral artery (VA)-occiput distance <4.0 mm was defined as "unfeasible" for OCS fixation, and occipital-atlas angulation was measured to assess the feasibility of screw placement. Next, the placement of 3.5 mm diameter OCS was simulated, the probability of breach of structures surrounding occipital condyles was calculated, and placement parameters were analyzed.

RESULTS

OCS placement was feasible in 91.1% (133/146) of occipital condyles, and the feasible probability also presented a significant sex-related difference: The probability was higher for males than for females (95.7% vs. 83.3%, p < 0.05). The incidence of anatomical structures injured under screw placement limitation was 18.8% (VA), 81.2% (hypoglossal canal), 59.4% (occipital-atlas joint), and 40.6% (occiput bone surface). There were no significant differences between the left and right condyles in relation to the measured parameters (p > 0.05). The screw range of motion was significantly smaller in females than in males (p < 0.05). The feasibility of OCS placement and OCS range of motion were significantly greater in the kyphosis group (>5°) than in the other two groups (p < 0.05).

CONCLUSION

OCS placement is a feasible technique for occipital-cervical fusion. The male group and occipitocervical region kyphosis group had a wider available space for OCS placement. Tangent angulation may be useful for the accurate and safe placement of an OCS.

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.

Morphometric analysis of occipital condyles using alternative imaging technique

PURPOSE

The occipital condyles (OCs) are crucial anatomical structures in the cranial base. To our knowledge, there is no cone beam computed tomography (CBCT)-based study on the morphometric analysis of OCs. The aim of this study was to evaluate the morphometric analysis of OCs using CBCT.

METHODS

CBCT images of 200 OCs from 100 patients of which 39 males and 61 females in the age group of 18-67 years were included in the study population. Linear and angular measurements of OCs were performed.

RESULTS

The average OC width, length, height, sagittal angle, and effective height were 10.3 ± 1.3 mm, 19.6 ± 2.0 mm, 9.1 ± 1.4 mm, 7.4 ± 1.7 mm, and 35.3 ± 5.2 mm. Condylar width and sagittal angle measurements were found significantly different between the right and left sides; and were not found significant difference between the right and left sides in the measurements of condylar height, length, and effective height. Also the average intercondylar anterior distance (ICAD), intercondylar posterior distance (ICPD), distance between the basion and the anterior apex of the occipital condyle (B-AAOC), distance between the basion and posterior apex of the occipital condyle (B-PAOC), distance between the opisthion and anterior apex of occipital condyle (O-AAOC), and distance between the opisthion and posterior apex of occipital condyle (O-PAOC) were 20.9 ± 1.5 mm, 44.0 ± 2.0 mm, 12.3 ± 1.9 mm, 34.5 ± 4.2 mm, 29.8 ± 1.7 mm, and 27.0 ± 2.1 mm. There was not significant difference in the morphometric measurements among age groups. All morphometric measurements showed a significant difference depending on gender.

CONCLUSIONS

The morphometric evaluation of OCs may be effectively examined using CBCT. Linear and angular measurements data of OCs in the present study may be used as a reference database for future morphometric and surgical investigations.

Feasibility of Sub-Axial Cervical Laminar Screws, Including C7, in the Indian Population: A Study on 50 Patients Using Computed Tomography-Based Morphometry Measurements

STUDY DESIGN

Observational study of computed tomography (CT) data.

PURPOSE

We performed a CT-based radiographic analysis of sub-axial cervical lamina in the Indian population to assess the feasibility of laminar screws.

OVERVIEW OF LITERATURE

Morphometric studies have been performed for populations of various ethnic groups, but none exist for Indian populations.

METHODS

Cervical spine CT scans of 50 adults with a minimum slice thickness of <2 mm (0.5-2 mm) were obtained from the database of a single center in northern India. Measurements (e.g., length, thickness, and height) were taken in millimeters along the axial, coronal, and sagittal planes. Three measurements were made to assess laminar anatomy, namely, the translaminar/screw length, laminar thickness, and sagittal laminar height.

RESULTS

The final sample comprised 500 laminae in 50 patients, resulting in 1,500 measurements. The mean translaminar lengths of the C3, C4, C5, C6, and C7 laminae were 19.48 mm, 19.60 mm, 19.61 mm, 20.49 mm, and 22.85 mm, respectively. The mean thick- , 19.60 , 19.60 mm, 19.61 mm, 20.49 mm, and 22.85 mm, respectively. The mean thick- mm, 19.61 mm, 20.49 mm, and 22.85 mm, respectively. The mean thick- , 19.61 , 19.61 mm, 20.49 mm, and 22.85 mm, respectively. The mean thick- mm, 20.49 mm, and 22.85 mm, respectively. The mean thick- , 20.49 , 20.49 mm, and 22.85 mm, respectively. The mean thick- mm, and 22.85 mm, respectively. The mean thick- , and 22.85 mm, respectively. The mean thick , and 22.85 mm, respectively. The mean thicknesses of these cervical laminae were 3.12 mm, 2.62 mm, 2.56 mm, 3.47 mm, and 5.20 mm, respectively. The mean sagittal heights of these laminae were 9.38 mm, 9.80 mm, 10.12 mm, 11.31 mm, and 13.84 mm, respectively. Except for the C7 vertebrae, all other levels had a success rate of <10% in the Indian population using the criteria of a laminar height of at least 9 mm and thickness of 4.5 mm. Limited success was achieved at the C5, C6, and C3 levels.

CONCLUSIONS

To the best of our knowledge, the present study is the only series on the feasibility of laminar screws in the sub-axial cervical spine in the Indian population. We found that Indian patients have smaller anatomical dimensions and thus, are not suitable for laminar screws in the sub-axial cervical spine, barring C7, which is contrary to findings for populations in western and south Asian countries.