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Background: Our previous study suggested that atlanto-occipital instability (AOI) is common in patients with type II basilar invagination (II-BI)., Objective: To further understand the pathogenesis of AOI in Chiari malformations (CM) and CM + II-BI through systematic measurements of the bone structure surrounding the craniocervical junction., Methods: Computed tomography data from 185 adults (80 controls, 63 CM, and 42 CM + II-BI) were collected, and geometric models were established for parameter measurement. Canonical correlation analysis was used to evaluate the morphological and positional relationships of the atlanto-occipital joint (AOJ)., Results: Among the 3 groups, the length and height of the condyle and superior portion of the lateral masses of the atlas (C1-LM) were smallest in CM + II-BI cases; the AOJ had the shallowest depth and the lowest curvature in the same group. AOJs were divided into 3 morphological types: type I, the typical ball-and-socket joint, mainly in the control group (100%); type II, the shallower joint, mainly in the CM group (92.9%); and type III, the abnormal flat-tilt joint, mainly in the CM + II-BI group (89.3%). Kinematic computed tomography revealed AOI in all III-AOJs (100%) and some II-AOJs (1.5%) but not in type I-AOJs (0%). Morphological parameters of the superior portion of C1-LM positively correlated with those of C0 and the clivus and significantly correlated with AOI., Conclusion: Dysplasia of the condyle and superior portion of C1-LM exists in both CM and II-BI cases yet is more obvious in type II-BI. Unstable movement caused by AOJ deformation is another pathogenic factor in patients with CM + II-BI., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the Congress of Neurological Surgeons.)

Background: Conventional 2-dimensional (2-D) definition of atlantoaxial dislocation (AAD) is inadequate for coexisting 3-D displacements., Objective: To prospectively classify AAD and its related abnormalities along 3 Cartesian coordinates and assess their association with torticollis., Methods: One hundred and fifty-four patients with congenital AAD were prospectively classified according to their C1-2 displacement along 3 Cartesian coordinates utilizing 3-D multiplanar CT. The impact of this 3-D dislocation on occurrence of clinically manifest torticollis was also evaluated and surgical treatment was planned., Results: Three dimensional CT assessment detected the following types of C1-2 dislocations: I:translational dislocation (along Z coordinate, n = 37 [24%]); II: central dislocation (along Y coordinate, n = 10 [6.5%]); III: translational+central dislocation (along Z+Y coordinates, n = 42 [27.3%]); IV: translational dislocation+ rotational dislocation+coronal tilt (along Z+X coordinates, (n = 6 [3.9%]); V: central dislocation (basilar invagination)+rotational dislocation+coronal tilt (along Y+X coordinates, n = 11 [7.1%]); VI: translational dislocation+ central dislocation+ rotational dislocation+ coronal tilt (along all 3 axes, n = 48 [31%]). Assessing degree of relative C1-2 rotation revealed that 27 (37%) of 85 patients with <50 rotation and 54 (78%) of 69 patients with >5° rotation had associated torticollis. Translational dislocation had negative association (odds ratio [OR] 0.1, 95% confidence interval [CI; 0.47-0.32], P = .00), while type VI (OR 5.0, 95% CI [2.2-11.19], P = .00), type V (OR 4.44, 95% CI [0.93-21.26], P = .04), and type IV (OR 1.84, 95% CI [0.32-10.38], P = .48) dislocations had strong positive association with torticollis. Sixty-two (40%) patients improved, 68 (44%) remained unchanged, and 24 (16%) patients worsened postoperatively. Twenty-eight patients required second-stage transoral decompression following posterior distraction-fusion due to neurological nonimprovement., Conclusion: Three-dimensional assessment of AAD including evaluation of culpable C1-2 facet joints addresses anomalous displacements in 3 Cartesian planes. This provides targets for adequate cervicomedullary decompression-stabilization, and helps in the management of accompanying torticollis.

Background: The endoscopic endonasal approach (EEA) has developed as an emerging surgical corridor to the craniovertebral junction (CVJ). In addition to understanding its indications and surgical anatomy, the ability to predict its inferior limit is vital for optimal surgical planning., Objective: To develop a method that accurately predicts the inferior limit of the EEA on the CVJ radiologically and to compare this with other currently used methods., Methods: Predissection computerized tomographic scans of 9 cadaver heads were used to delineate a novel line, the naso-axial line (NAxL), to predict the inferior EEA limit on the upper cervical spine. A previously described method with the use of the nasopalatine line (NPL or Kassam line) was also used. On computerized tomographic scans obtained following dissection of the EEA, the predicted inferior limits were compared with the actual extent of dissection., Results: The postdissection inferior EEA limit ranged from the dens tip to the upper half of the C2 body, which matched the limit predicted by NAxL, with no statistically significant difference between them. In contrast to the NAxL, the NPL predicted a significantly lower EEA limit (P < .001), ranging from the lower half of the C2 body to the superior end plate of C3., Conclusion: The novel NAxL more accurately predicts the inferior limit of the EEA than the NPL. This method, which can be easily used on preoperative sagittal scans, accounts for variations in patients' anatomy and can aid surgeons in the assessment of the EEA to address caudal CVJ pathology.

Background: Atlas occipitalization and congenital C2-3 fusion often result in atlantoaxial dislocation (AAD) and superior odontoid migration that requires occipitocervical fixation. The widely used technique is posterior occiput-C2 fixation with pedicle screws. However, congenital C2-3 fusion cases tend to have thinner C2 pedicles that are inadequate for normal-sized pedicle screw fixation. With the presence of AAD, the strength of the fixation is further compromised as the C2 pedicle screws (C2PS) sustain considerable cephalic shearing force during the reduction procedure. Therefore, a novel technique has been developed to augment the C2 pedicle screw fixation with a strengthening cable., Objective: To introduce and assess this new technique., Methods: Seventy-six patients who underwent this procedure were reviewed. The position of the instrument and resultant fusion were examined retrospectively. In the biomechanical test, 6 fresh specimens were subjected to 2 types of fixation in the order of Oc-C2 screw-plate fixation followed by additional use of strengthening cable. Under 3 loading modes (extension-flexion, lateral bending, and axial rotation), the relative movement between the occiput and C2 was measured and compared in the form of range of motion., Results: The average follow-up time was 26 months. Solid fusion was achieved in 75 patients (98.7%) as assessed radiologically. The only patient who experienced hardware failure eventually obtained solid fusion between the occiput and C2 after revision. Biomechanically, there was significant difference between the occiput and C2 fixation and cable-strengthened fixation in range of motion for all modes., Conclusion: This technique is a promising option for the treatment of AAD with congenital C2-3 fusion and occipitalization. Biomechanically, this technique can reduce the occipital-axial motion significantly compared with occiput-C2 fixation.

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.

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 degrees medial to the sagittal plane and 25.3 +/- 7.4 degrees posterior to the coronal plane. The mean working area was 71.2 mm (range, 49-103 mm)., 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.

Background: Occipitocervical instability with vertical migration of the odontoid is a rare but potentially debilitating anomaly of the craniocervical junction. Anterior decompression by means of a transoral or transcervical approach followed by posterior instrumentation commonly is used to treat this pathology., Objective: To develop an innovative operative technique to correct reducible occipitocervical instability using a purely posterior approach., Clinical Presentation: Two patients presented to our institution with occipitocervical instability. One patient developed vertical migration of the odontoid secondary to a retropharyngeal abscess after radiation treatment. The second patient developed occipitocervical instability as a result of pathological destruction of C2 from a breast metastasis. Both patients were myelopathic with severe neck pain., Technique: Both patients were brought to the operating room for intraoperative reduction and fixation using a purely posterior approach. This new technique obviated the need for an anterior decompression procedure or preoperative halo reduction. Postoperatively, both patients had excellent restoration of spinal alignment as well as improvement in both pain and myelopathy., Conclusion: We achieved intraoperative reduction of occipitocervical instability through a purely posterior approach. This technique adds a tool to the armamentarium of techniques used for the treatment of occipitocervical instability.

Background: C1-C2 fusion has significantly advanced from predominantly wiring/cable modalities to more biomechanically stable screw-rod techniques. Minimally invasive surgical techniques represents the most recent modification of atlantoaxial fixation. The indications, rationale, and surgical technique of this novel procedure are described., Methods: Six patients requiring C1-C2 fusion (5 type II odontoid fractures and 1 os odontoideum) underwent minimally invasive C1-C2 fusion over a 2-year period. The cohort consisted of 5 men and 1 woman with a mean age of 51 years (age range, 39-64 y). All 6 patients underwent bilateral segmental atlantoaxial fixation using an expandable tubular retractor., Results: The mean follow-up time was 32 months (age range, 24-46 mo) There were no intraoperative complications, and the mean estimated blood loss was 100 mL. Solid fusion was achieved in all 6 patients, without pathological motion on dynamic studies. Postoperative computed tomographic images showed no hardware malposition in the scanned patients (4 of the 6 patients)., Conclusions: Placement of C1 and C2 instrumentation using minimally invasive techniques is technically feasible. Because the instrumentation and the means of obtaining arthrodesis do not differ substantively from the standard approach, we would not anticipate long-term results to be different from those of an open procedure, apart from the approach-related morbidity.

Background: Rheumatoid arthritis (RA) is the most common inflammatory disease involving the spine. It has a predilection for involving the craniocervical spine. Despite widespread involvement of the cervical spine with RA, few patients need surgery. The 3 major spinal manifestations of RA in the cervical spine are basilar invagination, atlantoaxial instability, and subaxial subluxations. Surgical management of RA involving the craniovertebral junction remains a challenge despite a decline in severe cases and an improvement in surgical techniques., Methods: We conducted an exhaustive review of English-language publications discussing RA involving the craniovertebral junction. We paid special attention to publications detailing modern surgical management of these conditions. In addition, we outline our own surgical experience with such patients., Results: We discuss alternative surgical methods for treating basilar invagination, atlantoaxial instability, and concurrent subaxial subluxations. We detail our surgical technique for transoral odontoidectomy, occipital cervical fusion, and atlantoaxial fusion. We detail the use of spinal surgical navigation in both of these procedures., Conclusion: Surgical management of RA remains a challenging field. There clearly has been a decrease in cases of mutilating RA involving the craniovertebral junction. Surgical techniques for managing these conditions have steadily improved.

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.

Objective: Atlantoaxial rotatory fixation (AARF) remains a recondite entity. Our normative study using CT motion analysis shows that there is a high degree of concordance for rotational behavior of C1 and C2 in children 0 to 18 years. C1 always crosses C2 at or near 0 degree. The predictable relationship between C1 and C2 is depicted by 3 distinct regions on the motion curve: when C1 rotates from 0 to 23 degrees, it moves alone while C2 remains stationary at 0 (the single-motion phase). When C1 rotates from 24 to 65 degrees, C1 and C2 move together (the double-motion phase), but C1 always moves faster as C2 is being pulled by yoking ligaments. From 65 degrees onward, C1 and C2 move in unison (the unison-motion phase) with a fixed, maximal separation angle of approximately 43 degrees, the head rotation being carried exclusively by the subaxial segments. Because of this high concordance among patients and a relatively narrow variance from the mean, the physiological composite motion curve can be used as a normal template for the diagnosis and classification of AARF., Methods: Using a 3-position CT protocol to obtain the diagnostic motion curve, we identified 3 distinct types of AARF. Type I AARF patients show essentially unaltered ("locked") C1-C2 coupling regardless of corrective counterrotation, with curves that are horizontal lines in the upper 2 quadrants of the template. Type II AARF patients show reduction of the C1-C2 separation angle with forced correction, but C1 cannot be made to cross C2. Their curves slope downward from the right to left upper quadrants but never traverse the x axis. Type III AARF patients show C1-C2 crossover but only when the head is cranked far to the opposite side. Their motion curves traverse the x axis far left of 0 degree (C1 < -20). Thus, type I, II, and III AARF are in descending degrees of pathological stickiness. A fourth group of patients showing motion curve features between normal and type III AARF are designated as belonging to a diagnostic gray zone (DGZ). The AARF patients are further classified as acute if treatment is started less than 1 month from the onset of symptoms, as subacute if the delay in treatment is 1 to 3 months, and chronic if treatment delay exceeds 3 months. The treatment protocol for AARF consists of reduction using either halter or caliper traction and then immobilization with brace or halo, depending on the AARF type and chronicity. Recurrent slippage and irreducibility are treated with C1-C2 fusion., Results: The treatment course and outcome of AARF are analyzed according to the AARF type and chronicity. The difficulty and duration of treatment, the number of recurrent slippage, the rate of irreducibility, the need for halo and fusion, and the percentage ultimately losing normal C1-C2 rotation are significantly greater in type I patients than type III patients, with type II patients somewhere in between. Likewise, all parameters are much worse in patients with any type of chronic AARF than acute AARF. The worse subgroup is chronic type I versus the best subgroup of acute type III. Recurrent AARF patients do much worse than nonrecurrent AARF patients. Recurrence is, in turn, adversely influenced by both the severity (type) and chronicity of AARF. The symptoms of most DGZ patients will resolve with analgesics, but a few remain symptomatic or deteriorate to true AARF requiring the full treatment., Conclusion: Thus, children with painful torticollis should undergo the 3-position CT protocol not only to confirm the diagnosis of AARF but also to grade its severity. Closed reduction with traction should be instituted immediately to avoid the serious consequences of chronicity. Proper typing and reckoning of the pretreatment delay are requisites for selecting treatment modalities. Recurrent dislocation and incomplete reduction should be treated with posterior C1-C2 fusion in the best achievable alignment.

Objective: To evaluate the possible complications of overpenetrated C1 lateral mass screws and to identify and define a "safe zone" area anterior to the C1 vertebra., Methods: The study was performed on 10 cadavers and 50 random patients who had undergone computed tomographic scanning with contrast medium of the neck for other purposes. Atlas lateral mass screw trajectories were plotted, and the safe zone for screw placement anterior to the atlas vertebra was determined for each trajectory., Results: The trajectory of the internal carotid artery was measured from its medial wall. The trajectory of the internal carotid artery according to the ideal entrance point of the screw was 11.55 +/- 4.55 degrees (range, 2-22 degrees) in the cadavers and 9.78 +/- 4.55 degrees (range, -5 to 22 degrees) bilaterally in the patients. At 15 degrees (ideal screw trajectory), the thickness of the rectus capitis anterior muscle and longus capitis muscle was 6.69 +/- 0.83 mm (range, 5.32-7.92 mm) in the cadavers and 7.29 +/- 1.90 mm (range, 0.50-13.63 mm) bilaterally in the patients. The smallest distance from the internal carotid artery to the anterior cortex of the C1 vertebra was calculated as 4.33 +/- 2.03 mm (range, 1.15-8.40 mm) bilaterally in the cadavers and 5.07 +/- 1.72 mm (range, 2.15-8.91 mm) bilaterally in radiological specimens., Conclusion: The internal carotid artery trajectory is lateral to the ideal entrance point of C1 lateral mass screws. The medial angulation of a screw placed in the lateral mass of C1 seemed to increase the margin of safety for the internal carotid artery. The rectus capitis anterior and longus capitis muscles may be thought of as a safe zone area for C1 lateral mass screws. At more than 25 degrees of medial angulation, the risk of perforation of the oropharyngeal wall increases.

Objective: To evaluate surgical access to the craniocervical junction using 3 endoscopic approaches: endonasal, transoral, and transcervical., Methods: Nine cadaveric specimens were used. Image guidance was used in 1 specimen for each approach; fluoroscopy was used in every case. The Vitrea imaging station (Vital Images Inc., Minnetonka, MN) was used to evaluate the angles and distances to the target of the approach, centered on the tip of the odontoid. The entry site was defined as: 1) the endonasal approach (inferior midline of the nasal bone), 2) the transoral approach (the tip of the upper incisor), and 3) the transcervical approach (the skin at the C4-C5 level)., Results: Adequate lower clivus and craniocervical decompression was achieved using the endonasal and transoral approaches. Lower clivus decompression was not achieved with the transcervical approach. The average distance to the surgical target was as follows: endonasal (94 mm), transoral (102 mm), and transcervical (100 mm). The angle of attack was as follows: endonasal (28 degrees), transoral (30 degrees), and transcervical (15 degrees). The working area at the base of the field was as follows: endonasal (1305 mm2), transoral (1406 mm2), and transcervical (743 mm2)., Conclusion: The endonasal and transoral approaches allow wide exposure with large working angles to the craniocervical junction. The transcervical approach accesses the odontoid for resection from the body of C2 to the lip of the basion. The angles of attack in the transcervical approach when centered on the surgical target are limited, but this approach offers a clean, sterile operative field. Clinical investigation will be required to determine the optimal indications for each approach.

Objective: We measured the variability in the size of the anterior tubercle of C1 and the optimal depth and angle of placement of C1 lateral mass screws using axial and sagittal reconstructed computed tomographic scans to determine the utility of these parameters for preoperative planning and intraoperative guidance., Methods: One hundred consecutive cervical spine computed tomographic scans were reviewed (mean patient age, 44.6 years; age range, 7-96 years). The size of the anterior tubercle of C1, bilateral depths of optimal screw placement in the axial and sagittal planes, and optimal angles of placement in the axial and sagittal planes were measured in a standardized manner using the measuring tool included in our radiology server software. These measurements were correlated with age and sex., Results: The mean depth of the C1 tubercle was 6.9 mm (range, 2.7-11.2 mm; standard deviation, 1.7 mm). The depth of the C1 tubercle tended to increase with age, but the relationship was not significant. The optimal screw depth in the sagittal plane was significantly greater than in the axial plane (right 2.09 versus 1.93 cm; left 2.07 versus 1.91 cm). The depth of the right lateral mass increased significantly with age. No other relationships reached significance., Conclusion: The depth of the anterior tubercle of C1 varies considerably and should be studied carefully before using lateral fluoroscopy of this structure to guide depth of C1 lateral mass screw placement. Optimal angles and depths of placement of C1 lateral mass screws vary widely and should be examined preoperatively to plan appropriate depth and trajectory.

Objective: C2 translaminar (TL) screws rigidly capture the posterior elements of C2, avoid risk of vertebral artery injury, and are less technically demanding than C2 pedicle (PD) screws. However, a C2-TL screw breach places the spinal cord at risk, and the durability of C2-TL screws remains unknown. It is unclear if TL versus PD screw fixation of C2 is truly associated with less operative morbidity, greater accuracy of screw placement, or equivalent durability., Methods: We retrospectively reviewed the records of 167 consecutive patients undergoing posterior cervical fusion with either PD or TL screw fixation of C2. Perioperative morbidity, breach of the C2 lamina or pedicle on postoperative computed tomographic scans, and rates of operative revision were compared between PD and TL screw constructs in axial (C1-C2 or C1-C3) and subaxial (C2 and caudal) cervical fusions., Results: In total, 152 C2-TL screws and 161 C2-PD screws were placed in 167 patients. Thirty-one (19%) cases of axial cervical fusion (C1-C2 or C1-C3) were performed (mean age, 63.8 +/- 20.6 years) with either C2-TL (16 [52%]) or C2-PD (15 [48%]) screw fixation. One hundred thirty-six (81%) cases of subaxial cervical fusion (C2-caudal) were performed (mean age, 57.9 +/- 14.7 years) with either C2-TL (66 [49%]) or C2-PD (70 [51%]) screw fixation. For both axial and subaxial cervical fusions, baseline patient characteristics and all measures of perioperative morbidity were similar between C2-TL and C2-PD screw cohorts. In total, 11 (7%) PD screws breached the pedicle (0 requiring acute revision) versus only 2 (1.3%) TL screws that breached the C2 lamina (1 requiring acute revision) (P = 0.018). By 1 year postoperatively, pseudoarthrosis or screw pullout requiring reoperation was required in 4 (6.1%) patients with C2-TL screws versus 0 (0%) patients with PD screws (P < 0.05 for subaxial constructs). No cases of C2-TL or C2-PD axial fusion required reoperation or screw pullout or pseudoarthrosis., Conclusion: In our experience, radiographic breach of C2 pedicle screws occurred more frequently than C2 laminar screw breach. However, this was not associated with an increase in morbidity. By 12 months postoperatively, C2-TL screws were associated with a greater incidence of operative revision when used in subaxial constructs but similarly effective for axial cervical constructs. The 1-year durability of C2-TL screws might be inferior to C2 pedicle screws for subaxial fusions, but equally effective for axial cervical fusions.

Objective: The assessment of response to treatment in pediatric patients with congenital atlantoaxial dislocation (AAD) is performed using a disability grading system but may be better determined by a score based on clinical parameters. This study proposes a scoring system based on a comprehensive neurological examination to assess surgical outcome in these patients., Methods: Sixty-seven patients with congenital AAD aged 14 years or younger were included and analyzed prospectively. A scoring system based on six factors (motor power, gait, sensory involvement, sphincteric involvement, spasticity, and respiratory difficulty) was designed at the beginning of the study and all patients were assessed using this score as well as the Di Lorenzo's grade preoperatively, postoperatively, and at the time of each follow-up visit., Results: There was a very high incidence of occipitalized arch of atlas and fusion of the second and third cervical vertebrae in the irreducible variety. Most patients were classified in poor grades preoperatively; however, the changes in score were seen more often when using the scoring system we developed compared with the Di Lorenzo's grade. Our score also corroborated better with the clinical improvement., Conclusion: The clinical profiles of pediatric patients with AAD are similar with a higher incidence of atlas arch anomalies in patients with irreducible AAD. A scoring system based on clinical parameters is proposed for clinical evaluation of such patients. This system is easy to use and interpret and is more sensitive to the changes in the neurological status of patients.

Objective: The diagnosis of atlanto-occipital dislocation (AOD) remains problematic as a result of a lack of reliable radiodiagnostic criteria. In Part 1 of the AOD series, we showed that the normal occiput-C1 joint in children has an extremely narrow joint gap (condyle-C1 interval [CCI]) with great left-right symmetry. In Part 2, we used a CCI of 4 mm or greater measured on reformatted computed tomographic (CT) scans as the indicator for AOD and tested the diagnostic sensitivity and specificity of CCI against published criteria. The clinical manifestation, neuroimaging findings, management, and outcome of our series of patients with AOD are also reported., Method: For diagnostic sensitivity, we applied the CCI criterion on 16 patients who fulfilled one or more accepted radiodiagnostic criteria of AOD and who showed clinical and imaging hallmarks of the syndrome. All 16 patients had plain cervical spine x-rays, head CT scans, axial cervical spine CT scans with reconstruction, and magnetic resonance imaging scans. The diagnostic yield and false-negative rate of CCI were compared with those of four published "standard" tests, namely Wholey's dens-basion interval, Powers' ratio, Harris' basion-axis interval, and Sun's interspinous ratio. The diagnostic value of "nonstandard" indicators such as cervicomedullary deficits, tectorial membrane and other ligamentous damage, perimedullary subarachnoid hemorrhage, and extra-axial blood at C1-C2 were also assessed. For diagnostic specificity, we applied CCI and the "standard" and "nonstandard" tests on 10 patients from five classes of non-AOD upper cervical injuries. The false-positive diagnostic rates for AOD of all respective tests were documented., Results: The CCI criterion was positive in all 16 patients with AOD with a diagnostic sensitivity of 100%. Fourteen patients had bilateral AOD with disruption and widening of both OC1 joints. Two patients had unilateral AOD with only one joint wider than 4 mm. The abnormal CCI varied from 5 to 34 mm. Eight patients showed blatant left-right joint asymmetry in either CCI or anatomic conformation. The diagnostic sensitivities for the "standard" tests are as follows: Wholey's, 50%; Powers', 37.5%; Harris', 31%; and Sun's, 25%, with false-negative rates of 50, 62.5, 69, and 75%, respectively. The sensitivities for the "nonstandard" indicators are: tectorial membrane damage, 71%; perimedullary blood, 63%; and C1-C2 extra-axial blood, 75%, with false-negative rates of 29, 37, and 25%, respectively. Fifteen patients with AOD had occiput-cervical fusion. There were one early and two delayed deaths (19% mortality); two patients (12%) had complete or severe residual high quadriplegia, but 11 children (69%) enjoyed excellent neurological recovery. CCI was normal in all 10 patients with non-AOD upper cervical injuries with a diagnostic specificity of 100%. The false-positive rates for the four "standard" tests were: Sun's, 60%; Harris', 50%; Wholey's, 30%; and Powers', 10%; for the "nonstandard" indicator, the rates were: cervicomedullary deficits, 70%; tectorial membrane damage, 40%; C1-C2 extra-axial blood, 40%; and perimedullary blood, 30%., Conclusion: The CCI criterion has the highest diagnostic sensitivity and specificity for AOD among all other radiodiagnostic criteria and indicators. CCI is easily computed from reconstructed CT scans, has almost no logistical or technical distortions, can capture occiput-C1 joint dislocation in all three planes, and is unaffected by congenital anomalies or maturation changes of adjacent structures. Because CCI is the only test that directly measures the integrity of the actual joint injured in AOD and a widened CCI cannot be concealed by postinjury changes in the head and neck relationship, it surpasses others that use changeable landmarks.

Objective and Importance: More survivors of traumatic atlanto-occipital dislocation (AOD) in adults have recently been reported. Surgical management options are therefore of increasing interest. We present a new technique of posterior C0-C1-C2 fixation., Clinical Presentation: A 29-year-old motorcyclist survived a traumatic vertical AOD of 15 mm. No spinal cord or medullary lesion was present. Brain contusion and diffuse axonal injuries led to a cortical biplegia, which recovered progressively over a period of 6 months. Twelve months after surgery, no neurological deficit was present except for slightly increased deep tendon reflexes., Intervention: Posterior C0-C1-C2 fixation was performed with two bicortical occipital screws, one bicortical lateral mass screw in the atlas, and one monocortical pars screw in the axis on each side, connected to a plate-rod on the right and left sides. Fusion was performed with monocortical bone graft from the posterior iliac crest., Conclusion: The surgical technique described was thought to be safe to perform and resulted in immediate stability without external immobilization. Solid fusion was achieved 6 months after surgery.

Objective: We review our experience with the use of the plate and screw method of fixation in the treatment of 160 patients with atlantoaxial instability during a 14-year period at our center. We previously described this method of fixation in 1994., Methods: Between 1988 and 2001, 160 patients with atlantoaxial instability were treated with the use of a plate and screw method of fixation at the Department of Neurosurgery at King Edward Memorial Hospital in Bombay, India. The study group was composed of 91 males and 69 females (mean age, 23 yr; age range, 18 mo-79 yr). Atlantoaxial instability was a result of congenital abnormality in 132 patients (83%) and occurred after trauma in 28 patients (17%). All patients had mobile, completely reducible atlantoaxial dislocation. For 3 months postoperatively, a hard cervical collar was used. The mean follow-up period was 42 months (range, 4 mo-14 yr)., Results: Three patients died in the postoperative phase. Successful stabilization of the atlantoaxial region was documented with dynamic radiography in the other 157 patients. There was no incidence of implant rejection. In one patient, one screw was found to be broken 18 months after surgery; however, firm bony fusion was documented in this patient. There were no neurological, vascular, or infective complications., Conclusion: The plate and screw method of fixation with the use of intra-articular bone grafts in patients with atlantoaxial instability yielded a 100% fusion rate with a low incidence of complications.

Objective: To assess the outcomes associated with C1-C2 transarticular screw fixation., Methods: The clinical outcomes of 121 patients treated with posterior C1-C2 transarticular screws and wired posterior C1-C2 autologous bone struts were evaluated prospectively. Atlantoaxial instability was caused by rheumatoid arthritis in 48 patients, C1 or C2 fractures in 45, transverse ligament disruption in 11, os odontoideum in 9, tumors in 6, and infection in 2., Results: Altogether, 226 screws were placed under lateral fluoroscopic guidance. Bilateral C1-C2 screws were placed in 105 patients; each of 16 patients had only one screw placed because of an anomalous vertebral artery (n = 13) or other pathological abnormality. Postoperatively, each patient underwent radiography and computed tomography to assess the position of the screw and healing. Most screws (221 screws, 98%) were positioned satisfactorily. Five screws were malpositioned (2%), but none were associated with clinical sequelae. Four malpositioned screws were reoperated on (one was repositioned, and three were removed). No patients had neurological complications, strokes, or transient ischemic attacks. Long-term follow-up (mean, 22 mo) of 114 patients demonstrated a 98% fusion rate. Two nonunions (2%) required occipitocervical fixation. In comparison, our C1-C2 fixations with wires and autograft (n = 74) had an 86% union rate., Conclusion: Rigidly fixating C1-C2 instability with transarticular screws was associated with a significantly higher fusion rate than that achieved using wired grafts alone. The risk of screw malpositioning and catastrophic vascular or neural injury is small and can be minimized by assessing the position of the foramen transversaria on preoperative computed tomographic scans and by using intraoperative fluoroscopy and frameless stereotaxy to guide the screw trajectory.

Objective and Importance: Concomitant atlantoaxial and atlanto-occipital subluxation resulting from any cause is extremely rare. We have found only five previously reported cases and describe another, suggesting a treatment plan., Clinical Presentation: A 13-year-old female patient presented with a 3-month history of neck pain and decreased neck movements. All symptoms started after a localized neck infection had been treated successfully with antibiotics. There was no history of trauma. A diagnosis of postinfective atlanto-occipital and atlantoaxial rotatory subluxation was made based on a plain roentgenogram and was confirmed based on a computed tomographic scan., Intervention: The atlantoaxial and atlanto-occipital subluxation was reduced during surgery. A posterior C1-C2 fixation was performed, and the atlanto-occipital joint was stabilized by means of a halo body jacket for 3 months. One year after removal of the jacket, all subluxation remained reduced and the patient retained significant neck movement., Conclusion: Disruption of the occipito-atlanto-axial complex can result from relatively minor head and neck infections and should be suspected in children with persisting neck pain and decreased neck movements. It may not be necessary to perform an occipitoaxial fusion to treat these patients, and a more limited fusion may be successful.

Thirty-two patients who underwent atlantoaxial arthrodesis using Halifax interlaminar clamps and halo vests between January 1989 and December 1992 were reviewed. The atlantoaxial instabilities were related to trauma in 16 patients, including 14 patients with unstable odontoid fractures, 1 patient with a complex C2 fracture, and 1 patient with a disrupted transverse ligament. Of the other 16 patients, whose atlantoaxial instabilities were nontraumatic in origin, 9 had instabilities that were secondary to rheumatoid arthritis, 1 had instability that was secondary to tuberculous infection, and 6 had instabilities that were caused by os odontoideum. The patients were followed postoperatively with lateral cervical radiographs for an average of 37 months (range, 16-59 mo). Solid atlantoaxial arthrodeses were achieved in all (100%) of these 32 patients after 32 to 111 days (average, 84.5 d) of halo immobilization, indicating atlantoaxial arthrodeses can be reasonably anticipated when Halifax interlaminar clamps with autogenous iliac bone grafting are reinforced by halo vest immobilization for 3 months.

Posterior atlantoaxial fusion is a common procedure performed for instability at C1-C2. This operation requires intact posterior elements of both the atlas and the axis. When this is not the case, the incorporation of the occiput and the lower spinal segments is usually required for adequate posterior fusion, but such a procedure limits the mobility of the upper cervical spine. A technique for the reconstruction of the posterior arch of the atlas with calvarial bone is described in this report. This technique allowed the successful fusion of the C1 and C2 vertebrae in a patient with traumatic atlantoaxial subluxation who also had a congenital absence of the posterior arch of the atlas.

Segmental spinal stabilizations have been carried out in 72 patients (age, 5-79 yr) during the first 2 years of the availability of a new, flexible, multistranded stainless steel cable (Sof'wire, Hillway Surgical Ltd., London). A total of 519 sublaminar and occipital cables have been passed at 280 levels to fix an occipitocervical loop (36 patients) or contoured rectangle (14 patients). In 15 other patients, a Gallie fusion was combined with a C1-C2 lateral mass screw fixation; a cable-bone construct was used in five patients. Clinical and radiological follow-up at 1, 3, 6 (61 patients), 12 (48 patients), and 18 months (29 patients) and at 2 years (8 patients) has demonstrated no cable breakage or loosening. One postoperative death was due to inadequate transoral decompression before posterior fixation, and, in the 32 patients who underwent spinal monitoring, there were no major changes noted during surgery and no new postoperative neurological symptoms or signs. These preliminary observations are encouraging and merit further multicenter investigations.

Magerl's technique of combining C1-C2 posterior screw fixation with a supplemental bone-wire fusion has been advocated for the management of atlanto-axial instability. Between October 1990 and August 1992, a modification of this technique was used in the treatment of 22 patients with this disorder. In the absence of spinal deformity or neoplastic disease, screw fixation and bony fusion were used alone without associated wiring, thus avoiding the risk of neural injury resulting from the sublaminar passage of wire and the retrodisplacement of ventral structures. Patient ages ranged from 30 months to 80 years; follow-up ranged from 5 to 27 months, with a mean of 14.9 months. The causes of the instabilities were as follows: eight cases of nonunion of Type II odontoid fracture, four cases of rheumatoid arthritis, three cases of tumor, two cases of ligamentous instability, two cases of pseudoarthrosis after bone-wire fusion, two cases of halo noncompliance, and one case of Os odontoideum. All 20 patients who underwent fusion were placed in a Philadelphia collar for 12 weeks. Nineteen of 20 (95%) patients achieved solid fusion. Twenty-one of 22 (95%) had significant reduction in preoperative pain. No patient developed myelopathy or bulbar findings. The one intraoperative complication was an inability to achieve secure screw purchase on one side that required unilateral screw placement with a Gallie fusion-using cable. Postoperative complications included one patient with a superficial wound infection that resolved after local debridement and antibiotics and suboccipital numbness in two patients. Progression of spinal deformity, screw pullout or breakage, and neurological or vascular complications did not occur.(ABSTRACT TRUNCATED AT 250 WORDS)

A retrospective review of patients who underwent posterior cervical stabilization with Halifax Interlaminar Clamps in four neurosurgical centers in the United Kingdom was performed. Satisfactory bone fusion without complication occurred in all patients in whom lower cervical spinal stabilization (C3-C7) was performed. Complications occurred in 14 of 45 patients undergoing atlantoaxial arthrodesis. In 10 patients, one of the screws loosened, and in 4 patients, one of the clamps disengaged; additional operations to achieve bone fusion were required in 9 patients (20%). The Halifax Interlaminar Clamp is safe and effective for posterior stabilization in the lower cervical spine; there is a significant failure rate associated with its use for atlantoaxial arthrodesis.

Eight patients with atlantoaxial instability secondary to trauma or rheumatoid arthritis were treated with posterior C1-C2 arthrodesis using the Halifax interlaminar clamp and autogenous bone graft or methylmethacrylate. Thus far, with an average follow-up of 6 months, satisfactory stability has been achieved with no instrument failure.