Ventral screw osteosynthesis is a common surgical method for treating fractures of the odontoid peg, but there is still no consensus about the number and diameter of the screws to be used. The purpose of this study was to develop a more accurate measurement technique for the morphometry of the odontoid peg (dens axis) and to provide a recommendation for ventral screw osteosynthesis. Images of the cervical spine of 44 Caucasian patients, taken with a 64-line CT scanner, were evaluated using the measuring software MIMICS. All measurements were performed by two independent observers. Intraclass correlation coefficients were used to measure inter-rater variability. The mean length of the odontoid peg was 39.76 mm (. sd. 2.68). The mean screw entry angle α was 59.45° (. sd. 3.45). The mean angle between the screw and the ventral border of C2 was 13.18° (. sd. 2.70), the maximum possible mean converging angle of two screws was 20.35° (. sd. 3.24). The measurements were obtained at the level of 66% of the total odontoid peg length and showed mean values of 8.36 mm (. sd. 0.84) for the inner diameter in the sagittal plane and 7.35 mm (. sd. 0.97) in the coronal plane. The mean outer diameter of the odontoid peg was 12.88 mm (. sd. 0.91) in the sagittal plane and 11.77 mm (. sd. 1.09) in the coronal plane. The results measured at the level of 90% of the total odontoid peg length were a mean of 6.12 mm (. sd. 1.14) for the sagittal inner diameter and 5.50 mm (. sd. 1.05) for the coronal inner diameter. The mean outer diameter of the odontoid peg was 11.10 mm (. sd.  1.0) in the sagittal plane and 10.00 mm (. sd. 1.07) in the coronal plane. In order to calculate the necessary screw length using 3.5 mm cannulated screws, 1.5 mm should be added to the measured odontoid peg length when anatomical reduction seems possible. The cross-section of the odontoid peg is not circular but slightly elliptical, with a 10% greater diameter in the sagittal plane. In the majority of cases (70.5%) the odontoid peg offers enough room for two 3.5 mm cannulated cortical screws. Cite this article: Bone Joint J 2013;95-B:536–42

Introduction. Different subclinical neurological dysfunction has been reported in adolescent idiopathic scoliosis (AIS), including poor postural control and asymmetric otolith vestibulo-ocular responses when compared with normal controls. The objective of this pilot study is to establish whether abnormal MRI morphoanatomical changes arise in the CNS (brain and vestibular system), among left-thoracic versus right-thoracic AIS when compared with normal adolescent controls, with use of advanced computerised statistical morphometry techniques. Methods. We compared nine girls with left-thoracic AIS (mean age 14 years; mean Cobb angle 19°) with 11 matched controls, and 20 girls with right-thoracic AIS (mean age 15 years, mean Cobb angle 33·8°) with 17 matched controls. The statistical brain analysis was done with validated automatic segmentation and voxel-based morphometry (VBM). The T2W-MRI data for shape analysis of the vestibular system were obtained from 20 patients with right-thoracic AIS and 20 matched controls. A best-fit plane and a best-fit circle were calculated to approximate each semicircular canal. The shape of vestibular system was measured by: (1) the angle between each pair of best-fit planes; (2) the length; and (3) angle formed between the corresponding lines connecting the centres of each pair of circles. Statistical analysis was done with one-way ANOVA. Results. Patients with left-thoracic AIS had significantly lower white matter density in corpus callosum, left internal capsule, and white matter underlying orbitofrontal cortex of left hemisphere, which were not observed in patients with right-thoracic AIS. In the right-thoracic AIS group, the distance between centres of lateral and superior canals (p=0·0264) and the angle with vertex at the centre of posterior canal (p=0·02) of left-side vestibular system were significantly smaller than in the control group (figure). For vestibular analysis, there were no data for left-thoracic AIS. Conclusions. Findings from this pilot study have shown significant MRI morphoanatomical difference in CNS between patients with AIS and controls. In the brain analysis, corpus callosum (the principle commissural fibre bundle connecting left and right cerebral hemispheres, which might affect the coordination of left and right sides of the body), differed between left-thoracic and right-thoracic AIS. In the vestibular analysis, geometric morphological difference was detected on the left-side semicircular canals between right-thoracic AIS and healthy controls. These morphological changes are likely to be related to the subclinical postural, vestibular, and proprioceptive dysfunctions. Further association studies and longitudinal studies could help to further define the link between morphological and functional dysfunction, which might have important predictive and prognostic effect on curve development and progression

We undertook a comparative study of magnetic resonance imaging (MRI) vertebral morphometry of thoracic vertebrae of girls with adolescent idiopathic thoracic scoliosis (AIS) and age and gender-matched normal subjects, in order to investigate abnormal differential growth of the anterior and posterior elements of the thoracic vertebrae in patients with scoliosis. Previous studies have suggested that disproportionate growth of the anterior and posterior columns may contribute to the development of AIS. Whole spine MRI was undertaken on 83 girls with AIS between the age of 12 and 14 years, and Cobb’s angles of between 20° and 90°, and 22 age-matched controls. Multiple measurements of each thoracic vertebra were obtained from the best sagittal and axial MRI cuts. Compared with the controls, the scoliotic spines had longer vertebral bodies between T1 and T12 in the anterior column and shorter pedicles with a larger interpedicular distance in the posterior column. The differential growth between the anterior and the posterior elements of each thoracic vertebra in the patients with AIS was significantly different from that in the controls (p < 0.01). There was also a significant positive correlation between the scoliosis severity score and the ratio of differential growth between the anterior and posterior columns for each thoracic vertebra (p < 0.01). Compared with age-matched controls, the longitudinal growth of the vertebral bodies in patients with AIS is disproportionate and faster and mainly occurs by endochondral ossification. In contrast, the circumferential growth by membranous ossification is slower in both the vertebral bodies and pedicles

Objective. To compare the radiological and clinical outcomes following three different techniques used in the correction of Scheuermann's kyphosis. Materials and Methods. Twenty three patients with comparable preoperative radiographic and physical variables (age, gender, height, weight, body mass index) underwent correction of thoracic kyphotic deformity using three different surgical methods. Group A (n=8) had combined anterior and posterior fusion with instrumentation using morselised rib graft. Group B (n=7) had combined anterior and posterior fusion with instrumentation using titanium interbody cages. Group C (n=8) had posterior segmental pedicle screw fixation only. All groups had posterior apical multi-level chevron osteotomy and posterior instrumentation extending from T2 to L2/3. Preoperative and postoperative curve morphometry studied on plain radiographs included Cobb angle, sagittal vertical axis (SVA), sacral inclination (SI) and lumbar lordosis (LL). Preoperative and postoperative questionnaires including ODI, VAS and SRS-22 were also analysed. Results. The average follow-up was 70 months for group A, 66 months for group B and 35 months for group C. For the whole cohort, the preoperative median cobb angle for thoracic Kyphosis was 88.4°, SVA +3.5 centimeters (cms), lumbar lordosis was 66 °, and the median sacral inclination angle was 40°. The average immediate postoperative cobb angle for thoracic kyphosis was 42°, SVA -1.5 cms, lumbar lordosis 45 ° and sacral inclination angle was 30°. At follow-up, the average cobb angle for thoracic kyphosis was 42.0°, SVA +1 cm, lumbar lordosis 42.0 ° and sacral inclination angle was 22.0 °. There was a significant difference between preoperative and postoperative measurements in all three groups, indicating that good correction and satisfaction was achieved. Three patients had distal junctional Kyphosis in early cases. There was no significant difference obtained in the final cobb angle between group A, group B and group C. All three groups retained the postoperative correction with respect to thoracic kyphosis, and changes in ODI and SRS-22 scores were similar in three groups. Conclusion. In all groups the SVA became negative following correction and at long-term follow-up it was observed to return towards normal physiological limits. The compensatory lumbar curve reduces and this was associated with a decrease in sacral inclination. This method of compensation, without causing junctional kyphosis, has not previously been reported. We were unable to demonstrate a significant difference between the three groups with regards to the clinical outcome, the degree of initial correction, loss of correction and complications. Therefore, in conclusion, we believe a single stage posterior correction and segmental instrumentation not only provides the same clinical and radiological outcomes, but also reduces blood loss, operative time and hospital stay. Ethics approval: None. Interest Statement: None

We carried out an MRI study of the lumbar spine in 15 patients with achondroplasia to evaluate the degree of stenosis of the canal. They were divided into asymptomatic and symptomatic groups. We measured the sagittal canal diameter, the sagittal cord diameter, the interpedicular distance at the mid-pedicle level and the cross-sectional area of the canal and spinal cord at mid-body and mid-disc levels.

The MRI findings showed that in achondroplasia there was a significant difference between the groups in the cross-sectional area of the body canal at the upper lumbar levels. Patients with a narrower canal are more likely to develop symptoms of spinal stenosis than others.