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

Comparison of hinged and contoured rods for occipitocervical arthrodesis in adults: A clinical study

INTRODUCTION

A rigid construct that employs an occipital plate and upper cervical screws and rods is the current standard treatment for craniovertebral junction (CVJ) instability. A rod is contoured to accommodate the occipitocervical angle. Fatigue failure has been associated these acute bends. Hinged rod systems have been developed to obviate intraoperative rod contouring.

OBJECT

The aim of this study is to determine the safety and efficacy of the hinged rod system in occipitocervical fusion.

MATERIALS AND METHODS

This study retrospectively evaluated 39 patients who underwent occipitocervical arthrodesis. Twenty patients were treated with hinged rods versus 19 with contoured rods. Clinical and radiographic data were compared and analyzed.

RESULTS

Preoperative and postoperative Nurick and Frankel scores were similar between both groups. The use of allograft, autograft or bone morphogenetic protein was similar in both groups. The average number of levels fused was 4.1 (±2.4) and 3.4 (±2) for hinged and contoured rods, respectively. The operative time, estimated blood loss, and length of stay were similar between both groups. The occiput to C2 angle was similarly maintained in both groups and all patients demonstrated no movement across the CVJ on flexion-extension X-rays during their last follow-up. The average follow-up for the hinged and contoured rod groups was 12.2 months and 15.9 months, respectively.

CONCLUSION

Hinged rods provide a safe and effective alternative to contoured rods during occipitocervical arthrodesis.

Three-dimensional models: an emerging investigational revolution for craniovertebral junction surgery

Complex craniovertebral junctional anomalies can be daunting to treat surgically, and preoperative information regarding the osseous abnormalities, course of the vertebral arteries, size of the pedicles, and location of the transverse foramina is invaluable to surgeons operating on these challenging cases. The authors present their experience with the emerging technology of 3D model acquisition for surgery in 11 cases of complex craniovertebral junction region anomalies. For each case, a 3D printed model was made from thin CT scans using a 64-slice CT scanner. The inclination of the joints, the presence of false articulations, the size of the pedicles, and the course of the vertebral arteries were studied preoperatively on the 3D models. The sizes of the plates and screws to be used and the angle of insertion of the screws were calculated based on the data from the models. The model was scaled to actual size and was kept beside the operating surgeon in its anatomical position during surgery. The potential uses of the models and their advantages over conventional radiological investigations are discussed. The authors conclude that 3D models can be an invaluable aid during surgery for complex craniovertebral junction anomalies. The information available from a real life-size model supersedes the information available from 3D CT reconstructions and can also be superior to virtual simulation. The models are both cost effective and easy to build and the authors suggest that they may form the basis of investigations in the near future for craniovertebral junction surgery.

C2-3 Fusion, C3-4 Cord Compression and C1-2 Posterior Facetal Instability: An Evaluation of Treatment Strategy Based on Four Surgically Treated Cases

STUDY DESIGN

Four patients had C2-3 vertebral fusion and radiologically demonstrated cord compression at C3-4 level related to disc bulge with or without association of osteophytes and C1-2 posterior facetal dislocation. The outcome of treatment by atlantoaxial and subaxial facetal fixation is discussed.

PURPOSE

The article evaluates the significance of atlantoaxial facetal instability in cases having C2-3 vertebral fusion and cord compression at the level of C3-4 disc.

OVERVIEW OF LITERATURE

C2-3 vertebral fusions are frequently encountered in association with basilar invagination and chornic atlantoaxial dislocations. Even when basilar invagination and atlantoaxial dislocation are not identified by conventional parameters, atlantoaxial instability can be the nodal point of pathogenesis in cases with C2-3 vertebral fusion.

METHODS

Between June 2013 and November 2014 four patients having C2-3 fusion presented with progressive symptoms of myelopathy that were related to cord compression at the level opposite the C3-4 disc space. Further investigations revealed C1-2 posterior facetal dislocation.

RESULTS

All patients were males. Ages ranged from 18 to 50 years (average, 36 years). All patients were treated by atlantoaxial facetal plate and screw, and subaxial single or multi-segmental transarticular screw fixation. Follow-up (average, 15 months) using a recently described clinical grading system and the Japanese Orthopaedic Association scoring system confirmed marked improvement of symptoms.

CONCLUSIONS

Identification and treatment of atlantoaxial facetal instability may be crucial for a successful outcome in cases having C2-3 fusion and high cervical (C3-4) disc related cord compression.

Is atlantoaxial instability the cause of "high" cervical ossified posterior longitudinal ligament? Analysis on the basis of surgical treatment of seven patients

BACKGROUND

Multilevel ossified posterior longitudinal ligaments (OPLLs), particularly those that extend into the high cervical region, are formidable and challenging surgical problems. The aim of the presentation is to analyze the results of surgical treatment of seven consecutive patients having high cervical OPLL with atlantoaxial and subaxial facetal fixations.

OBJECTIVES

We analyze the role of atlantoaxial instability in the management of OPLL that extended into the high cervical region, above the lower border of C3 vertebra.

MATERIALS AND METHODS

All patients in the series were males. The age of the patients ranged 48-65 years. Clinical evaluation was done by a 5-point clinical grading scale described by us, Japanese Orthopedic Association (JOA) score, and visual analog scale (VAS). All patients were identified to have relatively "subtle" but definite atlantoaxial facetal instability on sagittal imaging and the instability was confirmed by direct handling of the facets during surgery. All patients were treated by multilevel facetal fixation that included fixation of atlantoaxial facets. The aim of surgery was stabilization and arthrodesis of the involved spinal segments, as instability was considered to be the prime pathogenetic factor of OPLL. Spinal canal decompression, either by anterior corpectomy or discoidectomy or by posterior laminectomy or laminoplasty was not done and no attempts were made to remove the OPLL. At an average follow-up of 8 months, all patients showed progressive symptomatic recovery.

CONCLUSION

Atlantoaxial facetal instability can be a cause or an association of high cervical OPLL. Stabilization of the atlantoaxial joint forms a remarkably effective method of treatment.

RESULTS OF THE USE OF PEEK CAGES IN THE TREATMENT OF BASILAR INVAGINATION BY GOEL TECHNIQUE

ABSTRACT Objective: Analysis of the use of polyetheretherketone (PEEK) cages for atlantoaxial facet realignment and distraction for treatment of basilar invagination by Goel technique. Method: Retrospective descriptive statistical analysis of the neurological status, pain, presence of subsidence and bone fusion with the use of PEEK cages in 8 atlantoaxial joints of 4 patients with basilar invagination. All patients were treated with atlantoaxial facet distraction and realignment and subsequent arthrodesis C1-C2 by the technique of Goel modified by the use of PEEK cage. Results: All patients showed improvement in Nurick neurological assessment scale and Visual Analogue Scale (VAS) of pain. There were no cases of subsidence, migration, or damage to the vertebral artery during the insertion of the cage. All joints evolved with bone fusion, assessed by dynamic radiographs, and computed tomography. Two patients developed neuropathic pain in dermatome of C2 and one patient had unilateral vertebral artery injury during C2 instrumentation treated with insertion of pedicle screw to control the bleeding. Conclusion: The results of the treatment of basilar invagination by the Goel technique with the use of PEEK cages shown to be effective and safe although further studies are needed to confirm this use.

The value of multimodality intraoperative neurophysiological monitoring in treating pediatric Chiari malformation type I

INTRODUCTION

Chiari malformation type I is defined as a descent of cerebellar tonsils below the level of the foramen magnum. The traditional treatment for symptomatic patients is foramen magnum decompression (FMD) surgery. Intraoperative neurophysiological monitoring (INM) is an established surgical adjunct, which is proposed to reduce the potential risk of various surgical procedures. Though INM has been suggested as being helpful in patient positioning and in determining the optimal surgical extent of FMD (i.e., duroplasty, laminectomy, tonsillectomy), its shortcomings include prolongation of anesthesia and surgery as well as monetary costs. Multimodality INM including transcranial-electric motor evoked potential (TcMEP) is not routinely employed in most practices. This study evaluates efficacy of multimodality INM during FMD.

METHODS

This work is a retrospective analysis of prospectively collected data. Twenty-two FMD surgeries in 21 pediatric patients (aged 1-18 years) were performed at our center utilizing multimodality INM. All patients presented Chiari malformation type I, 18 of which had presented with syringomyelia, underwent posterior fossa decompression (FMD + C1 laminectomy), accompanied in some with additional cervical laminectomies, duroplasty, and partial tonsillectomies. TcMEP and somatosensory evoked potentials (SSEP) were monitored throughout the procedure including before and after positioning. INM alarms were correlated with perioperative and long-term patient outcomes.

RESULTS

INM data remained stable during 19 operations. Three cases displayed significant attenuation in the monitoring signals, all concomitant with patient positioning on the surgical table. One case showed attenuation in SSEP data only, which remained attenuated following repositioning. Another displayed altered TcMEP concomitant with positioning which partially stabilized following repositioning and resolved following bony decompression. The third case showed unilateral attenuation of both TcMEP and SSEP data, which did not rectify until closure. In each of these three cases, no new neurological deficits were observed post operatively.

CONCLUSIONS

Multimodality INM can be useful in FMD surgery, particularly during patient positioning. TcMEP attenuations may occur independent of SSEPs. The clinical implications of these monitoring alerts have yet to be defined. There is a need to establish an optimal, cost-effective monitoring protocol for FMD.

The importance of atlantoaxial fixation after odontoidectomy

OBJECT

Although anterior odontoidectomy has been widely accepted as a procedure for decompression of the craniovertebral junction (CVJ), postoperative biomechanical instability has not been well addressed. There is a paucity of data on the necessity for and choice of fixation.

METHODS

The authors conducted a retrospective review of consecutively treated patients with basilar invagination who underwent anterior odontoidectomy and various types of posterior fixation. Posterior fixation included 1 of 3 kinds of constructs: occipitocervical (OC) fusion with atlantoaxial (AA) fixation, OC fusion without AA fixation, or AA-only (without OC) fixation. On the basis of the use or nonuse of AA fixation, these patients were assigned to either the AA group, in which the posterior fixation surgery involved both the atlas and axis simultaneously, regardless of whether the patient underwent OC fusion, or the non-AA group, in which the OC fusion construct spared the atlas, axis, or both. Clinical outcomes and neurological function were compared. Radiological results at each time point (i.e., before and after odontoidectomy and after fixation) were assessed by calculating the triangular area causing ventral indentation of the brainstem in the CVJ.

RESULTS

Data obtained in 14 consecutively treated patients with basilar invagination were analyzed in this series; the mean follow-up time was 5.75 years. The mean age was 53.58 years; there were 7 males and 7 females. The AA and non-AA groups consisted of 7 patients each. The demographic data of both groups were similar. Overall, there was significant improvement in neurological function after the operation (p = 0.03), and there were no differences in the postoperative Nurick grades between the 2 groups (p = 1.00). According to radiological measurements, significant decompression of the ventral brainstem was achieved stepwise in both groups by anterior odontoidectomy and posterior fixation; the mean ventral triangular area improved from 3.00 ± 0.86 cm2 to 2.08 ± 0.51 cm2 to 1.68 ± 0.59 cm2 (before and after odontoidectomy and after fixation, respectively; p < 0.05). The decompression gained by odontoidectomy (i.e., reduction of the ventral triangular area) was similar in the AA and non-AA groups (0.66 ± 0.42 cm2 vs 1.17 ± 1.42 cm2, respectively; p = 0.38). However, the decompression achieved by posterior fixation was significantly greater in the AA group than in the non-AA group (0.64 ± 0.39 cm2 vs 0.17 ± 0.16 cm2, respectively; p = 0.01).

CONCLUSIONS

Anterior odontoidectomy alone provides significant decompression at the CVJ. Adjuvant posterior fixation further enhances the extent of decompression after the odontoidectomy. Moreover, posterior fixation that involves AA fixation yields significantly more decompression of the ventral brainstem than OC fusion that spares AA fixation.

Volume change theory for syringomyelia: A new perspective

Background:

The etiopathogenesis of syringomyelia is still an enigma. The authors present a novel theory based on fluid dynamics at the craniovertebral (CV) junction to explain the genesis of syringomyelia (SM). The changes in volume of spinal canal, spinal cord, central canal and spinal subarachnoid space (SSS) in relation to the posterior fossa have been analysed, specifically during postural movements of flexion and extension. The effect of fluctuations in volume of spinal canal and its contents associated with cerebrospinal fluid (CSF) flow dynamics at the CV junction have been postulated to cause the origin and propagation of the syringomyelia. The relevant literature on the subject has been reviewed and the author's theory has been discussed.

Conclusion:

Volume of spinal canal in flexion is always greater than that in extension. Flexion of spine causes narrowing of the ventral subarachnoid space (SAS) and widening of dorsal SAS while extension causes reverse changes leading to fluid movement in dorsal spinal SAS in flexion and ventral spinal SAS in extension. Cervical and lumbar spinal region with maximum bulk hence maximum area and volume undergo maximum deformation during postural changes. SSS CSF is the difference between the volume of spinal canal and spinal cord, varies in flexion and extension which is compensated by changes in posterior fossa (CSF) volume in normal circumstances. Blocked SAS at foramen magnum donot permit spinal SAS CSF exchange which during postural changes is compensated by cavitatory/cystic (syrinx) change at locations in cervical and lumbar spine with propensity for maximum deformation. Augmentation of posterior fossa volume by decompression helps by normalization of this CSF exchange dynamics but immobilizing the spinal movement theoretically will cease any dynamic volume changes thereby minimizing the destructive influence of the fluid exchange on the cord. Thus, this theory strengthens the rational of treating patients by either methodology.

Craniovertebral Junction Instability: A Review of Facts about Facets

Craniovertebral junction surgery involves an appropriate philosophical, biomechanical and anatomical understanding apart from high degree of technical skill and ability of controlling venous and arterial bleeding. The author presents his 30-year experience with treating complex craniovertebral junction instability related surgical issues. The facets of atlas and axis form the primary site of movements at the craniovertebral junction. All craniovertebral junction instability is essentially localized to the atlantoaxial facet joint. Direct manipulation and fixation of the facets forms the basis of treatment for instability.

Bifid Anterior and Posterior Arches of Atlas

BACKGROUND:

On reviewing the database of patients with craniovertebral junction anomalies, the authors identified 70 patients with a bifid posterior arch of atlas.

OBJECTIVE:

To speculate on the pathogenesis of spondyloschisis of both the anterior and posterior arches of atlas, particularly as it relates to atlantoaxial instability.

METHODS:

Seventy patients with bifid anterior and posterior arches were identified by a retrospective review of the database from 2007 to 2013.

RESULTS:

The ages of the patients ranged from 14 months to 50 years. The patients were divided into 3 groups. Group 1 (3 patients) had multiple additional spinal bony and neural abnormalities. Group 2 (34 patients) had mobile and partially (5) or completely (29) reducible atlantoaxial dislocation. Group 3 (33 patients) had atlantoaxial instability and related basilar invagination. The os odontoideum was identified in 21 patients, and C2-3 fusion was seen in 24 patients. Two of 3 patients in group 1 were treated conservatively and without any surgery. All patients in groups 2 and 3 were surgically treated. Surgery was done using lateral mass plate/rod and screw fixation techniques. The general observation during surgery included identification of discrete movements of both halves of the atlas, lateral positioning of the facets of atlas in relation to the facets of the axis and occipital condyle and closer approximation of the occipital bone, atlas, and axis resulting in “crumpling” of bone and neural elements.

CONCLUSION:

Understanding of the pathogenesis and mechanical alterations in cases with a bifid arch of atlas can assist in evaluating the clinical implications and in conduct of surgery.