Posterior Atlantoaxial Fixation Research Articles

Evaluation of Different Techniques in the Management of Craniocervical Instability

Objectives: Evaluation of clinical picture and results of occipitocervical and atlanto-axial fusion with craniocervical instabilities Patients and Method: The investigation included 22 patients, 14 males (63.6%) and 8 females (36.4%). Ages ranged (10 to 70) years. Instability resulted fromfracture of the odontoid process in 8 cases(36.4%), transverse atlantal ligament injury with C1 C2 sub laxation in 6 cases(27.3%), osodontodium in 4 cases(18.2%), Morquio’s syndrome in 2 cases(9%) , C2 Hangman’s fracture type III one case(4.5%), and transverse atlantal ligament injury associated with sub axial sublaxation in one case(4.5%). Trauma was the most common cause of instability (73%).Single hollow titanium anterior odontoid screw was done in 4 cases (18,2%), posterior atlanto-axial fixation in 12 patients(54.5%) three of them (25%) needed trans oral odontoidectomy prior to fixation, fixation was performed from C1to C4 in one patient(4.5%) , and occipitocervical fixation in 5 patients(22.7%). Postoperative Philadelphia neck collar was applied for 8-12 weeks. Results: Postoperative clinical evaluation revealed good outcome of neurological ASIA grading. 10 patients improved (45.5%), while 11 patients (50%) remained at the same ASIA score as pre-operative, and only one patient (4.5%) deteriorated from ASIA score D to A. Pain and neck disability scores reduced postoperatively compared to preoperative. Fusion was achieved in 18 cases (81.8%) at last follow-up. Instrumentation failure occurred in only 2 cases (9%). Three mortality cases due to respiratory problems (2cases died in the first week after surgery and the third case died one month after the surgery).

Application of electric drill drive technique in atlantoaxial posterior screw trajectory preparation

Objective To investigate the application effect of electric drill drive in the preparation of atlanto-axial posterior screw trajectory. Methods A retrospective case-control study was conducted to analyze the clinical data of 29 patients with atlanto-axial fracture and dislocation admitted to the Lanzhou University Second Hospital from February 2016 to March 2019. There were 19 male and 10 females, aged from 10 to 72 years, with an average of 44.6 years. All patients received posterior atlantoaxial screw fixation. Electric drill drive was adopted in 14 patients to prepare the screw trajectory (electric drill group), and bare hand technique was used in 15 patients (bare hand group). In the electric drill group, 28 atlantal lateral screws and 28 axial pedicle screws were implanted; in the free hand group, 30 atlantal lateral screws and 30 axial pedicle screws were implanted. The trajectory preparation time and intraoperative blood loss between the two groups were compared. After the operation, the X-ray films and 3D CT were taken to observe the lateral mass of atlas as well as the position, loosening or rupture, and bone healing of axial pedicle screws, and complications. Frankel grading and visual analogue scale (VAS) at the last follow-up were compared between the two groups. Results All patients were followed up for 3 to 36 months, with an average of 21 months. The electric drill group took significantly shorter time in preparing both atlantal and axial pedicle screw trajectories than the bare hand group [(8.8±4.2)minutes ∶(16.5±9.7)minutes; (4.1±1.2)minutes∶ (6.1±3.2)minutes] (P 0.05). In the electric drill group, the penetration rate of atlantal screws was 0, the complete position rate was 96% (27/28), and the good rate of screw placement was 100% (28/28), superior to 23% (7/30), 73% (22/30) and 73%(22/30) in the bare hand group (P 0.05). There were no complications such as cerebrospinal fluid leakage, spinal cord injury, cerebellar infarction, loosening and fracture of internal fixation, and nonunion of bone. At the last follow-up, Frankel grading and VAS of the two groups were improved to different degrees (P 0.05). Conclusion For atlantoaxial fracture and dislocation, preparation of atlantoaxial internal fixation screw trajectories by electric power can significantly shorten the operation time and improve the accuracy of atlas screw placement. Key words: Atlanto-axial joint; Fracture fixation, internal; Electric drill

Efficacy comparison of posterior atlantoaxial screw-rod fixation combined with spinous process muscle-vessel complex bone graft or iliac bone graft for atlantoaxial instability

Objective To compare the clinical efficacy of posterior atlantoaxial screw-rod fixation combined with spinous process muscle-vessel complex bone graft or iliac bone graft for atlantoaxial instability. Methods A retrospective case-control study was conducted to analyze the clinical data of 56 patients with atlantoaxial instability admitted to the Sixth Hospital of Ningbo from September 2014 to October 2016. There were 35 males and 21 females, with the age range from 9 to 59 years [(50.3±3.2)years]. A total of 26 patients were treated with posterior atlantoaxial screw-rod fixation combined with spinous process muscle-vessel complex bone graft (complex group), while 30 patients were treated with iliac bone graft (ilium group). Patients showed different degrees of neck pain and limited neck activity preoperatively. X-ray films and three-dimensional CT examination of the cervical spine were taken before and after operation for evaluating the atlantoaxial reduction, bone graft fusion and internal fixation. The operation time, intraoperative bleeding, bone fusion time, visual analogue scale (VAS), Japanese Orthopaedic Association (JOA) score, atlantodental interval (ADI) and axial symptoms were compared between the two groups, and the complications were recorded. Results Both groups were followed up for 24-30 months, with an average of 27.4 months. In the complex group and the ilium group, the operation time was (2.21±0.25)hours and (2.72±0.26)hours (P 0.05), respectively. In the complex group, the VAS was (5.45±0.69)points before operation, (2.64±0.51)points at the follow-up one month after operation, (0.91±0.7)points at the follow-up 12 months after operation, and (0.45±0.16)points at the follow-up 24 months after operation; and in the ilium group, the VAS was (5.18±0.75)points, (2.45±0.52)points, (1.27±0.19)points and (0.41±0.18)points correspondingly. In terms of VAS, there were significant differences before and after operation within each group (P 0.05). In the complex group, the JOA score was (10.82±0.35)points before operation, (12.73±0.65)points at the follow-up one month after operation, (15.18±0.61)points at the follow-up 12 months after operation, and (15.64±0.15)points at the follow-up 24 months after operation; and in the ilium group, the JOA score was (10.73±1.19)points, (13.01±0.63)points, (14.73±0.91)points and (15.55±0.51)points correspondingly. In terms of JOA score, there were significant differences between before and after operation within each group (P 0.05). In the complex group, the ADI was (2.28±0.59)mm before operation, (1.83±0.56)mm at the follow-up one month after operation, (1.71±0.56)mm at the follow-up 12 months after operation, and (1.59±0.67)mm at the follow-up 24 months after operation; and in the ilium group, the ADI was (2.23±0.60)mm, (1.80±0.18)mm, (1.67±0.69)mm and (1.62±0.53)mm correspondingly. In terms of ADI, there were significant differences between before and after operation within each group (P 0.05). The axial symptom scores were graded as excellent in 23 patients and good in three patients of the complex group while excellent in 21 patients and good in nine patients in the ilium group (P>0.05). There were no patients with spinal nerve injury caused by pedicle screw placement after operation. One patient in the ilium group had incision errhysis and recovered after dressing change, and other patients had no incision infection. Conclusions For atlantoaxial instability, posterior atlantoaxial screw-rod fixation combined with spinous process muscle-vessel complex bone graft or autogenous iliac bone graft can both achieve satisfactory clinical results. The spinous process-muscle-vascellum complex graft has less operation time and intraoperative bleeding than the autogenous iliac bone graft, which can be a feasible alternative operation. Key words: Spinal fractures; Bone transplantation; Fracture fixation, internal

267. One stage atlantoaxial pedicle screw fixation for unstable atlas burst fracture

BACKGROUND CONTEXT Treatment of unstable atlas fracture is controversial. Some studies showed external fixation could achieve good clinical effect. Some showed internal fixation could get initial stability and perfect reduction. PURPOSE To assess the clinical results of one stage the posterior atlantoaxial pedicle screw fixation and fusion for unstable atlas burst fracture combined with atlantoaxial instability. STUDY DESIGN/SETTING A retrospective study. PATIENT SAMPLE Twenty-eight (9 females, 19 males) patients with an average age of 41.8 (22-59) years between May 2016 and December 2018 were studied. OUTCOME MEASURES The preoperative atlanto-dens interval (ADI) and lateral mass distance (LMD) were measured. All patients were assessed clinically for neurologic recovery, atlantoaxial reduction and bone graft fusion. METHODS Twenty-eight (9 females, 19 males) patients with an average age of 41.8 (range, 22-59) years between May 2010 and December2012 were studied. The patients had various degrees of occipital neck pain, limited mobility and associated with neurological dysfunction. Degree C in 1 case and degree D in 5 cases were assessed by the ASIA impairment scale. The preoperative atlanto-dens interval (ADI) and lateral mass distance (LMD) were measured. Patients were treated with posterior atlantoaxial pedicle screw fixation and fusion. All patients were assessed clinically for neurologic recovery, atlantoaxial reduction and bone graft fusion. RESULTS All 28 patients were followed up for an average of 15.6 months (range, 10-24 months). No intraoperative vertebral artery injury and spinal cord injury were noted. Postoperative cervical spine x-ray and CT showed that the sagittal cervical spine alignment was restored and no spinal cord compression was found. At last follow-up, solid bony fusion was achieved in all patients with no loosening, displacement, instability or breakage of the screws. All patients except 1 were substantially improved neurological status. At last follow-up the ADI and LMD were statistically significant difference between pre- and postoperation. CONCLUSIONS The posterior atlantoaxial pedicle screw instead of occipitocervical fusion for unstable atlas burst fracture combined with atlantoaxial instability seems to be effective, but it is technically demanding to place screw into the lateral mass of the atlas. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

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.

Surgical Treatment of Traumatic Type II Odontoid Fracture Using Polyaxial C1 Lateral Mass and C2 Pedicle Screws Fixation

Background Data: Posterior atlantoaxial fixation is indicated for C1-C2 instability or painful osteoarthritis. Different techniques were designed for atlantoaxial fixation as sublaminar wiring, transarticular screw fixation, and, recently, C1 lateral mass and C2 pedicle polyaxial screws and rod system. Purpose: To investigate the safety, advantages, and complications of posterior atlantoaxial fixation with polyaxial C1 lateral mass and C2 pedicle screws in C1-C2 instability. Study Design: A retrospective clinical case series. Patients and Methods: Fourteen consecutive patients, ten males and four females, with a mean age of 40.8±9.6 years were reported. All had traumatic C1-2 instability due to type II odontoid fractures and underwent posterior fixation with polyaxial C1 lateral mass and C2 pedicle screws. Nine patients suffered from motor vehicle accident (MVA) and 5 suffered from falls. All patients were neurologically intact except four patients who had neurological deficits. We used Japanese Orthopedic Association Score (JOA) for their functional evaluation. The average follow-up was 17±1.96 (range, 12–20 months). Operative time, operative blood loss, screw trajectory, screw length, and injury of neurovascular structures were reported. Fusion and construct stability were evaluated by plain radiography and/or CT. Visual Analogue Scale (VAS) of neck pain and JOA were used to evaluate the functional outcome. Results: The mean duration of surgery was 175.3±12.3 min. The mean blood loss was 553.6±106.5 ml and two patients required transfusion of one unit of blood. The mean length of C1 lateral mass and C2 pedicle screws were 30±1.6 mm and 16.4±1.8 mm, respectively. Correct screw placement and good stability were reported in all patients (100%) at the last follow-up. Mean neck pain on VAS was 2.8±0.8 and 2.3±0.5 at 6 and 12 months, respectively. The complications included moderate pain at iliac graft site for 3 months in 2 patients, pain and dysesthesia in C2 dermatome for 4 months in 3 patients, and superficial wound infection in 2 patients. Conclusion: Posterior atlantoaxial fixation with polyaxial C1 lateral mass and C2 pedicle screws is a safe and effective method in the treatment of traumatic atlantoaxial subluxation due to type II odontoid fractures. (2019ESJ176)

The Healing Rate of Type II Odontoid Fractures Treated With Posterior Atlantoaxial Screw-rod Fixation: A Retrospective Review of 77 Patients.

In theory, temporary posterior atlantoaxial screw-rod fixation for type II odontoid fractures is a way to preserve rotatory motion. However, the healing rate of type II odontoid fractures treated in this way is unknown; that is, the risk associated with conducting a temporary screw-rod fixation for type II odontoid fractures is unknown. This study investigates the healing rate of type II odontoid fractures treated with posterior atlantoaxial screw-rod fixation by CT imaging and evaluates the feasibility of conducting a temporary screw-rod fixation for type II odontoid fractures. Patients with type II odontoid fracture who underwent posterior atlantoaxial screw-rod fixation in our spine center from January 2011 to December 2014 were identified. Patients older than 65 years or younger than 18 years were excluded. Those who were confirmed to have healing odontoid fractures on CT imaging were included. Those in whom fracture healing was not confirmed were asked to undergo a CT examination. Fracture healing was confirmed on the basis of the presence of bridging bone across the odontoid fracture site on CT imaging. Seventy-seven patients (56 men and 21 women) were included in the study. The average age of the patients was 40.7 ± 11.6 years (range, 18 to 64 years). The mean duration of follow-up was 26.4 ± 4.6 months (range, 24 to 40 months). Fracture healing was observed in 73 patients (94.8%). The healing rate of type II odontoid fractures (with an age range of 18 to 64 years) treated with modern posterior atlantoaxial fixation is relatively high. For patients at that age range, posterior atlantoaxial temporary screw-rod fixation for type II odontoid fractures can be conducted with a low risk of nonunion. Level IV, therapeutic.

Differences in fixation strength among constructs of atlantoaxial fixation.

OBJECTIVETo avoid jeopardizing an aberrant vertebral artery, there are three common options in placing a C2 screw, including pedicle, pars, and translaminar screws. Although biomechanical studies have demonstrated similar strength among these C2 screws in vitro, there are limited clinical data to address their differences in vivo. When different screws were placed in each side, few reports have compared the outcomes. The present study aimed to evaluate these multiple combinations of C2 screws.METHODSConsecutive adult patients who underwent posterior atlantoaxial (AA) fixation were retrospectively reviewed. Every patient uniformly had bilateral C1 lateral mass screws in conjunction with 2 C2 screws (1 C2 screw on each side chosen among the three options: pedicle, pars, or translaminar screws, based on individualized anatomical consideration). These patients were then grouped according to the different combinations of C2 screws for comparison of the outcomes.RESULTSA total of 63 patients were analyzed, with a mean follow-up of 34.3 months. There were five kinds of construct combinations of the C2 screws: 2 pedicle screws (the Ped-Ped group, n = 24), 2 translaminar screws (the La-La group, n = 7), 2 pars screws (the Pars-Pars group, n = 6), 1 pedicle and 1 pars screw (the Ped-Pars group, n = 7), and 1 pedicle and 1 translaminar screw (the Ped-La group, n = 19). The rate of successful fixation in each of the groups was 100%, 57.1%, 100%, 100%, and 78.9% (Ped-Ped, La-La, Par-Par, Ped-Par, and Ped-La, respectively). The patients who had no translaminar screw had a higher rate of success than those who had 1 or 2 translaminar screws (100% vs 73.1%, p = 0.0009). Among the 5 kinds of construct combinations, 2 C2 pedicle screws (the Ped-Ped group) had higher rates of success than 1 C2 pedicle and 1 C2 translaminar screw (the Ped-La group, p = 0.018). Overall, the rate of successful fixation was 87.3% (55/63). There were 7 patients (4 in the Ped-La group and 3 in the La-La group) who lost fixation/reduction, and they all had at least 1 translaminar screw.CONCLUSIONSIn AA fixation, C2 pedicle or pars screws or a combination of both provided very high success rates. Involvement of 1 or 2 C2 translaminar screws in the construct significantly lowered success rates. Therefore, a C2 pars screw is recommended over a translaminar screw.

Clinical Application and Efficacy Analysis of 3D Navigation Module in the Treatment of Atlantoaxial Instability

Background: Posterior cervical atlantoaxial pedicle screw fixation is a very effective treatment for atlantoaxial instability (AAI). However, due to the complex anatomy of the cranial-cervical junction, the accuracy and safety of posterior atlantoaxial pedicle screw placement remains extremely challenging. Objective: To quantitatively evaluate the safety and accuracy of the 3D navigation module to assist the posterior atlantoaxial fixation. Methods: A total of 20 AAI patients were selected between June 2014 and September 2015. The Mimics v10.1 and 3-matic software were used. The 3D navigation module was designed as a double-sided positioning hole guide with a guide rod. All patients underwent posterior atlantoaxial posterior pedicle screw fixation with 3D navigation module. The actual entry point and screw trajectory were measured after operation, which were compared with the ideal entry point and screw trajectory. The Japanese Orthopaedic Association (JOA) score was measured before and after surgery to evaluate the neurological function improvement. The average operation time, blood loss, and frequency of intraoperative fluoroscopy were counted. Results: The posterior atlantoaxial pedicle screw fixation with a 3D navigation module was successfully performed in all patients. A total of 80 atlantoaxial pedicle screws were implanted in the 20 patients. Postoperative CT scan showed that two pedicle screws deviated from the medial aspect of the atlas pedicle cortex and entered the spinal canal approximately 1 mm, without causing neurological complications. There was no significant difference between the ideal and actual entry points or ideal and actual screw trajectories of the atlas and axis (P > 0.05). The preoperative JOA score was 12.45 ± 1.15 and postoperative JOA score was 15.5 ± 0.89, with statistically significant difference (P < 0.05). Conclusion: It was safe and effective to use the 3D navigation module to assist the posterior atlantoaxial pedicle insertion, with a high accuracy of pedicle screw placement. Keywords: atlantoaxial instability, pedicle screw, 3D navigation module, rapid prototyping

Clinical and radiological outcomes of image guided posterior C1-C2 fixation for atlantoaxial osteoarthritis (AAOA).

Atlantoaxial (C1-C2) osteoarthritis (AAOA) causes severe suboccipital pain exacerbated by lateral rotation. The pain is usually progressive and resistant to conservative therapy. Posterior fusion surgery is performed to stabilise the C1-C2 segment. This is the first Australian study reporting the outcome of posterior atlantoaxial fixation including hybrid fixations performed for AAOA. All patients who underwent posterior atlantoaxial fixation surgery for AAOA from 2005 to 2015 at our institutions were enrolled (N=23). Patient demographics and surgical technique were recorded. These techniques included transarticular screw (TAS) fixation using image guidance with iliac crest bone graft and supplemental posterior Sonntag wiring, or C1-C2 lateral mass fixation (Harms technique). Some patients required a combination of fixation due to anatomical variation. Primary outcome measures including patient satisfaction, pain, disability scores and range of motion were recorded for all patients pre- and post-operatively. Post-operative assessment was supplemented with CT and X-ray imaging. Twenty-three patients (19 women, 4 males, mean age 71.8±6.3 years) underwent surgical fixation. Eight underwent TAS fixation, 8 had Harms fixation, and 7 had a hybrid fixation. All patients reported statistically significant improvement in pain scores [Visual Analogue Scale (VAS) 9.4 pre-op compared to 2.9 post-op, P<0.005]. Disability scores [Neck Disability Index (NDI)] were statistically significantly reduced from 72.2±12.9 pre-operatively to 18.9±11.9 post-operatively, P<0.005. Mean follow-up was 55.3±36.1 months. Results did not vary according to the construct type. Ninety-five point five percent of patients showed radiographic evidence of fusion. Ninety-one percent of patients said they would undergo the surgery again. Posterior atlantoaxial fixation with TAS and Harms constructs are highly effective for the surgical treatment of intractable neck pain secondary to atlantoaxial lateral mass osteoarthritis (AAOA). Surgery offers a high rate of symptom relief. If anatomical variability exists, both transarticular and pedicle screw fixation could be safely used in the same patient.

Dysphagia following C1 laminectomy and posterior atlantoaxial fixation for retro-odontoid pseudotumor: a case report

Purpose: Although dysphagia is known potential complication of cervical spine surgery, it rarely occurs after a posterior approach. We describe an unusual case of a retro-odontoid pseudotumor that suffered dysphagia following a C1 laminectomy and posterior atlantoaxial fixation.Materials and methods: A 79-year-old man presented with progressive tetraparesis and bladder and bowel dysfunction due to severe compression to cervical cord at C1 from a retro-odontoid pseudotumor. After C1 laminectomy and atlantoaxial fixation, the symptoms improved, but dysphagia and aspiration developed, associated with pharyngeal and esophageal stases on videofluoroscopy.Results and conclusions: Possible explanations for postoperative dysphagia include limitation of cervical spine motion, and cervical cord reperfusion injury in addition to the baseline anterior osteophyte and aging. This is the first case of dysphagia developing after laminectomy and posterior atlantoaxial fixation not involving the occipital bone.

Posterior C2 Fixation Using Trans-C2 Inferior Articular Process Screws: A Case Series and Technical Note

Upper cervical fixation with C2 pedicle screw insertion may predispose patients to vertebral artery injury, in particular, patients with craniovertebral junction anomalies. The aim of this study was to describe an alternative technique with trans-C2 inferior articular process screw (C2IAPS) insertion for rigid C2 fixation, which can be used to anchor the C2 vertebra for upper cervical fixation. Records of 19 patients who underwent posterior atlantoaxial fixation using C2IAPS combined with C1 lateral mass screw were retrospectively reviewed. Efficacy was assessed by postoperative imaging and Japanese Orthopaedic Association scores. There were 22 C2IAPSs successfully implanted (3 on both sides and 16 on 1 side). With the exception of 2 screws that had intruded into the outlet of the intervertebral foramen, all screws were safely implanted. Average Japanese Orthopaedic Association scores improved from 11.8 ± 1.9 preoperatively to 15.3 ± 1.3 postoperatively. Bony fusion rate was 100%. For patients who are not eligible for C2 pedicle screw fixation, C2IAPS fixation can be considered as an alternative technique for upper cervical fixation of C2.

C1 Titanium Cables Combined with C2 Pedicle Screw-Rod Fixation for Atlantoaxial Instability Not Suitable for Placement of C1 Screws

We sought to develop a new posterior fusion technique composed of bilateral C1 titanium cables and C2 pedicle screw-rods for treatment of atlantoaxial instability not suitable for C1 screw placement. A study was conducted of 18 patients with atlantoaxial instability who had C1 broken screw trajectory or anatomic anomalies. All patients underwent posterior fixation with bilateral C1 titanium cables and C2 pedicle screws. The follow-up period was a minimum 1 year. Clinical outcomes measurements included visual analog scale score for neck pain assessment, the American Spinal Injury Association Impairment Scale and Japanese Orthopaedic Association score for neurologic status and function. According to preoperative computed tomography (CT) reconstruction and CT angiography, the patients selected in this study were not suitable for C1 screw placement. Postoperative plain radiographs and CT reconstruction were performed to evaluate the reduction, bony fusion, and implant position. All outcomes were evaluated at each follow-up. The average clinical follow-up period was 24 months (range 12-36 months). All patients had complete neck pain relief at postoperative 6 months. Their neurologic symptoms had improved significantly at 1-year follow-up. Radiologic outcomes indicated good bony fusion and construction stability in all patients without implant failure at the last follow-up. No neural or vascular complications related to this technique were observed. Posterior atlantoaxial fixation using C1 titanium cables and C2 pedicle screw-rod construct appears to be an effective and safe technique for treatment of atlantoaxial instability, which could be an alternative method for cases unsuitable for C1 screw placement when using C1-C2 screw fixation.

Designing patient-specific 3D printed devices for posterior atlantoaxial transarticular fixation surgery

Atlantoaxial transarticular screw fixation is an effective technique for arthrodesis. Surgical accuracy is critical due to the unique anatomy of the atlantoaxial region. Intraoperative aids such as computer-assisted navigation and drilling templates offer trajectory guidance but do not eliminate screw malposition. This study reports the operative and clinical performance of a novel process utilising biomodelling and 3D printing to develop patient specific solutions for posterior transarticular atlantoaxial fixation surgery. Software models and 3D printed 1:1 scale biomodels of the patient's bony atlantoaxial spine were developed from computed tomography data for surgical planning. The surgeon collaborated with a local medical device manufacturer using AnatomicsC3D to design patient specific titanium posterior atlantoaxial fixation implants using transarticular and posterior C1 arch screws. Software enabled the surgeon to specify screw trajectories, screw sizes, and simulate corrected atlantoaxial alignment allowing patient specific stereotactic drill guides and titanium posterior fixation implants to be manufactured using 3D printing. Three female patients with unilateral atlantoaxial osteoarthritis were treated using patient specific implants. Transarticular screws were placed using a percutaneous technique with fluoroscopy and neural monitoring. No screw malposition and no neural or vascular injuries were observed. Average operating and fluoroscopy times were 126.0 ± 4.1 min and 36.7 ± 11.5 s respectively. Blood loss was <50 ml per patient and length of stay was 4–6 days. Clinical and radiographic follow up data indicate satisfactory outcomes in all patients. This study demonstrates a safe, accurate, efficient, and relatively inexpensive process to stabilise the atlantoaxial spine using transarticular screws.

Atlantoaxial Fixation for Odontoid Fracture: Analysis of 124 Surgically Treated Cases.

The authors analyze 124 cases with fracture of odontoid process. All patients were surgically treated by posterior atlantoaxial fixation. There were 96 male and 28 female patients. The ages of the patients ranged from 12 to 80 years. Apart from Anderson and D'Alonzo type I (6 cases), type II (93 cases) and type III (25 cases), three sub-types of odontoid fractures were included in the classification. In type A (118 cases), there was vertical compression fracture that resulted in malalignment of the fractured odontoid process segments. Type B (49 cases) resulted when the fracture resulted in malalignment of the facets of atlas and axis. Type C (25 cases) included cases in which the fracture line involved the facet of axis. Fractures were divided into acute type when the injury was less than 3 months old (50 cases), delayed type when the injury was between 3 months to one year (34 cases) and chronic type when the injury was more than 1 year in duration (40 cases). All patients were treated with posterior atlantoaxial fixation with the techniques described in 1994 and 2004. Follow-up period ranged from 6 to 156 months (average 72 months). All patients improved in symptoms after surgery. There were no significant postoperative complications. Posterior atlantoaxial stabilization forms a safe surgical strategy for all kinds of odontoid fractures. Additional characteristics of odontoid fractures further subclassified them and assisted in surgical decision-making and in formulating the surgical strategy.

Postoperative Regression of Retro-odontoid Pseudotumor After Atlantoaxial Posterior Fixation: 11 Years of Experience in Patients With Atlantoaxial Instability.

Case series study. The aim was to investigate the incidence of retro-odontoid pseudotumor in patients with atlantoaxial instability (AAI) and evaluate pseudotumor regression after posterior fixation. The incidence of retro-odontoid pseudotumor in atlantoaxial instability patients remains uncertain. Moreover, the regression of retro-odontoid pseudotumor after posterior fixation in patients with various underlying diseases needs to be further investigated. From July 2004 to August 2015, 175 patients with AAI underwent posterior fixation operations at our institution. After excluding 11 patients (previous operation, n = 4; history of tumor, n = 7), the final study population comprised 164 patients. The final study population was categorized according to their underlying diseases (rheumatoid arthritis [RA], os odontoideum, atlanto-occipital assimilation, dens fracture, AAI of unknown cause, etc.) and age (adult and pediatric groups). The incidence of retro-odontoid pseudotumor in each group was analyzed. Pre- and postoperative magnetic resonance or computed tomography images were reviewed to assess its regression following surgery. Of the 164 patients included, 38 had retro-odontoid pseudotumor (23.2%). Three were diagnosed with RA and the rest were non-RA patients including os odontoideum (n = 12), dens fracture (n = 6), atlanto-occipital assimilation (n = 4), Morquio syndrome (n = 1), and AAI of unknown cause (n = 12). Pseudotumor size regressed in all 38 patients after atlantoaxial posterior fixation. There was a statistically significant decrease in pseudotumor size (the length between the anterior border of the odontoid process to the posterior border of the pseudotumor) from a mean length of 17.7 to 14.9 mm (P < 0.001). The patients had various underlying diseases and the overall incidence of retro-odontoid pseudotumor in patients with symptomatic AAI was 23.2% at our institution during the past 11 years. All patients who underwent posterior fixation for AAI showed a statistically significant decrease in pseudotumor size. 4.

Three-dimensional finite element analysis of biomechanical properties of a posterior atlanto-axial dynamic fixation system

Objective To evaluate the biomechanical features of a posterior atlanto-axial dynamic fixation system by finite element method. Methods A 25-age-year old healthy male volunteer underwent computed tomography (CT) scan at C0-C2 (slice width=1 mm). Three-dimensional finite element model of atlanto-axial was established by Mimics, Freeform and Ansys. Then, three-dimensional finite element model of atlanto-axial traditional fixtion and dynamic fixation were established. The range of motion (ROM) and load transfer under different direction were evaluated biomechanically in flexion-extension lateral bending and axial rotation load. Results The ROM in flexion-extension lateral bending and axial rotation of dynamic fixation were 8.9°, 8.2°, 2.8° and 10.4°, respectively, was better than traditional fixation in all direction, the ROM increased 21.9%, 10.8%, 12.0% and 126.9%, respectively. Stress in flexion-extension lateral bending and axial rotation of dynamic fixation were 1 410, 1 410, 1 410 and 1 520 mPa, respectively, were average three times bigger than traditional fixation and found concentrating around the bottom of atlanto, axial screws. Stress of vertebral in flexion-extension was bigger than traditional fixation. Stress of rod was bigger in traditional fixation. Conclusion Anterior transarticular screws show excellent biomechanical, meanwhile, maintain the atlanto-axial range of motion. Stress was found concentrating around the bottom of atlanto, axial screws, which predispose the instrument at failure. Key words: Atlanto-axial; Dynamic fixation system; Biomechanics; Finite element analysis

Treatment of odontoid fracture combined with lower cervical spinal cord injuries without fracture or dislocation

To discuss the clinical characteristics, mechanism, and treatment of odontoid fracture combined with lower cervical spinal cord injuries without fracture or dislocation. According to the inclusion and exclusion criteria, 7 male patients aged 37-71 years (mean, 51.4 years), suffered from odontoid fractures combined with lower cervical spinal cord injuries without fracture or dislocation were analyzed retrospectively between June 2007 and October 2015. The trauma causes were traffic accidents in 2 cases, fall in 2 cases, and hit injury in 3 cases. The time from injury to admission was 2 hours to 3 days with an average of 9 hours. According to Anderson-Grauer classification of odontoid fracture, 1 case of type IIA, 3 cases of type IIB, 2 cases of type IIC, and 1 case of shallow type III were found. The cervical spinal cord injuries affected segments included C 4, 5 in 1 case, C 4-6 in 2 cases, and C 5-7 in 4 cases. All the cervical spine had different degenerative changes: 2 of mild, 3 of moderate, and 2 of severe. The lower cervical spinal cord injury was assessed by Sub-axial Injury Classification (SLIC) with scoring of 4-6 (mean, 5.1). The visual analogue scale (VAS) score was used to evaluate the occipital neck pain with scoring of 7.8±1.0; the neurological function was assessed by American Spinal Injury Association (ASIA) as grade B in 1 case, grade C in 4 cases, and grade D in 2 cases; and Japanese Orthopedic Association score (JOA) was 9.2±3.9. For the odontoid fractures, 4 cases were fixed with anterior screw while the others were fixed with posterior atlantoaxial fixation and fusion. For the lower cervical spine, 4 cases were carried out with anterior cervical corpectomy and titanium fusion while the others with anterior cervical disecotomy and Cage fusion. The operation time was 178-252 minutes (mean, 210.2 minutes); the intraoperative blood loss was 60-140 mL (mean, 96.5 mL) and with no blood transfusion. All incisions healed primarily. All the patients were followed up 12-66 months (mean, 18 months). There was no direct surgical related complications during operation, and all bone grafting got a fusion at 6-9 months (mean, 7.7 months) after operation. There was no inter-fixation failure or loosening. At last follow-up, the VAS score declined to 1.7±0.7 and JOA score improved to 15.1±1.7, showing significant differences when compared with preoperative ones ( t=18.064, P=0.000; t=-7.066, P=0.000). The neurological function of ASIA grade were also improved to grade D in 5 cases and grade E in 2 cases, showing significant difference ( Z=-2.530, P=0.011). Complex forces and degeneration of lower cervical spine were main reasons of odontoid fracture combined with lower cervical spinal cord injuries without fracture or dislocation. The type of odontoid fracture and neurological deficit status of lower cervical spinal cord were important to guide making strategy of one-stage operation with a satisfactory clinic outcome.

Outcome of Bilateral C1 Laminar Hooks Combined With C2 Pedicle Screw Fixation for the Treatment of C1-C2 Instability: A Report of 18 Cases From a Single Chinese Center.

A retrospective technical report. To assess the effect of bilateral C1 laminar hooks combined with C2 pedicle screw fixation for the treatment of C1-C2 instability. Various posterior atlantoaxial fixations for C1-C2 instability have been developed. However, due to anatomic anomalies of the vertebral artery, the smallness of the pedicle, trajectories of broken screws, or a lack of surgical experience, a simple atlantoaxial fixation technique with good safety and effectiveness is urgently needed. From January 2007 to September 2012, 18 patients with C1-C2 instability who underwent posterior bilateral C1 laminar hooks combined with C2 pedicle screw fixation were evaluated. Six patients had acute odontoid fractures (Anderson IIc type), 8 patients had odontoid pseudarthrosis, 3 had os odontoideum, and 1 had a traumatic rupture of the transverse ligament. The mean age at the time of surgery was 34.1 years. The clinical and radiographic analyses were performed before and after the operation and at follow-up. The follow-up period was 12-78 months (with an average follow-up period of 25.6 mo). All patients were relieved of pain and their neurological symptoms were substantially improved. The postoperative JOA score improved significantly (t=-7.234, P<0.001). No neurological or vascular complications occurred in these cases. The device was placed well and had not loosened or broken and plain radiographs revealed bony fusion in 17 patients. One patient had C1 posterior arch fracture 3 weeks postoperatively and she was followed up for 18 months without revision surgery. When appropriate patients were selected, bilateral C1 laminar hooks combined with C2 pedicle screw fixation can be an alternative method to treat C1-C2 instability effectively with a relatively simple procedure. Preoperative planning and evaluation were crucial for the solid atlantoaxial fusion.

Comparison of outcomes after atlantoaxial fusion with C1 lateral mass-C2 pedicle screws and C1-C2 transarticular screws.

To compare the clinical and radiological outcomes of posterior atlantoaxial fixation and fusion using C1 lateral mass-C2 pedicle screws (screw-rod constructs, SRC) with C1-C2 transarticular screws (TAS). A retrospective review was conducted of 105 patients with atlantoaxial instability who underwent posterior C1-C2 fixation and fusion by SRC group (60 pt) and TAS group (45 pt). The follow-up period was minimum 2years. Clinical outcomes measurements included the Numeric Rating Scale (NRS) for pain assessment, the Neck Disability Index (NDI), the Japanese Orthopedic Association (JOA) score and the American Spinal Injury Association (ASIA) impairment scale for the functional and neurological outcomes that were assessed. Radiological outcomes were assessed by evaluating the fusion rate and proper screws position. Both outcomes were evaluated in the early postoperative period, 3, 6, 12 and 24months after surgery. Operative time, estimated blood loss, complications and length of stay were also reviewed. The majority of cases were caused by trauma and presented with axial neck pain. The improvement of NRS, NDI, JOA score and ASIA impairment scale were not different between the two groups. Proper screw position and fusion rate were also observed similarly between the two groups. Estimated blood loss was lesser and operative time was shorter in TAS group than SRC group (p=0.047, p=0.001, respectively). Operative complications and the length of hospital stay were also not different between the two groups. Both SRC and TAS produced excellent outcomes for atlantoaxial stabilization. But the volume of bleeding and operation time tended to be better in TAS group compared to SRC group.