1.Efficacy of Y type osteotomy in the treatment of severe post-tuberculous thoracolumbar kyphosis
Mamat MARDAN ; Abliz YAKUP ; Tao XU ; Chuanhui XUN ; Samat XIRALI ; Jian ZHANG ; Rui CAO ; Qiang DENG ; Weidong LIANG ; Weibing SHENG
Chinese Journal of Orthopaedics 2021;41(2):84-91
Objective:To explore the clinical efficacy and surgical indications of Y type osteotomy in the treatment of post-tuberculous thoracolumbar severe angular kyphosis.Methods:From March 2012 to June 2018, 36 patients with post-tuberculous thoracolumbar severe angular kyphosis were treated with Y type osteotomy, including 22 males and 14 females, aged 23.6±5.7 years (range, 7-57 years). The parietal vertebrae of kyphosis were located in the upper thoracic vertebra in 3 cases, the thoracic vertebra in 11 cases, the thoracolumbar segment in 17 cases, and the lumbar vertebra in 5 cases. The Cobb angle of kyphosis before the operation was 92.8°±23.3° (range, 60°-147°). The visual analogue scale (VAS), American Spinal Injury Association (ASIA) neurological function grade, and Kirkaldy-Willis function score were used to evaluate the clinical effect. The imaging evaluation indexes were interbody kyphosis angle and spinal bone fusion.Results:The operation was successful in all the 36 patients. The operation time was 210 ±25.9 min (range, 180-270 min), the intraoperative blood loss was 520 ±110 ml (range, 400-800 ml), and the postoperative follow-up time was 26.38±1.75 months (range, 22-30 months). The postoperative kyphosis Cobb angle was corrected to 16.5°±7.7° (range, 5°-35°), which was significantly improved compared with that before operation( t=25.438, P<0.01), and the correction rate was 82.2%. At the last follow-up, the kyphosis angle was 16.5°±7.1° (range, 6°-32°), which was not significantly different from that after the operation. The preoperative VAS score was 7.3±1.8 (range, 3-9), and the postoperative VAS score was 2.4±0.8 (range, 1-3), while the improvement rate was 67.1%. At the last follow-up, it was 1.1±0.6 (range, 0-2), and the improvement rate was 85.0%. According to the Kirkaldy-Willis functional score, the results were excellent in 25 cases, good in 8 cases, and fair in 3 cases at the last follow-up, with an excellent and good rate of 91.7%. Before the operation, 9 cases were accompanied by neurological dysfunction (ASIA grade: grade C in 2 cases, grade D in 7 cases). At the last follow-up, all the 9 patients recovered to grade E. During the operation, the electrophysiological nerve monitoring was abnormal in 2 patients, and the awakening test was negative in 1 case. In another patient, neuroelectrophysiological monitoring after posterior column osteotomy showed a decrease in bilateral sensory and motor function. There was no compression around the spinal cord in the osteotomy area, so the operating bed was gradually folded and partially restored to kyphosis and temporarily fixed with double rods. Neuroelectrophysiological monitoring suggested the recovery of nerve function. The awakening test showed that the nerve function of both lower limbs recovered close to the preoperative state, and further osteotomy and internal fixation was performed 2 weeks later. The nerve function of both lower limbs returned to normal after 3 months. After the operation, one patient's muscle strength of the lower limbs decreased from grade 5 to grade 3, and the sensory function was normal. After symptomatic support treatment such as neurotrophic drugs, it returned to normal 2 weeks later. 1 case developed delayed neurological dysfunction 1 year after the operation. Neurotrophic drugs and rehabilitation treatment improved it. The sinus of the incision was formed in one case 3 months after the operation and healed after debridement and suture. Conclusion:Y typeosteotomyis a safe and effective method for patients with post-tuberculous thoracolumbar severe angular kyphosis. Compared with traditional osteotomy, anterior support bone grafting can be avoided, and spinal shortening can be reduced.
2. Treatment of non-curable severe tuberculous thoracolumbar kyphosis by posterior deformity correction combined with anterior supporting bone graft
Mahmut MARDAN ; Abliz YAKUP ; Tao XU ; Mamat MARDAN ; Jianwei WANG ; Samat XIRALI ; Yang ZHOU ; Weibing SHENG
Chinese Journal of Orthopaedics 2019;39(12):727-736
Objective:
To explore the clinical effect of posterior deformity correction combined with anterior lesion re-moval and bone graft in the treatment of non-curable severe tuberculous thoracolumbar kyphosis.
Methods:
All of 27 patients with non-curable severe tuberculous thoracolumbar kyphosis treated by posterior deformity correction combined with primary or secondary anterior debridement and bone grafting from January 2013 to July 2017 were retrospective analyzed, including 10 males and 17 females. The age ranged from 2 to 38 years with an average of 17.3±9.9 years. Posterior column osteotomy, spinal cord de-compression, cantilever bar pressing technique and intraoperative longitudinal traction were used to correct kyphosis. According to clinical symptoms, Cobb angle correction rate of kyphosis deformity, sagittal SVA of spine, height difference before and after opera-tion, operation time, intraoperative bleeding volume, complications, and the effect of the operation was evaluated. Symptoms and functional evaluation indicators included visual analogue scale (VAS), American Spinal Injury Association (ASIA) spinal cord inju-ry classification, Oswestry dysfunction index (ODI), and Kirkaldy-Willis functional score. Laboratory tests included erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Eck fusion grading standard was used to evaluate the degree of bone graft fusion.
Results:
All the 27 patients successfully underwent the operation. The operation time was 210-530 minutes, with an aver-age of 343.0±71.5 minutes, while the bleeding volume was 300-2 600 ml, with an average of 1 168.5±606.7 ml. The preoperative Cobb angle ranged from 81 to 144 degrees, with an average of 105.2±17.7 degrees; the postoperative Cobb angle ranged from 5 to 47 degrees, with an average of 28.2±0.3 degrees, and the average correction rate was 72.9%±9.8%; the preoperative sagittal SVA ranged from 96.66 mm to 78.76 mm, with an average of 40.5±20.4 mm; and the postoperative sagittal SVA ranged from 33.61 mm to 44.96 mm, with an average of 26.6±12.6 mm. The height difference before and after operation was 26.8-172.7 mm, with an aver-age of 67.5±37.8 mm. The follow-up period ranged from 12 to 36 months, with an average of 19.3±6.7 months. At the last follow-up, the loss of Cobb angle ranged from 1 degree to 8 degree, with an average of 4.3°±1.8° degree. The postoperative nutritional sta-tus of all patients was significantly improved. At 3 months after operation, the average VAS score was 1.1±0.6 and the improve-ment rate was 47.5%. The difference was statistically significant (
3.Evaluation of related parameters and risk factors of shoulder balance in adolescent idiopathic scoliosis
Chinese Journal of Orthopaedics 2020;40(14):953-961
Adolescent idiopathic scoliosis (AIS) is one of the most common spinal deformities. Postoperative shoulder imbalance (PSI) is one of the issues that doctors and patients focus on, and it is also the focus of current research. At present, there is no unified consensus on the definition of shoulder balance in patients with AIS, which leads to different standards set in some studies, and the final conclusion may be the opposite. Now, most studies define shoulder imbalance as radiographic shoulder height (RSH)>10 mm, coracoid height difference (CHD)>9 mm, clavicle angle (CA)>2°or clavicle tilt angle difference (CTAD)>4.5°. In order to better describe the shoulder balance, scholars have proposed a lot of imaging parameters, in addition, aesthetic parameters have also been introduced into the study of shoulder balance. However, the two parameters have their own limitations, no single parameter can truly and accurately reflect the shoulder balance of patients. Although the evaluation results of aesthetic parameters are more real, they are the most easily obtained in clinic, and imaging parameters are the most widely used. Then, the correlation between imaging parameters and aesthetic parameters is not high, imaging parameters can not be used to completely replace aesthetic parameters. The risk factors of PSI are Risser sign grade, proximal wedge angle (PWA) size, postoperative proximal thoracic curve (PTC)/main thoracic curve (MTC) ratio, preoperative CA size or T1 tilt angle, PTC stiffness, MTC correction rate, upper instrumented vertebrae (UIV) selection and so on, but they are not independent risk factors. Recently, CCAD has been considered as a good predictor, but it has not been reported in other types of AIS except in patients with Lenke type 1 and 5. In the past, the most research on the preventive measures of PSI is the choice of upper fixation of vertebral body (UIV). Recently, it has been found that the degree of correction of deformity has an important effect on shoulder balance after operation. This article reviews the current research status of shoulder balance in adolescent idiopathic scoliosis, in order to provide ideas for further study of shoulder balance in adolescent idiopathic scoliosis.
4.Effect of proximal thoracic curve and main thoracic curve correction rate on postoperative shoulder balance in Lenke 1 adolescent idiopathic scoliosis
Samat XIRALI· ; Abliz YAKUP· ; Tao XU ; Abudurexiti MAIMAITIAILI· ; Yang ZHOU ; Kiram ERXAT· ; Ting WANG ; Mamat MARDAN· ; Weibing SHENG
Chinese Journal of Orthopaedics 2021;41(13):892-902
Objective:To investigate the effects of the correction rate of the proximal thoracic curve and main thoracic curve on postoperative shoulder balance in patients with Lenke1 type idiopathic scoliosis (AIS).Methods:Data of 50 patients with AIS who received posterior spinal deformity correction surgery from January 2013 to January 2020 and were followed up for more than 6 months were retrospectively analyzed, including 12 males and 38 females. The median age was 15 years (14,16) years (range 13 to 18 years). According to the clavicle angle (CA) absolute value >2° and 2.5° and 3° for shoulder imbalances standard, the patients were divided into the postoperative shoulder balance group and shoulder imbalance group. Main thoracic curve Cobb angle, proximal thoracic curve Cobb angle and clavicle angle (CA) were measured preoperative, postoperative and at the last follow-up, and the flexibility of proximal thoracic curve, the flexibility of main thoracic curve, correction rate of proximal thoracic curve, correction rate of the main thoracic curve and other indicators were calculated. Univariate analysis was conducted on the shoulder balance group's related indicators and the shoulder imbalance group, and correlation analysis was conducted with the postoperative shoulder balance and the last follow-up shoulder balance. Multivariate binary logistic regression was performed on statistically significant univariate factors to determine independent risk factors for postoperative shoulder imbalance and the last follow-up shoulder imbalance.Results:The median follow-up time of 50 patients was 18 months (11, 24) months (range 6-36 months). According to the three criteria of shoulder balance, the postoperative correction rate of the proximal thoracic curve in the shoulder imbalance group was significantly lower than that in the shoulder balance group. Under the standard of shoulder imbalance with CA absolute value >2° and 2.5°, there were significant differences in the postoperative correction rate of the main thoracic curve, and the postoperative correction rate of the main thoracic curve in the shoulder balance group was higher than that in the shoulder imbalance group. No matter which shoulder imbalance criteria were used, the postoperative correction rate of the proximal thoracic curve, the correction rate of the main thoracic curve, and the ratio of the correction rate of the main thoracic curve to the proximal thoracic curve was found to be correlated with the postoperative shoulder balance. Only in the group of CA absolute >3°, no correlation was found between the postoperative correction rate of the main thoracic curve and postoperative shoulder balance. The correlation between the correction rate of the proximal thoracic curve and shoulder balance was more significant in the three groups ( P<0.01). Logistic regression analysis showed that the postoperative correction rate of the proximal thoracic curve was an independent protective factor of postoperative shoulder balance ( P<0.05). A better postoperative shoulder balance can be obtained when the main thoracic curve/proximal thoracic curve correction rate was less than 1.5. However, at the last follow-up, no correlation was found between the correction rate and shoulder balance in all three groups. Binary logistic regression analysis showed that preoperative CA was a risk factor for the last follow-up shoulder imbalance. Conclusion:IIn patients with Lenke1 type AIS, the correction rate of the proximal thoracic curve, the correction rate of the main thoracic curve, and their ratio were correlated with postoperative shoulder balance. The matching of the amount of correction of the proximal thoracic curve and main thoracic curve can ensure postoperative shoulder balance, and the amount of correction of the proximal thoracic curve may be a protective factor of postoperative shoulder balance. However, for long-term shoulder balance, the effect of the proximal thoracic curve and main thoracic curve correction rate is not obvious. In contrast, compensatory factors such as proximal thoracic cure aggravation, torso tilt, and lumbar curve aggravation mayaffect.
5.Research progress of Chiari malformation type I and atlantoaxial instability
Kerem ERXAT· ; Mardan MURADIL· ; Abliz YAKUP· ; Samat XIRALI· ; Chuanhui XUN ; Tao XU ; Weibin SHENG ; Mamat MARDAN·
Chinese Journal of Orthopaedics 2023;43(7):458-464
Chiari malformation (CM) is a group of congenital cerebellar tonsillar hernia malformations involving the craniocervical junction. Chiari malformation type I (CMI) is the most common in clinic, however its pathogenesis is still unclear, and there is no consensus on the surgical treatment standard of CMI. At present, the most widely accepted is the theory of posterior fossa incompatibility, so doctors at home and abroad use posterior fossa decompression (PFD) and posterior fossa compression with duraplasty (PFDD) as the gold standard for surgical treatment, and have their own experience and technical improvement. However, the volume of the posterior cranial fossa in some patients is no different from that in healthy people, and about 30% of the patients with CMI have poor results after posterior cranial fossa decompression. As a result, this operation cannot treat all patients with CMI. In recent years, with the development of imaging, the progress of diagnostic technology and the deepening of understanding of CM, some studies have shown that CMI may be related to atlantoaxial instability, and proposed that CMI is the secondary factor of atlantoaxial instability, and atlantoaxial fusion is the standard of surgical treatment, which has caused great controversy in academic circles. Different clinical research results of scholars support or oppose this theory: some studies have shown that the clinical symptom relief rate of patients with CMI treated with atlantoaxial fusion is 96.9%; another study showed that 70% of patients with CMI underwent atlantoaxial fusion had improved neurological function, but the overall postoperative effect was not satisfactory. In short, CMI is related to many diseases and its clinical manifestations are complex. Therefore, individualized management and treatment should be carried out in combination with the clinical manifestations and auxiliary examination results of patients.
6.Unilateral or bilateral posterior fenestration debridement and bone graft fusion for the treatment of lumbosacral brucellosis spondylitis
Mamat MARDAN· ; Fengzhou BAI ; Mardan MURADIL· ; Tao XU ; Abliz YAKUP· ; Mollawudon ZULIYAR· ; Samat XIRALI· ; Kerem ERXAT· ; Weidong LIANG ; Chuanhui XUN ; Jian ZHANG ; Rui CAO ; Qiang DENG ; Weibin SHENG
Chinese Journal of Orthopaedics 2021;41(20):1459-1466
Objective:To analyze the application and clinical efficacy of one-stage unilateral or bilateral fenestration, debridement, interbody fusion combined with posterior internal fixation for the treatment of lumbosacral brucellosis spondylitis.Methods:All patients with lumbosacral brucellosis spondylitis were retrospectively analyzed, who underwent fenestration, debridement, interbody fusion combined with posterior internal fixation from June 2013 to June 2019. A total of 48 patients were enrolled in this study. According to the surgical method, they were divided into two groups. Unilateral fenestration group: 27 cases of one-stage posterior unilateral fenestration, debridement, interbody fusion combined with posterior internal fixation were performed, 21 males and 6 females, aged 23-71 years; Bilateral fenestration group: 21 cases of one-stage posterior bilateral fenestration, debridement, interbody fusion combined with posterior internal fixation were performed, aged 26-58 years. There were 16 males and 5 females. The preoperative and postoperative clinical symptoms, neurological function, C-reactive protein, the surgery duration time, the blood loss, and erythrocyte sedimentation rate were observed. The internal fixation device was evaluated for looseness or fracture by imaging examination. The Bridwell classification criteria were used to evaluate the bone graft fusion. Postoperative complications were also assessed.Results:All patients completed the operation successfully, and the diseased tissues were sent for pathological examination during the operation, and all of them were diagnosed as brucellosis. All patients were followed up for 12-48 months (mean 23.7 ±6.3 months). C-reactive protein, erythrocyte sedimentation rate, Visual Analogue Scale (VAS), Oswestry Disability Index (ODI) and Japanese Orthopaedic Association Scores (JOA) were significantly improved in both groups at different time points after operation. There was no significant difference in the general condition before operation between the two groups ( P>0.05). The mean operation time and mean blood loss were 120.5±34.1 min and 214.4±150.2 ml, in the unilateral fenestration group; 187.1±30.3 min and 455.8±250.5 ml in the bilateral fenestration group; and the difference was significant ( t=8.123, t=2.962, P<0.05) . The postoperative lumbar and leg pain were significantly relieved. There was no significant difference in C-reactive protein, erythrocyte sedimentation rate, VAS, ODI and JOA scores between the two groups at the same time point. In the bilateral fenestration group, one patient developed incision infection half a month after the operation, who underwent debridement and drainage, and finally cured. There was no significant difference in the time of bone graft fusion between the two groups ( t=0.542, P>0.05). At the last follow-up, all the patients were completely fused. Conclusion:Unilateral or bilateral fenestration, debridement and bone graft fusion and internal fixation for the treatment of lumbosacral brucellosis spondylitis can achieve good clinical results, and the former has the advantages of short operation time and low cost.
7.Comparative study of native vertebral osteomyelitis and pyogenic postoperative and analysis of prognostic factors
Abudurexiti MAIMAITIAILI· ; Mardan MURADIL· ; Kelimu HUERXIDAN· ; Feihua YAN ; Maihesumu BAWUDONG· ; Abliz YAKUP· ; Samat XIRALI· ; Yang ZHOU ; Tao XU ; Mamat MARDAN· ; Weibing SHENG
Chinese Journal of Orthopaedics 2022;42(15):950-960
Objective:To compare the microbiology, clinical characteristics and therapeutic efficacy of native suppurative spondylitis (NVO) and postoperative suppurative spondylitis (PVO), and analyze the factors affecting the prognosis.Methods:All patients with suppurative spondylitis were retrospectively analyzed from December 2010 to December 2019. A total of 46 patients were enrolled in this study. They were divided into two groups. There were 30 cases in NVO group, 18 males and 12 females; The age was 50.47±20.45 years, aged 15-73 years. There were 16 cases in PVO group, 10 males and 6 females; The age was 52.13±18.80 years, aged 14-73 years. In group NVO, 23 cases (76.7%) were in lumbar vertebrae, 5 cases (16.7%) in thoracic vertebrae and 2 cases (6.7%) in cervical vertebrae; in group PVO, 11 cases (68.8%) in lumbar vertebrae and 5 cases (31.2%) in thoracic vertebrae. Twenty-eight patients had neurological dysfunction before surgery. There were 25 cases of grade D (16 cases in group NVO and 9 cases in group PVO) and 3 cases of grade C (1 case in group NVO and 2 cases in group PVO), following the instructions of American Spinal Injury Association (ASIA) neurological function classification. All patients were given bed rest, nutritional support and antibiotic therapy; surgical treatment for patients with poor outcomes or aggravated symptoms. The patients were followed up after operation, the observation indexes included leukocyte count, erythrocyte sedimentation rate and C -reactive protein to evaluate the postoperative curative effect. The internal fixation device was evaluated for looseness and fracture by imaging examination. At the same time, the changes of visual analogue scale, ASIA neurological function grade were recorded to evaluate the clinical efficacy.Results:Two patients in NVO group were treated with antibiotics, and all the other patients successfully completed the operation. The diseased tissues were sent for pathological examination during the operation. The results showed that they were diagnosed as suppurative spondylitis. All patients were followed up for 12-24 months. Both groups were treated with intravenous and oral antibiotics, and the time of antibiotic treatment in group PVO was longer than that in group NVO without significant difference ( t=1.74, P=0.088). The leukocyte, C-reactive protein, erythrocyte sedimentation rate, visual analogue scale (VAS), were significantly improved in both groups at different time points after operation ( P<0.05) . There was no significant difference in leukocyte, C -reactive protein, erythrocyte sedimentation rate or VAS score between the two groups at the same time point after operation ( P>0.05). The neurological function of patients after operation was significantly improved compared with that before operation. In group NVO, 16 cases recovered from ASIA grade D to grade E, 1 case from grade C to grade D; 9 cases in group PVO recovered from grade D to grade E and 2 cases recovered from grade C to grade D. Till the last follow-up, 3 patients in group NVO recurred, the recurrence rate was 10% (3/30); 7 patients in group PVO recurred, the recurrence rate was 43.8%; the recurrence rate of group PVO was higher than that of group NVO, the difference was statistically significant (χ 2=5.14, P=0.023). Among 39 patients with spinal internal fixation, 12.8% (1 NVO, 4 PVO) had recurrent infection after internal fixation. Therefore, re-operation was performed to remove the internal fixator for infection control, patients recovered after conservative treatment such as immobilization and systemic anti-infection By univariate analysis, multiple vertebral involvement and abscess formation ( OR=11.00, P=0.006; OR=9.00, P=0.047) were significantly associated with pyogenic spondylitis recurrence; there was a tendency for pyogenic spondylitis recurrence among microbial infection ( OR=1.87, P=0.416), spinal prosthesis ( OR=7.20, P=0.074) and allogenic bone ( OR=1.78, P=0.478), yet not obvious. Multivariate analysis indicated that multiple vertebral involvement ( OR=10.49, P=0.038) was a risk factor for pyogenic spondylitis recurrence. Conclusion:The treatment of PVO is more challenging than NVO, especially in the cases of spinal implant infection. Although the antibiotic treatment time of PVO is longer than that of NVO, the recurrence rate of PVO is higher. Longer antibiotic therapy and, if necessary, surgical debridement or removal of implants are important approaches to successful treatment of PVO.
8.Imaging study of simple Chiari malformation type I and atlantoaxial instability
·Kerem ERXAT ; ·Mardan MURADIL ; ·Samat XIRALI ; ·Abliz YAKUP ; Tao XU ; Xiaoyu CAI ; Chuanhui XUN ; ·Matruze MAMATAKBAR ; Shihao GU ; Weibin SHENG ; ·Mamat MARDAN
Chinese Journal of Orthopaedics 2022;42(23):1579-1587
Objective:To investigate the relationship between simple Chiari malformation type I (CMI) and atlantoaxial instability from the imaging point of view.Methods:A retrospective analysis were performed on 46 patients diagnosed with simple CMI from January 2014 to December 2020. Forty-six normal people matched for age and sex were selected as the normal control group, while 30 patients with atlantoaxial dislocation were selected as the dislocation group. The degree of atlantoaxial joint degeneration in each group was assessed according to Weishaupt degeneration grading; the atlantoaxial joint angulation angle was measured in the control group of patients with simple CMI; and the sagittal imaging parameters of cervical spine X-ray were measured, including C 0-C 1 Cobb angle, C 0-C 2 Cobb angle, C 1-C 2 Cobb angle, C 1-C 7 Cobb angle, C 2-C 7 Cobb angle, C 7 Slope, C 2 Tilt, spino cranial angle (SCA), and C 2-C 7 sagittal vertebral axis (SVA). All radiographic parameters were measured twice independently by two spine surgeons, and intraclass correlation coefficient (ICC) were determined to demonstrate intra- and inter-observer reliability. Results:ICC ranged between 0.842 and 0.974 in the current study, demonstrating "excellent" reliability of radiographic measurements. No significant difference was noted regarding age and the distribution of genders among the three groups. There were significant differences in the distribution of Weishaupt degeneration grading of atlantoaxial joints between simple CMI, normal and dislocation group ( H=53.68, P<0.001 on the left side; H=43.39, P<0.001 on the right side). There were significant differences in the degree of atlantoaxial joint degeneration between the normal group and dislocation group (left, Z=6.60, P<0.001; right, Z=6.29, P<0.001); There were significant differences in the degree of atlantoaxial joint degeneration between the normal group and simple CMI patients (left, Z=5.31, P<0.001; right, Z=4.13, P<0.001); There were significant differences in the degree of atlantoaxial joint degeneration between simple CMI and dislocation group (left, Z=3.20, P=0.001; right, Z=3.15, P=0.002). There were significant difference in the angulation angle of the atlantoaxial articular surface between the normal group and simple CMI patients (left, Z=3.32, P<0.001; right, Z=5.74, P<0.001). There were significant differences in C 0-C 1 Cobb angle ( t=2.41, P=0.018), C 1-C 7 Cobb angle ( t=2.88, P=0.005), C 2-C 7 Cobb angle ( t=3.29, P=0.001), and C 2-C 7 SVA ( t=2.87, P=0.005) between the normal group and simple CMI patients, but there was no significant difference in other parameters. Conclusion:The degree of atlantoaxial joint degeneration in patients with simple CMI is higher than that in normal people, the angulation angle is larger, and the cervical lordosis is larger, suggesting that there may be atlantoaxial joint instability. This study provides further evidence that Chiari malformation type I is associated with atlantoaxial instability.