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

C2 Superior Facetal Osteotomy: A Novel Technique in Complex Craniovertebral Junction Surgery for C1 Lateral Mass Screw Placement

Complex craniovertebral junction (CVJ) defects account for a considerable proportion of CVJ diseases. Given the heavily assimilated C1, an unfavorable C1-C2 joint orientation, an overriding C2 superior facet, a low-hanging occiput, and an abnormal vertebral artery course with a high-riding vertebral artery, placement of C1 lateral mass screws might be difficult. To address this, a novel technique for placing C1 lateral mass screws that avoid vertebral artery injury, low-hanging occiput, and overriding C2 superior facet was developed in this study. This approach enables firm fixation of C1-C2 even in difficult situations where the placement of the C1 lateral mass is challenging.

Low occurrence of long-term subsequent fusion in pediatric patients following decompressive surgery for Chiari malformation: an institutional review

OBJECTIVE

Chiari I malformation is treated with suboccipital craniectomy with cervical laminectomy, a procedure which has been associated with the possibility of pre-existing or iatrogenic occipitocervical instability. The long-term risk of subsequent spinal deformity and need for occipito cervical fusion after standard Chiari decompression in pediatric patients has not yet been characterized.

METHODS

We queried our institutional electronic database for patients aged 18 and under, with at least 5 years of follow-up, that underwent surgical decompression for Chiari I malformation. Occurrence of subsequent occipitocervical fusion at follow-up comprised the primary endpoint. Cases with myelomeningocele, Chiari II, or fusion at time of decompression were excluded.

RESULTS

A total of 30 patients (median age 5.5 years, 60% males) were analyzed. Age distribution was as follows: n = 3 for 0-1 years, n = 11 for 1-5 years, n = 4 for 5-10 years, and n = 12 for 10-18 years. Median tonsillar descent below the foramen magnum was 12.5 mm (interquartile range [IQR]: 10.8-19.5 mm). Syringomyelia was observed in 43%, retroflexion of the dens in 55%, basilar invagination in 6.7%, and medullary kinking in 27%. The median clivo-axial angle was 142° (132-150°). The majority of patients underwent C1 laminectomy (n = 24, 80%), followed by C1-C2 laminectomy (n = 4, 13%), while one patient had C1-upper C2 and C1-C3 laminectomy each, respectively. At a median follow-up of 6.3 years, there was only one patient (3.3% of overall cohort) that underwent subsequent occipitocervical fusion. The patient (4-year-old male) initially had a suboccipital craniectomy with C1 laminectomy and duraplasty and presented with recurrence of posterior headaches and neck pain 4 months after original surgery. We proceeded with occiput-C2 fusion with subsequent resolution of his symptoms.

CONCLUSION

Current analysis shows that in the absence of clinical or imaging features suggestive of craniocervical instability, Chiari I decompressive surgery is associated with very low long-term risk of requiring occipitocervical fusion. This observance can be used to guide surgical treatment decisions, especially in young children with Chiari I malformations.

Craniocervical Stabilization After Failed Chiari Decompression: A Case Series of a Population with High Prevalence of Ehlers-Danlos Syndrome

BACKGROUND

In the treatment of Chiari malformation type I (CM-I), posterior fossa decompression is achieved via suboccipital craniectomy (SOC); however, some patients continue to experience symptoms after treatment, which may be due to craniocervical instability (CCI). The purposes of this study were to analyze data from patients who required an occipitocervical fusion (OCF) for the management of CCI after having previously undergone SOC for CM-I to determine if OCF is a safe and effective option and to determine any identifiable risk factors for CCI in these patients.

METHODS

A retrospective review was done on all patients who underwent an OCF performed by the senior author between November 2013 and June 2020 after having previously undergone SOC for CM-I. Demographic, radiographic, perioperative, and outcome data were collected and clivoaxial angles (CXAs) were measured pre- and postoperatively.

RESULTS

Fifteen patients were identified who developed symptomatic CCI after previously undergoing a suboccipital craniectomy for the treatment of CM-I. All 15 patients were treated by OCF with good outcome. Of these, 12 patients had a known diagnosis of Ehlers-Danlos syndrome (EDS). Overall, the CXAs of these patients were found to be corrected to a more anatomical alignment.

CONCLUSIONS

Symptomatic CCI should be recognized as a delayed postoperative complication in the surgical treatment of CM-I, with an underlying connective tissue hypermobility disorder such as EDS serving as a potential risk factor its development. CCI can be managed with OCF as a safe and effective treatment option for this patient population.

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.

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.

Ehlers-Danlos syndrome-associated craniocervical instability with cervicomedullary syndrome: Comparing outcome of craniocervical fusion with occipital bone versus occipital condyle fixation

Introduction:

Ehlers–Danlos syndrome (EDS) predisposes to craniocervical instability (CCI) with resulting cranial settling and cervicomedullary syndrome due to ligamentous laxity. This study investigates possible differences in radiographic outcomes and operative complication rate between two surgical techniques in patients with EDS and CCI undergoing craniocervical fusion (CCF): occipital bone (OB) versus occipital condyle (OC) fixation.

Methods:

A retrospective search of the institutional operative database between January 07, 2017, and December 31, 2019, was conducted to identify EDS patients who underwent CCF with either OB (Group OB) or OC (Group OC) fixation. For each patient, pre- and post-operative radiographic measurements and operative complications were extracted and compared between groups (OB vs. OC): pB-C2, clivoaxial angle (CXA), tonsillar descent, C2C7 sagittal Cobb angle, C2 long axis, and operative complications.

Results:

Of a total of 26 patients, 13 underwent OV and 13 underwent OC fixation. Eighty-five percent of the patients underwent OC underwent fusion from occiput to C2, while the remaining 15% fusion from occiput to C3. Radiographic outcome in the OC versus OB group was preoperative measurements were similar between OC and OB group: pB-C2 8.8 mm (1.5, 6–11) versus 8.3 mm (1.7, 4–9.6), P = 0.43; CXA 128.2° (5.4, 122–136) versus 131.9° (6.8,122–141), P = 0.41; tonsillar descent 6.2 mm (4.8, 0–15) versus 2.9 mm (3.4, 0–8), P = 0.05; C2 long axis 75.2° (6.7, 58–85) versus 67.2° (21.4, 1–80), P = 0.21; postoperative change of CXA + 14.4° (8.8, 0–30) versus 16.2° (12.4, −4–38), P = 0.43; change of pB-C2 − 2.6 mm (1.8, −-5.3 to 0) versus − 1.2 mm (4, −4.6–8), P = 0.26; and postoperative C2C7 sagittal Cobb angle − 2.6° (19.5, −43–39) versus − 2.6° (11.4, −21–12). Operative complications were seen in 1 out of 13 patients (8%) versus 2 out of 13 patients (16%), P = 1.

Conclusions:

In EDS, patients with CCI undergoing CCF radiographic and clinical outcome were similar between those with OC versus OB fixation. Both techniques resulted in sufficient correction of pB-C2 and CXA measurements with a low complication rate.

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.

Chiari malformation type I and basilar invagination originating from atlantoaxial instability: a literature review and critical analysis

Introduction

Recently, a novel hypothesis has been proposed concerning the origin of craniovertebral junction (CVJ) abnormalities. Commonly found in patients with these entities, atlantoaxial instability has been suspected to cause both Chiari malformation type I and basilar invagination, which renders the tried and tested surgical decompression strategy ineffective. In turn, C1-2 fusion is proposed as a single solution for all CVJ abnormalities, and a revised definition of atlantoaxial instability sees patients both with and without radiographic evidence of instability undergo fusion, instead relying on the intraoperative assessment of the atlantoaxial joints to confirm instability.

Methods

The authors conducted a comprehensive narrative review of literature and evidence covering this recently emerged hypothesis. The proposed pathomechanisms are discussed and contextualized with published literature.

Conclusion

The existing evidence is evaluated for supporting or opposing sole posterior C1-2 fusion in patients with CVJ abnormalities and compared with reported outcomes for conventional surgical strategies such as posterior fossa decompression, occipitocervical fusion, and anterior decompression. At present, there is insufficient evidence supporting the hypothesis of atlantoaxial instability being the common progenitor for CVJ abnormalities. Abolishing tried and tested surgical procedures in favor of a single universal approach would thus be unwarranted.

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.

Cervical medullary syndrome secondary to craniocervical instability and ventral brainstem compression in hereditary hypermobility connective tissue disorders: 5-year follow-up after craniocervical reduction, fusion, and stabilization

A great deal of literature has drawn attention to the "complex Chiari," wherein the presence of instability or ventral brainstem compression prompts consideration for addressing both concerns at the time of surgery. This report addresses the clinical and radiological features and surgical outcomes in a consecutive series of subjects with hereditary connective tissue disorders (HCTD) and Chiari malformation. In 2011 and 2012, 22 consecutive patients with cervical medullary syndrome and geneticist-confirmed hereditary connective tissue disorder (HCTD), with Chiari malformation (type 1 or 0) and kyphotic clivo-axial angle (CXA) enrolled in the IRB-approved study (IRB# 10-036-06: GBMC). Two subjects were excluded on the basis of previous cranio-spinal fusion or unrelated medical issues. Symptoms, patient satisfaction, and work status were assessed by a third-party questionnaire, pain by visual analog scale (0-10/10), neurologic exams by neurosurgeon, function by Karnofsky performance scale (KPS). Pre- and post-operative radiological measurements of clivo-axial angle (CXA), the Grabb-Mapstone-Oakes measurement, and Harris measurements were made independently by neuroradiologist, with pre- and post-operative imaging (MRI and CT), 10/20 with weight-bearing, flexion, and extension MRI. All subjects underwent open reduction, stabilization occiput to C2, and fusion with rib autograft. There was 100% follow-up (20/20) at 2 and 5 years. Patients were satisfied with the surgery and would do it again given the same circumstances (100%). Statistically significant improvement was seen with headache (8.2/10 pre-op to 4.5/10 post-op, p < 0.001, vertigo (92%), imbalance (82%), dysarthria (80%), dizziness (70%), memory problems (69%), walking problems (69%), function (KPS) (p < 0.001). Neurological deficits improved in all subjects. The CXA average improved from 127° to 148° (p < 0.001). The Grabb-Oakes and Harris measurements returned to normal. Fusion occurred in 100%. There were no significant differences between the 2- and 5-year period. Two patients returned to surgery for a superficial wound infections, and two required transfusion. All patients who had rib harvests had pain related that procedure (3/10), which abated by 5 years. The results support the literature, that open reduction of the kyphotic CXA to lessen ventral brainstem deformity, and fusion/stabilization to restore stability in patients with HCTD is feasible, associated with a low surgical morbidity, and results in enduring improvement in pain and function. Rib harvest resulted in pain for several years in almost all subjects.

Pediatric occipital condyle morphometric analysis using computed tomography with evaluation for occipital condyle screw placement

OBJECTIVE

Occipitocervical fusions in the pediatric population are rare but can be challenging because of the smaller anatomy. The procedure is even more exacting in patients with prior suboccipital craniectomy. A proposed method for occipitocervical fusion in such patients is the use of occipital condyle screws. There is very limited literature evaluating the pediatric occipital condyle for screw placement. The authors examined the occipital condyle in pediatric patients to determine if there was an age cutoff at which condylar screw placement is contraindicated.

METHODS

The authors performed a retrospective morphometric analysis of the occipital condyle in 518 pediatric patients aged 1 week-9 years old. Patients in their first decade of life whose occipital condyle was demonstrated on CT imaging in the period from 2009 to 2013 at the Augusta University Medical Center and Children's Hospital of Georgia were eligible for inclusion in this study. Exclusion criteria were an age older than 10 years; traumatic, inflammatory, congenital, or neoplastic lesions of the occipital condyles; and any previous surgery of the occipitocervical junction. Descriptive statistical analysis was performed including calculation of the mean, standard deviation, and confidence intervals for all measurements. Probability values were calculated using the Student t-test with statistical significance determined by p < 0.05.

RESULTS

Overall, male patients had statistically significantly larger occipital condyles than the female patients, but this difference was not clinically significant. There was no significant difference in left versus right occipital condyles. There were statistically significant differences between age groups with a general trend toward older children having larger occipital condyles. Overall, 20.65% of all patients evaluated had at least one measurement that would prevent occipital condyle screw placement including at least one patient in every age group.

CONCLUSIONS

Occipital condyle screw fixation is feasible in pediatric patients younger than 10 years. More importantly, all pediatric patients should undergo critical evaluation of the occipital condyle in the axial, sagittal, and coronal planes preoperatively to determine individual suitability for occipital condyle screw placement.

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.

Occipitocervical Fixation

BACKGROUND

Occipitocervical junction instability can lead to serious neurological injury or death. Open surgical fixation is often necessary to provide definitive stabilization. However, long-term results are limited to small case series.

OBJECTIVE

To review the causes of occipitocervical instability, discuss the indications for surgical intervention, and evaluate long-term surgical outcomes after occipitocervical fixation.

METHODS

The charts of all patients undergoing posterior surgical fixation of the occipitocervical junction by the senior author were retrospectively reviewed. A total of 120 consecutive patients were identified for analysis. Patient demographic characteristics, occipitocervical junction pathology, surgical indications, and clinical and radiographic outcomes are reported.

RESULTS

The study population consisted of 64 male and 56 female patients with a mean age of 39.9 years (range, 7 months to 88 years). Trauma was the most common cause of instability, occurring in 56 patients (47%). Ninety patients (75%) were treated with screw/rod constructs; wiring was used in 30 patients (25%). The median number of fixated segments was 5 (O-C4). Structural bone grafts were implanted in all patients (100%). Preoperative neurological deficits were present in 83 patients (69%); 91% of those patients improved with surgery. Mean follow-up was 35.1 ± 27.4 months (range, 0-123 months). Two patients died, and 10 were lost to follow-up before the end of the 6-month follow-up period. Fusion was confirmed in 107 patients (89.1%). The overall complication rate was 10%, including 3 patients with vertebral artery injuries and 2 patients who required revision surgery.

CONCLUSION

Occipitocervical fixation is a durable treatment option with acceptable morbidity for patients with occipitocervical instability.

Clinical significance of changes in pB-C2 distance in patients with Chiari Type I malformations following posterior fossa decompression: a single-institution experience

OBJECT The coexistence of Chiari malformation Type I (CM-I) and ventral brainstem compression (VBSC) has been well documented, but the change in VBSC after posterior fossa decompression (PFD) has undergone little investigation. In this study the authors evaluated VBSC in patients with CM-I and determined the change in VBSC after PFD, correlating changes in VBSC with clinical status and the need for further intervention. METHODS Patients who underwent PFD for CM-I by the senior author from November 2005 to January 2013 with complete radiological records were included in the analysis. The following data were obtained: objective measure of VBSC (pB-C2 distance); relationship of odontoid to Chamberlain's, McGregor's, McRae's, and Wackenheim's lines; clival length; foramen magnum diameter; and basal angle. Statistical analyses were performed using paired t-tests and a mixed-effects ANOVA model. RESULTS Thirty-one patients were included in the analysis. The mean age of the cohort was 10.0 years. There was a small but statistically significant increase in pB-C2 postoperatively (0.5 mm, p < 0.0001, mixed-effects ANOVA). Eleven patients had postoperative pB-C2 values greater than 9 mm. The mean distance from the odontoid tip to Wackenheim's line did not change after PFD, signifying postoperative occipitocervical stability. No patients underwent transoral odontoidectomy or occipitocervical fusion. No patients experienced clinical deterioration after PFD. CONCLUSIONS The increase in pB-C2 in patients undergoing PFD may occur as a result of releasing the posterior vector on the ventral dura, allowing it to relax posteriorly. This increase appears to be well-tolerated, and a postoperative pB-C2 measurement of more than 9 mm in light of stable craniocervical metrics and a nonworsened clinical examination does not warrant further intervention.

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.

Is atlantoaxial instability the cause of Chiari malformation? Outcome analysis of 65 patients treated by atlantoaxial fixation

OBJECT

Understanding that atlantoaxial instability is the cause of Chiari malformation (CM), the author treated 65 patients using atlantoaxial stabilization. The results are analyzed.

METHODS

Cases of CM treated using atlantoaxial fixation during the period from January 2010 to November 2013 were reviewed and analyzed. Surgery was aimed at segmental arthrodesis.

RESULTS

The author treated 65 patients with CM in the defined study period. Fifty-five patients had associated syringomyelia. Forty-six patients had associated basilar invagination. Thirty-seven patients had both basilar invagination and syringomyelia. Three patients had been treated earlier using foramen magnum decompression and duraplasty. According to the extent of their functional capabilities, patients were divided into 5 clinical grades. On the basis of the type of facetal alignment and atlantoaxial instability, the patients were divided into 3 groups. Type I dislocation (17 patients) was anterior atlantoaxial instability wherein the facet of the atlas was dislocated anterior to the facet of the axis. Type II dislocation (31 patients) was posterior atlantoaxial instability wherein the facet of the atlas was dislocated posterior to the facet of the axis. Type III dislocation (17 patients) was the absence of demonstrable facetal malalignment and was labeled as "central" atlantoaxial dislocation. In 18 patients, dynamic images showed vertical, mobile and at-least partially reducible atlantoaxial dislocation. All patients were treated with atlantoaxial plate and screw fixation using techniques described in 1994 and 2004. Foramen magnum decompression or syrinx manipulation was not performed in any patient. Occipital bone and subaxial spinal elements were not included in the fixation construct. One patient died, and death occurred in the immediate postoperative phase and was related to a vertebral artery injury incurred during the operation. One patient had persistent symptoms. In the rest of the patients there was gratifying clinical improvement. More remarkably, in 7 patients, the symptoms of lower cranial nerve paresis improved. No patient worsened in their neurological function after surgery. Reductions in the size of the syrinx and regression of the CM were observed in 6 of 11 cases in which postoperative MRI was possible. During the follow-up period, there was no delayed worsening of neurological function or symptoms in any patient. Sixty-three patients improved after surgery, and the improvement was sustained during the average follow-up period of 18 months.

CONCLUSIONS

On the basis of outcomes in this study, it appears that the pathogenesis of CM with or without associated basilar invagination and/or syringomyelia is primarily related to atlantoaxial instability. The data suggest that the surgical treatment in these cases should be directed toward atlantoaxial stabilization and segmental arthrodesis. Except in cases in which there is assimilation of the atlas, inclusion of the occipital bone is neither indicated nor provides optimum stability. Foramen magnum decompression is not necessary and may be counter-effective in the long run.

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.

Occipitocervical fusion using a contoured rod and wire construct in children: a reappraisal of a vintage technique

OBJECT

Many methods to stabilize and fuse the craniocervical junction have been described. One of the early designs was a contoured (Luque) rod fixated with wires, the so-called Hartshill-Ransford loop. In this study, the authors report their 20-year experience with this surgical technique in children.

METHODS

The authors reviewed the medical records of patients 18 years of age or younger who underwent dorsal occipitocervical fusion procedures between March 1992 and March 2012 at Le Bonheur Children's Hospital using a contoured rod and wire construct. Data on basic patient characteristics, causes of instability, neurological function at presentation and at last follow-up, details of surgery, complications, and radiographic outcome were collected.

RESULTS

Twenty patients (11 male) were identified, with a mean age of 5.5 years (range 1-18 years) and a median follow-up of 43.5 months. Fourteen patients had atlantooccipital dislocation, 2 patients had atlantoaxial fracture-dissociations, 2 had Down syndrome with occipitocervical and atlantoaxial instability, 1 had an epithelioid sarcoma from the clivus to C-2, and 1 had an anomalous atlas with resultant occipitocervical instability. Surgical stabilization extended from the occiput to C-1 in 3 patients, C-2 in 6, C-3 in 8, and to C-4 in 3. Bone morphogenetic protein was used in 2 patients. Two patients were placed in a halo orthosis; the rest were kept in a hard collar for 6-8 weeks. All patients were neurologically stable after surgery. One patient with a dural tear experienced wound dehiscence with CSF leakage and required reoperation. Eighteen patients went on to achieve fusion within 6 months of surgery; 1 patient was initially lost to follow-up, but recent imaging demonstrated a solid fusion. There were no early hardware or bone failures requiring hardware removal, but radiographs obtained 8 years after surgery showed that 1 patient had an asymptomatic fractured rod. There were no instances of symptomatic junctional degeneration, and no patient was found to have increasing lordosis over the fused segments. Five (31%) of the 16 trauma patients required a shunt for hydrocephalus.

CONCLUSIONS

Despite the proliferation of screw-fixation techniques for craniocervical instability in children, the contoured rod-wire construct remains an effective, less expensive, and technically easier alternative that has been in use for almost 30 years. It confers immediate stability, and therefore most patients will not need to be placed in a halo device postoperatively. A secondary observation in our series was the high (30%) rate of hydrocephalus requiring a shunt in patients with traumatic instability.

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.