Cadaveric study for placement of occipital condyle screws: technique and effects on surrounding anatomic structures

A Novel Technique for Basilar Invagination Treatment in a Patient with Klippel-Feil Syndrome: A Clinical Example and Brief Literature Review

Objectives and Background: To present a novel technique of treatment for a patient with basilar invagination. Basilar invagination (BI) is a congenital condition that can compress the cervicomedullary junction, leading to neurological deficits. Severe cases require surgical intervention, but there is debate over the choice of approach. The anterior approach allows direct decompression but carries high complication rates, while the posterior approach provides indirect decompression and offers good stability with fewer complications. Materials and Methods: A 15-year-old boy with severe myelopathy presented to our hospital with neck pain, bilateral upper limb muscle weakness, and hand numbness persisting for 4 years. Additionally, he experienced increased numbness and gait disturbance three months before his visit. On examination, he exhibited hyperreflexia in both upper and lower limbs, muscle weakness in the bilateral upper limbs (MMT 4), bilateral hypoesthesia below the elbow and in both legs, mild urinary and bowel incontinence, and a spastic gait. Radiographs revealed severe basilar invagination (BI). Preoperative images showed severe BI and that the spinal cord was severely compressed with odontoid process. Results: The patient underwent posterior surgery with the C-arm free technique. All screws including occipital screws were inserted into the adequate position under navigation guidance. Reduction was achieved with skull rotation and distraction. A follow-up at one year showed the following results: Manual muscle testing results and sensory function tests showed almost full recovery, with bilateral arm recovery (MMT 5) and smooth walking. The cervical Japanese Orthopedic Association score of the patient improved from 9/17 to 16/17. Postoperative images showed excellent spinal cord decompression, and no major or severe complications had occurred. Conclusions: Basilar invagination alongside Klippel-Feil syndrome represents a relatively uncommon condition. Utilizing a posterior approach for treating reducible BI with a C-arm-free technique proved to be a safe method in addressing severe myelopathy. This novel navigation technique yields excellent outcomes for patients with BI.

Anterior occipital condyle screw placement through the endonasal corridor: proof of concept study with cadaveric analysis

PURPOSE

Odontoidectomy for ventral compressive pathology may result in O-C1 and/or C1-2 instability. Same-stage endonasal C1-2 spinal fusion has been advocated to eliminate risks associated with separate-stage posterior approaches. While endonasal methods for C1 instrumentation and C1-2 trans-articular stabilization exist, no hypothetical construct for endonasal occipital instrumentation has been validated. We provide an anatomic description of anterior occipital condyle (AOC) screw endonasal placement as proof-of-concept for endonasal craniocervical stabilization.

METHODS

Eight adult, injected cadaveric heads were studied for placing 16 AOC screws endonasally. Thin-cut CT was used for registration. After turning a standard inferior U-shaped nasopharyngeal flap endonasally, 4 mm × 22 mm AOC screws were placed with a 0° driver using neuronavigation. Post-placement CT scans were obtained to determine: site-of-entry, measured from the endonasal projection of the medial O-C1 joint; screw angulation in sagittal and axial planes, proximity to critical structures.

RESULTS

Average site-of-entry was 6.88 mm lateral and 9.74 mm rostral to the medial O-C1 joint. Average angulation in the sagittal plane was 0.16° inferior to the palatal line. Average angulation in the axial plane was 23.97° lateral to midline. Average minimum screw distances from the jugular bulb and hypoglossal canal were 4.80 mm and 1.55 mm.

CONCLUSION

Endonasal placement of AOC screws is feasible using a 0° driver. Our measurements provide useful parameters to guide optimal placement. Given proximity of hypoglossal canal and jugular bulb, neuronavigation is recommended. Biomechanical studies will ultimately be necessary to evaluate the strength of AOC screws with plate-screw constructs utilizing endonasal C1 lateral mass or C1-2 trans-articular screws as inferior fixation points.

C1 Lateral Mass Screw Placement Through Endonasal Corridor for Purpose of O-C1 Fusion: Morphometric Analysis in Cadaveric Specimens

BACKGROUND

Odontoidectomy may pose some risks for O-C1 and/or C1-C2 instability, with previous authors reporting techniques for endonasal C1-C2 fusion. However, no technique for endonasal O-C1 fusion currently exists. We sought to describe the feasibility of endonasal anterior C1 (AC1) screw placement for endonasal O-C1 fusion.

METHODS

Seven adult cadaveric heads were studied for endonasal placement of 14 C1 screws. Using thin-cut computed tomography (CT)-based "snapshot" neuronavigation assistance, 4 mm x 22 mm screws were placed in the C1 lateral mass using a 0° driver. Post-placement CT scans were obtained to determine site-of-entry measured from C1 anterior tubercle, screw angulation in axial and sagittal planes, and screw proximity to the central canal and foramen transversarium.

RESULTS

Average site-of-entry was 16.57 mm lateral, 2.23 mm rostral, and 5.53 mm deep to the anterior-most portion of the C1 ring. Average axial angulation was 19.49° lateral to midline, measured at the C1 level. Average sagittal angulation was 13.22° inferior to the palatal line, measured from the hard palate to the opisthion. Bicortical purchase was achieved in 11 screws (78.6%). Partial breach of the foramen transversarium was observed in 2 screws (14.3%), violation of the O-C1 joint space in 1 (7.1%), and violation of the central canal in 0 (0%). Average minimum screw distances from the unviolated foramen transversaria and central canal were 1.97 mm and 4.04 mm.

CONCLUSIONS

Navigation-assisted endonasal placement of AC1 screws is feasible. Additional studies should investigate the biomechanical stability of anterior C1 screw-plating systems, with anterior condylar screws as superior fixation point, compared to traditional posterior O-C1 fusion.

Anatomical Parameters for Occipital Condyle Screws: An Analysis of 500 Condyles Using CT Scans

STUDY DESIGN

Retrospective observational study.

OBJECTIVE

To establish occipital condyle dimensions (length, width, height), as well as the medialization angle necessary for safe occipital condyle screw placement in occipitocervical fixation.

METHODS

Between 1/2014-6/2014, patients who presented to a single level 1 academic trauma center emergency room and received computed tomography (CT) imaging of the cervical spine as part of routine clinical care were identified. After excluding patients with cervical fractures, neoplastic disease, or infection, 500 condyles representing 250 patients were analyzed. Condyle length, height, and width (all reported in millimeters [mm]) were evaluated on the sagittal, coronal, and axial series, respectively. Medialization angle (reported in degrees) was evaluated on the axial series of CT imaging. Measurements were compared by sex and age.

RESULTS

The average condyle length, width, and height were 18.6 millimeters (mm) (range, 14.5-23.0 mm), 10.5 mm (range, 7.4-13.8 mm), and 11.3 mm (7.1-15.3 mm), respectively. Additionally, the average occipital condyle medialization angle was 23° (range, 14-32°). Occipital condyles of men were significantly longer, wider, and taller (all comparisons, p < 0.05). The medialization angle was significantly steeper for women than men (p < 0.05). No measurement differences were appreciated by age.

CONCLUSION

Our findings are similar to previous studies in the field; however, length appears slightly shorter. Further, measurement differences were appreciated by sex but not age. Thus, our measurement findings emphasize the importance of preoperative planning utilizing individual patient anatomy to ensure safe placement of occipital condyle screws for optimal outcomes.

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.

Electromyographic assessment of condylar screw placement during occipitocervical fusion

OBJECTIVE

This is a retrospective study of a series of occipitocervical fusion procedures with condylar screw fixation in which the authors investigated the utility of electromyography (EMG, free-running and triggered) as a reliable tool in assessing the positioning of condylar screws. This series consisted of 197 patients between 15 and 60 years of age who presented with craniocervical instability, and who were treated between October 2014 and December 2017.

METHODS

Intraoperative free-running EMG was observed at the placement of condylar screws, as well as at realigning of the spine. After placement the condylar screws were stimulated electrically, and the thresholds were recorded. CT scans were obtained intraoperatively soon after screw stimulation, and the results were analyzed by the surgeon in real time. Free-running EMG results and triggered EMG thresholds were tabulated, and the minimum acceptable threshold was established.

RESULTS

Intraoperative free-running EMG and triggered EMG were able to correlate alerts with condylar screw placement accurately. A triggered EMG threshold of 2.7 mA was found to be a minimum acceptable threshold. A combination criterion of free-running EMG and triggered EMG alerts was found to enable accurate assessment of condylar screw positioning and placement.

CONCLUSIONS

Intraoperative free-running EMG and triggered EMG were both found to be invaluable utilities in assessing the placement and positioning of condylar screws. Stimulation thresholds below 2.7 mA correlated with a superior or anterior condylar breach. Thresholds in the 2.7-mA to 9.0-mA range were generally acceptable but warranted additional inspection by the surgeon. Threshold values above 9.0 mA corresponded with solid condylar screw placement.

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.

The Feasibility of Anterior Occipital Condyle Screw for the Reconstruction of Craniovertebral Junction: A Digital Anatomical and Cadaveric Study of a Novel Technique

Background

Anterior occipital condyle screw (AOCS) could be a feasible alternative technique for occipitocervical fusion for reconstruction of craniovertebral junction. This study aimed to analyze the feasibility of AOCS.

Methods

The craniovertebral junction computed tomography (CT) scans of 40 adults were enrolled and imported into Mimics software. Then, the three-dimensional reconstruction digital model of craniovertebral junction was established to determine entry point, insertion angle, and screw’s trajectory. After AOCS insertion into ten human cadaver spine specimens, CT scans were performed to verify the location between screws and important structures.

Results

The optimal entry point was located caudally and medial to the ventral of occipital condyle. The optimal trajectory was in inclination angle (5.9°±3.4°) in the sagittal plane and divergence angle (26.7°±6.0°) in the axial plane with the screw length around 21.6±1.2mm. None of the screws invaded the hypoglossal canal and vertebral artery in any of the specimens.

Conclusion

AOCS fixation is a feasible, novel technique for anterior craniovertebral junction reconstruction, and it could be an effective alternative operation for anterior reconstruction with titanium mesh cage.

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.

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 screws: indications and technique

Occipitocervical instability is a life threatening and disabling disorder caused by a myriad of pathologies. Restoring the anatomical integrity and stability of the occipitocervical junction (OCJ) is essential to achieve optimal clinical outcomes. Surgical stabilization of the OCJ is challenging and technically demanding. There is a paucity of options available for anchorage in the cephalad part of the construct in occipitocervical fixation systems due to the intricate topography of the craniocervical junction combined with the risk of injury to the surrounding anatomical structures. Surgical techniques and instrumentation for stabilizing the unstable OCJ have undergone several modifications over the years and have primarily depended on occipital squama-based fixations. At present, the occipital-plate-screw-rod construct is the most commonly adopted technique of stabilizing the OCJ. In certain distinct scenarios like posterior fossa craniectomy (absence of occipital squama for screw placement), malignancy and infection of occipital squama (poor screw purchase in the diseased occipital bone) and in revision surgery for failed occipitocervical stabilization, occipital plate-based instrumentation is not feasible. To overcome these difficulties, recently, a novel technique of occipitocervical stabilization, using the occipital condyle (OC) as the cephalad anchor, namely the direct occipital condyle screw (OCS) fixation was described. Several cadaveric and biomechanical studies have suggested that OCSs are feasible options as additional augmentative anchors in a standard occipital plate-screw-rod construct or as salvage cephalad anchors in previous failed occipital-plate-screw-rod constructs. The OCS placement technique has a steep learning curve. We have done a review of the techniques of OCS fixation and have described the indications, biomechanical and technical considerations, preoperative planning, surgical technique, complications, advantages and limitations of OCS based occipitocervical fixation.

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.

Basilar invagination associated with chiari malformation type I: A literature review

Basilar invagination (BI) and Chiari malformation type I (CM-I) are very important anomalies that introduce instability and compression in the occipitocervical transition region and have complex clinical characteristics. These anomalies vary according to the affected structures. The present study revises current knowledge regarding the anatomy, anatomo-physiology, clinical manifestations, and radiological findings of these entities and the associated surgical treatment approaches. A bibliographic survey was performed through a search in the Medline, PubMed, SciELO, Science and LILACS databases. When associated, these craniovertebral malformations result in neurological deficits due to neural parenchyma compression; however, the presence of microtraumas due to repetitive lesions caused by the bulb and cervical marrow instability has been highlighted as a determinant dysfunction. Surgical treatment is controversial and has many technical variations. Surgery is also challenging due to the complex anatomical characteristics and biomechanics of this region. Nevertheless, advances have been achieved in our understanding of related mechanisms, and compression and atlantoaxial instability are considered key elements when selecting the surgical approach.

Morphometric Evaluation of Occipital Condyles: Defining Optimal Trajectories and Safe Screw Lengths for Occipital Condyle-Based Occipitocervical Fixation in Indian Population

Study Design

Computed tomographic (CT) morphometric analysis.

Purpose

To assess the feasibility and safety of occipital condyle (OC)-based occipitocervical fixation (OCF) in Indians and to define anatomical zones and screw lengths for safe screw placement.

Overview of Literature

Limitations of occipital squama-based OCF has led to development of two novel OC-based OCF techniques.

Methods

Morphometric analysis was performed on the OCs of 70 Indian adults. The feasibility of placing a 3.5-mm-diameter screw into OCs was investigated. Safe trajectories and screw lengths for OC screws and C0–C1 transarticular screws without hypoglossal canal or atlantooccipital joint compromise were estimated.

Results

The average screw length and safe sagittal and medial angulations for OC screws were 19.9±2.3 mm, ≤6.4°±2.4° cranially, and 31.1°±3° medially, respectively. An OC screw could not be accommodated by 27% of the population. The safe sagittal angles and screw lengths for C0–C1 transarticular screw insertion (48.9°±5.7° cranial, 26.7±2.9 mm for junctional entry technique; 36.7°±4.6° cranial, 31.6±2.7 mm for caudal C1 arch entry technique, respectively) were significantly different than those in other populations. The risk of vertebral artery injury was high for the caudal C1 arch entry technique. Screw placement was uncertain in 48% of Indians due to the presence of aberrant anatomy.

Conclusions

There were significant differences in the metrics of OC-based OCF between Indian and other populations. Because of the smaller occipital squama dimensions in Indians, OC-based OCF techniques may have a higher application rate and could be a viable alternative/salvage option in selected cases. Preoperative CT, including three-dimensional-CT-angiography (to delineate vertebral artery course), is imperative to avoid complications resulting from aberrant bony and vascular anatomy. Our data can serve as a valuable reference guide in placing these screws safely under fluoroscopic guidance.

Condylar Joint Fusion and Stabilization (by Screws and Plates) in Nontraumatic Atlanto-Occipital Dislocation: Technical Report of 2 Cases

BACKGROUND

Nontraumatic spontaneous atlanto-occipital dislocation (AOD) is rare. In this report, we discuss the technical steps of condylar joint fusion and stabilization (by screws and plates) in nontraumatic AOD. To the best of our knowledge, it is the first report of such techniques.

MATERIAL AND METHODS

A young girl and a young man with progressive quadriparesis due to nontraumatic spontaneous atlanto-occipital dislocation were managed by microsurgical reduction, fusion, and stabilization of the joint by occipital condylar and C1 lateral mass screw and plate fixation after mobilization of vertebral artery.

RESULT

In both cases, condylar joints fixation and fusion were done successfully.

CONCLUSION

Condylar joint stabilization and fusion may be a good or alternative option for AOD.

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.

Anatomical feasibility for safe occipital condyle screw fixation

PURPOSE

The occipital condyle (OC) screw can be a viable alternative option for the occipito-cervical fixation. However, the risk of vertebral artery (VA) injury during the direct OC screw fixation has not been adequately assessed. The purpose of this study was to establish the course of the VA (V3) relative to the nearby osseous structures to estimate the feasibility of OC screw fixation and describe its anatomical relationship depending on patient's age and sex.

METHODS

A total of 387 three-dimensional computed tomographic angiograms (3D-CTA) were used and compared between two age groups. The vertebral artery diameter and two kinds of bony space were measured. The occipito-C1 arch space (O-C1S) and VA-occipital bone distance (VOD, six entry points) were measured on both sides. The feasibility of direct OC screw fixation can be represented by the VOD value; the minimum feasible value was determined to be 4 mm. Angular measurements (O-C1A and O-C2A) were also taken to assess their relationship to the bony space.

RESULTS

The mean value of the O-C1S ranged from 9.0 to 9.9 mm. The mean value of the VOD ranged from 3.2 to 3.5 mm, and the proportion of individuals for which direct OC screw fixation was considered feasible ranged from 32 to 42 % in both age groups and there was no significant difference between two age groups. The VOD value was not affected by laterality or by gender (P > 0.05). The mean kyphosis of the O-C1A (-5° ± 5.2°, range -22° to 8°) was significantly smaller in the young age group compared to the older age group (-7.6° ± 5.3°, range -26° to 2°). The mean lordosis of the O-C2A (12.4° ± 6.4°, range 3°-33°) was significantly higher in the young age group compared to the older age group (10.4° ± 6.4°, range 0°-36°).

CONCLUSIONS

The direct OC screw fixation was not possible in a considerable number of cases due to the limited space and the position of the VA regardless of age group. Only about one quarter (21-24 %) of all patients was affordable to place the direct OC screw bilaterally. There was more space available to place the direct OC screw when the angle of the upper cervical spine is more kyphotic.

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.

C1 lateral mass screw placement in occipitalization with atlantoaxial dislocation and basilar invagination: a report of 146 cases

STUDY DESIGN

Retrospective study of 146 patients with the diagnosis of occipitalization, atlantoaxial dislocation (AAD) and basilar invagination, using a novel surgical treatment strategy.

OBJECTIVE

To introduce a novel fixation and reduction technique.

SUMMARY OF BACKGROUND DATA

Atlas occipitalization associated with basilar invagination often result in fixed AAD that need reduction and occipitocervical fixation. The widely used occipitocervical fixation with suboccipital screws has several limitations such as the poor screw purchase in maldevelopment of the occipital bone, limited area available for implants in previous suboccipital craniectomy. The placement of occipitalized C1 lateral mass screw is an alternative option.

METHODS

From June 2007 to June 2013, 146 patients of occipitalized atlas with fixed AAD and basilar invagination, underwent fixation and reduction via C1 lateral mass and C2 pars/pedicle screw.

RESULTS

A total of 143 patients achieved the follow-up in the range from 6 months to 4 years (average, 30 mo). Neurological improvement was seen in all the 143 patients, with the averaged Japanese Orthopedic Association scores increasing from 11.6 to 15.5. Radiographical evaluation showed that solid bony fusion was achieved in all patients, and complete reduction was attained in 95 patients, and partial reduction (>60%) in 40 patients, and no effective reduction in 8 patients who had additional transoral decompression. Magnetic resonance imaging demonstrated that the ventral cervicomedullary compression was relieved in all patients.

CONCLUSION

Although technically demanding, the C1 lateral mass placement in occipitalization is very useful in the rescue situation where more conventional stabilization alternatives are not technically possible, or as routine occipitocervical stabilization. It provides firm stabilization offering an optimum situation for bony fusion, and meanwhile the effective reduction of fixed AAD and basilar invagination. An extremely high fusion rate can be expected with minimal complications and minimal postoperative immobilization with this technique.

Computed tomographic morphometric analysis of the pediatric occipital condyle for occipital condyle screw placement

STUDY DESIGN

This study is a computed tomographic (CT)-based morphometric analysis of the pediatric occipital condyles as related to occipital condyle screw placement.

OBJECTIVE

To quantify reference data concerning the dimensions of the immature occipital condyles to guide the placement of occipital condyle screw.

SUMMARY OF BACKGROUND DATA

To the best of our knowledge, no published study has provided insight into the anatomy of occipital condyle of the pediatric population with different age groups.

METHODS

Sixty-nine pediatric patients were divided into 4 age groups, and their occipital condyles were studied on CT scans. Condylar length, width, height, sagittal angle, and sagittal angle lengths were measured on Philips Brilliance 16 CT.

RESULTS

The mean pediatric coronal height, sagittal length, and axial width noted statistically significant age-related differences were 9.0 mm, 21.3 mm, and 9.8 mm, respectively. The mean sagittal angle for all patients was 27.2 ± 5.1° (range, 15.1-41.0°). In 82.6% (114/138) of the occipital condyles, the anatomy could accept the occipital condyle screw (width ≥8 mm and height ≥6.5 mm).

CONCLUSION

Our investigation provides insight into the anatomy of occipital condyle of the pediatric population with different age groups. As the pediatric occipital condyles have sufficient occipital bone for appropriate fixation or fusion, the occipital condyle screws fixation is a feasible technique for children. Even so, given the evolution of this technique being still in its infancy and the complexity inherent to the craniovertebral junction, a careful radiological analysis of occipital condyle must be required in preoperative planning and feasibility determination.

LEVEL OF EVIDENCE

N/A.

Occipital condyle to cervical spine fixation in the pediatric population

Fixation at the craniovertebral junction (CVJ) is necessary in a variety of pediatric clinical scenarios. Traditionally an occipital bone to cervical fusion is preformed, which requires a large amount of hardware to be placed on the occiput of a child. If a patient has previously undergone a posterior fossa decompression or requires a decompression at the time of the fusion procedure, it can be difficult to anchor a plate to the occipital bone. The authors propose a technique that can be used when faced with this difficult challenge by using the occipital condyle as a point of fixation for the construct. Adult cadaveric and a limited number of case studies have been published using occipital condyle (C-0) fixation. This work was adapted for the pediatric population. Between 2009 and 2012, 4 children underwent occipital condyle to axial or subaxial spine fixation. One patient had previously undergone posterior fossa surgery for tumor resection, and 1 required decompression at the time of operation. Two patients underwent preoperative deformity reduction using traction. One child had a Chiari malformation Type I. Each procedure was performed using polyaxial screw-rod constructs with intraoperative neuronavigation supplemented by a custom navigational drill guide. Smooth-shanked 3.5-mm polyaxial screws, ranging in length from 26 to 32 mm, were placed into the occipital condyles. All patients successfully underwent occipital condyle to cervical spine fixation. In 3 patients the construct extended from C-0 to C-2, and in 1 from C-0 to T-2. Patients with preoperative halo stabilization were placed in a cervical collar postoperatively. There were no new postoperative neurological deficits or vascular injuries. Each patient underwent postoperative CT, demonstrating excellent screw placement and evidence of solid fusion. Occipital condyle fixation is an effective option in pediatric patients requiring occipitocervical fusion for treatment of deformity and/or instability at the CVJ. The use of intraoperative neuronavigation allows for safe placement of screws into C-0, especially when faced with a challenging patient in whom fixation to the occipital bone is not possible or is less than ideal.

CT and MRI-based diagnosis of craniocervical dislocations: the role of the occipitoatlantal ligament

BACKGROUND

Craniocervical dislocations are rare, potentially devastating injuries. A diagnosis of craniocervical dislocations may be delayed as a result of their low incidence and paucity of diagnostic criteria based on CT and MRI. Delay in diagnosis may contribute to neurological injury from secondary displacement resulting from instability. The purpose of this study was to define CT and MRI-based diagnostic criteria for craniocervical dislocations to facilitate early injury recognition and stabilization.

QUESTIONS/PURPOSES

Using CT and MRI, we (1) described the bony articular displacements characterize craniocervical injuries; (2) described the ligamentous injuries that characterize craniocervical injuries; and (3) determined whether neurologic injuries were associated with bony or ligamentous injury.

METHODS

Using a prospectively collected spinal cord injury database, we identified 18 patients with acute, traumatic occipitocervical injuries. We reviewed CT scans and MR images to document the height of the occipitoatlantal and atlantoaxial joints and integrity of craniocervical ligaments. Medical records were reviewed for neurological status. The primary measurements were number of patients with articular displacement, location of bony displacement, and number of patients with ligamentous injury.

RESULTS

Thirteen of 18 patients had displacement outside the normal range. Six patients demonstrated displacement of both occipitoatlantal and atlantoaxial joints, whereas five patients presented with displacement through the atlantoaxial joints only. Two patients had an abnormal basion-dental interval only. Of 17 patients with MR images, the cruciate ligament was injured in 11 patients, indeterminate in four, and intact in two. All five patients with occipitoatlantal articular displacement had injury to the occipitoatlantal capsule. No patient had occipitoatlantal capsular injury without occipitoatlantal articular displacement. Three cases of complete spinal cord injury were found after occipitoatlantal-atlantoaxial dislocations. Three patients with occipitoatlantal-atlantoaxial dislocations were neurologically intact. The five patients with atlantoaxial dislocations and patients without displacement or ligamentous injury were neurologically intact. Five patients had cruciate ligament rupture or indeterminate injury but no joint diastasis.

CONCLUSIONS

The occipitoatlantal joint capsules stabilize the occipitoatlantal joint; disruption of the occipitoatlantal capsule may suggest the presence of instability. Based on these findings, we identified two distinct injury patterns: isolated atlantoaxial injuries (Type I) and combined occipitoatlantal-atlantoaxial injuries (Type II). Occipitoatlantal joint capsule integrity differentiated these subsets and Type II injuries had a higher percentage of complete spinal cord injuries on presentation.

Biomechanical comparison of occiput-C1-C2 fixation techniques: C0-C1 transarticular screw and direct occiput condyle screw

STUDY DESIGN

In vitro human cadaveric biomechanical study.

OBJECTIVE

The objective was to evaluate and compare the construct stability of occiput-C1-C2 fixation provided by C0-C1 transarticular screws or occipital condyle screws.

SUMMARY OF BACKGROUND DATA

The placement of an occipital plate is commonly recommended in occipitocervical fixation surgery. However, there are unique clinical situations in which the placement of the occipital plate may not be possible or may have already failed. For these situations, 2 novel techniques that use the occipital condyle have been recently introduced: (1) C0-C1 transarticular screws fixation and (2) direct occipital condyle screws and C1 lateral mass screws fixation. However, there is a lack of thorough biomechanics studies of these techniques.

METHODS

Nondestructive kinematic tests and destructive tests were conducted in 16 fresh frozen cadaveric spines. As a nondestructive kinematic test, a pure moment of up to 2.0 N·m was applied in smooth continuous flexion/extension, lateral bending, and axial rotation motions. In addition to an intact-state case, a total of 5 different constructs (standard occipital plate, C0-C1 transarticular screws with/without occipital plate, and occipital condyle screws with/without occipital plate) were tested after destabilization of C0-C1 and C1-C2. All constructs had C2 pedicle screws fixation, and occipital condyle screws were incorporated with C1 lateral screws.

RESULTS

All fixation techniques significantly reduced ranges of motion compared with the intact state. In comparison with the standard occipital plate construct, the 2 novel techniques showed higher stability in axial rotation and lower stability in lateral bending. In both nondestructive and destructive tests, there were no statistical differences between C0-C1 transarticular screw construct and occipital condyle screw construct.

CONCLUSION

The C0-C1 transarticular screw technique and direct occipital condyle screw with C1 lateral mass screw technique can be salvage fixation methods when occipital plate fixation is not feasible.

Optimal trajectory for the occipital condylar screw

STUDY DESIGN

Evaluation by simulation of screw insertion using fine-cut computed tomographic (CT) scans and screw trajectory software.

OBJECTIVE

To evaluate the feasibility and optimal trajectory of the occipital condylar screw.

SUMMARY OF BACKGROUND DATA

To the best of our knowledge, no large series examining the feasibility and optimal trajectory of occipital condylar screws have been published.

METHODS

We simulated unicortical placement of a 4 × 18-mm screw using 1-mm sliced CT scans and 3-dimensional screw trajectory software in 314 occipital condyles of 157 patients. With the screw tip directed toward a point just below the tip of the basion on lateral fluoroscopy, 3 entry points were compared in view of success rate of screw placement, safe range of medial angulation in an axial plane, and maximum screw length.

RESULTS

The lateral entry point had the highest success rate (93.0%) of screw placement, mean safe range of the medial angulation (10.9°), and maximum screw length (20.7 mm), followed by the middle (92.0%, 10.8°, and 20.6 mm, respectively) and medial (74.2%, 7.7°, and 19.7 mm, respectively) entry points. While the lateral and the middle entry points did not have any statistically significant difference in the 3 parameters, they were significantly better than the medial entry point. All 3 entry points had highly variable ranges of safe medial angulation, making it difficult to provide a single recommended value.

CONCLUSION

Screw placement is feasible in up to 93% of the occipital condyles. The lateral and the middle entry points are significantly better than the medial entry point. Selection between the middle and the lateral entry points should be individualized taking into account local anatomic variation. Because the medial angulation of these screws is highly variable, preoperative 3-dimensional CT evaluation and possibly even intraoperative navigation may be required.

Anatomical determination of a safe entry point for occipital condyle screw using three-dimensional landmarks

The occipital condyle (OC) is an important area in craniovertebral surgery, but neither its anatomical features nor the procedures concerning the OC have been detailed yet. The morphological analysis of the structures were made in totally 704 sides of the occipital bones of adult skulls by 3D-Doctor Demo version. The length and width of the OC were found to be 23.9 ± 3.4 (right), 24 ± 3.3 (left) and 11.9 ± 2.3 (right), 10.7 ± 2.3 mm (left), respectively. The mean anterior intercondylar distance and the posterior intercondylar distance were measured as 20.9 ± 3.6 and 43.1 ± 4 mm, respectively. The sagittal intercondylar angle was observed as 68.7 ± 10.6º. The sagittal condylar angle was observed to be 32.9 ± 7.6º and 38.2 ± 7.3º in the right and left, respectively. The head circumference was observed to be 65.6 ± 7.8 and 64.4 ± 7.2 mm in the right and left, respectively. The head area was measured as 231.9 ± 53.3 and 214.9 ± 45.1 mm² in the right and left, respectively. The most common type was oval-like (59.67%), whereas the most unusual one was two-portioned condyle (0.32%). In Pearson correlation analysis, it was significant that a statistically strong relation was noticed between the length and area, and the circumference and area. The findings suggest that the oval type was more successful to work with, while the triangular, circular and two-portioned types were highly risky for the fixation resonance as the surface got quite smaller. As a result, we suggest that by resecting nearly half of the OC, the border of the hypoglossal canal can be involved.

Computed tomography–based morphometric analysis of the human occipital condyle for occipital condyle–cervical fusion

Object

Occipital condyle screws serve as an alternative fixation point in occipital-cervical fusion. Their placement requires a thorough understanding of the anatomy of the occipital condyles and associated structures. This study is a CT-based morphometric analysis of occipital condyles as related to occipital condyle–cervical fusion.

Methods

A total of 170 patients were examined with CT scans of the craniocervical junction at a single institution, for a total of 340 occipital condyles, between March 6, 2006, and July 30, 2006. All CT scans were negative for traumatic, degenerative, and neoplastic pathological entities. Condylar anteroposterior (AP) length, transverse width, height, projected screw angle, and projected screw lengths were measured on an EBW Portal 2.5 CT Viewer Workstation (Philips Electronics).

The longest axis in the AP orientation of the occipital condyle was accepted as the length. The transverse width was a line perpendicular to the midpoint of the long axis. The height was measured in the coronal projection that had the thickest craniocaudal portion of the condyle. The screw trajectory started 5 mm lateral to the medial edge of the condyle and a line was directed anteromedially in the longest axis. The angle was measured relative to the sagittal midline. The screw length was measured from the outer cortex of the posterior wall to the outer cortex of the anterior wall.

Results

The mean ± SD values for occipital condyle measurements were as follows: AP length was 22.38 ± 2.19 mm (range 14.7–27.6 mm); width was 11.18 ± 1.44 mm (range 7.4–19.0 mm); height was 9.92 ± 1.30 mm (range 5.1–14.3 mm); screw angle was 20.30° ± 4.89° (range 8.0°–34.0°); and screw length was 20.30 ± 2.24 mm (range 13.0–27.6 mm).

Conclusions

These measurements correlate with previous cadaveric and radiographic studies of the occipital condyle, and emphasize the role of preoperative planning for the feasibility of placement of an occipital condyle screw.

Placement of occipital condyle screws for occipitocervical fixation in a pediatric patient with occipitocervical instability after decompression for Chiari malformation

In cadaveric studies and recently in one adult patient the occipital condyle has been studied as an option to allow bone purchase by fixation devices. In the current case the authors describe the use of occipital condyle screws in a child undergoing occipitocervical fixation. To the best of the authors' knowledge this case is the first reported instance of this technique in a pediatric patient. This girl had a history of posterior fossa decompression for Chiari malformation Type I when she was 22 months of age. When she was 6 years old she presented with neck pain on flexion and extension of her head. Magnetic resonance imaging in flexion and extension revealed occipitocervical instability. She underwent an occiput to C-2 posterior arthrodesis with bilateral screw placement in the occipital condyles, C-2 lamina, and C-1 lateral masses. Postoperatively, she was neurologically intact. Computed tomography demonstrated a stable construct, and her cervical pain had resolved on follow-up.

Posterior occipitocervical (C0–3) fusion using polyaxial occipital condyle to cervical spine screw and rod fixation: a radiographic and cadaveric analysis

Numerous conditions affect the occipitocervical junction requiring treatment with occipitocervical fixation. In this paper the authors present their technique of craniocervical fixation achieved with the cephalad extension of posterior C1–3 polyaxial screw and rods to polyaxial screws placed in the occipital condyles. They retrospectively analyzed occipital condyle morphology obtained from CT analyses of 40 patients with normal cervical spines, evaluated occipital condyle screw placement feasibility in 4 cadavers, and provided a case report of a 70-year-old woman with rheumatoid arthritis, basilar invagination, and atlantoaxial instability who was treated with this novel technique. Based on radiographic analysis of occipital condyle anatomy, they concluded that on average a 3.5-mm-diameter × 20- to 30-mm-long screw can be safely placed at an angle of 20–33° from the sagittal plane. Overall, measuring the condylar heights (mean [± SD] 10.8 ± 1.5 mm, range 8.1–15.0 mm), widths (mean 11.1 ± 1.4 mm, range 8.5–14.2 mm), lengths (20.3 ± 2.1 mm, range 15.4–24.6 mm), and angles (mean 32.8 ± 5.2°, range 20.2–45.8°) by using CT studies is an accurate and precise method. This finding correlates with the results of prior anatomical studies of occipital condyles and is important in the planning of craniovertebral junction surgery.

Craniocervical fixation with occipital condyle screws: biomechanical analysis of a novel technique

STUDY DESIGN

A human cadaveric biomechanical study comparing craniocervical fixation techniques.

OBJECTIVE

To quantitatively compare the biomechanical stability of a new technique for occipitocervical fixation using the occipital condyles with an established method for craniocervical spine fusion.

SUMMARY OF BACKGROUND DATA

Stabilization of the occipitocervical junction remains a challenge. The occiput does not easily accommodate instrumentation because of access and spatial constraints. In fact, the area available for the implant fixation is limited and can be restricted further when a suboccipital craniectomy has been performed, posing a challenge to current fixation techniques. Occipital screws are also associated with the potential for intracranial complications.

METHODS

Six fresh frozen cadaveric specimens occiput-C4 were tested intact, after destabilization and after fixation as follows: (1) occipital plate with C1 lateral mass screws and C2 pars screws and (2) occipital condyle screws with C1 lateral mass screws and C2 pars screws. Specimens were loaded in a custom spine testing apparatus and subjected to the following tests, all performed under 50-N unconstrained axial preload: flexion, extension, lateral bending, and axial rotation at 1.5 Nm. The constructs were statistically compared with a one-way analysis of variance and compared with the intact condition.

RESULTS

Motions were reduced by approximately 80% compared with the intact condition for both configurations under all motions. There were no statistically significant differences in the range of motion (ROM) between the 2 instrumentation conditions. The mean values indicated decreased ROM with the novel occipital condyle screw construct in comparison with the standard occipital plate and rod system.

CONCLUSION

Craniocervical stabilization using occipital condyle screws as the sole cephalad fixation point is biomechanically equivalent with regard to the modes tested (ROM and stiffness) to the standard occipital plate construct.

Nuances of Occipitocervical Fixation

OBJECTIVE

To describe the indications and techniques for occipitocervical (OC) fixation.

METHODS

The operative nuances of current OC fixation techniques are described. A surgical technique video is included.

RESULTS

Pertinent literature is reviewed regarding OC fixation techniques.

CONCLUSION

OC fixation systems have evolved from wire and cable techniques to plates, rods, and screws. Screw-rod constructs are easy to implant and biomechanically more rigid than wire techniques.