[Anti-rotation biomechanical study of wire and various cable system in the posterior brooks instrumentation for atlantoaxial instability]

OBJECTIVE

To compare the anti-rotation biomechanical performances of wire and various cable fixation devices currently used in the posterior Brooks instrumentation for atlantoaxial instability.

METHODS

In this experiment,six specimens of the atlantoaxial complex (Occipital-C3) were used. The models of the normal complex,unstable complex (type II odontoid fracture) and fixed complex were established. On the WD-5 mechanics experimental machine,the parameters including the strength and rigidity of anti-rotation were quantified for the normal complex (group N),the atlantoaxial instability complex (group M), the new type Titanium cable (group A), Atlas titanium cable (group B), Songer Titanium cable (group C), stainless wire(group D).

RESULTS

The max strength of A, B, C, D groups was 12.5, 11.3, 11.52, 11.55 N x m respectively, the max rigidity was 58.81, 53.17, 54.11, 54.35 N x cm/deg respectively. The strength and rigidity of anti-rotation, compare to the unstable atlantoaxial complex which were fixed by the new double locking Titanium cable fixation system were superior to those of normal complex, instability complex, Songer or Atlas Titanium cable (P < 0.05).

CONCLUSION

Having been changed the locking method, the anti-rotation biomechanical characteristics of the new type double locking Titanium cable fixation system are superior or similar to the traditional Songer or Atlas Titanium cable.

Case report: nonoperative treatment of an unstable Jefferson fracture using a cervical collar

The treatment of unstable burst fractures of the atlas (Jefferson fractures) is controversial. Unstable Jefferson fractures have been managed successfully with either immobilization, typically halo traction or halo vest, or surgery. We report a patient with an unstable Jefferson fracture treated nonoperatively with a cervical collar, frequent clinical examinations, and flexion-extension radiographs. Twelve months after treatment, the patient achieved painless union of his fracture. The successful treatment confirms prior studies reporting unstable Jefferson fractures have been treated nonoperatively. The outcome challenges the clinical relevance of treatment algorithms that rely on the "rules of Spence" to guide treatment of unstable Jefferson fractures and illustrates instability may not necessarily be present in patients with considerable lateral mass widening. Additionally, it emphasizes a more reliable way of assessing C1-C2 stability in unstable Jefferson fractures is by measuring the presence and extent of anterior subluxation on lateral flexion and extension views.

In vivo segmental motion of the cervical spine in rheumatoid arthritis patients with atlantoaxial subluxation

OBJECTIVE

The dynamic mechanism underlying cervical spine involvement in rheumatoid arthritis (RA) remains unidentified. The purpose of the current study was to determine the in vivo cervical segmental motion in RA patients with atlantoaxial subluxation (AAS) using a patient-based three-dimensional magnetic resonance imaging (MRI) computer model.

METHODS

Healthy volunteers and RA patients with AAS (all females, n=10) underwent MRI examination of the cervical spine. Each vertebral body from the occipital bone (Oc) to the first thoracic vertebra (T1) was reconstructed from slices of T2-weighted sagittal MR images in the neutral, flexion, and extension positions. Using volume merge methods, each reconstructed vertebral body was virtually rotated and translated. Rotational segmental and translational segmental motions were obtained in three major planes.

RESULTS

Overall, the axial translational motions in the RA group were lower than those in the healthy volunteers; however the axial translational motion at only C1-C2 during flexion was at the same level as that in the healthy volunteers and was greater on the bottom side than that at other intervertebral levels. The frontal rotational motions at C1-C2 during extension were greater in the RA patients than those in the healthy volunteers (p<0.05).

CONCLUSION

The atlantoaxial joints in the RA patients with AAS showed great frontal rotational motion during extension and great axial translation on the bottom side during flexion. The current noninvasive MRI-based method could be useful in evaluating the 3-D dynamic mechanism underlying cervical involvement in RA in vivo.

[Clinical characteristics and diagnosis of rheumatoid arthritis of upper cervical spine: analysis of 71 cases]

OBJECTIVE

To study the clinical characteristics and diagnosis of rheumatoid arthritis (RA) in the upper cervical spine.

METHODS

The clinical data of 71 patients with RA in the upper cervical spine, 18 males and 53 females, aged 46.2 (23-76), with a mean duration of RA of 18.2 years (2 months-47 years) were retrospectively reviewed. Fifty-three patients received glucocorticoid for more than 3 months. In addition to routine examinations, all patients underwent plain X-ray film taking, CT and MRI scanning, and erythrocyte sedimentation rate, rheumatoid factor (RF) and antistreptolysin O testing.

RESULTS

The symptoms of upper cervical spine appeared at 8.3 years (2 months-46 years) after the diagnosis of RA was confirmed. The clinical manifestations of RA in the upper cervical spine were intractable pain in craniocervical junction or radiating pain. Abnormal postures in the neck and Sherp-Purser's sign were positive in some patients. Progressive neurological dysfunction with the involvement of spinal cord, medulla, or some cranial nerves might gradually appear. Irregular destruction of bone with osteoporosis around the lateral and median atlantoaxial joint was a common finding in the X-ray films and CT scans. Instability of the atlantoaxial joint, including anterior atlantoaxial subluxation, posterior atlantoaxial subluxation and anterior-posterior atlantoaxial subluxation were found in 68 cases, while rotation subluxation was presented in 37 cases. Vertical migration of the odontoid was seen in 11 cases. RF was positive in 18 cases. MRI revealed that the cause of spinal cord compression was the bone tissue and soft tissue pannus.

CONCLUSIONS

RA in the upper cervical spine is a common situation in the clinical settings. The key point in the diagnosis of this disease is the identification of instability in the atlantoaxial joint and assessment of the spinal neurological deficit. And a careful analysis of the natural history will further help to achieve a better treatment effect.

Traumatic atlantoaxial rotatory dislocation in adults

Pure traumatic atlantoaxial rotatory dislocation (TAARD) is a possible cause of torticollis in children, but very rare in adults. Aim of this study is to report three very rare cases of TAARD in adults, focusing anatomy, management, and outcome. All 3 patients had a head-on automobile accident. Cases included a 26-year old woman, a 21-year old woman, and a 29-year-old man. The first case had a 45-day delay in diagnosis; the second and third cases were suspected to have odontoid lateral mass asymmetry on transoral radiographs. In all cases CT scan confirmed diagnosis and clarified the type of subluxation. All had conservative treatment with reduction and immobilization with Halo-Vest for case 1 and 2, and a rigid cervical collar for case 3. After follow-up of 10 years for case 1 and 2, and 3 years for case 3, all had no sign of C1-C2 complex mobility/instability. Patients 2 and 3 had complete and pain free cervical spine range of motion, while case 1 had stiffness and straightness of the cervical spine, headache, and nerve roots deficits, probably due to the complex cervical spine injury with sagittal imbalance on X-ray and C5-C6 spinal cord compression (pre-existing the trauma). TAARD should be considered in the differential diagnosis of post-traumatic neck pain and limitation, with or without evident torticollis, even in adults. CT scan is mandatory for a correct evaluation of C1-C2 complex. Conservative treatment with reduction followed by 50-60 days of rigid cervical immobilization (3 months in delayed diagnosis) is usually effective. Delay in diagnosis could be the cause of a poor outcome.

[Rheumatoid arthritis with atlanto-axial subluxation. Pre-and postoperative symptoms, radiological findings and operative complications]

INTRODUCTION

The aim of the study was to study pre- and postoperative symptoms, radiological findings and operative complications in rheumatoid arthritis (RA) patients, operated in the atlantoaxial joint.

MATERIALS AND METHODS

A retrospective study of 31 RA patients (24 women, seven men) operated for anterior atlantoaxial subluxation (aAAS) at the Neurosurgical Department, Aarhus University Hospital, in the period of 1993-2003. Information was obtained retrospectively from the patients charge.

RESULTS

Mean age at RA debut was 38 years (16-69 yrs), and neck symptoms were seen after a mean time of 15 years (0-39 yrs) of illness. Radiological examination at this time showed irreversible atlantoaxial changes, and operation was performed within 0-9 years (mean 1.6 yrs). The patients were characterized by high disease activity: C-reactive protein, anaemia, positive IgM-rheumatoid factor (84%), and progressive radiological changes in the peripheral joints. All patients were treated with DMARDs (disease modifying anti rheumatic drugs). Neck pain (100%) and neurological symptoms/manifestations (87%) were seen preoperatively. After operation symptoms were relieved in 68% of the patients, while 22% were unchanged, and 10% had worsened. Postoperative complications included cardiac death, dislocation of the cervical spine, fracture of arcus atlantis, hemiparesis, dysphagia, bed sores and infection of the surgical scar (29%).

CONCLUSION

Neck symptoms were seen after 15 years of illness, and within the following 1.6 years patients were operated for aAAS. After the operation most of the patients (68%) had relief from symptoms, while 29% had postoperative complications, including cardiac death, dislocation of the cervical spine, fracture of arcus atlantis, hemiparesis, dysphagia, bed sores and infection in the surgical scar.

Upper cervical spine instability in pseudoachondroplasia

BACKGROUND

Pseudoachondroplasia (PSACH) is a rare autosomal dominant skeletal dysplasia associated with os odontoideum and atlantoaxial instability. This study aims to define the characteristics of upper cervical spine instability in patients with PSACH and analyze the relation between the incidence of upper cervical instability and os odontoideum.

METHODS

Fifteen patients (10 women and 5 men) with PSACH of Korean ethnicity with mean age of 23.7 years (range, 3-44 years) at presentation to our hospital with varied complaints, including short stature, limb deformity, neck pain, and neurological symptoms, were evaluated clinicoradiologically for upper cervical spine instability. The patients were separated into group 1 (n = 9) with os odontoideum and group 2 (n = 6) without os odontoideum. Comparisons were made using parameters such as instability index, rotational instability, atlantodens interval and space available for cord, and analysis done to correlate cervical instability with age and Japanese Orthopedic Association (JOA) score.

RESULTS

Significant differences were found statistically when the 2 groups were compared on the basis of the space available for the cord (SAC), JOA scoring, and rotational instability. Linear relationship was found between instability and age and JOA score. Incidence of os odontoideum was 60% in our study group.

CONCLUSIONS

Os odontoideum led to an increase in the incidence of upper cervical spine instability. Instability increased with the age. The presence of os odontoideum and atlantoaxial instability did not warrant for surgery because no signs of cervical myelopathy developed or progressed in our patients during the follow-up period, but these patients should undergo regular clinical and radiological evaluation.

LEVEL OF EVIDENCE

Level IV prognostic study.

Atlantoaxial rotatory fixation owing to neck burn

The purpose of this paper is to present a case of severe atlantoaxial rotatory fixation owing to a previously unreported etiology, and to discuss its pathogenesis and management. Conservative measures were unable to prevent progression, thus requiring surgical intervention.

Screw fixation via diploic bone paralleling to occiput table: anatomical analysis of a new technique and report of 11 cases

Several types of posterior approaches have been adopted for occipitocervical fusion. Prior to this study, Foerater et al. in 1927 used a fibular strut graft in the site between the occiput and the lower cervical spine to achieve fusion. Since then, various techniques including wrings, Hartshill loop, AO reconstructive plate, and AXIS occipital plate were described and used widely. As far as we know, all these techniques involve the screw placement vertical to the diploic bone; however none has ever addressed the feasibility of screw placement in occiput parallelling to the diploic bone. In our study, 30 dry specimens of human occiputs were measured manually using vernier calipers and protractors. The intradiploic screw was first supposed to be inserted inferiorly to the superior nuchal line (SNL) prominence. The entry point located at the superior edge of the SNL prominence. Afterward, the measurements of extracranial occiput in SNL area on midline and bilateral 15 mm to the midline saggital-cutting planes of the occiput were conducted. The thickness of the occipital bone at the location of SNL prominence, the entry point, the exit point and the screw orientation were measured, respectively. Afterward, 11 patients with craniocervical malformation were treated surgically using this alternative and their X-ray radiographs and CT scans were evaluated postoperatively. The data showed that the occipital at the site of SNL prominence was the thickest. The thickest point was external occipital protuberance (EOP), which was up to 14 mm. The thickness decreased gradually from the site of SNL to the superior border of surgical decompressed area. The actual length of screw channel was about 26 mm. The mean thickness for safe screw insertion ranged from 5.73 to 14.14 mm. A total of 22 intraocciput screws parallel to diploic bone were placed precisely, without injury to the cerebral and inner occipital venous sinus. The results confirm that occiput is available for holding intraocciput screw paralleling to diploic bone.

Comparison of Contemporary Occipitocervical Instrumentation Techniques with and Without C1 Lateral Mass Screws

Objective:

This study was designed to test the kinematic properties of three occiput-C2 instrumentation constructs with and without supplemental rigid C1 fixation. The results are compared with intact specimens and with constructs incorporating contemporary cabling techniques.

Methods:

Five unembalmed human cadaver specimens underwent range of motion (ROM) testing in the intact condition, followed by destabilization with odontoid osteotomy. Destabilized specimens then underwent ROM testing with each of seven occipitocervical instrumentation constructs, all incorporating occipital screws: C1 and C2 sublaminar cables with cable connectors, C2 pars screws +/− C1 lateral mass screws, C2 lamina screws +/− C1 lateral mass screws, and C1–C2 transarticular screws +/− C1 lateral mass screws.

Results:

All seven constructs demonstrated significantly lower ROM in all loading modes than intact specimens (P &lt; 0.05). With a single exception, the addition of C1 lateral mass screws to the screw-based constructs produced no significant change in ROM in any of the loading modes. Compared with intact specimens, constructs anchored by C1–C2 transarticular screws demonstrated the greatest decrease in ROM, and those anchored by sublaminar cables demonstrated the least decrease in ROM.

Conclusion:

Any of the tested screw-based constructs are likely to provide adequate support for the patient with an unstable craniocervical junction. Therefore, the choice of construct should be based on anatomic considerations. The routine incorporation of C1 lateral mass screws into occipitocervical instrumentation constructs does not seem necessary.

[Surgical treatment of craniocervical instability. Review paper]

The concept of spinal instability is still controversial. Anatomical, biomechanical, clinical and radiographic variants are involved and make the definition complicated. There are solid diagnostic bases in cases of fractures and degenerative disorders; however, pure spinal instability is still under study. The latter may be defined as increased mobility that goes beyond the physiological limits of one vertebra over another in at least one of the three spinal planes of motion. In the case of the craniocervical region, its understanding becomes even more challenging, since its anatomy and physiology are more complex and it is more mobile. Surgical treatment is possible with either an anterior or a posterior approach. Best results are obtained with occipitocervical or atlantoaxial stabilization through a posterior approach, since the anterior one has its limitations. For example, a transoral approach with a bone graft provides compression strength but does not enable immediate appropriate fixation and involves the risk of infection. The choice of the surgical approach must consider the patient's medical status, the specific spine levels involved, the extent of neurological compromise, the X-ray abnormalities and the individual pathology. The goals of surgery are achieved through an appropriate anatomical alignment, assuring the protection of the neural elements and achieving proper spine stabilization with as much preservation of the mobile vertebral segments as possible.

Efficacy of a C1-C2 self-sustained natural apophyseal glide (SNAG) in the management of cervicogenic headache

STUDY DESIGN

Randomized, double-blind, placebo controlled trial.

OBJECTIVES

To determine the effect of a C1-C2 self-sustained natural apophyseal glide (SNAG) on cervicogenic headache.

BACKGROUND

Cervicogenic headache is a common condition causing significant disability. Recent studies have shown a high incidence of C1-C2 dysfunction, evaluated by the flexion-rotation test (FRT), in subjects with cervicogenic headache. To manage this dysfunction, Mulligan has described a C1-C2 self-SNAG, though no studies have investigated the efficacy of this intervention approach.

METHODS

A sample of 32 subjects (mean _ SD age, 36 +/- 3 years) with cervicogenic headache and FRT limitation were randomized into a C1-C2 self-SNAG or placebo group. After an initial instruction and practice visit in the clinic, interventions consisted of exercises applied independently by the subject twice daily at home on a continual basis. FRT range was measured twice, before and immediately after the instruction and practice visit. Headache symptoms were determined by a headache index over time, assessed by questionnaire preintervention, at 4 weeks postintervention, and at 12 months postintervention.

RESULTS

No differences were found in baseline measures between groups. Immediately after the initial instruction and practice visit performed with the supervision of the therapist, FRT range increased by 15 degrees (SD, 9) for the C1-C2 self-SNAG group (P < .001), which was significantly more than 5 degrees (SD, 5) for the placebo intervention (P < .001). There was also a significant interaction for the variable headache index between group and time (P < .001), indicating that group difference was dependent on time. There was no difference in headache index scores at baseline between groups. Headache index scores were substantially less in the C1-C2 self-SNAG group (mean +/- SD points at 4 weeks, 31 +/- 9; mean +/- SD points at 12 months, 24 +/- 9) compared to the placebo group (mean +/- SD points at 4 weeks, 51 +/- 15; mean +/- SD points at 12 months, 44 +/- 13) at 4 weeks (P < .001) and 12 months (P < .001), with an overall (+/-SD) reduction of 54% (+/-17%) for the individuals in the C1-C2 self-SNAG group.

CONCLUSIONS

These results provide evidence for the efficacy of the C1-C2 self-SNAG technique in the management of individuals with cervicogenic headache.

Cervicomedullary compression secondary to massive calcium pyrophosphate crystal deposition in the atlantoaxial joint with intradural extension and vertebral artery encasement

BACKGROUND

Deposition of CPPD crystals occurs in the fibrous and hyaline cartilage of the joints and intervertebral disks of the spine. Half of patients known to have chondrocalcinosis had asymptomatic calcification in the odontoid region. The cases of 12 patients with a spinal cord syndrome secondary to CPPD deposition in the odontoid region were published in the literature. In all those cases, the mass lesion was extradural in location with good outcome after surgical decompression via the transoral route.

CASE DESCRIPTION

We report on a rare case of large periodontoid CPPD deposition causing cervicomedullary compression, erosion of the overlying bone, and underlying dura with intradural extension and vertebral artery encasement.

CONCLUSIONS

Calcium pyrophosphate dihydrate is a rare cause of cervicomedullary compression. Intradural extension of periodontoid CPPD has not been reported on.

Cervical spine range of motion in children with posterior occipitocervical arthrodesis

This prospective study compared cervical spine (c-spine) range of motion (ROM) in children with posterior occipitocervical arthrodesis to a control group of healthy participants. Cervical spine ROM is likely be altered after fusion. However, the extent to which posterior occipitocervical arthrodesis affects ROM in the c-spine of children has not yet been established. Furthermore, there are conflicting reports on this topic in the literature. To the best of our knowledge, no study has specifically addressed the effect of posterior occipitocervical arthrodesis on c-spine ROM in children. In this study, c-spine ROM of 15 patients who underwent posterior occipitocervical arthrodesis for upper c-spine instability was evaluated and compared with 15 healthy age-matched children. We used the CROM Goniometer (Performance Attainment Associates, St Paul, MN) to measure c-spine flexion, extension, lateral bending, and axial rotation. Student t test was used to evaluate the study results. Cervical spine ROM was significantly decreased in children with posterior occipitocervical arthrodesis compared with controls (P < 0.05). Axial rotation was the most affected movement, decreasing by an average of 30 degrees in each direction, flexion and extension each decreased by 13 degrees, and lateral bending decreased by approximately 7 degrees in each direction. Posterior occipitocervical arthrodesis decreases c-spine ROM in children compared with healthy controls.

The relationship of cervical joint position error to balance and eye movement disturbances in persistent whiplash

Cervical joint position error (JPE) has been used as a measure of cervical afferent input to detect disturbances in sensori-motor control as a possible contributor to a neck pain syndrome. This study aimed to investigate the relationship between cervical JPE, balance and eye movement control. It was of particular interest whether assessment of cervical JPE alone was sufficient to signal the presence of disturbances in the two other tests. One hundred subjects with persistent whiplash-associated disorders (WADs) and 40 healthy controls subjects were assessed on measures of cervical JPE, standing balance and the smooth pursuit neck torsion test (SPNT). The results indicated that over all subjects, significant but weak-to-moderate correlations existed between all comfortable stance balance tests and both the SPNT and rotation cervical JPE tests. A weak correlation was found between the SPNT and right rotation cervical JPE. An abnormal rotation cervical JPE score had a high positive prediction value (88%) but low sensitivity (60%) and specificity (54%) to determine abnormality in balance and or SPNT test. The results suggest that in patients with persistent WAD, it is not sufficient to measure JPE alone. All three measures are required to identify disturbances in the postural control system.

Biomechanical comparison of two new atlantoaxial fixation techniques with C1–2 transarticular screw–graft fixation

Object

Two new techniques for atlantoaxial fixation have been recently described. In one technique, C-2 intra-laminar screws are connected with C-1 lateral mass screws; in the second, C-1 and C-3 lateral mass screws are interconnected and C-2 is wired sublaminarly. Both techniques include a C1–2 interspinous graft. The authors compared these techniques with the gold-standard, interspinous graft–augmented C1–2 transarticular screw fixation and with a control C1–2 interspinous graft fixation procedure alone.

Methods

In six human cadaveric occiput–C4 specimens, nonconstraining 1.5-Nm pure moments were applied to induce flexion, extension, lateral bending, and axial rotation during which three-dimensional angular motion was measured optoelectronically. Each specimen was tested in the normal state, with graft alone (after odontoidectomy), and then in varying order after applying each construct with a rewired graft. All three constructs allowed significantly less angular motion at the C1–2 junction than the wired interspinous graft alone during lateral bending and axial rotation (p < 0.01, paired Student t-test) but not during flexion or extension. Transarticular screw fixation with an interspinous graft allowed less motion at the atlantoaxial junction than the two new constructs in several conditions. Differences were greater between the transarticular screw construct and the intralaminar screw construct than between the transarticular screw construct and the C1–3 lateral mass screw construct. During lateral bending and axial rotation, the C1–3 construct allowed less motion at the atlantoaxial junction than the intralaminar screw construct.

Conclusions

Biomechanically, the gold-standard C1–2 transarticular screw fixation outperformed the two new techniques during lateral bending and axial rotation. Wiring C-2 to C1–3 rods provided greater stability than C1–2 laminar screws, but it sacrificed C2–3 mobility. It is unknown whether the small differences observed biomechanically would lead to clinically relevant differences in fusion rates.

Fracture of the atlas through a synchondrosis of the anterior arch complicated by atlantoaxial rotatory fixation in a four-year-old child

Fracture of the atlas is rare in children. We report a case of fracture of the atlas through a synchondrosis of the anterior arch complicated by atlantoaxial rotatory fixation in a four-year-old girl.

Preoperative evaluation of extension capacity of the occipitoatlantoaxial complex in patients with rheumatoid arthritis: comparison between the Bellhouse test and a new method, hyomental distance ratio

BACKGROUND

The authors devised a new method, the hyomental distance ratio (HMDR), for preoperatively identifying patients with a reduced occipitoatlantoaxial extension capacity, which was defined as the ratio of the hyomental distance in head extension position to that in the neutral position. They compared the accuracy of the HMDR with that of the Bellhouse test in 40 patients with rheumatoid arthritis.

METHODS

Each patient wearing goggles on which a goniometer was mounted sat upright with the head in the neutral position and then extended the head maximally. The angle of the goggles and the hyomental distance were measured in the two head positions, and a lateral cervical radiograph was taken simultaneously. The Bellhouse angle was defined as a difference in the angles of the goggles between these positions.

RESULTS

Median values of the radiologic occipitoatlantoaxial extension angle and the Bellhouse angle were 11.2 degrees and 24.9 degrees , respectively. In 21 of 40 patients, the radiologic occipitoatlantoaxial extension angle was less than 12 degrees (reduced occipitoatlantoaxial extension capacity). In these patients, extension of the median angle of 16.4 degrees occurred at the subaxial regions and was greater than that of 8.5 degrees in patients with a radiologic occipitoatlantoaxial extension angle of 12 degrees or more (P < 0.01). As a result, a strong relation between the Bellhouse angle and radiologic occipitoatlantoaxial extension angle was not established (P < 0.01, r = 0.48). In contrast, the HMDR correlated well with the radiologic occipitoatlantoaxial extension angle (P < 0.0001, r = 0.88). The areas under the receiver operating characteristic curve of the Bellhouse test and the HMDR were 0.72 and 0.95, respectively.

CONCLUSIONS

The HMDR was a good predictor of a reduced occipitoatlantoaxial extension capacity in patients with rheumatoid arthritis, but the Bellhouse test was not a clinically reliable method.

[The biomechanical study of craniovertebral junction fixation with posterior transarticular screw]

OBJECTIVE

To evaluate the stability of biomechanics of occipitoatlantoaxial reconstruction with transarticular screw fixation.

METHODS

Twelve fresh human cadaveric occipitocervical spine specimens were mounted in a custom-designed, spine-testing machine that applied pure moments while recording the three-dimensional angular movement at occiput (Oc)-C(1) and C(1 - 2) segments. The specimens were tested under seven different conditions: the intact (intact group), the occipitoatlantoaxial instability (Destabilized group), fixation with Ti-cable plus bone graft group (cable + graf group), fixation with the transarticular fixation (CTS group), fixation with SUMMIT occitocervical spinal fixation system (SUMMIT group), fixation with transarticular screw plus bone graft (CTS + graf group), and fixation with SMMIT system and plus graft group (SUMMIT + graf group). The data obtained were statistically analyzed.

RESULTS

The CTS group reduced motion to well within the normal rang. In the Oc-C(1) segment, The CTS group and SUMMIT group allowed a very small rang of motion (ROM) and neutral zone (NZ) during lateral bending and axial rotation. The ROM and NZ during flexion and extension of the SUMMIT group, were significantly smaller than those of cable + graf group and CTS group (6.64 degrees +/- 0.59 degrees, 2.49 degrees +/- 0.26 degrees, 0.50 degrees +/- 0.03 degrees, 0.21 degrees +/- 0.01 degrees, 0.27 degrees +/- 0.07 degrees, 0.13 degrees +/- 0.01 degrees vs 10.01 degrees +/- 1.26 degrees, 3.80 degrees +/- 0.79 degrees, 7.93 degrees +/- 1.34 degrees, 3.18 degrees +/- 0.95 degrees, 9.54 degrees +/- 0.87 degrees, 5.93 degrees +/- 0.74 degrees, P < 0.05). In the C(1 - 2) segment, ROM and NZ in all directions of CTS group were smaller in rotation than SUMMIT group (1.64 degrees +/- 0.39 degrees, 0.61 degrees +/- 0.15 degrees, 0.14 degrees +/- 0.05 degrees, 0.02 degrees +/- 0.01 degrees, 0.32 degrees +/- 0.04 degrees, 0.08 degrees +/- 0.01 degrees, vs 0.21 degrees +/- 0.04 degrees, 0.07 degrees +/- 0.03 degrees, 0.21 degrees +/- 0.12 degrees, 0.10 degrees +/- 0.02 degrees, 2.92 degrees +/- 0.28 degrees, 1.27 degrees +/- 0.11 degrees, all P < 0.05). There was no significant difference in ROM and NZ in all directions between CTS + graf group and SUMMIT + Graf group (P > 0.05).

CONCLUSION

In vivo biomechanics studies show that posterior occipitocervical transarticular fixation has unique features in reconstructing dynamic stability of the occipitoatlantoaxis, especially in controlling stability of rotation and lateral flexion, thus ensuring successful fusion of the implanted bone and allowing for clinical use of the technique.

Atlantoaxial Subluxation in Different Intraoperative Head Positions in Patients with Rheumatoid Arthritis

Background

Disorders of the cervical spine are often observed in patients with rheumatoid arthritis (RA). However, the best head position for RA patients with atlantoaxial subluxation in the perioperative period is unknown. This study investigated head position during general anesthesia for the patients with RA and proven atlantoaxial subluxation.

Methods

During anesthesia of patients with RA and proven atlantoaxial subluxation, the authors used fluoroscopy to obtain a lateral view of the upper cervical spine in four different positions: the mask position, the intubation position, the flat pillow position, and the protrusion position. Copies of the still fluoroscopic images were used to determine the anterior atlantodental interval, the posterior atlantodental interval, and the angle of atlas and axis (C1-C2 angle).

Results

The anterior atlantodental interval was significantly smaller in the protrusion position (2.3 mm) than in the flat pillow position (5.1 mm) (P &lt; 0.05). The posterior atlantodental interval was significantly greater in the protrusion position (18.9 mm) than in the flat pillow position (16.2 mm) (P &lt; 0.05). The C1-C2 angle was, on average, 9.3 degrees greater in the protrusion position than in the flat pillow position (P &lt; 0.05).

Conclusion

This study showed that the protrusion position using a flat pillow and a donut-shaped pillow during general anesthesia reduced the anterior atlantodental interval and increased the posterior atlantodental interval in RA patients with atlantoaxial subluxation. This suggests that the protrusion position, which involves support of the upper cervical spine and extension at the craniocervical junction, might be advantageous for these patients.

Posterior atlantoaxial three-point fixation: comparison of intraoperative performance between open and percutaneous techniques

INTRODUCTION

Atlantoaxial instabilities, which require surgical fixation follow a variety of clinical disorders. Different surgical procedures are used for stabilization of the atlantoaxial complex, mainly posterior wiring techniques and transarticular screw fixation. Nowadays, often a combination of transarticular screws and a posterior one-point fixation is used to achieve a three-point fixation, with superior biomechanical stability and good clinical results. Different modifications were developed to improve this technique. In 1995, a percutaneous approach for atlantoaxial stabilization was introduced. In clinical studies, the technique showed a tendency towards better outcome. Beside the outcome, the intraoperative performance is of special interest for minimal invasive approaches. We therefore compared the operation time, screw angulation and blood loss, between the open and percutaneous posterior atlantoaxial techniques.

MATERIALS AND METHODS

Two groups, each consisting of 17 patients, with either open (group 1) or percutaneous (group 2) atlantoxial stabilization, were compared. The operation time was retrospectively acquired from the patient's charts. The data for blood loss was provided by our anaesthesiological department, separated for intraoperative, postoperative and total blood loss. Screw angulation was measured on the postoperative x-ray by an orthopaedic surgeon.

RESULTS

The percutaneous group showed an average intraoperative blood loss of 239.7 ml, compared to 929.4 ml for the open group (p< or =0.001). The analogue values for the postoperative blood loss were 142.9 ml and 379.4 ml for group 2 and group 1, respectively (p=0.008). Consecutively, the total blood loss showed also a statistically significant difference (p< or =0.001). The operation time was significantly different (p< or =0.001), with average values of 175.3 min (group 1) and 110.6 min (group 2). Screw angulation showed a trend towards a steeper angulation in the percutaneous group with an average angle of 56.8 degrees , compared to 53.9 degrees (group 1), although this was not statistically significant (p=0.053).

CONCLUSION

The percutaneous technique for atlantoaxial stabilization with a three-point fixation has clear intraoperative benefits, with shorter operation time and reduced blood loss. A trend towards steeper screw angulation was found and shows at least equal feasibility for transarticular screw placement with the percutaneous technique, compared to the standard open approach.

Cervical spine surgery in patients with rheumatoid arthritis: longterm mortality and its determinants

OBJECTIVE

Atlantoaxial subluxation (AAS) is a frequent manifestation of rheumatoid arthritis (RA). The instability of the craniocervical junction caused by AAS is a potentially fatal condition and may require surgical treatment. Systemic manifestations associated with RA may increase the risk of perioperative complications. We evaluated the longterm mortality and its determinants in RA patients with AAS after cervical spine surgery.

METHODS

A retrospective study of consecutive patients treated at Kuopio University Hospital between 1994 and 1998. Preoperative risk factors, neurological impairment using the Ranawat classification, perioperative course, functional outcome, and survival status were evaluated.

RESULTS

During the study period 86 rheumatoid patients with AAS underwent cervical spine surgery. The mean followup time was 7.5 years (range 5.0-9.8). During the followup, 32 patients (37%) died. The mean survival time after surgery was 7.2 years (95% CI 6.7-8.0). Seven patients experienced postoperative complications. Age, AAS other than horizontal, and occurrence of complications were independent predictors of mortality. In two-thirds of the patients there was relief or decrease of pain, and the functional capacity improved. Neurological deficits subsided in 53% of cases.

CONCLUSION

Patients with RA should be actively studied for AAS or other cervical instability, even when cervical symptoms are minor. Attention should be paid to perioperative management of these patients. Surgical treatment may not decrease the mortality of patients with RA, but it may result in more symptom-free life-years.