Improvise, adapt and overcome-challenges in management of pediatric congenital atlantoaxial dislocation

Posterior Atlantoaxial Fusion With C1-2 Pedicle Screw Fixation for Atlantoaxial Dislocation in Pediatric Patients With Mucopolysaccharidosis IVA (Morquio a Syndrome): A Case Series

OBJECTIVE

To investigate the efficacy and safety of posterior atlantoaxial fusion (AAF) with C1-2 pedicle screw fixation for atlantoaxial dislocation (AAD) in pediatric patients with mucopolysaccharidosis IVA (MPS IVA).

METHODS

This study included 21 pediatric patients with MPS IVA who underwent posterior AAF with C1-2 pedicle screw fixation. Anatomical parameters of the C1 and C2 pedicle were measured on preoperative computed tomography (CT). The American Spinal Injury Association (ASIA) scale was used to evaluate the neurological status. The fusion and accuracy of pedicle screw was assessed on postoperative CT. Demographic, radiation dose, bone density, surgical, and clinical data were recorded.

RESULTS

Patients reviewed included 21 patients younger than 16 years with an average age of 7.4 ± 4.2 years and an average of 20.9 ± 7.7 months follow-up. Fixation of 83 C1 and C2 pedicle screws was performed successfully and 96.3% of them were identified as being safe. One patient developed postoperative transient disturbance of consciousness and one developed fetal airway obstruction and died about 1 month after the surgery. Out of the remaining20 patients, fusion was achieved, symptoms were improved, and no other serious surgical complications were observed at the latest follow-up.

CONCLUSIONS

Posterior AAF with C1-2 pedicle screw fixation is effective and safe for AAD in pediatric patients with MPS IVA. However, the procedure is technically demanding and should be performed by experienced surgeons with strict multidisciplinary consultations.

A Novel Pedicle Screw Design with Variable Thread Geometry: Biomechanical Cadaveric Study with Finite Element Analysis

BACKGROUND

Pedicle screw fixation provides one of the most stable spinal constructs. Their designs together with osseous characteristics have been known to influence the screw-bone interplay during surgical maneuvers and thereafter the fusion process. Various technical modifications to enhance screw performance have been suggested. This study evaluated the pull-out strength and axial stiffness of a novel pedicle screw design with variable thread geometry and pitch.

METHODS

The newly designed triple threaded pedicle screw is tapered, and has unique out-turned flanges to hold the cancellous bone and a finer pitch at its distal and proximal end to engage the cortical bone. Five lumbar and 4 lower thoracic cadaveric vertebrae were divided into hemivertebrae. A standard cancellous pedicle screw and the newly designed pedicle screw were inserted into each hemivertebra. Axial stiffness and peak pull-out force between the screw types were compared; a finite element analysis was also performed to additionally compare the pull out under toggle forces.

RESULTS

In cadaveric study, the axial stiffness of the new screw was significantly better than that of the standard screw. However, the peak load between the screws was not statistically different. Finite element analyses suggested lesser stress at bone-implant interface for the new screw along with better axial stiffness under both co-axial and toggle forces.

CONCLUSIONS

Our novel pedicle screw design with variable thread geometry demonstrates greater axial stiffness compared with the standard screws, and therefore is likely to withstand a greater surgical manipulation.

Cranio-cervical decompression associated with non-instrumented occipito-C2 fusion in children with mucopolysaccharidoses: Report of twenty-one cases

BACKGROUND

Mucopolysaccharidosis (MPS) is a multisystemic storage disorder of glycosaminoglycan deposits. Infiltration of the dura mater and supporting ligaments caused spinal cord compression and consecutive myelopathy, especially at the cranio-cervical junction (CCJ). Craniocervical instability and posterior decompression often raise the problem of fixation in children. The main purpose of this paper was to report the result of an original technique of occipito-cervical arthrodesis using a cranial halo-cast system in pediatric population.

METHODS

We recorded 21 patients with cervical myelopathy. All of them had spinal cord decompression by enlargement of the foramen magnum, C1 laminectomy, and occipito-C2 fusion using corticocancellous bone graft. Only one child has an extended laminectomy from C1 to C3. The occiput-C2 arthrodesis was stabilized by the cranial halo-cast system. This immobilization was performed preoperatively and kept for three months then switched to rigid cervical collar. Clinical assessment, including the Goel grade and mJOA, radiographs and magnetic resonance imaging were performed before surgery. The occipito-cervical arthrodesis was controlled by standard X-rays and CT scan.

RESULTS

According to the type of mucopolysaccharidosis, the patients were divided into MPS type I: n= 3, II: n=7, IV: n=11. The mean age of patients at surgery was 6.76 years. All mucopolysaccharidoses cases required a foramen magnum decompression by craniectomy, C1 laminectomy and occipito-C2 arthrodesis. As major complications, a child had immediate post-operative paraplegia due to spinal cord ischemia. The postoperative follow-up ranged from 1.5 to 4 years, with an average of 3.3 years. The average preoperative mJOA score was 8.9, and it improved to 14 points at the last follow-up.

CONCLUSIONS

Satisfactory fusion and good clinical results were obtained with the 2-stage approach to CCJ anomalies.

C1-C2 arthroplasty for craniovertebral junction instability: A preliminary proof of concept in human cadavers

Background:

The atlantoaxial complex contributes to significant neck movements, especially the axial rotation. Its instability is currently treated with various C1-C2 fusion techniques. This however, considerably hampers the neck movements and affects the quality of life; a C1-C2 motion preserving arthroplasty could potentially overcome this drawback.

Objectives:

We evaluate the range of motion (ROM) of lateral C1-C2 artificial joints in cadaveric models.

Materials and Methods:

This is an in vitro cadaveric biomechanical study. After C1-C2 arthroplasty through a posterior approach, the C1-C2 ROM was tested in 4 fresh-frozen human cadaveric specimens, before and after destabilization.

Results:

The mean axial rotation demonstrated after the placement of C1-C2 joint implants was 15.46 degrees on the right and 16.03 degrees on the left side; the prosthesis provided stability, with 46% of the baseline C1-C2 axial rotation on either side. The ROM achieved in the other axes was less compared with that of intact specimens. To initiate rotation, a higher moment of 1.5 Nm was required in the presence of joint implants compared to 0.5 NM in unimplanted specimens.

Conclusions:

In our preliminary ROM evaluation, the C1-C2 arthroplasty appears to be stable and provides about half of the range of atlantoaxial rotation. It has the potential for joint motion preservation in the treatment of atlantoaxial instability resulting from lateral C1-C2 joint pathologies.

C2 Nerve Root Preservation During Posterior Fixation for Instability Secondary to Congenital Craniovertebral Junction Anomalies: Feasibility Factors and Related Outcomes

OBJECTIVE

Patients with instability because of congenital craniovertebral anomalies often have complex C1-C2 osseovascular anomalies. C2 nerve root sacrifice has been described to address such difficult anatomy during posterior C1-C2 fixation and has its own downsides. Its preservation as a recent alternative poses greater surgical challenge, and the considerations differ from other causes of craniovertebral junctional instability; the pertaining outcomes have been scarcely studied. The objective of this study was to prospectively determine the feasibility and outcomes related to C2 nerve root preservation in patients with congenital atlantoaxial dislocation (CAAD) after posterior C1-C2 fixation.

METHODS

In this observational study, 63 patients (126 nerve roots) with CAAD after posterior fixation were prospectively assessed. Underlying osseovascular anomalies affecting the feasibility of C2 nerve root preservation, and C2 nerve-related dysfunction at 12 months follow-up were analyzed.

RESULTS

The overall C2 nerve root preservation rate was 89.7%. Even in the presence of extreme joint obliquity/spondyloptosis and anomalous vertebral artery, it was feasible in about three fourths. After preservation, 28.3% patients developed new-onset C2 nerve root dysfunction: neuralgia in 2, dysesthesia in 6, and hypoesthesia/paresthesia in 9. The symptoms were not disabling in most patients.

CONCLUSIONS

In most patients with CAAD, C2 nerve root preservation is feasible despite an aberrant bony and vascular anatomy. A few patients after nerve root preservation develop related symptoms that are conservatively manageable, with no significant adverse consequences. Given the controversy in the literature on C2 nerve sacrifice-related outcomes, we favor an attempt at C2 nerve root preservation.

The enigma of acute worsening after a latent interval in post-operative patients of craniovertebral junction instability

OBJECTIVE

For reasons that are poorly understood and still undocumented, few patients of craniovertebral junction (CVJ) anomalies with instability/atlantoaxial dislocation (AAD) in our practice have been seen to suffer unprecedented acute neurological deterioration with respiratory compromise about 48-72 h post-surgery. This has been specifically observed after an uneventful, stable clinical condition in the immediate postoperative period. This study attempts to elucidate the factors and outcomes related to such latent worsening.

PATIENTS AND METHODS

The 4-year surgical data of 268-patients with CVJ instability (AAD/basilar-invagination) who underwent C1-C2 fixation were retrospectively studied. The relevant factors of 17 patients who showed such deterioration were compared with that of the remaining in a multivariate model.

RESULTS

Seventeen patients had acute neurological worsening with respiratory arrest after a latent period. Ten improved at follow-up. Contrary to the general expectation, poor preoperative neurological score or severe dislocation that needed considerable manipulation did not influence such worsening. Dural injury in patients with associated Chiari malformation and vertebral arterial (VA) injury emerged as independent factors (p < 0.01) associated with this pattern of delayed neurological decline.

CONCLUSIONS

We report our management and outcomes of a unique subset of AAD with neurological worsening in the postoperative period after 48-72 h. Such a subgroup was not previously identified in literature. Dural lacerations in AAD with Chiari, and VA injury seem to predispose to such complications and should be prevented at best. Close observation, and caution regarding early extubation (<72 h) is recommended in this subset despite an apparently uneventful immediate postoperative neurological status.

Displaced odontoid synchondrosis fracture with C1-2 dysjunction in an 18-month-old child: challenges and solutions

BACKGROUND

Odontoid synchondral fractures in very young children with displacement/angulation are highly unstable and require surgical intervention. Soft and small bones with poor pull-out strengths make instrumentation and manipulation difficult.

CASE REPORT

We report an 18-month-old child with such a fracture where minimal traction made C1-2 dysjunction apparent with neurological worsening. The C1-2 facets were fixed with a short plate and facetal screws. The child had a good outcome.

CONCLUSION

Traction should be applied cautiously to avoid distraction injuries. Careful intraoperative manipulation should be planned to avoid any pull outs/fractures while realigning the spine and fixing it.

Two-Stage Approach for Unstable Pediatric Craniocervical Junction Anomalies with a Halo Vest and Delayed Occipitocervical Fusion: Technical Note, Case Series, and Literature Review

OBJECTIVE

Malformations in the craniocervical junction (CCJ) are rare in the pediatric population but often need surgical treatment. We present a pediatric case series of patients treated with a 2-stage surgical approach with a halo vest and occipitocervical fusion and review complications and outcomes.

METHODS

A retrospective analysis of a single-center case series was performed. Pediatric patients affected by congenital craniocervical junction anomalies and treated with a 2-stage approach were included. A halo vest was implanted in the first surgery, and ambulatory progressive reduction was performed. When a favorable anatomic situation was observed, arthrodesis was performed. Safety analysis was undertaken by analyzing the incidence of complications in both procedures. Effectivity analysis was carried out analyzing radiologic and clinical outcome (Goel grade and modified Japanese Orthopaedic Association score). Student t test was used for statistical analysis.

RESULTS

Sixteen cases were included. Mean age of patients was 9.38 years. Safety analysis showed 2 halo loosenings, 1 pin infection, 2 wound infections, 1 cerebrospinal fluid leak, and 2 delayed broken rods. No major complications were observed. Radiologic analysis showed an improvement in the tip of the odontoid process to the McRae line distance (from -3.26 mm to -6.16 mm), atlantodental interval (from 3.05 mm to 1.88 mm), clival-canal angle (from 134.61° to 144.38°), and cervical kyphosis (from 6.39° to 1.54°). Clinical analysis also showed improvement in mean Goel grade (from 1.75 to 1.44) and modified Japanese Orthopaedic Association score (from 15.12 to 16.41).

CONCLUSIONS

The 2-stage approach was a suitable and effective treatment for craniocervical junction anomalies in pediatric patients.

Quantitative Reduction of Basilar Invagination: Correction Target of Clivo-Axial Angle

STUDY DESIGN

A mechanism-based reasoning and case-control study.

OBJECTIVE

To introduce correction target of clivo-axial angle (CXA) in quantitative surgical reduction of basilar invagination (BI).

SUMMARY OF BACKGROUND DATA

The exact mechanism of BI with or without atlantoaxial dislocation is still unclear. Sagittal deformity is a key feature of BI. Correction of CXA directly influences subaxial cervical lordosis (increase of CXA equals the decrease of cervical lordosis). However, a quantitative reference for correction surgery has not been established.

MATERIALS AND METHODS

CXA was divided by Chamberlain line into clivus tilt (CT) and axial tilt (AT). Patients diagnosed with BI were retrospectively included. Patients with degenerative cervical spine diseases or vascular diseases (without BI) were included as controls. CT, AT, and other common parameters were measured and analyzed with t test and multiple linear regression. Demonstration case was presented.

RESULTS

A total of 42 BI patients and 23 controls were included. Normal references for CXA, AT, and CT were 162.3±7.1, 93.8±6.5, and 68.6±3.8 degrees, respectively. BI patients had a 30.3-degree smaller CXA, a 15.5-degree smaller AT, and a 14.9-degree smaller CT. Basal angle (P=0.002) independently had a significant influence on extent of BI, while CT and AT did not. Demonstration case showed that CT was fixed and correcting AT to an ideal 94 degrees was optimal for an individual patient.

CONCLUSIONS

Proper quantitative correction of CXA needs to be individualized in consideration of CT and AT. The difference between actual AT and its ideal value (about 94 degrees) is the optimal target of CXA correction to decompress neural elements ventrally and recover better subaxial cervical lordosis.

LEVEL OF EVIDENCE

Level IV.

Quantitative Correction of Cervical Sagittal Deformity in Atlanto-Axial Dislocation

STUDY DESIGN

A mechanism-based reasoning and retrospective cohort study.

OBJECTIVE

To establish a quantitative relationship between the change of clivo-axial angle (CXA) and the change of subaxial cervical lordosis (CL) in correction surgery of atlantoaxial dislocation (AAD).

SUMMARY OF BACKGROUND DATA

The evolving understanding of mechanism has dramatically improved the treatment modality of AAD. Cervical sagittal alignment is another important aspect of the surgery, in addition to reduction of odontoid process. However, a quantitative reference for correction surgery has not been established.

METHODS

Frankfort-axial angle (FXA) was introduced. Based on two assumptions, (1) sagittal alignment of the spine aims at keeping horizontal gaze and (2) deformities at craniovertebral junction make little impact on slope of T1 vertebra, we deduced that the change of CXA equaled change of CL (ΔCXA = -ΔCL). We retrospectively reviewed our case cohort to validate this finding with linear regression analysis.

RESULTS

Sixteen cases (eight male and eight female, mean age 40.4±12.5 yr old) were included. Liner fitting equation for ΔFXA and ΔCXA is y=1.005x (coefficient of determination, R=0.966; significance of the estimated coefficients P<0.001, t-statistics) and that for ΔCL and ΔCXA is y=-1.023x (R=0.976, P<0.001). These results support our deduction that ΔCXA = -ΔCL, which can be used as a guidance of quantitative correction of sagittal deformity in AAD.

CONCLUSION

Correction of CXA will influence the subaxial cervical lordosis (ΔCXA = -ΔCL) of AAD patients. This equation can serve as a quantitative reference for preoperative planning and intraoperative refining of the correction of cervical sagittal deformity in AAD.

LEVEL OF EVIDENCE

4.

Change of Anatomical Location of the Internal Carotid Artery Relative to the Atlas with Congenital Occipitalization and the Relevant Clinical Implications

INTRODUCTION

The occipitalization of the atlas (OA) is always associated with multiplanar dislocation and olisthy of the C1 over C2 facets, which may change the anatomical relationship between the internal carotid artery (ICA) and the atlas. The purpose of this current study is to identify the location of the ICA relative to the anterior aspect of the atlas in patients with OA and define the clinical implications for screw placement.

METHODS

We retrospectively reviewed the computed tomography angiography data of 86 patients with OA and 86 control subjects. Several parameters were also measured to quantitatively evaluate the mutual relationship.

RESULTS

In the OA group, 25.6% of ICAs were located in area 3 and 74.4% in area 2, whereas the percentages were 57.4% and 42.6%, respectively, in the control group. There were 73 (42.4%) ICAs in which the shortest distance between the dorsal surface of the ICA and the ventral cortex of the atlas was less than 4 mm in the OA group and only 50 (29.1%) in the control group. The ideal angulation of C1 screw trajectory was about 5 degrees more medial in the OA group than that in the control group (P < 0.01).

CONCLUSIONS

The risk of ICA injury is much higher in OA patients than in non-OA patients during the C1 screw placement. A mean medial angulation about 20 degrees will permit a long and safe screw purchase, but should be individualized. We recommend careful preoperative computed tomography angiography evaluation in all patients before surgery.