Anatomic Considerations of Anterior Transarticular Screw Fixation for Atlantoaxial Instability

STUDY DESIGN: Cadaveric, observational study.PURPOSE: Atlantoaxial instability (AAI) is characterized by excessive movement at the C1–C2 junction between the atlas and axis. An anterior surgical approach to expose the upper cervical spine for internal fixation and bone grafting has been developed to fix AAI. Currently, no anatomic information exists on the anterior transarticular atlantoaxial screw or screw and plate fixation between C1 and C2 in the Indian population. The objective of this study is to assess the anatomic landmarks of C1–C2 vertebrae: entry point, trajectory, screw length, and safety of the procedure.OVERVIEW OF LITERATURE: Methods outlined by Magerl and Harms are the optimal approaches among the dorsal techniques. Contraindications for these techniques include aberrant location of vertebral arteries, fractures of C1–C2 posterior structures. In these cases, anterior transarticular fixation is an alternative. Several available screw insertion trajectories have been reported. Biomechanical studies have demonstrated that adequate rigidity of this fixation is comparable with posterior fusion techniques.METHODS: Direct measurements using Vernier calipers and a goniometer were recorded from 30 embalmed human cadavers. The primary parameters measured were the minimum and maximum lateral and posterior angulations of the screw in the sagittal and coronal planes, respectively, and optimum screw length, if it was placed accurately.RESULTS: The posterior and lateral angles of screw placement in the coronal and sagittal planes ranged from 16° to 30° (mean±standard deviation [SD], 23.93°±3.93°) and 8° to 17° (mean±SD, 13.3°±2.26°), respectively. The optimum screw length was 25–38 mm (mean±SD, 28.76±3.69 mm).CONCLUSIONS: If the screw was inserted without lateral angulation, the spinal canal or cord could be violated. If a longer screw was inserted with greater posterior angulation, the vertebral artery at the posterior or posterolateral aspect of the C1 superior facet could be violated. Thus, 26° and 30° of lateral and posterior angulations, respectively, are the maximum angles permissible to avoid injury of the vertebral artery and violations of the spinal canal or atlanto-occipital joint.

Challenges of Transarticular Screw Fixation in Young Children: Report of Surgical Treatment of a 5-Year-Old Patient's Unstable Os-Odontoideum

Surgical procedures for atlantoaxial (C1–C2) fusion in young children are relatively uncommon. The purpose of this study was to report on a surgical treatment for a case of atlantoaxial instability caused by os-odontoideum in association with quadriparesis and respiratory paralysis in a 5-year-old girl. We present the patient's history, physical examination, and radiographic findings, describe the surgical treatment and a five year follow-up, and provide a literature review. The instability was treated by halo immobilization, followed by C1–C2 transarticular screw fixation using a computed tomography-based navigation system. At the five year follow-up, the patient had made a complete recovery with solid union. The authors conclude that C1–2 transarticular screw fixation is technically possible as in a case of atlantoaxial instability in a five-year-old child.

Comparison of Outcomes after Atlantoaxial Fusion with Transarticular Screws and Screw-Rod Constructs

OBJECTIVE: The purpose of this study was to compare the radiological and neurological outcomes between two atlantoaxial fusion method for atlantoaxial stabilization; C1 lateral mass-C2 pedicle screws (screw-rod constructs, SRC) versus C1-2 transarticular screws (TAS). METHODS: Forty-one patients in whom atlantoaxial instability was treated with atlantoaxial fixation by SRC group (27 patients, from March 2005 to May 2011) or TAS group (14 patients, from May 2000 to December 2005) were retrospectively reviewed. Numeric rating scale (NRS) for pain assessment, Oswestry disability index (ODI), and Frankel grade were also checked for neurological outcome. In radiologic outcome assessment, proper screw position and fusion rate were checked. Perioperative parameters such as blood loss during operation, operation time, and radiation exposure time were also reviewed. RESULTS: The improvement of NRS and ODI were not different between both groups significantly. Good to excellent response in Frankel grade is shown similarly in both groups. Proper screw position and fusion rate were also observed similarly between two groups. Total bleeding amount during operation is lesser in SRC group than TAS group, but not significantly (p=0.06). Operation time and X-ray exposure time were shorter in SRC group than in TAS group (all p<0.001). CONCLUSION: Both TAS and SRC could be selected as safe and effective treatment options for C1-2 instability. But the perioperative result, which is technical demanding and X-ray exposure might be expected better in SRC group compared to TAS group.

Intraoperative Vertebral Artery Angiography to Guide C1-2 Transarticular Screw Fixation in a Patient with Athetoid Cerebral Palsy

We present a case of an athetoid cerebral palsy with quadriparesis caused by kyphotic deformity of the cervical spine, severe spinal stenosis at the cervicomedullary junction, and atlantoaxial instability. The patient improved after the first surgery, which included a C1 total laminectomy and C-arm guided righ side unilateral C1-2 transarticular screw fixation. C1-2 fixation was not performed on the other side because of an aberrant and dominant vertebral artery (VA). Eight months after the first operation, the patient required revision surgery for persistent neck pain and screw malposition. We used intraoperative VA angiography with simultaneous fluoroscopy for precise image guidance during bilateral C1-2 transarticular screw fixation. Intraoperative VA angiography allowed the accurate insertion of screws, and can therefore be used to avoid VA injury during C1-2 transarticular screw fixation in comorbid patients with atlantoaxial deformities.

Computer-assisted C1-C2 Transarticular Screw Fixation "Magerl Technique" for Atlantoaxial Instability

STUDY DESIGN: A retrospective study. PURPOSE: To evaluate the surgical results of computer-assisted C1-C2 transarticular screw fixation for atlantoaxial instability and the usefulness of the navigation system. OVERVIEW OF LITERATURE: We used a computed tomography (CT)-based computer navigation system in planning and screw insertion in Magerl's procedure, which provides the most rigid atlantoaxial fusion, to avoid risk of vertebral artery (VA) tear by avoiding high-riding VA during screw insertion. METHODS: Twenty patients who underwent atlantoaxial fusion under the CT-based navigation system were studied. The mean observation period was 33.5 months. The evaluated items included the existence of VA stenosis by preoperative magnetic resonance angiography, surgical time, blood loss volume, Japanese Orthopaedic Association (JOA) score and Ranawat's pain criteria before surgery and at final follow-up, postoperative screw position evaluated by CT, and bony fusion. RESULTS: The mean operation time was 205 minutes, with the mean blood loss volume of 242 ml. The mean JOA score was 11.6 points before surgery and 13.7 at final follow-up. Occipital and/or cervical pain presented before operation was remitted or resolved in all patients. Evaluation of screw insertion by CT revealed correct penetration to atlantoaxial joints, with a perforation rate of 2.6%. There was no complication, including VA tear, and all patients who were followed-up during one year or more after surgery achieved bony fusion. Some subjects who appeared inappropriate for surgery from CT images were assessed as eligible for surgery based on the evaluation results obtained using the navigation system. CONCLUSIONS: It was demonstrated that the CT-based navigation system is an effective support device for Magerl's procedure.

Unilateral Posterior Atlantoaxial Transarticular Screw Fixation in Patients with Atlantoaxial Instability : Comparison with Bilateral Method

OBJECTIVE: Bilateral C1-2 transarticular screw fixation (TAF) with interspinous wiring has been the best treatment for atlantoaxial instability (AAI). However, several factors may disturb satisfactory placement of bilateral screws. This study evaluates the usefulness of unilateral TAF when bilateral TAF is not available. METHODS: Between January 2003 and December 2007, TAF was performed in 54 patients with AAI. Preoperative studies including cervical x-ray, three dimensional computed tomogram, CT angiogram, and magnetic resonance image were checked. The atlanto-dental interval (ADI) was measured in preoperative period, immediate postoperatively, and postoperative 1, 3 and 6 months. RESULTS: Unilateral TAF was performed in 27 patients (50%). The causes of unilateral TAF were anomalous course of vertebral artery in 20 patients (74%), severe degenerative arthritis in 3 (11%), fracture of C1 in 2, hemangioblastoma in one, and screw malposition in one. The mean ADI in unilateral group was measured as 2.63 mm in immediate postoperatively, 2.61 mm in 1 month, 2.64 mm in 3 months and 2.61 mm in 6 months postoperatively. The mean ADI of bilateral group was also measured as following; 2.76 mm in immediate postoperative, 2.71 mm in 1 month, 2.73 mm in 3 months, 2.73 mm in 6 months postoperatively. Comparison of ADI measurement showed no significant difference in both groups, and moreover fusion rate was 100% in bilateral and 96.3% in unilateral group (p=0.317). CONCLUSION: Even though bilateral TAF is best option for AAI in biomechanical perspectives, unilateral screw fixation also can be a useful alternative in otherwise dangerous or infeasible cases through bilateral screw placement.

Posterior Atlantoaxial Transarticular Screw Fixation

OBJECTIVE: Posterior arthrodesis in atlantoaxial instability has been performed using various posterior C1-2 wiring techniques. Recently, transarticular screw fixation (TASF) technique was introduced to achieve significant immediate stability of the C1-2 joint complex. The purpose of this study is to assess the clinical outcomes associated with posterior C1-2 TASF for the patient of atlantoaxial instability. METHODS: We retrospectively reviewed data obtained from 17 patients who underwent C1-2 TASF and supplemented Posterior wiring technique (PWT) with graft between 1994 and 2005. There were 8 men and 9 women with a mean age of 43.5 years (range, 12-65 years). An average follow-up was 26 months (range, 15-108 months). RESULTS: Successful fusions were achieved in 16 of 17 (94%). The pain was improved markedly (3 patients) or resolved completely (14 patients). There was no case of neurological deterioration, hypoglossal nerve injury, or vertebral artery injury. Progression of spinal deformity, screw pullout or breakage, and neurological or vascular complications did not occur. CONCLUSION: The C1-2 TASF with supplemental wiring provided a high fusion rate. Our result demonstrates that C1-2 TASF supplemented by PWT is a safe and effective procedure for atlantoaxial instability. Preoperative evaluation and planning is mandatory for optimal safety.

Posterior Atlantoaxial Transarticular Screw Fixation

OBJECTIVE: Posterior arthrodesis in atlantoaxial instability has been performed using various posterior C1-2 wiring techniques. Recently, transarticular screw fixation (TASF) technique was introduced to achieve significant immediate stability of the C1-2 joint complex. The purpose of this study is to assess the clinical outcomes associated with posterior C1-2 TASF for the patient of atlantoaxial instability. METHODS: We retrospectively reviewed data obtained from 17 patients who underwent C1-2 TASF and supplemented Posterior wiring technique (PWT) with graft between 1994 and 2005. There were 8 men and 9 women with a mean age of 43.5 years (range, 12-65 years). An average follow-up was 26 months (range, 15-108 months). RESULTS: Successful fusions were achieved in 16 of 17 (94%). The pain was improved markedly (3 patients) or resolved completely (14 patients). There was no case of neurological deterioration, hypoglossal nerve injury, or vertebral artery injury. Progression of spinal deformity, screw pullout or breakage, and neurological or vascular complications did not occur. CONCLUSION: The C1-2 TASF with supplemental wiring provided a high fusion rate. Our result demonstrates that C1-2 TASF supplemented by PWT is a safe and effective procedure for atlantoaxial instability. Preoperative evaluation and planning is mandatory for optimal safety.

Anatomical measurement and clinical significance of anterior transarticular screw fixation / 中国矫形外科杂志

[Objective]To provide Chinese morphological data for anterior C1、2 transarticular screw fixation.[Method]With a digital vernier and a goniometer made in China,the anatomic parameters related to anterior C1、2 transarticular screw fixation were measured from 50 pairs of dried Chinese adult human C1 and C2 vertebrae.[Result]In the anterior transarticular screw fixation,the lateral angulation of the screw tract to the sagittal plane ranged from(10.8?2.10)? to(25.13?3.12)?,the posterior anguation to the coronal plane from(8.85?2.12)? to(26.96?3.09)?,the screw tract length was from(17.48?2.1) mm to(25.4?2.59)mm,the distance from medial part of C2 foramen to the middle of C2 body was(14.12?1.28)mm.[Conclusion]It is optimal for the anterior C1、2 transarticular screw fixation to place the anterior C1、2 transarticular screw with the length of 17 mm to 25 mm in lateral angulation ranged from 10? to 25? and the posterior angulation ranged from 9? to 27?.During the procedure,the dissecting distance from the middle of C2 to lateral should not exceed 14 mm.

Modified posterior transarticular screw fixation for atlantoaxial instability / 中国矫形外科杂志

[Objective]To explore the techniques and effect of atlantoaxial instability with posterior transarticular screw fixation.[Method]A prospective clinical analysis was performed for the results of the modified posterior C1、2 transarticular screw fixation,in which the middle site of lower margin in the axial inferior articular process was used as the screw entry point in the procedure.Twenty cases of atlantoaxial instability underwent the modified C1、2 stabilization with morselized autograft from September 2001 to September 2006.There were 15 males and 5 females,averaged 32.2 years(range 17 to 49 years).Of them,4 cases suffered from fresh injuries,14 from old trauma,1 from congenital deformity,and 1 from intraspinal tumor.Postoperative indexes including the reduction extent of vertebral body,internal fixation,bone fusion,clinical symptoms and their complication were observed periodically.[Result]Bilateral screw fixation was used alone in 17 cases,with Gallie interspinous wiring for added stability in 3.Anatomical reduction of the atlantoaxial joints was achieved in19 cases,while rotational dislocation was restored to a great extent in 1.Fixation of all the internal devices was very well in the group.All cases were followed up from 16 to 64 months(21 months on average).C1、2 bony fusion was obtained in postoperative 2 to 3 months,clinical symptoms relieved and no complications occurred.[Conclusion]The modified posterior transarticular screw fixation using new screw entry site is recommended as an effective treatment for C1、2 instability due to its simple procedure and satisfying curative effect.

Anatomic relationship of vertebral artery and screw trajectory of posterior atalanto-axial transarticular screw fixation / 中国矫形外科杂志

[Objective]To study the screw trajectory in the posterior atalanto-axial transarticular screw fixation.[Methods](1)The anatomical parameters related to the screw fixation were measured on 30 paired dry atlantoaxial specimens;(2)The X ray and CT scan were taken after C1、2 was fixed by posterior transarticular screws on 6 cadavers.These iterms were used to explore the anatomical relation of the vertebral artery and the screw trajectory in the posterior C1、2 fixation.[Results]The depth of the vertebral artery groove on the inferior surface of the superior facet of the axial was(5.86 1.45)mm;the vertebral artery groove extented the superior facet up to its medial third in 15 sides,up to the middle third and its lateral third respective in 35 and 9 sides,and the ideal screw trajectory medial angle of these specimens were(26.4?3.44)?,(16.1?2.44)?,(15.1?2.24)? respectively。The shortest distance between the vertebral artery and the screw trajectory lied in the topmost point of the vertebral artery groove of the axial on CT images,and the interval was(2.75～5.78)mm.[Conclusion]The position of vertebral artery groove of the axial is the key to decide the angle of the screw trajectory.The shortest interval between screw trajectory and vertebral artery,safe for posterior atalanto-axial transarticular screw fixation,locates on the inferior surface of the superior facet of the axial.

Biomechanical comparison between artificial atlanto-odontoid joint replacament and Magerl transarticular screw fixation / 中国矫形外科杂志

[Objective]To determine the initial stability and function of a new artificial joint in a cadaveric cervical spine model by comparing it with a conventional method. [Methods]Twelve fresh human cadaveric cervical spines(C0~3) were randomly divided into 2 groups: group 1,resection of the odontoid with artificial atlanto-odontoid joint(AAOJ),and group 2,resection of the odontoid with Magerl atlas and axis by transarticular screw fixation(Magerl).For each specimen,the intact and resection of the odontoid underwent a flexibility test firstly,followed by the instrumented construct.Rotational angles of the C0~3 segment were measured to study the immediate stability and function of resection of the odontoid and AAOJ,compared with the intact and resection of the odontoid and Magerl.[Results]Compared to the intact state,resection of the odontoid and AAOJ resulted in a significant decrease in the range of motion(ROM) and neutral zone(NZ) during flexion,extension,and lateral bending(P0.05).Compared to the intact state,resection of the odontoid and Magerl resulted in a significant decrease in the range of motion(ROM) and neutral zone(NZ) during all 6 degrees of freedom(P0.05).[Conclusion]A new type of artificial atlanto-odontoid joint has been designed for correcting atlantoaxial instability resulted from C1、2 anterior decompression procedures.It can restore,to a great extent,the C1、2 axial rotation that is lost during current stabilization procedures.

Measurement of the Axial Isthmus for Atlantoaxial Transarticular Screw Fixation / 대한해부학회지

Pre-operative evaluation of the anatomy of the axis, such as the size and angle of the axial isthmus, is very important to minimize complications in atlantoaxial transarticular screw fixation. To provide basic data useful for atlantoaxial transarticular screw fixation in Korean, the width and height of the axial isthmus as well as ideal insertion angle of the screw were measured in this study. Fifty seven (male, 36; female, 21) dried axes obtained from Korean adult cadavers, 60.5 years old in average, were used. The shortest distance in the width and height of the axial isthmus was measured at the level of transverse foramen by using Vernier calliper. The ideal screw insertion angle was set up as an angle between a parasagittal line and the line passing through the center of the isthmus and screw insertion point which is located 2 mm lateral to and 3 mm superior to the posteromedial end of the inferior articular surface of the axis. The mean width of the axial isthmus was 8.14 mm (8.42 mm in male; 7.86 mm in female) in the right and 8.46 mm (8.80 mm in male; 8.12 mm in female) in the left side, and 8.61 mm in male and 7.99 mm in female. Although the width of the axial isthmus was slightly greater in the left and in male, there was no significant difference between both sides or sexes. The mean height of the axial isthmus was 7.17 mm (7.49 mm in male; 6.84 mm in female) in the right and 7.43 mm (7.90 mm in male; 6.96 mm in female) in the left side, and 7.69 mm in male and 6.90 mm in female. However there was no significant difference between both sides or sexes, as like in the width. In the atlantoaxial transarticular screw fixation, the axis with isthmus lesser than 5 mm in its width or height is regarded as risk group in general. The frequency of the risk group in the width was 3.5% (2 cases) in the right and 1.8% (1 case) in the left, while that in the height was 8.8% (5 cases) in the right and 7.0% (4 cases) in the left. The mean ideal insertion angle of the screw was 5.6 degrees, 4.4 degrees in the right and left side of male, and 4.7 degrees, 5.5 degrees in the right and left side of female respectively. However the insertion angle dispersed over a wide range between 0 degree ~ 12 degrees. In conclusion, measurement of the isthmus height and insertion angle, besides the isthmus width, should be involved in the pre-operative examination, to minimize complications during the atlantoaxial transarticular screw fixation.

Treatment of C_(1～2) instability with 3D-fixation techniques / 中国矫形外科杂志

[Objective]To investigate the efficacy of treatment of C_(1～C) instability with 3D-fixation techniques.[Method]From July 2002 to July 2005,thirteen patients were treated with atlantal lateral mass screw associating with axoid pedicle screw;twelve patients were treated with axoid transarticular screw associating with posterior atlantal arch hook;sixteen patients were treated with Vertex and nine patients with Summit among them.[Result]There were 26 lateral mass screws,26 axoid transarticular screws,24 atlantoaxial transarticular screws and 24 posterior atlantal arch hooks were applied in the 25 patients.All patients were followed up.The follow up duration time was ranging from 10 to 36 months with the mean time of 16.7 months.No spinal injury and vertical artery injury was found. The postoperative JOA score was ranging from 13.6 to 15.9 with the mean score of 14.8 and the improvement rate of 89.5%.All fractures of odontoid process and all bone grafts had solid bone union.No failure and loosening of internal instrument was found.[Conclusion]The two 3D-fixation techniques are effective and reliable.

The Results and Complications of the C1-C2 Transarticular Screw Fixation Methods

OBJECTIVE: To evaluate the accuracy and safety of C1-C2 transarticular screw insertion, we retrospectively review surgical records and postoperative radiological findings. METHODS: From January 2001 to October 2003, the C1-C2 transarticular screw fixation and posterior wiring with iliac bone grafts was performed in 16 pateints. 6 patients had rheumatoid arthritis which caused cervical instability, 3 patients had os odontoideum, 3 patients had type 2 odontoid process fracture, 3 patients had traumatic transverse ligament injury and 1 patients who had been managed with C1-C2 wire fixation had psoriatic arthritis. RESULTS: Osseous fusion was documented in 15 patients(93.8%). Only one patient was recorded screw loosening because of postoperative infection. One patient had only one screw placed because of abnormal anatomical structure, one patients was breakage of a Kirschner wire, and one screw was medial location to lateral mass of C1, but clinical results was excellent and radiological instability was not noted. CONCLUSION: The author's experience demonstrates that C1-C2 transarticular screw fixation with wired bone graft is a safe procedure with higher fusion rate but precaution is needed to avoid the neural damage, vertebral artery injury, and hardware failure.

Analysis of the Rate of High Riding Vertebral Artery Using Sagittal Reformatted Computed Tomography / 대한정형외과학회잡지

PURPOSE: The rate of high riding vertebral artery (VA) was investigated, and the rate in rheumatoid arthritis (RA) group was compared with that in non-RA group. MATERIALS AND METHODS: 67 consecutive patients were recruited. The male to female ratio was 44: 23. Sixteen patients were diagnosed as RA and 51 as cervical spondylosis. Sagittal reformatted view transecting mid-portion of the atlantoaxial facet joint was obtained and the height of the isthmus and the internal height of the axis were measured using a Picture Archiving and Communication System (PACS). High riding VA was defined as less than 5 mm of isthmus height or less than 2 mm of internal height. RESULTS: Thirty-six joints (26.9%) and twenty-seven patients (40.3%) showed high riding VA, and there was no significant difference between right and left side (8 right, 10 left, 9 both sides) (p=0.20). There was no difference among age distribution (p=0.06). In rheumatoid patients, the rate of high riding VA (10/16, 62.5%) was higher than in non-rheumatoid patients 17/51, 33.3%) (p=0.04). CONCLUSION: Preoperative evaluation of the VA using the reformatted CT should be performed in all patients who plan to undergo atlantoaxial transarticular screw fixation. In rheumatoid patients, possibility of high riding VA should always be considered.

Transarticular screws versus Magerl lateral mass screws:an anatomic comparison of their possible effects on injury to spinal nerve roots / 中华创伤骨科杂志

Objective To compare anatomically the potential incidences of injury to the nerve roots of ventral and dorsal rami caused by the transarticular screws and Magerl lateral mass screws in the fixation of subaxial cervical spine.Methods Fixations with the transarticular screws and Magerl lateral mass screws were performed in this study.For each kind of fixation,20 screws were inserted from C3 to C7 in two specimens.A 20-ram long screw was used to over-penetrate the ventral cortex.The anterolateral aspect of the cervical spine was carefully dissected to allow ob- servation of the screw-ramus relationship.Results The overall percentage of nerve violation was significantly lower in the transarticular screw fixation(45%)than in the Magerl lateral mass screw fixation(90%).The difference was sta- tistically significant between the two fixation methods(P＜0.05).The greatest percentages of nerve violation caused by the transarticular screws and lateral mass screws were found at the dorsal ramus,25% and 45%,respectively. Conclusion The potential risk of nerve root violation caused by the transarticular screw technique is lower than that by the Magerl lateral mass screw technique in the lower cervical spine.

Atlantoaxial Instability due to Hypoplasia of the Odontoid Process

The authors present a case of a 39-year old man, admitted with neck pain and tingling sensation on his right upper extremity. On radiological investigation, atlantoaxial instability due to odontoid process hypoplasia and mild upper cervical cord compression by abnormal soft tissue were revealed. We performed posterior C1-2 transarticular screw fixation with posterior bone graft and could obtain good postoperative result.

Measurements of C1-2 region of Cervical Spine Using MRI for C1-2 Transarticular Screw Fixation / 대한척추외과학회지

STUDY DESIGN: The C1-2 region was measured using MRI for a C1-2 transarticular screw fixation. OBJECTIVES: To measure the first and second cervical spine, using MRI for a C1-2 transarticular screw fixation, and find the safe trajectory for the screw. SUMMARY OF LITERATURE REVIEW: Posterior atlantoaxial transarticular screw fixation is an excellent procedure that is associated with high fusion rates. However, there is a potential risk of vertebral artery injury. MATERIALS AND METHODS: Sagittal MR images, of the cervical spine transecting mid portion of the C1-2 facet joints, were obtained in 24 patients. The mean age of the patients was 45.5 years. The male to female ratio of the patients was 15:9. From the sagittal images the ideal screw trajectory was made, and 48 oblique axial MR images, depending on the ideal screw trajectory in the sagittal plane, were obtained. On the oblique sagittal images, the width of the isthmic portion of the C2, the ideal length of the transarticular screw, the ideal insertion angle of the screw and the ideal entry point were measured using a PACS digital measuring instrument. The location of the vertebral artery was also evaluated. RESULTS: The mean width of the isthmic portion of the C2 was 6.2 mm, ranging from 2.3 to 7.6 mm. The mean ideal screw length was 40.5 mm, ranging from 34.0 to 46.8 mm. The mean ideal insertion angle was 1.1 degrees, ranging from -2.4 to 4.7 degrees, medially. There were no significant differences in the width or the angle in relation to the sex of the patients. However, the length of the screw was significantly longer in the male (42.1 mm) than the female patients (38.0 mm). Three of 24 patients (3 of 48 C1-2 facet joints) had a narrow isthmus due to a high riding vertebral artery. CONCLUSIONS: A C1-2 transarticular screw fixation has a risk of injury to the vertebral artery. Therefore, the preoperative measurement of the C1-2 region and an evaluation of the vertebral artery are recommended in each patient. A magnetic resonance image is a useful method for easily evaluating the anatomic structure of the C1-2 region, with no additional study.

Atlantoaxial Subluxation due to Psoriatic Arthritis

Atlantoaxial subluxation causing spinal cord compression at the craniovertebral junction may develop in patients with rheumatoid or psoriatic arthritis. There have been only a few reports of atlantoaxial subluxation in patients with psoriatic arthritis in the world. The authors report a case of psoriatic arthritis with atlantoaxial subluxation accompaning periodontoid pannus formation. This 53-year-old man with a 3-year history of psoriatic skin lesion presented with nuchal pain and myelopathy. We performed decompression by C1 total laminectomy with transarticular screw fixation and obtained remarkable improvement in motor function and immediate postoperative stability.