The interspinous method of posterior atlantoaxial arthrodesis

Anatomical feasibility of pediatric cervical pedicle screw insertion by computed tomographic morphometric evaluation of 376 pediatric cervical pedicles

STUDY DESIGN

Prospective analysis of computed tomographic images of 376 normal pediatric cervical pedicles.

OBJECTIVE

To study the normal cervical pedicle morphometrics, the changes in pedicle morphology with skeletal growth, and the possibility of pedicle screw insertion.

SUMMARY OF BACKGROUND DATA

Although the usage of cervical pedicle screws in adults has become established, the feasibility of its application in children has not been studied. There are no in vivo studies that define the normal pediatric cervical pedicle morphometrics and its changes with growth and development of the child.

METHODS

A total of 376 normal pediatric cervical spine pedicles of 30 children (mean age = 6.7 ± 3.9 years) were analyzed for pedicle width (PW), pedicle height (PH), pedicle length (PL), pedicle axis length (PAL), transverse pedicle angle (TPA), and sagittal pedicle angle (SPA). The study population was categorized into three age groups (A: <5 years, B: 5-10 years, and C >10 years). The mean values of these parameters in the different age groups and the possibility of application cervical pedicle screws were studied. RESULTS.: The mean PW was lowest in the C3 vertebra and increased distally to be widest at C7. Sixty percent of C3 pedicles had a width less than 4 mm making screw passage risky and unsafe. With growth, the PW increased at all levels but this increase was significant only up to the age of 10 years. More than 75% of adult pedicle dimensions were achieved by 5 years of age. The mean PL at all levels remained the same with no significant increase with growth. However, the PAL showed continuous increase with growth similar to PW. The PAL also showed an increase from C3 to C7. The PH was always more than the PW at any level. Mild insignificant asymmetry was present between the right and left side pedicles in all values.

CONCLUSION

With growth, there was a gradual increase in PW, PH, and PAL but was mainly before the age of 10 years. Majority of C3 pedicles were thin making screw fixation unsafe. However, at all other levels, the pedicle morphometrics per se were adequate and do not restrict safe application of 3-mm cervical pedicle screw.

Intra-operative computer navigation guided cervical pedicle screw insertion in thirty-three complex cervical spine deformities

Background:

Cervical pedicle screw fixation is challenging due to the small osseous morphometrics and the close proximity of neurovascular elements. Computer navigation has been reported to improve the accuracy of pedicle screw placement. There are very few studies assessing its efficacy in the presence of deformity. Also cervical pedicle screw insertion in children has not been described before. We evaluated the safety and accuracy of Iso-C 3D-navigated pedicle screws in the deformed cervical spine.

Materials and Methods:

Thirty-three patients including 15 children formed the study group. One hundred and forty-five cervical pedicle screws were inserted using Iso-C 3D-based computer navigation in patients undergoing cervical spine stabilization for craniovertebral junction anomalies, cervico-thoracic deformities and cervical instabilities due to trauma, post-surgery and degenerative disorders. The accuracy and containment of screw placement was assessed from postoperative computerized tomography scans.

Results:

One hundred and thirty (89.7%) screws were well contained inside the pedicles. Nine (6.1%) Type A and six (4.2%) Type B pedicle breaches were observed. In 136 levels, the screws were inserted in the classical description of pedicle screw application and in nine deformed vertebra, the screws were inserted in a non-classical fashion, taking purchase of the best bone stock. None of them had a critical breach. No patient had any neurovascular complications.

Conclusion:

Iso-C navigation improves the safety and accuracy of pedicle screw insertion and is not only successful in achieving secure pedicle fixation but also in identifying the best available bone stock for three-column bone fixation in altered anatomy. The advantages conferred by cervical pedicle screws can be extended to the pediatric population also.

Seven Years of Experience With C2 Translaminar Screw Fixation: Clinical Series and Review of the Literature

BACKGROUND:

C2 translaminar screws offer biomechanical stability similar to that of other C2 fixation methods but with minimal risk to neural and vascular structures.

OBJECTIVE:

To report our experience with the technique since 2002 and to review the pertinent literature to advance the understanding of C2 translaminar screw fixation.

METHODS:

Fifty-two consecutive adult patients with disorders requiring axis stabilization were treated with C2 translaminar screws by a single surgeon. All patients underwent preoperative computed tomography scans to confirm the feasibility of screw placement. Patients were followed up with serial flexion/extension radiographs and/or computed tomography scans.

RESULTS:

The average age in our series was 58.1 years. One hundred three C2 translaminar screws were placed (average length, 28.9 mm). No vascular or neurological injuries occurred. Of 41 patients with sufficient follow-up (average, 13.3 months) to evaluate fusion, 1 instrumentation failure/pseudoarthrosis was observed. Five patients (average age, 78.7 years) died of complications related to medical comorbidities. In the literature, 169 cases of C2 translaminar fixation have been reported, with a fusion rate of 95.3% and no vertebral artery injuries. In biomechanical studies, C2 translaminar screws perform similarly to C2 pedicle screws and may outperform C2 pars screws in intact spine models. With disrupted atlantoaxial ligaments, constructs with C2 translaminar screws may not resist lateral bending as well as those with other screws, although they have more stability than uninstrumented, intact spines.

CONCLUSION:

This study reports 103 C2 translaminar screws, the largest single-surgeon series to date. C2 translaminar screws are a technically feasible, low-risk option for C2 fixation, with a 97.6% fusion rate in this series.

Pediatric cervical spine injuries: a comprehensive review

INTRODUCTION

Cervical spine injuries can be life-altering issues in the pediatric population. The aim of the present paper was to review this literature.

CONCLUSIONS

A comprehensive knowledge of the special anatomy and biomechanics of the spine of children is essential in diagnosis and treating issues related to spine injuries.

Symptomatic vertebral artery compression by the rod of a C1-C2 posterior fusion construct: case report and review of the literature

STUDY DESIGN

Case report.

OBJECTIVE

To report a rare complication of atlantoaxial fusion.

SUMMARY OF BACKGROUND DATA

Vertebral artery injury is a serious complication of screw-based atlantoaxial fusion. To our knowledge, injury to the vertebral artery has only been described as a result of screw placement. We describe the first case of atlantoaxial fixation complicated by symptomatic and reversible external compression of the vertebral artery by the rod in a Harms construct.

METHODS

Medical records and imaging reports were reviewed.

RESULTS

A neurologically intact 84-year-old woman presented after a ground-level fall. Imaging revealed a nondisplaced type II odontoid fracture associated with a C1 ring fracture. She underwent a minimally invasive Harms atlantoaxial fusion. After surgery, she developed fluctuating level of consciousness in the setting of an otherwise normal neurologic and metabolic workup. A computed tomographic angiogram was obtained and showed good screw placement except for compression of the right vertebral artery from the right transfixing rod causing 75% luminal narrowing. She underwent a revision with rod shortening, and after surgery, improved neurologically, without any further episodes of altered mental status.

CONCLUSION

In atlantoaxial fusion, the incidence of vertebral artery compression by the rod component of fusion construct may be underreported because it is difficult to detect with noncontrast computed tomography without computed tomographic angiography, which is not routinely obtained unless there is a high suspicion for vascular injury. We recommend inserting the rods with the cut (sharp) end pointing inferiorly, to avoid lacerating the vertebral artery. A vertebral artery compression from the rod in the absence of screw violation of the foramen transversarium should be considered in a patient with altered mental status after atlantoaxial fusion.

Biomechanical evaluations of various c1-c2 posterior fixation techniques

STUDY DESIGN

A biomechanical in vitro study using human cadaveric spine.

OBJECTIVE

To compare the biomechanical stability of pedicle screws versus various established posterior atlantoaxial fixations used to manage atlantoaxial instability.

SUMMARY OF BACKGROUND DATA

Rigid screw fixation of the atlantoaxial complex provides immediate stability and excellent fusion success though has a high risk of neurovascular complications. Some spine surgeons thus insert shorter C2 pedicle or pars/isthmus screws as alternatives to minimize the latter risks. The biomechanical consequences of short pedicle screw fixation remain unclear, however.

METHODS

Seven human cadaveric cervical spines with the occiput attached (C0-C3) had neutral zone (NZ) and range of motion (ROM) evaluated in three modes of loading. Specimens were tested in the following sequence: initially (1) the intact specimens were tested, after destabilization of C1-C2, then the specimens underwent (2) C1 lateral mass and C2 short pedicle screw fixation (PS-S), (3) C1 lateral mass and C2 long pedicle screw fixation (PS-L), (4) C1 lateral mass and C2 intralaminar screw fixation (ILS), (5) Sonntag's modified Gallie fixation (MG) and (6) C1-C2 transarticular screw fixation with posterior wiring (TAS 1 MG). (7) The destabilized spine was also tested.

RESULTS

All instrumented groups were significantly stiffer in NZ and ROM than the intact spines, except in lateral bending, which was statistically significantly increased in the TAS 1 MG group. The MG group's NZ and ROM values were statistically significantly weaker than those of the PS-S, PS-L, and the ROM values of the TAS 1 MG groups. The ILS group's NZ values were higher than those of the TAS 1 MG group and for ROM, than that of the PS-S and PS-L groups. In flexion, the NZ and ROM values of the TAS 1 MG group were significantly less than those of the PS-S, PS-L, ILS, and MG groups. In axial rotation, the NZ and ROM values of the MG group were statistically significantly higher than those of the PS-S, PS-L, ISL and TAS 1 MG groups.

CONCLUSION

The TAS 1 MG procedures provided the highest stability. The MG method alone may not be adequate for atlantoaxial arthrodesis, because it does not provide sufficient stability in lateral bending and rotation modes. The C2 pedicle screw and C2 ILS techniques are biomechanically less stable than the TAS 1 MG. In the C1 lateral mass-C2 pedicle screw fixation, the use of a short pedicle screw may be an alternative when other screw fixation techniques are not feasible.

Posterior fixation of the upper cervical spine: contemporary techniques

Instrumentation in the upper cervical spine has changed considerably in the past two decades. Previous stand-alone wiring techniques have been made largely obsolete with the development of occipital segmental plating, transarticular screws, and C1 lateral mass screws, as well as a myriad of C2 fixation options, including pedicle, pars, and translaminar screws. Polyaxial screws and segmental fixation are more user-friendly than stand-alone wiring and provide a stronger construct. Awareness of the risks and benefits associated with the use of modern instrumentation and thorough familiarity with the anatomy of the upper cervical spine are essential to avoid complications and optimize outcomes.

C-1 lateral mass screw fixation in children with atlantoaxial instability: case series and technical report

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To evaluate the feasibility, safety, and efficacy of incorporating C-1 lateral mass screws into fusion constructs in children with atlantoaxial instability.

SUMMARY OF BACKGROUND DATA

The operative treatment of atlantoaxial instability varies widely based on anatomy, patient age, and surgeon preference. The modified Harms construct, consisting of polyaxial C-1 lateral mass screws together with C-2 pedicle or pars screws and rods, has shown satisfactory fusion rates and minimal incidence of complications in adult patients. However, its utility in the pediatric population remains unproven, largely because of the technical challenges and risks inherent in placing C-1 lateral mass screws in children with immature bone quality, extensive anatomical variability, and smaller osseous structures.

METHODS

We retrospectively reviewed the records of all pediatric patients with atlantoaxial instability treated surgically, with a fusion construct incorporating C-1 lateral mass screws, at our institution between July 1, 2005 and June 30, 2008. Eight patients were identified and their relevant clinical data were abstracted from the medical record.

RESULTS

All patients had C-1 lateral mass screws placed as part of a fixation construct. Six cases used C-2 pedicle screws and 2 cases used C-3 lateral mass screw fixation for the inferior portion of the construct. There were 6 female and 2 male patients. Age at the time of the surgery ranged from 5 to 13 years (mean 9 y), and follow-up ranged from 11 to 38 months (mean 23 mo). No C-2 nerve root was sacrificed in any patient. There were no intraoperative or postoperative complications, including neurological injury, vascular injury, or hardware-related complications. Successful fusion was documented with dynamic cervical spine radiography in all cases.

CONCLUSIONS

C-1 lateral mass screw placement is generally feasible and safe in pediatric patients. With a nearly 2-year average follow-up, C1-2 rigid screw/rod fixation has proven to be an effective treatment modality for pediatric atlantoaxial instability in our series.

Avaliação da trajetória dos parafusos bicorticais pela técnica de harms e melcher em relação à artéria carótida interna: estudo experimental em cadáveres

OBJETIVO: O objetivo deste trabalho é estudar, em peças anatômicas; a relação entre os parafusos bicorticais pela técnica de Harms e Melcher e a artéria carótida interna. MÉTODOS: Nossa amostra consiste em cinco cadáveres. RESULTADOS: Os resultados encontrados foram: a média da menor distância entre o orifício de saída do parafuso e a borda medial da artéria carótida interna direita foi de 11,55 mm (com variação de 10,05 a 14,23 mm), enquanto do lado esquerdo a média foi de 7,50 mm (variando de 2,75 a 12,42 mm). A média da menor distância entre a borda posterior da artéria carótida interna e a cortical anterior da massa lateral de C1 à direita foi de 4,24 mm (variando de 2,08 a 7,48 mm), enquanto do lado esquerdo a média obtida foi de 2,98 mm (com variação de 1,83 a 3,83 mm). CONCLUSÃO: Os resultados encontrados estão de acordo com os estudos similares existentes na literatura que enfatizam a necessidade de uma avaliação imaginológica criteriosa da posição anatômica da artéria carótida interna antes da utilização de parafusos bicorticais na massa lateral de C1 por via posterior.

Intracranial hemorrhage and spinal cord injury from a fractured C1-C2 sublaminar cable: case report

OBJECTIVE

This is a unique case report of a fractured atlantoaxial interspinous multistranded cable leading to intracranial hemorrhage and spinal cord injury.

CLINICAL PRESENTATION

A 61-year-old woman, with a history of rheumatoid arthritis and C1-C2 interspinous wiring with allograft for atlantoaxial instability, presented with neck pain and progressive decline in mental status. Prior to transfer to our institution from a referral hospital, imaging studies revealed progressive hydrocephalus with interval development of subarachnoid and fourth ventricular hemorrhage. Initial and repeat angiographic work-up was negative for vascular lesions. Magnetic resonance imaging revealed a subdural hematoma and signal changes at the cervicomedullary junction. Computed tomography of the cervical spine revealed a fractured interspinous cable, intradural penetration, and atlantoaxial instability.

INTERVENTION

After ventriculostomy, both the patient's mental status and quadriparesis improved to a C on the American Spinal Injury Association (ASIA) scale. During surgery, the fractured cable and subdural hematoma were removed revealing an area of spinal cord impalement. She underwent C1-C3 lateral mass fixation with iliac crest autograft for fusion and was discharged to rehabilitation after a ventriculoperitoneal shunt was placed. At her 6-month follow-up, she was independent and had improved to ASIA E. Computed tomography confirmed fusion.

CONCLUSION

Spinal instrumentation eventually fails from pseudarthrosis and can cause neurological injury. In patients with atlantoaxial instability, direct C1-C2 screw fixation with posterior interspinous wiring using autograft offers the best chance for fusion. Cervical spine pathology can cause intracranial hemorrhage, and unconventional causes of injury must be considered when routine workup is negative.

Stabilization of the atlantoaxial joint with C1-C3 lateral mass screw constructs: biomechanical comparison with standard technique

BACKGROUND

Anatomically and biomechanically, the atlantoaxial joint is unique compared with the remainder of the cervical spine.

OBJECTIVE

To assess the in vitro stability provided by 2 C2 screw sparing techniques in a destabilized model of the atlantoaxial joint and compare with the gold standard system.

METHODS

The 3-dimensional intervertebral motion of 7 human cadaveric cervical spine specimens was recorded stereophotogrammetrically while applying nonconstraining, nondestructive pure moments during flexion-extension, left and right axial rotation, and left and right lateral bending. Each specimen was tested in the intact state, followed by destabilization (odontoidectomy) and fixation as follows: (1) C1 and C3 lateral mass screws rods with sublaminar wiring of C2 (LC1-C3 + SW), (2) C1 and C3 lateral mass screws rods with a cross-link in the C1-2 interlaminar space (LC1-C3 + CL), (3) C1 and C3 lateral mass screw rods alone (negative control), and (4) C1 lateral mass and C2 pedicle screws rods augmented with C1-2 interspinous wire and graft (LC1-PC2, control group).

RESULTS

Compared with the intact spine, each instrumented state significantly stabilized range of motion and lax zone at C1-2 (P < .001, 1-way repeated-measures analysis of variance). LC1-C3 + SW was equivalent to LC1-PC2 during flexion and lateral bending and superior to LC1-C3 + CL during lateral bending, while LC1-C3 + CL was equivalent to LC1-PC2 only during flexion. In all other comparisons, LC1-PC2 was superior to both techniques.

CONCLUSION

From a biomechanical perspective, both C2 screw sparing techniques provided sufficient stability to be regarded as an alternative for C1-2 fixation. However, because normal motion across C2-3 is sacrificed, these constructs should be used in patients with unfavorable anatomy for standard fixations.

Posterior rotating rod reduction strategy for irreducible atlantoaxial subluxations with congenital odontoid aplasia

STUDY DESIGN

Applying rotating rod techniques to reduce irreducible atlantoaxial dislocation.

OBJECTIVE

To spare the occipital-C1 motion by the strategy in reduction of before surgery irreducible atlantoaxial dislocation with obvious neurologic symptoms and congenital odontoid aplasia.

SUMMARY OF BACKGROUND DATA

The treatment of atlantoaxial dislocation (AAD) is a challenging problem for most surgeons. Posterior surgical stabilization of C1 and C2 include C1-C2 transarticular screws, or C1 lateral with C2 pars screws. These constructs, however, are based on preoperative reductions. When preoperative skull reduction fails and myelopathic symptoms coexist, long-segment cervico-occipital fusion and decompression are usually the only practical choice.

METHODS

The authors explored a different surgical technique to spare the axial occipital joints by rotating rods in polyaxial C1, C3 lateral mass, and C2 pars screws, functioning as a lever analogue. Three before surgery irreducible AAD cases with obvious neurologic symptoms and congenital odontoid aplasia were successfully reduced and fused with this procedure. The authors used intraoperative somatosensory-evoked potential monitoring and intraoperative fluoroscopy. Preoperative skull traction was employed to distract and help extend the atlantoaxial complexes.

RESULTS

Three C1-C2 dislocations were reduced completely without any deterioration of neurologic signs. Cervical myelopathic symptoms recovered soon after the operation. No atlantoaxial subluxation recurred. They returned to their normal work and/or activities.

CONCLUSION

The rotating rod strategy is a viable option to reduce and fuse C1-C3 for AAD with odontoid aplasia. It spares the occipital-C1 motion.

Anterolateral C1–C2 Transarticular Fixation for Atlantoaxial Arthrodesis: Landmarks, Working Area, and Angles of Approach

BACKGROUND:

An alternative route must be used for atlantoaxial arthrodesis to avoid the risks of transoral route or when posterior approaches are contraindicated.

OBJECTIVE:

To assess relevant quantitative anatomic parameters for C1–C2 anterolateral transarticular fixation and to demonstrate the nuances of an anterolateral approach to the upper cervical spine.

METHODS:

Five cadaveric necks were dissected bilaterally to demonstrate anatomic landmarks and surgical technique. The C2 pars interarticularis was used as the entry for inserting screws toward the C1 lateral mass. Ten computed tomography scans were analyzed to quantify working area and optimal angles of approach.

RESULTS:

The medial surface of sternocleidomastoid muscle was dissected extensively but not divided. The C2 transverse process was a landmark for guiding dissection posterior to the carotid sheath. In all specimens, the gray ramus communicans from the superior cervical ganglion to the C2 nerve was a landmark for locating the C2 pars. Slightly below that branch, the longus capitis muscle could be displaced medially to reach the C2 pars. The ideal angles for screw placement were 22.9 ± 5.7° medial to the sagittal plane and 25.3 ± 7.4° posterior to the coronal plane. The mean working area was 71.2 mm2 (range, 49–103 mm2).

CONCLUSION:

We propose a new anterolateral stabilization technique for atlantoaxial instability based on less traumatic dissection of the upper cervical region, different instrumentation, and guidance by reliable landmarks. For anterolateral transarticular C1–C2 screw fixation, the gray ramus communicans to the C2 nerve is a reliable landmark for locating the entry for a screw on the C2 pars.

Atlantoaxial stabilization utilizing atlas translaminar fixation

Atlantoaxial instability is a potentially devastating sequela of tumor invasion to the upper cervical spine. We aim to report an alternative technique for atlantoaxial stabilization. Stabilization is technically demanding due to limited bony elements and proximity of the regional neurovascular structures. While the C1 lateral masses are considered robust points of fixation, one or both of these structures may be destroyed by pathology. A 54-year-old female presented with a lytic, metastatic lesion to one of the C1 lateral masses, which precluded its use for fixation. We utilized the contralateral hemilamina of the atlas for screw fixation and devised a stable construct that provided immediate stability. Thus, atlas translaminar fixation is a feasible option when the lateral masses cannot be utilized.

Axis fractures

BACKGROUND

Traumatic fractures of the second cervical vertebra are common, representing nearly 20% of all acute cervical spinal fracture-dislocation injuries. They are divided into 3 distinct injury patterns: odontoid fractures, hangman's fracture injuries, and fractures of the axis body, involving all other fracture injuries to the C2 vertebra.

OBJECTIVE

An evidence-based overview of the medical and surgical treatment strategies for each axis fracture injury sub-type.

RESULTS

Current medical and surgical management of traumatic fractures of the axis.

Technique for drilling instrument monitoring electrical conductivity in pediatric cervical spine screw insertion: a preliminary report

BACKGROUND

To detail a technique of assisted screw placement in pediatric patients with cervical spine disorders. The use of a recently produced wireless electronic freehand drilling instrument is documented.

METHODS

We performed fixation of the cervical spine using different screws in 5 consecutive patients with various cervical spine disorders (posttraumatic, neoplastic or metabolic). Clinical and radiologic features of all cases are reported. The surgical technique is described.

RESULTS

Twenty-six cervical screws (lateral mass, pars, and/or laminar) were placed with the use of the same pedicle screw pilot hole preparation device, and by the same surgical team. The average age of this patient group was 13.4 years (range: 6 to 16 y). Average follow-up was 10 months (range: 5 to 14 mo). All screws were inserted after the correct trajectory was identified. No breaches were detected. No screw failure was encountered. However, 8 of 26 (30.8%) screws were, on average, 1.3 mm longer that expected (range: 0.5 to 2.4 mm). None of the patients developed neurologic or vascular complications as a result of screw placement.

CONCLUSIONS

Cervical screws placement, although safe, is not free of complications: neurovascular injuries, dural tears, and paraplegia have been described. The use of a wireless electronic handheld pedicle screw pilot hole preparation instrument is a useful tool in the armamentarium of the spinal surgeon dealing with patients with complex spinal deformities or difficult anatomy. Our experience outlines the applicability of this technique at different cervical levels. However, this device is not satisfactory in predicting the length of the screws. The device should be modified or a preoperative computed tomography scan should be used to estimate safe the length of the screws.

LEVEL OF EVIDENCE

Level IV (case series).

Percutaneous anterior transarticular screw fixation for atlantoaxial instability

We reviewed the outcome of a retrospective case series of eight patients with atlantoaxial instability who had been treated by percutaneous anterior transarticular screw fixation and grafting under image-intensifier guidance between December 2005 and June 2008.

The mean follow-up was 19 months (8 to 27). All eight patients had a solid C1–2 fusion. There were no breakages or displacement of screws. All the patients with pre-operative neck pain had immediate relief from their symptoms or considerable improvement. There were no major complications. Our preliminary clinical results suggest that percutaneous anterior transarticulation screw fixation is technically feasible, safe, useful and minimally invasive when using the appropriate instruments allied to intra-operative image intensification, and by selecting the correct puncture point, angle and depth of insertion.

Equivalence of fusion rates after rigid internal fixation of the occiput to C-2 with or without C-1 instrumentation

OBJECT

The object of this study was to assess a multiinstitutional experience with pediatric occipitocervical constructs to determine whether a difference exists between the fusion and complication rates of constructs with or without direct C-1 instrumentation.

METHODS

Seventy-seven cases of occiput-C2 instrumentation and fusion, performed at 9 children's hospitals, were retrospectively analyzed. Entry criteria included atlantooccipital instability with or without atlantoaxial instability. Any case involving subaxial instability was excluded. Constructs were divided into 3 groups based on the characteristics of the anchoring spinal instrumentation: Group 1, C-2 instrumentation; Group 2, C-1 and C-2 instrumentation without transarticular screw (TAS) placement; and Group 3, any TAS placement. Groups were compared based on rates of fusion and perioperative complications.

RESULTS

Group 1 consisted of 16 patients (20.8%) and had a 100% rate of radiographically demonstrated fusion. Group 2 included 22 patients (28.6%), and a 100% fusion rate was achieved, although 2 cases were lost to follow-up before documented fusion. Group 3 included 39 patients (50.6%) and demonstrated a 100% radiographic fusion rate. Complication rates were 12.5, 13.7, and 5.1%, respectively. There were 3 vertebral artery injuries, 1 (4.5%) in Group 2 and 2 (5.1%) in Group 3.

CONCLUSIONS

High fusion rates and low complication rates were achieved with each configuration examined. There was no difference in fusion rates between the group without (Group 1) and those with (Groups 2 and 3) C-1 instrumentation. These findings indicated that in the pediatric population, excellent occipitocervical fusion rates can be accomplished without directly instrumenting C-1.

Atlantoaxial Transarticular Screw Fixation

BACKGROUND

Transarticular screw (TAS) fixation is our preferred method for stable internal fixation of the atlantoaxial joint because of its excellent outcomes, versatility, and cost-effectiveness.

OBJECTIVE

In this article, we update our series of patients who have undergone TAS fixation, with attention to surgical technique, planning, complication avoidance, and anatomic suitability.

METHODS

We retrospectively reviewed 269 patients (150 women, 119 men; average age, 52.9 years; age range, 17–90 years) who underwent placement of at least 1 TAS. In total, 491 TASs were placed for stabilization necessitated by various pathologic conditions. The mean follow-up period was 15.7 months (range, 0–106 months).

RESULTS

Fusion was achieved in 99% of 198 patients monitored until fusion or nonunion requiring revision, or for 2 years. Forty-five patients had a complication, for a rate of 16.7%. Five early patients had vertebral artery injuries, 1 of which was bilateral and fatal. No recent patients had vertebral artery injuries. Other complications did not result in neurologic morbidity. Review of all atlantoaxial fusions by the senior author (R.I.A.) revealed that the TAS fixation technique could be successfully applied in 86.7% of sides considered. The main reasons for inapplicability were anatomic (recognized on preoperative planning) in 77% and abandonment secondary to concern about possible vertebral artery injury on the first side attempted in 13.8%.

CONCLUSION

The placement of TASs is safe and effective for stabilizing the atlantoaxial articulation. Refinements in technique, such as 3-dimensional stereotactic workstation for trajectory planning, have reduced the rate of serious complications. Clinical outcomes are excellent, with nearly 100% of patients achieving stable bony union.

C1 Lateral Mass Fixation

OBJECTIVE

We review our experience and technique for C1 lateral mass screw fixation. We compare the results of 3 different constructs incorporating C1 lateral mass screws: occipitocervical (OC) constructs, C1–C2 constructs, and C1 to mid/low cervical constructs.

METHODS

We performed a retrospective chart review of 42 consecutive patients who underwent C1 lateral mass fixation by 2 of the authors (PVM and DC). The patient population consisted of 24 men and 18 women with a mean age of 64 years. Twenty-two patients had C1–C2 constructs. Twelve patients had constructs that started at C1 and extended to the mid/low cervical spine (one extended to T1). Eight patients underwent OC fusions incorporating C1 screws (2 of which were OC-thoracic constructs). All constructs were combined either with a C2 pars screw (38 patients), C2 translaminar screw (1 patient), or C3 lateral mass screw (3 patients). No C2 pedicle screws were used. Fusion was assessed using flexion-extension x-rays in all patients and computed tomographic scans in selected cases. Clinical outcomes were assessed with preoperative and postoperative visual analog scale neck pain scores and Nurick grading. The nuances of the surgical technique are reviewed, and a surgical video is included.

RESULTS

Two patients (5%) were lost to follow-up. The mean follow-up for the remaining patients was 2 years. During the follow-up period, there were 4 deaths (none of which were related to the surgery). For patients with follow-up, the visual analog scale neck pain score improved a mean of 3 points after surgery (P &lt; .001). For patients with myelopathy, the Nurick score improved by a mean of 1 grade after surgery (P &lt; .001). The postoperative complication rate was 12%. The complication rate was 38% in OC constructs, 17% in C1 to mid/low cervical constructs, and 0% for C1–C2 construct cases. Patients with OC constructs had the statistically highest rate of complications (P &lt; .001). Patients with C1 to mid/low cervical constructs had more complications than those with C1–C2 constructs (P &lt; .001). Of the 42 cases, there were 3 pseudoarthroses (1 in an OC case, 1 in a C1 to midcervical construct, and 1 in a C1–C2 construct). OC constructs had the highest risk of pseudoarthrosis (13%) (P &lt; .001).

CONCLUSION

Patients treated with C1 lateral mass fixation constructs have a high fusion rate, reduced neck pain, and improved neurologic function. Constructs using C1 lateral mass screws do not need to incorporate C2 pedicle screws. Constructs incorporating C1 lateral mass screws are effective when combined with C2 pars screws, C2 translaminar screws, and C3 lateral mass screws. Constructs using C1 screws are associated with a higher complication rate and a higher pseudoarthrosis rate if extended cranially to the occiput or if extended caudally below C2.

Decisão no tratamento das fraturas do odontoide

OBJETIVO: avaliação e determinação de critérios que possam nortear o tratamento das fraturas do odontoide. MÉTODOS: foi realizado estudo retrospectivo e comparativo entre o tratamento conservador e o cirúrgico do odontoide em 24 pacientes com fratura decorrente de trauma. Os pacientes foram avaliados por meio de exame clínico e radiológico e o tratamento efetuado foi avaliado por meio de testes descritivos, distribuição de frequências e testes estatísticos comparativos. RESULTADOS: foram observados 17 pacientes do sexo masculino (70,8%) e 7 do sexo feminino (29,2%), com idades entre 12 e 80 anos (média de 39 anos) e seguimento pós-tratamento de 12 a 110 meses. Em relação às fraturas, não foram observadas fraturas do tipo I, 17 casos apresentaram fratura do tipo II (70,8%) e 7 do tipo III (29,2%), classificadas segundo Anderson e D'Alonzo. A decisão pelo tratamento cirúrgico ou conservador ocorreu em função de critérios de redução e instabilidade. Quando se decidia pelo tratamento cirúrgico, era utilizado o acesso de Southwick-Robinson, utilizando-se um parafuso canulado para a fixação da fratura. Nos pacientes tratados conservadoramente, optou-se pelo halo-gesso ou colar cervical tipo Philadelphia. Independentemente do tipo da fratura, a consolidação ocorreu em média em três meses para os pacientes tratados cirurgicamente, enquanto as fraturas tratadas conservadoramente consolidaram em torno de cinco meses. CONCLUSÕES: apesar de haver uma tendência à consolidação mais rápida quando é realizado o tratamento cirúrgico, o tratamento conservador deve ser considerado, tendo em vista os critérios de redução e instabilidade.

Fixation of the Axis

OBJECTIVE

To review and compare the techniques of fixation of the axis vertebral segment. Also, to review the anatomy of the axis vertebrae, ligamentous attachments, and unique biomechanics of this segment.

METHODS

The use of wire, cable, screw, and plate fixation techniques are reviewed and discussed in the treatment of fractures of C1 and C2 along with utilization of the halo vest and cervical collar during the postoperative period.

RESULTS

All fixation methods were useful. However, the appropriate fixation technique is best determined by the local anatomy (eg, anomalous vertebral artery), posterior element fractures, or the necessity to remove the posterior elements for treatment of the underlying condition.

CONCLUSION

New techniques for fixation and instrumentation for fixation of the axis are available. Advanced imaging allows for advanced aggressive instrumentation while avoiding injury to adjacent structures. Biomechanical studies have influenced the utility and popularity of each technique.

C1-C2 transarticular screw fixation for atlantoaxial instability due to rheumatoid arthritis: a seven-year analysis of outcome

STUDY DESIGN.: Observational study. Retrospective analysis of prospectively collected data. OBJECTIVE.: The purpose of this article was to report long-term (minimum 7 years) clinical and radiologic outcome of our series of patients with Rheumatoid Arthritis who underwent transarticular screw fixation to treat atlantoaxial subluxation. SUMMARY OF BACKGROUND DATA.: The indications for intervention in patients with atlantoaxial instability are pain, myelopathy, and progressive neurologic deficit. The various treatment options available for these patients are isolated C1-C2 fusion, occipitocervical fusion with or without transoral surgery. Review of current literature suggests that C1-C2 transarticular screw fixation has significant functional benefits, although there is discrepancy in this literature regarding improvement in function following surgery. METHODS.: Myelopathy was assessed using Ranawat myelopathy score and Myelopathy Disability Index. Pain scores were assessed using Visual Analogue Scale. The radiologic imaging was assessed and the following data were extracted; atlanto-dens interval, space available for cord, presence of signal change on T2 weighted image, and fusion rates. RESULTS.: Thirty-seven patients, median age 56, were included in the study. Average duration of neck symptoms was 15.8 months. Average duration of rheumatoid arthritis before surgery was 20.6 years. Preoperative symptoms: suboccipital pain in 26 patients; neck pain, 32; myelopathy, 22; and 5 were asymptomatic. After surgery: suboccipital pain, 2; neck pain, 3; and myelopathy, 10. Ninety percent patients with neck and suboccipital pain improved after surgery in their Visual Analogue pain scores, with all of them having >50% improvement in VAS scores (6.94-2.12 [P < 0.05]).Preoperative Ranawat grade was as follows: grade 1 in 15 patients, grade 2 in 7, and grade 3a in 14, grade 3b in 1.After surgery: grade 1 in 27 patients, grade 2 in 7, grade 3a in 1, and grade 3b in 2. The mean myelopathy score improved after surgery (59.62-32.75, P < 0.05).The space available for the cord was improved in 63%, unchanged in 33%, and worse in 4%.Twenty-seven percent had T2 signal change and 18% had cervicomedullary compression; 97% had bony fusion. BILATERAL SCREWS WERE USED IN 33 PATIENTS AND UNILATERAL SCREWS IN 4 PATIENTS (ABERRANT VERTEBRAL ARTERY).: Computer image guidance was used in 73%. CONCLUSION.: C1-C2 transarticular screw fixation is a safe technique for atlantoaxial subluxation for patients with rheumatoid arthritis. This study clearly demonstrates improvement in Visual Analogue Scale, Ranawat grading and the Myelopathy Disability Index even at long-term follow up.

Modification of Wright's technique for C2 translaminar screw fixation: technical note

PURPOSE

To describe a modification of Wright's technique for C2 translaminar screw fixation.

METHODS

Bilateral crossing C2 laminar screws have recently become popular as an alternative technique for C2 fixation. This technique is particularly useful in patients with anomalous anatomy, as a salvage technique where other modes of fixation have failed or as a primary procedure. However, reported disadvantages of this technique include breach of the dorsal lamina and spinal canal, early hardware failure and difficulty in bone graft placement due to the position of the polyaxial screw heads. To address some of these issues, a modified technique was used in six patients. In this technique, the upper part of the spinous process of C2 was removed and the entry point of the screw was in the base of this removed spinous process.

RESULTS

The screw position was satisfactory in all patients. There were no intraoperative or early postoperative complications.

CONCLUSIONS

Our modification enables placement of a bone graft on the C2 lamina and is also less likely to cause inadvertent cortical breach. Because of these advantages, it is especially suitable for patients with advanced rheumatoid arthritis with destruction of the lateral masses of C2 or as part of a hybrid construct in patients with a unilateral high-riding vertebral artery. This technique is not suitable for bilateral translaminar screw placement.

Use of allograft bone for posterior C1–2 fusion

Object

An iliac crest autograft is the gold standard for bone grafting in posterior atlantoaxial arthrodesis but can be associated with significant donor-site morbidity. Conversely, an allograft has historically performed suboptimally for atlantoaxial arthrodesis as an onlay graft. The authors have modified a bone grafting technique to allow placement of a bicortical iliac crest allograft in an interpositional manner, and they evaluated it as an alternative to an autograft in posterior atlantoaxial arthrodesis.

Methods

The records of 89 consecutive patients in whom C1–2 arthrodesis was performed between 2001 and 2005 were reviewed.

Results

Forty-seven patients underwent 48 atlantoaxial arthrodeses with an allograft (mean follow-up 16.1 months, range 0–49 months), and 42 patients underwent autograft bone grafting (mean follow-up 17.6 months, range 0–61.0 months). The operative time was 50 minutes shorter in the allograft (mean 184 minutes, range 106–328 minutes) than in the autograft procedure (mean 234 minutes, range 154–358 minutes), and the estimated blood loss was 50% lower in the allograft group than in the autograft group (mean 103 ml [range 30–200 ml] vs mean 206 ml [range 50–400 ml], respectively). Bone incorporation was initially slower in the allograft than in the autograft group but equalized by 12 months postprocedure. The respective fusion rates after 24 months were 96.7 and 88.9% for autografts and allografts. Complications at the donor site occurred in 16.7% of the autograft patients, including 1 pelvic fracture, 1 retained sponge, 1 infection, 2 hernias requiring repair, 2 hematomas, and persistent pain.

Conclusions

The authors describe a technique for interpositional bone grafting between C-1 and C-2 that allows for the use of an allograft with excellent fusion results. This technique reduced the operative time and blood loss and eliminated donor-site morbidity.

A novel computer-assisted drill guide template for placement of C2 laminar screws

The present method of C2 laminar screw placement relies on anatomical landmarks for screw placement. Placement of C2 laminar screws using drill template has not been described in the literature. The authors reported on their experience with placement of C2 laminar screws using a novel computer-assisted drill guide template in nine patients undergoing posterior occipito-cervical fusion. CT scan of C2 vertebrae was performed. 3D model of C2 vertebrae was reconstructed by software MIMICS 10.01. The 3D vertebral model was then exported in STL format, and opened in a workstation running software UG imageware12.0 for determining the optimal laminar screw size and orientation. A virtual navigational template was established according to the laminar anatomic trait. The physical vertebrae and navigational template were manufactured using rapid prototyping. The navigational template was sterilized and used intraoperative to assist the placement of laminar screw. Overall, 19 C2 laminar screws were placed and the accuracy of screw placement was confirmed with postoperative X-ray and CT scanning. There were not complications of related screws insertion. Average follow-up was 9 months (range 4-13 months), 77.8% of the patients exhibited improvement in their myelopathic symptoms; in 22.2% the symptoms were unchanged. Postoperative computed tomographic (CT) scanning was available for allowing the evaluation of placement of thirteen C2 laminar screws, all of which were in good position with no spinal canal violation. This study shows a patient-specific template technique that is easy to use, can simplify the surgical act and generates highly accurate C2 laminar screw placement. Advantages of this technology over traditional techniques include planning of the screw trajectory is done completely in the presurgical period as well as the ability to size the screw to the patient's anatomy.

Pre-operative irreducible C1-C2 dislocations: intra-operative reduction and posterior fixation. The "always posterior strategy"

BACKGROUND

According to Menezes' algorithm, pre-operative dynamic neuroradiological investigation in C1-C2 dislocations (C1C2D) instability is strongly advocated in order to exclude those patients not eligible for posterior fixation and fusion without previous anterior trans-oral decompression. Anterior irreducible compression due to C1C2D instability, it is said, needs trans-oral anterior decompression. We reviewed our experience in order to refute such a paradigm.

METHODS

The study involves 23 patients who were operated on for cranio-vertebral junction (CVJ) instability; all of them had C1C2D of varying degree on x-ray, computerised tomography (CT) and magnetic resonance (MR) imaging of the CVJ. Pre-operatively, irreducible C1C2D was demonstrated only in 3 patients, (2 with Down's Syndrome, one of them was harbouring os odontoideum, 1 Rheumatoid Arthritis), i.e. 13.04%; the remaining 19 (86.9%) had reducible C1-C2 dislocation. After an unsuccessful traction test conducted in the pre-operative phase under sedation, it was possible to completely reduce the C1C2D (with a combination of axial traction with light extension of the neck on the chest and a light flexion of the head on the neck by using a Mayfield head holder) and proceed to posterior fixation in all the patients under general anaesthesia using a precise "timing sequences fixation technique". Wiring (C0 and C3 were fixed first being stretched up to approximately 10 lbs, then C2 in order to pull up this vertebra last by forcing approximately 8 lbs) or screw fixation methods were used to achieve fusion along with post-operative external orthosis and neuroradiological assessment of the C1C2D. The instrumentation produced a lever and pulley effect which assisted reduction of the dislocation.

FINDINGS

At follow up (range 34-55 months-mean 45.33 months) the clinical picture was improved or stable in all patients.

CONCLUSIONS

Pre-operative irreducibility of the C1C2D should not be an absolute indication for trans-oral decompression. An attempt to reduce the dislocation under general anaesthesia and during posterior fixation should be attempted in Down's syndrome, os odontoideum and rheumatoid arthritis.

Outcomes of C1 and C2 posterior screw fixation for upper cervical spine fusion

To achieve stable fixation of the upper cervical spine in posterior fusions, the occiput is often included. With the newer techniques, excluding fixation to the occiput will retain the occiput-cervical motion, while still allowing a stable fixation. Harms's technique has been adapted at our institution and its effectiveness for indications such as C2 complex fractures and tumors using C1 or C2 as endpoints of a posterior fixation are reviewed. Fourteen cases were identified, consisting of one os odontoideum; four acute fractures and four non-unions of the odontoid; three tumors and two complex fractures of C2 vertebral body, and one C2-C3 post-traumatic instability. One misplaced screw without clinical consequences was the only complication recorded. Screw loosening or migration was not observed at follow-up, showing a stable fixation.

Atlantoaxial rotatory subluxation with ligamentous disruption: a biomechanical comparison of current fusion methods

OBJECTIVE

We evaluated the biomechanical effects of 4 instrumented configurations after induced atlantoaxial rotatory subluxation: transarticular screw fixation (T/A) and polyaxial C1 lateral mass and C2 pedicle screw and rod fixation (LC1-PC2) for atlantoaxial arthrodesis with unilateral and bilateral instrumentation.

METHODS

Three-dimensional intervertebral motion was tracked stereophotogrammetrically while 14 human cadaveric spine specimens underwent nonconstraining pure moment loading. Nondestructive loads were applied quasi-statistically in 0.25-Nm increments to a maximum load of 1.5 Nm during flexion-extension, right and left axial rotation, and right and left lateral bending. Hyperrotation injuries were created using torsional loads applied during left axial rotation until visible failure occurred.

RESULTS

In the normal condition, the values for angular range of motion, lax zone (zone of ligamentous laxity), and stiff zone (zone of ligamentous stretching) were similar in both groups in all directions of loading, with no significant differences (P > 0.05) between groups at C0-C1 or C1-C2. Both instrumentation systems (bilateral configurations) substantially stabilized angular motion at C1-C2 (P < 0.05) during all loading modes for the T/A group, and during all but right lateral bending (P = 0.072) for the LC1-PC2 group. The mean failure load for both intact and instrumented specimens was slightly greater, but not significant for the LC1-PC2 group compared with the T/A group (P > 0.14).

CONCLUSION

Both methods fixated atlantoaxial subluxation equally well. Compared with unilateral instrumentation, a bilateral configuration with the LC1-PC2 technique significantly increased stability during extension (P < 0.05). During axial rotation, bilateral T/A screws significantly increased stability compared with unilateral fixation (P < 0.02).

Cervical spine injuries in children: attention to radiographic differences and stability compared to those in the adult patient

The relative rarity of pediatric cervical spine injuries can impede rapid response and efficient care of this patient population. An understanding of the unique anatomical, radiographic, and biomechanical characteristics of the pediatric cervical spine is essential to the appropriate care of these challenging patients. Patterns of injury, diagnosis, and issues related to operative and nonoperative management are discussed with a focus on the developing spine. Our aim is to improve the understanding of traumatic cervical spine injuries in children for all practitioners involved with their care.

Operative management for atlantoaxial instability in case of bilateral high-riding vertebral artery

INTRODUCTION

In case of atlantoaxial instability dorsal C1-C2 screw fixation is the most appropriate procedure to get immediate and sufficient three-point fixation. However, this method cannot be performed in bilateral high-riding vertebral arteries because of high risk of VA injury.

CASE DESCRIPTION

In a 66-year-old woman who presented with neck pain due to atlantoaxial instability bilateral high-riding VAs were detected in CT. To avoid VA injury a dorsal stabilization procedure with a hook-rod system and interspinous autologous iliac crest graft was performed. The intra- and postoperative courses had no complications and the hook-rod construction clinically led to immediate postoperative stability. After 24 months the patient was painfree.

CONCLUSIONS

In case of atlantoaxial instability and bilateral high-riding VAs dorsal C1-C2 fixation procedure with a hook-rod system and interspinous bone grafting seems to be an appropriate alternative surgical technique and can get immediate and clinically sufficient stability with no risk of VA injury.

Estudo anatômico dimensional do arco posterior de C2 para a instrumentação com parafuso intralaminar

INTRODUÇÃO: A articulação atlantoaxial possui mecanismos estabilizadores C1-C2, ligamentares, ósseos e capsulares, mantendo a relação anatômica adequada entre C1 e C2. A falha, traumática ou atraumática, isolada ou um conjunto destes mecanismos leva à instabilidade atlantoaxial, podendo culminar em alterações neurológicas, dor e limitação da mobilidade cervical. Casos com déficit neurológico e de instabilidade moderada a grave, são passíveis de tratamento cirúrgico. Desde 1910 inúmeras técnicas de estabilização cirúrgica C1-C2 são praticadas e mesmo recentemente novas técnicas de estabilização C1-C2 vêm sendo desenvolvidas. Novas técnicas foram desenvolvidas utilizando parafusos bilaterais na massa lateral de C1 e na lâmina de C2, conectados por barras. OBJETIVO: Mensurar as dimensões da lâmina de C2 para avaliar a segurança e dimensão do parafuso a ser utilizado, pela técnica de Wright. MÉTODOS: Estudo anatômico com 29 cadáveres adultos dissecando a lâmina de C2, aferindo medidas externa e interna da lâmina no plano sagital, coronal e axial. RESULTADOS: A média das medidas das porções médias externas das lâminas de C2 foi 5,83 mm, das quais 8,93% foram abaixo de 3,5mm. CONCLUSÃO: Sugerimos um estudo tomográfico pré-operatório, para identificar pacientes com lâminas menores e logo em maior risco.

Os odontoideum: presentation, diagnosis, and treatment in a series of 78 patients

OBJECT

The most contentious issue in the management of os odontoideum surrounds the decision to attempt atlantoaxial fusion in patients with asymptomatic lesions. The authors examined the clinical presentation and outcome in patients with os odontoideum who underwent surgical stabilization, with an emphasis on 3 patients who initially received conservative treatment and suffered delayed neurological injury.

METHODS

Seventy-eight patients (mean age 20.5 years; median 15 years) were identified in a 17-year retrospective review. The median follow-up period was 14 months (range 1-115 months). Neck pain was the most common symptom (64%), and 56% of patients presented after traumatic injury. Eighteen patients had neurological signs or symptoms at presentation, and an additional 15 had a history of intermittent or prior neurological symptoms. Fifteen patients had undergone > or = 1 attempt at atlantoaxial fusion elsewhere.

RESULTS

Seventy-seven patients underwent posterior fusion and rigid screw fixation combined with a graft/wire construct: 75 had C1-2 fusion and 2 had occipitocervical fusion. One patient had an odontoid screw placed. Fusion was achieved in all patients at a median of 4.8 months (range 2-17 months). Approximately 90% of patients had resolution or improvement of their neck pain or neurological symptoms.

CONCLUSIONS

The authors believe that patients with os odontoideum are at risk for future spinal cord compromise. Forty-four percent of our patients had myelopathic symptoms at referral, and 3 had significant neurological deterioration when a known os odontoideum was left untreated. This risk of late neurological deterioration should be considered when counseling patients. Stabilization using internal screw fixation techniques resulted in 100% fusion, whereas 15% of patients had previously undergone unsuccessful wire and external bracing attempts.

SURGICAL TREATMENT OF OCCIPITOCERVICAL INSTABILITY

OBJECTIVE

Instability of the occipitocervical junction can be a challenging surgical problem because of the unique anatomic and biomechanical characteristics of this region. We review the causes of instability and the development of surgical techniques to stabilize the occipitocervical junction.

METHODS

Occipitocervical instrumentation has advanced significantly, and modern modular screw-based constructs allow for rigid short-segment fixation of unstable elements while providing the stability needed to achieve successful fusion in nearly 100% of patients. This article reviews the preoperative planning, the variety of instrumentation and surgical strategies, as well as the postoperative care of these patients.

RESULTS

Current constructs use occipital plates that are rigidly fixed to the thick midline keel of the occipital bone, polyaxial screws that can be placed in many different trajectories, and rods that are bent to approximate the acute occipitocervical angle. These modular constructs provide a variety of methods to achieve fixation in the atlantoaxial complex, including transarticular screws or C1 lateral mass screws in combination with C2 pars, C2 pedicle, or C2 translaminar trajectories.

CONCLUSION

Surgical techniques for occipitocervical instrumentation and fusion are technically challenging and require meticulous preoperative planning and a thorough understanding of the regional anatomy, instrumentation, and constructs. Modern screw-based techniques for occipitocervical fusion have established clinical success and demonstrated biomechanical stability, with fusion rates approaching 100%.

Fusions at the craniovertebral junction

INTRODUCTION

The surgical management of craniovertebral junction instability in pediatric patients has unique challenges. While the indications for internal fixation in children are similar to those of adults, the data concerning techniques, complications, and outcomes of spinal instrumentation comes from experience with adult patients. Diminutive osseous and ligamentous structures and anatomical variations associated with syndromic craniovertebral abnormalities frequently complicates the approaches and limits the use of internal fixation in children. Cervical arthrodesis in the pediatric age group has the potential for limiting growth potential and causing secondary deformity. Recent advances in image analysis have enabled preoperative planning which is critical to evaluate the size of instrumentation and its relation to the patient's anatomy. Newer techniques have recently evolved and have been incorporated in the management of pediatric patients with requirement for craniocervical stabilization.

MATERIALS AND METHODS

Over 750 craniovertebral junction fusions have been reviewed in children. The indications for atlantoaxial arthrodesis were: (a) absent odontoid process, dystopic os odontoideum, absent posterior arch of C1; (b) Morquio's syndrome, Goldenhar's syndrome, Conradi's syndrome, and spondyloepiphyseal dysplasia. The acquired abnormalities of trauma, postinfectious instability, and Down's syndrome completed the indication in children. The indications for occipitocervical fusion were: (a) anterior and posterior bifid C1 arches with instability, absent occipital condyles; b) severe reducible basilar invagination, unstable dystopic os odontoideum, and unilateral atlas assimilation; (c) acquired phenomenon with traumatic occipitocervical dislocation, complex craniovertebral junction fractures of C1 and C2, after transoral craniovertebral junction decompression, cranial settling in Down's syndrome and inflammatory disease such as Grisel's syndrome. Instability was seen in children with clivus chordoma and osteoblastoma. Atlantoaxial fusions were performed mainly with interlaminar rib graft fusion and more recently with the transarticular screw fixation in the older patient. In the teenager, lateral mass screws at C1 and rod fixation were made; C2 pars interarticular screw fixation and C2 pedicle screw fixation. A C2 translaminar screw fixation is described. Occipitocervical fusions were made utilizing rib grafts below the age of 6. A contoured loop fixation was made in children above the age of 7, and recently, rod and screw fixation was also utilized.

RESULTS

Abnormal cervical spine growth was not seen in children who underwent craniocervical stabilization below the age of 5. The authors have reserved rigid instrumentation for children above the age of 10 years and dependent on the anatomy.

Anatomical relationship of the internal carotid artery to C-1: clinical implications for screw fixation of the atlas

Object

Various C1–2 instrumentation techniques have been developed to treat atlantoaxial instability. Screw fixation of C1–2 poses a risk of injury to the vertebral artery and internal carotid artery (ICA). Injury to the ICA caused by C-1 screws is extremely rare, but has been described. To characterize this risk, the authors studied the anatomical relationship of the ICA to the lateral mass of C-1.

Methods

The authors studied 100 patients who had undergone computed tomography scanning and magnetic resonance imaging of the neck to assess the position of the ICA in association with the C-1 lateral mass. Each ICA was classified into 1 of the following 4 zones: Zone 1 (medial to lateral mass), Zone 2 (medial half of lateral mass), Zone 3 (lateral half of lateral mass), and Zone 4 (lateral to lateral mass). For patients with an ICA ventral to the lateral mass, the shortest distance between the ICA and lateral mass was measured to determine the margin of error with an overpenetrated bicortical screw.

Results

Of the 100 patients, 58% had a left ICA in Zones 2 and 3 with a mean distance from the anterior cortex of 3.5 ± 1.5 mm (± standard deviation), and 74% had a right ICA in Zones 2 and 3 with a mean distance from the anterior cortex of 3.9 ± 1.6 mm. Both ICAs anterior to the lateral mass were noted in 47% of patients, and 84% had ≥ 1 ICA anterior to the lateral mass. When the ICA was anterior to the lateral mass, it was more commonly in the lateral half (left ICA in 91% and right ICA in 92%). The left ICA was in Zone 1 in 1% and Zone 4 in 41%. The right ICA was in Zone 1 in 1% and Zone 4 in 25%.

Conclusions

A high percentage of patients demonstrate an ICA directly ventral to the C-1 lateral mass, which poses a risk of ICA injury caused by an overpenetrated bicortical screw.

Application of laminar screws to posterior fusion of cervical spine: measurement of the cervical vertebral arch diameter with a navigation system

STUDY DESIGN

Morphometric analysis.

OBJECTIVE

For safe and solid fixation, it is necessary to measure the diameter of the vertebral arch to ascertain whether or not screws can be used and if so, the appropriate size of screws to be used.

SUMMARY OF BACKGROUND DATA

Cervical pedicle screws are the most biomechanically stable screws. However, their use carries a high risk of neurovascular complications during screw insertion. In 2004, a new method to avoid such vertebral artery injuries was reported by insertion of screws with crosswise to the lamina of C2. For safe and solid fixation, it is necessary to measure the diameter of the vertebral arch to ascertain whether or not screws can be used and if so, the appropriate size of screws to be used. There is no report of the diameter of the vertebral arch by a navigation system.

METHODS

Morphometric analysis was performed on 42 patients who had undergone a CT scan of the cervical spine for either surgery or diagnostic purposes. To examine the possibilities to insert laminar screws, the diameter of the vertebral arch was measured using a navigation system.

RESULTS

The diameter of the vertebral arch in C2 was the largest in the cervical spine, individual differences ranging between 0.8 and 8.4 mm. In C2, insertion of screws with a diameter of 3 mm was possible in 80% of males and 63% of females. As for screws with a diameter of 4 mm, insertion was possible in 50% of the males and 24% of the females in C2. In C2, gender had a significant effect, but left-right differences and height did not.

CONCLUSION

Laminar screws are useful as they can prevent vascular injuries, but a preoperative evaluation is necessary.

Surgical treatment of nonrheumatoid atlantoaxial degenerative arthritis producing pain and myelopathy

STUDY DESIGN

A retrospective review.

OBJECTIVE

The purpose of this study was to evaluate the clinical and pathologic findings and surgical treatment outcomes for atlantoaxial osteoarthritis.

SUMMARY OF BACKGROUND DATA

Nonrheumatoid atlantoaxial osteoarthritic degeneration can occur at either the atlantodental articulation or lateral mass articulations. This condition may present with neck pain or myelopathy in the setting of a compressive degenerative pannus. There is a paucity of literature on this topic with only case reports and small case series.

METHODS

A retrospective chart review was performed to identify patients treated for C1-C2 osteoarthritis. Patient demographics, clinical presentation, neurologic examination, visual analog pain scores, radiographic findings, surgical treatment, outcomes, and complications were recorded for each patient.

RESULTS

Twenty-six patients (18 with pannus at the atlantodental articulation and 8 primarily with lateral mass articulation arthritis; 10 men, 16 women; mean age 74 years) were surgically treated for atlantoaxial osteoarthritis. Eleven patients presented primarily with complaints related to myelopathy (all with a degenerative pannus) and 15 presented with cervicalgia only. All patients were treated with posterior atlantoaxial arthrodesis, and 13 patients with myelopathy or severe canal compromise from an irreducible subluxation also had transoral odontoidectomy. All myelopathic patients had improvement in neurologic function (10 of 11 improved 1 Ranawat grade). Neck pain improved in 93% of patients with preoperative neck pain complaints (mean visual analog score before surgery = 7.0, follow-up = 1.3). Fusion was demonstrated in all patients with adequate follow-up.

CONCLUSION

Atlantoaxial osteoarthritis can result in neck pain and myelopathy. In the setting of a degenerative pannus and myelopathy, most patients will improve neurologically after transoral decompression and arthrodesis. Patients with pannus and no myelopathy were effectively treated with posterior fusion alone, although 2 with irreducible subluxation required an initial transoral decompression to allow realignment before fusion. Posterior arthrodesis alone provided significant pain relief in most patients.

The lasso technique for posterior C1-C2 fusion

OBJECTIVE

Posterior atlantoaxial arthrodesis requires placement of a bone graft in a properly prepared environment that includes decorticated bony surfaces, compressive forces between graft and native bone, and limited motion. To achieve posterior atlantoaxial arthrodesis, various cable-and-graft constructs have been used, all of which require an intact posterior arch of C1. For patients who lack an intact arch owing to congenital, iatrogenic, or traumatic causes, we have devised the "lasso technique," which uses the remnants of the posterior arch of C1 for placement of the graft to achieve fusion isolated to C1-C2 or to be part of an occipitocervical construct.

METHODS

A retrospective record review was conducted of all patients who underwent the lasso technique. Clinical and radiographic history, perioperative course, and time to fusion were recorded. We describe the technique in detail.

RESULTS

During the last 13 years, we have used this technique successfully in five female and four male patients. The absent or incompetent posterior arch was a congenital defect in one patient, a result of prior surgical removal in four patients, and caused by fracture associated with prior failed fusion attempts in four other patients. All patients experienced successful fusion after an average of 6.8 months.

CONCLUSION

Securing a bone graft in the absence of an intact C1 lamina is a challenge when a patient presents with atlantoaxial instability. We have devised the lasso technique to secure an interpositional C1-C2 graft using the remnants of the posterior atlantal arch. Although this technique has been required relatively infrequently, we have found it to be valuable and effective in our practice.

C1-2 Transarticular Screw Fixation in High-riding Vertebral Artery: Suggestion of New Trajectory

A significant drawback of atlantoaxial transarticular screw fixation is a potential risk of vertebral artery injury, especially with a high-riding type. The authors propose a relatively safe trajectory in cases of high-riding vertebral artery by using the 3-dimensional computerized tomography image reconstruction programs. Twelve consecutive patients with a pathologic condition in atlantoaxial complex were prospectively analyzed. Five other patients, whose high-riding vertebral arteries were incidentally found during the 3-dimensional computerized tomography performance for other cervical pathologic conditions, were also included. The preoperative screw simulation images, convergence angle, and caudal tilting angle for each screw were obtained from each patient. Of 17 subjects, 7 had high-riding vertebral artery unilaterally and 1 had bilaterally. All 12 patients with pathologic atlantoaxial complex, including 2 unilateral and 1 bilateral high-riding vertebral artery, had atlantoaxial transarticular screw fixation. For these 3 patients, the entry point and the trajectory for screw were moved more superiorly and medially as in cases with C2 pedicle screwing. The mean convergence angle and caudal tilt angle obtained during screw simulation for patients with high-riding vertebral arteries was 17.6 and 38 degrees compared with 21 and 53.3 degrees for patients with normal course of vertebral artery. It was possible to insert transarticular screws safely in patients with high-riding vertebral artery guided by preoperative screw insertion simulation program.

In vitro biomechanical comparison of transpedicular versus translaminar C-2 screw fixation in C2–3 instrumentation

Object

In instrumentation of the upper cervical spine, placement of pedicle screws into C-2 is generally safe, although there is the potential for injury to the vertebral arteries. Owing to this risk, translaminar screws into C-2 have been used. The aim of this study was to compare the stability of the in vitro cadaveric spine using C-2 laminar compared with C-2 pedicle screws in C2–3 instrumentation.

Methods

Eight fresh frozen human cadaveric cervical spines (C1–6) were potted at C1–2 and C5–6. Pure moments in increments of 0.3 Nm to a maximum of 1.5 Nm were applied in flexion, extension, right and left lateral bending, and right and left axial rotation. Each specimen was tested sequentially in three modes: 1) intact; 2) C2 pedicle screw–C3 lateral mass fixation; and 3) C2 laminar screw–C3 lateral mass fixation. The sequence of fixation testing was randomized. Motion was tracked with reflective markers attached to C-2 and C-3.

Results

Spinal levels with instrumentation showed significantly less motion than the intact spine in all directions and with all loads greater than 0.3 Nm (p < 0.05). Although there was no significant difference between C2 pedicle screw–C3 lateral mass fixation and C2 laminar screw–C3 lateral mass fixation, generally the former type of fixation was associated with less motion than the latter.

Conclusions

When pedicle screws in C-2 are contraindicated or inappropriate, laminar screws in C-2 offer a safe and acceptable option for posterior instrumentation.

Selection of a rigid internal fixation construct for stabilization at the craniovertebral junction in pediatric patients

OBJECT

Atlantoaxial and occipitocervical instability in children have traditionally been treated with posterior bone and wire fusion and external halo orthoses. Recently, successful outcomes have been achieved using rigid internal fixation, particularly C1-2 transarticular screws. The authors describe flow diagrams created to help clinicians determine which method of internal fixation to use in complex anatomical circumstances when bilateral transarticular screw placement is not possible.

METHODS

The records of children who underwent either atlantoaxial or occipitocervical fixation with rigid internal fixation over an 11-year period were retrospectively reviewed to define flow diagrams used to determine treatment protocols.

RESULTS

Among the 95 patients identified who underwent atlantoaxial or occipitocervical fixation, the craniocervical anatomy in 25 patients (six atlantoaxial and 19 occipitocervical fixations [26%]) required alternative methods of internal fixation. Types of screw fixation included loop or rod constructs anchored by combinations of C1-2 transarticular screws (15 constructs), C-1 lateral mass screws (11), C-2 pars screws (24), C-2 translaminar screws (one), and subaxial lateral mass screws (six). The mean age of the patients (15 boys and 10 girls) was 9.8 years (range 1.3-17 years). All 22 patients with greater than 3-month follow-up duration achieved solid bone fusion and maintained stable constructs on radiographic studies. Clinical improvement was seen in all patients who had preoperative symptoms.

CONCLUSIONS

Novel flow diagrams are suggested to help guide selection of rigid internal fixation constructs when performing pediatric C1-2 and occipitocervical stabilizations. Use of these flow diagrams has led to successful fusion in 25 pediatric patients with difficult anatomy requiring less common constructs.

Biomechanical comparison of a fully threaded, variable pitch screw and a partially threaded lag screw for internal fixation of Type II dens fractures

STUDY DESIGN

Stiffness and load to failure were studied in a human cadaver model of Type II odontoid fractures stabilized with either a single partially threaded lag screw and washer or a headless fully threaded variable pitch screw.

OBJECTIVE

To determine whether a headless fully threaded variable pitch screw provides biomechanically superior fixation of Type II odontoid fractures in comparison with a partially threaded, cannulated lag screw and washer.

SUMMARY OF BACKGROUND DATA

Surgical treatment of Anderson and D'Alonzo Type II odontoid fractures is often performed using a partially threaded cannulated screw and washer. Reported clinical failure rates of this construct are as high as 20%. This technique requires perforation of the cortex of the tip of the dens, placing the brainstem and vertebrobasilar circulation at risk. A headless fully threaded variable pitch screw has not been described for this application.

METHODS

A transverse osteotomy was created at the base of the dens in 16 human cadaver C2 specimens and stabilized using either a headless fully threaded variable pitch screw or a partially threaded cannulated lag screw and washer. Specimens were loaded to failure under a static, posteriorly directed force applied to the surface of the dens. Stiffness and load to failure were measured and the mode of failure for each specimen was determined.

RESULTS

Stiffness and load to failure were greater for the headless, fully threaded variable pitch screw compared with the partially threaded lag screw and washer. The mode of failure for all specimens was via anterior screw cut-out at the C2 vertebral body.

CONCLUSION

A headless, fully threaded variable pitch screw was biomechanically favorable in comparison with a partially threaded lag screw and washer in this cadaver model of Type II dens fractures. The mode of failure at the C2 vertebral body may have important implications for further improvements in construct strength.

Incorporation of C-1 lateral mass screws in occipitocervical and atlantoaxial fusions for children 8 years of age or younger. Technical note

The authors describe the novel use of C-1 lateral mass screws in four children 8 years of age or younger, in whom occipitocervical or atlantoaxial fusion was performed for trauma or os odontoideum. The authors retrospectively reviewed the demographics and procedural data of four children, ranging in age from 2 to 8 years, who required and underwent surgical fixation. Although C1-2 screw/rod constructs involving individual C-1 lateral mass screws and C-2 pars interarticularis or pedicle screws have been widely applied in adults, only C1-2 transarticular screw fixation has been reported in children less than 8 years of age. This report demonstrates the successful results of rigid occipitocervical and atlantoaxial fusion in four children in whom C-1 lateral mass screws were placed as part of a screw/rod construct. There was one instance of a vertebral artery injury, and the lessons learned from this complication are discussed.

Posterior C1-2 Fixation With Cancellous Screw and Rod System for Retro-odontoid Pseudotumor Associated With Chronic Atlantoaxial Subluxation-Technical Note-

Posterior C1-2 fixation with individual screw placement in C-1 and C-2 was performed in three patients presenting with progressive myelopathy caused by retro-odontoid pseudotumor associated with chronic atlantoaxial subluxation. Postoperatively, all patients demonstrated neurological recovery with gradually diminishing pseudotumor. Posterior C1-2 fixation with the cancellous screw and rod system is a safe and reliable method, and can be used to treat retro-odontoid pseudotumor associated with chronic atlantoaxial subluxation.

TECHNIQUES OF POSTERIOR C1–C2 STABILIZATION

INSTABILITY OF THE atlantoaxial complex may result from inflammatory, traumatic, congenital, neoplastic, or degenerative disorders and often requires surgical stabilization. Initial dorsal wiring techniques allow safe fixation but require rigid external immobilization and have been associated with high fusion failure rates. Rigid screw fixation techniques including transarticular screw fixation and C1–C2 rod-cantilever fixation offer higher fusion rates and less need for rigid immobilization but are more technically demanding. C1–C2 fixation using crossing C2 laminar screws offers rigid fixation but without the technical demands of C2 pars placement. The history and techniques of dorsal fixation of the atlantoaxial complex are reviewed, and the success rates and complications of each are discussed.

Anatomic considerations for the placement of C2 laminar screws

STUDY DESIGN

Cadaveric study.

OBJECTIVE

To study the applicability of C2 laminar screw placement in the general adult population and to provide useful guidelines for their safe placement.

SUMMARY OF BACKGROUND DATA

Laminar screws for fixation into the second cervical vertebra are becoming an increasingly used technique since they eliminate the risk of vertebral artery injury. Although it is being used clinically, there are no published data that describe the anatomic considerations and potential limitations of this technique in the general population.

METHODS

The C2 vertebrae of 420 adult specimens were studied. Laminar thickness, spinolaminar angle, and the length from the spinolaminar junction to the contralateral lamina/lateral mass junction were measured. Statistical analysis was performed using unpaired Student t tests and regression analysis (P < 0.05).

RESULTS

Mean laminar thickness was 5.77 +/- 1.31 mm; 70.6% of specimens had a laminar thickness > or =5 mm; 92.6% had a thickness > or =4.0 mm. The spinolaminar angle was 48.59 degrees +/- 5.42 degrees. The mean screw length that could be used was 2.46 +/- 0.23 cm. More than 99% of specimens had an estimated screw length of at least 20 mm. Gender had a significant effect on all of the measurements studied, but race, height, and weight did not.

CONCLUSION

The majority of specimens can safely accept placement of a laminar screw. This study establishes anatomic guidelines to allow for accurate screw selection and insertion. Preoperative planning is essential for safe screw placement via this technique.

Biomechanical comparison of two new atlantoaxial fixation techniques with C1–2 transarticular screw–graft fixation

Object

Two new techniques for atlantoaxial fixation have been recently described. In one technique, C-2 intra-laminar screws are connected with C-1 lateral mass screws; in the second, C-1 and C-3 lateral mass screws are interconnected and C-2 is wired sublaminarly. Both techniques include a C1–2 interspinous graft. The authors compared these techniques with the gold-standard, interspinous graft–augmented C1–2 transarticular screw fixation and with a control C1–2 interspinous graft fixation procedure alone.

Methods

In six human cadaveric occiput–C4 specimens, nonconstraining 1.5-Nm pure moments were applied to induce flexion, extension, lateral bending, and axial rotation during which three-dimensional angular motion was measured optoelectronically. Each specimen was tested in the normal state, with graft alone (after odontoidectomy), and then in varying order after applying each construct with a rewired graft. All three constructs allowed significantly less angular motion at the C1–2 junction than the wired interspinous graft alone during lateral bending and axial rotation (p < 0.01, paired Student t-test) but not during flexion or extension. Transarticular screw fixation with an interspinous graft allowed less motion at the atlantoaxial junction than the two new constructs in several conditions. Differences were greater between the transarticular screw construct and the intralaminar screw construct than between the transarticular screw construct and the C1–3 lateral mass screw construct. During lateral bending and axial rotation, the C1–3 construct allowed less motion at the atlantoaxial junction than the intralaminar screw construct.

Conclusions

Biomechanically, the gold-standard C1–2 transarticular screw fixation outperformed the two new techniques during lateral bending and axial rotation. Wiring C-2 to C1–3 rods provided greater stability than C1–2 laminar screws, but it sacrificed C2–3 mobility. It is unknown whether the small differences observed biomechanically would lead to clinically relevant differences in fusion rates.

Atlantoaxial stabilization with the use of C1–3 lateral mass screw fixation

✓ Atlantoaxial stabilization has evolved from simple posterior wiring to transarticular screw fixation. In some patients, however, the course of the vertebral artery (VA) through the axis varies, and therefore transarticular screw placement is not always feasible. For these patients, the authors have developed a novel method of atlantoaxial stabilization that does not require axial screws. In this paper, they describe the use of this technique in the first 10 cases.

Ten consecutive patients underwent the combined C1–3 lateral mass–sublaminar axis cable fixation technique. The mean age of the patients was 62.6 years (range 23–84 years). There were six men and four women. Eight patients were treated after traumatic atlantoaxial instability developed (four had remote trauma and previous nonunion), whereas in the other two atlantoaxial instability was caused by arthritic degeneration. All had VA anatomy unsuitable to traditional transarticular screw fixation.

There were no intraoperative complications in any of the patients. Postoperative computed tomography studies demonstrated excellent screw positioning in each patient. Nine patients were treated postoperatively with the aid of a rigid cervical orthosis. The remaining patient was treated using a halo fixation device. One patient died of respiratory failure 2 months after surgery. Follow-up data (mean follow-up duration 13.1 months) were available for seven of the remaining nine patients and demonstrated a stable construct with fusion in each patient.

The authors present an effective alternative method in which C1–3 lateral mass screw fixation is used to treat patients with unfavorable anatomy for atlantoaxial transarticular screw fixation. In this series of 10 patients, the method was a safe and effective way to provide stabilization in these anatomically difficult patients.