C1-C2 Motion Research Articles

Posterior Reduction and Temporary Fixation Through Intermuscular Approach for Odontoid Fracture.

Posterior reduction and temporary fixation (PRTF) through open approach can effectively avoid the loss of C1-C2 motion caused by posterior atlantoaxial fusion in the treatment of odontoid fracture. PRTF through intermuscular approach can preserve the integrity of the paravertebral muscle. However, its contribution to the preservation of C1-C2 rotation remains unassessed in the context of fresh odontoid fractures. The data of 31 patients with odontoid fractures who underwent PRTF through intermuscular approach were retrospectively reviewed. Operation time, intraoperative blood loss, the time of ambulation and surgery-related complications were recorded. After fracture healing, the instrumentation was removed. The Japanese Orthopedic Association score, Visual Analog Scale score for neck pain, and patient satisfaction were recorded. The range of motion in rotation of C1-C2 was calculated 1 month after removing the instrumentation. Fracture healing was observed in all patients, and the instrumentation was removed. After removing the instrumentation, the range of motion of C1-C2 in rotation was returned to 35.6° ± 4.8°. Patient satisfaction was improved (P < .05). There was no significant difference in Japanese Orthopedic Association scores and Visual Analog Scale score for neck pain between 2 values before and after removing the instrumentation (P > .05). No osteoarthritis was observed at the C1-C2 lateral mass joints. There were no perioperative complications. PRTF through intermuscular approach can be used as a salvage treatment of an odontoid fracture with an intact transverse ligament in cases of failure of, or contraindication to, anterior screw fixation. This minimally invasive technique can effectively preserve the rotational function of the atlantoaxial complex.

The use of a novel reduction plate in transoral anterior C1-ring osteosynthesis for unstable atlas fractures.

Transoral anterior C1-ring osteosynthesis has been reported as an effective treatment for unstable atlas fracture, which aims to preserve important C1-C2 motion. However, previous studies have shown that the anterior fixation plates used in this technique were not suitable for the anterior anatomy of the atlas and lacked an intraoperative reduction mechanism. This study aims to evaluate the clinical effects of a novel reduction plate used in transoral anterior C1-ring osteosynthesis for unstable atlas fractures. 30 patients with unstable atlas fractures treated by this technique from June 2011 to June 2016 were included in this study. The patients' clinical data and radiographs were reviewed, and the reduction of the fracture, internal fixation placement, and bone fusion were assessed using pre- and postoperative images. The patients' neurological function, rotatory range of motion, and pain levels were evaluated clinically during follow-up. All 30 surgeries were successfully performed, and the average follow-up duration was 23.5 ± 9.5 months (range 9-48 months). One patient suffered atlantoaxial instability during the follow-up and was treated with posterior atlantoaxial fusion. The remaining 29 patients had satisfactory clinical outcomes, with ideal fracture reduction, good screw and plate placement, well-preserved range of motion, neck pain alleviation and solid bone fusion. There were no vascular or neurological complications during the operation or follow-up. The use of this novel reduction plate in transoral anterior C1-ring osteosynthesis is a safe and effective surgical option in the treatment of unstable atlas fractures. This technique offers an immediate intraoperative reduction mechanism, which provides satisfactory fracture reduction, bone fusion, and preservation of C1-C2 motion.

Changes in intervertebral sagittal alignment of the cervical spine from supine to upright.

Cervical sagittal alignment is a critical component of successful surgical outcomes. Unrecognized differences in intervertebral alignment between supine and upright positions may affect clinical outcomes; however, these differences have not been quantified. Sixty-four patients scheduled to undergo one or two-level cervical arthrodesis for symptomatic pathology from C4-C5 to C6-C7, and forty-seven controls were recruited. Upright sagittal alignment was obtained through biplane radiographic imaging and measured using a validated process with accuracy better than 1° in rotation. Supine alignment was obtained from computed tomography scans. Coordinate systems used to measure supine and upright alignment were identical. Distances between adjacent bony endplates were measured to calculate disc height in each position. For both patients and controls, the C1-C2, C2-C3, and C3-C4 motion segments were in more lordosis when upright as compared with supine (all p < 0.001). However, the C4-C5, C5-C6, and C6-C7 motion segments were in less lordosis when upright as compared with supine (all p ≤ 0.004). There was an interaction between group and position at the C1-C2 (p = 0.002) and C2-C3 (p = 0.001) motion segments, with the controls demonstrating a greater increase in lordosis at both motion segments when moving from supine to upright. The results indicate that cervical motion segment alignment changes between supine and upright positioning, those changes differ among motion segments, and cervical pathology affects the magnitude of these changes. Clinical Significance: Surgeons should be mindful of the differences in alignment between supine and upright imaging and the implications they may have on clinical outcomes.

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

ABSTRACTBackground:The atlantoaxial complex contributes to significant neck movements, especially the axial rotation. Its instability is currently treated with various C1-C2 fusion techniques. This however, considerably hampers the neck movements and affects the quality of life; a C1-C2 motion preserving arthroplasty could potentially overcome this drawback.Objectives:We evaluate the range of motion (ROM) of lateral C1-C2 artificial joints in cadaveric models.Materials and Methods:This is an in vitro cadaveric biomechanical study. After C1-C2 arthroplasty through a posterior approach, the C1-C2 ROM was tested in 4 fresh-frozen human cadaveric specimens, before and after destabilization.Results:The mean axial rotation demonstrated after the placement of C1-C2 joint implants was 15.46 degrees on the right and 16.03 degrees on the left side; the prosthesis provided stability, with 46% of the baseline C1-C2 axial rotation on either side. The ROM achieved in the other axes was less compared with that of intact specimens. To initiate rotation, a higher moment of 1.5 Nm was required in the presence of joint implants compared to 0.5 NM in unimplanted specimens.Conclusions:In our preliminary ROM evaluation, the C1-C2 arthroplasty appears to be stable and provides about half of the range of atlantoaxial rotation. It has the potential for joint motion preservation in the treatment of atlantoaxial instability resulting from lateral C1-C2 joint pathologies.

Biomechanical comparison of a C1 posterior arch clamp with C1 lateral mass screws in constructs for C1-C2 fusion.

The aim of this experimental study was to assess the biomechanical performance of a novel C1 posterior arch (C1PA) clamp compared with C1 lateral mass (C1LM) screws in constructs used to treat atlantoaxial instability. These constructs had either C2 pedicle (C2P) screws or C2 translaminar (C2TL) screws. Eight fresh-frozen human cadaveric ligamentous spine specimens (C0-C3) were tested under six conditions: the intact state, the destabilized state after a simulated odontoid fracture, and when instrumented with four constructs (C1LM-C2P, C1LM-C2TL, C1PA-C2P, C1PA-C2TL). Each specimen was tested in a spinal loading simulator that separately applied axial rotation, flexion-extension and lateral bending. In each test condition, displacement controlled angular motion was applied in both directions at a speed of 2 deg/s until a resulting moment of 1.5 Nm was achieved. The measured ranges of motion (ROM) of the C1-C2 segments were compared for each test condition using nonparametric Friedman tests. The destabilized state had significantly more C1-C2 motion (p < 0.05) than the intact state in all cases, and all constructs greatly reduced this motion. C2 pedicle screw constructs that used the C1PA clamp had significantly less C1-C2 motion (p < 0.05) than those with C1LM screws in flexion-extension as well as axial rotation and no statistically significant difference was detected in lateral bending. C2 translaminar screw constructs that used the C1PA clamp had significantly less C1-C2 motion (p < 0.05) than those with C1LM screws in flexion-extension and no statistically significant difference was detected in axial rotation or in lateral bending. Data from the current study suggested that constructs using the novel C1PA clamp would provide as good, or improved, biomechanical stability to the C1-C2 segment compared with constructs using C1LM screws.

Refractory Syncope and Presyncope Associated with Atlantoaxial Instability: Preliminary Evidence of Improvement Following Surgical Stabilization

The proclivity to atlanto-axial instability (AAI) has been widely reported for conditions such as rheumatoid arthritis and Down syndrome. Similarly, we have found a higher-than-expected incidence of AAI in the hereditary connective tissue disorders. We demonstrate a strong association of AAI with manifestations of dysautonomia, in particular syncope and lightheadedness, and make preliminary observations as to the salutary effect of surgical stabilization of the atlanto-axial motion segment. In an IRB-approved retrospective study, twenty subjects (16 women, 4 men) with hereditary connective tissue disorders had AAI diagnosed by CT. Subjects underwent realignment (reduction), stabilization and fusion of C1-C2 motion segment. All subjects completed pre-operative and postoperative questionnaires in which they were asked about performance, function and autonomic symptoms, including lightheadedness, pre-syncope, and syncope. All patients with AAI reported lightheadedness, and 15 had refractory syncope or pre-syncope despite maximal medical management and physical therapy. Postoperatively, subjects reported statistically significant improvement in lightheadedness (p=.003), pre-syncope (p=.006), and syncope (p=.03), and in the frequency (p < 0.05) of other symptoms related to autonomic function, such as nausea, exercise intolerance, palpitations, tremors, heat intolerance, gastroesophageal reflux, and sleep apnea. This study draws attention to the potential for AAI to present with syncope or pre-syncope that is refractory to medical management, and for surgical stabilization of AAI to lead to improvement of these and other autonomic symptoms.

Modified C1 lateral mass screw insertion using a threaded K-wire. A technical note

Instrumented fixation of the C1-C2 motion segment is a standard surgical technique to stabilise that spinal segment. Instability at C1-C2 can arise from a number of conditions. Fixation of the C1 lateral mass usually involves dissection and exposure of the C2 nerve root and the posterior wall of the C2 lateral mass which can result in significant bleeding from the venous plexus. Whilst image guidance is increasing in accessibility, there are few public hospitals in Australia that have access to this technology. The authors describe their technique for insertion of a C1 lateral mass screw over a threaded K-wire to avoid extensive dissection of the C2 nerve root, reducing the risk of significant haemorrhage from the epidural venous plexus during the procedure. A retrospective analysis was undertaken on 18 consecutive patients who underwent C1-C2 instrumented fixation using this technique. Indications for C1-C2 instrumented fixation included traumatic injury (10 patients), failure of non-operative management of odontoid fractures (5 patients), pathological fractures of C2 (2 patients) and inflammatory conditions (1 patient). All patients underwent successful C1-C2 stabilisation using this technique. Blood loss did not exceed 400mls in any patient. There were no vertebral artery injuries and no patient experienced a neurological deterioration. The authors propose that their technique for insertion of a C1 lateral mass screw over a threaded K-wire is safe and effective with a low risk of neurological or vertebral artery injury. The technique may be considered as a slight modification of the Harm’s procedure to reduce disturbance of the adjacent venous plexus and thereby reduction in intraoperative bleeding and operative time.

Three-point atlantoaxial fixation with C1-C2 transarticular screws and C1 lateral mass screws.

Based on established posterior atlantoaxial fixation techniques, we present a novel technique that uses a polyaxial screw rod system and utilizes a combination of C1 lateral mass and C1-C2 transarticular screws. We conducted a retrospective review of six men and four women (mean age: 57, range: 20-86). Indication for atlantoaxial fixation was type II odontoid fractures or pseudarthrosis after odontoid fracture (n = 7), rheumatoid arthritis (n = 2) and os odontoideum (n = 1). The mean follow-up time was 48 months (range: 24-72). There were no intraoperative complications such as vertebral artery, nerve root or spinal cord injury. Post-operative imaging showed no screw malposition. During follow-up, no patient had screw loosening, screw fracture or bone absorption around the screws. Clinically, patient neck pain improved in all cases. C1 lateral mass and C1-C2 transarticular polyaxial screw rod fixation is a novel and potentially effective surgical technique for achieving immediate rigid immobilization of the C1-C2 motion segment. However, further biomechanical studies should be performed to prove our clinical results.

Anterior management of C2 fractures using miniplate fixation: outcome, function and quality of life in a case series of 15 patients

The classification systems by Anderson and D'Alonzo, Effendi, Benzel and others have limitations when it comes to morphologically categorising fractures of the second cervical vertebral body (C2) that present with or without an additional fracture of the dens or with or without an extension of the fracture line into the vertebral arch and displacement. Currently, there are no definitive recommendations for the treatment of fractures at the junction of the dens with the vertebral body of C2 on the basis of outcome and stability data. Depending on patient anatomy, either anterior or posterior approaches can be used to fuse C1 and C2 and to achieve definitive surgical stabilisation. The anterior management of C2 fractures without C1-C2 fusion has the theoretical advantage that it preserves rotational motion at this motion segment and that the anterior approach is associated with lower morbidity. In the study presented here, we followed up a group of our patients who underwent anterior miniplate fixation for C2 fractures. Fifteen patients underwent fixation of C2 fractures with titanium miniplates (Medartis Hand fixation system, 2.0 or 2.3mm) that were placed using a submental approach. To our knowledge, this construct has not yet been described in the literature. Where necessary, this procedure was combined with screw fixation of the dens as described by Böhler. We retrospectively analysed operative reports and medical records, evaluated the patients' health status using the Short Form (36) Health Survey (SF-36), and performed clinical follow-up examinations. From January 2009 to June 2015, 226 traumatic lesions of the cervical spine were managed at our institution in the inpatient setting. Ninety-two patients underwent conservative treatment. Of the 134 cases that required surgery for fractures and instability, 67 involved the C0-C3 motion segments. In 15 patients, stability was achieved using an anterior miniplate or miniscrews alone (n = 4) or in addition to other techniques (n = 11). Anderson and D'Alonzo type II and III dens fractures with involvement of the body or lateral mass of C2 accounted for eight cases. Effendi type II body fractures with or without instability were seen in four cases. There was no perioperative mortality and morbidity in this patient group. All fractures healed and stability was achieved in all cases. No patient had neurological deficits or required revision surgery. An assessment of postoperative quality of life showed that 11 patients (7 men, 4 women) with a mean age of 57 (± 5.3) years reached an SF-36 score that was normal for their age group after a mean period of 33 (± 6.3) months following their injury. Compared to a group of healthy subjects, the patients had a range of motion that was limited only at the extremes. In patients with appropriate indications, anterior fixation with miniplates alone or additionally is a further useful treatment option in the management of fractures at the junction of the dens with the vertebral body of C2. Since this type of treatment preserves motion at the C1-C2 motion segment after fracture healing and since an anterior approach is associated with less surgical trauma than posterior instrumentation, the technique presented here should be included in a discussion on (surgical) treatment options. These slides can be retrieved under Electronic Supplementary Material.

New technique for C1-C2 fixation.

Background:There are several techniques for treating atlantoaxial instability, including the Magerl transarticular screw fixation and the Harms/Goel C1-C2 screw rod techniques. Here, we present a novel technique utilizing a polyaxial screw rod system and a combination of C1 lateral mass and C1-C2 transarticular screws.Methods:We retrospectively reviewed 14 patients (7 women, 7 men; mean age 62) who underwent surgery for type II odontoid fractures (n = 7), pseudarthrosis after anterior odontoid screw placement (n = 3), Os odontoideum (n = 2), atlantoaxial instability after C3-C5 fusion (n = 1), and craniovertebral rheumatoid arthritis (n = 1). Ten patients underwent posterior C1-C2 fixation, three patients with osteoporosis had C1-C4 fixation, and one patient had C1-Th1 fixation. The mean follow-up time was 22 months.Results:Intraoperatively, there were no complications (e.g., vertebral artery, nerve root, or spinal cord injury). Postoperative imaging showed no screw malpositioning, and no screw loosening, fracture, or bone absorption around the screws. Furthermore, all patients exhibited postoperative improvement in neck pain.Conclusions:C1 lateral mass and C1-C2 transarticular polyaxial screw rod fixation techniques were effective in achieving immediate rigid immobilization of the C1-C2 motion segment.

Burst C2 Fractures Combined with Traumatic Spondylolisthesis: Can Atlantoaxial Motion Be Preserved? Including Some Technical Tips for Reduction and Fixation.

Study Design Retrospective comparative clinical case series.Objective Burst C2 fractures are very rare. Treatment options include conservative treatment or fusion (anterior, posterior, or anterior and posterior). Anterior fusion addresses mainly hangman component. The bursting body usually needs posterior or combined anterior-posterior fusion, but both permanently sacrifice atlantoaxial motion. Can anterior-“first” approach preserve C1–C2 motion and restore function?Methods We report nine cases of burst C2 combined with C2–C3 spondylolisthesis and an odontoid fracture. The surgical group included six patients treated initially with an anterior approach, moving to a posterior one when necessary. All were treated with anterior diskectomy fusion using one session and one incision. The halo group included three patients treated conservatively using halo traction followed by rigid collar. Assessments included self-reported, physiologic, and functional measures. Reduction was assessed using Roy-Camille's criteria and improvement of canal compression ratio. Clinical outcome was graded excellent, very good, good, or poor according to pain, range of motion, and work status.Results Mean follow-up was 44.5 ± 8.3 (range 36.0 to 62.0) weeks. Results in the surgical group were judged to be excellent in four and good in two. One patient developed atlantoaxial osteoarthritis. Results were good in one patient and poor in two patients in the halo group. Two patients developed atlantoaxial osteoarthritis. All three cases had work limitations.Conclusion A single anterior approach achieved union and preserved C1–C2 motion and function in some cases. Conservative treatment achieved union but failed to achieve good reduction or good clinical outcome in grossly instable fractures. However, we believe that the ideal management is yet to evolve.

The Fate of Type II Odontoid Fractures after Posterior Atlantoaxial Fusion: Where Does Healing Occur?

Anderson and D'Alonzo type II odontoid fractures often require surgical intervention. Our goal was to understand the pattern of healing in patients who had a posterior atlantoaxial fusion for a type II odontoid fracture. We conducted a retrospective study of patients who underwent posterior atlantoaxial instrumentation and fusion for a type II odontoid fracture at our institution between 1987 and 2011. Patients who had fusion evaluation by computed tomography (CT) scan ≥3 months after surgery were included. Surgical technique included placement of a posterior bone graft with transarticular screws, C1 lateral mass and C2 pars/pedicle screw construct, or a combination of screw fixation techniques. Postoperative CT scans were reviewed to determine the site where fusion occurred. Sixty-four patients underwent posterior atlantoaxial instrumentation and fusion for type II odontoid fractures, 12 of whom had fusion evaluation by CT scan. A total of 11 of 12 patients had fusion across the fracture site, 2 across the C1-C2 joint, and 11 at the posterior graft site. All 12 patients had at least one site of fusion. There is a high rate of fusion across the fracture site of a type II odontoid fracture after posterior atlantoaxial fixation. In young patients with acute type II fractures who are not candidates for anterior screw fixation, posterior atlantoaxial instrumentation without fusion may be sufficient for fracture healing, thus allowing for the possibility of implant removal and preservation of C1-C2 motion.

The biomechanical analysis of craniovertebral junction finite element model in atlas assimilation

To study the biomechanical change of the craniovertebral junction in conditions of atlas assimilation. Mimics software was used to process CT data of the craniovertebral junction in a health adult to obtain the three-dimensional reconstruction and the cloudy points of C1, C2 and part of the occipital bone. Then the cloudy points were imported into the Abaqus 6. 8 software to establish the occipito-atlantoaxial finite element model in normal structure. According to the established model in normal structure, the model in conditions of atlas assimilation was set by changing the model parameters. Both models of normal structure and atlas assimilation were loaded with 1. 5 N . m static moment to simulate four motions of flexion, extension, lateral bending and axial rotation respectively. The movement characteristics,joint stress force and ligament deformation was analyzed. Under 1. 5 N . m moment, in model of atlas assimilation the C1-C2 range of movement decreased from 13. 55° to 11.88° in flexion,increased from 13. 22° to 15. 24° in extension and from 4. 05° to 4. 23° in lateral bending and remained unchanged in axial rotation when compared with the normal model. In flexion movement, the contact force of the atlanto-dental joint increased from 1. 59 MPa to 3. 28 MPa and the deflection of apical ligament, tectorial membrane and alar ligament increased 129. 1%, 157. 6% and 75. 1% respectively when compared with the normal model. The normal C1-C2 motion mode is destructed in conditions of atlas assimilation, leading to the changes of the range of movement,joint stress force and the ligament deformation at C1 C2 junction. The atlantoaxial instability will likely occur in flexion motion.

Self-designed posterior atlas polyaxial lateral mass screw-plate fixation for unstable atlas fracture

Background contextMost atlas fractures can be effectively treated nonoperatively with external immobilization unless there is an injury to the transverse atlantal ligament. Surgical stabilization is most commonly achieved using a posterior approach with fixation of C1–C2 or C0–C2, but these treatments usually result in loss of the normal motion of the C1–C2 and C0–C1 joints. PurposeTo clinically validate feasibility, safety, and value of open reduction and fixation using an atlas polyaxial lateral mass screw-plate construct in unstable atlas fractures. Study designRetrospective review of patients who sustained unstable atlas fractures treated with polyaxial lateral mass screw-plate construct. Patient sampleTwenty-two patients with unstable atlas fractures who underwent posterior atlas polyaxial lateral mass screw-plate fixation were analyzed. Outcome measuresVisual analog scale, neurologic status, and radiographs for fusion. MethodsFrom January 2011 to September 2012, 22 patients with unstable atlas fractures were treated with this technique. Patients' charts and radiographs were reviewed. Bone fusion, internal fixation placement, and integrity of spinal cord and vertebral arteries were assessed via intraoperative and follow-up imaging. Neurologic function, range of motion, and pain levels were assessed clinically on follow-up. ResultsAll patients were followed up from 12 to 32 months, with an average of 22.5±18.0 months. A total of 22 plates were placed, and all 44 screws were inserted into the atlas lateral masses. The mean duration of the procedure was 86 minutes, and the average estimated blood loss was 120 mL. Computed tomography scans 9 months after surgery confirmed that fusion was achieved in all cases. There was no screw or plate loosening or breakage in any patient. All patients had well-preserved range of motion. No vascular or neurologic complication was noted, and all patients had a good clinical outcome. ConclusionsAn open reduction and posterior internal fixation with atlas polyaxial lateral mass screw-plate is a safe and effective surgical option in the treatment of unstable atlas fractures. This technique can provide immediate reduction and preserve C1–C2 motion.

Total Atlanto-odontoid Joint Arthroplasty System

An in vitro biomechanical study. To determine the initial stability and function of a novel total atlanto-odontoid joint arthroplasty system (TAAS) in human cadaveric cervical spine models by comparing it with a conventional method. Resection of the odontoid and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurological complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior atlantoaxial fusion. However, this results in considerable motion loss of the atlantoaxial complex. Flexibility tests were conducted on 24 human cadaveric craniocervical specimens in the following sequence: (1) intact, (2) after dissection of the atlantoaxial ligaments and odontoidectomy, (3) after the TAAS implantation, and (4) after Harms rigid fixation. Rotational angles of the C1-C2 segment were measured to study the immediate stability and function of the TAAS implantation compared with the intact and Harms rigid fixation. Comparing the TAAS implantation to the intact state, the range of motion and neutral zone changed little in flexion, extension, and lateral bending but increased significantly in axial rotation (P < 0.001). Compared with Harms rigid fixation, the TAAS implantation significantly increased range of motion and neutral zone in all directions (P < 0.001). We have designed the TAAS for correcting atlantoaxial instability arising from C1-C2 anterior decompression procedures. The unique aspect of the TAAS is that it restores, to a great extent, the C1-C2 motion that is lost during current stabilization procedures.

Biomechanical Evaluation of an Atlantoaxial Lateral Mass Fusion Cage With C1–C2 Pedicle Fixation

A biomechanical testing protocol was used to evaluate atlantoaxial fixation techniques in a human cadaveric model. To compare in vitro biomechanics of atlantoaxial lateral mass fusion cage combined with C1-C2 pedicle screw technique with those of C1-C2 pedicle screw technique alone and C1-C2 transarticular screws combined with Gallie wires. An atlantoaxial lateral mass fusion cage was designed, knowing that the cage, when rigidly combined with C1-C2 pedicle screws, could offer other fusion spots for atlantoaxial stabilization in cases when the posterior arch of the atlas is absent or removed for decompression and a Gallie fixation is impossible. No comparative in vitro biomechanical test has been conducted previously to evaluate the feasibility of this method. Anatomic measurements of the atlantoaxial lateral masses were taken using computed tomography in normal human subjects. Six fresh-frozen human cadaveric cervical spines (C0-C4) were used in the biomechanical study. Specimens were tested in their intact condition, after destabilization via transverse-alar-apical ligament disruption, and after implantation of 3 fixation constructs: (1) transarticular screws combined with Gallie wires, (2) C1-C2 pedicle screws, and (3) atlantoaxial lateral mass fusion cage combined with C1-C2 pedicle screws. Pure moment loading up to 1.5 Nm in flexion/extension, right-left lateral bending, and right-left axial rotation was applied to the occiput, and relative intervertebral rotations were determined using stereophotogrammetry. Range of motion for the intact, destabilized, and 3 fixation scenarios were determined. The anatomic data indicated that feasible cage design were in 3 sizes: 11/8, 12/9, and 13/10 mm for length/width, and 3.5, 4, and 4.5 mm for height. The biomechanical data indicated that transverse-alar-apical ligament disruption significantly increased C1-C2 motion for all directions. All the 3 fixation techniques significantly reduced motion compared with the intact and destabilized cases. There were no statistically significant differences among the 3 fixation techniques. The biomechanical study indicated that, contrary to expectation, addition of a cage did not increase the stability compared with C1-C2 pedicle screw alone. However, the C1 + C2 + Cage technique may be a viable alternative for atlantoaxial stabilization when the posterior arch of the atlas is absent or removed for decompression and a Gallie fixation is impossible.

Intraarticular Atlantooccipital Fusion for the Treatment of Traumatic Occipitocervical Dislocation in a Child

A case report of traumatic atlantooccipital dislocation (AOD) managed by intraarticular-posterior fusion from a posterior approach at the C0-C1 level with preservation of C1-C2 motion. To present a new technique for atlantooccipital fusion with long-term follow-up. There is an increasing number of patients with AOD who have preservation of neurologic function. The most frequent method used to treat this condition is occipitocervical fusion. There has been a tendency in recent years to minimize the extent of stabilization, performing occipitoatlantal fusion only. However, it is difficult to achieve a solid fusion between C0 and C1, and the long-term effect of the insufficiency of lig. alaria on C0-C2 stability is unknown. The authors present a modified technique of C0-C1 fusion that aims to enhance fusion and achieve greater stability. A 11-year-old child with AOD was initially treated unsuccessfully with a halo device for 3 months. As instability persisted, an isolated C0-C1 fusion was performed from a posterior approach. This anatomically based intraarticular fusion technique comprises removal of the articular cartilage of the atlantooccipital joints, and cancellous bone autografting at the atlantooccipital joints and between the occiput and posterior arch of C1, supported by an occipital plate linked by rods to lateral mass screws in the atlas. This technique of increased bony fusion surface and internal fixation provided an excellent result with full recovery of minor neurologic deficits. At long-term follow-up, 9 years after surgery, the patient was free of signs and symptoms; solid fusion of the C0-C1 joint, and normal values for rotation of the C1-C2 segment were recorded. Intraarticular and posterior fusion of the atlantooccipital joint was able to provide an excellent long-term clinical outcome in the treatment of traumatic AOD in a child. This is the first report of an intraarticular fusion of the C0-C1 segment and the longest follow-up published on isolated C0-C1 stabilization.

Biomechanical stability of fixation with bilateral C1 hooks plus C2 pedicle screws

Objective To compare the biomechanical stabilities of fixation with bilateral C1 hooks plus C2 pedicle screws, fixation with C1-C2 transarticular screws plus Gallic wires and fixation with C1-C2 pedicle screws. Methods Six specimens of cervical spines (C0-C4) taken from 6 fresh-frozen human their intact condition, destabilization by disrupting the transverse-Mar-apical ligament, fixation with transar-ticular screws plus Gallic posterior wires, fixation with C1 hooks plus C2 pedicle screws, and fixation with C1-C2 pedicle screws.Pure moment loading, up to 1.5 N·m, was applied to the occiput in flexion-extension, right-left lateral bending, and right-left axial rotation to determine the relative intervertebral rotations using a camera system. The ranges of motion (ROM) for the intact, destabilized and 3 fixation sce-narios were determined. Statistical analyses were performed using one-way analysis of variance, with Fishers least significant difference post hoc test for multiple comparisons. Results The data indicated that the C1-C2 motion significantly increased for all rotations in the cases of disrupted ligament. The motion in all the 3 fixations significantly reduced compared with the intact and destabilized cases (P 0.05). Conclusions The C1 hooks plus C2 pedicle screws fixation appears as effective as the fixations with transartieular screw-wiring construct and C1-C2 pedicle screws in reducing the relative atlantoaxial motion in a severely destabilized upper cervical spine. In cases where the latter two methods are not feasible, fixation with C1 hooks plus C2 pedicle screws may be a safe alternative for treatment of atlantoaxial stabilization. Key words: Atlantoaxial joint; Fracture fixation, internal; Biomechanics

Cervical Spine Motion Generated With Manual Versus Jackson Table Turning Methods in a Cadaveric C1–C2 Global Instability Model

STUDY DESIGN.: Cadaveric biomechanical study. OBJECTIVE.: To quantify spinal motion created by transfer methods from supine to prone position in a cadaveric C1-C2 global instability model. SUMMARY OF BACKGROUND DATA.: Patients who have sustained a spinal cord injury remain at high risk for further secondary injury until their spine is adequately stabilized. To date, no study has evaluated the effect of patient transfer methods from supine to prone position in the operating room, on atlantoaxial cervical spine motion. METHODS.: A global instability was surgically created at the C1-C2 level in 4 fresh cadavers. Two transfer protocols were tested on each cadaver. The log-roll technique entailed performing a standard 180 degrees log-roll rotation of the supine patient from a stretcher to the prone position onto the operating room Jackson table (OSI, Union City, CA). The "Jackson technique" involved sliding the supine patient to the Jackson table, securing them to the table, and then rotating them into a prone position. An electromagnetic tracking device registered motion between the C1 and C2 vertebral segments. Three different head holding devices (Mayfield, Prone view, and blue foam pillow) were also compared for their ability to restrict C1-C2 motion. Six motion parameters were tracked. Repeated measures statistical analysis was performed to evaluate angular and translational motion. RESULTS.: For 6 of 6 measures of angulation and translation, manual log-roll prone positioning generated significantly more C1-C2 motion than the Jackson table turning technique. Out of 6 motion parameters, 5 were statistically significant (P < 0.001-0.005). There was minimal difference in C1-C2 motion generated when comparing all 3 head holding devices. CONCLUSION.: The data demonstrate that manual log-roll technique generated significantly more C1-C2 motion compared to the Jackson table technique. Choice of headrest has a minimal effect on the amount of motion generated during patient transfer, except that the Mayfield device demonstrates a slight trend toward increased C1-C2 motion.

Comparing Cervical Spine Motion With Different Halo Devices in a Cadaveric Cervical Instability Model

Biomechanical evaluation of conventional and noninvasive halos in cadaveric C1-C2 and C5-C6 instability models. To compare the ability of a conventional halo and noninvasive halo (NIH) to immobilize the unstable cervical spine at the C1-C2 and C5-C6 levels. Many successful outcomes have been reported in cervical spine injury treatment with the conventional halo (CH); however, complications related to pin sites have been reported. The NIH was designed to overcome these complications. To date, no investigation has compared the biomechanical efficacy of the NIH with that of the CH in restricting three-dimensional cervical spine motion. A global instability was created at the C1-C2 level in 4 cadavers and at C5-C6 in 4 others. Relative motion was measured between the superior and inferior vertebrae during the donning process, execution of the log roll technique, and during the process of sitting up. This testing sequence was followed for all treatment conditions. During the application of the orthoses there was a significant increase in motion at C1-C2 instability and a trend toward increased motion at the C5-C6 instability with CH compared with NIH. In the log roll maneuver, the CH and NIH restrict motion to a similar degree at the C1-C2 instability level, except in frontal plane translation, where CH immobilizes the segment to a greater extent. For the C5-C6 instability the CH provides significantly better immobilization for lateral bending and axial translation. No significant differences were found between the NIH and CH for the sit-up maneuver at either of the levels. Donning of the NIH generates significantly less cervical spine motion than application of the CH. The CH provides superior immobilization for a C5-C6 instability during the log roll maneuver and a C1-C2 instability in the frontal plane during the log-roll maneuver. The CH and NIH immobilize the C1-C2 and C5-C6 instability to a similar degree during the sit-up maneuver.