Transoral Atlantoaxial Reduction Plate Research Articles

Biomechanical properties of different anterior and posterior techniques for atlantoaxial fixation: a finite element analysis

BackgroundMany techniques for atlantoaxial fixation have been developed. However, the biomechanical differences among various atlantoaxial fixation methods remain unclear. This study aimed to evaluate the biomechanical influence of anterior and posterior atlantoaxial fixation techniques on fixed and nonfixed segments.MethodsAn occiput-C7 cervical finite element model was used to construct 6 surgical models including a Harms plate, a transoral atlantoaxial reduction plate (TARP), an anterior transarticular screw (ATS), a Magerl screw, a posterior screw-plate, and a screw-rod system. Range of motion (ROM), facet joint force (FJF), disc stress, screw stress, and bone-screw interface stress were calculated.ResultsThe C1/2 ROMs were relatively small in the ATS and Magerl screw models under all loading directions except for extension (0.1°–1.0°). The posterior screw-plate system and screw-rod system generated greater stresses on the screws (77.6–1018.1 MPa) and bone-screw interfaces (58.3–499.0 MPa). The Harms plate and TARP models had relatively small ROMs (3.2°–17.6°), disc stress (1.3–7.6 MPa), and FJF (3.3–106.8 N) at the nonfixed segments. Changes in disc stress and FJF of the cervical segments were not consistent with changes in ROM.ConclusionsATS and Magerl screws may provide good atlantoaxial stability. The posterior screw-rod system and screw-plate system may have higher risks of screw loosening and breakage. The Harms plate and TARP model may more effectively relieve nonfixed segment degeneration than other techniques. The C0/1 or C2/3 segment may not be more susceptible to degeneration than other nonfixed segments after C1/2 fixation.

Prevertebral soft tissue swelling after anterior cervical internal fixation at different segments: a retrospective study

Atlantoaxial segments have not been discussed in existing studies on prevertebral soft tissue (PVST) swelling after cervical operations. This study aimed to investigate the characteristics of PVST swelling after anterior cervical internal fixation at different segments. This retrospective study included patients who underwent transoral atlantoaxial reduction plate (TARP) internal fixation (Group I, n=73), C3/C4 anterior decompression and vertebral fixation (Group II, n=77), or C5/C6 anterior decompression and vertebral fixation (Group III, n=75) at our Hospital. The PVST thickness at C2, C3, and C4 segments was measured before and 3 days after the operation. Time of extubation, number of patients with postoperative re-intubation and dysphagia were collected. Results show that all patients had significant postoperative PVST thickening (all P<0.01). PVST thickening at C2, C3, and C4 was significantly greater in Group I than in Groups II and III (all P<0.01). PVST thickening at C2, C3, and C4 in Group I was 1.87 (14.12mm/7.54mm), 1.82 (12.90mm/7.07mm) and 1.71 (12.09mm/7.07mm) times of that in Group II, respectively. PVST thickening at C2, C3, and C4 in Group I was 2.66 (14.12mm/5.31mm), 1.50 (12.90mm/8.62mm) and 1.32 (12.09mm/9.18mm) times of that in Group III, respectively. The patients in Group I had significantly later postoperative extubation (Both P<0.01) than the patients in Groups II and III. None of the patients had postoperative re-intubation or dysphagia. We conclude that PVST swelling was greater in patients who underwent TARP internal fixation than in patients who underwent anterior C3/C4 or C5/C6 internal fixation. Hence, after TARP internal fixation, patients should be given proper respiratory tract management and monitoring.

Research on pharyngeal bacterial flora in transoral atlantoaxial operation and the postoperative follow-up study

ObjectivesTo study the changes of bacterial flora after a series of preoperative oral disinfection and the postoperative recovery of nerve function of patients with craniovertebral junction disorders who were treated with transoral approach operations.MethodsThis research analyzed 20 cases collected from October 2009 to May 2010. All these patients were with CVJ disorders, including 8 males and 12 females, aged 2 to 66 (38.1 on average), and they were all treated with transoral approach operations. The mucosa samples of the posterior pharyngeal wall were sent for bacteria culture. These samples were collected by sterile cotton swabs at four crucial points, including 3 days before operation/before gargling, 3 days after continuous gargling/after anesthesia intubation on the day of operation, after intraoperative cleaning and washing of the mouth, and after intraoperative iodophor immersion. The microflora was stained by means of smear and further counted after an investigation by microscope. The neural function of patients was evaluated by the ASIA classification and the JOA scores. All patients but two with posterior stabilization performed respectively underwent transoral atlantoaxial reduction plate (TARP) fixation consecutively in the same sitting. A regular reexamination of cervical vertebra with lateral and open mouth X-ray, CT and MRI was conducted after operation to evaluate the reduction of atlantoaxial dislocation, internal fixation position, bone graft fusion, inflammatory lesions and tumor recurrence.ResultsThis bacteriological research showed that the mucosa of the posterior pharyngeal wall of all the patients was in a sterile state after a series of oral preoperative preparations and intraoperative iodophor disinfection, which was considered as type I incision. The bacterial culture results of the mucosa samples of the posterior pharyngeal wall collected at different time points showed significant differences (χ2 = 42.762, P = 0.000). All the patients had improvement in ASIA, and their neural functions were improved to different levels after operation. There was a significant difference in JOA scores before and after operation (t = 8.677, P = 0.000). Postoperative imaging examination showed that the atlantoaxial screw position was good and firm, and the CVJ disorders were treated appropriately.ConclusionIt is safe and effective to cut the posterior pharyngeal muscle layer and implant internal fixation by means of transoral approach.

Incidence and management of surgical site infection in the cervical spine following a transoral approach.

Transoral approach can accomplish ventral decompression directly. However, surgical site infection (SSI) cannot be ignored. This paper aims to review the prevalence of infection and conduct advice for the treatment of SSI in the cervical spine following the transoral approach. A retrospective analysis of patients with SSI after transoral atlantoaxial reduction plate (TARP) surgery was performed. SSI was classified into three kinds according to the modified American CDC criteria. 2.9% (17/581) patients who underwent TARP surgery, experienced SSI, of which five had superficial SSI (SI), eight had deep SSI (DI), and four had organ/space SSI (O/SI). The patients with SI underwent intravenous antibiotic treatment and were ultimately cured. Among the remaining 12 patients with DI and O/SI, 11 underwent reoperation for TARP system removal and subsequently one-stage posterior occipitocervical fixation, and one patient experienced infection twomonths post-operatively and died without receiving treatment. Among patients who underwent revision surgery, three experienced intracranial infection due to intra-operative dural tears, and continuous lumbar cerebrospinal fluid drainage and intrathecal injection of antibiotics were used as effective and appropriate treatments, with outcomes of one recovery and two deaths. All patients with SSI were begun on intravenous antibiotics with conversion to oral antibiotics. The incidence of SSI was 2.9% (17/581). Adequate peri-operative preparation, early diagnosis, and appropriate treatment of SSI require further research.

Usefulness of a Three-Dimensional-Printed Model in the Treatment of Irreducible Atlantoaxial Dislocation with Transoral Atlantoaxial Reduction Plate.

ObjectiveTo evaluate the usefulness of a 3D‐printed model for transoral atlantoaxial reduction plate (TARP) surgery in the treatment of irreducible atlantoaxial dislocation (IAAD).MethodsA retrospective review was conducted of 23 patients (13 men, 10 women; mean age 58.17 ± 5.27 years) with IAAD who underwent TARP from January 2015 to July 2017. Patients were divided into a 3D group (12 patients) and a non‐3D group (11 patients). A preoperative simulation process was undertaken for the patients in the 3D group, with preselection of the TARP system using a 3D‐printed 1:1 scale model, while only imaging data was used for the non‐3D group. Complications, clinical outcomes (Japanese Orthopaedic Association [JOA] and visual analogue score [VAS]), and image measurements (atlas–dens interval [ADI], cervicomedullary angle [CMA], and clivus‐canal angle [CCA]) were noted preoperatively and at the last follow up.ResultsA total of 23 patients with a follow‐up time of 16.26 ± 4.27 months were included in the present study. The surgery duration, intraoperative blood loss, and fluoroscopy times in the 3D group were found to be shorter than those in non‐3D group, with statistical significance. The surgery duration was 3.29 ± 0.45 h in the 3D group and 4.68 ± 0.90 h in the non‐3D group, and the estimated intraoperative blood loss was 131.67 ± 43.03 mL in the 3D group and 185.45 ± 42.28 mL in the non‐3D group. No patients received blood transfusions. The intraoperative fluoroscopy times were 5.67 ± 0.89 in the 3D group and 7.91 ± 1.45 in the non‐3D group. Preoperatively and at last follow up, JOA and VAS scores and ADI, CCA, and CMA were improved significantly within the two groups. However, no statistical difference was observed between the two groups. However, surgical site infection occurred in 1 patient in the 3D group, who underwent an emergency revision operation of the removal of TARP device and posterior occipitocervical fixation; the patient recovered 2 weeks after the surgery. In 2 patients in the traditional group, a mistake occurred in the placement of screws, with no neurological symptoms related to the misplacement.ConclusionPreoperative surgical simulation using a 3D‐printed real‐size model is an intuitive and effective aid for TARP surgery for treating IAAD. The 3D‐printed biomodel precisely replicated patient‐specific anatomy for use in complicated craniovertebral junction surgery. The information was more useful than that available with 3D reconstructed images.

Management of pediatric patients with irreducible atlantoaxial dislocation: transoral anterior release, reduction, and fixation.

Although transoral atlantoaxial reduction plate (TARP) surgery has been confirmed to be safe and effective for adults who have irreducible atlantoaxial dislocation (IAAD) with or without basilar invagination or upper cervical revision surgery, it is rarely used to treat these disorders in children. The authors of this study aimed to report on the use of the anterior technique in treating pediatric IAAD. In this retrospective study, the authors identified 8 consecutive patients with IAAD who had undergone surgical reduction at a single institution in the period between January 2011 and June 2104. The patients consisted of 5 males and 3 females. Three had os odontoideum, 2 had basilar invagination, and the other 3 experienced atlantoaxial rotatory fixed dislocation (AARFD). They were all treated using transoral anterior release, reduction, and fusion with the TARP. Preoperative and postoperative CT scans and MR images were obtained. American Spinal Injury Association (ASIA) Impairment Scale grades were determined. All symptoms were relieved in all 8 patients but to varying degrees. Intraoperative loose reduction and fixation of C1-2 were achieved in one stage. The 4 patients with preoperative neurological deficits were significantly improved after surgery, and their latest follow-ups indicated that their ASIA Impairment Scale grades had improved to E. Postoperative pneumonia occurred in 1 patient but was under complete control after anti-infective therapy and fiber optic-guided sputum suction. One-stage transoral anterior release, reduction, and fixation is an effective, reliable, and safe means of treating pediatric IAAD. The midterm clinical results are satisfactory, with the technique eliminating the need for interval traction and/or second-stage posterior instrumentation and fusion.

Patient-specific drill template for C2 transoral pedicle insertion in complete reduction of atlantoaxial dislocation: cadaveric efficacy and accuracy assessments

BackgroundThe transoral atlantoaxial reduction plate (TARP) is an effective advance in the treatment of atlantoaxial dislocation (AAD) and can enable the performance of anterior atlantoaxial release, reduction, decompression, and internal fixation in a one-stage operation. However, accurate transoral C2 pedicle insertion (C2TOPI) remains a challenge. The aim of this study is to develop a grouped patient-specific drill template (PDT) specifically for AAD with complete reduction and, furthermore, to compare its efficacy and accuracy in facilitating C2TOPI.MethodsAfter CT scanning, ten cadaveric C2 specimens were randomly assigned to two groups (the PDT and freehand group). A grouped PDT specifically for AAD with complete reduction was designed and manufactured. C2TOPI was performed using the PDT or the fluoroscopy-guided freehand technique. Postoperative CT scans were subsequently performed to analyze the deviations at the centroid of the cross section at the midpoint of the pedicle. Screw position grades were also assessed in both groups.ResultsCompared to the freehand group, the PDT group had a significantly shorter surgery time (p < 0.001). Significant differences between the two groups were observed in the absolute value of the deviations at the centroid of the pedicle on either the axial or sagittal planes (p < 0.05). No significant difference was found in the screw positions between the two groups (p > 0.05); however, two unacceptable breaches (20%) occurred in the freehand group.ConclusionA specifically designed PDT could provide an accurate and easy-to-apply method for C2TOPI in AAD with complete reduction.

Atlantoaxial Joint Distraction for the Treatment of Basilar Invagination: Clinical Outcomes and Radiographic Evaluation.

To investigate the causes of partial remission in patients with basilar invagination (BI) and irreducible atlantoaxial dislocation (IAAD) treated with transoral atlantoaxial reduction plate (TARP) without odontoidectomy and quantify the distance of odontoid descent. Between August 2010 and July 2012, 22 consecutive patients with BI with IAAD who underwent TARP surgery were reviewed. The preoperative and postoperative radiographic parameters were evaluated. Follow-up data and the symptom treatment interval (STI), defined as the interval between the onset of symptoms and surgical treatment, were assessed. Neurological function was evaluated as neurologic improvement, defined as ([Postoperative Japanese Orthopedic Association (JOA) score]- [Preoperative JOA score])/(17- [Preoperative JOA score]). The patients were assigned to group A (<50%) or group B (≥50%) based on their level of neurologic improvement. All 22 patients improved clinically to varying degrees. The mean preoperative STI was 105.6 ± 67.6 months for group A and 45.3 ± 46.7 months for group B (P<0.05). There were no significant between-group differences in follow-up (P > 0.05) or with respect to radiographic parameters (P > 0.05). Persistent brainstem compression was observed in 1 patient, whose symptoms were not adequately relieved after revision surgery (transoral odontoidectomy and posterior decompression and fusion). No fixation failure was observed. Descent of the odontoid process is useful for treating basilar invagination. TARP surgery without odontoidectomy may pull the dens caudally and ventrally to achieve sufficient decompression of the spinal cord. Neurologic improvement may be associated with STI.

Surgical Outcome and Prognostic Analysis of Transoral Atlantoaxial Reduction Plate System for Basilar Invagination: A Voxel-Based Morphometry Study.

The use of a transoral atlantoaxial reduction plate (TARP) system is an effective surgical approach for the treatment of basilar invagination. With the aim of improving the therapeutic efficacy of the TARP operation, we conducted a voxel-based morphometric study to quantitatively investigate the descent of the odontoid process and craniocervical volume changes. We enrolled 20 patients with basilar invagination who underwent a TARP procedure. Craniocervical computed tomography (CT) scanning and a 3-dimensional (3-D) reconstruction of the craniocervical junction were performed. Craniocervical volumes and odontoid process descent distances were measured preoperatively and postoperatively. Individual neurological function was evaluated according to the Japanese Orthopaedic Association (JOA) scoring system for cervical disorders. Pearson correlation analysis was applied for statistical testing. Surgical efficacy (the JOA-score improvement rate) was significantly associated with the craniocervical volume improvement rate, the odontoid descent distance, and the absolute craniocervical volume changes (p < 0.01 for all), with correlation coefficients (r) of 0.83, 0.80, and 0.61, respectively. No significant correlation was noted between surgical efficacy and age, symptom duration, preoperative neurological function, odontoid process displacement, or change in clivus-odontoid angle (p > 0.05). The craniocervical volume improvement rate was significantly associated with the odontoid descent distance (r = 0.8; p < 0.01), but it was not associated with the odontoid displacement or the change in the clivus-odontoid angle (p > 0.05). We found that the odontoid descent distance predicted the craniocervical volume improvement rate following TARP procedures in patients with basilar invagination, and we believe that both can serve as predictors of surgical efficacy. We believe that planning the odontoid descent distance preoperatively may help to improve the efficacy of TARP operations. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

An 11-Year Review of the TARP Procedure in the Treatment of Atlantoaxial Dislocation.

Retrospective study. The aim of the study was to introduce the surgical techniques and evaluate the clinical outcomes of transoral atlantoaxial reduction plate (TARP) for the treatment of atlantoaxial dislocation. Researchers have reported on transoral plate internal fixation for the treatment of irreducible atlantoaxial dislocation (IAAD) without long-term follow-up and detailed clinical experience. The clinical records of 388 patients with atlantoaxial dislocation (IAAD, 340 cases; fixed atlantoaxial dislocation [FAAD], 48 cases) who received the TARP procedure from April 2003 to September 2014 were retrospectively reviewed. They were treated separately with TARP-I or TARP-II (82 cases), TARP-III (248 cases), or TARP-IV (58 cases). X-ray and magnetic resonance imaging were used to evaluate the efficacy of reduction and the degree of decompression, respectively. The long-term clinical outcome was evaluated by Japanese Orthopaedic Association scoring and the Symon and Lavender standard. Immediate reduction was achieved for all the patients with IAAD (340/340), whereas anatomical reduction was achieved for 98.2% of patients (334/340). Anatomical reduction was achieved in 87.5% of patients with FAAD (42/48). The average degree of spinal cord decompression ranged from 75% to 100% with an average of 88.4%. The clinical data of 106 patients were evaluated in the latest follow-up (12-108 mo, average 60.5 mo). The average spinal cord improvement rate by Japanese Orthopaedic Association scoring was 62.1%. According to the Symon and Lavender standard, there were 85 cases rated as markedly effective, 104 cases as effective, and 2 cases as noneffective. The overall markedly effective rate was 80% and the effective rate was 98%. The TARP procedure showed good anterior atlantoaxial release, reduction, decompression, and internal fixation for patients with IAAD and FAAD through a single anterior approach. It has the advantages of three-dimensional immediate atlantoaxial reduction and sufficient decompression. 3.

Biomechanical Comparison of Modified TARP Technique Versus Modified Goel Technique for the Treatment of Basilar Invagination: A Finite Element Analysis.

A finite element analysis. The aim of this study was to determine the biomechanical differences between atlantoaxial fusion cage combined with transoral atlantoaxial reduction plate fixation (TARP + Cage, modified TARP technique) and that combined with C1 lateral mass screw and C2 pedicle screw fixation (C1LS + C2PS + Cage, modified Goel technique) in the treatment of basilar invagination (BI) by finite element analysis. Clinical studies have shown that transoral anterior atlantoaxial release followed by TARP fixation can achieve reduction, decompression, fixation, and fusion of C1-C2 through a transoral-only approach. Although cage has been used to reduce the BI through posterior approach, there are no studies referred to the cage combined with TARP for C1-C2 fusion. A finite element model was used to investigate and compare the stability between TARP + Cage fixation and C1LS + C2PS + Cage fixation in the treatment of BI. Vertical load of 40 N was applied on the C0, to simulate head weight, and 1.5 Nm torque was applied to the C0 to simulate flexion, extension, lateral bending, and rotation. In comparison with the C1LS + C2PS + Cage model, the TARP + Cage model reduced the ROM by 44.7%, 30.0%, and 10.5% in extension, lateral bending, and axial rotation, while the TARP + Cage model increased the ROM by 30.0% in flexion, and the TARP + Cage model also led to lower screw stress in all motions with one exception (anterior C2PS stress in extension). Our results indicate that the TARP + Cage fixation may offer higher stability to C1LS + C2PS + Cage in extension, lateral bending, and axial rotation but lower stability in flexion. Compared with modified Goel technique, the modified TARP technique not only has the capability of transferring the load and distributing the stress but also can provide neural decompression, stabilization and fusion, and restore C1-C2 normal fusion angle. N/A.

Cuff-leak test combined with interventional bronchoscopy benefits early extubation for patients who received tarp surgery.

This study explored the performance characteristics of a cuff-leak test (CLT) combined with interventional fiberoptic bronchoscopy (FBS) for evaluating whether early nasoendotracheal extubation was possible for patients who had received transoral atlantoaxial reduction plate (TARP) internal fixation surgery. 318 patients who underwent surgery were retrospectively analyzed (between January 2006 and December 2012). Extubation was performed by conventional approach (CA group, until December 2008) and improved approach (IA group, from January 2009) including CLT and an interventional FBS procedure. The extubation success within 1-3days after surgery, incidence of postextubation stridor and tracheal reintubation were examined. More IA-treated patients experienced extubation during the first 2days than those CA-treated, median extubation time was 3 (2, 3) days in the CA group and 2 (1, 2) days in the IA group (all P<0.01). The incidence of stridor and reintubation was 5.69 and 0.57% in IA and 11.98 and 4.93% in CA, respectively (both P<0.05). For the CLT-positive patients in the IA group that remained intubated until day 3-4, interventional FBS was applied for safe extubation and achieved 100% success. Early extubation through IA is safe and interventional FBS assists successful extubation for CLT-positive patients who underwent TARP surgery.

Treatment of Basilar Invagination With Klippel-Feil Syndrome: Atlantoaxial Joint Distraction and Fixation With Transoral Atlantoaxial Reduction Plate.

Klippel-Feil syndrome (KFS) is characterized by congenital vertebral fusion of the cervical spine and a wide spectrum of associated anomalies. In patients with KFS with basilar invagination (BI), compression of the brainstem and upper cervical cord results in neurological deficits, and decompression and occipitocervical reconstruction are required. The highly varied anatomy of KFS makes a posterior occipitocervical fixation strategy challenging. For these patients, the transoral atlantoaxial reduction plate (TARP) operation is an optimal option to perform a direct anterior fixation to achieve stabilization. To evaluate the effectiveness of TARP internal fixation for the treatment of BI with KFS. Ten consecutive patients with BI and KFS who underwent TARP reduction and fixation from 2010 to 2012 were reviewed. Clinical assessment and image measurements were performed preoperatively and at the most recent follow-up. Nine patients (9/10) were followed for an average of 31.44 months. Symptoms were alleviated in 9 of 9 patients (100.00%). The odontoid process was ideally corrected with the TARP system. The mean clivus canal angle improved from 124° preoperatively to 152° postoperatively. The average preoperative and postoperative Japanese Orthopedic Association scores were 10.56 (n = 9) and 14.67 (n = 9), respectively, indicating 63.82% improvement. There was bony bridge catenation on the computed tomography scans and no evidence of hardware failure at 6 months. The TARP operation is effective and safe for treating patients with BI with KFS. The midterm clinical results were satisfactory.

The development and evaluation of individualized templates to assist transoral C2 articular mass or transpedicular screw placement in TARP-IV procedures: adult cadaver specimen study

OBJECTIVES:The transoral atlantoaxial reduction plate system treats irreducible atlantoaxial dislocation from transoral atlantoaxial reduction plate-I to transoral atlantoaxial reduction plate-III. However, this system has demonstrated problems associated with screw loosening, atlantoaxial fixation and concealed or manifest neurovascular injuries. This study sought to design a set of individualized templates to improve the accuracy of anterior C2 screw placement in the transoral atlantoaxial reduction plate-IV procedure.METHODS:A set of individualized templates was designed according to thin-slice computed tomography data obtained from 10 human cadavers. The templates contained cubic modules and drill guides to facilitate transoral atlantoaxial reduction plate positioning and anterior C2 screw placement. We performed 2 stages of cadaveric experiments with 2 cadavers in stage one and 8 in stage two. Finally, guided C2 screw placement was evaluated by reading postoperative computed tomography images and comparing the planned and inserted screw trajectories.RESULTS:There were two cortical breaching screws in stage one and three in stage two, but only the cortical breaching screws in stage one were ranked critical. In stage two, the planned entry points and the transverse angles of the anterior C2 screws could be simulated, whereas the declination angles could not be simulated due to intraoperative blockage of the drill bit and screwdriver by the upper teeth.CONCLUSIONS:It was feasible to use individualized templates to guide transoral C2 screw placement. Thus, these drill templates combined with transoral atlantoaxial reduction plate-IV, may improve the accuracy of transoral C2 screw placement and reduce related neurovascular complications.

Treatment of basilar invagination with atlantoaxial dislocation: atlantoaxial joint distraction and fixation with transoral atlantoaxial reduction plate (TARP) without odontoidectomy.

Although direct transoral decompression and one-stage posterior instrumentation can obtain satisfactory cord decompression for the treatment of basilar invagination with atlantoaxial dislocation, surgical injuries run high as combinative anterior-posterior approaches were necessary. Furthermore, the complications will rise notably when involvement of dens and/or clivus in the decompression necessitates relatively complicated surgical techniques. First initiated in 2005, transoral atlantoaxial reduction plate (TARP) works as an internal fixation for the treatment of basilar invagination with irreducible atlantoaxial dislocation. Therefore, this article aimed to describe several operative experiences about this approach, which has delivered successful decompression, fixation and fusion. 21 consecutive patients with basilar invagination underwent the TARP operation. The pre- and postoperative medulla-cervical angles were measured and compared. The JOA scores of spinal cord function were calculated pre- and post-operatively. 20 cases (20/21) were followed up to average 12.5 months. Symptoms of all the 20 cases were relieved in different degrees. The postoperative imaging showed the odontoid processes obtained ideal reduction and the internal fixators were all in good position. The medulla-cervical angle was correctd from an average (± standard deviation) 128.7° + 11.9° (n = 20) before surgery to 156.5° + 8.1° (n = 20) after surgery (P < 0.01). The average preoperative and postoperative Japaneses Orthopedic Association scores were 11.25 (n = 20) and 15.9 (n = 20), respectively, indicating 76 % improvement. Screw-loosening was observed in one patient due to severe osteoporosis. After a revised operation with a TARP in another size, the neurological symptoms showed no obvious improvements. Then the treatment was terminated. The TARP operation and intra-operative traction could reduce the odontoid process superiorly migrating into the foramen magnum, directly ease the ventral compression of spinal cord, and fix the reduced atlantoaxial joints through a single transoral approach without the need of a posterior operation. In this stury, 21 patients were evaluated and 20 did well with TARP operation. The preliminary clinical result was satisfactory.

Radiographic and clinical assessment on the accuracy and complications of C1 anterior lateral mass and C2 anterior pedicle screw placement in the TARP-III procedure: a study of 106 patients.

To investigate the (1) radiographic and clinical accuracy of C1 anterior lateral mass screw (C1ALMS) and C2 anterior pedicle screw (C2APS) placement in the transoral atlantoaxial reduction plate (TARP)-III procedure, (2) screw insertion-associated clinical complications and (3) fusion status between C1 and C2. Radiographic and clinical data were obtained from the electronic medical record system. Studies were carried out to assess the accuracy of C1ALMS and C2APS placement, the screw insertion-associated clinical complications and the fusion status between C1 and C2. Placement of the screws was assessed using the modified All India Institute of Medical Sciences outcome-based classification. Two-hundred and twelve C1ALMS and 207 C2APS in 106 patients were assessed. The ideal accurate rates were 92.0% (195) and 53.1% (110), and the acceptable accurate rates were 97.6% (207) and 87.0% (180), respectively. One patient died postoperatively due to C2 screw misplacement. There were no symptoms of neurologic and vertebral artery injuries in the rest of the patients. 102 patients (97.1%) achieved solid fusion between C1 and C2. No instrumentation failure due to delayed union or nonunion was observed. C1ALMS placement in TARP-III procedures appears to be safe. The cortical breach rate of C2APS is high though clinically the neurovascular complication rate is similar to that of posterior atlantoaxial procedures. Advanced navigation strategies may help improve the accuracy of C2APS placement and decrease potential complications.

Transoral anterior revision surgeries for basilar invagination with irreducible atlantoaxial dislocation after posterior decompression: a retrospective study of 30 cases

To report the surgical techniques and clinical results of one-stage transoral anterior revision surgeries for basilar invagination (BI) with atlantoaxial dislocation (AAD) after posterior decompression. From September 2008 to June 2012, 30 patients (16 men and 14 women) who had BI with irreducible atlantoaxial dislocation (IAAD) after posterior decompression underwent anterior revision surgeries in our department. Dynamic cervical radiographs, computed tomographic scans and magnetic resonance imaging were obtained pre- and postoperatively to assess the degree of AAD and ventral compression on the cervical cord. The JOA scoring system was used to evaluate the neurological status. The revision surgeries were conducted by anterior approach, using the transoral atlantoaxial reduction plate (TARP) system. The revision surgeries were successfully performed in all of the cases. The average follow-up duration was 16months (range 6-39 months). For all of the cases, complete or more than 50% reduction and decompression of C1-C2 were achieved. The cervicomedullary angle was improved by an average of 32.9°. Bone fusion was achieved within 3-6months in all of the cases. Clinical symptoms were alleviated in 29 patients (96.7%) and stabilised in 1 patient (3.3%). No patients have developed recurrent or progressive atlantoaxial instability so far. Anterior revision surgeries using the TARP system achieved reduction, decompression and fixation of C1-C2 in one stage for BI with IAAD. This technique offers an effective, simple and safe method for the revision of such cases after posterior decompression.

Application of three-dimensional model in the management of irreducible atlanto-axial dislocation.

The aim of this study was to describe the application of the rapid prototyping (RP) life-size 3-dimensional model used to improve accuracy of screw insertion in irreducible atlanto-axial dislocation (IAD). The study included 10 patients with IAD. All patients were assessed using the Japanese Orthopedic Association (JOA) score. Radiographs, MRI and CT were conducted during the preoperative and postoperative procedure. A 3D RP model was created for each patient. The model was used to obtain detailed information of each pedicle and used as an intraoperative reference. Assisted by the model, transoral atlanto-axial reduction plate fixation was performed in each case. The average operation time was 145 (range: 90 to 180) minutes and average blood loss was 120 (range: 60 to 250) ml. JOA scores improved after surgery. All 40 transoral pedicle/lateral mass screws were placed without serious complications or internal fixation failure. Postoperative radiographs and CT scan showed 38 transoral pedicle/lateral mass screws located in the pedicle tracts. Satisfactory reduction was achieved in 95% of screws. Two screws perforated the lateral wall of the C2 pedicles in an extremely narrow pedicle case. No neurologic sequelae or vertebral artery injury were detected. The RP technique is effective and reliable in achieving an accurate and safe screw insertion during IAD surgery, especially in anatomically abnormal cases.

Application of reverse axis pedicle screws in the transoral anterior reduction to treat atlas-axis dislocation

Objective To investigate the clinical value of reverse axis pedicle screws in the transoral anterior reduction to treat atlas-axis dislocation.Methods From March 2009 to October 2011,25 patients with atlas-axis dislocation were treated in our department.They were 11 men and 14 women,17 to 65 years of age(mean,39 years).There were 17 traumatic atlas-axis dislocations and 8 atlantoaxial dislocations associated with ossification dens.They underwent transoral release,reduction and instrumentation with transoral atlantoaxial reduction plate (TARP).The atlas was fixated with lateral mass screws and the axis with reverse pedicle screws.After operation,all patients got CT scanning to evaluate screw path,outside tilt angle,downside angle and length of pedicle screw.The Japanese Orthopaedic Association (JOA) scoring system was used for evaluation of spinal function improvement.The atlantodens intervals (ADI) were measured pre-and post-operation to evaluate improvement of dislocation.Results Altogether 50 reverse axis pedicle screws were implanted in the 25 patients.The mean operation time ranged from 125 to 155 minutes and the mean blood loss was 94 mL.CT scan showed 47 screws were in a good trajectory in the axis pedicle.One screw violated into the spinal canal without nerve symptoms due to a too small outside tilt,and 2 screws violated into the vertebral artery foramen which gave rise to occlusion of the cerebellum in one patient who died in the end.The outside tilt angles averaged 20°,the downside angles 15° and the screw lengths 28 mm.The JOA scores increased significantly from 8.9 ± 1.7 pre-operation to 15.7 ± 1.1 (P ＜ 0.05) 3 months after operation.The ADI improved significantly from 8.7 ± 1.5 mm pre-operation to 0.8 ± 0.9 mm post-operation (t =2.937,P ＜ 0.05).Conclusions It is feasible to implant a reverse axis pedicle screw via the transoral approach,but this new technique has a potential risk that should be guarded against so that it should be used carefully in qualified hospitals. Key words: Atlas; Axis; Joint instability; Bone nail

New Clinical Classification System for Atlantoaxial Dislocation

The purpose of this study was to define a new clinical classification of atlantoaxial dislocation based on its clinical manifestations, namely reducible atlantoaxial dislocation (RAAD), irreducible atlantoaxial dislocation (IAAD), and fixed atlantoaxial dislocation (FAAD). A total of 107 patients with atlantoaxial dislocation were respectively treated based on this clinical classification, including 66 patients with RAAD, 39 patients with IAAD, and 2 patients with FAAD. Six of the 66 patients with RAAD with rotatory atlantoaxial dislocation were treated with traction and a cervical collar, 9 with fresh type II dens fracture were treated with cannulated screw fixation, and 51 were treated with posterior atlantoaxial or occipitocervical arthrodesis. Thirty-eight patients with IAAD received a transoral atlantoaxial reduction plate system, and 1 with a giant cell tumor was treated with lesion resection and vertebral reconstruction by a shaped titanium mesh system followed by posterior occipitocervical screw-rod fixation. The 2 patients with FAAD underwent anterior decompression and received a transoral atlantoaxial reduction plate system. Follow-up data were obtained for a minimum of 6 months. All patients' neurological symptoms improved postoperatively. Bony union was accomplished by 3-month follow-up. Donor-site infection was found in 1 patient, with no occurrence of other complications. This article proposes a new classification of atlantoaxial dislocation indicating the severity and difficulty in reduction of the atlantoaxial joint. The classification system assists with decision making regarding therapeutic options. Transoral atlantoaxial reduction plate fixation and posterior atlantoaxial screw-rod fixation are commonly performed for atlantoaxial dislocation.