Effect of a reduction of the atlanto-axial angle on the cranio-cervical and subaxial angles following atlanto-axial arthrodesis in rheumatoid arthritis

Radiographic Predictors of Subaxial Subluxation After Atlantoaxial Fusion

STUDY DESIGN

A retrospective study.

OBJECTIVE

The aim of this study was to clarify preoperative radiographic predictors associated with the development of subaxial subluxation (SAS) after surgery.

BACKGROUND

The incidence of atlantoaxial fusion for atlantoaxial instability has been increasing. SAS can develop after surgery despite atlantoaxial fusion with the optimal C1-C2 angle. We hypothesized that preoperative discordant angular contribution in the upper and subaxial cervical spine is associated with the occurrence of postoperative SAS.

MATERIALS AND METHODS

Patients who underwent surgery for atlantoaxial instability with a minimum 5-year follow-up and control participants were included. The O-C2 angle, C2 slope (C2S), C2-C7 cervical lordosis (CL), and T1 slope (T1S) were measured. We focused on the angular contribution ratio in the upper cervical spine to the whole CL, and the preoperative C2/T1S ratio was defined as the ratio of C2S to T1S.

RESULTS

Twenty-seven patients (SAS=11, no-SAS=16; mean age, 60.7 y old; 77.8% female; mean follow-up duration, 6.8 y) and 23 demographically matched control participants were enrolled. The SAS onset was at 4.7 postoperative years. Preoperatively, the O-C2 angle, C2-C7 CL, and T1S were comparable between the SAS, no-SAS, and control groups. The preoperative C2S and C2/T1S ratio were smaller in the SAS group than in the no-SAS or control group (C2S, 11.0 vs. 18.4 vs. 18.7 degrees; C2/T1S ratio, 0.49 vs. 0.77 vs. 0.78, P <0.05). The receiver operating characteristic curve analysis demonstrated that the C2/T1S ratio had higher specificity and similar sensitivity as a predictor of postoperative SAS than C2S (specificity: 0.90 vs. 0.87; sensitivity: 0.73 vs. 0.73). The estimated cutoff values of the C2S and C2/T1S ratio were 14 degrees and 0.58, respectively.

CONCLUSIONS

The preoperative C2/T1S ratio was closely associated with postoperative SAS. Patients with a C2/T1S ratio <0.58 were at a high risk of SAS after atlantoaxial fusion.

LEVEL OF EVIDENCE

Level 4.

Relationship between the atlantodental interval and T1 slope after atlantoaxial fusion in patients with rheumatoid arthritis

BACKGROUND

Atlantoaxial fusion has been widely used for the treatment of atlantoaxial instability (AAI). However, atlantoaxial fusion sacrifices the motion of atlantoaxial articulation, and postoperative loss of cervical lordosis and aggravation of cervical kyphosis are observed. We investigated various factors under the hypothesis that the atlantodental interval (ADI) and T1 slope may be associated with sagittal alignment after atlantoaxial fusion in patients with rheumatoid arthritis (RA).

METHODS

We retrospectively investigated 64 patients with RA who underwent atlantoaxial fusion due to AAI. Radiological factors, including the ADI, T1 slope, Oc-C2 angle, cervical sagittal vertical axis, and C2-C7 angle, were measured before and after surgery.

RESULTS

The various factors associated with atlantoaxial fusion before and after surgery were compared according to the upper and lower preoperative ADIs. There was a significant difference in the T1 slope 1 year after surgery (p = 0.044) among the patients with lower preoperative ADI values. The multivariate logistic regression analysis showed that the preoperative ADI (> 7.92 mm) defined in the receiver-operating characteristic curve analysis was an independent predictive factor for the increase in the T1 slope 1 year after atlantoaxial fusion (odds ratio, 4.59; 95% confidence interval, 1.34-15.73; p = 0.015).

CONCLUSION

We found an association between the preoperative ADI and difference in the T1 slope after atlantoaxial fusion in the patients with RA. A preoperative ADI (> 7.92 mm) was an independent predictor for the increase in the T1 slope after atlantoaxial fusion. Therefore, performing surgical treatment when the ADI is low would lead to better cervical sagittal alignment.

[Rheumatoid instability in the cervical spine : Diagnostic and therapeutic strategies]

BACKGROUND

The involvement of the cervical spine in rheumatoid arthritis (RA) continues to be of clinical importance even in this age of biologics. Pathophysiological changes begin with an isolated atlantoaxial subluxation and may progress to a complex craniocervical and subaxial instability. The onset of cervical myelopathy can occur at any time and leads to a deterioration of the prognosis for the patient.

THERAPY

Treatment of the rheumatoid cervical spine should be aimed at improvement of the symptoms and prevention of further progress of the disease. In the case of instability, this is only possible by surgical treatment. The increasing usage of biological agents has led to a change in the clinical picture of the cervical involvement in RA patients. There are fewer patients presenting with isolated atlantoaxial instability. In contrast, the number of patients with complex craniocervical and/or subaxial instabilities is increasing. Complex cervical instabilities may require a longer fusion from the occiput to the upper thoracic spine. Modern operative techniques make this complex surgery also possible in severely disabled patients with a high comorbidity.

Retrospective analysis of surgical outcomes for atlantoaxial subluxation

Background

Atlantoaxial subluxation (AAS) is characterized by excessive movement at the junction between the atlas (C1) and axis (C2) as a result of either a bony or ligamentous abnormality. Surgical intervention is a therapeutic choice for AAS. In addition to C1 laminectomy (LAM), surgical fixation for subluxation or instability is performed by various techniques. While surgical treatment options for AAS have increased, the outcomes of different surgical techniques remain unclear.

Methods

The authors conducted a retrospective analysis of the outcomes of 30 consecutive spinal surgeries performed for AAS patients, C1 LAM in 11 cases and C1/2 fixation in 19 cases. We investigated the correlation between the clinical outcomes and the surgical methods. We also examined the factors related to poor outcomes (the recovery rate of the Japanese Orthopedic Association score for cervical myelopathy < 40%) following AAS surgeries.

Results

From a surgical method perspective, the patients in the C1 LAM group were older than those in the C1/2 fixation group (74.6 years vs 68.0 years), and the average recovery rate from the preoperative status was as follows: the C1 LAM group, 39.4%; the C1/2 fixation group, 49.8%. The C-JOA score was significantly improved after surgery in the C1/2 fixation group (from 9.8 to 13.1 points). The fixation technique seemed to successfully reduce C1/2 displacement. Each group exhibited a slight increase in the C1/2 angle and a decrease in the C2–7 angles after the operation. A higher preoperative atlantodental interval (ADI) was associated with good outcomes after the C1/2 fixation. The postoperative ADI was significantly reduced from 8.6 mm to 3.8 mm in the good outcome group after fixation. Patients with higher C1/2 angle showed good outcomes after C1 LAM. Despite the good neurological improvement, the C1/2 fixation method showed higher complication rates compared with C1 LAM method.

Conclusions

The results of this study showed that the C1/2 fixation technique exhibited effectiveness in terms of neurological recovery. However, there was a high complication rate in surgeries for AAS, especially in the C1/2 fixation. C1 LAM would be considered for high-risk AAS cases such as elderly patients with multiple comorbidities.

Treatment of atlanto-axial subluxation secondary to rheumatoid arthritis by short segment stabilization with polyaxial screws

OBJECTIVE

The main aim of this study was to analyse the compex clinical and radiographic findings in a group of RA patients with atlanto-axial slip (AAS) treated with free-hand short C1 lateral mass and C2 trans-pedicular screw fixation. The surgical technique used and the pathology treated were the same in all patients, producing a very homogeneous cohort of patients This allowed the study and measurement of radiographic parameters and fusion process.

METHODS

Twenty-nine patients (21 female, 8 male, mean age 54.9 years, duration of RA 17.3 years) with AAS and without CS were treated by short C1/2 fixation. Mean follow-up was 4.5 years. Pain intensity was monitored using VAS. Radiographic assessment consisted of lateral cervical radiographs in neutral and dynamic views, MR and CT of the cervical spine. The AADI, PADI, AAA, sub-axial cervical Cobb angle and canal-clivus angle (CCA) were measured pre-operatively and during the follow-up.

RESULTS

Significant malposition was recorded in 4 (3.4%) out of 116 inserted screws. AADI, PADI, AAA and CCA values changed significantly after surgery and remained stable during follow-up. The Cobb C angle value showed no significant change after surgery. There was a significant decrease of the VAS after the surgery. Fusion or a stable situation was achieved in all patients at 2-year follow-up. Pannus regression was observed in the vast majority of patients; only in two cases was rheumatic tissue detected on MR at 2 years post-operatively.

CONCLUSION

C1 lateral mass and C2 trans-pedicular fixation with polyaxial screws followed by an autograft between C1 and C2 lamina allowed, with an acceptable complication rate and favourable clinical results, adequate slip reposition, introduction of optimal sagittal alignment in terms of the final AAA with no radiographic consequences for the sub-axial cervical spine and assurance of long-term stability.

A Retrospective Analysis of Subaxial Subluxation After Atlanto-axial Arthrodesis in Patients With Rheumatoid Arthritis Based on Annual Radiographs Obtained for 5 Years

STUDY DESIGN

Retrospective study.

OBJECTIVE

The purpose of this study was to investigate the incidence of subaxial subluxation (SAS) after atlanto-axial arthrodesis in rheumatoid arthritis (RA) patients using annual radiographs obtained for 5 years and clarify the characteristics of SAS after surgery.

SUMMARY OF BACKGROUND DATA

Rheumatoid SAS has been reported to occur after atlanto-axial arthrodesis. Many authors have noted that excessive correction of the atlanto-axial angle (AAA) results in a decrease in subaxial lordosis, thereby inducing SAS; therefore, we paid special attention to acquiring a suitable AAA in patients with atlanto-axial arthrodesis.

METHODS

Twenty-five patients with AAS treated with surgery were reviewed. In all patients, lateral cervical radiographs were obtained in neutral, maximal flexion, and maximal extension positions every year for 5 years after surgery. We investigated the occurrence and progression of SAS using these annual radiographs.

RESULTS

There were no significant differences between preoperative and postoperative value in AAA and subaxial angle (SAA), respectively. Before surgery, SAS was found in 10 patients. The occurrence and progression of SAS after surgery was found in 12 cases (SAS P+ group). There were no significant differences in age, sex, or the duration of RA between the SAS P+ group and the remaining 13 cases. We also found no differences in the preoperative and postoperative AAA and SAA between the 2 groups.

CONCLUSIONS

Although SAA was maintained after atlanto-axial arthrodesis in RA-AAS patients, 12 of 25 patients (48%) with AAS developed SAS after atlanto-axial fusion. Further surgery was not needed for SAS up to 5 years after the initial surgery. We did not find any relationship between the occurrence of SAS and the AAA and SAA before and after surgery. Therefore, our findings suggest that proper reduction of AAA in patients with atlanto-axial arthrodesis does not affect the occurrence of SAS at 5 years after surgery.

Utility of the clivo-axial angle in assessing brainstem deformity: pilot study and literature review

There is growing recognition of the kyphotic clivo-axial angle (CXA) as an index of risk of brainstem deformity and craniocervical instability. This review of literature and prospective pilot study is the first to address the potential correlation between correction of the pathological CXA and postoperative clinical outcome. The CXA is a useful sentinel to alert the radiologist and surgeon to the possibility of brainstem deformity or instability. Ten adult subjects with ventral brainstem compression, radiographically manifest as a kyphotic CXA, underwent correction of deformity (normalization of the CXA) prior to fusion and occipito-cervical stabilization. The subjects were assessed preoperatively and at one, three, six, and twelve months after surgery, using established clinical metrics: the visual analog pain scale (VAS), American Spinal InjuryAssociation Impairment Scale (ASIA), Oswestry Neck Disability Index, SF 36, and Karnofsky Index. Parametric and non-parametric statistical tests were performed to correlate clinical outcome with CXA. No major complications were observed. Two patients showed pedicle screws adjacent to but not deforming the vertebral artery on post-operative CT scan. All clinical metrics showed statistically significant improvement. Mean CXA was normalized from 135.8° to 163.7°. Correction of abnormal CXA correlated with statistically significant clinical improvement in this cohort of patients. The study supports the thesis that the CXA maybe an important metric for predicting the risk of brainstem and upper spinal cord deformation. Further study is feasible and warranted.

Adjacent-level failures after occipito-thoracic fusion for rheumatoid cervical disorders

INTRODUCTION

The natural history of cervical spine lesions in rheumatoid arthritis (RA) is variable. We have actively performed occipito-thoracic fusion for severe destructive rheumatoid cervical disorders and reported its clinical results and complications. In our previous study, the most frequent complication was the adjacent-level failures caused by the fragile spine. The objective of this study was to determine risk factors for adjacent-level failures after occipito-thoracic fusion.

MATERIALS AND METHODS

Subjects were 35 RA patients (31 females and 4 males) who underwent occipito-thoracic fusion using RRS Loop Spinal System(®) (Robert Reid Inc. Tokyo, Japan), and the incidence and characteristics of adjacent-level failures were investigated. Furthermore, the adjacent-level failures were divided into two types according to their levels, fracture at the lowest level of the fusion area and that at the level inferior to the fusion area, and the characteristics of each type were evaluated.

RESULTS AND CONCLUSION

Nine (26%) of 35 patients suffered adjacent-level failures (10 vertebral fractures). Adjacent-level failures occurred when the distance of fixation was "O-T4" or longer. The long fusion might cause adjacent-level failures due to greater mechanical stress. Seven fractures occurred at the lowest level of the fusion area, and all of them were cured without symptoms by conservative treatment. Three fractures occurred at the level inferior to the fusion area, and one of them needed additional surgery due to sudden paraplegia resulting from collapse of the adjacent vertebra. After occipito-thoracic fusion, burst fractures at the level inferior to the fusion area might cause sudden paraplegia, and therefore a careful observation should be required for patients with these fractures.