Geoffrey N. Askin

Variability in Cobb angle measurements using reformatted computerized tomography scans.

Study Design. Survey of intraobserver and interobserver measurement variability. Objective. To assess the use of reformatted computerized tomography (CT) images for manual measurement of coronal Cobb angles in idiopathic scoliosis. Summary of Background Data. Cobb angle measurements in idiopathic scoliosis are traditionally made from standing radiographs, whereas CT is often used for assessment of vertebral rotation. Correlating Cobb angles from standing radiographs with vertebral rotations from supine CT is problematic because the geometry of the spine changes significantly from standing to supine positions, and 2 different imaging methods are involved. Methods. We assessed the use of reformatted thoracolumbar CT images for Cobb angle measurement. Preoperative CT of 12 patients with idiopathic scoliosis were used to generate reformatted coronal images. Five observers measured coronal Cobb angles on 3 occasions from each of the images. Intraobserver and interobserver variability associated with Cobb measurement from reformatted CT scans was assessed and compared with previous studies of measurement variability using plain radiographs. Results. For major curves, 95% confidence intervals for intraobserver and interobserver variability were ±6.6° and ±7.7°, respectively. For minor curves, the intervals were ±7.5° and ±8.2°, respectively. Intraobserver and interobserver technical error of measurement was 2.4° and 2.7°, with reliability coefficients of 88% and 84%, respectively. There was no correlation between measurement variability and curve severity. Conclusions. Reformatted CT images may be used for manual measurement of coronal Cobb angles in idiopathic scoliosis with similar variability to manual measurement of plain radiographs.

The outcome of scoliosis surgery in the severely physically handicapped child. An objective and subjective assessment.

Study Design A prospective, functional assessment based on physical ability and independence in daily activities was performed of patients who had severe physical handicaps and spinal deformities and were undergoing scoliosis surgery. Objectives To determine whether improving spinal alignment and truncal balance improved the functional abilities of handicapped patients. Summary of Background Data Loss of truncal stability compromises the physical independence of children who are severely handicapped. Physiologic function also may be compromised. It is not clear whether improving truncal balance actually improves their level of independence or merely halts further deterioration. Methods Twenty patients with significant physical handicaps resulting from neuromuscular disorders or multiple congenital anomalies and significant spinal deformity and truncal imbalance were treated surgically to realign and stabilize their spines. Their level of physical independence was evaluated before surgery, including their ability to sit, ambulate, and complete activities of daily living. Evaluation was done before surgery, 6 months after surgery, and 12 months after surgery. A subjective assessment of cosmesis also was made. Results Corrective spinal surgery resulted in a deterioration of physical ability for the first 6 months. Most patients subsequently returned to their preoperative level of function. An improvement of function exceeding their preoperative level was not seen after 12 months. The cosmetic results of surgery were excellent. Conclusions Corrective spinal surgery in patients with severe physical handicap should be performed early to preserve function and should not be dictated solely by the severity of the curvature. Improvement in the patients level of independence may not necessarily occur after truncal stabilization. Cosmetic results in these patients with severe disabilities were extremely gratifying to the patients and their caregivers.

Recovery of pulmonary function following endoscopic anterior scoliosis correction: Evaluation at 3, 6, 12, and 24 months after surgery

Study Design. A series of patients with scoliosis undergoing endoscopic anterior instrumentation and fusion undertaking repeated pulmonary function assessments. Objective. To assess recovery of pulmonary function in the 2 years following endoscopic anterior scoliosis correction. Summary of Background Data. Recent studies have found that pulmonary function returns to preoperative levels 12–24 months following endoscopic anterior scoliosis correction, and a small improvement in forced expiratory volume (FEV1) has also been reported. Methods. A series of 44 patients with endoscopic anterior scoliosis correction had pulmonary function tests before surgery, and at 3, 6, 12, and 24 months after surgery. Forced vital capacity (FVC), FEV1, and total lung capacity (TLC) were measured. Nonparametric statistical analysis was used to investigate changes in pulmonary function between successive assessments. Results. Pulmonary function decreased by approximately 10% at 3 months after surgery. At 24 months after surgery, FVC and FEV1 recovered to 5% to 8% higher than preoperative levels, while TLC returned to preoperative levels. Statistically significant improvements in most pulmonary function values occurred between 3 and 6, and 6–12 months. Improvements in mean FVC, FEV1, and TLC continue between 12 and 24 months, although only the increase in absolute FVC for this time is statistically significant. Conclusions. Endoscopic anterior scoliosis surgery has no lasting negative effect on pulmonary function, and with prolonged follow-up, pulmonary capacity improves beyond preoperative levels.

Automatic measurement of vertebral rotation in idiopathic scoliosis.

Study Design. Development of an automatic measurement algorithm and comparison with manual measurement methods. Objectives. To develop a new computer-based method for automatic measurement of vertebral rotation in idiopathic scoliosis from computed tomography images and to compare the automatic method with two manual measurement techniques. Summary of Background Data. Techniques have been developed for vertebral rotation measurement in idiopathic scoliosis using plain radiographs, computed tomography, or magnetic resonance images. All of these techniques require manual selection of landmark points and are therefore subject to interobserver and intraobserver error. Methods. We developed a new method for automatic measurement of vertebral rotation in idiopathic scoliosis using a symmetry ratio algorithm. The automatic method provided values comparable with Aaro and Ho’s manual measurement methods for a set of 19 transverse computed tomography slices through apical vertebrae, and with Aaro’s method for a set of 204 reformatted computed tomography images through vertebral endplates. Results. Confidence intervals (95%) for intraobserver and interobserver variability using manual methods were in the range 5.5° to 7.2°. The mean (±SD) difference between automatic and manual rotation measurements for the 19 apical images was −0.5° ± 3.3° for Aaro’s method and 0.7° ± 3.4° for Ho’s method. The mean (±SD) difference between automatic and manual rotation measurements for the 204 endplate images was 0.25° ± 3.8°. Conclusions. The symmetry ratio algorithm allows automatic measurement of vertebral rotation in idiopathic scoliosis without intraobserver or interobserver error due to landmark point selection.

Perioperative aspects of endoscopic anterior scoliosis surgery: The learning curve for a consecutive series of 100 patients

The reported benefits of endoscopic versus open scoliosis surgery include improved visualization, a muscle sparing approach, reduced pulmonary morbidity, reduced pain, and improved cosmesis. Some aspects of the surgical learning curve for this technically demanding method have been previously reported; however, improvements in other factors with increasing experience have not been quantified. This paper presents a series of 100 consecutive endoscopic anterior scoliosis corrections performed between April 2000 and February 2006. We report changes in the following perioperative factors with increasing experience; operative set-up time, operative time, x-ray irradiation time, number of instrumented levels, blood loss, intercostal catheter drainage, chest drain removal time, days in intensive care, days to mobilize, days in hospital, and early complications. Statistical comparisons were made between the first 20 (1 to 20), middle 20 (41 to 60), and last 20 (81 to 100) cases. Results showed statistically significant improvements and increased consistency in operative time, operative set-up time, x-ray irradiation time, blood loss, hospital stay, and mobilization time with experience. The complication rate was comparable to other recently published endoscopic studies. In the last 20 cases of the series, operative times had reduced to 35 minutes per level, x-ray irradiation times to 15 seconds per level, and blood loss to 38 mL per level. Most perioperative surgical factors therefore improve significantly with increasing experience in endoscopic anterior scoliosis correction.

The jigsaw sign. A reliable indicator of congenital aetiology in os odontoideum

There is evidence in the literature for both a congenital and a post-traumatic aetiology for os odontoideum. In no series published to date has CT been used to aid in the diagnosis. This is a prospective study of the history of trauma and presence of diagnostic features on CT of 18 consecutive cases with os odontoideum. Our objective was to derive clinically useful radiological features enabling accurate differentiation between congenital and post-traumatic aetiologies. A mid-sagittal CT reconstruction of the atlanto-dens joint was obtained. Hypertrophy of the anterior arch of the atlas was quantified by measurement of the arch-peg-area ratio. The presence of dysplastic features (a positive “jigsaw” sign) of the atlanto-axial joint were noted. These included narrowing of the cartilage space and interdigitation of the two joint surfaces. A history of a potential traumatic aetiology was only obtained in one of the 18 (6%) in our series. A significant elevation of the arch–peg ratio was found when comparing this series to 85 controls. And a positive jigsaw sign was observed in 75% of cases. These features were not seen in paediatric cases of atlanto-axial instability, including odontoid non-union. In conclusion, an elevated arch–peg ratio and the presence of a jigsaw sign are sensitive and specific diagnostic criteria for os odontoideum. This series supports a congenital aetiology for this condition.

A Prospective Assessment of SRS-24 Scores After Endoscopic Anterior Instrumentation for Scoliosis

Study Design. Prospective clinical case series. Objective. To evaluate the clinical outcome of anterior endoscopic instrumention for scoliosis using the SRS-24 questionnaire and to examine how these scores change over a 2-year follow-up period. Summary of Background Data. Anterior endoscopic instrumentation correction has several advantages compared with open procedures. However, the clinical results of this technique using a validated outcome measure have rarely been reported in the literature. Methods. A total of 83 consecutive patients underwent endoscopic anterior instrumentation performed at a single unit. Patients completed the SRS-24 questionnaire before surgery and at 3, 6, 12, and 24 months after surgery. The SRS-24 scores were compared between each of the follow-up intervals. Results. The pain, general self-image, and function from back condition domains improved after surgery (P < 0.05). Activity level significantly improved between 3 and 6 months, and both function domains improved between 6 and 12 months (P < 0.05). None of the domains increased significantly after 1 year. Conclusions. Endoscopic anterior instrumentation for scoliosis significantly improved pain, self-image, and function. The greatest improvement in function occurred between 6 and 12 months after surgery. The SRS-24 scores at 1 year from surgery may provide a good indicator of patient outcome in the long-term.

The Natural History of Scoliosis in Females with Rett Syndrome

Study Design. Population-based longitudinal observational study. Objective. To describe the prevalence of scoliosis in Rett syndrome, structural characteristics and progression, taking into account the influences of age, genotype, and ambulatory status. Summary of Background Data. Scoliosis is the most common orthopedic comorbidity in Rett syndrome yet very little is known about its natural history and influencing factors such as age, genotype, and ambulatory status. Methods. The infrastructure of the Australian Rett Syndrome Database was used to identify all cases with confirmed Rett syndrome in Australia and collect data on genotype and walking status. We identified radiological records and described the Cobb angle of each curve. Time to event analysis was used to estimate the median age of onset of scoliosis and the log-rank test to compare by mutation type. Latent class group analysis was used to identify groups for the trajectory of walking status over time and a multilevel linear model used to assess trajectories of scoliosis development by mutation type and walking status. We used a logistic regression model to estimate the probability of developing a scoliosis with a Cobb angle >60° at 16 years in relation to Cobb angle and walking status at 10 years of age. Results. The median age of scoliosis onset was 11 years with earliest onset in those with a p.Arg255* mutation or large deletion. Scoliosis was progressive for all mutation types except for those with the p.Arg306Cys mutation. Scoliosis progression was reduced when there was capacity to walk independently or with assistance. Cobb angle and walking ability at age 10 can be reliably used to identify those who will develop a very severe scoliosis by age 16. Conclusion. These data on prognosis of scoliosis inform clinical decision making about the likelihood of progression to very severe scoliosis and the need for surgical management. Level of Evidence: 4

The Use of Fulcrum Bending Radiographs in Anterior Thoracic Scoliosis Correction: A Consecutive Series of 90 Patients

Study Design. A prospective, consecutive series of 90 patients receiving fulcrum bending radiographs before endoscopic anterior scoliosis correction. Objective. To assess the effectiveness of fulcrum bending radiographs in predicting correction of the structural curve in anterior scoliosis surgery for a series of 90 consecutive patients. Summary of Background Data. The fulcrum bending radiograph is highly predictive of scoliosis curve correction for posterior instrumented fixation. However, its use has been questioned in relation to anterior scoliosis surgery due to the disc removal in anterior procedures. Methods. Fulcrum bending radiographs were performed before endoscopic anterior scoliosis correction following the protocol of Cheung and Luk. All patients received a single anterior rod and vertebral body screws using a standard compression technique. In all cases, cleared disc spaces were packed with mulched femoral head allograft. Surgical correction was assessed using 6- to 8-week postoperative standing radiographs. Paired t tests and least squares linear regression analysis were used to compare the preoperative major Cobb angle achieved on the fulcrum bending radiograph with the postoperative Cobb angles for each patient. Results. Mean (±SD) major curve correction rate was 60.1% ± 12.4%. Mean instrumented curve correction rate was 63.7% ± 11.7%. Mean fulcrum flexibility was 60.8% ± 15.5%. Mean fulcrum bending correction index was 104%. There was no statistically significant difference between the mean fulcrum bending radiograph Cobb angle (20.4 ± 9°) and the mean postoperative major Cobb angle for the structural curve (20.5 ± 7.1°). Conclusion. The results of this study show that fulcrum bending radiographs are predictive of surgical correction for anterior scoliosis surgery.

Gravity-induced torque and intravertebral rotation in idiopathic scoliosis.

Study Design. Biomechanical analysis. Objective. To investigate the relationship between gravity-induced torques acting on the scoliotic spine and rotation within the vertebrae. Summary of Background Data. Vertebral rotation is an important aspect of spinal deformity in idiopathic scoliosis, associated with ribcage asymmetry. Although both lateral curvature and rotation seem to increase together in progressive scoliosis, the mechanisms driving vertebral rotation are not clearly established and it is not known whether lateral curvature precedes rotation, or vice versa. Methods. Three-dimensional spinal curvature was measured for a small group of idiopathic scoliosis patients using standing radiographs, and equations of static equilibrium were used to calculate gravity-induced torque profiles along the length of each spine because of head, neck, and torso weight. Vertebral rotations were then measured for the same patients using Aaro and Dahlborn’s technique with reformatted computed tomography images. The gravity-induced torque curves were compared with rotation measurements to see whether gravity-induced torque is a likely contributor to intravertebral rotation in scoliosis. Results. Gravity-induced torques as high as 7.5 Nm act on the spines of idiopathic scoliosis patients because of body weight in the standing position, and maximum intravertebral rotations (for a single vertebra) are approximately 4 degrees. There is a statistically significant relationship between gravity-induced torque and intravertebral rotation in the scoliotic spine. Conclusion. Gravity-induced torque is a likely cause of intravertebral rotation in progressive idiopathic scoliosis. Because the spine must be curved in 3-dimensions (out of plane) to produce such torques, vertebral rotation would be expected to occur subsequent to an initial lateral deviation, suggesting that lateral curvature precedes vertebral rotation in progressive idiopathic scoliosis.